Silicon nitride films, deposited by a low‐temperature photochemical vapor deposition method, were characterized by optical, physical, and chemical methods. The film reflectivity was a function of the wavelength of the incident beam and varied from 0.45 to 0.02 in the 4000–7000 Å region. These values changed upon annealing at high temperatures. Film uniformity, in terms of thickness and refractive index, was good over the substrate (±5% and ±0.5%, respectively). The refractive index was 1.95 in the as‐deposited condition and upon annealing exhibited a significant increase due to densification and a decrease in the nonstoichiometric nitride component along with a concurrent increase in the Si3N4 and excess Si amounts. The dramatic decrease in etch rate in buffered HF, from ∼1200 Å/min in the as‐deposited condition to <80 Å/min after annealing at 800 °C, was also consistent with the above observations. The pinhole density in these films also decreased considerably after annealing (from ∼100/cm2 to <15/cm2). X‐ray photoelectron and Auger electron spectroscopy were used to characterize the composition of these films. The composition profiles exhibited good uniformity through the films, with oxygen and carbon contamination limited to within 100 Å from the surface. The Si 2p photoelectron and the Si KLL Auger electron spectra were broad and upon deconvolution indicated the presence of four different silicon containing species. These were identified as SiO2, stoichiometric nitride (Si3N4), nonstoichiometric nitride (SiNx, 0<x≤1), and excess silicon bonded with hydrogen (SiHy, 0<y<2). SiO2 was detected only on the surface, due to exposure to atmosphere. After high‐temperature annealing, the intensities of the nonstoichiometric nitride component in both the Si 2p and the Si KLL spectra decreased and the intensities of the Si3N4 and excess Si peaks increased suggesting partial decomposition of SiNx to Si3N4 and excess Si.