Fig. 4. The etch rate over modification step duration a) for all studied materials, and b) enlarged for  $\mathrm{Al_2O_3}$ ,  $\mathrm{AlN_x}$ , and  $\mathrm{HfO_2}$ .

Etch rate as a function of modification step duration shows material-dependent behavior. SiO₂ increases nearly monotonically, reaching ~0.8 nm/cycle at long times. AlNₓ and Al₂O₃ exhibit mid-range maxima (~6–10 s) followed by a decline at longer durations. HfO₂ peaks later (~10–12 s) at a lower maximum rate. TiN remains near zero or slightly negative across the full duration range.

The enlarged view emphasizes distinct optimal modification windows: AlNₓ peaks earliest (~6–8 s), Al₂O₃ slightly later (~8–10 s), and HfO₂ latest (~10–12 s). Beyond these windows, etch rates decrease, indicating over-modification effects.

| Modification step duration (s) | Al₂O₃ (nm/cyc) | HfO₂ (nm/cyc) | AlNₓ (nm/cyc) | TiN (nm/cyc) | SiO₂ (nm/cyc) |
|---|---|---|---|---|---|
| 0  | ~0.02 | ~0.01 | ~0.02 | ~0.00 | ~0.05 |
| 4  | ~0.15 | ~0.06 | ~0.17 | ~0.00 | ~0.30 |
| 6  | ~0.17 | ~0.08 | ~0.18 | ~0.00 | ~0.45 |
| 10 | ~0.16 | ~0.09 | ~0.17 | ~0.00 | ~0.62 |
| 12 | ~0.15 | ~0.09 | ~0.16 | ~0.00 | ~0.65 |
| 14 | ~0.09 | ~0.07 | ~0.10 | ~−0.02 | ~0.82 |

| Modification step duration (s) | Al₂O₃ (nm/cyc) | HfO₂ (nm/cyc) | AlNₓ (nm/cyc) |
|---|---|---|---|
| 0  | ~0.02 | ~0.01 | ~0.02 |
| 4  | ~0.15 | ~0.07 | ~0.17 |
| 6  | ~0.17 | ~0.09 | ~0.19 |
| 10 | ~0.16 | ~0.10 | ~0.19 |
| 12 | ~0.16 | ~0.10 | ~0.18 |
| 14 | ~0.08 | ~0.06 | ~0.10 |

Answer: The etch ratio of different materials such as Al2O3, HfO2, AlNx, TiN, SiO2, is analyzed as a function of modification step duration.

Answer: The etch rate increases for all materials except for SiO2 up to approximately 5s, after which remains constant until 12s before finally decreasing. In contrast, the etch ratio of SiO2 depend on the duration of the modification step.

Answer: SiO2, and TiN

Answer: Using SiO2 enables higher etch ratios to be achieved in a shorter amount of tiem.

Answer: Yes

Answer: For AL2O3, HFO2, and AINx, the etch rate rises rapidly and peaks around 6-8 seconds. It then falls off. TiN's etch rate remains low/inactive across the whole duration. SiO2's etc rate rises throughout the whole duration range.

Answer: a2: TiN

Answer: SiO2 (highest etch rate by modification step t = 0)

Answer: Al2O3, HfO2, and AlNx show an ALE window. Their etch rate rises with increasing modification time and then becomes nearly constant, indicating self-limiting, surface-saturation behavior characteristic of ALE. SiO2 does not show a clear window because its etch rate keeps increasing with time, and TiN does not because it is essentially not etched.

Answer: Al2O3/TiN, HfO2/TiN, AlNx/TiN.

Answer: Between 5 and 12 seconds; Al2O3, HfO2 and AlNx.

Answer: TiN.

Answer: According to the authors, this is most likely due to the difference in volatility between the formed products: the sublimation point of titanium fluoride is at 284 ◦C and the boiling point of silicon-fluoride is -86 ◦C. Titanium fluoride is much less volatile, which makes etching more difficult and the etch rate slower. The sputtering rate of argon ions on SiO2 is also two to three times higher than that of the other studies materials, which adds to the etch rate.

Answer: Although insignificant, the minimal etching is attributed to sputtering by argon ions.

Answer: For SiO2 the etch rate increases linearly with modification step duration, for other materials it is more complex

Answer: With the increase of modification step duration, the etch rate of Al2O3, AlNx and HfO2 reaches saturation, providing the ALE window. Further rise of modification step leads to the decrease of the etch rate due to too thick film deposition

Answer: Increasing the modification time gives the activating chemicals more time to react with the surface, breaking more bonds and making the material easier to remove. This creates a thicker or more reactive modified layer, which leads to a higher etch rate. However, this effect eventually levels off once the surface is fully saturated.

Answer: HfO₂

Answer: SiO2 exhibits continuously increasing etch rate because silicon fluoride (SiF4) desorbs easily at lower temperatures, making it easily removed even with relatively low ion energy bombardment. In contrast, TiN shows virtually no etching because titanium fluoride has a much higher sublimation point, making desorption of reaction products extremely difficult at the process conditions used. This difference in etch behavior provides good selectivity for etching Al2O3, AlNx, and HfO2 over a TiN hard mask.

Answer: AlNx

Answer: About 5-6 seconds

Answer: No

Answer:
Highest: SiO₂ (~0.82).
Lowest: TiN (~0).

Answer: TiN.

Answer: SiO2 has a way higher etch rate than for example HfO2, at 15 s of modification duration. This indicates that SiO2, at least partially, can selectively be etch with respect to HfO2.

Answer: TiN does not etch for any modification duration.

Answer: 5 s of modification duration is most likely used as this would have similar etch results as longer times, but reduces the processing time.

Answer: No there is continuous etching. For all three materials the etch rate is non-zero at 0 s modification duration.

Answer: At short modification durations, the surface is only partially covered by the fluorocarbon film, resulting in very low etch rates due to insufficient surface activation. As the modification time increases, a more complete reactive layer forms, enabling efficient ion-assisted reactions during the activation step and causing the etch rate to rise. Beyond an optimal duration, the etch rate saturates, reflecting self-limiting behavior, and may slightly decrease at longer times due to excessive film thickness hindering ion penetration and surface reaction efficiency.

Answer: Yes

Answer: Al2O3, HfO2, AINx

Answer: At modification step duration of 5–12 seconds.

Answer: No

Answer: The etch rate of Al2O3, AlNx and HfO2 with rise of modification step to 12s lead to the decrease of the etch rate going out of saturation

Answer:
- AlNx: shows the highest etch-rate increase with duration.
- Al₂O₃: displays a moderate increase with duration.
- HfO₂: increases more slowly and remains the lowest of the three across the range.

Answer:
No.
 Al₂O₃ is not suitable for a process that must be highly precise and insensitive to modification-step duration.

Answer: All three materials show similar behavior with initial etch rate increase, followed by a plateau at 5-12 seconds representing the ALE window. After 12 seconds, the etch rate decreases. This self-limiting plateau demonstrates atomic layer etching behavior.

Answer: AlNₓ reaches its maximum etch rate earliest, around 6–8 s, followed by Al₂O₃ at roughly 8–10 s, while HfO₂ peaks later at about 10–12 s. This ordering suggests different kinetics for forming the modified surface state that enables removal, with HfO₂ requiring longer modification to reach maximum effectiveness.

Answer: TiN

Answer: Presence of an etch-rate saturation plateau with increasing modification time, Formation of a clear ALE window at intermediate modification durations, Reduced sensitivity to argon sputtering effects, Ability to form a self-limiting modified surface layer


Fig. 5. The etch rate over activation step duration. Negative values correspond to film formation.

Etch rate as a function of activation step duration shows a common negative starting value near −0.5 nm/cycle at 0 s for all materials, indicating net film formation without activation. As activation time increases, material-dependent removal emerges. SiO₂ exhibits the strongest response, increasing monotonically to ~0.7 nm/cycle at 20 s. AlNₓ and Al₂O₃ show intermediate increases, reaching ~0.3 nm/cycle at 20 s, while HfO₂ increases only modestly. TiN remains near zero across the range, indicating strong resistance to activation-induced removal.

| Activation step duration (s) | Al2O3 etch rate (nm/cyc) | HfO2 etch rate (nm/cyc) | AlNx etch rate (nm/cyc) | TiN etch rate (nm/cyc) | SiO2 etch rate (nm/cyc) |
|---|---|---|---|---|---|
| 0  | ~-0.55 | ~-0.55 | ~-0.55 | ~-0.55 | ~-0.55 |
| 5  | ~0.00  | ~0.00  | ~0.00  | ~0.00  | ~0.40  |
| 10 | ~0.18  | ~0.10  | ~0.18  | ~0.00  | ~0.55  |
| 20 | ~0.30  | ~0.15  | ~0.30  | ~0.05  | ~0.72  |

Answer: They are studying the etch rate  (nm/cyc) as a function of the activation step duration (s) for the different materials used in the process (Al2O3, HfO2, AlNx, TiN, SiO2)

Answer: Yes

Answer: TiN

Answer: No, because all materials demonstrate film deposition when activation step duration is less than 5s (2.5s for SiO2).

Answer: No it does not seem to matter. Both Al2O3 and AlNx have similar etch results.

Answer: Yes it is possible, SiO2 can be selectively etched wrt to all other materials at an activation time of 5 seconds.

Answer: Yes, there is an increase in etch rate for increasing activation time

Answer: 20 s for HfO2 and 10 s for Al2O3.

Answer: Yes

Answer:
SiO2 at 20 s with ≈ 0.70nm/cycle.
Evidence: Its marker/line is highest among the series at 20 s.

Answer: The etch-per-cycle response depends on material. SiO2 shows the steepest increase with activation time, while AlNx and Al2O3 rise more modestly and TiN remains near zero. By 20s, the ranking is SiO2 ≫ AlNx ~ Al2O3 ≫ HfO2≫ TiN. This indicates [concise implication about selectivity or sensitivity to activation] grounded in the plotted slopes.

Answer:
Stop layer: TiN — its curve stays ~0 across the range (slope ≈ 0).
Longest activation to achieve net removal: TiN— remains negative or near 0 until  10s, then crosses into positive etch.

Answer: At zero activation, polymer deposits at -0.5 nm/cycle on all surfaces. Increasing activation duration causes etch rates to shift from negative to positive as ions first remove polymer then activate material etching. The gradual increase in etch rate with activation time reflects the sequential sputtering and surface reaction activation processes.

Answer: Around 0.5 nm/cycle (i.e. negative etch rate of -0.5 nm/cycle)

Answer: It is 0.16 nm/cycle

Answer: No. The reason is that the deposited polymer film must first be sputtered away before material etching can begin.

Answer: The activation step duration directly controls the etch rate by determining the extent of surface modification. At very short durations, incomplete reactions lead to net film formation, but as duration increases, the surface becomes fully saturated, allowing the etch rate to rise sharply. Once the surface is completely modified, the process reaches a self-limiting plateau where further increases in activation time no longer affect the etch rate.

Answer:
1.	At very short durations, film formation (negative etch rate) occurs.
2.	As duration increases, the process transitions from net deposition to net etching.
3.	At intermediate durations, the etch rate rises sharply.
4.	At long durations, the etch rate plateaus at a higher value.

Answer: Yes . HfO₂ etches more slowly than Al₂O₃ because its higher sputtering threshold reduces ion-induced material removal.

Answer: Yes

Answer: After 5s of activation steps, the etch rate begins to increase for all materials except TiN

Answer: No, the etch rate remains low and only goes up to 0.02nm/cycle after 20s of activation steps

Answer: Yes, Al2O3 and AlN show similar behaviour in etch rate vs activation steps and also have similar etch rates.

Answer: SiO2 requires the least number of activation as the etch rate increases after ~2.5s of activation step duration.

Answer: A negative etch rate corresponds to film growth/formation, rather than etching.

Answer: 10 seconds.

Answer: HfO2 has a higher sputtering threshold.

Answer: It is probably due to the non-monoenergetic ion distribution function. The incline observed in the ALE window for the activation step may hamper reproducibility.

Answer: No

Answer: A strong time-dependent increase in etch rate indicates that more volatile products are generated as the activation time increases. Almost no volatile species are produced during the activation of TiN, since its etch rate remains essentially zero over the entire activation-time range. In contrast, SiO₂ is the most volatile, exhibiting the highest etch rate and a continuous rise with activation time.

Answer: At around 5 seconds.

Answer: About 1 nm thick (0.5 nm/cycle).

Answer: Al₂O₃, HfO₂, and AlNₓ all show a  shallow rise in etch rate as the activation step becomes increases. TiN stays close to zero throughout, only moving slightly upward from a negative value at short times. SiO₂  increases far more strongly than the other materials, becoming the most rapidly etched surface at longer activation durations.

Answer: SiO2

Answer: Yes

Answer: Al2O3, HfO2, SiO2

Answer: Zero activation: polymer film deposition (~0.5 nm) results in negative etch rate, Early activation (5–10 s): transition from deposition to etching, Moderate activation (10–15 s): onset of positive etch rate and initiation of steady etching, Longer activation (15–20 s): gradual increase in etch rate, no clear plateau

Answer: 0.0 nm/cycle for both materials (transition point from deposition to etching).

Answer: No

Answer: HfO₂ shows a slower increase in etch rate compared to Al₂O₃, with the slope of the etch rate approximately half that of Al₂O₃. This difference arises from HfO₂’s higher sputtering threshold and stronger resistance to argon ion bombardment, which reduces etching efficiency and delays the onset of steady material removal, highlighting how intrinsic material properties influence ALE performance.

icdar2026-competition-data/train/atomic-layer-etching/experimental-usecase/16/Selective atomic layer etching of Al2O3, AlNx and HfO2.pdf


Fig. 6. The etch depth over the number of cycles in ALE process (activation step duration is  $10~\mathrm{s}$ ).

