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Proceedings Paper

Diffraction image processing algorithms for in-situ monitoring of submicron polysilicon linewidths
Author(s): Phillip Chapados
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Paper Abstract

A technique using diffraction grating test patterns has been used to monitor in situ the pre and post etch linewidths on a polysilicon etch chamber. The technique is capable of linewidth measurements to 0.25 microns with pitches as small as 0.7 microns. A comparison of in situ polysilicon linewidth measurements with off-line SEM measurements shows measurement differences of less than 10% indicating a measurement precision on that order. The repeatability of the diffraction technique is shown to be approximately 0.01 micron in comparison to the typical SEM repeatability of 0.025 micron. The implementation of this technique on a production etch chamber required the design of specialized optics and image processing systems. The optics system allows the monitoring of one and a half dimensions of the diffraction pattern. It consists of a CCD camera and some reflective optics for the focusing of the diffraction patterns. The image processing system uses a commercially available frame grabber and several image processing algorithms to record these patterns and extract the linewidth information. Algorithms unique to this application include an image indexing scheme used to store the diffraction images, a blob classification scheme based on a rigorous examination of the three dimensional vector field problem, and a non-linear iterative modeling algorithm used to fit the data to Fourier theory predictions. The resulting system is capable of linewidth measurements on each wafer with an overall reduction in product cycle time relative to the previously used SEM and pilot monitoring schemes.

Paper Details

Date Published: 6 May 1993
PDF: 8 pages
Proc. SPIE 1907, Machine Vision Applications in Industrial Inspection, (6 May 1993); doi: 10.1117/12.144814
Show Author Affiliations
Phillip Chapados, Texas Instruments Inc. (United States)

Published in SPIE Proceedings Vol. 1907:
Machine Vision Applications in Industrial Inspection
Frederick Y. Wu; Benjamin M. Dawson, Editor(s)

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