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THE REACTIVITY OF HCI AND METHYLTRICHLOROSILANE WITH SILICON CARBIDE SURFACES MARK D. ALLENDORF AND DUANE A. OUTKA Sandia National Laboratories, Livermore, CA 94551-0969 ABSTRACT This work explores the reactivity of HCl and methyltrichlorosilane (MTS) with polycrystalline 13-silicon carbide (SiC) surfaces using temperature-programmed desorption (TPD) and Auger electron spectroscopy. HCl is a corrosive gas that inhibits SiC deposition. The results show that HCl is adsorbed by SiC, forming a stable surface chloride that could inhibit SiC deposition. TPD shows that chlorine desorbs as HCl or SiCb4, confirming that HCI can etch SiC surfaces. Desorption is rate-limited by the breaking of Si-Cl bonds. MTS is also adsorbed by SiC; its desorption is similar to that of HCI. I.

INTRODUCTION.

Silicon carbide (SiC) has a wide variety of applications, including structural ceramics, wearand chemical-resistant coatings, high-power electronic devices, and blue LED's. A broad range of processing methods are currently under consideration for the manufacturing of these products. One important subset of these processes uses methyltrichlorosilane (Cl 3 SiCH3 ; MTS) in hydrogen carrier gas to deposit SiC. 1-4 Temperatures employed vary between 1200 K and 1700 K; reactor pressures are typically 1 atmosphere, although a few studies have been performed at pressures as low as 25 torr. The surface reactivities of species produced by MTS decomposition in the gas-phase are not well known. Data of a fundamental nature concerning the rates of surface reactions are important, since the complexity of SiC deposition processes mandates the use of computational models to assist in process optimization and scale-up. One of the most important species whose surface reactivity must be understood before model development can proceed is HCl, which has been shown to reduce SiC deposition rates, possibly by blocking reactive surface sites. 5 , 6 The surface reactions of MTS are also important since low pressures (i.e., high-diffusion rates) and/or low deposition temperatures (i.e., slow gas-phase decomposition) may produce high fluxes of this reactant to the surface. In this paper, we describe measurements of HCl and MTS adsorption and desorption on polycrystalline 1-SiC surfaces. The results show that both species are dissociatively adsorbed by SiC and indicate that surface chlorine can inhibit deposition by forming strong Si-Cl bonds on the surface. II.

EXPERIMENTAL PROCEDURES.

The experiments were performed in a stainless steel vacuum chamber with a base pressure of 5.0 x 10-10 torr. The chamber includes a double pass cylindrical mirror electron energy analyzer for Auger electron spectroscopy (AES), a quadrupole mass spectrometer for temperature programmed desorption (TPD), and an argon ion gun for cleaning the surface. The SiC sample was deposited by CVD on a graphite substrate at atmospheric pressure from mixtures of MTS and hydrogen. X-ray crystallography showed that only the 13-phase of SiC is present in the samples. The oxygen content of the samp