SiN films were grown in a production scale vertical MOCVD reactor and studied for in-situ passivation of III-nitride HEMT structures. The SiN was near-stoichiometric in composition and uniform in thickness across 4-, 6- and 8-inch diameter substrates. Its surface exhibited low roughness of about 0.3nm when the films were grown using H₂ carrier gas. Contamination of the SiN with Al and Ga elements was as low as 1e16cm^-3 and the H concentration was approximately 1at.% when optimized growth conditions were employed. It was demonstrated that the density of states at the SiN/III-nitride interface can be controlled by SiN growth conditions.