FIG. 9. (Color online) Calculation method of band-gap energy by the linear fit of the relative absorption edge.

The graph repesents the Tauc plot,  calculation method of band-gap energy by the linear fit of the relative absorption edge.  The linear fit line meets the x axis at the band gap value. the y axis in this curve represents the relative absorption coefficient.

| Photon energy (eV) | [(-ln T)(hν)]² (a.u.) |
|--------------------|-----------------------|
| 3.0                | 0.00                  |
| 3.5                | 0.00                  |
| 4.0                | 0.00                  |
| 4.5                | 0.00                  |
| 4.7                | 0.01                  |
| 4.8                | 0.05                  |
| 4.9                | 0.20                  |
| 5.0                | 0.60                  |
| 5.1                | 1.20                  |
| 5.2                | 2.00                  |
| 5.3                | 3.20                  |
| 5.4                | 4.60                  |
| 5.5                | 6.20                  |
| 5.6                | 8.00                  |
| 5.7                | 10.00                 |
| 5.8                | 12.20                 |
| 5.9                | 14.60                 |
| 6.0                | 17.00                 |
| 6.1                | 19.50                 |
| 6.2                | 22.00                 |

Answer:
Measure the transmittance T spectrum as a function of wavelength λ.

Convert wavelength to photon energy using  hν=1240/𝜆	 (with λ in nm and energy in eV).

Compute an absorption coefficient proxy such as −ln(𝑇)−ln(T) or 𝛼α.

Apply the Tauc transformation by calculating [−ln(T)⋅hν]^2.

Plot the transformed quantity against the photon energy to determine the optical band gap.

Answer:
AES with High-Energy Ions: Pro: Faster sputtering. Con: Can cause more atomic mixing and roughening, distorting depth resolution.

XPS with Low-Energy Ions: Pro: Better depth resolution and more accurate quantification of light elements due to gentler sputtering.

For accurate light-element quantification with minimal distortion, XPS with low-energy ions is preferable. The trade-off is slower data acquisition, but it preserves interfacial sharpness for more reliable profiling.

Answer: The flat Ga and O profiles indicate excellent compositional uniformity throughout the film's bulk. For a dielectric application, this uniformity is crucial as it suggests a consistent bandgap and defect density with depth, which should lead to a high and predictable breakdown voltage, as electric fields would be evenly distributed without weak points from stoichiometric variations.

Answer:
No.

While the sharp interface and low bulk carbon are positive, the as-deposited film likely has a high density of point defects and disorder. These defects would act as charge traps, leading to poor channel mobility and unstable threshold voltage in a HEMT. Post-deposition annealing is typically required to reduce these defects and improve dielectric quality.

icdar2026-competition-data/dev/atomic-layer-deposition/experimental-usecase/17/F. K. Shan et al.pdf


FIG.5.XRD  $\Phi$  scan of  $20 \mathrm{nm}$  Ti/20 nm PE-ALD  $\mathrm{Co / Si(001)}$  annealed at  $800^{\circ}\mathrm{C}$  The capping layer and remaining Co film were selectively etched before analysis.

The line chart displays intensity values against angles measured in degrees for an XRD measurement.

| φ (degree) | Intensity (a.u.) |
|---|---|
|-180|0 |
|-135|1|
|-90|0 |
|-45|1|
|0|0 |
|45|1|
|90|0 |
|135|1|
|180| 0|

Answer: angular symmetry. Possitive and negative angles give the same intensity

Answer: Cristallinity

Answer: Zero

Answer: From -180 to 180 degrees. Any more would not result in different data as the angles will have radial symmetry


Fig.4 PBE-D3 level minimum energy paths corresponding to the different reaction pathways (a, b) for  $\mathrm{MeCpPtMe}_3$  and (c)  $\mathrm{Pt(acac)_2}$  binding on pristine graphene. First and last points on the reaction coordinate correspond to the physisorbed and chemisorbed species, respectively. Physisorbed species of (a, b) and (c) are  $-0.56$  and  $-1.15\mathrm{eV}$  with respect to the separated species (pristine graphene and  $\mathrm{MeCpPtMe}_3$  or  $\mathrm{Pt(acac)_2}$

Minimum energy pathway for MeCpPtMe₃ binding on pristine graphene, showing the transition from a physisorbed state to a chemisorbed state with a high activation barrier and an overall endothermic reaction.

Alternative reaction pathway for MeCpPtMe₃ on pristine graphene, showing a large kinetic barrier that limits chemisorption, explaining poor ALD nucleation on defect-free graphene.

Minimum energy pathway for Pt(acac)₂ on pristine graphene, showing a strongly stabilized physisorbed state and a very high activation barrier, making chemisorption both thermodynamically and kinetically unfavorable.

| Reaction coordinate | Relative energy (eV) |
|---|---|
| Physisorbed state | −0.56 |
| Transition region | 0.40 |
| Activation barrier | 0.96 |
| Chemisorbed state | 0.36 |

| Reaction coordinate | Relative energy (eV) |
|---|---|
| Physisorbed state | −0.56 |
| Transition region | 0.75 |
| Activation barrier | 1.38 |
| Chemisorbed state | 0.63 |

| Reaction coordinate | Relative energy (eV) |
|---|---|
| Physisorbed state | −1.15 |
| Rising energy region | 1.50 |
| Activation barrier (chemisorption) | 4.14 |
| Chemisorbed state | 3.80 |

Answer: No. The calculated minimum energy paths show high activation barriers, making the chemisorption process kinetically unfavorable.

Answer: Pt(acac)₂ shows the more stable physisorbed state, with a physisorption energy of −1.15 eV.

Answer: The energy profiles indicate that pristine graphene is a poor substrate for Pt ALD with both MeCpPtMe₃ and Pt(acac)₂. High kinetic barriers limit the formation of chemisorbed species, while strong physisorption and low reverse barriers favor desorption. As a result, only trace amounts of Pt are expected to nucleate, explaining the experimentally observed low ALD efficiency on defect-free graphene.

