Optical: systems and elements – Compound lens system – Microscope
Reexamination Certificate
2000-02-22
2001-02-27
Spyrou, Cassandra (Department: 2872)
Optical: systems and elements
Compound lens system
Microscope
C359S204200, C359S214100
Reexamination Certificate
active
06195202
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a laser microscope for scanning a specimen under inspection with laser light.
The present invention also relates to a pattern checking apparatus using a laser microscope, and more particularly to a pattern checking apparatus, in which a periodically formed pattern can be checked at a high speed. It should be noted that in the present specification, the term laser microscope means a microscope in which laser light emitted by a laser light source is projected onto a specimen, light reflected by the specimen or transmitted through the specimen is received by a photo-detector by means of a pin hole or a frame defining an aperture of a light receiving area, and an image of the specimen is formed by processing an output signal from the photo-detector. Further, a term confocal optical system means an optical system in which a light beam emitted from a point-like light source is projected onto a specimen as a light spot and light reflected by the specimen or transmitted through the specimen is received by a photo-detector by means of a pin hole.
2. Statement of the Related Art
There has been known to check or detect a defect in a substance having a plurality of patterns such as LSI, wafer with a pattern and photomask, by illuminating a whole surface of the substance with illumination light in a two-dimensional manner and light reflected by the specimen is received by a two dimensional CCD array. In this known defect detecting apparatus, a whole surface of the substance to be checked is illuminated, an image of the substance is picked-up by the two-dimensional CCD array, and output signals from respective light receiving elements of two-dimensional CCD array are read out in a serial manner by means of a transfer circuit, and a defect is detected from the thus read out output signals.
There has been also known to detect defects by utilizing a laser microscope. Such a laser microscope has been known from, for instance U.S. Pat. No. 4,736,110. In case of detecting defects by using the laser microscope, a light source is formed by a laser diode, laser light is deflected two-dimensionally by means of two beam deflecting devices such as vibrating mirror, light reflected by a specimen is received by a photo-detector such as a photo-multiplier, and defects are detected on the basis of an output signal from the photo-multiplier. In order to perform a high speed scanning, it has been also known to use an acoustic-optical deflection element and a vibrating mirror. Since the above mentioned laser microscopes constitute the confocal optical system, it is possible to attain a high resolution, and therefore the laser microscopes are particularly suitable for detecting defects of a specimen having fine patterns such as LSI.
In the above mentioned defect detecting apparatus, in which a two-dimensional image of the specimen is picked-up by means of the two-dimensional CCD array and defects are detected from output signals of respective light receiving elements of the CCD array, the output signals from a number of light receiving elements of the CCD are read out in a serial manner, and therefore a relatively long time is required for reading out the CCD array and thus a defect detection requires a long time. In case of the laser microscope using two vibrating mirrors, a longer time is required for scanning a whole surface of a specimen, and therefore a longer time is required for performing the defect detection. In the laser microscope using a combination of an acoustic-optical deflection element and a vibrating mirror, a high speed scanning can be effected, and thus a whole specimen can be checked within a relatively short time. However, the high speed scanning is limited by a fact that only one laser beam is used. Moreover, in order to drive the acoustic-optical element, a circuit for generating a high frequency electric signal is required and not only the construction of the microscope becomes complicated but also a manufacturing cost becomes high.
SUMMARY OF THE INVENTION
The present invention has for its object to provide a laser microscope which can scan a specimen at a high speed, while merits of the confocal optical system can be attained.
It is another object of the invention to provide a pattern defect detecting apparatus using such a laser microscope and defects can be detected at a high speed. According to the invention, a pattern to be checked may be LSI, photomask and wafer with patterns.
According to the invention, a laser microscope comprises a light source means for emitting a plurality of light beams aligned in a first direction; an objective lens for projecting said plurality of light beams onto a specimen under inspection to form an array of fine light spots on the specimen; a specimen stage for supporting the specimen under inspection; a stage driving mechanism for moving said specimen stage in a second direction which is perpendicular to said first direction; and a linear image sensor having a plurality of light receiving elements arranged in a direction corresponding to a direction in which said plurality of light spots on the specimen are aligned; whereby light beams reflected by the specimen are made incident upon corresponding light receiving elements of said linear image sensor.
According to the invention, a specimen is illuminated by a multiple spot illumination. It has been known to convert a light beam emitted by a laser light source into a rectilinear light beam by means of a cylindrical lens and the rectilinear light beam is scanned in a direction perpendicular to a direction in which the rectilinear light beam extends to perform the two-dimensional illumination. However, such a rectilinear light beam has various drawbacks. For instance, when a speckle pattern is generated in the laser beam, it is no more possible to obtain the rectilinear light beam having a uniform intensity distribution, and noise might be generated in an image. Moreover, the illumination light is projected onto an unnecessary portion, and therefore all illumination light could not be used effectively and a loss in light amount might occur. Contrary to this, according to the invention, the multiple spot illumination is performed and light beams from respective light spots formed on the specimen are made incident upon respective light receiving elements of the linear image sensor. Therefore, all illumination light can be utilized effectively.
In a preferable embodiment of the laser microscope according to the invention, there are provided a light source means for emitting a plurality of light beams aligned in a first direction; a beam deflecting means for deflecting these light beams into a second direction perpendicular to the first direction; an objective lens arranged between said beam deflecting means and the specimen under inspection for converging said plurality of deflected light beams and projecting them onto the specimen as a fine light spot array; and a linear image sensor having a plurality of light receiving elements arranged in a direction corresponding to a direction in which said light spot array on the specimen is aligned; whereby the light beams reflected from respective light spots on the specimen under are made incident upon corresponding light receiving elements of said linear image sensor by means of said objective lens and beam deflecting means.
According to the invention, the multiple spot illumination is performed by means of a plurality of light beams and plural portions of the specimen under inspection are scanned simultaneously. To this end, a plurality of light beams emanating from the light source means are deflected by the beam deflecting means into the direction perpendicular to the direction in which the light beams are aligned. The thus deflected light beams are projected onto the specimen by means of the objective lens to scan plural portions of the specimen simultaneously. Light beams reflected by the specimen are collected by the objective lens and are then made incident upon the li
Lasertec Corporation
Oliff & Berridg,e PLC
Robinson Mark A.
Spyrou Cassandra
LandOfFree
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