Etch profile control of gate contact opening

A method comprising:

• forming a gate structure between gate spacers;
• depositing in sequence an etch stop layer and an interlayer dielectric (ILD) layer over the gate structure;
• performing a first etching process to form a gate contact opening in the ILD layer at least until the etch stop layer is exposed;
• after performing the first etching process, performing an oxygen plasma treatment to form a treated region in the etch stop layer and around a bottom portion of the gate contact opening, while leaving a remaining region of the etch stop layer un-treated;
• after performing the oxygen plasma treatment, performing a second etching process to extend the gate contact opening toward the gate structure, wherein the treated region of the etch stop layer has a higher etch resistance than the un-treated region of the etch stop layer in the second etching process;
• and
• after performing the second etching process, forming a gate contact in the gate contact opening.

A device comprising:

• a gate structure over a substrate;
• an etch stop layer over the gate structure;
• an interlayer dielectric (ILD) layer over the etch stop layer;
• and
• a gate contact extending through the ILD layer and the etch stop layer to electrically connect with the gate structure, wherein the etch stop layer has a first oxidized region laterally surrounding the gate contact and a first un-oxidized region laterally surrounding the first oxidized region.