Abstract: The present invention comprises means for sublimating and handling ammonium chloride (NH.sub.4 Cl) vapor, a bi-product of a silicon nitride growth process, thereby preventing backstreaming into the reactor and ingestion of vapor and particulates by the vacuum pump. The exhaust circuit comprises a novel combination of valves, sublimation and cold traps, cooling and heating elements to facilitate reduction of condensed NH.sub.4 Cl volume from a first path trap thus reducing maintenance, increasing production up-time and enhancing product yield.