Answer: High activation barriers for chemisorption reactions, Endothermic reaction energies for precursor conversion, Strong stabilization of physisorbed precursor species, Easy backward reactions that favor desorption over binding

icdar2026-competition-data/dev/atomic-layer-deposition/simulation-usecase/13/Bora Karasulu et al.pdf


Fig.8 PBE-D3 level minimum energy paths corresponding to the different reaction pathways for  $\mathrm{MeCpPtMe}_3$  binding on (a) epoxydated and (b) hydroxylated graphene oxide. First and last points on the reaction coordinate correspond to the physisorbed and chemisorbed species, respectively. Physisorbed species of (a) and (b) are  $-1.55\mathrm{eV}$  and  $-0.46\mathrm{eV}$  with respect to the separated species  $(\mathrm{MeCpPtMe}_3$  and GO-epoxy or GO-hydroxy). Activation energy for (b) is computed with respect to the lowest-energy minimum along the pathway (around  $7\dot{A}$  -

Minimum-energy pathway for MeCpPtMe₃ binding on epoxydated graphene oxide, showing energy decrease from physisorbed to chemisorbed states. Adsorption is thermodynamically favorable and kinetically feasible, with a low activation barrier. Chemisorption is slightly stronger compared to hydroxylated GO.

Minimum-energy pathway for MeCpPtMe₃ binding on hydroxylated graphene oxide, showing energy decrease from physisorbed to chemisorbed states. Adsorption is thermodynamically favorable and kinetically feasible, with low activation barriers, though slightly weaker than on epoxydated GO.

| Reaction Coordinate [Å] | Energy [eV] |
|---|---|
| 0   | 0.0   |
| 5   | -1.0  |
| 7   | -2.31 |
| 10  | -3.00 |
| 15  | -4.24 |

| Reaction Coordinate [Å] | Energy [eV] |
|---|---|
| 0   | 0.0   |
| 5   | -0.8  |
| 7   | -2.00 |
| 10  | -2.75 |
| 15  | -3.50 |

Answer: Yes. The computed paths show an energetically downhill transition from physisorbed to chemisorbed states.

Answer: Epoxydated graphene oxide exhibits slightly stronger chemisorption (−4.24 eV) than hydroxylated graphene oxide (−3.50 eV).

Answer: Graphene oxide provides thermodynamically favorable and kinetically accessible sites for MeCpPtMe3 chemisorption due to its surface oxygen functionalities. The low activation barriers and highly exothermic reaction pathways, regardless of whether the GO is epoxydated, hydroxylated, or a mixture, allow for stable Pt adsorption. Uniform functionalization further ensures continuous and controllable Pt loading, making GO a promising substrate for ALD applications.

Answer: Type of oxygen functionality (epoxy vs hydroxyl), Distribution of oxygen groups (uniform vs mixed), Single-sided versus double-sided functionalization, Planarity and structural order of the GO layer


Fig.9 PBE-D3 level minimum energy paths corresponding to the different reaction pathways for  $\mathsf{Pt(acac)}_2$  binding on (a) epoxydated and (b) hydroxylated graphene oxide. First and last points on the reaction coordinate correspond to the physisorbed and chemisorbed species, respectively. Physisorbed species of (a) and (b) are  $-1.96\in V$  and  $-0.86$  eV with respect to the separated species  $(\mathsf{Pt}(\mathsf{acac})_2$  and GO-epoxy or GO-hydroxyl).

Minimum-energy pathway for Pt(acac)₂ binding on epoxydated graphene oxide, showing transition from physisorbed to chemisorbed species. The physisorption energy is −1.96 eV relative to the separated species, and the energy profile illustrates the reaction progression along the surface-specific reaction coordinate.

Minimum-energy pathway for Pt(acac)₂ binding on hydroxylated graphene oxide, showing transition from physisorbed to chemisorbed species. The physisorption energy is −0.86 eV relative to the separated species, with the energy profile reflecting the reaction pathway along the hydroxylated surface.

| Reaction Coordinate [Å] | Energy [eV] |
|---|---|
| 0   | 0.0   |
| 2   | -0.8  |
| 4   | -1.2  |
| 6   | -1.5  |
| 8   | -1.8  |
| 10  | -1.96 |
| 12  | -0.48 |

| Reaction Coordinate [Å] | Energy [eV] |
|---|---|
| 0   | 0.0   |
| 2   | -0.4  |
| 4   | -0.6  |
| 6   | -0.8  |
| 8   | -0.86 |

Answer: Yes. The minimum-energy paths show that the precursor first physisorbs on the surface before transitioning to the chemisorbed state.

Answer: The physisorption energy is −1.96 eV for epoxydated GO and −0.86 eV for hydroxylated GO, indicating stronger initial adsorption on epoxydated surfaces.

Answer: The energy profiles indicate that Pt(acac)₂ chemisorption is significantly hindered on both epoxydated and hydroxylated GO. High barriers and the formation of stable intermediates, particularly on hydroxylated GO, make the process energetically less favorable. Consequently, Pt(acac)₂ is not ideal for practical Pt nucleation or ALD on graphene oxide surfaces.

Answer: Epoxydated GO: stronger physisorption (−1.96 eV), larger energy drop along the path, Hydroxylated GO: weaker physisorption (−0.86 eV), smaller energy drop, Both types influence the relative stabilization of chemisorbed products and the overall reaction energy


Figure 6. DFT (GGA/PBE-D3) level minimum energy paths for the Hacac adsorption on (a)  $\mathrm{Al}_2\mathrm{O}_3$  and (b)  $\mathrm{SiO}_2$  surfaces, as described by the corresponding chemical equations. Minimum energy structures of the important steps are also shown (yellow, green, and blue dots and corresponding insets), where some oxygen and hydrogen atoms are hidden for clarity. First points of the energy profiles correspond to the Hacac species physisorbed on each surface and have  $\Delta E_{\mathrm{p}} = -0.75$  and  $-0.37 \mathrm{eV}$  with respect to the separated Hacac gas phase and  $\mathrm{Al}_2\mathrm{O}_3 / \mathrm{SiO}_2$  surfaces. These are taken as reference points  $(0 \mathrm{eV})$  to calculate the activation and final-state energies. Color code for atoms: silicon, pink; aluminum, light gray; hydrogen, white; oxygen, red; carbon, gray.

The diagram represent the Density Functional Theory (DFT)-calculated reaction energy values comparing the chemisorption of Hacac on Al₂O₃ surface. The diagrams show the activation energy (Eₐ) and reaction energy (ΔE) for the ligand-exchange reaction where Hacac replaces a surface hydroxyl group.

