Abstract: Intrinsic hydrogenated amorphous silicon oxide (i-a-SiO_x:H) is one of the important passivation materials in a-Si: H/c-Si heterojunction solar cells. In this paper, the passivation properties of i-a-SiO_x:H deposited on the surface of n-Cz-Si at different substrate temperatures were studied by PECVD. The minority carrier lifetime of silicon wafers was measured by microwave photo-conductivity (MW-PCD) and radio frequency photo-conductivity (RF-PCD). The crystal form of the deposited films was examined by spectroscopic ellipsometry. The results show that: (1) the ellipsometer results show that the deposited films are amorphous; (2) MW-PCD and RF-PCD tests show that the minority carrier lifetime of the silicon wafer is very low after i-a-SiO_x:H deposited on both sides of n-Cz-Si at room temperature. With the increase of deposition substrate temperature, the minority carrier lifetime of the silicon wafer increases first and then decreases, and the passivation effect is optimal at 200℃~ 220℃.