JP2004085213A - Surface observation device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface observation device capable of detecting and correcting eccentricity generated in an optical system by a change in the observation magnification. <P>SOLUTION: This surface observation device has an observing optical means 3 for observing the surface of an observed object 1 by changing the observation magnification, and a placing means 2 horizontally movable while placing the observed object 1. The surface observation device observing a requested portion on the surface of the observed object 1 by horizontally moving the placing means 2, has a reference mark 13 for detecting eccentricity, in a position independent of the placing means 2. The placing means 2 is further movable into a position not to intercept light from the reference mark 13, to detect the eccentricity of the observing optical means 3 generated when changing the observation magnification. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a surface observation device suitable for observing the surface of a semiconductor wafer, a liquid crystal substrate, or the like.
[0002]
[Prior art]
Conventionally, in order to observe a pattern formed on a semiconductor wafer, a liquid crystal substrate, or the like (hereinafter, referred to as a “substrate”), an objective lens having a desired magnification is selected by rotating a revolver provided with a plurality of objective lenses. A microscope that can be observed is used. When observing the substrate using such a microscope, a desired portion of the substrate surface (the portion to be observed) is selected and arranged at the center of the field of view while observing at a low magnification, and the portion is observed at a high magnification. That method is adopted.
[0003]
[Problems to be solved by the invention]
However, when observing the pattern formed on the substrate by the method using the above-mentioned microscope, when rotating the revolver and selecting a desired objective lens, an image of the pattern observed that the stop precision of the revolver is poor is low. There is a problem of shifting.
[0004]
The present invention has been made in view of the above problems, and has as its object to provide a surface observation apparatus capable of detecting and correcting eccentricity generated in an optical system due to a change in observation magnification.
[0005]
[Means for Solving the Problems]
In order to solve the above problems, the present invention
Observation optical means for observing the surface of the observation object by changing the observation magnification,
Mounting means for mounting the observation target and moving in the horizontal direction,
In the surface observation device for observing a desired portion on the surface of the observation target by horizontally moving the placement means,
It has a reference mark at a position independent of the placing means,
The placing means is further movable to a position where light from the reference mark is not blocked,
A surface observation device is provided, which detects an eccentricity of the observation optical unit that occurs when the observation magnification is changed.
[0006]
The surface observation device according to claim 2 is
The surface observation device according to claim 1,
A relay optical unit is disposed so that a field of view of the objective lens in the observation optical unit on the object plane and the reference mark are optically conjugate.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
1 and 2 are schematic configuration diagrams of a surface observation device according to an embodiment of the present invention. In the surface observation device according to the present embodiment shown in FIG. 1, an observation target 1 such as a substrate is placed on a stage 2. The stage 2 is movable in the horizontal direction (xy direction) and the vertical direction (z direction). By moving the stage 2, the observation target 1 can be moved in the xy direction and z direction. An observation optical system 3 including an objective lens 4 and an imaging optical system 9 is disposed above the observation target 1. An epi-illumination optical system 8 for guiding light from the epi-illumination light source 7 is arranged in the optical path between the objective lens 4 and the imaging optical system 9.
Here, the objective lens 4 is attached to a rotatable revolver 6, and the objective lens 5 is further attached to the revolver 6. Thereby, the observation optical system 3 can change the observation magnification by rotating the revolver 6 and switching the objective lenses 4 and 5.
An image pickup device 10 such as a CCD (Charge Coupled Device) or an image tube is arranged on an image plane above the observation optical system 3.
[0008]
With the above configuration, the illumination light emitted from the epi-illumination light source 7 enters the observation target 1 via the epi-illumination optical system 8 and the objective lens 4. The light emitted from the observation target 1 is condensed by the objective lens 4 and transmits through the epi-illumination optical system 8. The light transmitted through the epi-illumination optical system 8 is imaged at a predetermined position (imaging position) 11 by the imaging optical system 9. The imaging surface of the above-described imaging device 10 is arranged at the image forming position 11, and the image of the observation target 1 can be observed by the imaging device 10 by photoelectric conversion.
[0009]
In the case of visual observation, a configuration is provided in which a prism for branching or switching the optical path, an eyepiece optical system for visual observation, and an eccentric monitor system for measuring the amount of eccentricity of the observation optical system 3 are provided. And As a result, the light focused on the image forming position 11 is branched or switched, and one of the branched lights or the light transmitted through the optical path switching mechanism is focused on the retina of the observer via the eyepiece optical system, thereby enabling visual observation. The amount of eccentricity of the observation optical system 3 by guiding the other of the split light or the light reflected by the optical path switching mechanism to the imaging surface of the imaging element arranged at a position optically conjugate with the imaging position 11. Can be measured.
