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

摘要

A method and apparatus for controlling the seed laser in a laser produced plasma (LPP) extreme ultraviolet (EUV) light system are disclosed. In one embodiment, a seed laser generates both pre-pulses and main pulses which are amplified and irradiate a target material. The widths of the main pulses are adjusted, for example by the use of an EOM or other optical switch, without adjusting the widths of the pre-pulses, to keep the EUV output energy at a desired level. Only if the main pulse widths are longer or shorter than a desired range is the duty cycle of the laser amplifier adjusted, to keep the main pulse widths in the desired range. Adjusting the main pulse widths in this way before adjusting the pump RF duty cycle allows for less adjustment of the duty cycle, thus causing less adjustment to the pre-pulses.

主权项

1. A method of controlling the output of an EUV LLP system having seed lasers which produce pre-pulses and main pulses, comprising:
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 RE pump rate and irradiating a target material with the amplified pukes 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.