Proton exchange membrane (PEM) fuel cells are typically classified as methanol-based or hydrogen-based depending on the fuel used to convert chemical energy into electricity. Although direct methanol fuel cells have advantages of fuel availability and storage, long unsolved problems of poor anode kinetics and high methanol crossover limit their potential use mainly to applications with low power requirements, such as portable appliances.
In June 2007, Intel announced a new pixelated mask technology. This technology was created to address the problem caused by the growing gap between the lithography wavelength and the feature sizes patterned with it. As this gap has increased, the quality of the image has deteriorated. About a decade ago, Optical Proximity Correction (OPC) was introduced to bridge this gap, but as this gap continued to increase, one could not rely on the same basic set of techniques to maintain image quality. The computational lithography group at Intel sought to alleviate this problem by experimenting with additional degrees of freedom within the mask. This paper describes the resulting pixelated mask technology, and some of the computational methods used to create it. The first key element of this technology is a thick mask model. We realized very early in the development that, unlike traditional OPC methods, the pixelated mask would require a very accurate thick mask model. Whereas in the traditional methods, one can use the relatively coarse approximations such as the boundary layer method, use of such techniques resulted not just in incorrect sizing of parts of the pattern, but in whole features missing. We built on top of previously published domain decomposition methods, and incorporated limitations of the mask manufacturing process, to create an accurate thick mask model. Several additional computational techniques were invoked to substantially increase the speed of this method to a point that it was feasible for full chip tapeout. A second key element of the computational scheme was the comprehension of mask manufacturability, including the vital issue of the number of colors in the mask. While it is obvious that use of three or more colors will give the best image, one has to be practical about projecting mask manufacturing capabilities for such a complex mask. To circumvent this serious issue, we eventually settled on a two color mask -comprising plain glass and etched glass. In addition, there were several smaller manufacturability concerns, for example a "1X1" glass pillar (an isolated 0 phase pixel) were susceptible to collapse under the stress of mask processing, and therefore these had to be constrained out of the final configuration. A third key element was defining the objective function. We experimented with a large number of choices and eventually settled on a form that allows us to trade-off fidelity and contrast. A fourth key element was the optimization algorithm. The number of possible configurations for a trillion pixels present on our final product mask is greater than the number of total elementary particles in the known universe, so finding the proverbial needle in this haystack was difficult to say the least. We chose a mixture of stochastic and direct descent algorithms to find an arrangement that meets the demands. While we have not proved we are close to the absolute global minimum, we conducted several experiments to suggest this is the case. A fifth key element, and a large one at that, was scalin...
To be competitive with the next-generation lithography technologies, synchrotron-based proximity x-ray lithography (PXRL) must prove to be extendible to produce minimum feature sizes of 70 nm and below. We present here a relatively simple and practical method to improve the PXRL system performance for the replication of features down to 50 nm with reasonable process latitude at large (g≈15μ) mask–wafer gaps. Contrary to previous conclusions indicating λ=1 nm as the best operating region, we find that a significant improvement can be achieved by a modest decrease in the effective wavelength of present PXRL systems, and by the use of non-silicon-based materials in beamline filters and masks. The proposed PXRL system requires a synchrotron storage ring with slightly higher energy than older rings such as Aladdin, but well within the design parameters of the newer generation of synchrotrons, and some beamline modifications. In addition, a diamond mask substrate is also utilized to eliminate the x-ray absorption due to the Si-absorption edge at 1.75 keV.
Articles you may be interested inExperimental measurements of telecentricity errors in high-numerical-aperture extreme ultraviolet mask images Cleaning of extreme ultraviolet lithography optics and masks using 13.5 nm and 172 nm radiation Extreme ultraviolet lithography mask patterning and printability studies with a Ta-based absorberThe problem of image formation in extreme ultraviolet lithography from the mask to the wafer is studied by physical modeling along with computer simulations. The reflective properties of multilayer mirrors and some of the demands that they impose upon the optical system design for accurate replication of mask patterns is discussed. Numerical aperture size effects in relation to the critical dimension at the wafer is presented along with several illustrative examples.
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The Center for Nanotechnology has developed an advanced beamline dedicated to nanopatterning using the radiation from a new undulator on the Aladdin storage ring at the Synchrotron Radiation Center of the University of Wisconsin-Madison. Computer generated holograms and transmission interferometric gratings were fabricated and tested on the new extreme ultraviolet (EUV) exposure system. The authors have developed an accurate model, based on Fresnel-Kirchhoff integral diffraction theory, to analyze performance of real EUV interferometric and holographic lithography systems.
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