HDP-CVD SiON films for gap-fill

The present invention pertains to methods of depositing low stress/high index multi-layer films on a substrate using an HDP-CVD process. The multi-layer films include two lining layers and a bulk gap-fill layer and the HDP-CVD process employs a reduced substrate bias power during deposition of at least the second lining layer. Deposition of the three layers occurs at reduced deposition temperatures which further reduces the stress of the multi-layer film. The lower stress results in less defectivity which improves the films ability to maintain optical confinement of radiation.