Silicon nitride films were deposited by mercury-sensitized photochemical vapor deposition utilizing a gaseous mixture of Si2H6 (2% in Ar) and NH3 under 253.7 run ultraviolet light irradiation. Non-stoichiometric silicon-rich and nitrogen-rich samples were deposited by varying gas flow ratio. High partial pressure of disilane results in the formation of clusters, with the incorporation of hydrogen in the form of Si-H and N-H stretching modes below the detection level of Fourier transform infrared spectroscopy. In the nitrogen-rich sample the bonded hydrogen concentration is 0.56 x 10(18) cm(-2). After annealing the samples at 350 T for 3 h in a pressure of 50 mTorr, the interface electronic state density decreases for silicon-rich sample and increases for nitrogen-rich sample.