Mosfet with selective dopant deactivation underneath gate

A semiconductor device, comprising:

• a substrate;
• a channel region comprising a doped region in the substrate and an undoped epitaxial layer over the doped region, wherein the doped region comprises dopants of a first type;
• a gate structure over the channel region, wherein sidewalls of the gate structure are aligned with sidewalls of the epitaxial layer;
• a source in the substrate, wherein the source comprises dopants of a second type;
• a drain in the substrate, wherein the drain comprises dopants of the second type, and the channel region is between the source and the drain;
• and
• a deactivated region in the substrate and underneath the gate structure, wherein the deactivated region is partially within the channel region, dopants within the deactivated region are deactivated, and the deactivated region comprises carbon.

A method of fabricating a semiconductor device, comprising:

• doping a region of a substrate with dopants to provide a doped region;
• epitaxially growing an undoped epitaxial layer over the doped region;
• forming a dummy gate over the undoped epitaxial layer;
• removing the dummy gate to provide a cavity;
• performing selective dopant deactivation in a portion of the doped region underneath the cavity, wherein performing the selective dopant deactivation comprises deactivating dopants in the portion of the doped region underneath the cavity to form a deactivated region;
• and
• forming a gate structure in the cavity.