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Epitaxial Silicon Layers Made by Reduced Pressure/Temperature CVD

In a rapid thermal processing system working at a total pressure of a few Torr, we have obtained selective epitaxial growth of silicon at temperatures as low as 650°C. When using SiH 2 Cl 2 (DCS) as the reactive gas, no addition of HCl is needed. Nevertheless, using SiH 4 below 950°C a small amount of HCl should be added. Some kinetic aspects of the two systems, DCS/HCI/H 2 and SiH 4 /HCl/H 2 , are presented and discussed. For the DCS system, we show that the rate-limiting reactions are slightly different from those commonly accepted in the literature, where the results are from systems working at atmospheric pressure or in the 20-100 Torr range. Our model is based on the main decomposition of DCS, SiH 2 Cl→SiHCl + HCl, instead of the widely accepted reaction SiH 2 Cl 2 →SiCl 2 + H 2 . This is the main reason why no extra HCl is required in the DCS/H 2 system to obtain full selectivity from above 1000°C down to 650°C.