Abstract: The multistage gas distribution system of large-sized square carrier metal-organic chemical vapor deposition (MOCVD) for the preparation of gallium arsenide (GaAs) thin film in the photovoltaic industry is introduced. The core parameters in the design process of the reactor structure, such as the size of the showerhead hole and the spacing between the showerhead and carrier (chamber spacing) are discussed. Based on a self-developed MOCVD reactor model with a carrier of 36×4 inches wafers, the computational fluid dynamics (CFD) method and the gas reaction and surface reaction during GaAs film deposition were used to simulate the gas distribution and chemical vapor deposition (CVD) process with different parameters and chamber spacing. The relationship between cross-orifice pressure difference and gas flow distribution uniformity, and the effect of chamber spacing on gas flow and GaAs film deposition were investigated. The results show that after the primary "spider" plate divides the main gas inlet into 64 sub-gas intakes, the gas distribution uniformity is better, and the fluctuation amplitude of mass flow rate value is only 0.22%. Increasing the hole depth of the showerhead increases the hole pressure difference slowly and linearly, while reducing the hole diameter increases the pressure difference very quickly. Increasing the hole pressure difference of the showerhead can improve the uniformity of secondary gas separation, but the lifting effect is slow. The deposition rate is low and the uniformity is poor at large chamber spacing. With the decreasing of the spacing and the increasing of deposition rate, the deposition uniformity becomes better at first, and then becomes worse gradually due to the turbulence of gas flow.

Key words: MOCVD, GaAs, numerical simulation, gas distribution