Silicon nitride layers deposited by an excimer laser reactive ablation of silicon target in ammonia on Si(100) wafers kept at 300 or 600 °C have been studied by infrared absorption and angular resolved x‐ray photoelectron spectroscopy. Presence of hydrogen in the deposits unexpected at the high substrate temperatures is documented. The observed deposit thicknesses, stoichiometry, and the hydrogen content as a function of ammonia pressure suggest a picture of the deposition process with Si3N4synthesis taking place on the growing deposit surface, contrary to the liquid phase reaction model suggested for analogous TiN deposition. ©1995 American Institute of Physics.