Etch depth increases approximately linearly with the number of ALE cycles for most materials, indicating a near-constant etch-per-cycle under a 10 s activation step. SiO₂ exhibits the steepest slope and the largest accumulated etch depth, reaching ~27 nm after 40 cycles. AlNₓ and Al₂O₃ show moderate linear removal, while HfO₂ etches slowly. TiN shows essentially no measurable etch depth across all cycles, indicating strong resistance to the ALE process. Dashed lines represent linear fits to the experimental data.

| Cycles | Al2O3 etch depth (nm) | HfO2 etch depth (nm) | AlNx etch depth (nm) | TiN etch depth (nm) | SiO2 etch depth (nm) |
|---|---|---|---|---|---|
| 0  | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| 15 | ~2.0 | ~1.5 | ~3.0 | ~0.0 | ~6.0 |
| 20 | ~3.5 | ~2.5 | ~5.0 | ~0.0 | ~12.0 |
| 30 | ~5.0 | ~3.2 | ~6.0 | ~0.0 | ~20.0 |
| 40 | ~6.0 | ~4.0 | ~7.5 | ~0.0 | ~27.0 |

Answer: The etch depth as a function of the number of cycles, for different materials.

Answer: TiN, because the etch depth value is close to 0, regardless of the number of cycles.

Answer: No, because, unlike other materials, the etch depth continues to increase with each cycle. However, after 30 cycles, the etch depth appears to remain constant for Al2O2, HfO3, AlNx, and TiN.

Answer: SiO2 is preferred because its slope is steeper than that of the other materials. This means that a greater etching depth can be achieved in the same number of cycles.

Answer: SiO2 does not show that good of a fit. This suggests that, if the characterization is performed well, that the process is not that controlled. This in turn suggests that perfect ALE is not acquired.

Answer: HfO2 shows the highest etch resistivity as for this material, the total etch depth is the lowest.

Answer: Al2O3 and AlNx.

Answer: 30 cycles are required.

Answer: Yes, approximately linear for Al2O3, HfO2, AlNx, SiO2;  TiN shows flat/near-zero change.

Answer:
“SiO2”
Evidence: “At 40 cycles it has the largest etch depth  compared with other materials."

Answer: EPC depends strongly on material. SiO2 has the highest slope, followed by AlNx and Al2O3, while HfO2 is low and TiN is ≈0. This ranking indicates, how etch depth varies with increasing number of cycles.

Answer: TiN is the best candidate for an etch-stop under these ALE conditions. Its etch depth stays zero after 40 cycles, giving an etch-per-cycle of 0 nm/cycle. In the plot, its markers lie near the x-axis and the dashed fit has nearly zero slope, whereas other materials show measurable slopes and larger depths. Therefore, TiN would maintain thickness during etching and serve as an effective mask/stop layer.

Answer:
Al₂O₃ – black squares

HfO₂ – red circles

AlNₓ – blue triangles

SiO₂ – black asterisks

TiN – red crosses

Answer: 10 seconds.

Answer: Roughly, 5 to 6 nm.

Answer: The process doesn't drift quickly with time. That allows predictable depth control just by choosing the cycle number.

Answer:
Yes, the data in Figure 6 confirms the process's adherence to the self-limiting mechanism, as evidenced by the perfectly linear relationship between etch depth and the number of cycles.
This linearity is governed by material-specific properties, including the surface's ability to saturate during the activation step and the volatility of the etched byproducts during the removal step.
For the material tested here, these properties are well-suited to the ALE process, whereas materials with poor surface saturation or low byproduct volatility would show a sub-linear, reaction-limited etch rate.

Answer:
The linear relationship is significant because it confirms the process is self-limiting itself , highly controllable and predictable.
In a perfect ALE process, each cycle removes exactly one layer of atoms and then stops on its own. It cannot continue etching deeper, no matter how long you leave the reactants there. This trend is very well observed for most of the materials studied here.

Answer:
1) The Etch Per Cycle (EPC) for various different materials
2) The total etch depth for a given number of cycles.

Answer:
Yes
(This trend allows device manufacutures to achieve atomic-scale precision by simply controlling the number of cycles. Also, they can reliably etch to a target depth with minimal risk of damaging the underlying substrate, which is crucial for manufacturing advanced semiconductor devices.)

Answer: No

Answer: From the graph, SiO2 has higher etch rate compared to other materials

Answer: The etch depth has a linearly dependence  with the number of cycles

Answer: From the graph, it is evident that TiN is not etched at all, while SiO2 has high etch rate, therefore with the current process, SiO2 could be selectively etched from a target containing both TiN and SiO2 films.

Answer: 10 seconds for both steps each.

Answer: 0.16, 0.20, and 0.11 nm per cycle, respectively.

Answer: About 30, 40, and 20, respectively.

Answer: The measured etch rates for Al2O3, AlNx and HfO2 are comparable to the Al-O bond length of 0.169 nm, which means that the ALE process has close to single-atom precision.

Answer: TiN would make the best mask. From the graph, its etch depth stays close to zero even after 40 cycles, meaning it is almost not etched at all. It can protect underlying layers while the other materials are removed.

Answer: Approximately 24 - 25 cycles.

Answer: SiO2, AlNx, Al2O3, HfO2.

Answer: SiO2 (largest fluctuations in etch depth).

Answer: TiN

Answer: Yes

Answer: The five materials show noticeably different slopes. SiO₂ increases the most rapidly and reaches the largest etch depth. AlNₓ, Al₂O₃, and HfO₂ all rise more moderately, with HfO₂ showing the slowest increase of the three. TiN remains nearly flat across the entire range, with only a slight upward shift at the highest cycle count.

Answer: SiO2, AINx, Al2O3, HfO2

Answer: Highest: AlNₓ (0.20 nm/cycle), Medium: Al₂O₃ (0.16 nm/cycle), HfO₂ (0.11 nm/cycle), Lowest: TiN (0.006 nm/cycle), Poor repeatability: SiO₂ (0.62 nm/cycle)

Answer: 8 nm.

Answer: The chart shows that etch depth increases linearly with cycles, but the rate differs strongly between materials. Al₂O₃, AlNₓ, and HfO₂ exhibit controlled, moderate etch rates, indicating effective ALE behavior. TiN shows almost no etching, confirming resistance to the process, while SiO₂ has high variability, indicating poor repeatability. This illustrates that the ALE process can selectively remove material layer-by-layer depending on the chemical and physical properties of each substrate, highlighting the importance of tuning parameters for selective etching.

Answer: Yes


Figure 11 displays the time evolution of the HF exposure together with the  $\mathrm{H}_2\mathrm{S}^+$  ion signal at  $m / z$  34 produced by the

The multi-line chart shows how the etch rate (Å/cycle) of ZnS ALD changes with temperature for depositions carried out at 100 °C, 200 °C, and 300 °C. As the temperature increases, the etch rate also increases.The film deposited at 100 °C etches the fastest, while the film deposited at 300 °C etches the slowest at any given temperature. This implies that films deposited at higher temperatures are denser or chemically more robust.

| Temperature (°C) | Etch Rate (Å/cycle) | Condition        |
|------------------|----------------------|------------------|
| 225              | 1.40                 | ZnS ALD 100°C    |
| 225              | 1.02                 | ZnS ALD 200°C    |
| 225              | 0.77                 | ZnS ALD 300°C    |
| 250              | 1.80                 | ZnS ALD 100°C    |
| 250              | 1.44                 | ZnS ALD 200°C    |
| 250              | 1.33                 | ZnS ALD 300°C    |
| 275              | 2.00                 | ZnS ALD 100°C    |
| 275              | 1.75                 | ZnS ALD 200°C    |
| 275              | 1.65                 | ZnS ALD 300°C    |
| 300              | 2.11                 | ZnS ALD 100°C    |
| 300              | 1.98                 | ZnS ALD 200°C    |
| 300              | 1.85                 | ZnS ALD 300°C    |

Answer: The setpoint should be 300 °C.

Answer: The higher etch rate for the 100 °C film (black curve) indicates it is structurally weaker and less dense than the 300 °C film. The "looser" atomic network of the low-temperature film allows the etchant species to diffuse and react more readily, whereas the 300 °C film is more crystalline and compact, offering greater resistance to chemical attack.

Answer: Films deposited at lower temperatures (100 °C) typically have lower density and higher impurity content (e.g., unreacted ligands).

Answer: At high etch temperatures (300 °C), the etch rates for all films begin to converge (gap narrows to ~0.2 Å/cycle ). This suggests the process is transitioning from a surface-reaction-limited regime (where film density/quality dominates) to a mass-transport-limited regime (or saturation). In this regime, the supply of etchant or the desorption of byproducts becomes the bottleneck, making the intrinsic quality of the film less of a differentiator than it is at lower temperatures.

icdar2026-competition-data/train/atomic-layer-etching/experimental-usecase/23/Thermal Atomic Layer Etching of Zinc Sulfide.pdf


Figure 12.  $\mathrm{ZnS}$  etch rates vs temperature for  $\mathrm{ZnS}$  ALD films grown at different temperatures.

The multi-line chart shows how the etch rate (Å/cycle) of ZnS ALD changes with HF pressures for depositions carried out at TMA pressures of 20 m.Torr and 200 m.Torr. As the pressure increases till  50, the etch rate increases and plateus.

| HF Pressure (mTorr) | Etch Rate (Å/cycle) | TMA Pressure |
|----------------------|----------------------|--------------|
| 0                    | 0.00                 | 20 mTorr     |
| 0                    | 0.00                 | 200 mTorr    |
| 50                   | 1.65                 | 20 mTorr     |
| 50                   | 2.00                 | 200 mTorr    |
| 100                  | 1.75                 | 20 mTorr     |
| 100                  | 2.24                 | 200 mTorr    |
| 150                  | 1.81                 | 20 mTorr     |
| 150                  | 2.43                 | 200 mTorr    |
| 200                  | 1.83                 | 20 mTorr     |
| 200                  | 2.43                 | 200 mTorr    |
| 250                  | 1.83                 | 20 mTorr     |
| 250                  | 2.46                 | 200 mTorr    |
| 300                  | 1.83                 | 20 mTorr     |
| 300                  | 2.48                 | 200 mTorr    |

Answer: First, the TMA pressure must be set and stabilized at 200 mTorr. Then, the HF pressure must be set and stabilized at 50 mTorr for the duration of the ALE cycle before measuring the etch depth.

Answer: 200 mTorr TMA is better for throughput as it gives a higher etch rate. The trade-off is higher precursor consumption and potentially more stringent pumping requirements to maintain process pressure.

Answer: The plateau occurs because all available surface reaction sites become saturated with HF-derived species within the pulse time. This reveals the self-limiting nature of the HF half-reaction, a defining characteristic of ideal ALE.

Answer: It implies the tool requires excellent pressure control and uniformity for both precursors. Any drift or non-uniformity in pressure will directly translate into etch rate variations, affecting device yield and performance consistency.


Figure 6. Etch rate during  $\mathrm{ZnS}$  ALE vs precursor exposure time at  $300^{\circ}\mathrm{C}$ . The HF pressure was  $40\mathrm{mTorr}$  and the TMA pressure was  $45\mathrm{mTorr}$ . Initial  $\mathrm{ZnS}$  ALE films were grown at  $100^{\circ}\mathrm{C}$ .

This muliple line chart  shows the etch rate per cycle (Å/cycle) as a function of precursor exposure time for two different ALE process conditions: one varying HF exposure time (x) with fixed TMA time (4 s), and the other varying TMA exposure time (y) with fixed HF time (1 s). Both show a rapid increase in etch rate with exposure time up to ~2 seconds, followed by a saturation plateau, indicating self-limiting surface reactions.

| Precursor Exposure Time (s) | Etch Rate (Å/cycle) | HF-Purging-TMA-Purging     |
|-----------------------------|----------------------|-----------------------------|
| 0                           | 0                    | x-30-4-30 (s)               |
| 0                           | 0.006                | 1-30-y-30 (s)               |
| 1                           | 2.08                 | x-30-4-30 (s)               |
| 1                           | 0.57                 | 1-30-y-30 (s)               |
| 2                           | 2.02                 | x-30-4-30 (s)               |
| 2                           | 1.8                  | 1-30-y-30 (s)               |
| 3                           | 2.03                 | x-30-4-30 (s)               |
| 3                           | 2.03                 | 1-30-y-30 (s)               |
| 4                           | 2.05                 | x-30-4-30 (s)               |
| 4                           | 2.05                 | 1-30-y-30 (s)               |
| 5                           |                      | x-30-4-30 (s)               |
| 5                           |                      | 1-30-y-30 (s)               |
| 6                           | 2.04                 | x-30-4-30 (s)               |
| 6                           | 2.05                 | 1-30-y-30 (s)               |

Answer:
For the solid red  line (x-30-4-30): 1) HF exposure for ‘x’ seconds → 2) Purge for 30 s → 3) TMA exposure for 4 s → 4) Purge for 30 s.
For the blue line (1-30-y-30): 1) HF exposure for 1 s → 2) Purge for 30 s → 3) TMA exposure for ‘y’ seconds → 4) Purge for 30 s.

Answer: TMA requires a longer exposure to reach saturation (etch rate plateaus after ~3 s) compared to HF (~1 s). This implies that the TMA half-reaction is kinetically slower, so process optimization must balance sufficient TMA exposure for complete etching against throughput, as longer TMA times increase cycle time.

Answer: The saturation indicates that the surface reaction is self-limiting; after ~2 seconds, all available surface sites have reacted. This reveals that the etching mechanism is governed by monolayer-level surface saturation rather than continuous etching, which is the hallmark of ideal ALE.

Answer: It ensures robust uniformity despite inevitable local variations in precursor flux or exposure time. As long as the exposure time exceeds the saturation threshold everywhere on the wafer, the etch rate will be identical, eliminating thickness variations caused by flow non-uniformities.


FIG.2. (a) SIMS depth profiles of F as a function of the sputtering time after  $\mathrm{NF}_3$  plasma treatment for  $60~\mathrm{s}$  at 0, 10, 50, and  $100W$  b) F 1s XPS peak from  $\mathrm{Al}_2\mathrm{O}_3$  films; and (c) saturation of atomic fractions as  $\mathrm{NF}_3$  plasma exposure time at  $10W$  and  $100^{\circ}C$

The chart shows the intensity of F-  at different depths for various powers (0, 10, 50, 100 W). Increasing power leads to penetration of the F⁻ deeper into the film.

The XP-spectrum t displays the intensity of F 1s peaks at different times (Reference, 5s, 20s, 50s, 60s)  during plasma fluorination. The Al–F peak grows strongly after fluorination and then changes more modestly at longer times.

