For EUV-lithography, reliable measurements of the radiant power throughout the optical chain are an essential requirement for the optimization of the lithographic production process as well as for the development of new applications like EUV-based metrology tools. From dose control to aerial imaging, specialized detectors are required - ranging from simple diodes to sophisticated imaging detectors like CCD or CMOS systems. For all these applications, sensitivity, homogeneity and lifetime are crucial parameters. While extended lifetime and sub percent homogeneity requirements are common among all detector uses, sensitivity targets range from single photon sensitivity for spectroscopy detectors to deliberately reduced sensitivity for dose control at high-power sources. Photon detector calibration in the EUV spectral range is therefore a prerequisite for new detector developments and a basis for the introduction of EUV-lithography into volume manufacturing. PTB employs two dedicated and complimentary EUV beamlines for radiometric characterizations of photon detectors. The wavelength range covered reaches from below 1 nm to 45 nm for the two EUV beamlines. Longer wavelengths coverage in the VUV range (out-of-band) is provided at PTB’s VUV radiometry beamline. The standard spot size is 1 mm by 1 mm with an option to go as low as 0.1 mm by 0.1 mm. For lifetime testing, a dedicated exposure setup with power densities of up to 20 W/cm2 is operated. It enables exposures in the range of 100 kJ/cm2 within a reasonably short time. Lower fluence levels are available by attenuation or exposure farther out of focus. We will explain calibration basics, describe PTB's calibration capabilities in the EUV spectral range and show exemplary data for the respective detector types.
The advance of the semiconductor industry requires new metrology methods, which can deal with smaller and more complex nanostructures. Particularly for inline metrology a rapid, sensitive and non destructive method is needed. Small angle X-ray scattering under grazing incidence has already been investigated for this application and delivers significant statistical information which tracks the profile parameters as well as their variations, i.e. roughness. However, it suffers from the elongated footprint at the sample. The advantage of EUV radiation, with its longer wavelengths, is that larger incidence angles can be used, resulting in a significant reduction of the beam footprint. Targets with field sizes of 100 μm and smaller are accessible with our experimental set-up. We present a new experimental tool for the measurement of small structures based on the capabilities of soft X-ray and EUV scatterometry at the PTB soft X-ray beamline at the electron storage ring BESSY II. PTB’s soft X-ray radiometry beamline uses a plane grating monochromator, which covers the spectral range from 0.7 nm to 25 nm and was especially designed to provide highly collimated radiation. An area detector covers the scattered radiation from a grazing exit angle up to an angle of 30° above the sample horizon and the fluorescence emission can be detected with an energy dispersive X-ray silicon drift detector. In addition, the sample can be rotated and linearly moved in vacuum. This new set-up will be used to explore the capabilities of EUV-scatterometry for the characterization of nanometre-sized structures.
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