US Patent 7923305 Patterning method for high density pillar structures

A method of making a device includes forming a first sacrificial layer over an underlying layer, forming a first photoresist layer over the first sacrificial layer, patterning the first photoresist layer to form first photoresist features, rendering the first photoresist features insoluble to a solvent, forming a second photoresist layer over the first photoresist features, patterning the second photoresist layer to form second photoresist features, etching the first sacrificial layer using both the first and the second photoresist features as a mask to form first sacrificial features, forming a spacer layer over the first sacrificial features, etching the spacer layer to form spacer features and to expose the sacrificial features, removing the first sacrificial features, and etching at least part of the underlying layer using the spacer features as a mask.