The chart illustrates the atomic percentage changes of O1 s, Al 2p, F 1s, and C 1s with increasing plasma fluorination time. O, Al and C decrease rapidly and then plateau, F increases rapidly and then plateaus.

| Depth (nm) | 0W: Intensity (arb.units) | 10W: Intensity (arb.units) | 50W: Intensity (arb.units) | 100W: Intensity (arb.units) |
|---|---|---|---|---|
| 0 | 2 | 65 | 63 | 66 |
| 1 | 2|  43| 52 | 60 |
| 2 | 2 | 15 | 15 | 20 |
| 3 | 2 | 8 | 10 | 11 |
| 4 | 2 | 6 | 8 | 7 |

| Measurement | Peak: Intensity (arb.units) | Peak: Binding energy [eV]  |
|---|---|---|
| Reference | 2.15 | 685 |
| 5s |  29 | 686.1 |
| 20s| 38 | 686.4 |
| 50s| 42 | 686.4 |
| 60s| 42 | 686.4 |

| Plasma fluorination time (s) | Atomic % O 1s | Atomic % Al 2p | Atomic % F 1s | Atomic % C 1s |
|---|---|---|---|---|
| 0 | 52.1% | 28.8% | 0% | 18.5% |
| 5 | 42% | 27.9% | 21.2% | 9% |
| 20 | 38.7% | 27% | 21.8% | 10.8% |
| 50 | 37.5% | 27.9% | 24.9% | 8.6% |
| 60 | 38.4% | 27.9% | 25.3% | 8.1% |

Answer: The depth profiles indicate that increasing RF power leads to greater fluorine incorporation and a deeper fluorinated layer. This is attributed to higher RF power producing a larger flux of reactive fluorine radicals in the NF₃ plasma, which enhances fluorination. The fluorine signal still decreases with depth because the formed fluorinated layer acts as a diffusion barrier and hinders further transport.

Answer: Approx. 50 s (F 1s peak stops increasing).

Answer: Noticeable binding energy shift suggest that the dominant bonding environment might be evolving between 5s and 20s (consistent with the probed surface becoming more uniformly fluorinated).

Answer: Fluorination does not appear to modify the entire region probed by XPS. The F atomic % increases but reaches a plateau while O remains predominant. It is consistent with a picture of a fluorine-enriched surface layers over underlying oxide that is still largely unfluorinated.

icdar2026-competition-data/train/atomic-layer-etching/experimental-usecase/28/Atomic layer etching of Al2O3 with NF3 plasma fluorination.pdf


FIG. 4. (a) TMA exposure time at 290, 300, and  $330^{\circ}\mathrm{C}$  of the removal step; (b) EPC using  $\mathrm{NF}_3 / \mathrm{TMA} = 60 / 30\mathrm{s}$  at the range of  $250 - 480^{\circ}\mathrm{C}$  of the removal step; and (c) C 1s XPS peak from  $\mathrm{Al}_2\mathrm{O}_3$  films after  $\mathrm{NF}_3$  plasma exposure time at  $10\mathrm{W}$  and  $100^{\circ}\mathrm{C}$  and after removal step at an elevated temperature range of  $280 - 480^{\circ}\mathrm{C}$ .

The etch per cycle as a function of TMA exposure time shows a rapid rise and then saturation, with 300 °C   removal-step temperature highest etch rate.

The etch per cycle versus removal-step temperature increases sharply from low temperature, peaks around 300 °C, and then decreases at higher temperatures,

XP-Spectrum shows that the peak intensity of C-C and C-Fx species increase with temperature.

| TMA exposure time (s) | Temperature (°C) | Etch per cycle (nm/cycle) |
|---|---|---|
| 0 | 290 | 0.0 |
| 0 | 300 | 0.0 |
| 0 | 330 | 0.0 |
| 10 | 290 | 0.097 |
| 10 | 300 | 0.17 |
| 10 | 330 | 0.14 |
| 20 | 290 | 0.17 |
| 20 | 300 | 0.25 |
| 20 | 330 | 0.23 |
| 30 | 290 | 0.20 |
| 30 | 300 | 0.30 |
| 30 | 330 | 0.27 |
| 40 | 290 | 0.21 |
| 40 | 300 | 0.30 |
| 40 | 330 | 0.27 |

| Removal step temperature (°C) | Etch per cycle (nm/cycle) |
|---|---|
| 250 | 0.0 |
| 275 | 0.09 |
| 290 | 0.20 |
| 300 | 0.3 |
| 330 | 0.27 |
| 400 | 0.20 |
| 480 | 0.0 |

| Measurement | Binding energy [eV] | Intensity (a.u.) | Assignment |
|---|---|---|---|
| NF3 plasma | 284.7 | 22 | C-C |
| NF3 plasma | 289.0 | 5 | C-Fx|
| 280 °C | 284.7 | 28 | C-C |
| 280 °C | 288.9 | 5 | C-Fx|
| 290 °C | 284.7 | 26 | C-C |
| 290 °C | 288.8 |4 | C-Fx|
| 300 °C | 284.7 | 35 | C-C |
| 300 °C | 288.8 | 5 | C-Fx|
| 400 °C | 284.7 | 51 | C-C |
| 400 °C | 288.7 | 9 | C-Fx |
| 480 °C | 284.7 | 58 | C-C |
| 480 °C | 288.7 | 10 | C-Fx |

Answer: 30 s (etch per cycle plateaus after 30 s).

Answer: 300 °C (fastest etching)

Answer: The EPC curve has a volcano-like shape because different mechanisms dominate at different temperatures. At low removal-step temperature, the etch per cycle is low because the ligand-exchange reaction between TMA and the fluorinated film is likely  kinetically hindered.  As the temperature increases into the intermediate range, this reaction proceeds more efficiently, leading to a higher EPC. At the highest temperatures, the EPC drops back to low values,  because TMA might be thermally decomposing, which hinders the reaction.

Answer: At the high removal-step temperatures (400 °C  and 480 °C ), the C 1s spectra show a much stronger C–C peak, compared to lower temperatures. This suggests that non-volatile carbon residues are accumulating on the surface with higher temperatures. Since TMA is the only significant source of carbon in the process, this strongly hints thermal decomposition of TMA at high temperatures.


FIG. 5. (a) Depth comparison of each half cycle of the fluorination step for  $60 \text{s}$ $\mathrm{NF}_3$  plasma at 10, 50, and  $100 \text{W}$  and a temperature of  $100^{\circ}\text{C}$ , and the removal step with TMA for  $30 \text{s}$  at an elevated temperature of  $300^{\circ}\text{C}$  and (b) surface atomic fraction tendency at each half cycle at  $10 \text{W}$ .

The chart shows the relationship between RF power and the depth of fluorinated layer and etched depth, demonstrating  both depths increasing with power, with the fluorinated layer always thicker than the removed thickness.

The chart displays the atomic percentage of O1s, Al2p, F1s, and C1s across NF3 and TMA half-cycles. Percentage of fluorine is increasing after NF₃, then decreasing after TMA.

| RF power (W) | Fluorinated layer depth (nm) | Etched depth (nm) |
|---|---|---|
| 0 | 0.0 | 0.0 |
| 10 | 0.79 | 0.3 |
| 50 | 0.95 | 0.38 |
| 100 | 1.14 | 0.43 |

| Cycle number | Step |O 1s | Al 2p | F 1s | C 1s |
|---|---|---|---|---|---|
| 0 | Start NF3  | 51 | 29 | 0 |18 |
| 0.5 | Start TMA  | 38 | 29 | 26 | 9 |
| 1 | Start NF3  | 44 | 30 |  15 | 10 |
| 1.5 | Start TMA | 39 | 26 | 25 | 9 |
| 2 | Start NF3  | 48 | 29 | 14 | 9 |
| 2.5 | Start TMA | 38 | 28 | 25 | 9 |
| 3 | Start NF3  | 48 | 30 | 13 | 9 |
| 3.5 | Start TMA | 38 | 28 | 26 | 9 |
| 4 | End TMA | 46 | 30 | 13 | 11 |

Answer: TMA is not removing fluorine completely, as the etched depth is always smaller than the fluorinated-layer depth.

Answer: 50 W.

Answer: NF₃ acts as the fluorination step: during the NF₃ half-cycles the F1s signal rises, showing that the surface is converted to an F-rich layer. TMA then serves as the removal step: in the TMA half-cycles the F1s signal decreases. This is consistent with TMA consuming surface fluorine to form volatile Al-containing products.

Answer: No


FIG. 7. Normalized NBE signal intensity of GaN underneath the AlGaN film: (a) after the BT step, (b) after exposure to  $\mathrm{Cl}_2$  plasma, and (c) after exposure to Ar plasma as a function of plasma exposure time.

The normalized NBE signal intensity decreases with increasing plasma exposure time for both Ar plasma and Cl2 plasma.

| Plasma Exposure Time (s) | Normalized NBE Signal Intensity (a.u.) Cl2 plasma| Normalized NBE Signal Intensity (a.u.) Ar plasma|
|---|---|---|
| 0 | 1.0 | 1.0|
| 50 | 0.5 |0.7|
| 100 | 0.45 |0.6|
| 200 | 0.35 |0.5|
| 300 | 0.25 |0.35|
| 350 | 0.25 |0.3|

Answer: Both plasmas inflict ion bombardment, but only the Cl2 plasma also has a chemical effect on the substrate.

Answer: Especially for the Cl2 plasma curve there seems to be saturating behaviour, so yes.

Answer: Around 70 %.

Answer: 0.3

icdar2026-competition-data/train/atomic-layer-etching/experimental-usecase/29/Atomic layer etching of AlGaN using Cl2 and Ar gas.pdf


FIG. 7. Depth profiles of atomic concentrations of Ti, N, O, and C in the pristine TiN film. The thickness of the native oxide was approximately  $3\mathrm{nm}$ .

The atomic concentration of Ti, N, O, and C changes over sputtering time, with Ti and N reaching a plateau at 50% while O and C decrease significantly.

| Sputtering Time (min.) | Atomic Concentration (%) |
|---|---|
| 0 | Ti: 25, N: 25, O: 28, C: 22 |
| 1 | Ti: 44, N: 44, O: 12, C: 0 |
| 2 | Ti: 49, N: 46, O: 5, C: 0 |
| 3 | Ti: 49, N: 46, O: 5, C: 0 |
| 4 | Ti: 49, N: 46, O: 5, C: 0 |

Answer: The native oxide is 3 nm thick, the oxygen levels out at 5% after 2 min of etching, so the etch rate is 0.25 angstrom/s.

Answer: The measured carbon is advantitious carbon and likely comes from storing in ambient conditions.

Answer: The Ti:N ratio is 1:1.

Answer: Yes, there is a constant level of oxygen at around 5%, indicating that there are impurities.

icdar2026-competition-data/train/atomic-layer-etching/experimental-usecase/33/Atomic layer etching of titanium nitride.pdf


FIG. 2. (a) EPC vs cycle number with  $40 \text{s} H_{2}$  plasma exposures only (triangles),  $40 \text{s} SF_{6} / Ar$  plasma exposures only (squares), and both half-cycles (circles). All processes occur at  $0^{\circ}C$ . The dashed lines are guides to the eye. (b) EPC versus  $H_{2}$  plasma exposure time with  $SF_{6} / Ar$  plasma exposure time fixed at  $30 \text{s}$ . (c) EPC versus  $SF_{6} / Ar$  plasma exposure time with  $H_{2}$  plasma exposure time fixed at  $30 \text{s}$ . The etch rates are observed to saturate with exposure time, demonstrating the self-limiting nature of the process.

Thickness change remains near zero over 50 cycles for H₂-only and SF₆/Ar-only plasma exposures, while the combined H₂+SF₆/Ar sequence produces an approximately linear thickness decrease reaching ~80 nm by 50 cycles.

With SF₆/Ar exposure fixed at 30 s, the etch per cycle increases with H₂ plasma exposure time and saturates near ~1.45–1.5 nm/cycle beyond ~40 s.

With H₂ exposure fixed at 30 s, the etch per cycle similarly increases with SF₆/Ar exposure time and approaches a plateau near ~1.5–1.6 nm/cycle, indicating saturation.

| Curve | Number of cycles | Thickness change (nm) |
|---|---|---|
| H₂ (triangles) | 50 | ~ -1.0 |
| SF₆ (squares) | 50 | ~ -2.0 |
| H₂ + SF₆ (circles) | 10 | ~ -12.0 |
| H₂ + SF₆ (circles) | 20 | ~ -32.0 |
| H₂ + SF₆ (circles) | 30 | ~ -51.0 |
| H₂ + SF₆ (circles) | 40 | ~ -67.0 |
| H₂ + SF₆ (circles) | 50 | ~ -80.0 |

| H₂ exposure time (s) | Etch rate (nm/cycle) |
|---|---|
| 0 | ~0.0 |
| 10 | ~1.00 |
| 20 | ~1.30 |
| 30 | ~1.40 |
| 40 | ~1.45 |
| 50 | ~1.50 |

| SF₆ exposure time (s) | Etch rate (nm/cycle) |
|---|---|
| 0 | ~0.00 |
| 10 | ~1.20 |
| 20 | ~1.30 |
| 30 | ~1.40 |
| 40 | ~1.50 |
| 50 | ~1.60 |

Answer: No

Answer: The H₂-only and SF₆-only conditions show little to no net thickness change over 50 cycles, with both traces staying close to 0 nm. In contrast, the combined H₂+SF₆ sequence produces a large, cumulative thickness decrease that reaches ~80 nm by 50 cycles. The comparison is consistent with effective etching occurring only when both half-cycles are applied in sequence.

Answer: Saturation ensures that additional exposure does not increase material removal beyond a fixed amount per cycle. This makes the process insensitive to small timing variations and enables precise, repeatable etch control. Such behavior is a defining requirement for true atomic layer etching.

Answer: At approximately 40 s.

icdar2026-competition-data/train/atomic-layer-etching/experimental-usecase/39/Isotropic atomic layer etching of MgO-doped lithium niobate.pdf


FIG. 2. (a) Energy scan and (b) synergy scan of the ITO ALE process at  $150^{\circ}\mathrm{C}$ . Error bars in (a) and (b) show standard deviation from the mean, when multiple measurements are done with the same parameters.

The line chart shows the relationship between DC bias and EPC (Å) for two conditions: ALE and Ar milling only.

