| 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: | Younghee Lee, University of Colorado, Boulder |
| Authors: | Y. Lee, University of Colorado, Boulder J.W. DuMont, University of Colorado, Boulder S.M. George, University of Colorado, Boulder |
| Correspondent: | Click to Email |
A new approach for the atomic layer etching (ALE) of Al2O3 was demonstrated using sequential, self-limiting thermal reactions with trimethylaluminum (TMA) and hydrogen fluoride (HF) as the reactants. Previously, Al2O3 thermal ALE was reported using Sn(acac)2 and HF as the reactants [1,2]. HfO2 ALE was also demonstrated using Sn(acac)2 and HF as the reactants [3]. This new approach using TMA expands the variety of ALE reactants and excludes the possibility that Sn could be left on the etched Al2O3 film.
Quartz crystal microbalance (QCM) experiments monitored Al2O3 ALE at temperatures from 275-325°C. The Al2O3 ALE was linear versus number of TMA and HF reaction cycles. The QCM studies showed that the sequential TMA and HF reactions were self-limiting versus reactant exposure. The QCM analysis measured a mass change per cycle (MCPC) of -16 ng/(cm2 cycle) at 300°C. This MCPC corresponds to an Al2O3 etch rate of 0.53 Å/cycle. X-ray reflectivity analysis confirmed the linear removal of Al2O3 and etching rates. Fourier transform infrared spectroscopy measurements also monitored Al2O3 ALE by observing the loss of infrared absorbance from Al-O stretching vibrations.
Al2O3 ALE is believed to follow the reaction: Al2O3 + 4Al(CH3)3 + 6HF → 6AlF(CH3)2 + 3H2O. The proposed reaction mechanism involves fluorination and ligand-exchange. The HF exposure fluorinates Al2O3 and forms AlF3 with H2O as a reaction product. During ligand-exchange, Al(CH3)3 accepts F from AlF3 and donates CH3 to AlF3 to produce volatile AlF(CH3)2 reaction products. Similar reaction mechanisms based on fluorination and ligand-exchange reactions may extend the range of thermal ALE to a wide variety of additional materials.
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).