Patterning method for high density pillar structures

A method of making a device, comprising:

• forming a sacrificial layer over a semiconductor seed layer;
• forming a hard mask layer over the sacrificial layer;
• forming a first photoresist layer over the hard mask 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;
• forming a spacer layer over the first and second photoresist features;
• etching the spacer layer to form spacer features and to expose the first and second photoresist features;
• forming third photoresist features between the spacer features;
• removing the spacer features;
• etching the hard mask layer using the first, second and third photoresist features as a mask to form hard mask features;
• trimming the hard mask features;
• etching the sacrificial layer using the hard mask features as a mask to form sacrificial features;
• etching the semiconductor seed layer using the sacrificial features as a mask;
• forming an insulating filler layer between the sacrificial features and between remaining portions of the etched semiconductor seed layer;
• removing the sacrificial features to form openings in the insulating filler layer;
• and
• forming semiconductor pillars in the openings over the remaining portions of the etched semiconductor seed layer.