The line chart illustrates the synergy percentage at different DC bias voltages.

| DC bias (-V) | EPC (Å) ALE | EPC (Å) Ar milling only |
|---|---|---|
| 0 | 0.1 | 0 |
| 6 | 0.5 |  |
| 9 | 1 | 0.1 |
| 12 | 1.5 | 0.25 |
| 18 | 1.5 | 0.5 |

| DC bias (-V) | Synergy (%) |
|---|---|
| 0 |  |
| 6 |  |
| 9 | 80 |
| 12 | 75 |
| 18 | 55 |

Answer: The resulting EPC as a function of RF power starts to plateau at 20-30 W. Meanwhile, when observing just the effect of the Ar ions, which is the case for "Ar milling only", the Ar ions become energetic enough to significantly etch the surface above 15 W. This means that extra care should be taken when analysing the process above 15 W, as Ar etching might influence the observed EPC.

Answer: 1.5 Å.

Answer: 0.5 Å.

Answer: 80%.

icdar2026-competition-data/train/atomic-layer-etching/experimental-usecase/4/Atomic layer etching of indium tin oxide.pdf


Figure 10. Etch rates of  $\mathrm{Al}_2\mathrm{O}_3$  at different temperatures using (a)  $\mathrm{Sn(acac)}_2,$  b) DMAC and c) TMA as the metal precursor.

Etch rate versus temperature is plotted for Al2O3 using TMA, DMAC, Sn(acac)2

| Temperature (°C) | Sn(acac)₂ Etch Rate (Å/cycle) | DMAC Etch Rate (Å/cycle) | TMA Etch Rate (Å/cycle) |
|------------------|--------------------------------|---------------------------|--------------------------|
| 150              | 0.15                          | —                         | —                        |
| 175              | 0.20                          | —                         | —                        |
| 200              | 0.28                          | —                         | —                        |
| 225              | 0.40                          | 0.10                     | —                        |
| 250              | 0.50                          | 0.35                     | 0.15                    |
| 275              | —                              | 0.50                     | 0.30                    |
| 300              | —                              | 0.65                     | 0.45                    |
| 325              | —                              | —                         | 0.65                    |

Answer: No

Answer: The Al2O3 etching has different threshold temperatures for each metal precursor,  hence the etch rate changes for TMA and DMAC. The Al2O3 etch rates all increase at higher temperatures after exceeding the threshold temperature.

Answer:
1. Sn(acac)2 etched Al2O3 at temperatures ≥150 °C
2. In comparison, DMAC etched Al2O3 at higher temperatures ≥225 °C
3. TMA etched Al2O3 at even higher temperatures ≥250 °C

Answer:
The different temperature thresholds may be attributed to varying activation barriers for the ligand-exchange reactions. The
different temperature thresholds for the etching may provide another method for obtaining selective thermal ALE.

icdar2026-competition-data/train/atomic-layer-etching/experimental-usecase/42/Selectivity in Thermal Atomic Layer Etching.pdf


Figure 9. Etch rates of  $\mathrm{ZrO_2}$ $\mathrm{HfO_2}$  and  $\mathrm{Al}_2\mathrm{O}_3$  versus temperature using  $\mathrm{SiCl_4}$  as the metal precursor.

The chart plots the etch rate of SiCl4  versus temperature for ZrO2, HfO2, and Al2O3.

| Temperature (°C) | ZrO₂ Etch Rate (Å/cycle) | HfO₂ Etch Rate (Å/cycle) | Al₂O₃ Etch Rate (Å/cycle) |
|------------------|---------------------------|---------------------------|---------------------------|
| 250              | 0.00                    | 0.00                    | 0.00                    |
| 300              | 0.055                 | 0.015                   | 0.005                   |
| 350              | 0.15                    | 0.06                  | 0.01                    |

Answer: No

Answer:
1. At 250 °C, Etch rate is almost 0
2. At 300 °C, Etch rate is 0.055 Å/cycle
3. At 350 °C, Etch rate is 0.15 Å/cycle

Answer: The ligand-exchange reaction between SiCl4 and AlF3 is unfavorable at all the temperatures hence the etch rate is nil.

Answer: The ligand-exchange reaction between SiCl4 and ZrF4 or HfF4 is feasible at >200 °C, hence increasing etch rates observed at >250 °C . The ZrO2 etch rate is higher than the HfO2 etch rate even though their predicted ΔG values are nearly equivalent. There must be additional kinetic factors that determine the actual etch rates


Fig. 6. ToF-SIMS depth profiles of  $\mathrm{Al}_2\mathrm{O}_3$  film after ALE process. The ALE cycle was repeated 5 times, and the samples were analyzed after the fluorination and removal steps. The  $\mathrm{AlF_2^-}$  concentration profiles were plotted for the different ALE process temperatures of (a)  $200^{\circ}\mathrm{C}$ , (b)  $250^{\circ}\mathrm{C}$ , and (c)  $300^{\circ}\mathrm{C}$ . The  $\mathrm{AlOF_2^-}$  concentration profiles were also plotted for (d)  $200^{\circ}\mathrm{C}$ , (e)  $250^{\circ}\mathrm{C}$ , and (f)  $300^{\circ}\mathrm{C}$  respectively.

This figure shows Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) depth profiles of Al₂O₃ films after five Atomic Layer Etching (ALE) cycles, measured after the fluorination and removal steps at different process temperatures.AlF₂⁻ depth profile at 200 °C, showing fluorine incorporation near the surface after fluorination and its partial removal during the etching step.

AlF₂⁻ depth profile at 250 °C, indicating enhanced fluorine penetration and modified removal behavior compared to 200 °C.

AlF₂⁻ depth profile at 300 °C, exhibiting deeper fluorine incorporation and more pronounced temperature-dependent effects.

AlOF₂⁻ depth profile at 200 °C, reflecting the formation of mixed oxyfluoride species confined near the surface.

AlOF₂⁻ depth profile at 250 °C, showing increased formation and redistribution of oxyfluoride species.

AlOF₂⁻ depth profile at 300 °C, indicating stronger oxyfluoride formation and deeper distribution at higher temperature.

| Sputter Time (s) | Intensity (c/s) | Method |
|---|---|---|
| 0 | 1E+02 | Fluorination |
| 0 | 1E+02 | Removal |
| 1 | 1.5E+02 | Fluorination |
| 1 | 1.5E+02 | Removal |
| 2 | 1E+02 | Fluorination |
| 2 | 1E+02 | Removal |
| 3 | 1.5E+01 | Fluorination |
| 3 | 1.5E+01 | Removal |
| 4 | 1E+01 | Fluorination |
| 4 | 1E+01 | Removal |
| 5 | 1.5E+00 | Fluorination |
| 5 | 1.5E+00 | Removal |
| 6 | 1E+00 | Fluorination |
| 6 | 1E+00 | Removal |

| Sputter Time (s) | Intensity (c/s) | Method |
|---|---|---|
| 0 | 1E+02 | Fluorination |
| 0 | 1E+02 | Removal |
| 1 | 1.5E+02 | Fluorination |
| 1 | 1.4E+02 | Removal |
| 2 | 1E+02 | Fluorination |
| 2 | 9E+01 | Removal |
| 3 | 5E+01 | Fluorination |
| 3 | 4E+01 | Removal |
| 4 | 1E+01 | Fluorination |
| 4 | 8E+00 | Removal |
| 5 | 1.5E+00 | Fluorination |
| 5 | 1.4E+00 | Removal |
| 6 | 1.2E+00 | Fluorination |
| 6 | 1.1E+00 | Removal |

| Sputter Time (s) | Intensity (c/s) | Method |
|---|---|---|
| 0 | 1E+02 | Fluorination |
| 0 | 8E+01 | Removal |
| 1 | 1.5E+02 | Fluorination |
| 1 | 1.3E+02 | Removal |
| 2 | 1E+02 | Fluorination |
| 2 | 8E+01 | Removal |
| 3 | 5E+01 | Fluorination |
| 3 | 3E+01 | Removal |
| 4 | 1E+01 | Fluorination |
| 4 | 8E+00 | Removal |
| 5 | 1.5E+00 | Fluorination |
| 5 | 1.3E+00 | Removal |
| 6 | 1.2E+00 | Fluorination |
| 6 | 1E+00 | Removal |

Answer: At 200°C, the overlapping curves indicate that the TMA cannot overcome the activation barrier to effectively react with or volatilize the AlF_x layer, leaving the surface structure largely unchanged. At 300°C, the significant drop in signal confirms that the thermal energy enables the ligand-exchange mechanism to function, restoring the surface closer to the underlying bulk oxide composition by stripping away the fluorinated layer.

Answer: The drop is caused by the Ligand-Exchange Reaction with Trimethylaluminum (TMA).

Answer: The process is not viable at 200°C. The trade-off for the low thermal budget is a complete failure of the etch mechanism; the temperature must be raised to at least 250°C to activate the ligand exchange.

Answer: NO, While the fluorination is shallow at 200°C, the AlOF₂⁻ profile (d) shows the removal step is incomplete, leaving a modified interface. For a 2 nm film, this residual modified layer constitutes a significant fraction of the total thickness, drastically altering the interface properties. A higher temperature (like 250°C) with complete removal, despite slightly deeper penetration, would better preserve the electrical properties of the underlying interface.

icdar2026-competition-data/train/atomic-layer-etching/experimental-usecase/43/Surface reaction during thermal atomic layer etching of aluminum oxide.pdf


Figure 2. Mass changes during 10 consecutive HF exposures on  $\mathrm{TiO}_2$  ALD film at 200, 250, and  $300^{\circ}\mathrm{C}$

The chart shows the mass change over time for 10 HF exposures on ALD TiO₂ at different temperatures (200°C, 250°C, and 300°C). The mass decreases over time, indicating a loss of material

| Time (s) | 200°C (Mass Change, ng/cm^2) | 250°C (Mass Change, ng/cm^2) | 300°C (Mass Change, ng/cm^2) |
|---|---|---|---|
| 0 | 0 | 0 | 0 |
| 50 | -20 | -25 | -28 |
| 100 | -35 | -45 | -55 |
| 150 | -50 | -75 | -85 |
| 200 | -60 | -95 | -120 |
| 250 | -75 | -105 | -125 |
| 300 | -85 | -125 | -155 |
| 350 | -95 | -150 | -185 |
| 400 | -105 | -175 | -190 |
| 450 | -115 | -200 | -240 |
| 500 | -125 | -220 | -250 |
| 550 | -135 | -245 | -280 |
| 600 | -160 | -255 | -310 |

Answer: Each step represents one discrete HF exposure pulse, with the flat regions corresponding to N₂ purge periods between exposures.

Answer: Higher temperatures increase the mass loss per HF exposure: −17 ng/cm² at 200°C, −25 ng/cm² at 250°C, and −32 ng/cm² at 300°C. This corresponds to TiO₂ removal of 0.45–0.85 Å per exposure, based on TiO₂ density of 3.76 g/cm³.

Answer: This result validates the core mechanism: if HF can spontaneously etch TiO₂ to form volatile TiF₄ and H₂O, then oxidizing TiN to TiO₂ first enables its removal. Without this spontaneous etching, the oxidation-fluorination ALE approach would not work.

Answer: The reaction has ΔG° = −6.1 kcal/mol at 25°C (favorable) but becomes +6.3 kcal/mol at 250°C (unfavorable under standard conditions). However, etching still occurs because excess HF and rapid removal of volatile products (TiF₄, H₂O) by N₂ purge drive the reaction forward.

icdar2026-competition-data/train/atomic-layer-etching/experimental-usecase/45/Thermal Atomic Layer Etching of Titanium Nitride.pdf


This figure presents quartz crystal microbalance (QCM) data showing mass changes during chemical exposures at 170 °C. In panel (a), only BCl₃ or WF₆ dosing leads to mass gain or negligible change, and WF₆/Sn(acac)₂ cycling results in net deposition, whereas alternating WF₆ and BCl₃ produces a continuous linear mass loss, confirming atomic layer etching (ALE) of TiO₂.

The image zooms into the ALE process, revealing a sawtooth profile in which the WF₆ pulse increases mass due to surface fluorination, followed by a sharp mass decrease during the BCl₃ pulse from ligand exchange and volatilization, yielding net material removal.

| Time (s) | Mass loading (ng/cm²) | Sample |
|---------:|----------------------:|--------|
| 16000 | 4228.46 | WF₆/BCl₃ |
| 16000 | 4664.16 | WF₆/Sn(acac)₂ |
| 16000 | 5358.22 | WF₆ doses |
| 16000 | 6120.32 | BCl₃ doses |
| 17000 | 4483.84 | WF₆/BCl₃ |
| 17000 | 4919.33 | WF₆/Sn(acac)₂ |
| 17000 | 5722.26 | WF₆ doses |
| 17000 | 6341.46 | BCl₃ doses |
| 18000 | 4773.03 | WF₆/BCl₃ |
| 18000 | 5211.92 | WF₆/Sn(acac)₂ |
| 18000 | 6011.45 | WF₆ doses |
| 18000 | 6776.95 | BCl₃ doses |
| 19000 | 4555.29 | WF₆/BCl₃ |
| 19000 | 5647.41 | WF₆/Sn(acac)₂ |
| 19000 | 6341.46 | WF₆ doses |
| 19000 | 6668.08 | BCl₃ doses |
| 20000 | 4300.12 | WF₆/BCl₃ |
| 20000 | 5613.38 | WF₆/Sn(acac)₂ |
| 20000 | 6375.48 | WF₆ doses |
| 20000 |  | BCl₃ doses |
| 21000 | 3827.21 | WF₆/BCl₃ |
| 21000 | 5501.11 | WF₆/Sn(acac)₂ |
| 21000 | 6304.04 | WF₆ doses |
| 21000 |  | BCl₃ doses |
| 22000 | 3279.45 | WF₆/BCl₃ |
| 22000 | 5245.94 | WF₆/Sn(acac)₂ |
| 22000 | 6266.16 | WF₆ doses |
| 22000 |  | BCl₃ doses |
| 23000 | 2877.99 | WF₆/BCl₃ |
| 23000 | 5137.07 | WF₆/Sn(acac)₂ |
| 23000 |  | WF₆ doses |
| 23000 |  | BCl₃ doses |
| 24000 | 2333.63 | WF₆/BCl₃ |
| 24000 | 4956.75 | WF₆/Sn(acac)₂ |
| 24000 |  | WF₆ doses |
| 24000 |  | BCl₃ doses |

| ALE cycle number | Mass loading (ng/cm²) | Pulse |
|-----------------:|----------------------:|-------|
| 20   | 4559.39 | WF₆ |
| 20   | 4629.66 | WF₆ |
| 20.5 | 4526.56 | BCl₃ |
| 20.5 | 4615.65 | BCl₃ |
| 21   | 4507.95 | WF₆ |
| 21   | 4542.97 | WF₆ |
| 21.5 | 4468.11 | BCl₃ |
| 21.5 | 4521.96 | BCl₃ |
| 22   | 4453.88 | WF₆ |
| 22   | 4491.53 | WF₆ |
| 22.5 | 4414.04 | BCl₃ |
| 22.5 | 4468.11 | BCl₃ |

Answer: It would fail. The black line shows a positive slope (mass increase) over time, indicating that combining WF₆ and Sn(acac)₂ results in chemical vapor deposition (CVD) or film growth rather than etching. Substituting BCl₃ with Sn(acac)₂ would therefore add material instead of removing it.

