Method for fabricating semiconductor device using a double patterning process

A method for fabricating a semiconductor device, the method comprising:

• forming an amorphous carbon layer over an etch target layer;
• forming a hard mask layer having a stack structure of a first layer, a second layer and a third layer in sequence over the amorphous carbon layer;
• forming a first photoresist pattern over the third layer;
• etching the third layer to form third layer patterns by using the first photoresist pattern as an etch barrier;
• forming a second photoresist pattern over the third layer patterns;
• etching the second layer to form second layer patterns by using the second photoresist pattern and the third layer patterns as an etch barrier;
• removing the second photoresist pattern;
• etching the first layer to form first layer patterns by using the second layer patterns as an etch barrier;
• etching the amorphous carbon layer to form amorphous carbon patterns by using the first layer patterns as an etch barrier;
• and
• etching the etch target layer to form patterns by using the amorphous carbon patterns as an etch barrier.