System and method for adjusting seed laser pulse width to control EUV output energy

A system for controlling the output energy of an EUV LLP system having seed lasers which produce a pre-pulse and a main pulse, each of the pre-pulse and the main pulse having a respective pulse width, comprising:

• optical switches capable of passing the pre-pulse and main pulse and opening and closing at a desired time to determine the width of each pulse that is passed through the switch;
• an amplifier having a duty cycle for amplifying the main pulse;
• a target chamber for irradiating a target material with the amplified pulses such that EUV output energy is produced;
• a sensor for measuring the EUV output energy and generating a sensor signal indicating the level of the EUV output energy compared to a desired EUV output energy;
• a pulse width controller for:
• receiving the sensor signal and generating a first pulse width signal instructing the optical switch to shorten the width of the next main pulse if the EUV output energy is above the desired energy and lengthen the width of the next main pulse if the EUV energy is below the desired output energy, and
• generating a second pulse width signal indicating the length of the pulse width of the main pulse compared to an acceptable range;
• and
• a duty cycle controller for receiving the second pulse width signal and increasing the duty cycle if the pulse width of the main pulse is longer than the acceptable range and decreasing the duty cycle if the pulse width of the main pulse is shorter than the acceptable range.

A non-transitory computer-readable medium having embodied thereon a program, the program being executable by a processor to perform a method of controlling the output of an EUV LLP system having a seed laser which produces pre-pulses and main pulses, the method comprising the steps of:

• operating the seed lasers to generate a pre-pulse and a main pulse, each of the pre-pulse and the main pulse having a respective pulse width;
• amplifying the main pulse with an amplifier having a duty cycle controlled RF pump rate and irradiating a target material with the amplified pulses to generate an EUV output having energy;
• adjusting the pulse width of the main pulse by shortening the pulse width of the main pulse if the generated EUV output energy is above a desired EUV output energy and lengthening the pulse width of the main pulse if the EUV energy is below the desired EUV output energy;
• adjusting the duty cycle by increasing the duty cycle if the pulse width of the main pulse is longer than a desired range and decreasing the duty cycle if the pulse width of the main pulse is shorter than the desired range.