Multi-spectral techniques for defocus detection

Abstract

A method and apparatus for improved defocus detection on wafers. The use of hyperspectral imaging provides increased sensitivity for local defocus defects, and the use of Fourier Space analysis provides increased sensitivity for extended defocus defects. A combination of the two provides improved overall sensitivity to local and extended defocus defects.

Description

CROSS-REFERENCE TO RELATED APPLICATION [0001] This application is related to U.S. Provisional Application No. 60 / 646,447, filed Jan. 24, 2005, and to U.S. Provisional Application No. 60 / 707,440, filed Aug. 11, 2005, and claims priority from both.FIELD OF THE INVENTION [0002] This invention relates to integrated circuit processing, and in particular to detection of focus errors caused by the lithography stepper / scanner. BACKGROUND OF THE INVENTION [0003] As integrated circuits become smaller and faster, Critical Dimensions (CD's) of devices must decrease. Current state-of-the-art requires critical dimensions of approximately 0.1 micron, and manufacturers are striving to move to lateral dimensions of 65 nm. Consequently, better lithographic resolution is required in order to print smaller features. As per the Rayleigh limit, resolution r is inversely proportional to Numerical Aperture (NA) according to the equation r∝λNA, where λ is the wavelength of the radiation, for a diffraction-...

AI Technical Summary

Benefits of technology

"The patent describes an improved method and apparatus for detecting defocus in images. The method does not use a wobbler and is more compact and sensitive to extended defocus defects. The apparatus uses hyperspectral imaging and Fourier Space analysis to achieve these improvements. The technical effects of this patent include improved accuracy and efficiency in detecting defocus defects in images."

Problems solved by technology

This presents challenges in lithography, since out-of-focus exposure of features in photoresist smears the resist edges, as illustrated in FIG. 1.

If defocus is not detected, the microcircuit yields will suffer and the problem may not be detected until many steps later in the manufacturing process.

However, several factors can cause local or global focus problems: 1) The mounting of the reticle, i.e., the master pattern, may have a tilt.

This causes full-field focus problems.

2) The autofocus on the stepper may have a problem, which could cause a full-field defocus.

Either of these problems would result in a defocus region of about one inch dimension.

Color changes result from out-of-focus regions, due to the fact that changing the profile of diffraction grating edges can drastically change its scattering profile and therefore can cause an apparent color change.

The manual observation of color changes to detect defocused regions has severe limitations, due to the tri-stimulus color response of the eye, and its limited gray-scale depth at any wavelength.

It is expected that existing automated macro-inspection systems will find it progressively more and more difficult to detect defocus as the CD's shrink, because visible wavelengths are being used, and the diffraction gratings created by the photoresist will have a pitch much smaller than the wavelength of the light used.

Shorter wavelength light may damage the photoresist.

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