Following the PMD 1 and CESL dry etch steps, the contact holes are physically opened down to the silicon source/drain regions P3.However, a thin layer of native oxide or residual pad oxide inevitably remains or regrows on the exposed silicon surface P1.To achieve low contact resistance, this interfacial oxide must be entirely removed prior to Ti/TiN deposition T1.This Pad Oxide Etch step prepares the pristine silicon surface necessary for reliable Ti silicide formation, which is a principal requ