Method for preparing semiconductor device with annular semiconductor fin

A method for preparing a semiconductor device, comprising:

• forming a ring structure over a semiconductor substrate;
• etching the semiconductor substrate by using the ring structure as a mask to form an annular semiconductor fins;
• epitaxially growing a first bottom source/drain structure within the annular semiconductor fin and a second bottom source/drain structure surrounding the annular semiconductor fin;
• forming a first silicide layer over the first bottom source/drain structure and a second silicide layer over the second bottom source/drain structure;
• forming a first gate structure over the first silicide layer and a second gate structure over the second silicide layer;
• and
• epitaxially growing a top source/drain structure over the annular semiconductor fin;
• implanting dopants into a top surface of the semiconductor substrate exposed by the annular semiconductor fin to form a first processed area at an inner sidewall of the annular semiconductor fin and a second processed area at an outer sidewall of the annular semiconductor fin, wherein the first and second processed areas are formed on and in direct contact with the top surface of the semiconductor substrate;
• and
• after the first and second processed areas are formed, forming an inner spacer on the inner sidewall of the annular semiconductor fin and an outer spacer on the outer sidewall of the annular semiconductor fin;
• wherein a top side of the first processed area is covered by the inner spacer while two sides of the first processed area are covered by the inner sidewall of the annular semiconductor fin and a sidewall of the first bottom source/drain structure respectively;
• wherein a top side of the second processed area is covered by the outer spacer while two sides of the second processed area are covered by the outer sidewall of the annular semiconductor fin and a sidewall of the second bottom source/drain structure respectively.