LASER-ILLUMINATED STEPPER OR SCANNER WITH ENERGY SENSOR FEEDBACK

摘要

A laser-illuminated wafer-exposing system such as a stepper (20) or scanner having a first light intensity detector (44) located within the exposing system near a mask (36) and second light intensity detector (46) located near the output of the laser (12). A feedback control system (14) controls the output of the laser based on signals detected by at least one of the detectors. The feedback control system includes a processor programmed with an algorithm which is used to control the laser discharge voltage in order to provide light pulses having desired intensity at the mask with the laser operating in a burst mode. The algorithm utilizes at least the following parameters; a previously measured pulse energy, a calculated energy error, a calculated dose error, a value for the rate of change of pulse energy with voltage, and at least one reference voltage. In a preferred embodiment the algorithm uses the pulse energy measured with the light intensity detector located near the mark to provide the feedback control and uses the light intensity detector at the output of the laser to assure that the output of the laser is maintained within a predetermined range.