A compact capillary discharge table top soft X ray laser was used for a table top photolithography tool using different
approaches: holographic printing, interferometric lithography and coherent Talbot self imaging. Large areas, of the
order of millimeter square, with periodic and arbitrary patterns were printed in a photoresist in short exposure times.
The proof of principle of the lithographic technique achieved the expected ~100 nm resolution.
Extreme ultraviolet interferometric lithography (EUV-IL) is a powerful nanopatterning technique, exploiting the interference of two beams of short-wavelength radiation (13 nm) to form high-accuracy fringe patterns. Transmission diffraction gratings of appropriate period (40-100 nm) are used to form the beams; the substrate is located in the region of overlap to expose the photoresist material, recording 20-50 nm interference fringe patterns. Although the physics of EUV-IL is simple, its actual implementation is not and requires attention to detail in order to fully exploit the power of the technique. In order to understand the impact of realistic physical conditions on the performance of EUV-IL, we have developed a set of accurate numerical models based on the Rayleigh-Sommerfeld diffraction theory. These modeling tools are then applied to generate a complete and accurate analysis of EUV-IL, taking into account all the relevant physical processes, from finite extent of the gratings to the partial coherence of the source, and including detailed physical structure of the mask. The results are used to guide the design and implementation of EUV-IL exposure systems, down to the sub-11-nm range.
We report the demonstration of Extreme Ultraviolet Holographic Lithography - EUV-HL - using a compact table top extreme ultraviolet laser. The image of the computer-generated hologram (CGH) of a test pattern was projected on the surface of a sample coated with a high resolution photoresist. Features with a 140 nm pixel size were printed using for the reconstruction a highly coherent table top 46.9 nm extreme ultraviolet laser. We have demonstrated that the combination of a coherent EUV source with a nanofabricated CGH template allows for the extension of nanolithography in an extremely simple set up that requires no optics. The reconstructed image of CGH was digitized with an atomic force microscope, yielding to reconstructions that are in excellent agreement with the numerical predictions.
Digital micromirror device (DMD) based maskless lithography has a number of advantages including process
flexibility, no physical photomask requirement, fast turnaround time, cost effectiveness. It can be particularly
useful in the development stage of microfluidic and bioMEMS applications. In this report, we describe the initial
results of thick resist SU-8 patterning, soft lithography with polydimethylsiloxane (PDMS) and lift-off of Cr
features using a modified DMD maskless system. Exposures of various patterns and microfluidic channels reveal
that the system is well capable of printing 60 μm thick resist at a resolution as small as a single pixel (less
than 13 μm) with an aspect ratio about 5:1. Both negatively and positively tapered sidewalls are achieved by
projecting the UV light from front side of the SU-8 coated Si wafer and from the back side of the coated glass,
respectively. The positive sidewall has an angle 88o which is ideal to serve as a mold for subsequent PDMS
soft lithography. Both SU-8 and PDMS microfluidic devices for biomolecular synthesis were fabricated with this
maskless system. In addition, a lift-off process was also developed with the intention to create built-in metal
features such as electrodes and heaters.
Extreme Ultraviolet Interferometric lithography (EUV-IL) can generate periodic patterns useful to characterize
photoresist materials and to create templates for self-assembled geometries. The Center for NanoTechnology has
developed a novel EUV-IL beamline dedicated to nanopatterning using radiation from an undulator on the Aladdin
storage ring at the University of Wisconsin-Madison. The beamline and the EUV-IL system were commissioned in
2006; we have completed several characterization studies, and modified several key components to improve resolution
and usability. The EUV-IL system can expose different pitches at the same time producing patterns with a range of halfpitch
from 55nm down to 20nm and less on the wafer. We can also introduce a variable image modulation by performing
double exposures, overlapping the interference pattern with the transmitted zero order. Recently we have demonstrated
down to 20nm half-pitch printed IL image in PMMA resist.