[0010]
Next, a characteristic configuration of the surface observation device according to the embodiment of the present invention will be described in detail.
The surface observation apparatus according to the present embodiment moves the stage 2 in the direction of the arrow (-x direction) in FIG. 1 while the observation target 1 is placed, and moves the observation target 1 and the stage 2 to the observation optical system 3. From the field of view.
Further, in the surface observation apparatus according to the present embodiment, a relay for forming an image of a reference mark 13 described later on the visual field 16 on the object plane of the objective lens 4 in the observation optical system 3 below the observation optical system 3. An optical system 12 is provided. In addition, a reference mark 13 is disposed at a position optically conjugate with a visual field 16 on the object plane of the objective lens 4 in the observation optical system 3 via the relay optical system 12. Note that the reference mark 13 is also optically conjugate with the imaging surface of the imaging device 10. Below the reference mark 13, a transmission illumination optical system 14 for illuminating the reference mark 13 and a transmission illumination light source 15 are arranged.
[0011]
FIG. 2 is a schematic configuration diagram when the stage 2 in the surface observation device according to the embodiment of the present invention is retracted from the visual field of the observation optical system 3.
In FIG. 2, illumination light emitted from a transmitted illumination light source 15 enters a reference mark 13 via a transmitted illumination optical system 14. Then, the light having passed through the reference mark 13 is focused on the field of view 16 of the observation optical system 3 by the relay optical system 12, and then enters the observation optical system 3. This light is imaged by the observation optical system 3 at the image forming position 11.
[0012]
FIG. 3A is a diagram illustrating a configuration of the reference mark 13. The reference mark 13 is a light-shielding member having a cross-shaped light transmitting portion. Therefore, the light having passed through the above-described reference mark 13 forms a cross-shaped image of the reference mark 13 at the image forming position 11.
In addition, the reference mark 13 is connected to the center of the cross-shaped image of the reference mark 13 (hereinafter, referred to as the “image center of the reference mark 13”) when the optical elements constituting the observation optical system 3 do not have eccentricity. It is arranged so that the center of the imaging surface of the imaging device 10 arranged at the image position 11 coincides with the center. Therefore, when the objective lens 4 in the observation optical system 3 is decentered due to the stopping accuracy of the revolver 6 when the objective lens 4 is switched by rotating the revolver 6 (see FIG. 4), The image center of the mark 13 does not match the center of the imaging surface. FIG. 4 shows a shift amount between the image center O of the reference mark 13 and the center P of the imaging surface when the objective lens 5 in the observation optical system 3 is decentered in the surface observation apparatus according to the present embodiment. FIG.
With such a configuration, when the revolver 6 is rotated and the objective lenses 4 and 5 are switched, the image center of the reference mark 13 is aligned with the center of the imaging surface of the imaging device 10 arranged at the imaging position 11. By adjusting the stop position of the revolver 6 or the mounting position of the objective lenses 4 and 5 to the revolver 6, the eccentricity of the objective lens in the observation optical system 3 can be corrected.
[0013]
Here, a method of calculating the coordinates of the image center of the reference mark 13 on the imaging surface of the imaging device 10 will be described. The coordinates of the image center of the reference mark 13 on the imaging surface of the imaging device 10 can be obtained by integrating the image signals of the reference mark 13 detected by the imaging device 11.
FIG. 3B is a diagram illustrating an image of the reference mark 13 formed on the imaging surface of the imaging device 10. FIGS. 3C and 3D are signals for obtaining the y-coordinate of the image center O obtained by integrating the image signals of the reference mark 13 detected by the image sensor 10 (y-direction integrated signal). FIG. 5 is a diagram showing a signal (x-direction integrated signal) for obtaining the x coordinate of the image center O.
[0014]
The coordinates of the image center O of the reference mark 13 are obtained by calculating the middle point between two points a and a 'where the y-direction integrated signal crosses a predetermined threshold, and determining the middle point as the y coordinate of the image center O and the x-direction integrated signal as a predetermined value. (B), (b), and (b), and the midpoint is determined as the x coordinate of the image center O (see FIGS. 3B, 3C, and 3D). . In this way, the coordinates of the image center O of the reference mark 13 on the imaging surface can be obtained.
This makes it possible to calculate the shift between the image center of the reference mark 13 and the center of the imaging surface of the imaging element 11, that is, the amount of eccentricity of the objective lens. Therefore, after switching the objective lens, the rotation stop position of the revolver 6 or the mounting positions of the objective lenses 4 and 5 are adjusted so that the coordinates of the image center of the reference mark 13 coincide with the center of the imaging surface of the imaging device 10. By doing so, the eccentricity of the objective lenses 4 and 5 in the observation optical system 3 can be corrected.
