Plasma deposition of SiO2on silicon substrates in a microwave (2.45 GHz) electron cyclotron resonance N2O/SiH4/He discharge has been investigated as a function of radio frequency (13.56 MHz) self‐biasing of the sample, pressure, microwave power, substrate temperature, and gas mixture. Deposition rates between 30 and 90 nm/min have been observed with quality films over a range of parameter combinations. The films have been analyzed for thickness and index of refraction by ellipsometry and for chemical structure by Fourier transform infrared spectroscopy. The deposition process yielded films with virtually no Si–H, N–H, or Si–N bonding groups and only traces of OH bonds. Analysis of the Si–O–Si stretching peak reveals a film quality which compares favorably with good quality thermal oxides grown at much higher substrate bulk temperatures. Also, the relative insensitivity to the He content of the gas mixture indicates the surface chemistry of this process is fundamentally different from previously reported plasma enhanced chemical vapor deposition processes.