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Proceedings Paper

Refractive microlenses for ultraflat photolithographic projection systems
Author(s): Reinhard Voelkel; Martin Eisner; Christian Ossmann; Kenneth J. Weible
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Paper Abstract

We report on the fabrication of high quality microlens arrays on 4', 6' and 8'-fused silica wafers. Refractive, plano-convex microlenses are fabricated by using photolithography; a reflow or melting resist technique and reactive ion etching. A diffraction-limited optical performance (p-v wave aberrations of < (lambda) /8, Strehl ratio $GTR 0.97) is achieved. Aspherical lens profiles are obtained by varying the etch parameters during the reactive ion etching transfer. The microlens arrays are used for Microlens Projection Lithography (MPL) and within UV-light illumination systems. Microlens Projection Lithography is an innovative technique using KARL SUSS Mask Aligners equipped with an ultra-flat microlens-based projection system. The projection system consists of 500.000 identical micro-objectives side- by-side. Each micro-objective consists of 3 to 4 microlenses. A fully symmetrical optical design eliminates coma, distortion and lateral color. The lens system is frontal- and backside telecentric to provide a unit magnification (+1) over the whole depth of focus. Each micro- objective images a small part of the photomask pattern onto the wafer. The partial images from different channels overlap consistently and form a complete aerial image of the photomask. Microlens Projection Lithography provides an increased depth of focus ($GTR 50 microns) at a larger working distance ($GTR 1 mm)than standard proximity printing. Microlens Projection Lithography allows photolithography on curved on non-planar substrates, in V-grooves, holes, etc. using a KARL SUSS Mask Aligner.

Paper Details

Date Published: 18 August 2000
PDF: 7 pages
Proc. SPIE 4179, Micromachining Technology for Micro-Optics, (18 August 2000); doi: 10.1117/12.395683
Show Author Affiliations
Reinhard Voelkel, Karl Suss KG Neuchatel (Switzerland)
Martin Eisner, Karl Suss KG Neuchatel (Switzerland)
Christian Ossmann, Karl Suss KG Neuchatel (Switzerland)
Kenneth J. Weible, Weible OpTech (Switzerland)

Published in SPIE Proceedings Vol. 4179:
Micromachining Technology for Micro-Optics
Sing H. Lee; Eric G. Johnson, Editor(s)

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