A HDP CVD process for depositing a USG liner followed by a FSG dielectric layer on a metal line pattern is described. The substrate is heated in a chamber with a plasma comprised of Ar and O2. A USG liner is deposited in two steps wherein the first step is without an RF bias and the second step is with a moderate RF bias that does not damage the metal lines or an anti-reflective coating on the metal. The moderate RF bias is critical in forming a sputtering component that redeposits USG to form more uniform sidewalls and better coverage at top corners of metal lines. The USG deposition process has a good gap filling capability and significantly reduces device failure rate by preventing corrosion of metal lines during subsequent thermal process cycles. The method also includes a PECVD deposited FSG layer that is planarized to complete an IMD layer.
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