Comparison of the processes induced by nitrogen dilution on the photodissociation of silane and disilane at 193 nm

Abstract

We compare the influence of the dilution of silane and disilane in nitrogen during laser photodissociation to produce silicon at 193nm, at room temperature in a static reaction chamber. The experimental results show that the conversion of the reactant gas and its deposition yield can be controlled by varying adequately the extent of dilution. So, two total pressure regions have been observed, independent of the dilution: below 40–50Torr, the variations of stable species concentration are very important but above these values the variation in the dilution rate has practically no effects on their concentrations. In the first region, during the silane photodissociation at the initial reactant pressure below 5Torr, the conversion of silane increases with increasing dilution, and at higher initial reactant pressure the conversion of silane tends to rise only a little. In contrast, at any initial reactant pressure, the conversion of disilane during its photodecomposition decreases with increasing dilution. In the second region, the concentration of each stable gaseous species tends to reach a pressure stationary-state. For both the silane and disilane photodissociation, the deposition yield of silicon increases with decreasing the initial reactant gas pressure and it reaches a pressure stationary-state above 50% dilution; but in all the cases, it is greater in disilane photolysis than that of silane. A simple kinetic model is proposed for which the computed results predict the time-evolution of gas composition and amount of silicon deposited.