The diagram represent the Density Functional Theory (DFT)-calculated reaction energy values comparing the chemisorption of Hacac on SiO₂surfaces. The diagrams show the activation energy (Eₐ) and reaction energy (ΔE) for the ligand-exchange reaction where Hacac replaces a surface hydroxyl group. The key difference is that the reaction is exothermic and low-barrier on Al₂O₃ (ΔE = -0.49 eV, Eₐ = 0.01/0.25 eV) but endothermic and high-barrier on SiO₂ (ΔE = +0.98 eV, Eₐ = 2.35 eV).

| Reaction step | Energy (eV) |
| ------ | ------- |
| Physisorbed state | 0.05  |
| Transition State  | 0.25  |
|  Chemisorbed Product State | -0.49 |

| Reaction step | Energy (eV) |
| ------ | ------- |
| Physisorbed state | 0.05  |
|  Transition State  | 2.25  |
|  Chemisorbed Product State | 0.98 |

Answer: It implies the Al–O(acac) bond is significantly stronger than the Si–O(acac) bond relative to their respective starting surface OH bonds.

Answer: It suggests performing DFT calculations of the inhibitor's adsorption reaction energy (ΔE) and activation energy (Eₐ) on both target and non-target surfaces. A successful selective process will likely require a large thermodynamic and kinetic preference (exothermic/low-barrier on target, endothermic/high-barrier on non-target) similar to the Al₂O₃/SiO₂ case shown here. This computational screen can rapidly identify promising inhibitor candidates before costly experimentation.

Answer:
Physisorbed State: Hacac near the surface (0 eV reference).

Transition State: Peak at ~0.25 eV (Eₐ).

Chemisorbed Product State: Al(acac)⁺ + H₂O(g) at -0.49 eV (ΔE).

Answer: The very low Eₐ on Al₂O₃ (0.25 eV) means Hacac reacts easily at low temperature, while the much higher Eₐ on SiO₂ (2.35 eV) means it barely reacts at all under the same conditions. This large gap ensures that at typical ALD temperatures (~250–300 °C), Hacac will strongly chemisorb on Al₂O₃ but remain essentially inactive on SiO₂. As a result, the process naturally becomes highly selective without needing extreme temperatures or additional steps.

icdar2026-competition-data/dev/atomic-layer-deposition/simulation-usecase/4/Alfredo Mameli et al.pdf


Fig. 5 Saturation curves at  $350^{\circ}\mathrm{C}$  for (a) Hhfac pulses using a  $25\mathrm{~s~H}_2$  plasma and (b)  $\mathrm{H}_{2}$  plasma exposure using  $15\times 50\mathrm{~ms}$  pulses of Hhfac per cycle. The lines are guides to the eye.

Panel (a) demonstrates a saturating trend in EPC with increasing number of Hhfac pulses, indicating that the surface becomes increasingly modified until further pulses yield no significant additional etching.

Panel (b) reveals that EPC also increases with H₂ plasma exposure time, but plateaus earlier, suggesting a time threshold beyond which further plasma exposure does not significantly enhance etching. Together, these panels show that both precursor dose and plasma activation are necessary for etching, but only up to saturation limits where the EPC levels off.

| Number of Hhfac pulses | EPC (nm) |
|------------------------|----------|
| 0                      | 0.00     |
| 2                      | 0.04     |
| 4                      | 0.07     |
| 6                      | 0.09     |
| 8                      | 0.10     |
| 10                     | 0.12     |
| 12                     | 0.14     |
| 14                     | 0.15     |
| 16                     | 0.16     |
| 18                     | 0.17     |
| 20                     | 0.17     |

| H₂ plasma exposure time (s) | EPC (nm) |
|-----------------------------|----------|
| 0                           | 0.00     |
| 5                           | 0.07     |
| 10                          | 0.10     |
| 20                          | 0.12     |
| 30                          | 0.16     |
| 60                          | 0.15     |

Answer: Hhfac pulses increase EPC to saturation, H₂ plasma time increases EPC then plateaus

Answer: Around 15 - 20 pulses.

Answer: The observed saturation of EPC with respect to both Hhfac pulses and H₂ plasma exposure indicates a self-limiting process characteristic of atomic layer etching. In panel (a), the surface reaches a state where additional precursor does not further modify it, suggesting that all reactive sites have been consumed. In panel (b), the plasma step reaches a threshold where all chemically modified species have been activated or removed, and further exposure has negligible effect. This behavior supports the controlled, layer-by-layer removal fundamental to ALE.

Answer: No

icdar2026-competition-data/dev/atomic-layer-etching/experimental-usecase/10/Investigation of the atomic layer etching mechanism for Al2O3.pdf


Fig. 6 Thickness evolution as a function of pulses/cycles for (a) only Hhfac dosing, (b) only  $\mathsf{H}_2$  plasma exposure and (c) ALD cycles with Hhfac and  $\mathsf{H}_2$  plasma pulses. Experiments were performed at  $350^{\circ}\mathrm{C}$  table temperature.

Panel (a) shows no change in thickness when only Hhfac is used, even after 20 pulses. Similarly, panel (b) indicates no measurable thickness reduction with H₂ plasma alone. In contrast, panel (c) demonstrates a steady linear decrease in film thickness when both Hhfac and H₂ plasma are applied in combination, highlighting the synergistic effect of this treatment for etching. These results suggest that neither precursor nor plasma alone is sufficient to etch the surface, but their combination results in controlled material removal.

| Number of pulses/cycles | Thickness change (nm) |
|--------------------------|------------------------|
| 0                        | 0                      |
| 5                        | 0                      |
| 10                       | 0                      |
| 15                       | 0                      |
| 20                       | 0                      |

| Number of pulses/cycles | Thickness change (nm) |
|--------------------------|------------------------|
| 0                        | 0                      |
| 5                        | -0.5                   |
| 10                       | -1.0                   |
| 15                       | -1.5                   |
| 20                       | -2.0                   |

Answer: (a): Hhfac, no thickness change, (b): H₂ plasma, no thickness change, (c): Hhfac + H₂ plasma, linear decrease in thickness

Answer: The thickness decreases by approx. 2.0 nm after 20 cycles.

Answer: In atomic layer etching, precursor adsorption alone often does not result in material removal due to the lack of activation energy. Similarly, plasma exposure alone may not modify the surface sufficiently for etching to occur. The combination of Hhfac and H₂ plasma enables a two-step mechanism where Hhfac modifies the surface chemically, and the H₂ plasma provides energetic species to drive desorption or reaction of surface-bound fragments. This synergy allows for a self-limiting, layer-by-layer etching process, as shown by the controlled thickness decrease in panel (c).

Answer: No


Fig. 7 (a) Etched thickness as a function of ALE cycles using 15 pulses of Hhfac dose/hold and  $25\mathrm{~s~H}_{2}$  plasma each cycle. Experiments were performed at  $300^{\circ}\mathrm{C}$  table temperature, yielding an EPC of  $0.08\pm 0.01$  nm per cycle. (b) Reflection mode absorbance spectra for  $\mathrm{Al}_2\mathrm{O}_3$  and  $\mathrm{SiO}_2$  planar films exposed to a  $100\mathrm{~ms}$  Hhfac dose, referenced to their as-deposited surfaces. The Al-O and hfac absorbance regions are highlighted in the figure.

