PREPARATION OF SILICON EPITAXIAL FILM

PURPOSE:To prevent cloudiness of silicon substrate and acquire a base material for forming thereon a high quality epitaxial thin film by controlling amount of H2 carrier gas during the epitaxial reaction process in the silicon epitaxy due to depressurized hot wall CVD. CONSTITUTION:In the total epitaxy process, the hydrogen H2 is caused to flow in the reciprocal process where a substrate 5 is transferred to a high temperature part and a high temperature H2 annealing process where natural or artificial oxide film of substrate is removed. In this case, high vacuum exhaustion is not required but in the normal pressure system, the interior is pressurized positively and the hydrogen H2 may leak to the external area from the pressure reduction structure. Therefore, it is enough to reduce a pressure to 10-100Torr only with a rotary pump 19. In the epitaxial reaction process, a pressure is selected to 0.1-10Torr so that the source gas and doping gas are sufficiently diffused between narrow substrates erected vertically and thereby film thickness and resistance coefficient can be uniformed. In this case, an exhausting operation combining mechanical boosters 17, 18 and rotary pump 19 is necessary in order to keep the specified pressure while causing the source gas, doping gas and carrier gas to flow. As described above, amount of flow of H2 is different in the epitaxial reaction process and in the other process, and in the latter case it is necessary to set a flow condition of H2 which satisfies the condition, Reynolds number Re>20 in order to prevent reverse flow of HC.