Mechanisms of chemical-mechanical planarization of copper/tantalum thin films using fumed silica abrasives

Copper metallization in ULSI silicon devices is becoming widespread by combining dual damascene technique with an appropriate choice of a barrier film like Ta or TaN and planarizing the excess material by chemical-mechanical polishing (CMP). There are three key components in CMP, namely, the slurry (abrasives and chemicals), the polishing pad and the film being polished. The role of particulate properties in Cu and Ta CMP was investigated using both silica (fumed) and alumina (calcined) powders as the abrasive. It was found that silica does not polish copper but has a significant polish rate of harder Ta in DI water. The polish rate increases with increasing specific surface area of silica particles, indicating chemical interaction between the silanol groups on the silica particle surface and the Ta or Cu surface. This hypothesis was confirmed by conducting polishing experiments using surface-modified silica powders.; The role of chemical components in Cu CMP was investigated by conducting polishing experiments in different chemical environment, including ferric nitrite, hydrogen peroxide/glycine, and potassium iodate, etc., with an emphasis on the polishing mechanism. Preliminary results regarding the transport of slurry also shed light on the role of abrasives and chemicals during the polishing. With continuous supply of slurry during the polishing, both chemicals and particles are quickly replaced by the incoming fresh slurry, although not completely.; Polishing of Ta was also performed in the same chemical environment as for Cu CMP. In all cases, pH has a great impact on the removal rate of Cu and Ta. Cu removal rate increases with decreasing pH due to the higher dissolution rate of copper and copper oxide(s) at low pH values. In contrast, Ta removal rate increases significantly at higher pH values (>10). In situ potentiodynamic polarization also indicates higher anodic current density and lower corrosion potential at high pH values. The great impact of pH on the polish rates of Cu and Ta suggests that, potentially, a favorable polishing selectivity of Cu to Ta can be achieved by optimizing some of the slurry and abrasive characteristics. (Abstract shortened by UMI.)...