Abstract: A process for forming a thin sealing layer of silicon nitride directly upon a silicon substrate to minimize bird's beak encroachment. The process employs in situ fabrication whereby the native oxide is removed from the silicon substrate by etching the hydrogen or hydrogen chloride and followed in direct succession, and in the absence of exposure to an oxidizing environment, with the deposition of a silicon nitride layer by LPCVD. Bird's beak encroachment is incrementally reduced by the absence of the native oxide layer as a path for oxygen species movement during the field oxide growth.