FinFET structure and method for fabricating the same

A device comprising:

• a substrate comprising silicon;
• a fin structure protruding over the substrate, wherein the fin structure comprises:
• a lower portion formed of silicon and enclosed by an isolation region;
• a middle portion formed of silicon-germanium-carbon, wherein the middle portion is enclosed by an oxide layer;
• an upper portion formed of silicon, wherein the upper portion comprises a channel;
• and
• a silicon-carbon layer formed between the middle portion and the upper portion;
• a first source/drain region comprising a first silicon-phosphorus region and a first silicon-carbon layer formed underlying the first silicon-phosphorus region;
• and
• a second source/drain region comprising a second silicon-phosphorus region and a second silicon-carbon layer formed underlying the second silicon-phosphorus region.

A device comprising:

• a fin structure over a silicon substrate, wherein the fin structure comprises:
• a lower portion formed of silicon;
• a middle portion formed of silicon-germanium-carbon;
• an upper portion formed of silicon;
• and
• a silicon-carbon layer formed between the middle portion and the upper portion;
• a first source/drain region comprising a first silicon-phosphorus region and a first silicon-carbon layer formed underlying the first silicon-phosphorus region;
• and
• a second source/drain region comprising a second silicon-phosphorus region and a second silicon-carbon layer formed underlying the second silicon-phosphorus region.