Residue Removal in Metal Gate Cutting Process

A method comprising:

• forming a gate stack over and contacting a dielectric dummy fin, wherein the gate stack comprises:
• a first portion on a first side of the dielectric dummy fin;
• a second portion on a second side of the dielectric dummy fin;
• a third portion overlapping the gate stack, wherein the third portion interconnects the first portion and the second portion;
• etching the third portion to reveal a top surface and sidewalls of the dielectric dummy fin, wherein after the etching, a residue portion of the third portion is left, and the residue portion interconnects the first portion and the second portion;
• and
• etching the residue portion.

A method comprising:

• forming a metal gate strip;
• forming an amorphous layer over the metal gate strip;
• forming a patterned hard mask over the amorphous layer;
• etching the amorphous layer using the patterned hard mask as an etching mask, wherein the metal gate strip is revealed;
• etching the metal gate strip to form a recess in the metal gate strip, wherein the recess has a bottom surface lower than a top surface of an underlying dielectric dummy fin, and the top surface and opposite sidewalls of the underlying dielectric dummy fin are exposed to the recess;
• performing a thermal etching process to remove a residue portion of the metal gate strip;
• and
• filling a dielectric material into the recess.