New Si CVD Precursors: Preparation and Pre-Screening
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D. Gaines*, M. Hop*, T. Kuech,** J. Redwing**, D. Saulys*, and A. Thon** *University of Wisconsin at Madison, Department of Chemistry, Madison, Wi. "**Universityof Wisconsin at Madison, Department of Chemical Engineering, Madison, Wi.
INTRODUCTION Silanes and their organo-derivatives are of interest as precursors and dopants in chemical vapor deposition (CVD) to prepare (modified) thin films with unique surface properties. Applications of these films are widespread: transitors, laser diodes, optoelectronic devices, etc. Film growth, however, is capital intensive and mechanistically complex, while film characterization is time-consuming and often requires sophisticated instrumentation. A tool is needed to prescreen precursors' CVD behavior, preferrably a technique requiring a minimum of time and sample to provide information directly related to aspects of the film growth process. Precursor decompositions in a mass spectrometer resemble those occuring in a low pressure CVD or flow tube pyrolysis apparatus to the extent that all are non-equilibrium processes involving fragmentation of a gaseous molecule in response to physical stimuli. As mass spectra can be obtained in minutes and require only microliters of sample, we are investigating the suitability of mass spectrometry as a precursor screening tool. In a systematic study of the effect of precursor structure on gas phase behavior, we have examined all nine isomers of the formula SiC 4 H12 (Figure 1) by means of metastable ion (MI) and collision-induced dissociation (CID) mass spectrometry. The former technique indicates the precursors' fragmentation pathways, while the latter provides structural information. The kinetic energy released by each of the isomers upon fragmentation was also measured; these data provide a rough sketch of the potential energy curve of the process in question. In totality, these results provide the basis for a structure-reactivity correlation. Data from preliminary flow tube pyrolysis studies of the SiC 4 H 12 isomers are discussed in terms of this correlation.
EXPERIMENTAL The MI and CID mass spectra (MS) were recorded with a VG Analytical ZAB-2F instrument (Fig. 2) and corrected for isotopic interference from ions of lower mass. He was the target gas (80% transmission) for the CID experiments. MI and CID spectra were recorded with all slits fully open, while metastable peak shapes for kinetic energy release (T) measurement were recorded with a main beam width of < 2V at an accelerating voltage of 8,000 V. The reported T values are based on the width of the signals at half height, T0 .5. Tetramethylsilane, diethylsilane, and dimethylethylsilane were of commercial origin; the preparation and purification of t-butylsilane, s-butylsilane, i-butylsilane, n-butylsilane, methyl-ipropylsilane and methyl-n-propylsilane are described in reference 1. Deuterated analogues of the silane isomers were prepared by reaction of LiAID 4 with the appropriate chloride in a manner analogous to that described in reference 1.
81 Mat. Res. Soc. Symp. Proc. V
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