The PMD 4 Etch step initiates the sequential patterning of the Pre-Metal Dielectric (PMD) stack to form high-aspect-ratio contacts (HARC) connecting the first metal layer to the underlying gate and source/drain regions P2.Following the contact opening photolithography step, this anisotropic dry etch transfers the resist pattern into the uppermost dielectric layer A1.Because modern scaled devices utilize multi-layered PMD stacks with varying compositions to manage gap-fill and thermomechanical st