Panel (a) shows that the Al₂O₃ film undergoes a steady decrease in thickness over repeated cycles at 300 °C, with an etch-per-cycle (EPC) of ~0.08 nm. In contrast, the SiO₂ film exhibits negligible thickness change under identical conditions, indicating that the process is selective for Al₂O₃.

Panel (b) supports this observation by displaying FTIR spectra with distinct vibrational signatures for Al–O bonds and hfac ligands on the Al₂O₃ sample, while SiO₂ shows minimal spectral activity. Together, the panels demonstrate selective etching of Al₂O₃ and surface chemical verification via absorbance spectroscopy.

| Cycles | Thickness change (nm) – SiO₂ | Thickness change (nm) – Al₂O₃ |
|--------|------------------------------|-------------------------------|
| 0      | 0.00                         | 0.00                          |
| 5      | 0.00                         | -0.40                         |
| 10     | 0.00                         | -0.80                         |
| 15     | 0.00                         | -1.20                         |
| 20     | 0.00                         | -1.60                         |
| 25     | 0.00                         | -2.00                         |
| 30     | 0.00                         | -2.40                         |

| Wavenumber (cm⁻¹) | Absorbance – Al₂O₃ | Absorbance – SiO₂ |
|-------------------|---------------------|--------------------|
| 4000              | ~0.0001             | ~0.00005           |
| 3300              | ~0.0001             | ~0.00005           |
| 1650              | Peak (hfac)         | —                  |
| 1000              | Strong peak (Al–O)  | Low/no peak        |

Answer: The ALE process selectively etches Al₂O₃ without affecting SiO₂ under the tested conditions. This selectivity is important in applications where material-specific removal is critical, such as semiconductor patterning. The result implies that the chemical reactions involved are highly dependent on the film’s composition, likely due to differences in surface chemistry and bonding environments.

Answer: 0.08 nm per cycle

Answer: Al–O stretching peak at ~1000 cm⁻¹, Hhfac ligand peak at ~1650 cm⁻¹

Answer: No


Fig. 4. Influence of reactant exposure time and temperature on the sample mass changes during thermal ALE  $\mathrm{Al}_2\mathrm{O}_3$  films using TMA and HF. (I): effect of TMA (a) and HF (b) exposure time on mass changes ( $\Delta \mathrm{M}_{\mathrm{TMA}}$  and  $\Delta \mathrm{M}_{\mathrm{HF}}$ ) at  $300^{\circ}\mathrm{C}$ , respectively; (II): effect of temperature on  $\Delta \mathrm{M}_{\mathrm{TMA}}$  and  $\Delta \mathrm{M}_{\mathrm{HF}}$  of TMA, HF half-reaction (a) and mass change per ALE cycle (MCPC). Reproduced from Ref. [28].

Shows mass change (ΔM_TMA) during the TMA half reaction versus TMA exposure time at 300°C. The curve approaches saturation around −29 ng/cm² after ~2 s, demonstrating self limiting ligand exchange behavior.

Shows mass change (ΔM_HF) during the HF half reaction versus HF exposure time at 300°C. The curve saturates at ~13 ng/cm² after ~1 s, confirming self limiting fluorination.

Shows temperature dependence of both half reaction mass changes. ΔM_HF (red) shows slight increase with temperature while ΔM_TMA (blue) becomes more negative, indicating enhanced etching at higher temperatures.

Shows mass change per cycle (MCPC) versus temperature. The increasingly negative MCPC from 250°C to 325°C indicates higher etch rates at elevated temperatures.

| TMA Exposure Time (s) | Delta M_TMA (ng/(cm^2 cycle)) |
|---|---|
| 0.0 | 0 |
| 0.6 | -14 |
| 1.0 | -20 |
| 1.5 | -23 |
| 1.75 | -27 |
| 2.0 | -29 |
| 2.25 | -32 |
| 2.5 | -32 |

| HF Exposure Time (s) | Delta M_HF (ng/(cm^2 cycle)) |
|---|---|
| 0.00 | 0 |
| 0.60 | 12 |
| 0.75 | 12 |
| 1.00 | 13 |
| 1.25 | 14 |
| 1.50 | 15 |
| 1.75 | 15 |

| Temperature (°C) | Delta M_HF (Red Circles) | Delta M_TMA (Blue Squares) |
|---|---|---|
| 250 | 6 | -10 |
| 275 | 9 | -20 |
| 300 | 13 | -29 |
| 325 | 19 | -42 |

| Temperature (°C) | MCPC (ng/(cm^2 cycle)) |
|---|---|
| 250 | -4 |
| 275 | -10 |
| 300 | -16 |
| 325 | -23 |

Answer: The etch rate increases with temperature, from about 0.14 Å/cycle at 250°C to 0.75 Å/cycle at 325°C, as shown by the increasingly negative MCPC values.

Answer: Both curves show saturation behavior where mass change plateaus after sufficient exposure time. For TMA, ΔM_TMA saturates at approximately −29 ng/cm² after 2 s exposure. For HF, ΔM_HF saturates at approximately 13 ng/cm² after 1 s exposure. This saturation indicates that the surface reactions terminate once available reactive sites are consumed, confirming self limiting behavior.

Answer: The x axes represent the precursor exposure time in seconds for each half reaction: TMA exposure time in (a) and HF exposure time in (b).

Answer: ΔM_TMA is negative because the ligand exchange step removes AlF₃ as volatile AlF(CH₃)₂, causing mass loss. ΔM_HF is positive because fluorination adds fluorine to form the heavier AlF₃ surface layer.

icdar2026-competition-data/dev/atomic-layer-etching/experimental-usecase/19/Thermal atomic layer etching Mechanism, materials and prospects.pdf


Figure 1. Mass change versus time for  $\mathrm{Al}_2\mathrm{O}_3$  ALE using sequential TMA and HF exposures at  $300^{\circ}\mathrm{C}$

This QCM measurement shows the mass change during 100 Al₂O₃ ALE cycles using sequential TMA and HF exposures at 300°C. The reaction sequence "2-30-1-30" indicates a 2.0 s TMA dose, 30 s N₂ purge, 1.0 s HF dose, and 30 s N₂ purge per cycle. The highly linear decrease in mass demonstrates that Al₂O₃ ALE proceeds at a constant rate, yielding a mass change per cycle (MCPC) of −15.9 ng/(cm² cycle), equivalent to an etch rate of 0.51 Å/cycle. The slight initial mass gain during the first cycle corresponds to the nucleation period where the AlF₃ surface layer is established on the hydroxylated Al₂O₃ substrate.

| Time (s) | Mass Change (ng/cm²) |
|---|---|
| 0 | 0 |
| 500 | -125 |
| 1000 | -250 |
| 1500 | -375 |
| 2000 | -500 |
| 2500 | -625 |
| 3000 | -750 |
| 3500 | -875 |
| 4000 | -1000 |
| 4500 | -1125 |
| 5000 | -1250 |
| 5500 | -1375 |
| 6000 | -1500 |

Answer: As the mass decreases over the time and negative values are displayed, the process corresponds to atomic layer etching.

