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Direct Modulation Transfer Function and Aerial Image Measurement Technique

IP.com Disclosure Number: IPCOM000044856D
Original Publication Date: 1984-Nov-01
Included in the Prior Art Database: 2005-Feb-06
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Badami, DA: AUTHOR [+3]

Abstract

The following technique allows one to directly measure the image illumination profile in an optical imaging system by scanning microdetector across the line/space grid patterns of various spatial frequencies, down to submicron feature size. The detectors that can resolve down to 0.2 mm are semiconductor diodes, made similar to diode-lasers. An array of these stripe detectors, each stripe being Z 0.2 mm wide, can be scanned across the aerial image in the desired plane. This gives Imax, Imin and the complete aerial image profile.

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Direct Modulation Transfer Function and Aerial Image Measurement Technique

The following technique allows one to directly measure the image illumination profile in an optical imaging system by scanning microdetector across the line/space grid patterns of various spatial frequencies, down to submicron feature size. The detectors that can resolve down to 0.2 mm are semiconductor diodes, made similar to diode-lasers. An array of these stripe detectors, each stripe being Z 0.2 mm wide, can be scanned across the aerial image in the desired plane. This gives Imax, Imin and the complete aerial image profile.

The diode lasers to be used as detectors should be operated below threshold so that they are not lasing. Now the active region, which is submicron in width and can be about 100 m long, acts as the sensitive area on the diode. For increased sensitivity, a number of such diodes can be longitudinally aligned. For MTF evaluation, a mask with long lines and spaces is used. The diode array is then scanned across the aerial image of the mask such that the long active region remains parallel to the feature that is scanned. Since the detector width is finite, the detected signal will be convolved from the aerial image and the detector response. Thus, a deconvolution will yield the required MTF information.

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