The development of EUV lithography is critically based on the availability of suitable metrology equipment. To meet the requirements of industry, the Physikalisch-Technische Bundesanstalt has recently installed a new EUV reflectometer at the BESSY II electron storage ring. The EUV reflectometer is designed for at-wavelength metrology of full-size EUVL optics and allows samples with a maximum weight of 50 kg and a diameter of up to 550 mm to be investigated on the entire surface. Likewise, besides wavelength and angle scans, the measurement of bidirectional scattering within the full sample surface is possible. Not only a single mirror of the projection optics but up to five masks or various smaller samples can be simultaneously mounted. All angular and translational movements can be performed with an accuracy of 0.01 • or 10 µm, respectively. Different types of detectors can be movably mounted inside the vacuum or at a particular position on the vacuum chamber. In front of the vacuum chamber a class 100 clean room is installed. Here, the samples are fastened to the sample holder. With the help of a robot the sample holder is mounted onto the sample stage inside the reflectometer tank. For future lithography production tools, the requirements for optics and masks are very stringent. From the start of the EUV reflectometer operation we were able to assure the low measurement uncertainty demonstrated with our previous instrument. Diffusely scattered radiation limits the uncertainty of the measured peak reflectance. A total relative uncertainty of 0.14 % is achieved with a reproducibility of 0.07 %. The uncertainty of the center wavelength is mainly given by the uncertainty for the reference wavelength of the Kr 3d5/2-5p resonance. The reduction of all other uncertainty sources yields an overall uncertainty of the center wavelength of 0.014 % with a reproducibility of 0.008 %. We present a detailed description of the EUV reflectometer and discuss the optimized beamline conditions with the different uncertainty sources. The results are illustrated by recent measurements.

No abstract

No abstract

No abstract