TRENCH FORMATION USING HORN SHAPED SPACER

摘要

A disclosed method includes forming a mandrel layer over a target layer, and etching the mandrel layer to form mandrels. The mandrels have top widths greater than respective bottom widths, and the mandrels define a first opening in the mandrel layer. The first opening has an I-shape and includes two parallel portions and a connecting portion interconnecting the two parallel portions. Spacers are formed on sidewalls of the first opening. The spacers fill the connecting portion, wherein a center portion of each of the two parallel portions is unfilled by the spacers. Portions of the first opening that are unfilled by the spacers are extended into the target layer.