METHOD FOR DITHER FREE ADAPTIVE AND ROBUST DOSE CONTROL FOR PHOTOLITHOGRAPHY

摘要

A method and apparatus for controlling a dose of radiation generated by a laser light source is disclosed. In one embodiment, a dose controller receives measurements of the deviation of output energy from an expected output energy, or "energy sigma," and the standard deviation of the error in the dose received by the item being processed from the desired dose. The ratio of the energy sigma to the standard deviation of dose error is calculated, and the laser controller adjusts the controller gain based upon the calculated ratio so as to adjust the voltage determined by the controller, and consequently the output energy and thus the dose to the item. This is an improvement over the prior art, in which the controller gain is adjusted based upon sending a voltage dither to the laser and correlating it to its response in energy at only one frequency.