Abstract
A new technique has been developed for discrimination between flaws and deposited contaminant particles (dusts) on smooth and transparent surfaces such as photomask-blanks and flat-panel-display substrates. This method is based on the measurement of the angular distribution and polarization characteristics of scattered light which is generated by a focused He-Ne laser beam.
Various flaws and dusts with sizes of the micron order were investigated using this method. While the ratio of scattering intensity at different angles was more than 0.20 for dusts, it was less than 0.08 for flaws. The polarization ratio of more than 0.1 was measured for dusts as compared with less than 0.06 for flaws. These results show that each way was enough to discriminate between flaws and dusts. Moreover, it was comfirmed that a combination of ways to measure the angular distribution with polarization characteristics improves the efficiency and accuracy of discriminating the two as compared with the individual measurement mentioned above.
