Input/output devices

A semiconductor device, comprising:

• a first transistor in a first area, the first transistor comprising:
• a first gate structure extending lengthwise along a first direction;
• and
• a first gate spacer layer, a second gate spacer layer, a third gate spacer layer, and a fourth gate spacer layer over sidewalls of the first gate structure;
• a second transistor in a second area, the second transistor comprising:
• a second gate structure extending lengthwise along the first direction, and
• the first gate spacer layer, the third gate spacer layer and the fourth gate spacer layer over sidewalls of the second gate structure;
• and
• an interlayer dielectric (ILD) layer around the first gate structure and the second gate structure,
• wherein the fourth gate spacer layer, the third gate spacer layer, and the second gate spacer layer are of different compositions,
• wherein the third gate spacer layer is directly on sidewalls of the first gate spacer layer in the second area,
• wherein the second gate spacer layer is disposed on a top-facing surface of the first gate spacer layer,
• wherein the ILD layer is spaced apart from the first gate structure by a first distance about equal to a total width of the first, second, third, and fourth gate spacer layers along a second direction perpendicular to the first direction,
• wherein the ILD layer is spaced apart from the second gate structure by a second distance about equal to a total width of the first, third, and fourth gate spacer layers along the second direction.

A semiconductor device, comprising:

• a gate structure extending lengthwise along a first direction, the gate structure having a gate dielectric layer;
• and
• a gate spacer disposed along a sidewall of the gate structure, the gate spacer having a first, a second, and a third gate spacer layer,
• wherein the first gate spacer layer is in direct contact with a sidewall of the gate dielectric layer, the second gate spacer layer is in between the first and third gate spacer layers, and the third gate spacer layer is disposed on a top-facing surface of the second gate spacer layer,
• wherein the first gate spacer layer is thicker than the second and third gate spacer layers along a second direction perpendicular to the first direction,
• wherein the first gate spacer layer has a dielectric constant smaller than 3.9 and the third gate spacer layer has a dielectric constant greater than 3.9.