Semiconductor structure having multiple nanostructures with different widths and method for forming the same

A semiconductor structure, comprising:

• first channel layers formed over a first base fin structure along a first direction;
• second channel layers formed over a second base fin structure along the first direction;
• a first gate structure formed over the first channel layers along a second direction;
• and
• a second gate structure formed over the second channel layers along the second direction,
• wherein each of the first channel layers has a first width along the second direction, each of the second channels layers has a second width along the second direction, the first base fin structure has a first base width, and the first base width is greater than the first width, the second base fin structure has a second base width, and the second base width is greater than the second width, and a difference between the first base width and the first width is greater than a difference between the second base width and the second width.

A method for forming a semiconductor structure, comprising:

• forming a first fin structure and a second fin structure over a first region and a second region of a substrate, wherein the first fin structure comprises first semiconductor material layers and second semiconductor material layers alternately stacked, and the second fin structure comprises first semiconductor material layers and second semiconductor material layers alternately stacked;
• removing a portion of the first fin structure, such that a width of the first fin structure is reduced;
• forming a first dummy gate structure over the first fin structure and the second fin structure along a second direction;
• removing the first dummy gate structure to expose the first fin structure and the second fin structure;
• removing all of the second semiconductor material layers to expose the first semiconductor material layers;
• and
• forming a first gate structure to wrap around the first semiconductor material layers of the first fin structure and the first semiconductor material layers of the second fin structure, such that first nanostructures and second nanostructures are formed, wherein each of the first nanostructures has a first width along the second direction, each of the second nanostructures has a second width along the second direction, and the first width is smaller than the second width.