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Evaluation of Modulation Transfer Function Using Photoresists

IP.com Disclosure Number: IPCOM000089525D
Original Publication Date: 1977-Nov-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 26K

Publishing Venue

IBM

Related People

Moritz, H: AUTHOR

Abstract

To measure the modulation transfer function (MTF) of an optical system, the image of a test pattern containing line gratings with different frequencies and a spot with maximum transparency may be formed by the optical system, and then analyzed with regard to contrast and image line resolution.

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Evaluation of Modulation Transfer Function Using Photoresists

To measure the modulation transfer function (MTF) of an optical system, the image of a test pattern containing line gratings with different frequencies and a spot with maximum transparency may be formed by the optical system, and then analyzed with regard to contrast and image line resolution.

It is proposed to use a (positive) photoresist as a light detector. Once exposed, the resist contains the various MTF information in the form of illumination-induced differences of development rates. A convenient method of extracting this information is described below.

After exposure of the test pattern on the photoresist, the development time (t(max)) and the development rate (R(max)) of the transparent spot in the image are measured by conventional methods [*]. Then the development time is increased by Delta t. The development rate of the image areas, which are fully developed in the time t(max) + Delta t (but not in the time t(max)), is R(i) = R(max) . t(max) over t(max) + Delta t. (as the thickness variations of the photoresist over the entire image area are less than 1%).

To locate such areas, the substrate of the photoresist is etched, using the developed resist as a mask. Thus, the visually observable etch pattern consists of all image areas with R >/= R(i).

The illumination level I corresponding to development rate R(i) is determined from the known sensitivity diagram of the photoresist employed, as show...