Optics: measuring and testing – By configuration comparison – With photosensitive film or plate
Patent
1990-10-15
1993-03-02
Rosenberger, Richard A.
Optics: measuring and testing
By configuration comparison
With photosensitive film or plate
250560, 2504922, 2504611, 385 8, G01B 1102, A61N 500
Patent
active
051913933
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to the optical measurement of the dimensions, submicron or close to a micron, of an object and measurement of the amplitude amount of overlay of two superimposed objects or patterns, and more particularly a method and device for obtaining very high measurement accuracy, less than one tenth of a micron. The invention finds a particularly important, although not exclusive, application in the automatic control of the widths of lines on wafers carrying patterns of integrated circuits with larger scale integration, overlay of the thin layers forming said wafers and/or integrated circuit wafer mapping.
The technology of production of integrated circuits evolves rapidly and particularly the width of the lines of the integrated circuits does not cease to diminish. At the present time, integrated circuit production technologies make it possible to etch lines of about one micron, but these technologies are rapidly outstripped. Lines of 0.1 micron can already be obtained experimentally and the American SEMATEC program (Semiconductor Manufacturing Technology) foresees the development of a technology for producing static memories SRAM of 16 Mbits with line widths of 0.3 micron and wastage less than 3% for the beginning of the 1990s.
It then becomes imperative to improve, both from the accuracy and reliability points of view, the measurement of the critical dimensions of submicron lines. The objective in the accuracy of measurement of the critical dimensions for future technologies in the production of integrated circuits is about 0.01 micron. No process, no device of the prior art makes it possible to fulfil such specifications.
Similarly, the degrees of overlay between the patterns, which are normally superimposed, of two layers of integrated circuits must be controlled with better accuracy; in fact, measurements of the overlay of layers by optical vernier or by electronic control are not satisfactory, at least in certain stages of production of a wafer.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an improved optical particularly in that they make possible an accuracy up to now unequalled in the measurement of the width of lines and the measurement of the overlay between layers, with great reliability and repeatability, making it possible to automate them. For example, an accuracy of about .+-.0.02 micron has been obtained on lines of a width of 0.5 micron on a thin layer (thickness less than 800 nm) or an accuracy of about .+-.50 nm on the overlay of thick metal layers (>4 micron).
For this, we have oriented their research to an opto-mechanical type device using a microscope with an arc lamp, whereas, a priori, such a conception is not satisfactory for reaching the desired results. The optical resolution is in fact limited to about 0.5 micron in visible light. In addition, the heat released by an arc lamp and/or the luminance losses observed with prior art devices when the light source is distant from the measurement position are too high for contemplating interesting results.
The use of ultraviolets (U.V) giving better resolution seems a priori excluded, again because of the considerable luminance losses observed with devices of the above type in the prior art and/or of the heat released by the U.V. emitting arc lamps.
The inventors have moreover met the problem of obtaining substantially constant uniformity, within .+-.2%, in the pupil (II) and object (I) planes of the optical system used.
By way of indication, the prior art optical devices have at best far field uniformity in the object plane (I) of about 10% and near field uniformity in the pupil plane (II) which is frankly poor (>20%). Such defects in the prior art devices are a serious obstacle and do not allow the desired performances for controlling the critical dimensions of the high integration circuits (VLSI) of future years. As an example of the prior art, means must be further mentioned for the mathematical modeling of the image which allows the dimensions of an
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Hignette Olivier
Lacombat Michel
Micro-Controle
Pham Hoa Q.
Rosenberger Richard A.
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