Improved high precision optical angle measurement system with no interference of light gradients and mismatch

Previously presented optical angle detection systems for incoming light have been proven to be sensitive to inhomogeneities in the intensity distribution of incoming light rays. In addition, it was found that gradients in some wafer parameters may also have a considerable influence on the measurement accuracy. An improved sensor design is presented that uses a common centroid architecture. Influences from gradient effects in the intensity distribution of the light source as well as process mismatch are successfully overcome by this design.