Gate structure fabrication techniques for reducing gate structure warpage

A method comprising:

• forming a gate opening that exposes a channel region;
• forming a gate dielectric layer in the gate opening;
• forming a work function layer in the gate opening over the gate dielectric layer;
• forming a metal glue layer in the gate opening over the work function layer;
• performing a stress reduction treatment on the metal glue layer;
• after the stress reduction treatment, forming a metal fill layer in the gate opening over the metal glue layer, wherein the gate dielectric layer, the work function layer, the metal glue layer, and the metal fill layer form a gate stack of a gate structure that fills the gate opening;
• and
• wherein:
• the gate structure has a first gate spacer and a second gate spacer,
• the gate opening is between the first gate spacer and the second gate spacer,
• a first distance is between the first gate spacer and the second gate spacer before forming the metal glue layer in the gate opening,
• a second distance is between the first gate spacer and the second gate spacer after forming the metal glue layer in the gate opening, and
• the stress reduction treatment is tuned to reduce the second distance to the first distance.

A device comprising:

• a channel region disposed between epitaxial source/drains;
• and
• a gate stack disposed over the channel region, wherein the gate stack includes:
• a gate dielectric layer,
• a work function layer over the gate dielectric layer,
• a metal glue layer over the work function layer, wherein the metal glue layer has a residual stress of −2.5 gigapascals (GPa) to 0.8 GPa, wherein the metal glue layer includes a metal layer disposed between a first glue sublayer and a second glue sublayer, wherein the first glue sublayer and the second glue sublayer include a metal and nitrogen and the metal layer includes the metal, and
• a metal fill layer over the metal glue layer.