Post-planarization densification

A method of processing a silicon-and-oxygen-containing layer on a patterned substrate having a narrow trench and a recessed open area, the method comprising:

• forming a nitride layer on the patterned substrate;
• forming a silicon-and-oxygen-containing layer on the nitride layer including in the narrow trench and in the recessed open area;
• planarizing the silicon-and-oxygen-containing layer leaving a narrow gapfill portion in the narrow trench and a wide gapfill portion in the recessed open area, wherein planarizing the silicon-and-oxygen-containing layer comprises removing a portion of the silicon-and-oxygen-containing layer above the narrow trench and exposing a post-planarization dielectric interface disposed closer to the narrow trench than a corresponding pre-planarization dielectric interface;
• removing exposed portions of the nitride layer;
• and
• treating the substrate, after removing the exposed portions of the nitride layer, to increase a density of the narrow gapfill portion, wherein the post-planarization dielectric interface disposed closer to the narrow trench allows the narrow gapfill portion to become denser than had the substrate been treated before the planarizing operation.