In the MOL CONTACT module, after etching through the Contact Etch Stop Layer (CESL) and pad oxide to open the contact holes, the Poly/Si Back Etch is performed to expose and shape the underlying polysilicon gate and silicon source/drain regions A1.Unlike backside silicon thinning steps performed much later in BSI integration, this front-side step directly prepares the local device contacts before the subsequent Ashing, Ti/TiN barrier deposition, and W plug fill A2.As device dimensions scale down