Thermodynamic Simulation of Polycrystalline Silicon Chemical Vapor Deposition in Si-Cl-H System

Based on thermodynamic data for related pure substances, the relations of (n(Cl)/n(H))(Eq) and (n(Cl)/n(H))(o) have been plotted in the Si-Cl-H system. The results show that the difference of (n(Si)/n(Cl))(o) and (n(Si)/n(Cl))(Eq) is the driving force for polycrystalline silicon chemical vapor deposition (CVD). SiHCl3 is preferred for polycrystalline silicon deposition to SiCl4 center dot SiH2Cl2 would be even better, but it is not stable as a gas and hence it is less frequently used. Then, thermodynamic simulation of polycrystalline silicon CVD in the Si-H-Cl system has been investigated. The pressure has a negative effect on polycrystalline silicon yield. The optimum temperature is 1400 K, at which the kinetic rate of rate-determining step for the main reaction is large enough. The excess hydrogen is necessary for polycrystalline silicon CVD in the Si-Cl-H system. However, the silicon deposition rate increases then decreases with increasing H-2 molar fraction. The optimum H-2 molar fraction should be determined by considering thermodynamics and transport phenomena simultaneously. Finally, the optimum conditions have been obtained as 1400 K, about 0.1 MPa, and H-2 to SiHCl3 ratio of 15, which are close to the limited reported values in the open literature. Under the optimum conditions, the silicon yield ratio is 34.82% against 20% reported in the open literature.