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Publication Date: 2004-Sep-16
Document File: 1 page(s) / 17K

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Immersion lithography image sensor

    Peter Dirksen, Paul Duineveld, Oleksiy Kolesnychenko, Helmar van Santen, Jan van der Werf

    This article relates to immersion lithography and provides a solution for qualifying, stabilizing and measuring the imaging quality of an immersion wafer scanner.

    Keywords: Optical lithography, Immersion lithography, Image sensor, Image quality

     The solution is an adaptationof the 'reflection image sensor' (RIS) of a wafer stepper such as e.g. an ASML wafer stepper. The RIS is a Moiré measurement system using the actinic wavelength. The reticle transmission mark is imaged on a phase grating on a feducial on the wafer stage, see ref [1] for details.

    As indicated in the figure, the new sensor has detectors integrated in the water hood to capture the diffracted light. For an immersion system it is important to mimic the exposure conditions as close as possible. Therefore the grating marks are etched in a silicon reference wafer preferentially coated with photo resist to match the wetting properties of the wafer. Also the effects of bubble formation, out-gassing of photo- resist and water contamination during exposure may be investigated.

    The gratings may be so-called long scribe-lane marks, with a length equal to the image field, parallel to the scanning direction. These marks can be used to measure the image quality under high velocity scanning conditions.

    Reference: "Automatic on-line wafer stepper calibration system", M v.d. Brink...