Answer: As the exposure time increases, the mass change decreases.

Answer: 30s of N2 after TMA dosing, and 30s after HF.

Answer: Mass change is inversely proportional at 300C. As, the time increases, mass change decreases.

Answer: The stepwise decrease in mass indicates that there are two steps needed to remove material. This is characteristic for ALE.

Answer: The observed etch rate is the slope. This gives an etch rate of 0.25ng/(cm²*s)

Answer: The notation 2-30-1-30 represent the standard way of reporting the dosing scheme in ALD and ALE sources. For this process it corresponds to 2 s of TMA dose, 30 s purge, 1 s HF dose, ending with another 30 s purge.

Answer: No the data does not provide enough information. For this also the thickness of the film before and after etch should be known.

Answer: The annotation indicates alternating exposures of TMA and HF, each followed by purge steps, repeated continuously during the measurement. In ALE, one half-reaction modifies the surface while the other removes material in a controlled way. The nearly constant negative slope in the curve shows that each cycle produces a similar net mass loss, resulting in steady cumulative etching over time.

Answer:
-The mass decreases monotonically with time.
-The slope is approximately constant over most of the plot.
-Mass loss scales proportionally with elapsed time.
-No long plateaus or reversals are observed.

Answer: Al2O3 at 300°C.

Answer: A near-linear mass-loss curve implies that the ALE process is highly repeatable from cycle to cycle. Each exposure sequence removes approximately the same amount of material. This behavior indicates good controllability, allowing total removal to be estimated directly from time or cycle count.

Answer: It represents a 2.0 s TMA exposure, followed by a 30 s N₂ purge, then a 1.0 s HF exposure, and finally a 30 s N₂ purge.

Answer: During the first ALE cycle, the initial hydroxylated Al₂O₃ substrate undergoes reactions that result in net mass gain rather than loss. The first TMA exposure produces AlCH₃* surface species through reaction with surface AlOH* groups, causing a mass gain of approximately 32 ng/cm². The subsequent first HF exposure fluorinates the Al₂O₃ to form an AlF₃ surface layer while converting AlCH₃* to AlF*, adding another ~33 ng/cm². This first cycle establishes the initial AlF₃ layer necessary for the ligand-exchange etching mechanism. Only after this nucleation period do subsequent cycles exhibit the characteristic mass loss associated with material removal.

Answer: The MCPC of −15.9 ng/(cm² cycle) corresponds to an etch rate of 0.51 Å/cycle, based on an Al₂O₃ film density of 3.1 g/cm³.

Answer: The highly linear mass decrease over 100 ALE cycles demonstrates that the etching process is extremely reproducible and proceeds at a constant rate throughout the experiment. This linearity is a hallmark of well-controlled atomic layer processes, indicating that each TMA and HF half-cycle removes a consistent amount of material regardless of how much Al₂O₃ has already been etched. It confirms that the sequential reactions are self-limiting and that there is no degradation or accumulation of byproducts that would alter the etch rate over time. This predictable behavior is essential for applications requiring precise thickness control at the atomic scale.

Answer:
1) TMA (Trimethylaluminum) for 2.0 s
2) purged with nitrogen (N₂) for 30 s
3) HF (Hydrogen Fluoride) for 1.0 s
4) purged again with N₂ for 30 seconds

Answer: Yes, A  linear etching of the Al₂O₃ film with a  slope of the mass change versus time yields a mass change per cycle (MCPC) of −15.9 ng/(cm² cycle)

Answer: The density provides the mass-to-volume relationship for the material. By dividing the MCPC (-15.9 ng/cm²/cycle) by the density, you calculate the volume of material removed per unit area per cycle. Converting this volumetric thickness (cm³/cm²) into angstroms yields the linear etch rate of 0.51 Å/cycle, linking a bulk material property to a nanoscale process metric.

Answer: It implies the first cycle serves as an activation or conditioning step, likely modifying the surface chemistry for subsequent etching. In manufacturing, this means the process recipe must account for an initial "dead cycle" to achieve stable, predictable etch rates. This stabilization is critical for achieving uniform depth control across a wafer.

Answer: No

Answer:
One ALE cycle consists of
I. TMA dose of 2.0 s
II.  N2 purge of 30 s
III. HF dose of 1.0 s
IV. N2 purge of 30 s.

Answer: All ALE cycles show mass loss except during the first ALE cycle. The first cycle displays mass gains.

Answer:
slope of
the mass change versus time yields a mass change per cycle
(MCPC) of −15.9 ng/(cm2 cycle). This MCPC represents the
removal of 9.4 × 1013 “Al2O3” units/(cm2 cycle). This MCPC is
also equivalent to an etch rate of 0.51 Å/cycle based on the
Al2O3 ALD film density of 3.1 g/cm3 determined by XRR.

Answer: 1) Exposure to TMA, 2 seconds, 2)System purge with N2, 30 seconds, 3) Exposure to HF, 1 second, 4) System purge with N2, 30 seconds.

Answer: No, pressure transients were observed during the TMA and HF exposures, which were 40 and 80 mTorr, respectively.

Answer: The observed MCPC was -15.9 ng/(cm^2 cycle), which corresponds to an etch rate of 0.51 Å/cycle.

Answer: The first cycle displays mass gains of 32 ng/cm^2 for TMA and 33 ng/cm^2 for HF. The mass gain for TMA is attributed to the formation of AlCH3* surface species on the initial hydroxylated Al2O3 substrate. Exposure to HF can lead to the formation of AlF* surface species (by reaction with AlCH3*), but the underlying Al2O3 substrate can also be fluorinated to form AlF3. The initial ALE cycle primarily forms AlF3, which is why mass gain is observed rather than etching.

Answer: The first ALE cycle.

Answer: Etching of the Al₂O₃ film

Answer: 63 seconds (2s + 30s + 1s + 30s).

