Method for dither free adaptive and robust dose control for photolithography

A laser system for laser light dose control comprising:

• a sensor for measuring output energy generated by a laser source for each of a plurality of pulses;
• a dose controller configured to:
• receive an energy target and a first laser voltage;
• cause the laser source to fire a plurality of pulses starting at the first laser voltage;
• for a number of laser pulses, after one or more pulses, adjust the first laser voltage based upon a difference between the energy target and the measured output energy;
• receive from a scanner, for the plurality of pulses, a measurement of dose energy received at the scanner;
• once the number of laser pulses has been fired, determine an energy sigma representing variation in average output energy over the number of pulses;
• determine a dose sigma representing variation between the dose energy received at the scanner and the dose target;
• calculate a ratio of the energy sigma to the dose sigma;
• update the controller gain in response a change in the ratio;
• update the first laser voltage in response to a change in a controller gain;
• cause the laser source to fire additional laser pulses using the updated first laser voltage.

A non-transitory computer readable storage medium having embodied thereon instructions for causing a computing device to execute a method for laser light dose control, the method comprising:

• receiving, by a dose controller, an energy target and a first laser voltage;
• causing, by the dose controller, a laser source to fire a plurality of laser pulses starting at the first laser voltage;
• measuring, by a sensor, output energy generated by the laser source for each of the plurality of pulses;
• for a number of laser pulses, after one or more pulses, adjusting, by the dose controller, the first laser voltage based upon a difference between the energy target and the measured output energy;
• receiving, by the dose controller, a measurement of dose energy received at a scanner from the plurality of pulses;
• once the number of laser pulses has been fired, determining, by the dose controller, an energy sigma representing variation in average output energy over the number of pulses;
• determining, by the dose controller, a dose sigma representing variation between the dose energy received at the scanner and the dose target;
• calculating, by the dose controller, a ratio of the energy sigma to the dose sigma;
• updating, by the dose controller, a controller gain, in response to a change in the ratio;
• updating, by the dose controller, the laser voltage in response to a change in the controller gain;
• causing, by the dose controller, the laser source to fire additional laser pulses using the updated laser voltage.