Automatic Width And Overlay Measurement

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Abstract
Integrated circuit processes for producing horizontal geometries can be effectively monitored by precise linewidth measurements in both x and y directions. This paper describes a noncontact dimensional measurement system that is fully automatic and has a precision of ±0.025 µm for symmetric lines from 1 to 3 µm wide--e.g., 5-kÅ thermal oxide over silicon structure. Based on the analysis of diffraction patterns, the system operates on a wide variety of well defined line structures. By suitable choice of target, this system can also be applied to the measurement of mask-wafer overlays. The performance of the system for large numbers of samples is described and compared to the classical linear input. The signals are the same for structures having the same linewidth but produced by different processes. For some thick semiconductor structures, the edges defining the pattern boundaries have significant width themselves. Methods for measuring such struc-tures precisely by analysis of diffraction patterns are described.

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