We have investigated the structure and stability of SiN (x) films deposited with very high rates (> 50 nm/s) in atmospheric-pressure (AP) He-based plasma excited by a 150 MHz very high-frequency (VHF) power using a cylindrical rotary electrode at room temperature. The SiN (x) films are prepared on Si(001) substrates with varying VHF power density (P (VHF)), H(2) concentration and source ratio (NH(3)/SiH(4)). Infrared absorption spectroscopy is used to analyze the bonding configurations in the films. The results show that increasing H(2) concentration under the supply of a moderately large P (VHF), together with the adjustment of NH(3)/SiH(4) ratio, enables us to prepare SiN (x) showing reasonable stability against a buffered hydrofluoric acid solution in spite of the very high deposition rate of 130 nm/s. The achievement of such a high-rate deposition at room temperature is primarily due to the significant enhancement of both gas-phase and surface-phase reactions in AP-VHF plasma.