Method for fabricating semiconductor device

A method for fabricating semiconductor device, comprising:

• providing a substrate having a first region and a second region;
• forming a first fin-shaped structure on the first region and a second fin-shaped structure on the second region;
• forming a first spacer adjacent to the first fin-shaped structure and a second spacer adjacent to the second fin-shaped structure;
• using the first spacer and the second spacer as mask to remove part of the substrate for forming a third fin-shaped structure on the first region and a fourth fin-shaped structure on the second region, wherein the third fin-shaped structure comprises a first top portion and a first bottom portion and the fourth fin-shaped structure comprises a second top portion and a second bottom portion;
• forming a first doped layer on the first fin-shaped structure and the second fin-shaped structure;
• forming a first hard mask on the first doped layer;
• removing the first hard mask and the first doped layer on the second region;
• and
• forming a second doped layer on the first region and the second region.