STI CMP: Exploration of a Colloidal Silica Based Slurry System

Abstract

With the size shrinking of IC transistors, more stringent polishing performance in shallow trench isolation (STI) CMP processes is requested in advanced fabrication processes. Up to date, most available STI slurries are ceria based. Technical challenges, such as scratches, rate instability, and handling, are the challenges to overcome. In addition, lower CoO is also desired. In this paper, colloidal silica based STI slurries are explored as an alternative. Different types of colloidal silica abrasives and chemicals are examined to understand their effects on HDP oxide removal rate and polishing selectivity of silicon nitride to silicon oxide. Planarization efficiency and slurry colloidal stability are also investigated. The results show that an abrasive type can make great difference on the removal rates of silicon nitride and silicon oxide. Certain proprietary chemicals can also greatly increase the selectivity of silicon oxide to silicon nitride without significant oxide losses in trenches. The capability of step height repairing can be tuned by carefully selected additives. The possible mechanism is also proposed. In addition, slurry handling can be improved by special designed dispersion agents. The preliminary data from the studies indicate that it is feasible to develop a silica based STI slurry to replace the traditional ceria based STI slurry. It also shows the potential to offer additional performance and cost benefits.