Answer: At 170 °C, WF₆ can fluorinate the TiO₂ surface, creating non-volatile metal fluorides or oxyfluorides and adding mass. However, without a second reagent such as BCl₃ to drive a ligand-exchange reaction and convert these surface species into volatile products (e.g., TiClₓ or volatile oxychlorides), the modified surface layer remains solid, blocking further etching.

Answer:
Modification step: WF₆ exposure (mass increase).
Removal step: BCl₃ exposure (mass decrease).
Identification: The BCl₃ exposure is the removal step, indicated by the sharp drop in mass below the starting baseline of that cycle.

Answer: Cycles: Approximately 167 cycles (100 Å / 0.6 Å·cycle⁻¹). It is preferred for its digital controllability. A continuous wet etch is time-dependent and prone to under- or over-etching due to diffusion and timing errors, whereas ALE removes a fixed amount per cycle independent of time, enabling precise thickness control by simply counting cycles.

icdar2026-competition-data/train/atomic-layer-etching/experimental-usecase/46/Thermal Selective Vapor Etching of TiO2.pdf


Figure 1. QCM analysis at  $220^{\circ}\mathrm{C}$  of (a) 200 cycles of  $\mathrm{Al}_2\mathrm{O}_3$  or  $\mathrm{TiO}_2$  followed immediately by  $50\mathrm{WF}_6 / \mathrm{Ar}$  exposures of  $1 / 60\mathrm{s}$  each and (b) initial loading of  $1\mathrm{WF}_6$  exposure of  $50\mathrm{s}$  versus  $50\mathrm{WF}_6 / \mathrm{Ar}$  exposures of  $1 / 60\mathrm{s}$  on  $\mathrm{TiO}_2$  (200 cycles).

This figure presents QCM data demonstrating material selectivity during WF₆ exposure at 220 °C. The TiO₂ film (red line) shows continuous mass loss, indicating etching, whereas the Al₂O₃ film (black line) exhibits an initial mass gain followed by saturation, indicating no etching.

QCM data comparing WF₆ dosing strategies on TiO₂. Pulsed WF₆ dosing (red line) results in cumulative mass loss (etching), while the initial exposure (black line) is dominated by strong adsorption and fluorination, seen as a large mass gain before etching kinetics dominate.

| Time (s) | Mass loading (ng/cm²) | Sample | Condition |
|---------:|----------------------:|--------|-----------|
| 8000  | 3713.81 | Al₂O₃ | Metal Oxide ALD |
| 8000  | 2935.80 | TiO₂ | Metal Oxide ALD |
| 8500  | 3920.90 | Al₂O₃ | Metal Oxide ALD |
| 8500  | 3025.36 | TiO₂ | Metal Oxide ALD |
| 9000  | 4130.79 | Al₂O₃ | Metal Oxide ALD |
| 9000  | 3084.13 | TiO₂ | Metal Oxide ALD |
| 9500  | 4729.68 | Al₂O₃ | WF₆ Doses |
| 9500  | 3294.02 | TiO₂ | WF₆ Doses |
| 10000 | 4788.45 | Al₂O₃ | WF₆ Doses |
| 10000 | 3145.70 | TiO₂ | WF₆ Doses |
| 10500 | 4819.24 | Al₂O₃ | WF₆ Doses |
| 10500 | 3025.36 | TiO₂ | WF₆ Doses |
| 11000 | 4788.45 | Al₂O₃ | WF₆ Doses |
| 11000 | 2756.70 | TiO₂ | WF₆ Doses |
| 11500 | 4757.67 | Al₂O₃ | WF₆ Doses |
| 11500 | 2216.57 | TiO₂ | WF₆ Doses |
| 12000 | 4757.67 | Al₂O₃ | WF₆ Doses |
| 12000 | 1351.82 | TiO₂ | WF₆ Doses |

| Time (s) | Mass loading (ng/cm²) | Condition |
|---------:|----------------------:|-----------|
| 18200 | 1546.58 | TiO₂ ALD |
| 18200 | 816.87  | 220 °C, 1.75 Torr |
| 18300 | 1566.23 | TiO₂ ALD |
| 18300 | 857.10  | 220 °C, 1.75 Torr |
| 18400 | 1566.23 | TiO₂ ALD |
| 18400 | 887.04  | 220 °C, 1.75 Torr |
| 18500 | 1806.66 | 50 WF₆ doses (1 s) |
| 18500 | 1106.89 | 1 WF₆ dose (50 s) |
| 18600 | 1796.37 | 50 WF₆ doses (1 s) |
| 18600 | 1117.18 | 1 WF₆ dose (50 s) |
| 18700 | 1776.72 | 50 WF₆ doses (1 s) |
| 18700 | 1136.82 | 1 WF₆ dose (50 s) |
| 18800 | 1726.21 | 50 WF₆ doses (1 s) |
| 18800 | 1136.82 | 1 WF₆ dose (50 s) |
| 18900 | 1706.56 | 50 WF₆ doses (1 s) |
| 18900 | 1147.11 | 1 WF₆ dose (50 s) |
| 19000 | 1676.72 | 50 WF₆ doses (1 s) |
| 19000 | 1156.47 | 1 WF₆ dose (50 s) |

Answer: Selective pattern transfer. The TiO₂ film will be etched away, as indicated by the continuous mass loss (negative slope) in the red curve. The Al₂O₃ mask will remain intact and essentially unetched, as indicated by the black curve, which shows only stable mass gain due to surface fluorination. This confirms that WF₆ provides excellent selectivity for removing TiO₂ relative to Al₂O₃.

Answer: Etchability vs. inertness. TiO₂ (red line) is superior as a sacrificial spacer because it spontaneously etches in WF₆ at 220 °C, whereas Al₂O₃ (black line) is inert and resistant, meaning it would not be removed, failing the sacrificial requirement.

Answer: Surface fluorination/adsorption. The WF₆ molecules react with surface oxygen to form a heavy layer of non-volatile metal fluorides (TiFₓ) or tungsten oxyfluorides (WOₓFᵧ). This accumulation of heavy F and W atoms adds mass to the crystal before the slow volatilization step can remove any material.

Answer: Continuous vapor etching (CVE). True ALE requires a self-limiting mechanism where the etch stops after removing one layer. The red curve shows a steep, continuous linear drop in mass as long as WF₆ is pulsed, indicating that at 220 °C, the thermal energy is sufficient to drive the reaction continuously without stopping. This is a CVE process, not a self-limiting ALE process.


Figure 10. (a) QCM analysis at  $170^{\circ}\mathrm{C}$  and 1.75 Torr of  $\mathrm{TiO_2}$  ALD followed by  $25\mathrm{BCl}_3 / \mathrm{Ar}$  doses (pink),  $50\mathrm{WF}_6 / \mathrm{Ar}$  doses (red),  $50\mathrm{WF}_6 / \mathrm{Ar} / \mathrm{Sn}(\mathrm{acac})_2 / \mathrm{Ar}$  cycles (black), or  $50\mathrm{WF}_6 / \mathrm{Ar} / \mathrm{BCl}_3 / \mathrm{Ar}$  cycles (blue). (b) Enlarged view of the  $\mathrm{WF}_6 / \mathrm{Ar} / \mathrm{BCl}_3 / \mathrm{Ar}$  etch sequence. (c) QCM of  $\mathrm{WF}_6 / \mathrm{Ar} / \mathrm{BCl}_3 / \mathrm{Ar}$  sequence at 110, 130, 150, 170, and  $190^{\circ}\mathrm{C}$ .

| Time (s) | Mass loading (ng/cm²) | Condition                     | Temperature |
|---------:|----------------------:|-------------------------------|-------------|
| 3000 | 696.55  | TiO₂ ALD (TiCl₄/H₂O) | 110 °C |
| 3000 | 759.00  | TiO₂ ALD (TiCl₄/H₂O) | 130 °C |
| 3000 | 905.00  | TiO₂ ALD (TiCl₄/H₂O) | 150 °C |
| 3000 | 821.45  | TiO₂ ALD (TiCl₄/H₂O) | 170 °C |
| 3000 | 852.67  | TiO₂ ALD (TiCl₄/H₂O) | 190 °C |
| 4000 | 1051.71 | TiO₂ ALD (TiCl₄/H₂O) | 110 °C |
| 4000 | 1062.44 | TiO₂ ALD (TiCl₄/H₂O) | 130 °C |
| 4000 | 1114.16 | TiO₂ ALD (TiCl₄/H₂O) | 150 °C |
| 4000 | 1093.67 | TiO₂ ALD (TiCl₄/H₂O) | 170 °C |
| 4000 | 1093.67 | TiO₂ ALD (TiCl₄/H₂O) | 190 °C |
| 5000 | 1260.51 | TiO₂ ALE (WF₆/BCl₃) | 110 °C |
| 5000 | 1240.02 | TiO₂ ALE (WF₆/BCl₃) | 130 °C |
| 5000 | 1166.85 | TiO₂ ALE (WF₆/BCl₃) | 150 °C |
| 5000 | 1093.67 | TiO₂ ALE (WF₆/BCl₃) | 170 °C |
| 5000 | 1020.49 | TiO₂ ALE (WF₆/BCl₃) | 190 °C |
| 6000 | 1135.62 | TiO₂ ALE (WF₆/BCl₃) | 110 °C |
| 6000 | 1082.93 | TiO₂ ALE (WF₆/BCl₃) | 130 °C |
| 6000 | 947.31  | TiO₂ ALE (WF₆/BCl₃) | 150 °C |
| 6000 | 727.78  | TiO₂ ALE (WF₆/BCl₃) | 170 °C |
| 6000 | 518.98  | TiO₂ ALE (WF₆/BCl₃) | 190 °C |
| 7000 |          | TiO₂ ALE (WF₆/BCl₃) | 110 °C |
| 7000 | 925.85  | TiO₂ ALE (WF₆/BCl₃) | 130 °C |
| 7000 | 800.96  | TiO₂ ALE (WF₆/BCl₃) | 150 °C |
| 7000 | 414.58  | TiO₂ ALE (WF₆/BCl₃) | 170 °C |
| 7000 | -55.70  | TiO₂ ALE (WF₆/BCl₃) | 190 °C |

Answer:
WF₆ dose

Ar purge

BCl₃ dose

Ar purge

Temperature control is critical because it directly governs the reaction kinetics and ensures the process remains self-limiting.

Answer: The self-limiting ALE process at 170°C is required for perfect conformality in high-aspect-ratio structures. Its layer-by-layer nature ensures uniform etching down the trench sidewalls. The trade-off is a much slower etch rate (~0.6 Å/cycle) compared to the rapid, isotropic material removal of the continuous CVE process at 220°C.

Answer: The etch rate (mass loss per cycle) increases significantly with temperature. This is due to the Arrhenius behavior of the surface reactions: higher thermal energy accelerates the fluorination of TiO₂ by WF₆ and the subsequent removal of the modified layer by BCl₃, leading to more complete reactions per cycle.

Answer: This high selectivity means the ALE process can precisely and completely remove the TiO₂ spacer while using the Al₂O₃ layer as a reliable etch stop. This enables the fabrication of more scaled transistor architectures by allowing the selective etching of one oxide without damaging other critical oxide layers in the stack.


Figure 11. Thermodynamic modeling results showing the expected equilibrium species concentrations from 25 to  $400^{\circ}C$  for (a) reactions 2 and 3, exposing  $\mathbb{N}_2$  -diluted  $\mathrm{BCl}_3$  at 1.5 Torr to  $\mathrm{TiF_4 / WO_3}$  ..  $3\mathrm{mol}$  of  $\mathrm{BCl}_3(\mathrm{g}) + 1$  mol of  $\mathrm{TiF_4(s) + 1}$  mol of  $\mathrm{WO}_3(\mathrm{s})$  ; and (b) the analogous reactions for the  $\mathrm{Al}_2\mathrm{O}_3$  system: 3 mol of  $\mathrm{BCl}_3(\mathrm{g}) + 1$  mol of  $\mathrm{AlF}_3(\mathrm{s}) + 1$  mol of  $\mathrm{WO}_3(\mathrm{s})$  . At equilibrium at  $170^{\circ}\mathrm{C},$ $\mathrm{BCl}_3 + \mathrm{TiF}_4 / \mathrm{WO}_3$  produces predominantly volatile  $\mathrm{BF}_3,$ $\mathrm{TiCl}_4,$  and  $\mathrm{WOCl_4}$  and solid  $\mathrm{B}_2\mathrm{O}_3$

TiO₂ System: At 170 °C, the reaction of BCl₃ with fluorinated TiO₂ surface species produces exclusively volatile products such as TiCl₄ (black line) and WOCl₄ (red line), along with solid B₂O₃. The absence of solid titanium species confirms that etching is thermodynamically favorable.

