We demonstrate high resolution reduction imaging in the soft x-ray spectral region using multilayer-coated reflective optics. In particular, a Schwarzschild objective was used at 20:1 reduction with 14 nm radiation to image line and space features from a transmission mask onto a resist-coated silicon wafer with a resolution better than 0.1 μm. The mirrors of the objective were coated with Mo/Si multilayers to provide nearly 40% reflectance at near-normal incidence for the 14 nm radiation. Our results demonstrate that multilayer coatings are capable of enhancing the reflectance of optical components at soft x-ray wavelengths without significantly degrading their imaging performance.
Atomic force microscopy (AFM) is an important tool in nanotechnology. This method makes it possible to observe nanoscopic surfaces beyond the resolution of light microscopy. In order to provide undergraduate and secondary-school students with insights into this world, we have developed a very robust low-cost AFM setup with a Fabry–Perot interferometer as a detecting device. This setup is designed to be operated almost completely manually and its simplicity gives access to a profound understanding of the working principle. Our AFM is operated in a constant height mode, i.e. the topography of the sample surface is represented directly by the deflection of the cantilever. Thus, the measuring procedure can be understood even by secondary-school students; furthermore, it is the method with the lowest cost, totalling not more than 10–15 k Euros. Nevertheless, we are able to examine a large variety of sample topographies such as CD and DVD surfaces, IC structures, blood cells, butterfly wings or moth eyes. Furthermore, force–distance curves can be recorded and the tensile moduli of some materials can be evaluated. We present our setup in detail and describe its working principles. In addition, we show various experiments which have already been performed by students.
A projection optical system with 20:1 reduction has been used with radiation at ∼36 nm to evaluate resists for use in soft-x-ray projection lithography. The high absorption of soft x rays by carbon-based polymers requires that an imaging resist layer be very thin. The sensitivities and contrasts of several such resists are reported. By incorporating a thin imaging layer into a trilayer resist scheme, we have exposed, developed, and transferred features as small as 0.2 μm into silicon.
We demonstrate nearly diffraction-limited printing of 0.2-microm features, using soft x rays of approximately 36-nm wavelength. An open-stencil transmission mask with minimum features of 4 microm was imaged by a twentyfold-reduction Schwarzschild-type objective onto silicon wafers coated with various e-beam resists. Implications for soft-x-ray projection lithography are discussed.
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