Answer: From the figure, one ALE cycle consists of 2 s TMA exposure, 30 s purge, 1 s HF exposure, and a further 30 s purge, giving a total cycle time of  63 s/cycle. Using two points from the graph, for example, (53 s; 65 ng/cm²) and (4648s; -1095 ng/cm²), the change in mass is Δ𝑀= - 1095 - 65 = - 1160 ng/cm². The change in time is  Δ𝑡 = 4648 - 53 = 4595 s. The slope is therefore  Δ𝑀/ Δ𝑡 = -1160/4595 ≈ - 0.25245 ng/(cm²⋅s).  Multiplying by the cycle time gives the mass change per cycle: MCPC = (- 0.25245)(63) ≈ - 15.9 ng/(cm² ⋅ cycle).

Answer: 300 °C

Answer: The mass decreases steadily throughout the entire experiment. The slope is quite consistent, this gives the appearance of a near-linear drop in mass as the cycles proceed. By the end of the 6000 s window, the sample has lost around 1500 ng/cm², showing that the etching process continues at a  nearly uniform rate.

Answer: No

Answer: TMA dose (2), purge (30), HF dose (1), purge (30).

Answer: During the first cycle, mass gains are observed in both the TMA and HF steps (+32 and +33 ng/cm², respectively), reflecting precursor adsorption on the Al₂O₃ surface. After several cycles, the process reaches a steady regime where the mass decreases linearly with each ALE cycle. The slope of this linear decrease corresponds to a mass loss of −15.9 ng/cm² per cycle, indicating a consistent etch rate and demonstrating stable layer-by-layer removal over 100 cycles.

Answer: 0.51 Å per cycle.

Answer: Yes

Answer: TMA dose for 2 seconds, N₂ purge for 30 seconds, HF dose for 1 second, N₂ purge for 30 seconds, Repetition over 100 cycles

icdar2026-competition-data/dev/atomic-layer-etching/experimental-usecase/24/Trimethylaluminum as the Metal Precursor for the Atomic LayerEtching.pdf


Figure 2. Enlargement of linear region of Figure 1 showing the individual mass changes during the sequential TMA and HF exposures at  $300^{\circ}\mathrm{C}$

This QCM enlargement shows the stepwise mass changes during individual TMA and HF exposures in the steady-state Al₂O₃ ALE regime at 300°C. Each TMA exposure causes a mass decrease (ΔM_TMA = −29 ng/cm²) as AlF₃ is removed via ligand-exchange. Each HF exposure causes a mass increase (ΔM_HF = +13 ng/cm²) as Al₂O₃ is fluorinated to form a new AlF₃ layer. The net mass change per cycle (MCPC = ΔM_TMA + ΔM_HF) is −15.9 ng/(cm² cycle), corresponding to 0.51 Å/cycle etch rate.

| Time (s) | Mass change (ng/cm²) | Precursor | Stage         |
|--------|--------------------|-----|--------------------------|
| 6120     | -1440                | –   | Start of shown segment   |
| 6130     | -1455                | TMA | Mass decrease (ΔM_TMA)   |
| 6160     | -1465                | TMA | End of TMA segment       |
| 6185     | -1455                | HF  | Mass increase (ΔM_HF)    |
| 6210     | -1485                | HF  | End of HF segment        |
| 6240     | -1475                | TMA | TMA pulse   |
| 6260     | -1510                | HF  | HF pulse     |
| 6290     | -1490                | HF  | End of last HF segment   |

Answer: The figure shows a zoom-in view of the entire mass change graph. Here, it is possible to observe the mass change after TMA and HF dosing at 300 °C on Al2O3, with decreasing values over the time and slight mass gains after the HF dose.

Answer: The figure shows a slight decrease as time increases. After the TMA dose, a mass loss can be observed. Subsequently, the HF dose leads to mass gain.

Answer: TMA

Answer: TMA can etch the fluorinated Al2O3 films, removing the AlF3 from the surface. This explains why decreases are observed after TMA dose.

Answer: The MCPC is around -20 ng/cm².

Answer: CH3 has an atomic mass of 15 amu, F has an atomic mass of 19 amuu. So the replacement of a singel CH3 group with a F atom increases the mass with 4 amu.

Answer: Around 65 seconds.

Answer: Based on the few shown cycles it seems that the mass changes are constant for the different cycles.

Answer: The mass increases (becomes less negative), appearing as an upward step corresponding to ΔM_TMA.

Answer: The mass decreases (becomes more negative), appearing as a downward step associated with ΔM_HF.

Answer: The HF step produces the larger step magnitude, reaching a lower mass level of roughly −1510 ng/cm². The TMA step shows a smaller upward recovery to around −1470 ng/cm². Visually, the HF-related drop is sharper and deeper than the TMA-related gain in this zoomed window.

Answer:
-ΔM_TMA from the upward mass step during TMA.
-ΔM_HF from the downward mass step during HF.
-MCPC from the net mass change across one full cycle.
-Presence of plateaus indicating stepwise behavior.

Answer: ΔM_TMA is the mass change after TMA exposure (−29 ng/cm²) and ΔM_HF is the mass change after HF exposure (+13 ng/cm²).

Answer: TMA causes mass loss because it removes the AlF₃ surface layer through ligand-exchange, producing volatile AlF(CH₃)₂ that desorbs. HF causes mass gain because fluorination converts lighter Al₂O₃ (102 amu) into heavier AlF₃ (168 amu for 2AlF₃), a 65% mass increase for the converted layer.

Answer: MCPC = ΔM_TMA + ΔM_HF = (−29) + (+13) = −15.9 ng/(cm² cycle).

Answer: It indicates highly reproducible, steady-state etching with constant material removal per cycle.

Answer:
The formation of volatile byproducts.
In ALD, TMA adsorbs onto the surface and remains there, leading to a net mass gain. In contrast, during this ALE process, TMA reacts with the fluorinated surface (AlF₃) to form volatile species such as dimethylaluminum fluoride, which desorb from the surface. This desorption removes surface atoms, resulting in the observed mass loss (ΔM_TMA).

Answer: The HF/TMA ALE cycle provides true layer-by-layer control, as the mass drop is discrete and self-limiting. A purely thermal HF etch would cause continuous, non-self-limiting mass loss, leading to poor depth control and potential damage from excessive etching, as it lacks the crucial TMA step to regulate the reaction.

Answer: The immediate, sharp drop indicates a fast, self-limiting surface reaction. The mass loss is not gradual, confirming that TMA rapidly reacts with the pre-formed AlF₃ layer in a ligand-exchange process that is limited only by the number of AlF₃ sites created in the previous HF step.

