| AVS 63rd International Symposium & Exhibition | |
| Plasma Science and Technology | Wednesday Sessions |
| Session PS-WeA |
| Session: | Atomic Layer Etching and Low Damage Processing |
| Presenter: | Chen Li, University of Maryland, College Park |
| Authors: | D. Metzler, University of Maryland, College Park C. Li, University of Maryland, College Park C.S. Lai, Lam Research Corporation E.A. Hudson, Lam Research Corporation G.S. Oehrlein, University of Maryland, College Park |
| Correspondent: | Click to Email |
The evaluation of a plasma-based native oxide surface cleaning process for Si and SiGe substrates is described. Objectives include removal of the native oxide while minimizing substrate damage and surface residues. This work is based on recent advances in atomic layer etching (ALE) of SiO2[1]. To achieve controlled etching of SiO2 at the Ångstrom level a cyclic approach consisting of a deposition step and etch step was initially employed. The deposition step deposits fluorocarbon (FC) films up to 10 Å thick on the surface. Subsequent low energy Ar+ ion bombardment during the etch step induces mixing of the FC film with the substrate and removal of the FC film together with the mixed, reacted substrate material. Oxide layer thicknesses were measured using in situ ellipsometry and surface chemistry was analyzed by X-ray photoelectron spectroscopy. The cyclic ALE approach did not remove native oxide from a Si substrate at the level required. A modified process was evaluated which used continuously biased Ar plasma with periodic CF4 injection. By eliminating a dedicated FC film deposition step, optimizing process times and ion energies, significant O removal from the Si surface was achieved, while leaving residual C. An additional H2/Ar plasma exposure performed at higher pressure and minimizing ion bombardment successfully removed residual C and F originating from the surface cleaning process. The combined treatment reduced O and C levels to about half compared to as received Si surfaces but removed ≈37 Å of Si. Similar to Si substrates, SiGe substrate oxide removal was seen upon applying this cleaning process, while the H2/Ar post treatment subsequently removed F and C-related species. O and C levels are reduced to ≈70% after the combined treatment while ≈55 Å of SiGe are removed. In addition, the surface is Ge richer after the cleaning process compared to SiGe surfaces as received. This feasibility study of Ar/FC based native oxide cleaning approaches for Si and SiGe substrates shows the potential to reduce O levels but at the cost of substantial substrate material loss and introducing low levels of C and F.
The authors gratefully acknowledge the financial support of this work by the National Science Foundation (CBET-1134273) and Lam Research Foundation.
References:
[1] D. Metzler and et al., J Vac Sci Technol A 32, 020603 (2014)