High-pressure annealing and reducing wet etch rates

A method of filling a trench in a patterned substrate, the method comprising:

• forming a dielectric film on the patterned substrate, wherein forming the dielectric film comprises flowing dielectric material into the trench after initial deposition elsewhere onto the patterned substrate, wherein the dielectric material in the trench comprises pores but otherwise fills the trench on the patterned substrate and wherein the dielectric material comprises silicon and hydrogen, wherein an aspect ratio of the height to the width of the trench is greater than 5:1;
• and
• placing the patterned substrate into a substrate processing region of a substrate processing chamber, and
• densifying the dielectric material in the trench by exposing the dielectric material to gas-phase H2O at a partial pressure of H2O within the substrate processing region to form densified gapfill dielectric, wherein the partial pressure of H2O within the substrate processing region is between 145 psi and 864 psi, and wherein a temperature of the patterned substrate is between 300° C. and 700° C. during the densifying of the dielectric material.