Afterglow Chemical Processing for Oxide Growth on Silicon Carbide
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1246-B06-03
Afterglow Chemical Processing for Oxide Growth on Silicon Carbide Andrew M. Hoff, Eugene Short III, Helen B. Thomas, and Elena I. Oborina Department of Electrical Engineering, University of South Florida, Tampa, FL 33620, U.S.A. ABSTRACT The unique capabilities and characteristics provided by afterglow or remote plasma chemical oxide growth processing of silicon carbide are reviewed. Such processing provides for thermal growth of oxide films at temperatures far below those employed by conventional atmospheric processing methods. Overshadowing this growth capability is the ability to create chemistries, sequential procedures, and specific process environments to address material and defect issues in a manner not possible under conventional atmospheric conditions. The details and outcomes of multi-step afterglow oxidation processing of SiC will be discussed. An example sequence might include; 1) surface conditioning, 2) film growth at 850C and 1 Torr total pressure, and 3) reduced pressure unexcited media post-growth treatments. Surface conditioning impacts the thickness uniformity of the final oxide film and the oxidation rate. The film growth interval produces a nominal 500Å of oxide film in 90 minutes at 850C, a temperature that would not produce any significant oxide film at atmospheric pressure. And the post-growth processing improves the performance of the dielectric film. Using in-line corona-Kelvin metrology the electrical characteristics stemming from these processes have been determined. Electrical effective oxide thickness results were used to assess thickness uniformity and to estimate process rate constants for comparison to other process methods. Fowler-Nordheim, F-N, characteristics determined with the same metrology demonstrate that afterglow, AG, oxides require higher field levels to produce the same F-N current as thermal oxides and that AG films are less susceptible to stress fluence. Process extensions from these and other results are discussed and related to chemical, physical, and electrical film outcomes and potential pathways to improve control over dielectric SiC structures. INTRODUCTION Oxide thin films are grown on single crystal silicon carbide, SiC, by a chemical reaction between the crystal constituents and oxidant species. This reaction and the transport of oxidant to the reaction interface are based on the similar process technology that forms the same film and represents the basis of silicon mosfet fabrication [1]. Recent efforts have extended the oxidation model for silicon to SiC by considering the possible transport mechanisms to include both oxidant transport to the crystal as well as byproduct transport out of the film[2]. The latter atmospheric kinetic model fits thermal oxidation thickness data for the silicon face of 4H-SiC quite well for temperatures in the range of 1050C to 1150C, and dry oxygen as the oxidant. However, in the same work, only the carbon face exhibited an activation energy for the parabolic rate constant, B, near 2eV, implying oxidant diffusion do
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