Method for high aspect ratio HDP CVD gapfill

A method for forming a silicon oxide layer over a substrate disposed in a high density plasma substrate processing chamber having a coil operatively coupled to form a plasma within the chamber and bias plasma system, said method comprising:

• heating the substrate to a temperature of at least 500° C. by introducing a first gas consisting of argon and/or an oxygen-containing source either alone or in combination into the substrate processing chamber and applying RF energy to the coil to form a plasma from the first gas without biasing the plasma toward the substrate;
• thereafter, flowing a process gas consisting of a silicon containing source, an oxygen-containing source, helium and optionally a dopant source into the substrate processing chamber, wherein a ratio of a flow rate of said helium to a combined flow rate of said silicon-containing source and said oxygen-containing source is at least 0.5:1;
• and
• applying RF energy to the coil to form a plasma from said process gas in order to deposit said silicon oxide layer, wherein said plasma has an ion density of at least 1.0×1011 ions/cm3.