| AVS 65th International Symposium & Exhibition | |
| Thin Films Division | Tuesday Sessions |
| Session TF+PS-TuA |
| Session: | Atomic Layer Processing: Chemistry & Surface Reactions for Atomic Layer Processing |
| Presenter: | Joel Clancey, University of Colorado Boulder |
| Authors: | J.W. Clancey, University of Colorado Boulder A.S. Cavanagh, University of Colorado Boulder S.M. George, University of Colorado Boulder |
| Correspondent: | Click to Email |
Atomic layer etching (ALE) using sequential, self-limiting surface reactions is an important technique for removing material with atomic layer control. In addition, selective ALE is required for the maskless fabrication of advanced devices as feature sizes become smaller than available lithography. This study reports the study of volatile etch products produced by ligand-exchange reactions during thermal ALE and develops our understanding of selective thermal ALE.
Previous studies have revealed selective thermal ALE in the etching of Al2O3, ZrO2 and HfO2 using fluorination and ligand-exchange reactions [1]. In this work, we used metal fluoride powders to study volatile etch products produced by fluorination and ligand-exchange reactions during thermal ALE. An in situ quadrupole mass spectrometer (QMS) was employed to characterize the etch products produced during the thermal etching of AlF3, ZrF4 and HfF4 powders between 200°C and 300°C using TMA, DMAC, SiCl4 and TiCl4 as the metal precursors.
Thermal Al2O3 ALE occurs using HF and TMA as the precursors [2]. For the reaction of TMA with AlF3 powders, the observed etch products are dimers such as [AlF(CH3)2]2 and [AlF(CH3)2-Al(CH3)3]2. These products are equivalent to the dimer etch products observed earlier for the reaction of TMA with fluorinated Al2O3 during thermal Al2O3 ALE. In contrast, Al2O3 ALE does not occur with either SiCl4 or TiCl4 as the metal precursors [1]. For the reaction of SiCl4 and TiCl4 with AlF3 powders, the observed reaction products are SiFCl3 and TiFCl3, respectively. There is halide-exchange between the SiCl4 and TiCl4 metal precursors and the AlF3 surface. However, there is no observation of volatile Al-containing products that would be consistent with Al2O3 etching.
We are developing a matrix that correlates volatile etch or ligand-exchange products with the previous etching results. We are also using density functional theory (DFT) to predict the etch products during thermal ALE. These DFT calculations correctly predict the dimer etch products during Al2O3 ALE. This approach is advancing our understanding of selective thermal ALE.
[1] Younghee Lee, Craig Huffman, and Steven M. George, “Selectivity in Thermal Atomic Layer Etching Using Sequential, Self-Limiting Fluorination and Ligand-Exchange Reactions”, Chem Mater. 28, 7657 (2016).
[2] Younghee Lee, Jaime W. DuMont and Steven M. George, “Trimethylaluminum as the Metal Precursor for the Atomic Layer Etching of Al2O3 Using Sequential, Self-Limiting Thermal Reactions”, Chem. Mater. 28, 2994 (2016).