| CPC H01L 21/0337 (2013.01) [H01L 21/3086 (2013.01); H01L 21/31051 (2013.01); H01L 21/31144 (2013.01)] | 20 Claims |

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1. A method for forming a semiconductor structure, comprising:
forming first mandrels over a target layer;
forming a first opening to cut off one of the first mandrels;
forming a spacer layer over the first mandrels;
forming second mandrels over the spacer layer and between the first mandrels;
forming a second opening to cut off one of the second mandrels;
etching the spacer layer; and
etching the target layer,
wherein a top surface of the spacer layer in the first opening is higher than a top surface of the spacer layer between the first mandrels.
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