High precision electron-beam-lithography for optical high performance applications

Due to its high resolution end flexibility, electron beam lithography (EBL) became an essential fabrication technique for micro-optical elements that are used in high performance applications. Nevertheless, the sequential writing strategy used in EBL enforces a stitching approach in order to fabricate large area micro-optical elements. Inherently, the stitching of special subareas leads to inaccuracies in the optical function of the fabricated micro-optics, which usually appears as stray light. In this paper we report about a method to calibrate the stitching process and to reduce the stray light artefacts, respectively. The optimization method is based on the evaluation of angle resolved stray light measurements of special test gratings. In particular, the optimization concerns about spurious stray light peaks, also known as “Rowland ghosts”. In a first step, the qualitative and quantitative characteristics of the observed Rowland ghosts are investigated in a theoretical model in order to deduce the modality of the stitching inaccuracy and the strength of the alignment error. In a second step, the calibration of the subarea-stitching is demonstrated on the example of a contemporary spectrometer grating. It is shown that the Rowland ghosts can be reduced significantly and the stitching process can be controlled in the nm-range

Migration Patterns, Use of Stopover Areas, and Austral Summer Movements of Swainson\u27s Hawks

From 1995 to 1998, we tracked movements of adult Swainson’s Hawks (Buteo swainsoni), using satellite telemetry to characterize migration, important stopover areas, and movements in the austral summer. We tagged 46 hawks from July to September on their nesting grounds in seven U.S. states and two Canadian provinces. Swainson’s Hawks followed three basic routes south on a broad front, converged along the east coast of central Mexico, and followed a concentrated corridor to a communal area in central Argentina for the austral summer. North of 20°N, southward and northward tracks differed little for individuals from east of the continental divide but differed greatly (up to 1700 km) for individuals from west of the continental divide. Hawks left the breeding grounds mid-August to mid-October; departure dates did not differ by location, year, or sex. Southbound migration lasted 42 to 98 days, northbound migration 51 to 82 days. Southbound, 36% of the Swainson’s Hawks departed the nesting grounds nearly 3 weeks earlier than the other radio-marked hawks and made stopovers 9.0–26.0 days long in seven separate areas, mainly in the southern Great Plains, southern Arizona and New Mexico, and northcentral Mexico. The birds stayed in their nonbreeding range for 76 to 128 days. All used a core area in central Argentina within 23% of the 738 800-km2 austral summer range, where they frequently moved long distances (up to 1600 km). Conservation of Swainson’s Hawks must be an international effort that considers habitats used during nesting and non-nesting seasons, including migration stopovers

Enhanced e-beam pattern writing for nano-optics based on character projection

The pattern generation for nano-optics raises high demands on resolution, writing speed and flexibility: nearly arbitrary complex structures with feature sizes below 100 nm should be realized on large areas up to 9 inches in square within reasonable time. With e-beam lithography the requirements on resolution and flexibility can be fulfilled but the writing time becomes the bottle neck. Acceleration by Variable Shaped Beam (VSB) writing principle (geometrical primitives with flexible size can be exposed with a single shot) is sometimes not sufficient. Character Projection (CP) is able to speed up the writing drastically because complex pattern of a limited area can be exposed by one shot [1]. We tested CP in the Vistec SB350 OS for optical applications and found a shot count reduction up to 1/1000, especially for geometries which are hard to approximate by geometrical primitives. Additionally, the resolution and the pattern quality were influenced in a positive way. Ano ther benefit is the possibility to spend a part of the gain in writing speed to the use of a high resolution but low sensitive resist like HSQ. The tradeoff between speed and flexibility should be compensable by a large number of characters available