Metal layer protection during wet etching

A semiconductor fabrication method comprising:

• receiving a structure having a plurality of gate stacks, a source/drain (S/D) region disposed between two of the gate stacks, and a metal layer disposed over the gate stacks and the S/D region;
• forming a BARC (bottom anti-reflective coating) layer over a portion of the metal layer disposed over the S/D region and between the two gate stacks;
• forming a crust layer on top of the BARC layer through implanting operations with a dopant;
• and
• removing unwanted metal layer sections using wet etching operations, wherein the crust layer and BARC layer protect metal layer sections under the BARC layer from metal loss during the wet etching operations;
• wherein forming the crust layer comprises controlling an implant energy level to achieve:
• a desired carbon ratio in the BARC layer, a desired oxygen ratio in the BARC layer during implanting operations, a desired carbon concentration intensity near the surface of the BARC layer, or zero or near zero metal loss during the wet etching operations;
• and
• wherein forming the crust layer further comprises controlling an implant dosage level to achieve:
• zero or near zero metal loss during the wet etching operations or a desired etching rate during the wet etching operations.