JPH05312510A - Position detector - Google Patents

Abstract

PURPOSE:To detect the position on the surface of a substrate accurately even when light is reflected on the rear surface of the substrate. CONSTITUTION:In the position detector, light of predetermined pattern is projected onto the surface of a substrate 7 through one of two regions devided by a plane containing the optical axis of an objective lens 6 and an image of projected light pattern reflected on the surface of the substrate 7 is photoelectrically detected by a detector through the other region thus detecting the position of the substrate 7. Members 4, 9 for blocking the light reflected on the rear surface of the substrate 7 and going through the second region to the light receiving face of the detector are disposed at positions spaced apart by a predetermined distance from the light receiving face.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a position detecting device for detecting the position of a substrate as an object to be inspected and, for example, to a device suitable for detecting the focus of a microscope.

[0002]

2. Description of the Related Art A focus detecting device used in an epi-illumination type microscope is known, for example, from US Pat. No. 3,721,827. Therefore, the focus detection device disclosed in US Pat. No. 3,721,827 will be specifically described with reference to FIG.

In FIG. 6, (a) shows a focused state, (b) shows
Shows the front pinned state, and (c) shows the rear pinned state. First, as shown in FIG. 6A, the light from the light source 1 is condensed by the condenser lens 2 and the slit plate 3 having the slit-shaped opening is illuminated to form a slit-shaped light source. Then, of the light flux passing through the slit plate 3 which is divided into two by the surface including the optical axis of the condenser lens 2 (the surface perpendicular to the paper surface in the drawing), half of one light flux (lower light flux) is shielded. Half of the other light flux (upper light flux) L is shielded by the plate 4.
₁ reflects the half mirror 5. Then, the light flux L ₁ reflected by the half mirror 5 passes through the left half of the objective lens 6 (the left half of the pupil of the objective lens 5) and the surface 70 to be inspected.
It is condensed on (the object plane of the objective lens 6).

The slit plate 3 is provided on the surface 70 to be inspected.
The image of the aperture of the image is formed, and the light flux L ₂ reflected on the test surface 70 passes through the right half of the objective lens 6 (right half of the pupil of the objective lens 5) and then the half mirror 5. Then, the light is collected on the light receiving surface of the photoelectric detector 8, and an image of the opening of the slit plate 3 is formed here. The light-receiving surface of the photoelectric detector 8 has light-receiving areas 8a and 8b on the left and right with the area intersecting the optical axis Ax of the objective lens 6 as a boundary, and the image-forming state of the image of the opening of the slit plate 3 To detect.

Further, as shown in FIG. 6B, the surface to be inspected 70
Is located at a position P ₁ below the position P ₀ of the object plane (reference plane) of the objective lens 6, a light flux L ₂ reflected by the surface 70 to be measured and passing through the right half of the objective lens 6 is The light is collected before the light receiving surface of the photoelectric detector 8 and reaches the left side region 8a of this light receiving surface. Here, since the slit image is formed at the condensing position A in front of the light receiving surface of the photoelectric detector 8,
The photoelectric detector 8 photoelectrically detects the defocus image of the slit in the front focus state.

Further, as shown in FIG. 6C, the surface to be inspected 70
Is located at a position P ₂ above the position P ₀ of the object plane (reference plane) of the objective lens 6, the light beam reflected by the surface 70 to be detected and passing through the right half of the objective lens 6 is photoelectrically detected. Bowl 8
The light reaches the right side region 8b of the light receiving surface so that the light is collected behind the light receiving surface. