Method for forming fin structure in fin field effect transistor process and fin structure

A method for forming a fin structure in a fin field effect transistor process, comprising:

• step S1:
• growing a core layer thin film on a substrate;
• step S2:
• performing photolithography and etching for a first time to form a first core layer pattern and a second core layer pattern, the first core layer pattern being used to form fins and the second core layer pattern being used to form a reference layer overlay mark;
• step S3:
• depositing an etching mask layer, the etching mask layer covering tops and side surfaces of the first core layer pattern and the second core layer pattern, and a surface of the substrate;
• step S4:
• etching back the etching mask layer to form sidewalls of the first core layer pattern and sidewalls of the second core layer pattern;
• step S5:
• performing photolithography for a second time to form a first photoresist pattern and a second photoresist pattern, the first photoresist pattern being used to form a planar active area and the second photoresist pattern covering the second core layer pattern;
• step S6:
• removing the first core layer pattern, reserving the sidewalls of the first core layer pattern, and reserving the second photoresist pattern and the first photoresist pattern;
• step S7:
• etching the substrate for a first time to form the fins and the planar active area consisting of a substrate material;
• step S8:
• removing the first photoresist pattern, the second photoresist pattern, and the sidewalls of the second core layer pattern, and reserving the second core layer pattern;
• step S9:
• performing photolithography for a third time to form a third photoresist pattern which covers all of the planar active area and fins outside a fin cut area, and expose the second core layer pattern and the fins inside the fin cut area;
• and
• step S10:
• etching the substrate for a second time to form at least one reference layer overlay mark and the fin cut area consisting of the substrate material.