Pellicle reflectivity monitoring system having means for compensating for portions of light reflected by the pellicle

摘要

A pellicle reflectivity monitoring system comprising a radiation source for directing radiation through a pellicle to an object to be inspected, a sensor device positioned to receive the portion of the radiation reflected by the pellicle, a processor, responsive to the sensor device, for determining the intensity of the portion of the radiation reflected by the pellicle, and a lens assembly, positioned in an optical path between the pellicle and the sensor device, for directing the portion of the radiation reflected by pellicles of different heights onto the sensor device. A comparator device compares the intensity of the radiation directed at the object to be inspected with the intensity of the portion of the radiation reflected by the pellicle and outputs a correction factor based on the comparison in order to compensate for the portion of the radiation reflected by the pellicle.