FIG. 3. Infrared difference spectra recorded after  $\mathrm{BCl}_3$  and  $\mathrm{H}_2\mathrm{O}$  exposures during 13th  $\mathrm{B}_2\mathrm{O}_3$  ALD cycle at  $40^{\circ}\mathrm{C}$ . (a) Difference spectra between 400 and  $1800~\mathrm{cm^{-1}}$ . (b) Difference spectra between 2500 and  $4000~\mathrm{cm^{-1}}$ .

The subfigure compares infrared difference spectra between 400 and 1800 cm⁻¹ recorded after BCl3→H2O and H2O→BCl3 exposures during the 13th B2O3 ALD cycle at 40 °C. Differences in the B–O stretching, B–Cl, and B–O–B bending regions show that the order of precursor exposure strongly affects surface bonding.

The subfigure shows corresponding difference spectra in the O–H stretching region. The presence and intensity of BO–H and hydrogen-bonded O–H features indicate different hydroxylation behavior depending on whether H2O or BCl3 is dosed first.

| Wave number region (cm⁻¹) | Vibrational assignment | Difference between exposure sequences |
|--------------------------|------------------------|---------------------------------------|
| ~1400–1600 | B–O stretch | Stronger feature for BCl3→H2O sequence |
| ~1000 | B–Cl related mode | Present after BCl3 exposure, reduced after H2O |
| ~700–800 | B–O–B bend | Appears more clearly after H2O exposure |
| ~500–600 | O–B–O bend | Small but distinct differences between sequences |

| Wave number region (cm⁻¹) | Vibrational assignment | Difference between exposure sequences |
|--------------------------|------------------------|---------------------------------------|
| ~3700 | BO–H stretch | Sharp feature associated with hydroxyl formation |
| ~3600–3200 | H-bonded O–H | Broad positive band stronger for H2O→BCl3 sequence |

Answer: Changing the exposure order alters which surface bonds form first during the ALD cycle. This is reflected in differences in the B–O stretching, B–Cl, and bending modes, showing that surface chemistry depends strongly on whether chlorination or hydroxylation occurs first.

Answer: The band near ~1000 cm⁻¹.

Answer: Yes

Answer: The H2O→BCl3 sequence.


FIG. 4. Infrared difference spectra between 400 and  $1800~\mathrm{cm^{-1}}$  recorded after consecutive HF exposures on the  $\mathrm{B}_2\mathrm{O}_3$  ALD film at  $150^{\circ}\mathrm{C}$  using the original  $\mathrm{B}_2\mathrm{O}_3$  ALD film as reference. Original  $\mathrm{B}_2\mathrm{O}_3$  ALD film is nearly completely removed after  $>5$  HF exposures.

The figure shows multiple infrared difference spectra of a B2O3 ALD film recorded after consecutive HF exposures at 150 °C. The progressive deepening of the B–O stretching band and the persistence of the B–O–B bending feature indicate rapid removal of the B2O3 film, which is nearly complete after more than five HF exposures.

| Wavenumber region (cm⁻¹) | Vibrational assignment | Evolution with HF exposure |
|--------------------------|------------------------|----------------------------|
| ~1250–1600 | B–O stretch | Strong negative band that deepens with increasing HF exposure; nearly saturated after ~5 exposures |
| ~700–800 | B–O–B bend | Distinct negative feature that persists throughout HF cycling |
| ~1000 | Baseline region | Minor changes relative to main B–O features |

Answer: The increasing depth of the B–O stretching band shows that B–O bonds are progressively removed as HF exposure continues. The saturation of this feature after several cycles indicates that most of the B2O3 film has been etched away.

Answer: After about five HF exposures.

Answer: The B–O–B bending mode.

Answer: Yes

icdar2026-competition-data/test/gold_standard_test_set/atomic-layer-etching/simulation-usecase/28/Spontaneous etching of B2O3 by HF gas studied using infrared spectroscopy.pdf


FIG. 5. Infrared difference spectra between 3350 and  $3850~\mathrm{cm^{-1}}$  recorded after consecutive  $\mathrm{HF}$  exposures on the  $\mathrm{B}_2\mathrm{O}_3$  ALD film at  $150^{\circ}\mathrm{C}$  using the original  $\mathrm{B}_2\mathrm{O}_3$  ALD film as reference.

