Fabrication of silicon nano-crystal dots on SiO₂ by ultrahigh-vacuum chemical vapor deposition

We report a process for Silicon (Si) nano-crystal dots fabrication using a cold-wall Ultrahigh-Vacuum Chemical Vapor Deposition (UHV-CVD) system. Si₂H₆ gas was used as the pre-curser and irradiated upon sin₂ on Si wafer to form Si nano-crystal dots. In our system, nucleation, growth, and coalescence phases of nano-crystal dots on SiO₂ were found to be related with the optical pyro-meter's read-out curve. At first, the optimum gas irradiation time which gives the highest dot density without coalescence was decided for every gas irradiation condition by using an optical pyro-meter. Then, the dependence of optimum gas irradiation time, dot diameter and dot density on gas flow rate and wafer temperature were investigated. A decrease of wafer temperature or an increase of gas flow rate during the nucleation and growth phase results in a decrease of dot diameter and an increase of dot density. The optimum gas irradiation time was prolonged by decreasing wafer temperature or gas flow rate. Finally, a reproducible process of forming non-coalesced, small size, and high-density Si nano-crystal dots of about 5.5nm in diameter with density of 1×10¹² dots/cm² were obtained. Typical process time to get such dot formation characteristics was about 10 minutes, which were long enough for ensuring reproducibility.