Semiconductor device and manufacturing method thereof

A device, comprising:

• a substrate;
• a first semiconductor fin and a second semiconductor fin over the substrate;
• an isolation structure between the first semiconductor fin and the second semiconductor fin;
• a liner between the second semiconductor fin and the isolation structure, wherein a bottommost surface of the isolation structure is coterminous with a bottommost surface of the liner at a region between the first and second semiconductor fins;
• a first epitaxy structure in contact with at least three sides of the first semiconductor fin, wherein the first semiconductor fin and the first epitaxy structure are doped with n-type dopants;
• and
• a second epitaxy structure in contact with at least three sides of the second semiconductor fin.

A device, comprising:

• a substrate;
• a first semiconductor fin over the substrate, wherein an upper portion of the first semiconductor fin and a lower portion of the first semiconductor fin are made of a same material but with different dopant concentrations;
• a second semiconductor fin over the substrate, wherein an upper portion of the second semiconductor fin and a lower portion of the second semiconductor fin are made of different materials;
• an isolation structure between the first semiconductor fin and the second semiconductor fin, wherein the isolation structure is in contact with the lower portion of the first semiconductor fin;
• and
• a liner in contact with the lower portion of the second semiconductor fin.