The 'spectral fingerprints' and the 'sounds' of CMP

Spectral analysis of friction data obtained during ILD CMP was used effectively to elucidate the tribology of the process in terms of stick-slip phenomena by quantifying the total amount of mechanical interaction in the pad-slurry-wafer interface as a function of various pad types and textures, fumed silica concentrations, relative pad-wafer velocities and applied wafer pressures. A new parameter termed the 'Interfacial Interaction Index' (γ) was defined and determined empirically by integrating the amplitude of the force spectra over a wide range of frequencies. In 90 percent of the cases investigated, values of γ extracted from individual force spectra quantitatively agreed with the tribological information obtained from Stribeck curve analysis over a wide range of operating conditions. The newly developed method was remarkable from the standpoint of its potential to eliminate having to perform a multitude of experiments needed for constructing and interpreting Stribeck curves. For a given tribological mechanism, analysis of the spectra for various types of pad textures indicated significant differences in the 'spectral fingerprint' of various pads depending on their texture, as well as on the type of slurry and processing conditions. This notion was further extended to reproducing the 'sound' of CMP by superimposing the sounds and tempi of individual peaks in the spectrum on one another. It is envisaged that the aforementioned-pad 'fingerprinting' can provide a pathway for fundamental analysis of the effect of pad grooving on stick-slip phenomena which will eventually lead to improved pad designs.