In the 40nm BSI CMOS Image Sensor flow, the Shallow Trench Isolation (STI) module requires robust gap-fill to provide electrical and structural isolation between adjacent pixel transistors P3.Following trench etching, liner deposition, and pre-clean steps, the STI Fill Conformal CVD Oxide serves as the primary gap-fill material to bridge the high-aspect-ratio trench P2.This step is fundamentally distinct from the preceding "STI Fill Conformal CVD Liner"; whereas the liner is a very thin layer de