PMD 1 Etch represents the final phase of bulk dielectric patterning within the middle-of-line (MOL) contact formation module A1.Preceded by the sequential etching of upper pre-metal dielectric layers (PMD 4 through 2), this specific step targets the lowest SiO2-based layer of the dielectric stack P1.The primary objective is to complete the high-aspect-ratio contact holes while stopping reliably and uniformly on the underlying Contact Etch Stop Layer (CESL), which is typically composed of silicon