Patent ID: 8216907

Claim:
A method to form a metal high dielectric constant (MHK) transistor, comprising: providing a MHK stack disposed on a substrate, the MHK stack comprising a layer of high dielectric constant material and an overlying layer comprised of a metal, the MHK stack having an overlying layer comprised of silicon; selectively removing only the overlying layer comprised of silicon and the overlying layer comprised of metal, without removing the layer of high dielectric constant material, to form an upstanding portion of a MHK gate structure comprised of an underlying portion of the layer comprised of metal, and an overlying portion of the layer comprised of silicon; forming a first sidewall layer comprised of silicon on sidewalls of the upstanding portion of the MHK gate structure; forming a second sidewall layer on sidewalls of the first sidewall layer; removing a portion of the layer of high dielectric constant material to form exposed surfaces of the layer of high dielectric constant material; forming an offset spacer layer over the second sidewall layer and over the exposed surfaces of the layer of high dielectric constant material; and forming in the substrate extensions that underlie the first and second sidewall layers and that extend under a portion but not all of the upstanding portion of the MHK gate structure, wherein each substrate extension overlaps the upstanding portion of the MHK gate structure by an overlap distance.