Semiconductor structure and method for forming the same

A method for forming a semiconductor structure, comprising:

• forming a stack in which first semiconductor layers and second semiconductor layers are alternatingly stacked over a substrate;
• patterning the stack to form a first fin structure, a second fin structure and a third fin structure;
• forming a first patterned mask layer to cover the second fin structure and the third fin structure;
• laterally recessing the second semiconductor layers of the first fin structure while the second fin structures and the third fin structure are covered by the first patterned mask layer;
• removing the first patterned mask layer;
• forming a second patterned mask layer to cover the third fin structure;
• forming a first epitaxial material with a first conductivity type on the first fin structure and the second fin structure;
• removing the second patterned mask layer;
• forming a third patterned mask layer to cover the first fin structure and the second fin structure;
• and
• forming a second epitaxial material with a second conductivity type on the third fin structure, wherein the second conductivity type is opposite to the first conductivity type.

A semiconductor structure, comprising:

• a first p-type transistor with a first threshold voltage, wherein the first p-type transistor comprises:
• a plurality of first nanostructures;
• first and second source/drain features adjoining the first nanostructures;
• and
• a first gate stack wrapping around the first nanostructures;
• and
• a second p-type transistor with a second threshold voltage that is different than the first threshold voltage, wherein the second p-type transistor comprises:
• a plurality of second nanostructures;
• third and fourth source/drain features adjoining the second nanostructures;
• and
• a second gate stack wrapping around the second nanostructures,
• wherein a first distance between the first and second source/drain features is less than a second distance between the third and fourth source/drain features.