The VIA 4 - Photo step defines the vertical interconnect structures that link Metal 4 to the underlying Metal 3 in the back-end-of-line (BEOL) module A1.Positioned immediately after the deposition of the ILD 4-2 oxide and a pre-lithography clean, this patterning step provides the protective photoresist template required for the subsequent selective plasma etch of the dielectric T2.These vertical connections are essential for routing electrical signals and power across the multilayer interconnect