Linewidth measurement with an optical microscope: the effect of operating conditions on the image profile
- 1 August 1977
- journal article
- Published by Optica Publishing Group in Applied Optics
- Vol. 16 (8), 2223-2230
- https://doi.org/10.1364/ao.16.002223
Abstract
A theoretical model of the optical microscope based on the theory of partial coherence is used to predict the image profiles of lines on IC photomasks and assess factors contributing to measurement errors for different conditions of microscope operation. A comparison of experimental and theoretical image profiles is given, showing good agreement with theory for a 0.9 N.A. and linewidths as small as 0.5 μm. The primary sources of differences appear to be edge quality and accuracy of focus. The theory indicates that for well-corrected microscope optical systems, spectrally filtered to eliminate longitudinal chromatic aberration and chromatic difference of magnification, accurate determinations of linewidth may be made from the image profile using a threshold of 25% of maximum intensity (corrected for finite background transmittance in the opaque region). The correspondence between the edge location and the 25% threshold appears to be nearly invariant with small amounts of defocus and spherical aberration as well as variation in the numerical aperture of the condenser.This publication has 14 references indexed in Scilit:
- Partially Coherent Imaging in a Microdensitometer*Journal of the Optical Society of America, 1972
- Imaging of Tri-Bar Targets and the Theoretical Resolution Limit in Partially Coherent IlluminationJournal of the Optical Society of America, 1971
- Partially Coherent Imagery in the Presence of AberrationsOptica Acta: International Journal of Optics, 1970
- Light Distribution in the Defocused Image of a Coherently Illuminated Edge*Journal of the Optical Society of America, 1969
- Diffraction Images of Circular Objects in High-Resolution MicroscopyJournal of the Optical Society of America, 1963
- Diffraction Images of Circular Openings with Partially Coherent IlluminationOptica Acta: International Journal of Optics, 1962
- Diffraction Images of Disk-Shaped Particles Computed for Full Köhler IlluminationJournal of the Optical Society of America, 1960
- Measurement of Submicron Circular Apertures by Scanning MicroscopyJournal of the Optical Society of America, 1959
- Applications of Coherence Theory in Microscopy and Interferometry*Journal of the Optical Society of America, 1957
- Images of Incoherently Illuminated Bright and Opaque DisksJournal of the Optical Society of America, 1955