Using reactive radio-frequency magnetron sputtering, ZnO films have been deposited on Si(001) substrate with a two-step growth method. The first step: depositing a ZnO buffer layer at low temperature and annealing at 800 ℃, the second step: growing the ZnO at the temperature of 750 ℃. In this paper, we discuss the dependence of the ZnO film growth on the etching time of Si chips and the deposition time of the buffer layer. It is found that different deposition time of the buffer layer results in the difference in the morphology of ZnO films. The difference can be related to the coverage of the buffer layer. When the buffer layer does not cover the substrate, the ZnO film has small grains similar to the film without buffer layer and quite large roughness and internal stress. When the substrate is completely covered by the buffer layer, a ZnO film can be obtained with large-sized grains, smooth surface and low internal stress. The growth behavior of the ZnO films is also related to the etching time of Si chip. With the increase of etching time, both the roughness of the ZnO films and the correlation length of the self-affine morphology decrease.