| AVS 66th International Symposium & Exhibition | |
| Atomic Scale Processing Focus Topic | Thursday Sessions |
| Session AP+PS+TF-ThM |
| Session: | Thermal Atomic Layer Etching |
| Presenter: | Jessica A. Murdzek, University of Colorado at Boulder |
| Authors: | J.A. Murdzek, University of Colorado at Boulder S.M. George, University of Colorado at Boulder |
| Correspondent: | Click to Email |
Thermal atomic layer etching (ALE) can be achieved with sequential, self-limiting surface reactions. One mechanism for thermal ALE is based on fluorination and ligand-exchange reactions. For metal oxide ALE, fluorination converts the metal oxide to a metal fluoride. The ligand-exchange reaction then removes the metal fluoride by forming volatile products. Previous studies have demonstrated the thermal ALE of amorphous Al2O3 films. However, no previous investigations have explored the differences between the thermal ALE of amorphous and crystalline Al2O3 films.
This study explored the thermal ALE of amorphous and crystalline Al2O3 films. HF or XeF2 was used as the fluorination reactant. Dimethylaluminum chloride (DMAC) or trimethylaluminum (TMA) was employed as the metal precursor for ligand-exchange. The amorphous Al2O3 films had a much higher etch rate per cycle than the crystalline Al2O3 films. When using HF and TMA at 300 °C, the amorphous Al2O3 was removed at 0.78 Å/cycle, whereas the crystalline Al2O3 showed no significant thickness removal after 250 cycles (See Supplemental Figure 1). When using XeF2 and TMA at 300 °C, the etch rate was 0.66 Å/cycle for the amorphous Al2O3 film. In comparison, ALE only removed up to 10 Å of the crystalline Al2O3 film. XeF2 may be able to fluorinate the near surface region of the crystalline Al2O3 film easier than the crystalline bulk of the film.
The differences between amorphous and crystalline Al2O3 are sufficient to obtain selective thermal ALE of amorphous Al2O3 in the presence of crystalline Al2O3. The investigations also examined the effect of annealing temperature on the etch rate per cycle. Amorphous Al2O3 was etched at approximately the same etch rate until the crystallization of amorphous Al2O3 at >880 °C. The thermal ALE of crystalline films is important because amorphous films may not crystallize easily when they are too thin. Consequently, amorphous films may have to be grown thicker, crystallized, and then etched back to obtain the desired ultrathin crystalline film thickness.