Versatile DUV scatterometer of the PTB and FEM based analysis for mask metrology

At PTB a new type of DUV scatterometer has been developed. The concept of the system is very variable, so that many different types of measurements like e. g. goniometric scatterometry, ellipsometric scatterometry, polarisation dependent reflectometry and ellipsometry can be performed. The main applications are CD, pitch and edge profile characterisation of nano-structured surfaces mainly, but not only, on photomasks. Different operation wavelength down to 193nm can be used. The system is not only a versatile tool for a variety of different at-wavelength metrology connected with state-of-the-art photolithography. It allows also to adapt and to vary the measurand and measurement geometry to optimise the sensitivity and the unambiguity for the measurement problem. For the evaluation of the measurements the inverse diffraction problem has to be solved. For this purpose we developed a special FEM-based software, which is capable to solve both the direct diffraction problem and the inverse diffraction problem. The latter can be accomplished using different optimisation schemes. Additionally this software allows also to estimate the quality of the measured data and the model based measurement uncertainty. This paper gives an overview about the PTB DUV scatterometer, it's metrological potential and the evaluation methods applied using the software DIPOG2.1.