Automated overlay metrology system

Abstract

Non-imaging measurement is made of misalignment of lithographic exposures by illuminating periodic features of a mark formed by two lithographic exposures with broadband light and detecting an interference pattern at different wavelengths using a specular spectroscopic scatterometer including a wavelength dispersive detector. Misalignment can be discriminated by inspection of a spectral response curve and by comparison with stored spectral response curves that may be empirical data or derived by simulation. Determination of best fit to a stored spectral curve, preferably using an optimization technique can be used to quantify the detected misalignment. Such a measurement may be made on-line or in-line in a short time while avoiding tool induced shift, contact with the mark or use of a tool requiring high vacuum.

Description

[0001] 1. Field of the Invention[0002] The present invention generally relates to multiple sequential lithography processes and, more particularly, to metrology techniques for measurement and characterization of overlay and alignment accuracy for sequential lithographic exposures and in-line and on-line lithographic exposure, scanner or stepper tools.[0003] 2. Description of the Prior Art[0004] Lithography processes are currently used in many research and manufacturing environments. Among these environments, one of the more economically important is that of semiconductor integrated circuit manufacture. In this field, increased functionality, performance and potential economy of manufacture has driven the development of numerous successive generations of devices having minimum feature size regimes of increasingly small dimensions and correspondingly increased device density. Currently, feature size regimes of one-quarter micron are available in commercial devices with significant fur...

AI Technical Summary

Benefits of technology

[0014] The meritorious effects of the invention include provision of an optical metrology technique which does not rely upon imaging of features for inspection, increased resolution and quantitative accuracy and repeatability which can be performed with apparatus of much reduced expense and complexity at greatly increased throughput, and simultaneous and non destructive overlay position and feature profile measurements.

[0015] In order to obtain these effects, a method and apparatus are provided which perform non-imaging metrology apparatus comprising storage of spectral curves, measurement with a specular spectroscopic scatterometer of reflection from a plurality of marks formed by two lithographic exposures and forming a periodic structure, and providing comparison of processed signals output from said specular spectroscopic scatterometer with said spectral curves to evaluate misalignment of said two lithographic exposures.

[0016] The foregoing and other objects, aspects and advantages will be better understood from the following detailed description of a preferred embodiment of the invention with reference to the drawings, in which:

[0017] FIGS. 1A, 1B and 1C are illustrations of a box-in-box image used in known metrology techniques,

[0018] FIG. 2 shows respective feature levels in accordance with a preferred form of the invention,

[0019] FIG. 2A shows the images of the features of FIG. 2 overlaid in desired alignment,

Problems solved by technology

However, such measurement techniques require complex and expensive SEM or AFM tools which are inherently of low throughput and the measurement is necessarily destructive, decreasing manufacturing yield.

Perhaps more importantly, decreases in minimum feature size and increases in integration density have required increasingly complex, expensive and difficult to use measurement tools while measurements produced are of reduced repeatability, reproducibility, tool induced shift (which are the principal components of the metrology error budget) and quantitative certainty (e.g. confidence factor) as limits of both lithographic and microscopic resolutions are approached, particularly when the imaged features measured are necessarily much larger than the minimum feature size.

Thus, it is seen that, at the present state of the art, known overlay measurement techniques can only be extended to smaller regimes of feature size at relatively great tool expense and process difficulty and complexity and increasing uncertainty and decreasing repeatability of result.

Further, it is not at all clear that advances in microscopy processes or other inspection devices which rely upon imaging of features will be able to support manufacturing processes of foreseeable regimes of integrated circuit feature size and integration density.

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