Pushing the boundaries of EUV scatterometry: reconstruction of complex nanostructures for next-generation transistor technology

EUV scatterometry can retrieve geometrical information from nanoscale grating structures through elastic scattering of EUV radiation and the evaluation of the diffraction intensities. Its geometry and energy range place it in between grazing incidence x-ray scattering (GISAXS) and optical critical dimension (OCD). PTB recently commissioned a new scatterometry setup for the EUV and soft x-ray region that can address sample areas below 100 × 100 μm size by using a comparably steep, grazing angle of incidence of up to 30°. At the same time, the full cone of exit angles of 30° can be detected such that also the higher orders can be recorded in scatterometry measurements. It has been commissioned at PTB's monochromatic soft x-ray beamline at the synchrotron radiation facility BESSY II and can also be used for simultaneous x-ray fluorescence detection. Its great tunability and energy resolution allows to scan across absorption edges of the relevant semiconductor materials to increase the contrast between different materials. The nanoscale geometry of modern transistor designs features different materials and structure sizes in the single digit nanometer range. Using the information wealth of spectrally resolved scatterometry measurements from the new setup, we present data and first geometrical reconstructions of selected, complex, industry-relevant design studies. The geometrical reconstruction of these structures relies on precise measurements, modelling of the scattering process, and statistical data evaluation methods.