Patterning method for high density pillar structures

1. A method of making a device, comprising:

forming a first photoresist layer over a 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;

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;

patterning the sacrificial layer using the first, second and third photoresist features as a mask to form sacrificial features;

forming an insulating filler layer between the sacrificial features;

removing the sacrificial features to form openings in the insulating filler layer;

depositing semiconductor features in the openings in the insulating filler layer;

recessing the semiconductor features to form recesses; and

forming switching material features in the recesses over the semiconductor features;

wherein:

the semiconductor features comprise at least a portion of steering elements of non-volatile memory cells; and

the switching material features comprise storage elements of the non-volatile memory cells.

2. The method of claim 1 , wherein the step of forming third photoresist features between the spacer features comprises:

forming a third photoresist layer between and over the spacer features; and

planarizing the third photoresist layer using top of the spacer features as a stop.

3. The method of claim 1 , wherein:

the first photoresist layer comprises a first composition;

the second photoresist comprises a second composition;

the third photoresist comprises a third composition; and

the first, second and third compositions are the same or different from each other.

4. The method of claim 1 , wherein:

the step of rendering the first photoresist pattern insoluble to the solvent forms a barrier layer over the first photoresist pattern;

the barrier layer comprises a thin polymer film having a thickness of less than 10 nm which is disposed on a surface of first photoresist features, such that the sacrificial layer is exposed in area between first photoresist features; and

the barrier layer protects the first photoresist pattern from being dissolved by the solvent used during the step of patterning the second photoresist layer.

5. A method of making a device, comprising:

forming a first photoresist layer over a 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;

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;

patterning the sacrificial layer using the first, second and third photoresist features as a mask to form sacrificial features;

forming an insulating filler layer between the sacrificial features;

removing the sacrificial features to form openings in the insulating filler layer;

selectively growing semiconductor features in the openings in the insulating filler layer to leave recesses over the semiconductor features; and

forming switching material features in the recesses over the semiconductor features;

wherein:

the semiconductor features comprise at least a portion of steering elements of non-volatile memory cells; and

the switching material features comprise storage elements of the non-volatile memory cells.