Synchrotron-radiation X-ray topography of surface strain in large-diameter silicon wafers

Using a 300 mm-wide monochromatic X-ray beam obtained at beamline BL20B2 of SPring-8, the difference in surface-strain distribution caused by various steps of silicon-wafer manufacturing, i.e. slicing, lapping, etching, grinding and polishing, was studied. The asymmetric 511 reflection of 21.45 keV X-rays, incident at a glancing angle of 0.26°, was used to obtain topographs over the whole surface of a 200 mm-diameter (100) CZ silicon wafer. Differences in crystallinity and in warp between the surfaces at different steps of the manufacturing process (firstly after the lapping following the slicing, and then after successive etching, grinding and polishing) were clearly observed. The former gave a topographic image over the whole area with a one-shot exposure because of their wide rocking curves (50–70 arcsec FWHM), which indicate poor crystallinity. The latter, on the other hand, showed sharper curves (4–5 arcsec FWHM), which indicate good crystallinity in local areas, and the existence of warp, and therefore required step scanning of ω-rotation to cover the whole surface in topography measurements. The effect of each step in the process is also discussed.