Answer:
No.
While QCM confirms self-limiting chemistry at the sensor spot, perfect wafer-scale uniformity depends on gas flow dynamics, temperature uniformity, and precursor delivery across the entire reactor chamber, which this single-point measurement cannot verify.

Answer: Yes. It helps understand the pronouned mass changes after reactant exposure.

Answer: The TMA exposure results in a mass decrease. This behavior indicates TMA can remove the AlF3 surface layer on the Al2O3 film.

Answer:
1. A mass loss of ΔMTMA = −29 ng/cm2 was observed after 2.0 s of TMA exposure.
2. A mass gain of ΔMHF = 13 ng/cm2 after 1.0 s of HF exposure.

Answer: This mass gain is consistent with the fluorination of Al2O3 to form an AlF3 surface layer. This AlF3 surface layer is then ready for the ligand-exchange reaction during the next TMA exposure.

Answer: Exposure to TMA causes the mass change to decrease by 29 ng/cm^2, whilst exposure to HF causes the mass change to increase by 13 ng/cm^2.

Answer: That TMA can successfully remove the AlF3 surface layer on Al2O3.

Answer: Yes, each ALE cycle results in a net loss of mass and the mass loss per ALE cycle is constant.

Answer: -16 ng/cm^2.

Answer: 3 cycles.

Answer: MCPC = -1474 - (-1457) = - 17 (ng/cm²⋅ cycle)

Answer: The plateaus occur because after each TMA or HF pulse, the surface reactions quickly reach completion, so the mass stops changing. During the purge periods, excess precursor and volatile byproducts are flushed out without further reaction on the surface, which also keeps the signal flat. The graph therefore shows step changes during dosing and stable plateaus once the chamber returns to a reactant-free state.

Answer: TMA exposure, Purge, HF exposure, Purge

Answer: The plot shows that each HF pulse produces a larger mass decrease than each TMA pulse. TMA steps create small, shallow decreases, while HF steps cause deeper drops. This difference in step magnitude reflects the stronger etching action of HF compared to the ligand-exchange removal associated with TMA.

Answer: 300 °C.

Answer: No

Answer: ΔM_TMA, ΔM_HF, TMA, HF arrows

Answer: TMA leads to mass loss, while HF leads to mass gain.

Answer: HF reacts with Al₂O₃, AlF₃ forms on the surface, This structural change results in mass increase

Answer: Yes, the figure shows a stable and repeatable pattern of mass loss followed by mass gain, demonstrating that the etching process is operating as expected. The consistency of these responses across exposures confirms that both half-reactions are self-limiting and that the ALE mechanism is performing effectively at 300°C.

Answer: Yes


Figure 7. Enlargement of linear region of Figure 5 showing the individual mass changes during the sequential TMA and HF exposures at a) 250,b) 275 and c  $325^{\circ}C$

The line chart shows mass change versus time at 250 °C during alternating TMA and HF exposures. The mass change exhibits small stepwise variations, indicating a  relatively low mass change per cycle at this temperature.

The line chart shows mass change versus time at 275 °C. Stepwise increases during TMA exposure and decreases during HF exposure are more pronounced than at 250 °C, indicating a higher mass change per cycle.

The line chart shows mass change versus time at 325 °C. The stepwise mass changes are largest at this temperature, reflecting the highest mass change per cycle among the three conditions.

| Time (s) | Mass change (ng/cm²) |
|----------|----------------------|
| 6150     | ~-320                |
| 6200     | ~-330                |
| 6250     | ~-320                |
| 6300     | ~-330                |

| Time (s) | Mass change (ng/cm²) |
|----------|----------------------|
| 6150     | ~-950                |
| 6200     | ~-980                |
| 6250     | ~-950                |
| 6300     | ~-980                |

| Time (s) | Mass change (ng/cm²) |
|----------|----------------------|
| 6150     | ~-2240               |
| 6200     | ~-2280               |
| 6250     | ~-2240               |
| 6300     | ~-2280               |

Answer: The mass change per cycle (MCPC) is given by the difference between the mass change after the TMA exposure and the mass change after the HF exposure.

Answer: Eventhough in all three cases the same dose times are used, based on the curves it can be said that saturation is faster reached for higher temperatures.

Answer: The sharp drop suggests a rapid removal of material from the surface during the HF exposure step, which is consistent with an etching process.

Answer: 275°C is the better choice. While slower, its more moderate reaction kinetics offer greater control and reduce the risk of over-etching or damaging underlying layers, which is crucial for precision etching of ultrathin films.

Answer: Larger mass decreases are observed after the TMA exposures at 275 and 325 °C. A  mass loss of ΔMTMA = −20.5 ng/cm2 is observed after a TMA exposure for 2.0 s at 275 °C and an even larger mass loss of ΔMTMA = −41.9 ng/cm2 after a TMA exposure for 2.0 s at 325 °C

Answer: -20.5 ng/cm^2.

Answer: First cycle (−11 ng/cm²) shows larger MCPC that the second cycle (−9 ng/cm²).

Answer: Yes

Answer: The mass losses after TMA and mass gains after HF exposures both increase with temperature: smallest at 250 °C, intermediate at 275 °C, and largest at 325 °C.

Answer: Knowing how mass changes vary with temperature helps optimize ALE processes for precise etching. Higher temperatures produce larger mass losses during TMA exposures and larger mass gains during HF exposures, indicating more efficient removal of AlF₃ and fluorination of Al₂O₃. This information allows control over etch rates and surface layer formation, which is critical for applications requiring uniform, conformal, and predictable etching in microfabrication or semiconductor processing.

Answer: Increasing temperatures produce higher values of mass change after HF exposure.

Answer: The highest etch rate is achieved at 325 degrees Celcius. The MCPC is the biggest for this temperature.

Answer: The MCPC is around -25 ng/cm^2

Answer: The mass change per cycle is significantly larger at 325°C compared to the results at 250°C and 275°C. The steps in panel (c) are much more pronounced, spanning a range of over 60 ng/cm² within a single cycle, whereas the changes at lower temperatures are much smaller. This indicates a strong temperature dependence of the process.

Answer: Based on an Al₂O₃ density of 3.1 g/cm³, this MCPC corresponds to an etch rate of 0.75 Å/cycle.

Answer: The sharp drop indicates the rapid removal of material. The TMA reacts with the surface aluminum fluoride (AlF) layer created by the previous HF step. This reaction produces volatile byproducts (like dimethylaluminum fluoride) which immediately desorb into the gas phase, carrying away aluminum atoms and reducing the film mass.

