Direct simulation Monte Carlo of monosilane low pressure chemical vapor deposition

Chemical vapor deposition of monosilane between two 4-inch wafers with 5 mm wafer spacing is simulated at molecular level under 973 K and 0.1, 1.0, 10 Torr. Four gas-phase reactions are considered, with a detailed reaction ki netics simulation on the first decomposition step of SiH4 to yield H-2 and highly reactive SiH2. Also four surface reactions of SiH4. SiH2, Si2H6, Si3 H8 are included in simulation. Monosilane, with its lowest sticking coeffic ients among film-forming species, is the major reason for thickness uniform ity over large area in silane CVD. Si2H6 and SiH2, both of higher sticking coefficients, are the contributors of film thickness non-uniformity. The si mulation results indicate an interesting role switching between disilane an d silylene as SiH4 pressure varies from 0.1 to 1 Torr. When SiH4 pressure i s low, SiH2 has a higher probability to impinge on the wafer surface and de posit. Its contribution to deposition rate is higher than that of Si2H6; On the other hand, when the pressure is high, SiH2 tends to insert itself int o SiH4 or Hz to generate Si2H6 or SiH4. Therefore disilane becomes the prim ary factor of non-uniformity, instead of silylene.