Evaluation Method Applying Fourier Transform Analysis for Conditioned Polishing Pad Surface Topography

Abstract

The Fourier transform analysis is proposed to quantitatively evaluate the 3D surface topography of Chemical Mechanical Polishing (CMP) pads used for flattening and smoothing processed semiconductor substrates. The conditioned polishing pad surfaces have a wide range of irregular topographies ranging from topographies of a sub-micrometer to those of a hundredmicrometer order. Hence, a Confocal Laser Scanning Microscope (CLSM), which can provide nanometer resolution in wide range of lateral directions by means of linear encoded mechanical stage translation, was employed to obtain numerical data of the three-dimensional topographic surfaces of polishing pad samples. The measured topographic surfaces were analyzed using the spatial Fourier transform. We discuss the power spectrum in the spatial wavelengths of polishing pad surfaces which were conditioned with diamond grits of various shapes. The analyzed power spectra indicated that the surface topography characteristics varied with differently shaped diamond grits of the same size. The diamond grits roughened the polishing pad surface. We also found that a rough polishing pad surface, one that was roughed in a spatial wavelength that of less than 20 micrometers, removed more material than comparatively smooth pad surfaces.