This Nitride Hard Mask Deposition step is strictly positioned within the Dual Gate Oxide (DGOX) module to safeguard the previously grown thin gate oxide T1.By physically covering the thin oxide regions, the nitride layer prevents oxygen penetration and unintended oxide growth during the subsequent thick gate oxide photo, etch, and thermal processing A3.Silicon nitride is specifically chosen here because the diffusion of oxygen through the film is extremely slow, making it an ideal mask against h