Transistors having nanostructures

A semiconductor device, comprising:

• a first transistor comprising:
• a first nanostructure over and spaced apart from a first base portion, and
• a first gate structure wrapping around the first nanostructure;
• and
• a second transistor comprising:
• a second nanostructure over and spaced apart from a second base portion, and
• a second gate structure disposed over the second nanostructure
• wherein the first nanostructure has a first width and a first height smaller than the first width,
• wherein the second nanostructure has a second width and a second height greater than the second width,
• wherein the first nanostructure extends lengthwise between a first source/drain feature and a second source/drain feature along a direction,
• wherein the first nanostructure includes a channel portion directly under the first gate structure and a connection portion between the channel portion and the first source/drain feature along the direction, and
• wherein a height of the connection portion is greater than a height of the channel portion.

A method, comprising:

• depositing, on a substrate, a stack comprising a plurality of silicon layers interleaved by a plurality of silicon germanium layers;
• patterning the stack and the substrate into a first fin-shaped structure and a second fin-shaped structure extending lengthwise along a first direction;
• forming a first dummy gate stack over a first channel region of the first fin-shaped structure and a second dummy gate stack over a second channel region of the second fin-shaped structure;
• removing the first dummy gate stack and the second dummy gate stack;
• selectively removing the silicon germanium layers in the first channel region and the second channel region to form first nanostructures in the first channel region and second nanostructures in the second channel region;
• selectively trimming the first nanostructures in the first channel region while the second nanostructures are covered in a masking layer;
• forming a first gate structure over the first nanostructures;
• and
• forming a second gate structure over the second nanostructures,
• wherein a width of the first fin-shaped structure along a second direction perpendicular to the first direction is greater than the second fin-shaped structure along the second direction.