Refractive microlenses for ultraflat photolithographic projection systems

Reinhard Voelkel; Martin Eisner; Christian Ossmann; Kenneth J. Weible

doi:10.1117/12.395683

18 August 2000 Refractive microlenses for ultraflat photolithographic projection systems

Reinhard Voelkel, Martin Eisner, Christian Ossmann, Kenneth J. Weible

Proceedings Volume 4179, Micromachining Technology for Micro-Optics; (2000) https://doi.org/10.1117/12.395683
Event: Micromachining and Microfabrication, 2000, Santa Clara, CA, United States

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.

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Reinhard Voelkel, Martin Eisner, Christian Ossmann, and Kenneth J. Weible "Refractive microlenses for ultraflat photolithographic projection systems", Proc. SPIE 4179, Micromachining Technology for Micro-Optics, (18 August 2000); https://doi.org/10.1117/12.395683

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KEYWORDS

Microlens

Microlens array

Photomasks

Reactive ion etching

Projection lithography

Projection systems

Silica

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