Abstract: SiN_x thin films were deposited by Plasma-Enhanced Chemical Vapor Deposition (PECVD) method under different RF frequency, and the influence of RF frequency on both the deposition process and properties of the SiN_x film were studied. It was found that SiN_x films deposited at low frequency (100KHz) have large density; low etch rate and compressive stress; while the films deposited at high frequency (13.56MHz) have a relative low density, large etch rate and tensile stress. The IR results showed that the films deposited at low frequency containted less hydrogen.By using low and high frequency RF power alternatively, SiN_x film with stress as low as -10⁹Pa was deposited. On heating at 500°C, the film with tensile stress oracked; the compressive stress film buckled; while the low stress film sustained higher temperature. When the temperature is over 700°C, the film bubbled at last due to hydrogen evolution.