A silicon oxide gap-filling process is described, wherein a CVD process having
an etching effect is performed to fill up a trench with silicon oxide. The reaction
gases used in the CVD process include deposition gases and He/H2 mixed
gas as a sputtering-etching gas, wherein the percentage of the He/H2 mixed
gas in the total reaction gases is raised with the increase of the aspect ratio
of the trench.