Answer: It implies the process must have excellent temperature control and uniformity across the wafer. A stable, uniform temperature (likely at the higher end, e.g., 300-325°C) is required to ensure reproducible etch rates and consistent film removal across all devices on a production wafer.

Answer:
In contrast, mass increases are observed after the HF fluorination reactions.
1. A mass increase of ΔMHF =6.3 ng/cm2 is observed after the HF exposure for 1.0 s at 250°C
2. HF exposures for 1.0 s produce larger mass gains of ΔMHF = 9.9 ng/cm2 at 275 °C
3. ΔMHF = 18.6 ng/cm2 at 325 °C double the mass gain from 275 °C

Answer: -41.9 ng/cm^2.

Answer: TMA half-cycle.

Answer: 250 °C: ΔMₜₘₐ ≈ −10.5 ng/cm², ΔM_HF ≈ 6.3 ng/cm², 275 °C: ΔMₜₘₐ ≈ −20.5 ng/cm², ΔM_HF ≈ 9.9 ng/cm², 325 °C: ΔMₜₘₐ ≈ −41.9 ng/cm², ΔM_HF ≈ 18.6 ng/cm²

Answer: The increase in mass after HF exposure is directly related to surface fluorination.

Answer: Yes

Answer: In the figure this adsorption is visible, since this happens after 6100 s of processing, it can be assumed that it occurs every cycle, as usually deviations occur in the initial cycles.

Answer: The step-like changes correspond to the alternating exposures of the surface to the TMA and HF precursors. Each precursor introduction causes a distinct surface reaction, resulting in a measurable change in the mass of the sample. The mass then remains relatively stable until the next precursor is introduced, creating the stepwise pattern.

Answer: The consistency of the mass change steps from one cycle to the next indicates a highly controlled and self-limiting process. This repeatability is crucial for ALE, as it ensures that a precise and predictable amount of material is removed in each cycle, allowing for accurate control over the final etch depth.

Answer: ΔM_TMA increases from −10.5 ng/cm² at 250°C to −20.5 ng/cm² at 275°C to −41.9 ng/cm² at 325°C, indicating more AlF₃ removal at higher temperatures.

Answer: HF fluorinates the Al₂O₃ surface to form a heavier AlF₃ layer (Al₂O₃ + 6HF → 2AlF₃ + 3H₂O), causing mass gain. TMA then removes this AlF₃ layer through ligand-exchange, producing volatile AlF(CH₃)₂ that leaves the surface, causing mass loss.

Answer: The dashed lines indicate the mass change per cycle (MCPC), which is the net mass loss after one complete TMA + HF cycle, equal to ΔM_TMA + ΔM_HF.

Answer: In label (a) at 250°C, the step height is tiny (almost flat), implying an etch rate near zero. In label (c) at 325°C, the step height is huge (dropping by tens of ng/cm² per cycle). This exponential-like increase in material removal proves that the rate-limiting chemical reaction (likely ligand exchange) has a high activation energy and requires temperatures well above 250°C to proceed efficiently.

Answer: Yes

Answer: A small  mass decrease is observed after the TMA exposure at 250 °C, a  mass loss of ΔMTMA = −10.5 ng/cm2 after the TMA exposure for 2.0 s at 250 °C.

Answer: -10.5 ng/cm^2.

Answer: The overall mass loss becomes larger as temperature increases.

Answer: 3 cycles.

Answer: Net etching (MCPC slightly negative)

Answer: TMA exposure.

Answer: The magnitude of the stepwise mass change increases with temperature. The 250 °C trace shows the smallest changes, while the 325 °C trace shows the largest stepwise mass loss, indicating stronger reactions at higher temperature.

Answer: a3: 250 °C, 275 °C, 325 °C

Answer: Yes. Mass decreases observed after TMA exposures indicate the removal of the AlF₃ layer.


Figure 2. Change in EPC vs  $\mathrm{NbF}_5$  pulse time at the etch temperature of  $460^{\circ}\mathrm{C}$ . The  $\mathrm{CCl}_4$  pulse time was set to  $3\mathrm{~s~}$  and in-between  $\mathrm{N}_2$  purges were  $6\mathrm{~s~}$  each.

The chart shows the relationship between the pulse time of NbF5 and the etch per cycle in Å/cycle in the cycle (X/6s/3s/6s). The temperature was fixed at 460°C.

| NbF5 pulse time [s] | etch per cycle [Å/Cycle] |
|---|---|
| 0.0 | -0.05 |
| 0.5 | 0.49 |
| 1.75 | 0.87 |
| 3.0 | 1.46 |

Answer: No, it doesn't. When the process is self-limiting, the graph should look like a plateau, because adding more precursor doesn't increase etch rate any further, when the surface is saturated. Here, the EPC keeps increasing with increasing pulse time.

Answer: The pulse sequense is X/6/3/6 s (variable NbF5, 6s Purge, 3s CCl4, 6s Purge). The temperature is 460°C.

Answer: No. The data point corresponding to a NbF5 pulse time of 0 seconds is centred at 0.0 Å/cycle. Although there are error bars due to experimental uncertanty, the deviation is small and eessentially zero material is removed without the second precursor.

Answer: 1.46 Å/Cycle.

icdar2026-competition-data/dev/atomic-layer-etching/simulation-usecase/30/Thermal Atomic Layer Etching of Aluminum Oxide (Al2O3) Using Sequential Exposures of Niobium Pentafluoride.pdf


Figure 4. Effect of  $\mathrm{CCl_4}$  pulse time variation on EPC at  $460^{\circ}\mathrm{C}$ . A total of 150 etch cycles were performed per data point.

The chart shows the etch per cycle at different CCl₄ pulse times. The NbF5 and nitrogen pulse times were set to 3 and 6 seconds respectively. The temperature was fixed at 460 °C.

| CCl₄ pulse time [s] | etch per cycle [Å/Cycle] |
|---|---|
| 0.5 | 1.1 |
| 1.5 | 1.05 |
|1.75 | 1.0 |
| 3.0 | 1.43 |

Answer: Between 0.5 and 1.75 seconds.

Answer: The EPC displays partial self-limiting behavior rather than strict saturation. While it shows a plateau at roughly 1.1 Å/cycle, it noticebly increases to 1.4 Å/cycle when the pulse time is extended to 3 seconds. This suggests the reaction is not completely self-limiting.

Answer: 1.05 Å/cycle.

Answer: 0.5 seconds (EPC is nearly identical to that at 1.75 seconds pulse time, but saves time and precursor).