The HKD/AR2 Etch step is a critical subtractive process in the backside illuminated (BSI) CMOS image sensor bond pad module P1.Positioned after the BPMD (Bond Pad Metal Dielectric) etch, this step selectively removes the upper anti-reflective (AR2) and high-k dielectric (HKD) layers to prepare for the subsequent AR1 and silicon back etch operations A2.In advanced packaging and interconnect schemes, exposing a bonding pad requires sequentially clearing a complex stack of optical and passivation f