A method of forming a silicon dioxide layer includes forming a high density plasma proximate a substrate, the plasma comprising silicon dioxide precursors; forming silicon dioxide from the precursors, the silicon dioxide being deposited over the substrate at a deposition rate; and while depositing, etching the deposited silicon dioxide with the plasma at an etch rate; a ratio of the deposition rate to the etch rate being at least about 4:1. Another method includes forming a high density plasma proximate a substrate; flowing gases into the plasma, at least some of the gases forming silicon dioxide; depositing the silicon dioxide formed from the gases over the substrate; and while depositing the silicon dioxide, maintaining a temperature of the substrate at greater than or equal to about 500° C. As an alternative, the method may include not cooling the substrate with a coolant gas while depositing the silicon dioxide.