1. A method for forming a FinFET, comprising: providing a semiconductor layer; forming a first layer of a first material over the semiconductor layer; patterning the first layer to form a patterned feature having a pair of sidewalls; forming a pair of first sidewall spacers of a second material adjacent to the pair of sidewalls of the patterned feature; forming a pair of second sidewall spacers of a third material that is a different type from the second material, wherein the pair of second sidewall spacers are adjacent to the pair of first sidewall spacers; removing the pair of first sidewall spacers; after removing the pair of first sidewall spacers, etching the semiconductor layer using the pair of second sidewall spacers and the patterned feature as a mask to leave semiconductor fins patterned as per the pair of second sidewall spacers and the patterned feature; and wherein channels of the FinFET are implemented in the semiconductor fins.