[0015]
The method of calculating the image center of the reference mark 13 is not limited to the above-described reference mark 13 having a cross-shaped pattern. The above-described method of calculating the image center can be applied to a reference mark of a pattern having a peak value in a portion where the amount of received light on the imaging surface is present. For example, the present invention can be applied to a reference mark having a circular light transmitting portion shown in FIG. FIG. 5A is a diagram illustrating a configuration of a circular reference mark. FIG. 5B is a diagram showing an image of the circular reference mark shown in FIG. 5A formed on the imaging surface of the imaging device 10. FIGS. 5C and 5D show the y-direction integrated signal and the x-direction integrated signal, respectively. Further, a pattern obtained by inverting the brightness of the above-described pattern may be used. In this case, the mark center is a portion where the amount of light is minimal, but can be similarly obtained by taking the center of a point crossing the threshold.
[0016]
As described above, in the surface observation device according to the present embodiment, in order to match the image center of the reference mark 13 with the center of the imaging surface of the imaging device 10, the rotation stop position of the revolver 6 or the objective lens 4, 5 is a configuration for adjusting the mounting position. Further, in the surface observation device according to the present embodiment, an eccentric mechanism for moving the revolver 6 in a plane perpendicular to the optical axis (in the xy plane) is provided, and the revolver 6 is moved in the xy plane. With this configuration, the eccentricity of the objective lenses 4 and 5 can be corrected.
In addition, when the observation optical system 3 is an infinity optical system, the amount of displacement between the image center of the reference mark 13 and the center of the imaging surface of the imaging device 10 due to the eccentricity of the objective lenses 4 and 5 Is equal to the product of the amount of eccentricity and the observation magnification of the observation optical system 3 (see FIG. 4). For this reason, an offset is given to a stage driving unit (not shown) for horizontally moving the stage 2 based on the amount of eccentricity of the objective lenses 4 and 5 in the observation optical system 3, and the position at which the stage 2 moves is determined by the objective lens 4. , 5 can be corrected by correcting the eccentricity of the objective lenses 4, 5 by shifting the eccentricity by an amount corresponding to the amount of eccentricity.
[0017]
A relay optical system 12 for forming an image of the reference mark 13 in the field of view of the observation optical system 3 is a stage on which the observation target 1 is placed between the relay optical system 12 and the field of view of the observation optical system 3. A working distance is required to insert 2 into the optical path. Therefore, a large numerical aperture of the relay optical system 12 cannot be secured. Therefore, it is desirable that the numerical aperture on the stage 2 side of the relay optical system 12 be about 0.1, which is almost the same as that of the low-magnification objective lens. In this case, the resolution limit is about 3.3 μm for visible light. When observing with a higher magnification objective lens, since the numerical aperture of the light beam forming the image of the reference mark 13 remains fixed, the edge of the image observed on the imaging surface (imaging position 11) is distorted ( Although it becomes unclear), the image center of the reference mark 13 can be accurately and constantly detected by the above-described method of calculating the image center of the reference mark 13.
[0018]
The line width of the pattern of the reference mark 13 is determined based on the numerical aperture of the relay optical system 12 so that a sufficient resolution and light amount can be secured. For example, when the numerical aperture of the relay optical system is 0.1 as described above, the resolution limit is about 3.3 μm, and the line width of the pattern is about 2 to 3 times the resolution limit, that is, 6 μm to 6 μm. 10 μm is desirable. A high-magnification objective lens generally has a larger numerical aperture than a low-magnification objective lens, so there is no problem in resolution. Rather, if the line width is too large, the pattern image will be larger than the field of view, so that it will not be possible to observe a pattern with an excessively large line width. However, when the line width is too small, it is difficult to detect an image because a sufficient amount of light cannot be obtained with a low-magnification objective lens. Therefore, it is desirable to use a pattern having a line width of about two to three times the resolution limit of the low-magnification objective lens as described above. Further, in the surface observation device according to the present embodiment, in order to further improve the detection accuracy of the edge of the image, the pattern may be configured by a plurality of lines and the average of the edge may be calculated.
[0019]
Further, as described above, the surface observation device according to the present embodiment is configured to retreat the observation target 1 and the stage 2 from the visual field of the observation optical system 3 by horizontally moving the stage 2. However, the present invention is not limited to this, and a configuration is provided in which the stage 2 is provided with an opening having a size that does not block light passing through the reference mark 13 when the observation optical system 3 and the reference mark 13 are relatively fixed. It can also be. With this configuration, when the revolver 6 is rotated to switch the objective lenses 4 and 5, the stage 2 is horizontally moved to adjust the above-described opening to the visual field position of the observation optical system 3, and the above-described method is used. The eccentricity of the objective lenses 4 and 5 can be corrected.
