Semiconductor device and formation method thereof

A method for forming a semiconductor device, comprising:

• providing a to-be-etched layer including a first region and a second region adjoining the first region;
• forming a first mask layer on the to-be-etched layer;
• forming a patterned core layer on the first mask layer of the first region;
• forming a sidewall spacer on a top surface and a sidewall surface of the core layer and a surface of the first mask layer;
• forming a first sacrificial layer on the sidewall spacer on the surface of the first mask layer of the second region;
• forming a second sacrificial layer on the sidewall spacer, the second sacrificial layer exposing the sidewall spacer on the top of the core layer and a top of the first sacrificial layer;
• removing the first sacrificial layer, the sidewall spacer on the surface of the first mask layer of the second region and the sidewall spacer on the top of the core layer;
• removing the core layer;
• etching the first mask layer of the first region to form a first trench;
• and
• etching the first mask layer of the second region to form a second trench.