Mechanisms of colloidal ceria contamination and cleaning during oxide post CMP cleaning

Abstract

Ceria removal during the STI post-CMP cleaning process has recently become a serious concern in the semiconductor industry. Understanding ceria adhesion and its removal mechanism is necessary for designing a suitable post CMP cleaning methodology. Recently, colloidal ceria slurries have been heavily used due to the low defectivity factor. In this work, colloidal ceria adhesion and removal behaviors were studied as a function of particle sizes. It was found that polishing produces more contamination of ceria to oxide surface than dipping conditions and the strength of adhesion is increased with decreasing ceria size due to a higher Ce3+ concentration for smaller size particles resulting in more Ce-O-Si bonding. Ceria adhesion is mainly attributed to Ce-O-Si bond formation. Different cleaning methods (megasonic, brush scrubbing, SC1 (standard cleaning solution 1), DHF (diluted hydrofluoric acid) and SPM (sulfuric acid and hydrogen peroxide solution) were employed in removing these ceria particles. It was found that larger particles could be removed effectively with physical force, and smaller particles could be removed using chemicals such as DHF or SPM. Hence, it is concluded that an appropriate cleaning method should be chosen based on the size of the ceria.