[0020]
In the present embodiment, the surface observation apparatus that changes the magnification of the observation optical system 3 by rotating the revolver 6 to switch the objective lenses 4 and 5 has been described. However, the present invention is not limited to this, and can be similarly applied to a surface observation apparatus having a configuration in which the observation optical system 3 includes a variable power optical system and performs variable power using the variable power optical system. In this case, in addition to correcting the eccentricity generated in the observation optical system 3 by adjusting the eccentricity of the variable power optical system, the eccentricity can be corrected by performing eccentricity by a parallel plate glass or eccentricity of an optical path by a wedge prism. it can.
[0021]
As described above, the surface observation device according to the embodiment of the present invention can detect and correct the eccentricity caused by the change in the observation magnification of the observation optical system. Thus, observation can be performed while always placing the test object at the center of the visual field.
[0022]
Therefore, according to the surface observation device according to the embodiment of the present invention, even when the observer visually observes a large number of substrates (objects to be inspected) by sequentially switching the magnification sequentially from low magnification to high magnification, Efficient observation can be performed in a short time.
Further, according to the surface observation device according to the embodiment of the present invention, the movable member such as the revolver is located above the substrate mounted on the stage. After retreating, the revolver is rotated to switch the magnification. Therefore, it is possible to prevent a new foreign substance from falling on the substrate by switching the magnification by rotating the revolver.
[0023]
Further, after inspecting a substrate using a defect inspection apparatus, a visual check (so-called review operation) of a foreign substance, a defect, or the like of the substrate detected by the defect inspection apparatus is often performed. In addition, by using the surface observation device according to the present embodiment, it is possible to prevent a foreign object, a defect, or the like from being lost, to perform an observation at a high magnification immediately, and to perform an efficient visual observation. it can.
[0024]
In addition, by configuring the so-called automatic defect inspection device that scans the surface of the substrate to detect defects using the surface observation device according to the present embodiment, the image plane visual field can be accurately defined. In addition, it is possible to prevent the inspection of the substrate surface from being duplicated or the omission of the inspection. Therefore, since it is not necessary to capture an image by overlapping the scanning regions of the substrate, an automatic defect inspection apparatus with improved inspection efficiency can be realized.
[0025]
【The invention's effect】
According to the present invention, it is possible to provide a surface observation device that can detect and correct eccentricity that occurs in an optical system due to a change in observation magnification.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a surface observation device according to an embodiment of the present invention.
FIG. 2 is a schematic configuration diagram when the stage 2 in the surface observation device according to the embodiment of the present invention is retracted from the visual field of the observation optical system 3.
3 (a), (b), (c), and (d) are diagrams each showing a configuration of a reference mark 13 in the surface observation device according to the embodiment of the present invention, and an imaging surface of the imaging element 10. FIG. FIG. 3 is a diagram showing an image of a reference mark 13 formed in FIG. 2, a diagram showing a y-direction integrated signal, and a diagram showing an x-direction integrated signal.
FIG. 4 is a diagram illustrating a shift amount between the image center O of the reference mark 13 and the center P of the imaging surface when the objective lens 5 in the observation optical system 3 is decentered in the surface observation device according to the embodiment of the present invention. FIG.
5 (a), (b), (c), and (d) are diagrams each showing a configuration of a circular reference mark, and FIGS. FIG. 3 is a diagram illustrating an image, a diagram illustrating a y-direction integrated signal, and a diagram illustrating an x-direction integrated signal.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Observation object 2 Stage 3 Observation optical systems 4, 5 Objective lens 6 Revolver 7 Epi-illumination optical system 8 Epi-illumination light source 9 Imaging optical system 10 Imaging element 11 Imaging position 12 Relay optical system 13 Reference mark 14 Transmission illumination optics System 15 Light source for transmitted illumination

Claims (2)

Observation optical means for observing the surface of the observation object by changing the observation magnification,
Mounting means for mounting the observation target and moving in the horizontal direction,
In the surface observation device for observing a desired portion on the surface of the observation target by horizontally moving the placement means,
It has a reference mark at a position independent of the placing means,
The placing means is further movable to a position where light from the reference mark is not blocked,
A surface observation apparatus for detecting an eccentricity of the observation optical unit generated when the observation magnification is changed. The surface observation device according to claim 1,
A surface observation apparatus, wherein a relay optical unit is arranged so that a field of view of the objective lens in the observation optical unit on an object plane and the reference mark are optically conjugate.

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