Schematic of the EUV source and optics system. On the left a pinhole camera image of the EUV plasma is displayed.
Left: absolute EUV energy in focus of Schwarzschild objective vs pulse energy of Nd:YAG laser. Right: AFM image of EUV structured PMMA (250 mJ laser pulse energy, 10 EUV pulses) and the corresponding cross sections across the center of the crater. From measured EUV energy and spot area the energy density in the focus could be derived.
Chemical structures of PMMA, PTFE, and PC.
Left: depth of etched PMMA depending on the number of EUV pulses and the EUV energy density (inset: AFM cross section of craters generated at ). Right: etch rates of PMMA determined for different EUV energy densities using a gold target for high (dots) and a xenon gas target for low fluences (Ref. 18) (squares).
Etch rates of polymers as a function of EUV energy density. The straight lines represent linear fits for low fluences. The right diagram displays the expanded PMMA and PC data. There is no threshold level detectable for all three polymers.
AFM images and horizontal cross sections of etched profiles (, PTFE, PC: 20 pulses, PMMA: 15 pulses).
Etch depths (solid squares) and related fragmentation depths (blank dots) for PTFE, PMMA, and PC for depending on the number of EUV pulses.
Output parameters of the laser-based EUV plasma source.
Etch rates of polymers and rms roughness on nonirradiated surface and in crater bottom. The roughness increases by 20%–30% due to the etch process.
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