Radiant energy – Inspection of solids or liquids by charged particles – Electron probe type
Reexamination Certificate
2000-08-30
2003-06-24
Lee, John R. (Department: 2881)
Radiant energy
Inspection of solids or liquids by charged particles
Electron probe type
C250S311000, C250S307000, C250S306000
Reexamination Certificate
active
06583413
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a circuit pattern inspecting instrument and a circuit pattern inspecting method, and in particular to an instrument and a method for inspecting circuit patterns on a wafer or the like in a semiconductor device manufacturing process.
For a comparison testing method of detecting defects in circuit patterns formed on a wafer in a semiconductor device manufacturing process, there has been put to practical use an instrument for inspecting the wafers by comparing images of two or more LSI circuits of the same pattern formed on a single wafer with each other.
Particularly, instruments for pattern comparison and pattern inspection using an electron beam are described in Japanese Patent Application Laid Open No. Sho 59-192943; P. Sandland et al., “An electron-beam inspection system for x-ray mask production”, Journal of Vacuum Science & Technology B, Vol. 9, No. 6, November/December 1991, pp. 3005-3009; D. Fleming et al., “Prospects for x-ray lithography”, Journal of Vacuum Science & Technology B, Vol. 10, No. 6, November/December 1992, pp. 2511-2515; D. Hendricks et al., “Characterzation of a New Automated Electron-Beam Wafer Inspection System, Integrated Circuit Metrology, Inspection, and Process Control IX, February 20-22, 1995, Santa Clara, CA, Proceedings of SPIE, Vol. 2439, May 1995, pp. 174-183; and Japanese Patent Application Laid Open No. Sho 5-258703. In those instruments, for obtaining a practical throughput, it is necessary to acquire images at a very high speed, and at least 100 times (at least 10 nA) the electron beam current with an ordinary scanning electron microscope is used to ensure a sufficient S/N ratio of the images acquired at high speed as well as a practical inspection speed. The electron beam diameter is spread fairly wider than that in an ordinary scanning electron microscope and is about 0.05 to 0.2 &mgr;m. This is because of an increase in chromatic aberration caused by widening of the electron energy width which is attributable to a large beam current, a limitation to brightness of an electron gun and a limitation by the Coulomb effect.
The images formed by such an electron optic system are fed to an image processing unit, in which images of the adjacent circuits of the same pattern are compared with each other for inspection. If a portion having different brightness occurs between the compared images, the portion is regarded as a defect and coordinates of the portion are stored.
With the above configuration, it is possible to detect even a defect as small as 0.1 &mgr;m or so.
Further, instruments for inspecting defects in semiconductors by reducing the energy of the electron beam with a voltage applied to a sample and an electrode disposed close to the sample are disclosed in Japanese Patent Application Laid Open Nos. Hei 7-78855, 9-181139, 10-19538, 10-27834, 10-27835, and 11-25901. But these references do not describe an instrument having a review function to be described later, or an instrument having a combination of the review function and an energy analyzing function to be described later.
SUMMARY OF THE INVENTION
Before an inspection is started using one of the above instruments, there are various parameters to be set in advance. As parameters to be set for an electron optic system there are an irradiation energy of an electron beam, a gain of a signal detection system for image forming. secondary electrons (or charged particles such as back-scattered electrons), a pixel size (a minimum picture unit), and the amount of a beam current. On the other hand, it is necessary to set a threshold value for judging whether a signal indicates a defect in comparison of two images obtained from the two adjacent areas of the same pattern by an image processing unit. If this threshold value is set too low, the defect detection sensitivity is high, but it increases a possibility that a faultless portion is judged defective. On the other hand, if the threshold value is set too high, the detection sensitivity becomes too low.
Optimum values of the above parameters differ depending on a process to be inspected, a pattern size, and a type of defects to be inspected. Therefore, it is necessary to optimize the parameters by conducting a test inspection in which an image at the coordinates of a detected defect is displayed to confirm that a defect desired to be detected has been detected, before a regular inspection.
It is also necessary to for an operator to obtain the image at the coordinates of the defect after the inspection and check what kind of defects has been detected.
In addition to acquiring an image at a high speed so as to see whether a defect is present and then detecting a defect by processing the image, it is also essential to produce an image of a specific small area and observe the image visually as in the case with an ordinary scanning electron microscope.
A mode for this observation will be hereinafter referred to as “a review mode.” in this specification.
If it is necessary to make distinction between this review and the inspection mode based on high-speed acquisition of images for detecting the presence of a defect over a relatively large area, the inspection mode based on high-speed acquisition of images will be referred to as “a defect detecting inspection.”
For the review, it is not necessary to form images at such a high speed as in the defect detecting inspection, but a high resolution image is needed because it is necessary, not only to recognize whether a defect is present or not, but also to recognize the shape and type of the defect to some extent.
In the conventional instruments, however, an electron optic system used therein is designed so as to be best suited for the acquisition of an image by high-speed scanning at a large current, and it has so far been impossible to obtain a resolution high enough for images for the review. Consequently, it was impossible to judge accurately whether a detected defect is a true defect or a false defect due to an erroneous detection caused by inappropriate setting of parameters. Accordingly, inspection has often been conducted with the parameters being not set to optimum values.
It is an object of the present invention to provide an inspecting instrument making possible efficient setting of the conditions for inspecting with an electron beam, defects in repeating design patterns, foreign matters, residues and the like in a semiconductor device on a wafer in a semiconductor device manufacturing process, for example.
According to the present invention, the above-mentioned object is achieved by the following configurations.
According to an aspect of the present invention, a circuit pattern inspecting instrument includes a cathode for emitting an electron beam; a stage for mounting a sample thereon; an electron-optical system for focusing the electron beam; a deflector for scanning the electron beam on the sample; a detector for detecting secondary charged particles from the sample irradiated by the electron beam; and a mode setting unit for switching between a first mode and a second mode; wherein in the first mode, a current of the electron beam is set to a first value and the electron beam is scanned at a first speed; wherein in the second mode, the current of the electron beam is set to a second value smaller than the first value and the electron beam is scanned at a second speed lower than the first speed; and wherein the circuit pattern inspecting instrument is configured so that first the sample is observed in the first mode, then a particular position on the sample is selected based on image data produced by an output of the detector in the first mode, and then the particular position on the sample is observed in the second mode.
According to another aspect of the present invention, a circuit pattern inspecting instrument includes a first electron-optical system including a first cathode for emitting a first electron beam, a first objective lens having a first focal length for focusing the first electron beam on a sample positioned at a
Kaneko Yutaka
Kasai Yuji
Makino Hiroshi
Murakoshi Hisaya
Ninomiya Takanori
Antonelli,Terry, Stout & Kraus, LLP
Fernandez Kalimah
LandOfFree
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