Adhesion of Cu and low-k Dielectric Thin Films with Tungsten Carbide

The adhesion of copper and various dielectric materials to tungsten carbide was studied using interfacial critical debond energies obtained by the four-point flexure method. Tungsten carbide (W₂C), films 33.3 nm thick, were vapor deposited onto SiO₂, spin-on carbon polymer resin (CPR), chemically vapor deposited organosilicate glass (OSG), and spin-on siloxane-organic polymer (SOP) surfaces using direct-current magnetron sputtering of a W metal target and a methane substrate plasma. Thick copper films (42.5 nm) were vapor deposited onto W₂C. Some interfaces were modified by an Ar plasma, 1-nm W deposition, or O₂ plasma treatment prior to Cu deposition. A W₂C film deposited onto a CPR substrate was annealed for 2 h at 673 K in a 99% N2/1% H₂gas mixture. For the untreated dielectric surfaces, the debond energy ranged from 39.9 to 3.95 J/m₂. In order of descending adhesion energy, the substrates are ranked CPR, SiO₂, SOP, and OSG. Ar plasma treatment of the SiO2 surface increased the debond energy from 20.3 to 41.3 J/m₂. The Cu/W₂C debond energy was 20.4 J/m₂. Ar plasma or 1-nm W deposition treatment to the carbide surface moved the point of delamination from the Cu/W₂C interface to the W₂C/CPR interface for a Cu/W₂C/CPR multilayer structure.