The figure shows multiple infrared difference spectra of a B2O3 ALD film recorded after consecutive HF exposures at 150 °C. A sharp H–F stretching feature appears after HF dosing, while the B–O–H band decreases, indicating loss of specific hydroxyl configurations. Simultaneously, a broad hydrogen-bonded O–H band deepens with increasing HF exposure, reflecting progressive changes in surface O–H bonding.

| Wavenumber region (cm⁻¹) | Vibrational assignment | Evolution with HF exposure |
|--------------------------|------------------------|----------------------------|
| ~3750–3800 | H–F stretch | Sharp positive peak appears after initial HF exposure |
| ~3700 | B–O–H stretch | Negative feature indicating loss of B–O–H species |
| ~3650–3450 | H-bonded O–H | Broad negative band that deepens and broadens with repeated HF exposures (cycles 4–9) |

Answer: The increasing depth and width of the O–H stretching band indicate that the surface O–H environment becomes more strongly hydrogen-bonded as HF exposure continues. At the same time, the negative B–O–H feature shows depletion of specific hydroxyl configurations present in the initial film. Together, these trends reflect progressive modification of surface O–H bonding during repeated HF exposure.

Answer: The sharp band near 3750–3800 cm⁻¹.

Answer: It decreases in intensity, indicating loss of B–O–H species.

Answer: Yes


FIG. 6. Infrared difference spectra showing absorbance after first HF exposure referenced to the initial  $\mathrm{B}_2\mathrm{O}_3$  ALD film and ninth HF exposure referenced to absorbance after the eighth HF exposure. Inverted absorbance for original  $\mathrm{B}_2\mathrm{O}_3$  ALD film is also shown for comparison.

The figure compares multiple infrared difference spectra of a B2O3 ALD film recorded after the first and ninth HF exposures at 150 °C, together with an inverted reference spectrum. The progressive loss of the B–O stretching band and the appearance of B–F related features indicate systematic chemical modification and fluorination of the B2O3 film with repeated HF exposure.

| Wavenumber region (cm⁻¹) | Assignment | Trend across spectra |
|--------------------------|------------|----------------------|
| ~1400–1600 | B–O stretch | Strong in B2O3 ALD, progressively reduced after repeated HF exposure |
| ~1350 | B–F mode | Appears after HF exposure and strengthens with cycling |
| ~800–900 | Framework modes | Minor changes between spectra |

Answer: The decrease of the B–O stretching band shows that B–O bonds are being removed or altered during HF exposure. At the same time, new features associated with B–F bonding appear, indicating fluorination of the surface as the reaction proceeds.

Answer: The band in the ~1400–1600 cm⁻¹ region.

Answer: The ninth HF exposure shows a weaker B–O stretch and more pronounced B–F related features.

Answer: Yes


FIG. 7. Infrared difference spectra between 400 and  $1800~\mathrm{cm^{-1}}$  recorded after consecutive HF exposures on  $\mathrm{B}_2\mathrm{O}_3$  ALD film at  $40^{\circ}\mathrm{C}$  using the original  $\mathrm{B}_2\mathrm{O}_3$  ALD film as reference. Original  $\mathrm{B}_2\mathrm{O}_3$  ALD film is nearly completely removed after 2 HF exposures.

The subfigure shows infrared difference spectra of a B2O3 ALD film recorded after consecutive HF exposures at 40 °C. A strong loss of the B–O stretching band and a clear B–O–B bending feature indicate progressive removal of the B2O3 film, which is nearly complete after the second HF exposure.

| Wavenumber (cm⁻¹) | Feature | Absorbance change |
|------------------|---------|-------------------|
| ~1400–1550 | B–O stretch | Strong negative band after 2nd HF exposure |
| ~1000 | Baseline region | Minor change |
| ~720 | B–O–B bend | Distinct negative peak |

Answer: The strong decrease in the B–O stretching band intensity shows that B–O bonds are being broken during HF exposure. The appearance and growth of negative features in the difference spectrum indicate loss of the original B2O3 vibrational modes, consistent with progressive etching of the film.

Answer: The B–O stretching mode.

Answer: The second HF exposure shows much stronger negative absorbance, indicating more extensive removal of the B2O3 film.

Answer: Yes