Flatness measurement by UV moire

摘要

A moire method using phase shifting technique is proposed for flatness measurement with highly accurate and fast measurement time. Two new methods are suggested for the elimination of the reflected light from the back plane of the glass substrate and for the reduction of contour line errors caused by waviness or warp of the sample surface. The former is UV moire technique and the latter is angle error reduction technique. In the UV moire technique a light of the 313nm wavelength is used for generating a moire. The light is able to eliminate the reflection from the back plane of the Liquid Crystal Display (LCD) glass substrate because it is absorbed inside the glass. The angle error reduction technique is to extrapolate data, which are measured in different distance between the grating and the sample, because the angle error is proportional to the distance between them. Using these two techniques, the proposed system realizes such high accuracy as 0.6 microns, while in the conventional system accuracy is 10 microns.