Integration of dense and variable pitch fin structures

A method for forming fin structures, comprising:

• lithographically forming a first set of mandrels in a uniform fin pitch region with uniform width and spacing over a hardmask layer to be patterned;
• lithographically forming a second set of mandrels in a variable fin pitch region with variable width and spacing over the hardmask layer to be patterned;
• forming a protective layer over a set of mandrels in a variable fin pitch region;
• forming first sidewalls around a set of mandrels in a uniform fin pitch region;
• removing the set of mandrels in the uniform fin pitch region;
• removing the protective layer;
• forming second sidewalls around the first sidewalls in the uniform fin pitch region and the mandrels in the variable fin pitch region;
• removing the first sidewalls and the mandrels;
• and
• etching an underlying layer around the second sidewalls to form fins, wherein fins in the uniform fin pitch region have a spacing that is less than half of a minimum pitch of a lithography process used to form the mandrels and wherein fins in the variable fin pitch region have a spacing that is greater than half, but less than the minimum pitch of the lithography process.