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The semiconductor industry continues in its relentless march to miniaturization [1]. Every four years or so, the dimensions of the features on an integrated circuit are halved, yielding an increase in density and functionality of the electronic “chip.” The economic advantages of more devices per unit area outweigh increases in fabrication costs and performance limitations, pushing the industry to seek ever-smaller patterns. At the time of writing (April 2008) advanced devices are patterned with the smallest features hovering around 45 nm, and the next generation of ∼32 nm devices is on the horizon. What is perhaps most remarkable is that this level of nanopatterning is achieved with optical imaging tools and processes that use an actinic wavelength of 193 nm, the ArF laser emission line. As taught in any elementary physics textbook, the wavelength of light ultimately limits the achievable optical resolution [2]. So how can we pattern 32 nm features using 193 nm radiation?

Alumina ceramic samples prepared under different sintering temperatures and varied additives were measured to indicate the trap density and trap energy located in alumina materials by using thermally stimulated current (TSC). The surface charges on alumina in vacuum after applying a negative pulse voltage (0.7/4 /spl mu/s), and flashover performances of the materials in vacuum also were measured. We found that the trap distribution in alumina has a correlation with surface charges and flashover performances in vacuum. It is shown that the higher is the trap density in the material, the higher is the surface charge density, and the lower is the flashover voltage on alumina surface. It is believed that the trapping and de-trapping mechanisms of carriers could play an important role during the development of the discharge processes, together with the secondary electron emission mechanism.

Table-top extreme ultraviolet lasers at λ=46.9 allow compact photo-lithography systems utilizing coherent imaging techniques. Interferometric lithography, holographic lithography and Talbot lithography were demonstrated with sub-100 nm resolution in compact setups.

We present results with different nanopatterning techniques using table top extreme ultraviolet lasers. The three approaches are interferometric lithography, Talbot self imaging and holographic projection lithography.

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.

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.

We discuss different nanopatterning approaches using table top extreme ultraviolet lasers based on interferometric lithography, Talbot self imaging and holographic projection lithography.

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.

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.

The authors report the initial results from a holographic lithography technique using extreme ultraviolet (EUV) radiation. This approach removes the need for complex EUV reflective masks and optics, replacing them with a binary, nanopatterned transmission mask. Computer generated holograms were fabricated on 100nm thick silicon nitride membranes with a 100nm thick chromium absorber layer. Reconstructed images have been recorded in an 80nm thick polymethylmetacrylate photoresist using 13nm wavelength EUV radiation from an undulator source. The pattern was characterized by optical and atomic force microscopies, and compared with simulation results from the TOOLSET diffraction simulation program, yielding excellent agreement.

We present a high resolution extreme ultraviolet patterning approach based on Talbot self imaging and holographic projection imaging using for illumination a table top extreme ultraviolet laser.