Energy characteristics control of high-repetition frequency KrF excimer laser

Energy stability and dose accuracy are important indicators of high-repetition frequency excimer lasers for semiconductor lithography, which must be controlled by high-precision control algorithms. Firstly, the single-pulse energy characteristics of the excimer laser were analyzed. Based on the analysis, a simulation model of the output energy of the excimer laser was established and had been experimentally proven to be effective. Then, the energy stability control algorithm, the double closed-loop dose accuracy control algorithm based on PID and the dose accuracy control algorithm based on decision algorithm were designed respectively and the control effects of the algorithms were tested separately on the simulation model. The simulation analysis results showed that the dose accuracy control algorithm based on the decision algorithm is more adaptable. The algorithm based on decision was validated on a KrF excimer laser with a repetitive frequency of 4 kHz. Controlled by the algorithm, the 3σ of laser energy stability was less than 5% and the dose accuracy was less than 0.4%, which satisfied the requirements of semiconductor lithography. The effectiveness of the energy characteristic control algorithm in the research had been proved in both simulation and actual experiments.