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Calibration of Scanning Electron Microscopes for Image Size Measurements

IP.com Disclosure Number: IPCOM000050121D
Original Publication Date: 1982-Sep-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 2 page(s) / 29K

Publishing Venue

IBM

Related People

Narasimham, MA: AUTHOR [+2]

Abstract

Calibration for pattern size measurements by optical microscopy provides accurate measurement to +/- 0.05 Mum for lines down to about 1 Mum width in thin chrome films on glass substrates. Limitations arise from diffraction effects due to the wavelength of optical radiation.

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Calibration of Scanning Electron Microscopes for Image Size Measurements

Calibration for pattern size measurements by optical microscopy provides accurate measurement to +/- 0.05 Mum for lines down to about 1 Mum width in thin chrome films on glass substrates. Limitations arise from diffraction effects due to the wavelength of optical radiation.

Scanning electron microscopes (SEMs) are not affected by such disturbances and, therefore, can measure not only smaller lines but (because of the large depth of focus) do not require threshold calibration. Only a scale (i.e., periodicity) calibration is needed.

This calibration can be provided by chrome line space values of different sizes which have been generated with laser controlled optical lithographic systems at 10X size. It is common knowledge that periodicity errors of such a system are controlled to better than 1/10 of the laser wavelength. Consequently, the 10X pattern periodicity is accurate to at least +/- 60 nm. Photoreduction of these patterns to 1X size then provides scale calibration standards to +/- 6 nm assuming that no resist related processing and etch errors interfere.

After studies of a multitude of potential errors, it was found that the principal source of dimensional error is related to minute noncontrollable resist thickness variations in combination with small residual lens aberrations and uncertainty of focus of the reduction camera. These errors, however, can be eliminated by over exposure and...