Browse Prior Art Database

High Spatial Frequency MTF Measurement Measurement Scheme

IP.com Disclosure Number: IPCOM000045343D
Original Publication Date: 1983-Mar-01
Included in the Prior Art Database: 2005-Feb-06
Document File: 2 page(s) / 57K

Publishing Venue

IBM

Related People

Goodman, DS: AUTHOR [+2]

Abstract

A method is described for measuring the modulation transfer function (MTF) of an optical system at a spatial period which is less than the resolution of the measuring device to be used. Two grating images are formed having a spatial period less than the resolution of the measuring device, at least one of the grating images being formed with the optical system to be measured. Then a Moire pattern is formed from the two grating images, the Moire pattern having a spatial period which is greater than the resolution of the measuring device. The MTF of the Moire pattern is then measured, and the MTF of the optical system is derived therefrom.

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High Spatial Frequency MTF Measurement Measurement Scheme

A method is described for measuring the modulation transfer function (MTF) of an optical system at a spatial period which is less than the resolution of the measuring device to be used.

Two grating images are formed having a spatial period less than the resolution of the measuring device, at least one of the grating images being formed with the optical system to be measured. Then a Moire pattern is formed from the two grating images, the Moire pattern having a spatial period which is greater than the resolution of the measuring device. The MTF of the Moire pattern is then measured, and the MTF of the optical system is derived therefrom.

MTF measurement of optical systems at periods of a few microns or less is extremely difficult. There are problems both with the recording medium and with measuring the modulation of an image that is formed. Photographic film is grainy and nonlinear. The modulation transfer function of lithography optics may be measured by exposing photoresist to line images, which is then developed, and the lines are measured using a scanning electron microscope. This is a tedious process due to the difficulty in separating the contrast and processing variations of the photoresist/developer system from the imaging capabilities of the exposure tool. A microdensitometer fails at these high spatial frequencies.

The disclosed method combines a recording film with a means for modulation measurem...