Development of extreme ultraviolet light sources and techniques for optical power meter calibration

Abstract

In order to calibrate the spectral responsivity (unit: A/W) of an extreme ultraviolet (EUV) optical power meter designed to be used in EUV lithography chambers, a wavelength switchable EUV light source has been developed. The EUV light source includes a table-top coherent light source based on high-order harmonic generation (HHG) and a custom-built EUV spectrometer. The energy (wavelength) range of the reporting EUV light source is from 40 eV to 120 eV (~ 10 nm to 30 nm), covering the mostly used wavelength of 13.5 nm for EUV lithography. Instead of conventional diffraction mounting of gratings, the EUV spectrometer is based on the conical diffraction mounting geometry. Such design successfully increases light emitting efficiency. The output optical power of this EUV light source is close to 1 μW. On the other hand, calibration methods of EUV detector responsivity were evaluated, using a synchrotron light source. Several data processing techniques were studied to compensate light source fluctuation and to reduce the measurement uncertainty. In the future, the reporting EUV light source will be considered as a standard light source for EUV detector responsivity calibration. Our final goal is to develop simple and reliable methods for EUV optical power and dosage measurements.