Development of Low-Temperature Epitaxy of Silicon by Photo-Chemical Vapor Deposition

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The necessary dimension of an epitaxial layer under typical high-temperature processing conditions are limited by the diffusion length of dopants out of the substrate. Therefore, it has become essential to develop low-temperature silicon epitaxy to reduce further the dimensions of high-performance integrated circuitry.With these backgrounds, the purpose of this research has been developments of low-temperature epitaxy of silicon using photo-chemical vapor deposition technique. Using the photo-CVD technique, the growth temperature could be drastically reduced, because the reactant gases are not decomposed thermally but photochemically. We have obtained following results.1. It was shown that the plasma-etching prior to the growth using SiF_4 gas was very effective to reduce the pileup of impurities as a cleaning method for Si substrates at low-temperature of 250゜c.2. From the experiments, it was found that the presence of SiH_2F_2 and H_2 in the gas phase was essential for the growth of Si epitaxy at this low-temperature.On the basis of these results, we have fabricated both Si/SiGe strained-layer superlattices (SLSS) and heavily P-doped silicon thin films to clarify the merits of photo-assisted chemical vapor deposition.3. The Si/SiGe superlattices were grown by photo-CVD at a very low-temperature of 250゜c. The superlattice structures were directly observed by transmission electron microscopy (TEM) measurements and it seems likely that SLSs could be useful as a buffer layer for silicon epitaxial technology.4. Heavily P-doped silicon films was successfully grown by the photo-CVD technique at 250゜c. The best values of carrier concentration and resistivity were 1.7x10^<21>cm^<-3> and 3.2x10^<-4> cm, respectively.From above mentioned results, it was shown that the photo-chemical vapor deposition technique has been the best candidate for future epitaxial technology of silicon.