Semiconductor wafer and technical flat planeness testing interferometer

An interferometer for planeness testing of technical surfaces is described and real-time interferometric evaluations of 10-cm (4-in.) diam silicon wafers were carried out. The interferometer, using the principles of phase sampling interferometry, is a combination of an oblique incidence Fizeau interferometer with a moire interferometer. The interference pattern is a pure two-beam pattern. To get low frequency moire fringes the live interference fringes must have about the same spatial frequency as the moving grating used for reference phase stepping. Assuming that an automatic alignment device is included in the design, up to three wafers per minute could be measured and classified.