Effect of retaining ring slot designs, conditioning discs and conditioning schemes on the slurry bow wave width during chemical mechanical planarization

This study investigates the effect of various retaining ring slot designs, conditioning schemes and conditioning disc types on the width of the slurry bow wave formed at the leading edge of the retaining ring during polishing. A method using high-speed videography is employed for visualizing and quantifying slurry bow wave width. In contrast to many limitations associated with previous techniques, this new method allows the use of a concentrically grooved pad with its natural white color commonly used in industrial applications. In general, results show that polishing with a retaining ring having rounded-angle slots, and a full-face conditioner, generates wider slurry bow waves. In contrast, using a retaining ring with sharp-angle slots, in combination with a conditioner having CVD-coated protruding vanes results in narrower bow waves. Compared to ex-situ conditioning, in-situ conditioning causes narrower bow waves due to its inherent role in transporting the slurry through periodic sweeping. Using Fast Fourier Transformation (FFT), bow wave width fluctuations are converted from time domain to frequency domain, showing a consistent spectral fingerprint. Major peaks are observed at frequencies of 1, 2, 4, 8 to 9, and 12 to 14 Hz for all experiments and they are attributed to the carrier, platen and conditioning disc rotation and oscillation, as well as to the presence of slots on the retaining ring.