Large-area full-field thickness measurement of glass plates by an optical interferometric system

Thickness uniformity has been a crucial issue for glass plates used in the flat panel display (FPD). However, point-by-point measurement and/or phase-shifting technique must be employed in the current optical interferometric techniques. Therefore, instantaneous full-field thickness measurement cannot be implemented. Besides, the measurement area is limited by the dimensions of optical components employed in the current optical interferometric techniques. In this paper, an optical interferometric system named angular incidence interferometry (AII) was proposed so that large-area full-field thickness measurement can be achieved. By using AII, the full-field continuous phase difference can be determined by using only one interference image. When the thickness at one point of the specimen is known, the full-field thickness distribution can be obtained immediately. Moreover, with the use of only a basic point-expanded laser light and an image acquisition system, no other special optical components are needed in AII. The applicability and feasibility of AII on the measurement of thickness were investigated by a typical commercially available glass plate of 0.7 mm nominal thickness.