Experimental verification of EUV mask limitations at high numerical apertures

In this work, we use a high accuracy synchrotron-based reflectometer to experimentally determine the effects of angular bandwidth limitations on high NA EUV performance. We characterized mask blank and mask pattern diffraction performance as a function of illumination angle, scatter angle, and wavelength. A variety of pattern feature sizes ranging down to coded sizes of 11 nm (44 nm on the mask) are considered. A Rigorous Coupled-Wave Analysis (RCWA) model is calibrated against the experimental data to enable future model-based performance predictions. The model is optimized against the clearfield data and verified by predicting the mask pattern diffraction data. We thus have confirmed the degradation and asymmetry of diffraction orders at high AOI.