Bilayer HDP CVD/PE CVD cap in advance BEOL interconnect structures and method thereof

A method for forming an interconnect structure on a substrate, the method comprising the steps of:

• depositing a dielectric material on the substrate, thereby forming a dielectric layer,
• depositing a hardmask material on said dielectric layer, thereby forming a hardmask layer, said hardmask layer having a top surface;
• forming at least one opening in said dielectric layer;
• filling said opening with a conductive material, thereby forming at least one conductor, said conductor having a surface coplanar with the top surface of said hardmask layer;
• depositing a first material on said conductor, thereby forming a first cap layer, wherein said first material is deposited by a high density plasma chemical vapor deposition (HDP CVD) process;
• and
• depositing a second material on said first cap layer, thereby forming a second cap layer, wherein said second material is deposited by a plasma-enhanced chemical vapor deposition (PE CVD) process.