Date of Graduation

2008

Document Type

Thesis

Degree Type

MS

Committee Chair

Dimitris Korakakis

Abstract

Silicon carbide (SiC) is a material long known for its potential uses in extreme conditions or environments. This includes high temperature, high power, high frequency, and high radiation conditions. Major research efforts have focused on improving substrate quality (i.e., the reduction of bulk defects) and the processing of devices fabricated on these substrates. This thesis focuses on the preparation of high quality substrate surfaces for both the Si- and C-face of 6H-SiC. Specifically, the goal of this research is the production of atomically flat surfaces having good stoichiometry, Si-C bonding, and crystallography and low oxygen contamination. Terraced 6H-SiC surfaces with 1.5 nm step heights are routinely produced by atmospheric pressure etching of as-received 6H-SiC in a 5% hydrogen in argon mixture at 1500 o C. Although this removes all evidence of polishing damage and yields large (200 nm wide) flat terraces, the surface is generally contaminated with a residual oxide that cannot be completely removed by a simple HF acid dip. In this thesis, four different wet etching procedures and atomic hydrogen etching were studied to determine their effectiveness in removing surface oxides from both the Si- and C-faces of stepped 6H-SiC. In addition, inductively coupled plasma-reactive ion etching using CF4 and SF6 on as-received Si- and C-faces of 6H-SiC was studied as a possible replacement for high temperature, high pressure H2 etching. The surfaces produced in these studies were characterized by a variety of tools. Surface composition, Si/C ratio, Si-C bonding, and oxide level, were assessed using Auger electron spectroscopy and Auger line shape analysis. The crystal structure of the surface was monitored using reflection high-energy electron diffraction. Surface morphology was characterized qualitatively using field emission scanning electron microscopy and quantitatively using atomic force microscopy. Despite many claims in the literature, this study found that wet etching alone was not sufficient to remove the last vestiges of oxygen from stepped 6H-SiC. Moreover, wet etching generally left the surface with a C-rich stoichiometry. Of the methods studied here, inductively coupled plasma-reactive ion etching using CF4 was found to be most effective in producing atomically flat surfaces having good stoichiometry, Si-C bonding, and crystallography and low oxygen contamination.

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