The utilization of ultrashort pulsed laser radiation enables the precise generation of microstructures and the processing of a wide variety of materials. However, for massive parallel processing, the raw intensity distribution of the beam emitted by the laser source usually has to be transformed into an arrangement of multiple laser beams with specific intensity distributions. Here, sophisticated, application-adapted optical systems serve as a key technology. This paper gives an overview of the optical design fundamentals of multi-beam optics. It also investigates the causes for one of the main challenges in the use of multi-beam optical systems: the distortion of the spot-array on the work piece. The distortion leads to individual spot position errors and can heavily limit the processing accuracy. Finally, active and passive concepts and technologies to reduce or eliminate distortion in multi-beam systems are presented.

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The authors report on experimental and simulative scattering analyses of phase and amplitude defects found in extreme ultraviolet multilayer mirrors, such as mask blanks for EUV lithography. The goal of the analyses is to develop a novel mask blank inspection procedure using one single inspection tool that allows to determine whether a defect is a surface type (amplitude) defect, or a buried type (phase) defect. The experiments were carried out with an actinic dark-field reflection microscope. Programmed defects of both types were fabricated, using different nanostructuring techniques. Analytical and rigorous scattering simulations were carried out to predict and support the experimental results

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