| AVS 62nd International Symposium & Exhibition | |
| Plasma Science and Technology | Wednesday Sessions |
| Session PS+SS+TF-WeM |
| Session: | Atomic Layer Etching (ALE) and Low-Damage Processes I |
| Presenter: | Steven George, University of Colorado at Boulder |
| Authors: | S.M. George, University of Colorado at Boulder Y. Lee, University of Colorado at Boulder J.W. DuMont, University of Colorado at Boulder |
| Correspondent: | Click to Email |
Thermal atomic layer etching (ALE) of Al2O3 and HfO2 has recently been demonstrated using sequential, self-limiting reactions [1-3]. Al2O3 and HfO2 ALE were performed using Sn(acac)2 and HF as the reactants [1-3]. Recent work has also shown that Al2O3 ALE can be accomplished using Al(CH3)3 and HF as the reactants. The ALE reaction mechanism is believed to involve fluorination and ligand-exchange. For Al2O3 ALE using Sn(acac)2 and HF, HF exposures convert Al2O3 to AlF3. Sn(acac)2 then accepts F from AlF3 and donates acac to AlF3 to produce volatile Al(acac)3 or AlF(acac)2.
The prospects for thermal ALE are very promising. Thermochemical calculations suggest that many materials should be etched with similar reactions. Metal oxides, metal nitrides, metal phosphides, metal arsenides and elemental metals can all be fluorinated with fluorine reactants such as HF or XeF2 to form the corresponding metal fluoride. Ligand-exchange reactions can then be conducted with a variety of metal precursors that accept fluorine from the metal fluoride and donate one of their ligands to the metal in the metal fluoride. The metal reaction products then can leave the surface if they are stable and volatile. Preliminary results for GaN etching suggest that metal nitrides are good candidates for thermal ALE.
The metal fluoride reaction products produced by the ligand-exchange process provide pathways for selectivity during thermal ALE. Selectivity can arise depending on the stability of the metal reaction product. For example, Sn(acac)2 is a metal beta-diketonate that donates acac ligands to the metal in the metal fluoride. Because most metals bind with acac ligands, Sn(acac)2 may not lead to significant selectivity. In contrast, Al(CH3)3 is a metal alkyl that donates CH3 ligands to the metal in the metal fluoride. Because some metals do not easily form sigma-bonds to bond to CH3 ligands, more complete selectivity between different materials may be expected for Al(CH3)3. The selectivity observed between Al2O3 and ZrO2 etching will illustrate this concept.
1. Younghee Lee and Steven M. George, “Atomic Layer Etching of Al2O3 Using Sequential, Self-Limiting Thermal Reactions with Sn(acac)2 and HF”, ACS Nano 9, 2061 (2015).
2. Younghee Lee, Jaime W. DuMont and Steven M. George, “Mechanism of Thermal Al2O3 Atomic Layer Etching Using Sequential Reactions with Sn(acac)2 and HF” Chem. Mater. (In Press).
3. Younghee Lee, Jaime W. DuMont and Steven M. George, “Atomic Layer Etching of HfO2 Using Sequential, Self-Limiting Thermal Reactions with Sn(acac)2 and HF”, J. Solid State Sci. Technol. 4, N5013 (2015).