Gas-Surface Reaction Studies Relevant to SiC Chemical Vapor Deposition
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GAS-SURFACE REACTION STUDIES RELEVANT TO SiC CHEMICAL VAPOR DEPOSITION C.D. Stinespring, A. Freedman, and J.C. Wormhoudt Center for Chemical and Environmental Physics, Aerodyne Research, 45 Manning Road, Billerica, MA 01821
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ABSTRACT Reactions of C2 H4 , C3 H8 , and CH4 on Si(ll1) and C2 H4 on Si(100) have been investigated for surface temperatures in the range of 1062 K to 1495 K. These studies used x-ray photoelectron spectroscopy to identify the reaction products, characterize the solid state transport process, determine the nucleation mechanism and growth kinetics, and assess orientation effects. The results are used to provide insight into the mechanisms of SiC CVD processes.
INTRODUCTION The use of epitaxial n-SiC as a high temperature semiconductor has motivated a number of studies of hydrocarbon reactions on Si. During the late 1960's, the reactions of C H2 and C2 H4 on Si surfaces were investigated by Kahn and Summergrad.11 These and similar studies performed during this time frame focused on thin film morphology and characteristics. 2 1 1 More recently, Yates and coworkers[ -4 and the authors of this paper[5 have used surface sensitive techniques such as x-ray photoelectron spectroscopy (XPS) to gain a more fundamental understanding of hydrocarbon-Si surface chemistry and its relationship to the growth process. The surface studies described in this paper were performed to provide a basis for understanding the SiC chemical vapor deposition (CVD) process developed at the NASA Lewis Research Center.[61 RELATIONSHIP OF GAS-SURFACE REACTION STUDIES TO SiC CVD The NASA CVD procedure is a two step process. In the first step, an initial layer of SiC approximately 10 nm thick is deposited by flowing a dilute mixture of C 3 H8 in H2 over the Si substrate as its temperature is 1 ramped (70 K s- ) to 1673 K. The second step involves homoepitaxy of SiC on the initial deposit using a dilute mixture of C 3 H8 and SiH4 in H2 at 1673 K. Deposition during the initial step is found to be essential if high quality epitaxial SiC is to be deposited during the second step. The work described here focused primarily on the initial deposition step. In defining the surface studies relevant to this process, it is important to note that the species which interact with and on the surface to form SiC need not be the input species, but may also include non-equilibrium thermal decomposition and reaction products. In gas phase 1 chemical kinetics calculations reported by the authors,[7 this was found to be the case for C3 H8 . At low temperatures in the ramp (i.e.,
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