Hot paper on selective Atomic Layer Etching using fluorination and ligand-exchange reactions

Here is a very recent publication on Atomic Layer Etching (ALE) shared to me by my co-worker at Lund Nano Lab MD Sabbir Ahmed Khan (Now at Aalto University, Finland) - Thank you! The paper is from the group of Steven M. George at CU Boulder and Sematech on selective ALE using fluorination and ligand-exchange reactions - sort of backwards thermal ALD.

For those of you with interest in ALE please remember that the 4th International Atomic Layer Etching Workshop (ALE2017) will be featured at the 17th International Conference on Atomic Layer Deposition, July 15-18, 2017, Denver, Colorado. ALE2017 is chaired by Prof. Steven .M. George and Keren Kanarik from Lam Research.

Selectivity in Thermal Atomic Layer Etching Using Sequential, Self-Limiting Fluorination and Ligand-Exchange Reactions

Younghee Lee^†, Craig Huffman^‡, and Steven M. George^*†§

^† Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309, United States

^‡ SUNY Poly SEMATECH, Albany, New York 12203, United States

^§ Department of Mechanical Engineering, University of Colorado, Boulder, Colorado 80309, United States

Chem. Mater., Article ASAP

DOI: 10.1021/acs.chemmater.6b02543

(Figure Shared under Rightsink Account #:   3000915597)

Abstract: Atomic layer etching (ALE) can result from sequential, self-limiting thermal reactions. The reactions during thermal ALE are defined by fluorination followed by ligand exchange using metal precursors. The metal precursors introduce various ligands that may transfer during ligand exchange. If the transferred ligands produce stable and volatile metal products, then the metal products may leave the surface and produce etching. In this work, selectivity in thermal ALE was examined by exploring tin(II) acetylacetonate (Sn(acac)2), trimethylaluminum (TMA), dimethylaluminum chloride (DMAC), and SiCl4 as the metal precursors. These metal precursors provide acac, methyl, and chloride ligands for ligand exchange. HF-pyridine was employed as the fluorination reagent. Spectroscopic ellipsometry was used to measure the etch rates of Al2O3, HfO2, ZrO2, SiO2, Si3N4, and TiN thin films on silicon wafers. The spectroscopic ellipsometry measurements revealed that HfO2 was etched by all of the metal precursors. Al2O3 was etched by all of the metal precursors except SiCl4. ZrO2 was etched by all of the metal precursors except TMA. In contrast, SiO2, Si3N4, and TiN were not etched by any of the metal precursors. These results can be explained by the stability and volatility of the possible reaction products. Temperature can also be used to obtain selective thermal ALE. The temperature dependence of ZrO2, HfO2, and Al2O3 ALE was examined using SiCl4 as the metal precursor. Higher temperatures can discriminate between the etching of ZrO2, HfO2, and Al2O3. The temperature dependence of Al2O3 ALE was also examined using Sn(acac)2, TMA, and DMAC as the metal precursors. Sn(acac)2 etched Al2O3 at temperatures ≥150 °C. DMAC etched Al2O3 at higher temperatures ≥225 °C. TMA etched Al2O3 at even higher temperatures ≥250 °C. The combination of different metal precursors with various ligands and different temperatures can provide multiple pathways for selective thermal ALE.