US Patent 11664272 Etch profile control of gate contact opening

A method comprises forming a gate structure over a semiconductor substrate; forming an etch stop layer over the gate structure and an ILD layer over the etch stop layer; performing a first etching process to form a gate contact opening extending through the ILD layer into the etch stop layer, resulting in a sidewall of the etch stop layer being exposed in the gate contact opening; oxidizing the exposed sidewall of the etch stop layer; after oxidizing the exposed sidewall of the etch stop layer, performing a second etching process to deepen the gate contact opening; and forming a gate contact in the deepened gate contact opening.