Design and realization of an industrial stand-alone EUV resist qualification setup

The EUV laboratory exposure tool (EUV-LET) is a compact nanostructuring setup used for large-area patterning of arbitrary to periodic structures as well as industrial photoresist characterization in terms of sensitivity, contrast and resolution. The setup utilizes partially coherent radiation of a compact discharge-produced plasma (DPP) EUV source, spectrally filtered by a multilayer mirror to a wavelength of 13.5 nm with 4 % bandwidth (full width at half maximum, FWHM). The system is equipped with a precise positioning system for mask and wafer, which allows resist exposures at defined distances. For the generation of large area nanopatterns, the achromatic Talbot lithography is applied which is well suited for high-resolution patterning of periodic structures with partially coherent radiation from plasma-based EUV sources. Optimized transmission masks enable the generation of contrast rich intensity modulations leading to structure sizes below 40 nm. The theoretical resolution limit is in the sub-10 nm range by taking advantage of a two times mask pattern demagnification. The achievable practical resolution is mainly limited by the fabrication of the required transmission masks and the optical properties of the mask illumination. In this contribution, the EUV-LET serves as a basis to identify design rules for core building blocks of a future industrial EUV resist qualification setup (EUV-REQS). These core building blocks try to overcome the main limitations to resist testing at highest resolution as stated above. For the optimization of the illumination properties, the design of highly efficient illumination optics is investigated and presented. Aims of the illumination optics are the generation of high throughput, homogeneous illumination of the patterned mask area and the optimization of the EUV radiation properties to fulfill the requirements for Talbot lithography. For the generation of high-resolution intensity patterns in wafer plane, the design of resolution test masks is analyzed and evaluated by means of the achievable resolution and patterning uniformity. The fabrication of a resolution test mask and selected exposure results are shown as well.