Semiconductor structure and method of forming thereof

A method, comprising:

• forming a first channel region over a substrate;
• forming a second channel region over the substrate, wherein a width of the first channel region is less than a width of the second channel region;
• forming first semiconductor material layers on opposite sides of the first and second channel regions;
• forming second semiconductor material layers on the first semiconductor material layers, wherein a process temperature of forming the second semiconductor material layers is less than a process temperature of forming the first semiconductor material layers;
• forming a third semiconductor material layers over the second semiconductor material layers, wherein the first, second and third semiconductor material layers form first source/drain regions on the opposite sides of the first channel regions and second source/drain regions on the opposite sides of the second channel regions;
• forming a first gate structure over the first channel region;
• and
• forming a second gate structure over the second channel region.

A semiconductor structure, comprising:

• a first channel region over a substrate;
• a second channel region over the substrate, wherein a width of the first channel region is less than a width of the second channel region;
• first source/drain regions on opposite sides of the first channel region;
• second source/drain regions on opposite sides of the second channel region, wherein one of the first and second source/drain regions comprises:
• a first semiconductor material layer;
• a second semiconductor material layer over the a first semiconductor material layers, wherein from a top view, an angle from a sidewall of the second semiconductor material layer to an interface of the second semiconductor material layer and one of the first and second channel regions is in a range from about 54 degrees to about 90 degrees;
• and
• a third semiconductor material layer over the second semiconductor material layer;
• and
• a gate structure wrapping around the first and second channel regions.