Al₂O₃ System: At 170 °C, aluminum remains as solid AlF₃ (purple line), and significant formation of volatile AlCl₃ (black line) occurs only above 300 °C. This explains the selectivity: Ti-fluorides volatilize at low temperatures, whereas Al-fluorides do not.

| Temperature (°C) | Equilibrium Phase Concentration (mol) | Material |
|-----------------:|---------------------------------------:|----------|
| 0   | 1.30 | BF₃ |
| 0   | 1.00 | TiCl₄ |
| 0   | 0.65 | B₂O₃ |
| 0   | 0.30 | BCl₃ |
| 0   | 0.05 | WO₃ |
| 0   | 0.90 | WOCl₄ |
| 0   | 0.00 | WO₂Cl₂ |
| 100 | 1.30 | BF₃ |
| 100 | 1.00 | TiCl₄ |
| 100 | 0.65 | B₂O₃ |
| 100 | 0.30 | BCl₃ |
| 100 | 0.05 | WO₃ |
| 100 | 0.90 | WOCl₄ |
| 100 | 0.00 | WO₂Cl₂ |
| 200 | 1.30 | BF₃ |
| 200 | 1.00 | TiCl₄ |
| 200 | 0.65 | B₂O₃ |
| 200 | 0.32 | BCl₃ |
| 200 | 0.05 | WO₃ |
| 200 | 0.85 | WOCl₄ |
| 200 | 0.05 | WO₂Cl₂ |
| 300 | 1.30 | BF₃ |
| 300 | 1.00 | TiCl₄ |
| 300 | 0.60 | B₂O₃ |
| 300 | 0.40 | BCl₃ |
| 300 | 0.05 | WO₃ |
| 300 | 0.60 | WOCl₄ |
| 300 | 0.30 | WO₂Cl₂ |
| 350 | 1.30 | BF₃ |
| 350 | 1.00 | TiCl₄ |
| 350 | 0.45 | B₂O₃ |
| 350 | 0.55 | BCl₃ |
| 350 | 0.05 | WO₃ |
| 350 | 0.35 | WOCl₄ |
| 350 | 0.60 | WO₂Cl₂ |
| 400 | 1.30 | BF₃ |
| 400 | 1.00 | TiCl₄ |
| 400 | 0.35 | B₂O₃ |
| 400 | 0.80 | BCl₃ |
| 400 | 0.05 | WO₃ |
| 400 | 0.15 | WOCl₄ |
| 400 | 0.90 | WO₂Cl₂ |

| Temperature (°C) | Equilibrium Phase Concentration (mol) | Material |
|-----------------:|---------------------------------------:|----------|
| 0   | 1.65 | BCl₃ |
| 0   | 1.00 | AlF₃ |
| 0   | 0.65 | B₂O₃ |
| 0   | 0.05 | AlCl₃ |
| 0   | 0.85 | WOCl₄ |
| 0   | 0.00 | WO₂Cl₂ |
| 0   | 0.00 | BF₃ |
| 100 | 1.65 | BCl₃ |
| 100 | 1.00 | AlF₃ |
| 100 | 0.65 | B₂O₃ |
| 100 | 0.05 | AlCl₃ |
| 100 | 0.85 | WOCl₄ |
| 100 | 0.00 | WO₂Cl₂ |
| 100 | 0.00 | BF₃ |
| 200 | 1.65 | BCl₃ |
| 200 | 1.00 | AlF₃ |
| 200 | 0.65 | B₂O₃ |
| 200 | 0.05 | AlCl₃ |
| 200 | 0.85 | WOCl₄ |
| 200 | 0.05 | WO₂Cl₂ |
| 200 | 0.05 | BF₃ |
| 300 | 1.68 | BCl₃ |
| 300 | 1.00 | AlF₃ |
| 300 | 0.60 | B₂O₃ |
| 300 | 0.05 | AlCl₃ |
| 300 | 0.60 | WOCl₄ |
| 300 | 0.30 | WO₂Cl₂ |
| 300 | 0.20 | BF₃ |
| 350 | 1.70 | BCl₃ |
| 350 | 1.00 | AlF₃ |
| 350 | 0.45 | B₂O₃ |
| 350 | 0.05 | AlCl₃ |
| 350 | 0.35 | WOCl₄ |
| 350 | 0.60 | WO₂Cl₂ |
| 350 | 0.60 | BF₃ |
| 400 | 1.50 | BCl₃ |
| 400 | 1.00 | AlF₃ |
| 400 | 0.30 | B₂O₃ |
| 400 | 0.05 | AlCl₃ |
| 400 | 0.20 | WOCl₄ |
| 400 | 0.75 | WO₂Cl₂ |
| 400 | 0.90 | BF₃ |

Answer: TiCl₄ (Titanium Tetrachloride).Temperature: It is stable and maximized across the entire temperature range shown (from 25 °C upwards), indicating very favorable thermodynamics.

Answer: Thermodynamic selectivity. At 200 °C, the TiCl₄ concentration in panel (a) is high (≈1.0 mol), indicating that titanium is efficiently driven into the gas phase. In contrast, in panel (b), the AlCl₃ concentration is effectively zero, with aluminum remaining trapped as solid AlF₃, providing a robust thermodynamic etch stop.

Answer: From the tungsten oxide (WO₃). The WO₃ acts as an oxygen source, which is scavenged by boron from BCl₃ to form stable solid B₂O₃, while tungsten forms volatile oxychlorides (WOCl₄).

Answer: This implies BCl₃ acts as the coreactant that removes the modified surface layer. After WF₆ fluorinates TiO₂ to form a TiF₄-like surface, BCl₃ exchanges fluorine for chlorine, producing volatile TiCl₄ and regenerating the surface for the next WF₆ dose. The thermodynamic drive for this exchange exists for TiO₂ but not for Al₂O₃, enabling selective ALE.


Figure 12. (a) QCM analysis of  $\mathrm{Al}_2\mathrm{O}_3$  and  $\mathrm{TiO}_2$  ALD followed by  $50\mathrm{WF}_6 / \mathrm{BCl}_3$  ALE cycles at  $170^{\circ}\mathrm{C}$ . The ALE sequence follows  $\mathrm{WF}_6 / \mathrm{Ar} / \mathrm{BCl}_3 / \mathrm{Ar}$ $(0.2 / 45 / 2.5 / 60\mathrm{s})$ . (b) Enlarged view of (a).

This figure uses Quartz Crystal Microbalance (QCM) data to demonstrate the selective etching of Titanium Dioxide (TiO₂) over Aluminum Oxide (Al₂O₃) at 170 °C. The image shows the full process timeline. Both materials are first deposited via ALD (staircase growth). Upon switching to the ALE recipe (WF₆/BCl₃), TiO₂ (red line) immediately begins to lose mass linearly (etching), while Al₂O₃ (black line) gains a small amount of mass and then remains stable (resistant).

A magnified view of the first few ALE cycles. TiO₂ loses mass in every cycle (sawtooth down), whereas Al₂O₃ gains mass during the WF₆ pulse and barely loses it during the BCl₃ pulse, confirming the formation of a stable, non-volatile fluoride layer on aluminum.

| Time (s) | Mass loading (ng cm⁻²) | Material | Process condition |
|---------:|-----------------------:|----------|-------------------|
| 8000  | 1500 | Al₂O₃ | Metal oxide ALD |
| 8000  | 950  | TiO₂  | Metal oxide ALD |
| 8500  | 1700 | Al₂O₃ | Metal oxide ALD |
| 8500  | 1050 | TiO₂  | Metal oxide ALD |
| 9000  | 2100 | Al₂O₃ | Metal oxide ALD |
| 9000  | 1200 | TiO₂  | Metal oxide ALD |
| 9500  | 2500 | Al₂O₃ | WF₆/BCl₃ ALE |
| 9500  | 1100 | TiO₂  | WF₆/BCl₃ ALE |
| 10000 | 2500 | Al₂O₃ | WF₆/BCl₃ ALE |
| 10000 | 900  | TiO₂  | WF₆/BCl₃ ALE |
| 10500 | 2500 | Al₂O₃ | WF₆/BCl₃ ALE |
| 10500 | 750  | TiO₂  | WF₆/BCl₃ ALE |
| 11000 | 2500 | Al₂O₃ | WF₆/BCl₃ ALE |
| 11000 | 650  | TiO₂  | WF₆/BCl₃ ALE |
| 11500 | 2500 | Al₂O₃ | WF₆/BCl₃ ALE |
| 11500 | 500  | TiO₂  | WF₆/BCl₃ ALE |

| Time (s) | Mass loading (ng cm⁻²) | Material | Cyclic condition |
|---------:|-----------------------:|----------|------------------|
| 9000 | 1500 | Al₂O₃ | ALD  |
| 9000 | 1200 | TiO₂  | ALD  |
| 9100 | 1550 | Al₂O₃ | ALD |
| 9100 | 1250 | TiO₂  | ALD |
| 9200 | 1850 | Al₂O₃ | WF₆  |
| 9200 | 1400 | TiO₂  | WF₆  |
| 9250 | 1800 | Al₂O₃ | BCl₃ |
| 9250 | 1250 | TiO₂  | BCl₃ |
| 9300 | 1850 | Al₂O₃ | WF₆  |
| 9300 | 1300 | TiO₂  | WF₆  |
| 9350 | 1800 | Al₂O₃ | BCl₃  |
| 9350 | 1200 | TiO₂  | BCl₃  |
| 9400 | 1850 | Al₂O₃ | WF₆  |
| 9400 | 1250 | TiO₂  | WF₆  |
| 9450 | 1800 | Al₂O₃ | BCl₃ |
| 9450 | 1150 | TiO₂  | BCl₃  |
| 9500 | 1850 | Al₂O₃ | WF₆ |
| 9500 | 1200 | TiO₂  | WF₆ |

Answer: Mass jump / no etch. No, it does not lose mass. Instead, it shows a distinct upward jump (mass gain) of ~300 ng/cm² initially, followed by a stable plateau. This indicates surface fluorination (adsorption) rather than material removal.

Answer: The thermal WF₆/BCl₃ ALE process is superior. Its purely chemical, self-limiting nature ensures perfect conformality in high-aspect-ratio structures without the directional ion damage inherent to plasma etching, which can degrade sidewall quality and introduce defects in sensitive nanostructures.

Answer: TiO₂ mass decreases because its fluorination/chlorination products (e.g., TiF₄ and TiCl₄) are volatile at 170°C, allowing material removal. Al₂O₃ mass remains stable because its potential reaction products (e.g., AlF₃, AlCl₃) are non-volatile at this temperature, causing the surface reactions to self-passivate rather than etch.

Answer: This implies the process can precisely remove the TiO₂ spacer while using the Al₂O₃ layer as a perfect etch stop. This enables the creation of self-aligned, scaled transistor architectures by selectively etching one material without damaging the other, a critical capability for advanced manufacturing.


Figure 2. Thermodynamic modeling results showing the expected equilibrium species concentrations from 25 to  $400^{\circ}\mathrm{C}$  for  $\mathrm{N}_2$ -diluted  $\mathrm{WF}_6$  exposed to  $\mathrm{TiO}_2$  or  $\mathrm{Al}_2\mathrm{O}_3$  at  $P = 1.5$  Torr: (a)  $1\mathrm{mol}$ $\mathrm{WF}_6 + 1\mathrm{mol}$ $\mathrm{TiO}_2$  and (b)  $1\mathrm{mol}$ $\mathrm{WF}_6 + 0.667\mathrm{mol}$ $\mathrm{Al}_2\mathrm{O}_3$ .

Equilibrium analysis for the WF₆–TiO₂ system shows a temperature-dependent transition from solid TiF₄(s) to gaseous TiF₄(g) above ~120 °C, enabling etching; at higher temperatures, tungsten oxide byproducts such as WO₃(s) convert to volatile species (e.g., WF₂O₂(g)).

Equilibrium analysis for the WF₆–Al₂O₃ system shows that AlF₃(s) remains solid and stable over the entire temperature range, indicating fluorination without volatilization or etching.

| Temperature (°C) | Equilibrium Concentration (mol) | Material        |
|------------------|----------------------------------|----------------|
| 0   | 1.00 | TiF₄ (s) |
| 0   | 0.00 | TiF₄ (g) |
| 0   | 0.65 | WO₃ (s)  |
| 0   | 0.30 | WF₆ (g)  |
| 0   | 0.00 | WF₂O₂ (g) |
| 50  | 1.00 | TiF₄ (s) |
| 50  | 0.00 | TiF₄ (g) |
| 50  | 0.65 | WO₃ (s)  |
| 50  | 0.30 | WF₆ (g)  |
| 50  | 0.00 | WF₂O₂ (g) |
| 100 | 0.00 | TiF₄ (s) |
| 100 | 1.00 | TiF₄ (g) |
| 100 | 0.65 | WO₃ (s)  |
| 100 | 0.30 | WF₆ (g)  |
| 100 | 0.00 | WF₂O₂ (g) |
| 150 | 0.00 | TiF₄ (s) |
| 150 | 1.00 | TiF₄ (g) |
| 150 | 0.60 | WO₃ (s)  |
| 150 | 0.25 | WF₆ (g)  |
| 150 | 0.10 | WF₂O₂ (g) |
| 200 | 0.00 | TiF₄ (s) |
| 200 | 1.00 | TiF₄ (g) |
| 200 | 0.40 | WO₃ (s)  |
| 200 | 0.20 | WF₆ (g)  |
| 200 | 0.40 | WF₂O₂ (g) |
| 250 | 0.00 | TiF₄ (s) |
| 250 | 1.00 | TiF₄ (g) |
| 250 | 0.10 | WO₃ (s)  |
| 250 | 0.05 | WF₆ (g)  |
| 250 | 0.90 | WF₂O₂ (g) |
| 300 | 0.00 | TiF₄ (s) |
| 300 | 1.00 | TiF₄ (g) |
| 300 | 0.00 | WO₃ (s)  |
| 300 | 0.00 | WF₆ (g)  |
| 300 | 1.00 | WF₂O₂ (g) |
| 350 | 0.00 | TiF₄ (s) |
| 350 | 1.00 | TiF₄ (g) |
| 350 | 0.00 | WO₃ (s)  |
| 350 | 0.00 | WF₆ (g)  |
| 350 | 1.00 | WF₂O₂ (g) |
| 400 | 0.00 | TiF₄ (s) |
| 400 | 1.00 | TiF₄ (g) |
| 400 | 0.00 | WO₃ (s)  |
| 400 | 0.00 | WF₆ (g)  |
| 400 | 1.00 | WF₂O₂ (g) |

| Temperature (°C) | Equilibrium Concentration (mol) | Material |
|------------------|----------------------------------|----------------|
| 0   | 1.30 | AlF₃ (s) |
| 0   | 0.65 | WO₃ (s)  |
| 0   | 0.30 | WF₆ (g)  |
| 0   | 0.00 | WF₂O₂ (g) |
| 50  | 1.30 | AlF₃ (s) |
| 50  | 0.65 | WO₃ (s)  |
| 50  | 0.30 | WF₆ (g)  |
| 50  | 0.00 | WF₂O₂ (g) |
| 100 | 1.30 | AlF₃ (s) |
| 100 | 0.65 | WO₃ (s)  |
| 100 | 0.30 | WF₆ (g)  |
| 100 | 0.00 | WF₂O₂ (g) |
| 150 | 1.30 | AlF₃ (s) |
| 150 | 0.60 | WO₃ (s)  |
| 150 | 0.25 | WF₆ (g)  |
| 150 | 0.10 | WF₂O₂ (g) |
| 200 | 1.30 | AlF₃ (s) |
| 200 | 0.40 | WO₃ (s)  |
| 200 | 0.20 | WF₆ (g)  |
| 200 | 0.40 | WF₂O₂ (g) |
| 250 | 1.30 | AlF₃ (s) |
| 250 | 0.10 | WO₃ (s)  |
| 250 | 0.05 | WF₆ (g)  |
| 250 | 0.90 | WF₂O₂ (g) |
| 300 | 1.30 | AlF₃ (s) |
| 300 | 0.00 | WO₃ (s)  |
| 300 | 0.00 | WF₆ (g)  |
| 300 | 1.00 | WF₂O₂ (g) |
| 350 | 1.30 | AlF₃ (s) |
| 350 | 0.00 | WO₃ (s)  |
| 350 | 0.00 | WF₆ (g)  |
| 350 | 1.00 | WF₂O₂ (g) |
| 400 | 1.30 | AlF₃ (s) |
| 400 | 0.00 | WO₃ (s)  |
| 400 | 0.00 | WF₆ (g)  |
| 400 | 1.00 | WF₂O₂ (g) |

