Phase Detection Using Scanning Optical Microscopy

Jozef P.H Benschop

doi:10.1117/12.968359

1 January 1988 Phase Detection Using Scanning Optical Microscopy

Jozef P.H Benschop

Proceedings Volume 0921, Integrated Circuit Metrology, Inspection, and Process Control II; (1988) https://doi.org/10.1117/12.968359
Event: Santa Clara Symposium on Microlithography, 1988, Santa Clara, CA, United States

Abstract

Most optical inspection systems are mainly sensitive to the amplitude changes of the light reflected from an object. An example is a scanning optical microscope which uses a detector in the pupil of the objective lens. Another example is a confocal scanning optical microscop 1. Both detection modes however do not measure the phase changes of the light reflected from the object in an easily interpretable way. These phase changes give useful information on the height variations of the object, such as topography and roughness. A very simple and powerful measuring technique called differential phase contrast can be used in scanning optical microscopes to give information on phase objects. Height variations down to 1 nm can be measured with this detection mode. One of the disadvantages of differential phase contrast detection is the fact that structures out of focus give a large modulation of the output signal. Especially on integrated circuits many structures are higher than the focal depth, thus giving blurred images due to out of focus parts of the object. This problem can be overcome when combining differential phase contrast detection with confocal microscopy. Using confocal differential phase contrast detection, phase changes introduced by an object in focus are measured while parts of the object out of focus do not contribute to the signal. The principles of differential phase contrast detection and confocal differential phase contrast detection will be explained. A description of the scanning optical microscope we built will be given. With this microscope we have measured the amplitude and phase of several objects. Both thinner and thicker objects than the focal depth have been measured. Some results are shown which illustrate the advantages of differential phase contrast and confocal differential phase contrast.

Citation Download Citation

Jozef P.H Benschop "Phase Detection Using Scanning Optical Microscopy", Proc. SPIE 0921, Integrated Circuit Metrology, Inspection, and Process Control II, (1 January 1988); https://doi.org/10.1117/12.968359

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