Fractional In Situ Pad Conditioning in Chemical Mechanical Planarization

Material removal rate, shear force and variance of shear force during copper polishing are studied as a function of pad conditioning scheme: 0% in situ conditioning (i.e., basically the equivalent of ex situ conditioning) and fractional in situ conditioning variants (i.e., conditioning during the first 25, 50, 75 or 100% of the total polish time). Spectral analysis of raw shear force data is employed to help elucidate the fundamental physical phenomena during copper chemical mechanical planarization. Fast Fourier transform is performed to convert the shear force data from time domain into frequency domain. The energy distribution of copper polishing is quantified which sheds light on the effect of fractional in situ pad conditioning. Variance of shear force and spectral analysis indicate that pad micro-texture evolution ceases after 50% fractional conditioning, thereby indicating that in situ conditioning time can be reduced during a given polishing process thus extending pad life. This study shows that a combination of unique spectral fingerprinting and analysis of force variance can be used to monitor the effect of pad conditioning in real time. This work also underscores the importance of real-time detection and non-destructive method to extend pad life and consumable usage during CMP by optimizing the pad conditioning time.