The present invention relates to semiconductor device fabrication and more specifically to a method and material for forming high density shallow trench isolation structures in integrated circuits capable of withstanding wet etch treatments. A silica dielectric film is formed on a substrate. The silica dielectric film has a density of from about 1.0 to about 2.3 g/ml, a SiC:SiO bond ratio of about 0.015 or more, a dielectric constant of about 4.0 or less, a breakdown voltage of about 2 MV/cm or more, and a wet etch resistance in a 100:1 by volume mixture of water and hydrogen fluoride of about 30 .ANG./minute or less.