Answer: Approximately 120°C.Reason: Below this temperature, the byproduct TiF4 is solid. Instead of removing material (etching), the process would simply convert the surface into a crust of solid fluoride salts, potentially increasing the film thickness and creating particles.

Answer: The equilibrium model may predict low volatility at lower temperatures (e.g., 170°C). However, ALE bypasses this by using a sequential, non-equilibrium process. The BCl₃ step in ALE actively removes the fluorinated surface layer (e.g., as TiCl₄), shifting the local equilibrium and driving the reaction forward kinetically, enabling etching at temperatures where a continuous, equilibrium-driven process would stall.

Answer: The modeling predicts that the TiO₂ system forms volatile products like TiF₄(g) and WOFₓ(g), while the Al₂O₃ system forms non-volatile solids like AlF₃(s) or Al₂O₃(s) remains. This difference in product volatility is the thermodynamic origin of etching selectivity: TiO₂ can be removed as gases, whereas Al₂O₃ forms a stable, non-volatile layer that halts the reaction.

Answer: This provides a built-in etch stop capability. Engineers can design a stack where a thin Al₂O₃ layer is placed beneath or adjacent to the TiO₂ layer intended for removal. The WF₆-based etch will spontaneously stop on the Al₂O₃, allowing for precise, self-aligned patterning without the need for complex real-time endpoint detection, simplifying integration and improving yield.


Figure 3. (a) QCM analysis of  $\mathrm{TiO_2}$  ALD followed by  $50~\mathrm{WF}_6$  doses at 120 and  $220^{\circ}C$  and (b) an enlarged view of the mass loading during the  $\mathrm{WF}_6$  doses, showing net mass loss during each  $\mathrm{WF}_6$  step at  $220^{\circ}C$  and little to no change at  $120^{\circ}C$

The chart represents the QCM data showing TiO₂ mass changes during ALD and subsequent WF₆ doses at 120°C and 220°C; only the 220°C sample exhibits noticeable mass loss per dose, indicating active etching.

Magnified view of the WF₆ dosing period; 220°C shows stepwise mass loss (etching), while 120°C shows negligible change, confirming the reaction is thermally activated.

| Time (s) | Mass Loading (ng/cm²) | Temperature (°C) | Condition |
|---------:|-----------------------|------------------|-----------|
| 18000 | 5200 | 120 |TiO₂ ALD |
| 18000 | 4000 | 220 |TiO₂ ALD |
| 18500 | 5500 | 120 | TiO₂ ALD |
| 18500 | 4200 | 220 | TiO₂ ALD |
| 19000 | 5650 | 120 | WF₆ dose  |
| 19000 | 4100 | 220 | WF₆ dose  |
| 19500 | 5750 | 120 |  WF₆ dose |
| 19500 | 3950 | 220 | WF₆ dose  |
| 20000 | 5800 | 120 | WF₆ dose  |
| 20000 | 3700 | 220 | WF₆ dose  |
| 20500 | 5800 | 120 | WF₆ dose  |
| 20500 | 3300 | 220 | WF₆ dose  |
| 21000 | 5800 | 120 | WF₆ dose  |
| 21000 | 2600 | 220 | WF₆ dose  |

| Time (s) | Mass Loading (ng/cm²) | Temperature (°C) | Condition |
|---------:|-----------------------|------------------|-----------|
| 19920 | 5820 | 120 | |
| 19920 | 5720 | 220 | |
| 19940 | 5820 | 120 | WF₆ |
| 19940 | 5736 | 220 | WF₆|
| 19960 | 5820 | 120 | |
| 19960 | 5679 | 220 | |
| 20000 | 5820 | 120 | WF₆ |
| 20000 | 5700 | 220 | WF₆ |
| 20040 | 5820 | 120 | |
| 20040 | 5650 | 220 | |
| 20060 | 5820 | 120 | WF₆ |
| 20060 | 5658 | 220 | WF₆ |
| 20080 | 5820 | 120 | |
| 20080 | 5600 | 220 | |

Answer:
Deposit a TiO₂ film on the QCM sensor via ALD.

Stabilize the system at 220°C and the desired pressure.

Expose the film to a sequence of 50 WF₆ doses, each followed by an inert purge.

Continuously record the QCM frequency (converted to mass loading) throughout the dose sequence.

Answer: The lower temperature (120°C) is forced to protect the polymers. The trade-off is that no etching occurs at this temperature, so the desired material removal cannot be achieved with thermal WF₆ alone. An alternative approach, such as using a more reactive chemistry or a non-thermal activation method (like plasma), would be required, introducing complexity or potential damage.

Answer: This implies that a purely thermal WF₆ etch process is not compatible with such a low thermal budget. Since significant etching only occurs at 220°C, exceeding the 150°C limit, integration would require a fundamental process change. Options include performing the etch earlier in the flow (before temperature-sensitive layers) or developing a plasma-assisted WF₆ process that could lower the required substrate temperature.

Answer: Temperature drastically affects the etching rate. At 220°C, etching proceeds readily, while at 120°C, it is negligible. This is because the reaction is thermally activated; sufficient thermal energy is required to overcome the activation barrier for breaking Ti–O bonds and forming volatile titanium fluoride (TiF₄) and tungsten oxyfluoride products.


Figure 7. (a) QCM analysis of  $\mathrm{WF}_6$  etching following 50, 100, and  $200\mathrm{TiO}_2$  ALD cycles on a bare Au QCM crystal at  $220^{\circ}C$  and 1.75 Torr. (b) Enlarged view of  $\mathrm{WF}_6$  etching showing an "incubation" period for the vapor etching that is dependent on the initial  $\mathrm{TiO}_2$  film thickness.

QCM data showing TiO₂ etching for different thicknesses (50, 100, 200 ALD cycles) at 220 °C. Thin films etch immediately, while thick films show an incubation period (mass gain/plateau) before etching due to crystallization increasing chemical resistance.

This mutliple line chart focusing on the mass loading of TiO₂ cycles and WF₆ doses over time, highlighting the effect of 50 doses at specific intervals.

| Time (s) | Mass Loading (ng/cm²) | Condition |
|---------:|----------------------|-----------|
| 0     | 0       | 50 TiO₂ cycles + 50 WF₆ doses |
| 0     | 0       | 100 TiO₂ cycles + 50 WF₆ doses |
| 0     | 0       | 200 TiO₂ cycles + 50 WF₆ doses |
| 2000  | 250     | 50 TiO₂ cycles + 50 WF₆ doses |
| 2000  | 90     | 100 TiO₂ cycles + 50 WF₆ doses |
| 2000  |355     | 200 TiO₂ cycles + 50 WF₆ doses |
| 4000  | 552     | 50 TiO₂ cycles + 50 WF₆ doses |
| 4000  | 405     | 100 TiO₂ cycles + 50 WF₆ doses |
| 4000  | 700     | 200 TiO₂ cycles + 50 WF₆ doses |
| 6000  | 234     | 50 TiO₂ cycles + 50 WF₆ doses |
| 6000  | 675    | 100 TiO₂ cycles + 50 WF₆ doses |
| 6000  | 1100    | 200 TiO₂ cycles + 50 WF₆ doses |
| 8000  | 220    | 50 TiO₂ cycles + 50 WF₆ doses |
| 8000  | 1555    | 100 TiO₂ cycles + 50 WF₆ doses |
| 8000  | 1500    | 200 TiO₂ cycles + 50 WF₆ doses |
| 10000 |  | 50 TiO₂ cycles + 50 WF₆ doses |
| 10000 | 300     | 100 TiO₂ cycles + 50 WF₆ doses |
| 10000 | 2000    | 200 TiO₂ cycles + 50 WF₆ doses |
| 12000 |  | 50 TiO₂ cycles + 50 WF₆ doses |
| 12000 | 0      | 100 TiO₂ cycles + 50 WF₆ doses |
| 12000 | 2100    | 200 TiO₂ cycles + 50 WF₆ doses |
| 16000 |  | 50 TiO₂ cycles + 50 WF₆ doses |
| 16000 |  | 100 TiO₂ cycles + 50 WF₆ doses |
| 16000 | 3400    | 200 TiO₂ cycles + 50 WF₆ doses |
| 18000 |  | 50 TiO₂ cycles + 50 WF₆ doses |
| 18000 | | 100 TiO₂ cycles + 50 WF₆ doses |
| 18000 | 3800    | 200 TiO₂ cycles + 50 WF₆ doses |
| 22000 | | 50 TiO₂ cycles + 50 WF₆ doses |
| 22000 | | 100 TiO₂ cycles + 50 WF₆ doses |
| 22000 | 3200    | 200 TiO₂ cycles + 50 WF₆ doses |

| Time (s) | Mass Loading (ng/cm²) | Condition |
|---------:|----------------------|-----------|
| 200  | 500  | 50 TiO₂ cycles |
| 200  | 1700 | 100 TiO₂ cycles |
| 200  | 3300 | 200 TiO₂ cycles |
| 400  | 590  | 50 TiO₂ cycles |
| 400  | 1872 | 100 TiO₂ cycles |
| 400  | 3332 | 200 TiO₂ cycles |
| 600  | 680  | 50 TiO₂ cycles |
| 600  | 2096 | 100 TiO₂ cycles |
| 600  | 3500 | 200 TiO₂ cycles |
| 800  | 340  | 50 TiO₂ cycles + 50 WF₆ doses  |
| 800  | 1850 | 100 TiO₂ cycles + 50 WF₆ doses|
| 800  | 3600 | 200 TiO₂ cycles + 50 WF₆ doses |
| 1000 | 325  | 50 TiO₂ cycles + 50 WF₆ doses|
| 1000 | 1700 | 100 TiO₂ cycles + 50 WF₆ doses |
| 1000 | 3620 | 200 TiO₂ cycles + 50 WF₆ doses|
| 1200 | 280  | 50 TiO₂ cycles + 50 WF₆ doses |
| 1200 | 1500 | 100 TiO₂ cycles + 50 WF₆ doses |
| 1200 | 3600 | 200 TiO₂ cycles + 50 WF₆ doses |
| 1400 | 258  | 50 TiO₂ cycles + 50 WF₆ doses |
| 1400 | 1200 | 100 TiO₂ cycles + 50 WF₆ doses |
| 1400 | 3600 | 200 TiO₂ cycles + 50 WF₆ doses |

Answer: The WF₆ vapor etch process introduces a significant challenge. In an ideal ALE process, each cycle removes a fixed thickness regardless of initial film thickness. Here, the thickness-dependent incubation means etching would initiate at different times across the wafer if the starting thickness varies, leading to severe non-uniformity. The trade-off for using this simpler vapor etch is loss of uniformity control.

Answer: Surface fluorination. The WF₆ reacts with the surface to form solid fluorides (TiFₓ) or adsorbed tungsten species. Because the underlying film is resistant (incubation), these heavy species accumulate on the surface, adding mass before the volatilization reaction (TiF₄ ↑) initiates material removal.

Answer: Crystalline resistance. The 50-cycle film is likely amorphous (disordered structure), making it chemically vulnerable and allowing immediate etching. The 200-cycle film has likely crystallized into a denser phase (e.g., Anatase), which is thermodynamically more stable and resistant to chemical attack, requiring an incubation period to roughen the surface and create active sites before rapid etching can proceed.

Answer: It implies the process requires a robust endpoint detection method and likely an over-etch period. Since the etch start time is unpredictable based on thickness, one cannot rely on timed etching alone. The process must monitor for the end of the incubation/etch transition (e.g., via mass spectrometry or optical emission) and then continue for a controlled over-etch to ensure complete clearance across all thickness variations.


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The multiple line graph shows the density of Si and Cl atoms at different Z positions along the y-axis, indicating that after the first chlorination step Cl remains near the surface while Si dominates the bulk.

The multiple line graph shows the density of Si and Cl atoms at different Z positions along the y-axis, indicating that after the first ion bombardment step the near-surface Si density decreases and the Cl profile becomes slightly redistributed.

The multiple line graph shows the density of Si and Cl atoms at different Z positions along the y-axis, indicating that after the fourth chlorination step Cl penetration into the near-surface region increases while Si density near the surface is further reduced.

