Radiant energy – Inspection of solids or liquids by charged particles – Electron probe type
Reexamination Certificate
1999-10-19
2002-11-05
Lee, John R. (Department: 2881)
Radiant energy
Inspection of solids or liquids by charged particles
Electron probe type
C250S311000, C250S307000, C250S306000, C324S754120
Reexamination Certificate
active
06476388
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a scanning electron microscope capable of acquiring electron beam image having high resolution in respect of various defect portions present on an object substrate (sample) such as various semiconductor substrates or the like and analyzing characteristic amounts or properties of defect portions based on the acquired electron beam image having high resolution, and a method of analyzing defect portions using the same as well as an automatic image sampling apparatus having a scanning electron microscope preferable for efficiently carrying out review of defects particularly in semiconductor fabrication process.
In recent years, progress of miniaturization of a circuit pattern formed on an object substrate (sample) such as various semiconductor substrates or the like has been remarkable and there is a case in which a defect size of an object to be observed is smaller than the wavelength of light. Hence, in place of optical observation, there has been carried out defect observation using image by a scanning electron microscope. However, when a defect image is taken by a scanning electron microscope, there poses a problem in which even when an object substrate is moved to a position of a defect detected by an appearance inspecting apparatus, the defect which is an object to be observed in the field of view is not present.
The reason is that in addition to a difference in coordinate control between the appearance inspecting apparatus and the scanning electron microscope, an error in accuracy of a sample stage for each of the appearance inspecting apparatus and the scanning electron microscope and so on, the magnification of image taking is much higher than optical magnification in the appearance inspecting apparatus and the field of view is narrow.
Hence, when a foreign particles is observed by a scanning electron microscope, the foreign particle can be discovered most efficiently when low magnification so that a search area is brought into the field of view in one operation, is selected. However, when a size of the foreign particle is small, there is a case that presence of the foreign particle is not noticed with low magnification. Hence, according to Japanese Patent Laid-open No. 5-223747 (prior art 1), in a foreign particle observing apparatus having an optical inspecting device of a foreign particle on a wafer surface and its similar device and an electron microscope for carrying out shape observation or analysis of foreign particle, defects or the like by using wafer coordinates and foreign particle information provided by the devices, there are provided means for determining a level of a size of a foreign particle provided by the optical inspecting device and its similar device and means for dividing an observation area of the wafer into N×M of divided areas when the foreign particle level is equal to or smaller than a constant value and dividedly observing the respective divided areas by the electron microscope.
In the meantime, a microscope starting from a scanning electron microscope has various objects of image taking and magnification for taking image thereof has various values. It is very important to take image without causing pseudo noise even under the various conditions. When image is taken manually, an operating person always monitors whether or not pseudo noise is caused in taken image and when pseudo noise is caused, image can be taken again after erasing the noise. However, when observation by the microscope is not carried out manually, for example, when information on positions of a plurality of portions on a sample to be observed is previously inputted to a microscope and the plurality of portions are observed automatically to thereby acquire data of taken image, a control for preventing the above-described noise from being produced is required to be carried out automatically.
However, according to the prior art 1, sufficient consideration is not given to that image is taken without causing pseudo noise in respect of such various object substrates (image taken objects).
Further, according to the prior art 1, it is necessary to enlarge observation magnification to be able to observe fine defects and to search the fine defects over an observation area having M×N of the divided areas and wasteful search is obliged to be carried out. In particular, when a number of fine defects are present in an object substrate, an amount of wasteful search is significantly increased.
SUMMARY OF THE INVENTION
In order to solve the above-described problem, it is an object of the present invention to provide a scanning electron microscope capable of analyzing characteristic amounts or properties of a defect portion in respect of the defect portion by automatically specifying a position of the defect portion to accurately take an image thereof without generating pseudo noise on a provided digital image even when an image of any object substrate is taken by any magnification and a defect portion analyzing method using the same.
Further, it is other object of the present invention to provide an apparatus and a method of automatically sampling an image by a scanning electron microscope capable of analyzing characteristic amounts and properties (categories) thereof and so on by positioning the fine defect in an image taking field of view of a high magnification in a short period of time to acquire a digital image signal having a high resolution and to take an image of a fine defect with a high magnification.
In order to achieve the above-described object, the present invention is featured in a scanning electron microscope which provides an image taking magnification setting means for setting a magnification of image taking, and takes the image by controlling a spot diameter of irradiating beam on a sample by using information concerning image taking magnification set to the image taking magnification setting unit and background information at an image taking portion.
Further, the present invention is featured in a scanning electron microscope which provides an image taking magnification setting unit for setting magnification of image taking, and carries out a signal processing of a filtering processing or the like to an analog electric signal converted from an intensity of an electron beam signal of secondary electron, reflected electron or absorbed electron from an object substrate (sample) or a digital signal provided from the analog electric signal by using information concerning image taking magnification set to the image taking magnification setting unit and background information at an image taking portion.
Further, the present invention is featured in a scanning electron microscope which includes a switching control unit for controlling to switch at least scanning means so as to be obtained a digital image signal of a low magnification based on a wide image taking field of view and a digital image signal of a high magnification based a narrow image taking field of view being switched from an A/D conversion unit, and a beam spot diameter control unit for controlling to switch a spot diameter of an electron beam at a surface of an object substrate in controlling to switch the signals by the switching control unit or a beam spot diameter control unit for controlling the beam spot of the electron beam based on information concerning a surface texture on an image taking portion of the object substrate in taking an image thereof in a wide image taking field of view by controlling to switch the signals by the switching control unit.
Further, the present invention is featured in a scanning electron microscope which includes a switching control unit for controlling to switch at least scanning means so as to be obtained a digital image signal of a low magnification based on a wide image taking field of view and a digital image signal of a high magnification based on a narrow image taking field of view being switched from an A/D conversion unit, and a control unit for controlling so as to restrain pseudo noise component
Bamba Hideka
Isogai Seiji
Kurosaki Toshiei
Nakagaki Ryo
Obara Kenji
Antonelli Terry Stout & Kraus LLP
Fernandez Kalimah
Hitachi , Ltd.
Lee John R.
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