Gate All Around Transistor Device and Fabrication Methods Thereof

A semiconductor device, comprising:

• a substrate;
• a plurality of first suspended nanostructures vertically stacked over one another and disposed in an n-type region of the semiconductor device;
• a first gate stack wrapping around each of the first suspended nanostructures;
• a plurality of second suspended nanostructures vertically stacked over one another and disposed in a p-type region of the semiconductor device;
• and
• a second gate stack wrapping around each of the second suspended nanostructures,
• wherein the second suspended nanostructures include a threshold modifying impurity, and the first suspended nanostructures are free of the threshold modifying impurity.

A method of forming a semiconductor device, comprising:

• providing a structure having a substrate, a plurality of first nanostructures stacked in a vertical direction and suspended above a first region of the substrate, and a plurality of second nanostructures stacked in the vertical direction and suspended above a second region of the substrate;
• doping a threshold modifying impurity into the first nanostructures;
• forming a first gate stack wrapping around the first nanostructures, thereby forming a first transistor with a first threshold voltage;
• and
• forming a second gate stack wrapping around the second nanostructures, thereby forming a second transistor with a second threshold voltage that is different from the first threshold voltage.