Profile controlof epitaxial structures in semiconductor devices

A semiconductor device, comprising:

• a substrate comprising first and second substrate regions;
• a first fin base disposed on the first substrate region;
• a second fin base disposed on the second substrate region;
• a first fin structure disposed on the first fin base;
• a second fin structure comprising an undoped semiconductor material disposed on the second fin base;
• a first source/drain region disposed on the first fin base;
• and
• a second source/drain region disposed on the second fin structure.

A method, comprising:

• forming first and second fin structures on first and second fin bases, respectively, on a substrate;
• forming third and fourth fin structures on third and fourth fin bases, respectively, on the substrate;
• forming a first pair of spacers with a first height on opposite sidewalls of each of the first and second fin structures;
• forming a second pair of spacers with a second height on opposite sidewalls of each of the third and fourth fin structures;
• etching portions of the first and second fin structures between the first pair of spacers;
• etching portions of the first and second fin bases under the portions of the first and second fin structures to form first openings;
• etching portions of the third and fourth fin structures between the second pair of spacers to form second openings;
• forming a first source/drain region in the first openings;
• and
• forming a second source/drain region in the second openings.