The doping procedure in crystalline silicon solar cell fabrication usually contains oxygen injection during drive-in process and removal of phosphorous silicate glass(PSG). In this paper, we studied the effect of oxygen injection and PSG on conversion efficiency of solar cell. The mono crystalline silicon wafers with 156 × 156 ㎟, 200 ㎛, 0.5-3.0 Ωㆍ㎝ and p-type were used. After etching 7 ㎛ of the surface to form the pyramidal structure. the P(phosphorous) was injected into silicon wafer using diffusion furnace to make the emitter layer. After then, the silicon nitride was deposited by the PECVD with 80 ㎚ thickness and 2.1 refractive index. The silver and aluminium electrodes for front and back sheet, respectively. were formed by screen-printing method, followed by firing in 400-425-450-550-880 ℃ five-zone temperature conditions to make the ohmic contact. Solar cells with four different types were fabricated with/without oxygen injection and PSG removal. Solar cell that injected oxygen during the drive-in process and removed PSG after doping process showed the 17.9 % conversion efficiency which is best in this study. This solar cells showed 35.5 ㎃/㎠ of the current density, 632㎷ of the open circuit voltage and 79.5 % of the fill factor.