Comparison of Trichlorosilane and Trichlorogermane Decomposition on Silicon Surfaces Using FTIR Spectroscopy
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COMPARISON OF TRICHLOROSILANE AND TRICHLOROGERMANE DECOMPOSITION ON SILICON SURFACES USING F"IR SPECTROSCOPY A.C. Dillon, M.B. Robinson and S.M. George Department of Chemistry and Biochemistry, Univ. of Colorado
Boulder, Colorado 80309 ABSTRACT Fourier transform infrared (FTIR) transmission spectroscopy was used to compare the decomposition of trichlorosilane (SiHCl3 ) and trichlorogermane (GeHCl 3 ) on silicon surfaces. Chlorosilanes, such as SiHC13 are employed in silicon chemical vapor deposition (CVD). Chlorosilanes and chlorogermanes are also possible molecular precursors for the controlled atomic layer growth of silicon and germanium. GeHCI may be useful for the deposition of germanium on silicon surfaces and the growth of Sil_ Gex heterostructures. The FTIR studies were performed in-situ in an ultra-high vacuum chamber on high surface area, porous silicon samples. The FTIR spectra revealed that SiHCI 3 dissociatively adsorbs at 200 K to form SiH, SiCl, CISiH and Cl2 SiT- surface species. The presence of ClISiH species is revealed by Cl SiH stretching (2196 cm ) and bending (775, 744 cm ) vibrations. The presence of these modes indicates that there is incomplete decomposition of SiHCl3 upon adsorption at 200 K. GeHCI3 also dissociatively adsorbs at 200 K to form SiH and liCI species. An infrared absorption feature in the Ge-H stretching region (1970-1995 cm ) was not detected in the FTIR spectrum. The absence of a Ge-H absorption feature argues that there is a complete transfer of hydrogen from germanium to surface silicon atoms at 200 K. The thermal stabilities of the surface species were studied with annealing experiments. The Cl1SiH formed upon initial SiHCl exposures at 200 K were observed to decompose between 200 - 590 K and form additional surfiace SiR and SiCI species. For both GeHC13 and SiHCl. dissociative adsorption on porous silicon, the SiCI (x = 2 or 3) surface species were convertedto silicon monochloride surface species between 20& - 600 K. In addition, SiH surface species were lost upon annealing between 680 - 780 K as H2 desorbed from the surface. The adsorption kinetics of SiHCl 3 and GeHCl3 were also monitored on porous silicon at various isothermal temperatures. These experiments provide insight into the surface chemistry of chlorosilanes and chlorogermanes during CVD and atomic layer controlled growth.
INTRODUCTION Chlorosilanes have been widely used in chemical vapor deposition (CVD) processing for the growth of silicon, silicon nitride and silicon dioxide films (1-3). Recently, dichlorosilane (SiH 2 Cl 2 ) has been suggested as a precursor for the atomic layer epitaxy (ALE) of silicon (4-6). In its simplest form, ALE is a self-regulating adsorption process in which one full monolayer or a partial monolayer of a compound is deposited per operational cycle. Trichlorosilane may also be a promising molecular precursor for silicon ALE. The deposition of germanium on silicon surfaces is important because of the use of Si/Si 1 Gex/Si heterostructures in electronic devices. Devices which are
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