Palladium and nickel interactions with stepped 6H-silicon carbide

Abstract

PALLADIUM AND NICKEL INTERACTIONS WITH STEPPED 6H-SILICON CARBIDE Andrew A. Woodworth Silicon carbide (SiC) has long been recognized as a semiconductor with potential for use in a number demanding environments. Recent developments in the quality of bulk grown 6H-SiC (and other hexagonal poly-types) have increased interest in issues surrounding the stability of device structures that operate at temperatures in excess of 600 o C. It has been observed that the performance of metal-semiconductor devices created on SiC tend to degrade when operating at these temperatures. This change in device performance has been linked to inter-diffusion and reaction at the metalsemiconductor interface. Most of these devices have been fabricated on SiC substrates with surface and sub-surface damage associated with the polishing process (standard surfaces). Recent studies have shown that high temperature hydrogen etching of these substrates removes this damage and produces surfaces with wide atomically flat terraces and nanometer scale steps (stepped surfaces). The basic question this poses is, can such improvements in substrate quality lead to improvements in device performance. The goal of this research is to better understand the interaction of metals on these stepped surfaces. To accomplish this, detailed surface studies of thermally induced Pd-SiC and Ni-SiC surface interactions have been performed on both the standard and stepped surfaces. The metal films range in thickness from the monolayer level (~0.4 nm) to actual device dimensions (~50 nm) and are deposited under ultrahigh vacuum conditions at ~50 o C. These films were characterized in-situ using Auger electron spectroscopy both before and after annealing at 670 o C for Pd and 700 o C for Ni. The Auger lineshapes provide quantitative and qualitative information on the chemistry of the reaction products. Ex-situ atomic force microscopy was used to characterize changes in surface morphology. The results of these experiments yield important insights into the nature of the transport process at the metal-semiconductor interface and the influence of initial surface structure in these processes. In addition differences in the interfacial chemistry for carbide forming metals has been revealed. The results provided insight into the mechanisms where by improvements in substrate quality may lead to improvements in device performance.

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