Optimization of post-CMP ultrasonic cleaning parameters by Taguchi DOE

Post-CMP cleaning effectiveness is best assessed by studying the cleanliness of polished wafers obtained directly from the CMP process. In this study, a Taguchi DOE was designed as an L27 orthogonal array, and 3 levels of ten CMP and ultrasonic parameters were incorporated in the experimental matrix. The CMP parameters studied were: CMP velocity, pressure, slurry concentration, pH and temperature. The sonication parameters investigated were: frequency, amplitude, pH of the cleaning solution, surfactant type and concentration. The output properties measured were erodability and cleanability. High Level Analysis (HLA) of the DOE data indicate that under conditions of CMP that can embed particles with greater force, lower-frequency (more cavitational) conditions are more effective in particle removal. In general, ultrasonic frequencies in excess of 132 kHz are ineffective in removing strongly-adhered or embedded particles. Ionic surfactants are, in general, more conducive to CMP residue removal compared to non-ionic surfactants (natural, or man-made). ©The Electrochemical Society.