An integrated circuit manufacturing method includes forming mandrel patterns over a patterning layer of a substrate; and forming a spacer layer over the patterning layer, over the mandrel patterns, and onto sidewalls of the mandrel patterns. The method further includes trimming the spacer layer using a dry etching technique such that a space between adjacent sidewalls of the spacer layer substantially matches a dimension of the mandrel patterns along a pattern width direction. The method further includes etching the spacer layer to expose the mandrel patterns and the patterning layer, resulting in a patterned spacer layer on the sidewalls of the mandrel patterns. After the trimming of the spacer layer and the etching of the spacer layer, the method further includes removing the mandrel patterns. The method further includes transferring a pattern of the patterned spacer layer to the patterning layer.