Browse Prior Art Database

Dark-field Fiber-optic Mask Illuminator

IP.com Disclosure Number: IPCOM000061959D
Original Publication Date: 1986-Aug-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Jain, K: AUTHOR

Abstract

An auxiliary optical system is described which is designed to provide dark-field illumination at the mask and wafer for alignment purposes for a photolithographic exposure tool which us laser light source.

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Dark-field Fiber-optic Mask Illuminator

An auxiliary optical system is described which is designed to provide dark- field illumination at the mask and wafer for alignment purposes for a photolithographic exposure tool which us laser light source.

The auxiliary light source comprises a visible, spectrally selected (green), collimated light beam which is provided by a short-arc mercury lamp used with a collimating lens and a band- pass filter. This light is combined collinearly with the laser beam, which may comprise an excimer laser beam, for example, by using a dichroic beamsplitter. For exposures, the laser beam reaches the mask through a "fly's-eye" lens array and a fiber- optic coupler 1.

For dark-field illumination of the mask, a specially fabricated auxiliary flys'- eye lens array 2 is brought into the proper position in the path of the auxiliary beam. This lens array differs from the arrays used for exposure since each of its lens elements 3 has a central obscuration region produced by a suitable opaque coating 4. Thus, each lens element 3 produces a ring-field illumination cone 5 surrounding a central obscuration cone 6. The desired f numbers of these cones are obtained by appropriate choice of the focal length of the lenses 3 and diameter of the opaque coating 4.

Disclosed anonymously.

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