Flatness measurement by UV moire technique

A moire method using phase shifting technique is proposed for a flatness measurement with highly accurate and fast measurement time, especially of computer discs, wafers or glass substrates Two methods are proposed for the expansion of measurement size and for the elimination of the reflected light from the back plane of the glass substrate. One is to join small measured areas one another the flatness of which are measured in advance and the other is UV moire technique. Using these techniques, the proposed system realizes higher accuracy than conventional techniques without any limitation of the size in the glass substrate measurement.