Impurity control in HDP-CVD DEP/ETCH/DEP processes

A method of depositing a silicon oxide film on a substrate disposed in a substrate processing chamber, the substrate having a gap formed between adjacent raised surfaces, the method comprising:

• depositing a first portion of the silicon oxide film over the substrate and within the gap using a high-density plasma process;
• thereafter, etching back a portion of the deposited first portion of the silicon oxide film, wherein etching back the portion comprises:
• flowing a halogen precursor through a first conduit from a halogen-precursor source to the substrate processing chamber;
• forming a high-density plasma from the halogen precursor by inductively coupling a source radio-frequency power into the substrate processing chamber, the source radio-frequency power providing a power density on the substrate between 85,000 and 140,000 W/m2;
• and
• terminating flowing the halogen precursor after the portion has been etched back;
• thereafter, flowing a halogen scavenger to the substrate processing chamber to react with residual halogen in the substrate processing chamber;
• and
• thereafter, depositing a second portion of the silicon oxide film over the first portion of the silicon oxide film and within the gap using a high-density plasma process.