Multi-exposure lithography employing a single anti-reflective coating layer

A method of forming a patterned structure comprising:

• forming a stack on a substrate, said stack including, from bottom to top, an underlying layer, an optically dense layer comprising a hydrocarbon-based polymer, an anti-reflective coating (ARC) layer, and a first photoresist;
• lithographically patterning said first photoresist with a first pattern and transferring said first pattern into said ARC layer and an upper portion of said optically dense layer, but not into a lower portion of said optically dense layer, by a first etch;
• applying a second photoresist on said optically dense layer and said ARC layer;
• lithographically patterning said second photoresist with a second pattern and transferring said second pattern into said ARC layer by a second etch;
• and
• transferring a composite pattern of said first pattern and said second pattern through said optically dense layer and into said underlying layer, wherein said first pattern is a pattern of a periodic array having a lithographic pitch, wherein said second pattern is a pattern of another periodic array having said lithographic pitch, wherein said first pattern and said second pattern are congruent and are offset relative to each other by one half of said lithographic pitch.