Electron beam lithography systems have historically had low throughput. The only practical solution to this limitation is an approach using many beams writing simultaneously. For single-column multi-beam systems, including projection optics (SCALPEL® and PREVAIL) and blanked aperture arrays, throughput and resolution are limited by space-charge effects. Multibeam micro-column (one beam per column) systems are limited by the need for low voltage operation, electrical connection density and fabrication complexities. In this paper, we discuss a new multi-beam concept employing multiple columns each with multiple beams to generate a very large total number of parallel writing beams. This overcomes the limitations of space-charge interactions and low voltage operation. We also discuss a rationale leading to the optimum number of columns and beams per colunm. Using this approach we show how production throughputs 60 wafers per hour can be achieved at CDs nm, independent of both wafer diameter and die size. The Cost-of-Ownership (CoO) advantages of direct-write (maskless) lithography are significant especially for small-volume semiconductor fabrication, for example ASICs, SOCs and MPUs.
Laboratory measurements using a stabilized CO(2) laser and a 1-km long path absorption cell are presented here for pure water vapor and water vapor-air mixtures. An empirical extinction coefficient equation is presented and used to compute absorption for a variety of atmospheric slant paths. Finally, the laboratory results are confirmed by comparison with outdoor transmission studies over a 1.95-km path.
A new class of fluorescent probes for measuring temperature is described. The intensities of the strong fluorescence bands of uranyl acetate, uranyl nitrate hexahydrate, and uranyl orthophosphate were recorded when the uranyl compound was illuminated with an argon-ion laser operating at 488 nm. The intensity ratio of two fluorescence bands of uranyl acetate at room temperature were determined for five freshly prepared samples and shown to be independent of the intensity of the laser excitation and optical alignment. The intensities of the fluorescence bands lying between 500 and 570 nm were measured at various temperatures ranging from 77 to 295 K. The ratio of the intensities of two fluorescence bands was calculated and shown to vary linearly with temperature. A linear fit provided the slope. The largest positive slope of all the intensity ratios associated with uranyl acetate was 6.02 × 10−3 K−1, that associated with uranyl orthophosphate was 4.68 × 10−3 K−1, and that associated with uranyl nitrate hexahydrate was 1.81 × 10−3 K−1. The potential of uranyl compounds as a new group of temperature probes is discussed.
The power and gain capabilities of a CO2 laser are dependent upon the saturation intensity of the laser media. Saturation intensities reported in the literature range from 22 to 100 W/cm2 for seemingly similar laser discharge tube bores, currents, gas flow rates, and gas mixtures. Measurements of saturation intensities between 7.5 and 57 W/cm2 in a CO2 laser amplifier indicate that this parameter is inversely related to the radius of the amplified beam. A significant increase in saturation intensity for small beam radii is attributed to diffusion of excited CO2 molecules into the beam. The experimental results are in qualitative agreement with a simplified derivation of a relation governing the saturation intensity which includes molecular diffusion. This effect can result in a serious overestimate of the capabilities of a large beam laser system designed with saturation intensities obtained from small diameter probe beams.
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