The multiple line graph shows the density of Si and Cl atoms at different Z positions along the y-axis, indicating that after the fourth ion bombardment step Si is further sputtered from the surface and the Cl distribution becomes more diffuse.

The multiple line graph shows the density of Si and Cl atoms at different Z positions along the y-axis, indicating that after the eighth chlorination step a pronounced Cl-rich surface layer forms with a corresponding depletion of Si near the interface.

The multiple line graph shows the density of Si and Cl atoms at different Z positions along the y-axis, indicating that after the eighth ion bombardment step the surface Si density continues to decrease while the Cl profile is partially flattened due to repeated sputtering and mixing.

| Z Position (Å) |  Si Density (atom/Å³) | Cl Density (atom/Å³) |
|----------------|----------------------|----------------------|
| 0  | 0.075 | 0.000 |
| 5  | 0.048 | 0.000 |
| 10 | 0.049 | 0.000 |
| 15 | 0.047 | 0.000 |
| 20 | 0.052 | 0.000 |
| 25 | 0.049 | 0.000 |
| 30 | 0.050 | 0.000 |
| 35 | 0.049 | 0.000 |
| 40 | 0.049 | 0.000 |
| 45 | 0.050 | 0.001 |
| 50 | 0.049 | 0.002 |
| 55 | 0.002 | 0.068 |
| 60 | 0.000 | 0.000 |

| Z Position (Å) | Si Density (atom/Å³) | Cl Density (atom/Å³) |
|----------------|----------------------|----------------------|
| 0  | 0.070 | 0.000 |
| 5  | 0.048 | 0.000 |
| 10 | 0.050 | 0.000 |
| 15 | 0.049 | 0.000 |
| 20 | 0.052 | 0.000 |
| 25 | 0.050 | 0.000 |
| 30 | 0.050 | 0.000 |
| 35 | 0.052 | 0.001 |
| 40 | 0.050 | 0.002 |
| 45 | 0.048 | 0.003 |
| 50 | 0.038 | 0.005 |
| 55 | 0.012 | 0.005 |
| 60 | 0.000 | 0.000 |

| Z Position (Å) | Si Density (atom/Å³) | Cl Density (atom/Å³) |
|----------------|----------------------|----------------------|
| 0  | 0.075 | 0.000 |
| 5  | 0.046 | 0.000 |
| 10 | 0.048 | 0.000 |
| 15 | 0.049 | 0.000 |
| 20 | 0.051 | 0.000 |
| 25 | 0.050 | 0.000 |
| 30 | 0.052 | 0.002 |
| 35 | 0.048 | 0.004 |
| 40 | 0.050 | 0.003 |
| 45 | 0.042 | 0.004 |
| 50 | 0.035 | 0.015 |
| 55 | 0.008 | 0.008 |
| 60 | 0.000 | 0.000 |

| Z Position (Å) | Si Density (atom/Å³) | Cl Density (atom/Å³) |
|----------------|----------------------|----------------------|
| 0  | 0.075 | 0.000 |
| 5  | 0.045 | 0.000 |
| 10 | 0.049 | 0.000 |
| 15 | 0.048 | 0.000 |
| 20 | 0.051 | 0.000 |
| 25 | 0.050 | 0.000 |
| 30 | 0.050 | 0.001 |
| 35 | 0.051 | 0.003 |
| 40 | 0.052 | 0.004 |
| 45 | 0.050 | 0.003 |
| 50 | 0.042 | 0.003 |
| 55 | 0.010 | 0.003 |
| 60 | 0.000 | 0.000 |

| Z Position (Å) | Si Density (atom/Å³) | Cl Density (atom/Å³) |
|----------------|----------------------|----------------------|
| 0  | 0.072 | 0.000 |
| 5  | 0.048 | 0.000 |
| 10 | 0.046 | 0.000 |
| 15 | 0.048 | 0.000 |
| 20 | 0.050 | 0.000 |
| 25 | 0.051 | 0.000 |
| 30 | 0.050 | 0.001 |
| 35 | 0.050 | 0.003 |
| 40 | 0.052 | 0.002 |
| 45 | 0.045 | 0.004 |
| 50 | 0.038 | 0.009 |
| 55 | 0.010 | 0.015 |
| 60 | 0.000 | 0.000 |

| Z Position (Å) | Si Density (atom/Å³) | Cl Density (atom/Å³) |
|----------------|----------------------|----------------------|
| 0  | 0.073 | 0.000 |
| 5  | 0.047 | 0.000 |
| 10 | 0.049 | 0.000 |
| 15 | 0.048 | 0.000 |
| 20 | 0.050 | 0.000 |
| 25 | 0.051 | 0.000 |
| 30 | 0.049 | 0.001 |
| 35 | 0.048 | 0.004 |
| 40 | 0.051 | 0.003 |
| 45 | 0.046 | 0.004 |
| 50 | 0.040 | 0.006 |
| 55 | 0.009 | 0.005 |
| 60 | 0.000 | 0.000 |

Answer: It implies a Steady-State Regime. Since the thickness of the damaged/mixed layer stops growing and remains constant from Cycle 4 to Cycle 8, the process has stabilized. This means the Etch Rate per Cycle (EPC) is now constant and predictable, which is the ideal operating condition for manufacturing precision devices.

Answer: Amorphization (or Lattice Damage). The vertical drop in (a) represents an atomically sharp, ordered crystal. The gradual slope in (f) indicates that the repeated ion bombardment has disordered the lattice, creating a region of low-density amorphous silicon and mixing it with the surface, rather than maintaining a perfect crystal termination.

Answer: It represents the Total Etch Depth (or material removed). The receding boundary shows that the cyclic ALE process is successfully removing silicon layer-by-layer, resulting in a 10 \AA trench depth after 8 cycles.

Answer: Contamination / Defect Generation. The tail shows that Chlorine is trapped inside the silicon lattice, not just on top. If a new layer is grown on this surface, the trapped Chlorine acts as a contaminant. It can diffuse out, causing corrosion, void formation, or electrical defects that ruin the crystal quality of the subsequent epitaxial growth.

icdar2026-competition-data/train/atomic-layer-etching/simulation-usecase/15/Molecular dynamics study of silicon atomic layer etching by chlorine gas and argon ions.pdf


FIG. 9. Si and Cl number density profiles at the beginning of  $\mathsf{Ar}^+$  ion bombardment step [panel (a)] and after  $150\mathrm{Ar}^+$  ion impacts [panel (b)]. The black dotted line corresponds to the density of Si at  $300\mathrm{K}$  (Ref. 43). The cycle in this case corresponds to  $2255\mathrm{Cl}_2$  molecule impacts and  $1000\mathrm{Ar}^+$  ion impacts.

This figure displays the depth profiles (density vs. Z-position) of Silicon (blue) and Chlorine (red) during an ALE cycle. Panel (a) shows the state immediately after chlorination but before ion bombardment, where a significant chlorine-rich layer exists at the surface (high Z).

The label shows the state after 150 Argon ion impacts, revealing how the ion bombardment has begun to remove the surface material and push some chlorine deeper into the silicon lattice.

| Z Position (Å) | Si Density (atom/Å³) | Cl Density (atom/Å³) |
|----------------|----------------------|----------------------|
| 0  | 0.060 | 0.000 |
| 5  | 0.047 | 0.000 |
| 10 | 0.048 | 0.000 |
| 15 | 0.048 | 0.000 |
| 20 | 0.049 | 0.000 |
| 25 | 0.050 | 0.000 |
| 30 | 0.053 | 0.000 |
| 35 | 0.045 | 0.005 |
| 40 | 0.051 | 0.002 |
| 45 | 0.048 | 0.002 |
| 50 | 0.038 | 0.009 |
| 55 | 0.005 | 0.012 |
| 60 | 0.000 | 0.000 |

| Z Position (Å) | Si Density (atom/Å³) | Cl Density (atom/Å³) |
|----------------|----------------------|----------------------|
| 0  | 0.070 | 0.000 |
| 5  | 0.046 | 0.000 |
| 10 | 0.050 | 0.000 |
| 15 | 0.049 | 0.000 |
| 20 | 0.051 | 0.000 |
| 25 | 0.052 | 0.000 |
| 30 | 0.050 | 0.001 |
| 35 | 0.048 | 0.003 |
| 40 | 0.051 | 0.003 |
| 45 | 0.044 | 0.005 |
| 50 | 0.038 | 0.008 |
| 55 | 0.008 | 0.010 |
| 60 | 0.000 | 0.000 |

Answer: Residue vs. Damage. Stopping at 150 impacts leaves a high concentration of residual chlorine (red line is still prominent), which could contaminate the next layer. However, continuing to 1000 impacts ensures a cleaner surface but risks deeper ion damage to the underlying silicon crystal structure.

Answer: This is caused by Knock-on Implantation or Mixing. The energetic Ar+ ions transfer momentum to the surface chlorine atoms, driving some of them deeper into the silicon lattice rather than just sputtering them off. This creates a mixed, amorphous Si-Cl sub-surface layer.

Answer: Increased Roughness. The gradual density transition indicates that the surface is not atomically flat but rather rough or intermixed, which can degrade carrier mobility in the final semiconductor device.

Answer: Physical Sputtering / Ion Bombardment. The 150 Ar^+ ion impacts have physically sputtered away the top-most layer of chlorinated silicon, reducing the total amount of chlorine and receding the surface (Z position decreases).


Fig. 6. Line plots illustrating the effects of the gap distance on precursor separation, of which operating condition is (a) Case 1, (b) Case 2, (c) Case 3, and (d) Case 4 as described in Table 3. The shaded area indicates the precursor intermixing zone.

The line chart shows the mole fraction of HF and TMA at different positions along the x-axis.

The line chart displays the mole fraction of HF and TMA with sharp transitions at specific positions related to the tool geometry.

The line chart shows the mole fraction of HF and TMA with sharp transitions at specific positions related to the tool geometry.

The line chart illustrates the mole fraction of HF and TMA with sharp transitions at specific positions related to the tool geometry.

| Position (mm) | Mole Fraction HF |Mole Fraction TMA |
|---|---|---|
|-100 | 0.2 |0.12|
|-50 | 0.21 |0.13|
|0 | 0.15 |0.18|
|50 | 0.13 |0.26|
|100 | 0.11 |0.25|

| Position (mm) | Mole Fraction HF |Mole Fraction TMA |
|---|---|---|
|-100 | 0 |0|
|-50 | 0.67 |0|
|0 | 0 |0|
|50 | 0 |0.55|
|100 | 0 |0|

Answer: The width of the slits is equal to the width of the plateau, which is about 30 mm.

Answer: Part of the gases penetrates into the gas shield regions, which is why there is no precise cut-off.

Answer: No there will not be ALE, as TMA and HF already mix in the gas phase. This can result in continuous etching.

Answer: Low gap sizes usually mean that lower flows of precursor are required so there will be less gas consumption.

icdar2026-competition-data/train/atomic-layer-etching/simulation-usecase/16/Multiscale computational fluid dynamics modeling.pdf


Fig. 7. Line plots illustrating the effects of the  $\mathbb{N}_2$  flow rate on precursor separation, of which operating condition is (a) Case 1, (b) Case 5, (c) Case 6, and (d) Case 7 as described in Table 3. The shaded area indicates the precursor intermixing zone.

The line chart shows the mole fraction of HF and TMA at different positions along the x-axis. Where the blue area depicts gas mixing.

| Position (mm) | Mole Fraction HF |Mole Fraction TMA |
|---|---|---|
|-100 | 0.09 |0.03|
|-50 | 0.11 |0.04|
|0 | 0.05 |0.06|
|50 | 0.03 |0.12|
|100 | 0.03 |0.11|

| Position (mm) | Mole Fraction HF |Mole Fraction TMA |
|---|---|---|
|-100 | 0.05 |0.01|
|-50 | 0.08 |0.01|
|0 | 0.03|0.03|
|50 | 0.02 |0.08|
|100 | 0.01 |0.06|

| Position (mm) | Mole Fraction HF |Mole Fraction TMA |
|---|---|---|
|-100 | 0.02 |0.00|
|-50 | 0.05 |0.00|
|0 | 0.02|0.02|
|50 | 0.01 |0.05|
|100 | 0.00 |0.02|

Answer: Yes this could be a problem, in that case the flows of reactants should also increase.

Answer: The TMA slit is located on the right side as there the TMA signal is the highest.

Answer: The gas mixing will result in continuous etching, which is detrimental to ALE.

Answer: Yes there is.


Fig. 8. Line plots illustrating the effects of the precursor flow rate on precursor separation, of which operating condition is (a) Case 1, (b) Case 8, (c) Case 9, and (d) Case 10 as described in Table 3. The shaded area indicates the precursor intermixing zone.

The line chart shows the mole fraction of HF and TMA at various positions along the x-axis, where the mixing of HF and TMA is shown blue.

The line chart displays the mole fraction of HF and TMA at different positions, where the mixing of HF and TMA is shown blue.

The line chart illustrates the mole fraction of HF and TMA at varying positions, where the mixing of HF and TMA is shown blue.

The line chart depicts the mole fraction of HF and TMA at different positions, where the mixing of HF and TMA is shown blue.

| Position (mm) | Mole Fraction HF |Mole Fraction TMA |
|---|---|---|
|-100 | 0.27 |0.14|
|-50 | 0.29 |0.16|
|0 | 0.19 |0.22|
|50 | 0.12 |0.31|
|100 | 0.11 |0.30|

| Position (mm) | Mole Fraction HF |Mole Fraction TMA |
|---|---|---|
|-100 | 0.33 |0.13|
|-50 | 0.35 |0.14|
|0 | 0.2 |0.22|
|50 | 0.11 |0.4|
|100 | 0.11 |0.38|

| Position (mm) | Mole Fraction HF |Mole Fraction TMA |
|---|---|---|
|-100 | 0.4 |0.11|
|-50 | 0.42 |0.12|
|0 | 0.25 |0.26|
|50 | 0.08 |0.43|
|100 | 0.08 |0.43|

Answer: The flow of nitrogen in the gas shield can be greatly increased.

Answer: It is likely that there will be continuous etching, even though the mole fractions of TMA and HF in their designated locations are way larger.

Answer: TMA has a higher mole fraction in the HF region as compared to HF in the TMA region. So TMA diffuses more into the other region.

Answer: 0.21