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.