Semiconductor device with particular fin-shaped structures and fabrication method thereof

A method of fabricating a semiconductor device, comprising:

• providing a semiconductor substrate having a first region and a second region;
• forming a patterned mask in the first and second regions of the semiconductor substrate;
• etching the semiconductor substrate by using the patterned mask as an etch mask so as to form a patterned structure on the surface of the semiconductor substrate;
• forming a spacer disposed on the sidewall of the patterned structure in the second region;
• etching the semiconductor substrate by using the patterned mask and the spacer as an etch mask so as to form a plurality of fin-shaped structures in the first and second regions of the semiconductor substrate;
• forming a first mask layer covering the fin-shaped structures in the first region and a number of the fin-shaped structures in the second region;
• forming an oxide layer on sidewalls of the fin-shaped structures exposed from the first mask layer, the patterned mask and the spacer in the second region;
• and
• removing the oxide layer, so that the number of the fin-shaped structures in the second region have base portions narrower than top portions and the other fin-shaped structures in the second region have base portions wider than top portions.