Ultra low-dielectric-constant materials for 65nm technology node and beyond

Pore characteristics including pore size distribution, porosity, and pore interconnectivity of PECVD SiCOH inter-layer dielectric (ILD) materials with different dielectric constant (κ) values have been studied. Oxygen plasma damage to SiCOH low-κ films increases dramatically as the κ value decreases. Simulations showed that, compared to the ILD film, the overhead dielectric films have a significant impact on the overall effective κ (κeff)of the BEOL interconnects. Reducing the κ values of these overhead films helps to alleviate the pressure on the κ value requirement of the ILD materials while still meeting the κeff target. Ultra low-κ (ULK) PECVD hydrogenated silicon carbide (H:SiC) films with a κ of 3.0 have been studied for the etch-stop applications. Studies of the chemical composition and bonding structure suggest that less Si-C networks are formed and more micro-porosity are incorporated in the ULK H:SiC film. The leakage current of the ULK H:SiC film is found to be about 5 times lower than the H:SiC and H:SiCN films with higher κ values. The etch rate of ULK H:SiC film using a standard SiCOH ILD etch chemistry has been found to be negligible. Such an extremely high etch selectivity makes these films very good etch-stop layers.