In the 40nm BSI CMOS Image Sensor flow, the backside substrate contact (SBST_CONT) is essential for providing a stable electrical bias to the thinned silicon substrate, which defines the depletion region and prevents pixel blooming A2.Following the photoresist patterning and initial BPMD/AR2 etching, the HKD/AR1 Etch step is responsible for breaking through the remaining high-k dielectric (HKD) and anti-reflective (AR1) passivation layers to prepare the underlying structure for further processin