Entrance pupil | EPFL Graph Search

In an optical system, the entrance pupil is the optical image of the physical aperture stop, as 'seen' through the front (the object side) of the lens system. The corresponding image of the aperture as seen through the back of the lens system is called the exit pupil. If there is no lens in front of the aperture (as in a pinhole camera), the entrance pupil's location and size are identical to those of the aperture. Optical elements in front of the aperture will produce a magnified or diminished image that is displaced from the location of the physical aperture. The entrance pupil is usually a : it lies behind the first optical surface of the system. The geometric location of the entrance pupil is the vertex of the camera's angle of view and consequently its center of perspective, perspective point, view point, projection centre or no-parallax point. This point is important in panoramic photography, because the camera must be rotated around it in order to avoid parallax errors in th

Spatial coherence properties of an LED-based illumination system for mask-aligner lithography

Johana Bernasconi, Hans Peter Herzig, Raoul Kirner, Wilfried Noell, Toralf Scharf

A high-power LED-based illumination system has been developed as a replacement for the mercury arc lamps used in mask-aligner lithography. LEDs are arranged in a grid array and placed in the entrance aperture of individual reflectors. Those reflectors decrease the angular extent of the light. With this multisource approach, different groups of LEDs can be switched on independently. The illumination patterns created determine the illumination angles and the spatial coherence in the mask plane. The spatial coherence is measured in the mask plane by using a circular double slits approach. The interference pattern for different illumination patterns are measured, showing the effect of the asymmetry and size of the angular extent of the illumination light. The effect of the different illumination patterns on the quality of the prints are also illustrated with print tests.

SPIE2019

High power modular LED-based illumination system for lithography applications

Johana Bernasconi, Marcel Groccia, Hans Peter Herzig, Raoul Kirner, Wilfried Noell, Toralf Scharf

Mask-aligner lithography is a technology used to transfer patterns with critical dimensions in the micrometer range from below 1 micron for contact printing to a dozen of microns in proximity printing. This technology is widely used in the fabrication of MEMS, micro-optical components, and similar ﬁelds. Traditionally, the light sources used for mask-aligners are high-pressure mercury arc lamps, which emit in the UV rang of the spectrum with peaks at 365 nm, 405 nm and 435 nm, respectively the g-, h- and i- lines. These lamps suﬀer from several disadvantages (ineﬃcient, bulky, dangerous), which makes alternatives interesting. In recent years, high power UV LEDs at the same wavelengths appeared on the market, opening the door to new illumination systems for mask-aligners. We have developed a modular 250 W LED-based illumination system, which can advantageously replace a 1 kW mercury arc lamp illumination. LEDs, arranged in a 7x7 grid array, are placed in the entrance apertures of individual reﬂectors, which collimate the individual irradiation to an output angle of 10◦. A subsequent ﬂy’s eye integrator homogenizes the illumination in the mask plane. It is followed by a Fourier lens, superimposing the individual channels in the mask plane, and a ﬁeld lens to ensure telecentric illumination. This multisource approach allows the shaping of the source by switching individual illumination channels, determining the illumination angles and the spatial coherence in the mask plane. This concept can be used, for example, to do source-mask optimization. Compared to mercury arc lamp illumination, our system is simultaneously more eﬃcient, compact, versatile, economic and sustainable. In our contribution, we present the design of the system as well as lithographic test prints done with diﬀerent illumination patterns.

2018

Optical prism for creating multiple views of an image

Stefan Geissbuehler, Theo Lasser, Marcel Leutenegger

Optical prism comprising two external parallel and reflecting surfaces, one internal interface, parallel to said surfaces and acting as light splitter; said prism furthermore comprising an entrance side forming an angle β with respect to said interface and at least two exit sides forming an angle γ with respect to said interface, said external surfaces being located at different distances from said interface, the lengths and the thicknesses of the prism are chosen such that at least one beam entering through said entrance side may cross said interface at least twice and exits through said exit sides.

2016

High power modular LED-based illumination system for lithography applications

Johana Bernasconi, Marcel Groccia, Hans Peter Herzig, Raoul Kirner, Wilfried Noell, Toralf Scharf

2018