Surface Investigations of Germanium Chemical Vapor Deposition on Silicon
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SURFACE INVESTIGATIONS OF GERMANIUM CHEMICAL VAPOR DEPOSITION ON SILICON C. MICHAEL GREENLIEF, DEBRA-ANN KLUG, WEI DU, AND LORI A. KEELING
Department of Chemistry, University of Missouri-Columbia, Columbia, MO 65211. ABSTRACT
The adsorption and decomposition of several Ge-containing compounds on Si(100) have been investigated with the intent of elucidating the surface processes leading to the deposition of epitaxial Ge films from these gaseous sources. Exposure of digermane, Ge2H6, to Si(100) at 110 K results in molecular adsorption and ab initio calculations are used to help interpret the low temperature ultraviolet photoelectron spectrum. Diethylgermane, GeH 2 Et 2 , chemisorbs dissociatively on Si(100) at 110 K. The adsorption products are GeH2 and adsorbed ethyl groups. Large exposures of GeH 2 Et 2 result in the formation of a physisorbed layer of molecular GeH 2 Et 2 on top of the dissociated layer. The surface ethyl groups thermally decompose near 670 K via a P-hydride elimination reaction evolving C 2 H 4 into the gas phase. The interactions of Ge2H6 and GeH2Et 2 with Si(100) are discussed and compared to similar experiments with GeH--4 as the Ge-containing gas source. INTRODUCTION Sil-xGex alloys offer the potential to generate materials with a bandgap that is variable over a wide range of alloy compositions. Chemical vapor deposition of these materials is possible1 ,2 with a variety of Si- and Ge-containing molecules. The surface phenomena involved in the synthesis of these materials however, are largely unexplored. We are interested in determining the surface decomposition mechanisms and kinetics of Ge-containing molecules on Si in an effort to further the knowledge of Ge film growth. Some of the possible surface reactions of a Ge-containing molecule include adsorption, decomposition to elemental Ge, and evolution of by-products into the gas phase. In this paper, we present the results of recent experiments examining the adsorption and decomposition of Ge2H 6 and GeH 2 Et 2 on the Si(100)-(2xl) surface. The surface processes are followed by temperature programmed desorption (TPD) and ultraviolet photoelectron spectroscopy (UPS). EXPERIMENTAL The experiments are carried out in a stainless steel ultra-high vacuum chamber. The chamber is equipped with a double-pass cylindrical mirror analyzer (CMA) for Auger electron and photoelectron spectroscopies, a differentially pumped ultraviolet discharge lamp, twin X-ray source, ion gun, low energy electron diffraction optics, and quadrupole mass spectrometer for
Mat. Res. Soc. Symp. Proc. Vol. 282. @1993 Materials Research Society
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both temperature programmed desorption and secondary ion mass spectrometry. The base pressure of the system is 5x10 11 torr with a typical working pressure of 1x10 4 0 torr. The sample preparation and cleaning, gas purification, and calibration procedures have been described in detail elsewhere 3 . X-ray photoemission spectra are taken with AI(K00 radiation (1486.6 eV) with the anode operating at 435 W of power. The CMA is opera
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