Following the backside photolithography step, the BPMD (Backside Pre-Metal Dielectric) Etch transfers the substrate contact pattern into the previously deposited SiO layer A2.This step creates the initial vertical pathway through the thick isolation dielectric, preparing the structure for subsequent high-k dielectric (HKD) and anti-reflective (AR) layer removal P4.Unlike standard front-side PMD etches, this specific backside process must align precisely with the underlying silicon grid and isola