Detecting irregularities in a coating on a substrate

摘要

Irregularities in a coating on a substrate in which the coating includes optical scattering centers can be detected by irradiating the coating with polarized light and examining light from the coating through a filter which removes light having the same polarization as the initial beam. Light scattered by the optical scattering centers is transmitted through the filter, while specularly reflected light from the top surface of the coating, from the substrate exposed by gaps in the coating, or reflected by alien material on the coating is filtered out. As a result irregularities can be detected as intensity minima of the transmitted radiation.