Quantification of shear induced agglomeration in chemical mechanical polishing slurries under different chemical environments

Abstract

The impact of shear on agglomeration in CMP slurries needs to be studied to reduce the defectivity resulting from large agglomerates (>0.5 μm) during Chemical Mechanical Planarization/Polishing (CMP) process. In this work the impact of the change in the pH of CMP slurries on their agglomeration behavior at different quantified shear rates are studied. The threshold value of Camp number (equal to shear rate x time) which represents total shear that is required for causing agglomeration in CMP slurries for different pH values (pH 2, 7 and 10) are measured. The value of the threshold Camp number required to cause agglomeration in a slurry was lowest for acidic pH conditions (Camp number 1E5), highest for basic pH conditions (Camp number 1.5E6) and value of threshold Camp number for neutral pH conditions (Camp number 1.5E5) was between acidic and basic conditions. It was concluded that the value of the threshold Camp number is dependent on the inter-particle forces or surface charges on silica particles in the slurry, and higher inter-particle repulsive forces increases the threshold value of Camp number. Good co-relations between Camp number and the extent of agglomeration in different CMP slurry samples are demonstrated. This method can be used for designing better slurry delivery systems for different slurry chemistries, to reduce the formation of the shear induced agglomerates during slurry handling and in turn reducing the defects during CMP process.