EUV OUTPUT ENERGY CONTROL SYSTEM AND METHOD

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,