Investigating surface structures by EUV scattering

As the industry continues to progress along the ITRS roadmap, not only the device dimensions shrink, but the architectures also increase in 3D complexity. Therefore, new metrology approaches for small structures are required. Small angle X-ray scattering has the potential for fast in line metrology but suffers from the large spot size needed in grazing incidence reflection and the low signal for the transmission geometry. Turning the incidence angle closer to normal and tuning the wavelengths into the EUV spectral range allows to decrease the spot size while keeping the signal high. We present an exploration of soft X-ray and EUV-scatterometry from grazing to near normal incidence, including a new approach in the design of metrology targets to avoid the footprint problem in grazing incidence geometry. Measurements were performed on e-beam written silicon gratings. The reconstructed geometrical line shape models are statistically validated by applying a Markov-Chain Monte Carlo sampling technique. Experimental data and simulation results provide a first insight into the potential of EUV Scatterometry.