Low Temperature Silicon Epitaxy Grown by Electron-Beam Evaporation in an Ultra-High Vacuum System
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LOW TEMPERATURE SILICON EPITAXY GROWN BY ELECTRON-BEAM EVAPORATION IN AN ULTRA-HIGH VACUUM SYSTEM YUNG-JEN LIN AND TRI-RUNG YEW *Materials Science Center, National Tsing-Hua University, Hsinchu, Taiwan, ROC ABSTRACT This paper presents the results of silicon epitaxial growth on silicon windows surrounded with oxide walls by electron-beam evaporation in an ultra-high vacuum system with a load-lock chamber. The wafer surface was in-situ cleaned in the growth chamber to remove native oxide by thermal desorption at about 8401C and a base pressure of better than 2 x 10-9 Torr. The growth temperature was 200 0 C or higher. The pre-epitaxial silicon surface structure was inspected by reflection high energy electron diffraction (RHEED). The influence of the thermal desorption on the quality of the epi/substrate interface and epitaxial layers was studied. In addtion, the deposition parameters which control the epitaxial quality were investigated. The epitaxial films were characterized by cross-sectional trasmission electron microscopy (XTEM) and secondary ion mass spectroscopy (SIMS). I. INTRODUCTION There are increasing needs for high speed electronic device fabrication to grow epitaxial films on oxide patterned silicon wafers at low temperatures because it can avoid dopant redistribution via solid-state diffusion in low temperature process. Silicon-molecular beam epitaxy (Si-MBE) is one of the promising techniques for low temperature epitaxial growth [1, 2]. However, when one considers the application of Si-MBE to the electronic device fabrication process, there are some problems of low throughput, irregular-shaped surface defect formation, and the difficulty of selective growth and n-type doping [3]. The introduction of a new possible method such as electron-beam evaporation in an UHV system is an interesting approach for Si epitaxial growth on oxide patterned wafers at low tempratures because its growth mechanism is similar to Si-MBE. Conventionally electron-beam evaporation system was used to deposit metal or silicide on substrates 14]. In this work, the silicon epitaxial growth on oxide patterned wafers by electron-beam evaporation in an UHV system at 200'C or higher was investigated. II. EXPERIMENTAL PROCEDURES Epitaxial layers were grown onto 2-inch, (100), p-type silicon wafers and oxide patterned silicon wafers. All the wafers were chemically pretreated by Shiraki method 5], then dipped in a dilute HF solution (HF : H2 0 = 1: 50) immediately prior to loading into the loading chamber. The evaporation system is composed of a loading chamber, which is pumped by a rotary and a turbo-molecular pump, and a growth chamber pumped by a turbo-molecular pump and an ion pump. The wafer was transfered from the loading chamber to the growth7 chamber when the base pressure of the loading chamber was better than 5 x 10 - Torr. After loading, the base pressure of growth chamber was about 7 x lff1oTorr. Before growth, the wafer was heated to 840 0 C in the growth chamber to remove oxide by thermal desorption. The base pressure post
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