In-band energy is one of the key parameters of extreme ultraviolet (EUV) light sources. High in-band energy signifies higher photon flux and stronger exposure capability, while stable in-band energy ensures consistency and reliability in the lithography process. The detection of in-band energy enables the evaluation of EUV light source intensity and stability, providing essential guidance for system optimization and performance enhancement of EUV light sources. Therefore, it is imperative to develop in-band energy detection devices suitable for EUV metrology. To ensure the accuracy of EUV light source in-band energy measurements, precise calibration of the detection devices is required. Given that the spectral detection range of the device differs from the in-band spectral range, spectral calibration must be applied to the measured energy for accurate in-band energy calculation. In this study, we propose an EUV radiation detection system and analyze the impact of the key components characteristics on the system performance. Quantitative relationships between the component characteristics and in-band energy measurement accuracy are established, which leads to the optimization of the system structure. The system is calibrated using Hefei National Synchrotron Radiation Source. On this basis, the calculation method for the in-band energy of the EUV light source is optimized for the system, and an uncertainty analysis of the calculation results is conducted.

In-band energy detection is one of the core tasks for evaluating the performance of EUV light sources. In this study, an EUV radiation detection system is constructed for detecting the in-band energy of EUV light sources. The quantitative relationships between component characteristics and measurement precision are established by analyzing key parameters of the system, including the incidence angle, number of multilayer mirrors, reflective spectra of the mirrors, as well as the waveform broadening and response time of the detector. These analyses guide the optimization of the system configuration. The integrated system, comprising two multilayer mirrors and a detector, is calibrated using the Hefei Synchrotron Radiation Source to determine its overall responsivity. Additionally, the transmittance of the filter is independently calibrated. On this basis, the calculation method for the EUV radiation detection system is optimized, resulting in a method to calculate the in-band energy of the light source from the narrowband energy detected by the system. Finally, the reliability of the EUV radiation detection system measurement results (at 13.5 nm) is quantified by evaluating five major sources of uncertainty, including the spectral responsivity of the EUV radiation detection system (excluding the filter), transmittance of the filter, oscilloscope integration signal, oscilloscope resistance, and solid angle.

Based on the analysis of multilayer mirror and the detector, an EUV radiation detection system is designed (Fig.7). For the radiation from the EUV light source, the size of the incident beam is limited by an aperture. The filtering is achieved using a Zr filter and two multilayer mirrors placed parallel with an incidence angle of 5°. The filtered radiation is received by the photodiode. After calibration, the transmittance curve of the Zr filter is multiplied with the system spectral responsivity curve, with the exception of the filter, to obtain the calibration result of the complete system. The calibration result is in good agreement with the theoretical curve (Fig.11). The spectral energy distribution obtained by the method of calculating the in-band energy of EUV light source is shown in Fig. 12, in which the in-band energy accounts for 59.78% of the total energy, and the calibration factor is 0.0284 A/W. The uncertainty analysis is presented in Table 2. The results indicate that the total uncertainty of the EUV radiation detection system measurements (at 13.5 nm) is 2.3%, which is mainly determined by the uncertainty of the system spectral responsivity except the filter (1.43%). By multiplying the total uncertainty by the t-value (t=2.074), corresponding to the 95% confidence level, the expanded uncertainty of the system measurements (at 13.5 nm) is found to be 4.8%, which satisfies the industrial tolerance requirements for exposure dose measurement.

In this study, an EUV radiation detection system is designed and developed. The system utilizes a Zr filter and combination of two parallel-placed planar multilayer mirrors for spectral filtering. The system is calibrated using the Hefei National Synchrotron Radiation Source. On this basis, the calculation method of the EUV light source in-band energy is optimized for this system, and uncertainty analysis is conducted. This system is calibrated using the metrology beamline at Hefei National Synchrotron Radiation Laboratory. Furthermore, the system is characterized in the wavelength range of 12.5 nm to 14.5 nm, with a central wavelength of 13.51 nm and a full width at half maximum (FWHM) of 0.43 nm. The spectral responsivity at the peak wavelength of 13.56 nm is 0.0150 A/W. The calibration factor for the calculation of the system EUV in-band radiation energy is 0.0284 A/W, and the expanded uncertainty at 13.5 nm is 4.8% (t=2.074). This uncertainty level meets industry requirements, making the system suitable as a metrology tool for in-band energy detection of EUV light sources.