Multiple patterning with mandrel cuts formed using a block mask

Methods of self-aligned multiple patterning. A mandrel line is formed over a hardmask layer, and forming a block mask is formed over a first portion of the mandrel line that is linearly arranged between respective second portions of the mandrel line. After forming the first block mask, the second portions of the mandrel line are removed with an etching process to cut the mandrel line and expose respective portions of the hardmask layer. A second portion of the mandrel line is covered by the block mask during the etching process to define a mandrel cut in the mandrel line.