US Patent 9312354 Contact etch stop layers of a field effect transistor

The disclosure relates to a field effect transistor. An exemplary structure for a field effect transistor comprises a substrate; a source region and a drain region disposed in the substrate; a gate structure over the substrate comprising sidewalls and a top surface, wherein the gate structure interposes the source region and the drain region; a contact etch stop layer (CESL) over at least a portion of the top surface of the gate structure; an interlayer dielectric layer over the CESL; a gate contact extending through the interlayer dielectric layer; and a source contact and a drain contact extending through the interlayer dielectric layer, wherein a first distance between an edge of the source contact and a first corresponding edge of the CESL is about 1 nm to about 10 nm.