Gapfill of variable aspect ratio features with a composite PEALD and PECVD method

A method of filling a gap on a substrate surface, the method comprising:

• (a) introducing a first reactant in vapor phase into a reaction chamber having the substrate therein, and allowing the first reactant to adsorb onto the substrate surface;
• (b) introducing a second reactant in vapor phase into the reaction chamber;
• (c) exposing the substrate surface to plasma to drive a surface reaction between the first and second reactants on the substrate surface to form a film lining the gap;
• (d) sweeping or purging the reaction chamber;
• (e) introducing at least a third reactant in vapor phase into the reaction chamber;
• and
• (f) generating a plasma from at least the third reactant to drive a gas phase reaction, wherein the gas phase reaction produces a gap-filling material, and wherein the gap-filling material partially or completely fills the gap on the substrate surface.