Novel dielectric capping layer approach for advanced copper interconnects using chemical grafting

Due to its low bulk resistivity copper has become the material of choice for ULSI interconnects. However its high diffusivity in dielectrics and weak chemical bonding to low-k materials require a capping layer as diffusion barrier and to improve adhesion. In order to control the copper-capping layer interface and reduce the risk for electromigration, this paper presents a novel approach in which a dielectric capping layer was chemically grafted on copper lines prior to SiC(N) deposition. Selection of chemically graftable precursors consisted into compatibility tests of these precursors with both layers using adhesion measurements. The robustness to the SiC(N) deposition process was validated by exposing as-deposited films to reducing chemistry plasma at high temperature. Improved copper-capping layer interface quality is demonstrated by the enhancement of the interface adhesion energy on a 500nm Cu/chemical grafting/40nm SiN stack. Validation tests also included electrical measurements on two selected precursors. This paper presents a novel dielectric capping process approach, for 45nm and beyond, that enhances selective adhesion without compromising line resistivity and yield. The enhanced adhesion energy obtained using chemical grafting is expected to result into improved electromigration resistance.