Method for the stabilization of the radiation output of a gas discharge-coupled radiation source in pulsed operation

A method for the stabilization of the radiation output of a gas discharge-coupled radiation source in pulsed operation, particularly of an EUV radiation source, in which a constant pulse energy is to be radiated within a sequence of many consecutive radiation pulses, comprising the following steps:

• measuring the pulse energy of every radiation pulse of the EUV source;
• measuring at least one influencing variable;
• forming of time averages of the pulse energy and influencing variable;
• calculating the deviation of the actual measurement values from the average values of the pulse energy and influencing variable;
• determining the ratio of pulse energy and influencing variable at least for an operating point in which the pulse energy is to be kept constant, wherein the ratio is assumed to be linear based on the small magnitude of the fluctuations compared to the averages and is determined in the form of a proportionality factor of the functional dependence;
• determining scaled correlation coefficients of the measured influencing variables in order to determine the degree of statistical dependence of the influencing variables upon the pulse energy;
• and
• regulating the pulse energy by means of PI regulation based on the actual proportionality factor (a) corresponding to at least one influencing variable with the greatest correlation coefficient.