Method for cutting off fin field effect transistor

A method of cutting off a fin in making a field effect transistor comprising a plurality steps:

• step 1:
• providing a semiconductor substrate, wherein the semiconductor substrate comprises a plurality of fins, first spacing regions each formed between two adjacent fins of the plurality of fins;
• wherein the plurality of fins comprises a first type of fins designed to be cut off in making the field effect transistor and a second type of fins designed to be reserved in making the field effect transistor;
• disposing a first material layer to fill the first spacing regions up to a level above top surfaces of the plurality of fins, and planarizing the first material layer;
• step 2:
• forming a first pattern structure on the first material layer, wherein the first pattern structure comprises a plurality of first strip structures and second spacing regions, wherein each of the second spacing regions is placed between two adjacent ones of the plurality of first strip structures;
• wherein each of the plurality of first strip structures is configured to align to one of the first type of fins and the first spacing regions at two sides of said fin;
• wherein each of the second spacing regions is configured to align to one of the first type of fins, two of the second type of fins and the first spacing regions between two adjacent fins;
• wherein a sum of a width of one of the plurality of first strip structures and a width of one of the second spacing regions is equal to four times of a sum of a width of one of the plurality of fins and a width of one of the first spacing regions;
• step 3:
• forming second sidewalls on side surfaces of the plurality of first strip structures, wherein the second sidewalls are configured to align to the plurality of fins on two sides of one of the plurality of first strip structures;
• step 4:
• removing the plurality of first strip structures and forming a second pattern structure by the second sidewalls, wherein third spacing regions are formed between two adjacent ones of the second sidewalls;
• step 5:
• removing by etch the first material layer and the first type of fins under the third spacing regions by using the second sidewalls as a mask to realize the cutting-off of the first type of fins;
• and
• step 6:
• removing the second sidewalls and the first material layer.