Study on the Mechanism of Micro-Defect Reduction during Si Final Polishing with Water-Soluble Polymers

The effect of water-soluble polymer in alkaline slurry on the micro-defect during Si final polishing was investigated. With the concentration of hydroxyethyl cellulose (polymer A) 0.15wt% and polyoxyethylene ether (polymer B) 0.05wt%, Haze value and the number of micro-defects (larger than 120nm) were reduced to 0.01 ppm and 7, respectively, on a 300mm silicon wafer surface. Also, the surface roughness was reduced from 17.2 to 0.153nm. Through the comprehensive analysis of slurry viscosity and Zeta Potential measurement, the mechanism of water-soluble polymers for micro-defect reduction during Si final polishing was discussed. Polymer B coated on the surface of SiO2 particle forming a "soft shell", which functions as a "soft abrasive" and thus reduces friction between wafer surface and slurry abrasives. As for polymer A, the O atomic of -OH group in polymer A molecular could combine with Si-H bond on the surface of silicon wafer to form the hydrogen bond, like Si-H...O bond. As such, polymer A can be adsorbed on the surface of the silicon wafer to form a hydration film, which also can reduce friction between wafer surface and slurry abrasives/pad asperities. With the joint action of polymer A and polymer B, as experimental results showed, the number of micro-defects and Haze value in Si final polishing process can be significantly reduced.