Patent ID: 8741778

Claim:
A method of etching silicon oxide from multiple trenches on a surface of a patterned substrate in a substrate processing region of a substrate process chamber, the method comprising the sequential steps of: dry etching the silicon oxide in each of the multiple trenches in a first dry-etch stage using plasma effluents generated from a fluorine-containing precursor and a hydrogen-containing precursor to form first solid by-products on the surface of a remaining silicon oxide in the multiple trenches, wherein the silicon oxide is removed at a first etch rate during the first dry-etch stage; increasing a flow ratio of the hydrogen-containing precursor to the fluorine-containing precursor and/or decreasing plasma power used to form the plasma effluents to reduce an etch rate of the dry etching the silicon oxide in each of the multiple trenches in a second dry-etch stage to form second solid-by-products on the surface of remaining silicon oxide in the multiple trenches, wherein a second etch rate of the silicon oxide during the second dry-etch stage is less than the first etch rate; and sublimating the first and second solid by-products from the multiple trenches.