US Patent 7981592 Double patterning method

A method of making a device includes forming a first photoresist layer over an underlying layer, patterning the first photoresist layer to form a first photoresist pattern comprising a first grid, rendering the first photoresist pattern insoluble to a solvent, forming a second photoresist layer over the first photoresist pattern, patterning the second photoresist layer to form a second photoresist pattern over the underlying layer, where the second photoresist pattern is a second grid which overlaps the first grid to form a photoresist web, and etching the underlying layer using the photoresist web as a mask.