US Patent 9991131 Dual mandrels to enable variable fin pitch

A double masking process is used to form semiconductor fin arrays having a controlled and variable fin pitch within different arrays. During the process, a top mandrel layer overlies a bottom mandrel layer over a semiconductor substrate. Sidewall structures formed on first mandrels within a first region of the substrate define a patterned hard mask that cooperates with a patterned photoresist layer over a second region of the substrate to form second mandrels within first and second regions of the substrate. Sidewall structures formed on the second mandrels are used as a masking layer to form a plurality of fins over the substrate.