Facility for Pulsed Extreme Ultraviolet Detector Calibration
Steven E. Grantham, Robert E. Vest, Charles S. Tarrio, Thomas B. Lucatorto
All of the Extreme Ultraviolet light sources currently under consideration for Extreme Ultraviolet lithography are based on plasmas that emit radiation with a wavelength of approximately 13.4 nm. These sources whether they are produced by a discharge or laser-produced plasma, are pulsed and operate at high repetition rate (>1 kHz). The specifications for Extreme Ultraviolet lithography put the required power rating of these sources to be >100W average power at the intermediate plane of a lithography stepper. This translates to peak powers in the range of 100's of kW or higher. As the output power of potential Extreme Ultraviolet lithography sources approaches these power levels, Extreme Ultraviolet detectors used to observe these sources will be subjected to higher and higher peak powers. For this reason it is necessary to accurately characterize detectors under similar power and temporal conditions to make accurate observations of output power and source performance.NIST is currently in the process of commissioning a system for the calibration of Extreme Ultraviolet detectors under pulsed conditions similar to those produced by potential sources for Extreme Ultraviolet lithography. This system incorporates a laser-produced plasma source based on a Kr droplet target. The plasma's output is collimated and split by a Mo/Si multilayer beamsplitter to provide two channels of illumination. Each channel is refocused onto filtered detectors to provide two signals that are proportional to the plasma Extreme Ultraviolet output. Calibration is done by comparing detector under test to a detector calibrated at NIST's Synchrotron Ultraviolet Research Facility. In this presentation we will describe this calibration facility and present performance of the two-channel normalization scheme. In addition, conversion of continuous wave to pulsed calibration will be discussed.