In the dual-gate oxide (DGOX) module for 40nm CMOS image sensors, the silicon nitride hard mask protects specific regions during the localized growth of the thick gate oxide P1.Once the thick thermal oxide has been grown to accommodate high-voltage operating requirements, the protective nitride hard mask must be entirely removed to expose the underlying regions for subsequent gate stack formation A1.This step is positioned immediately before the As-doped PolySi deposition to ensure that the gate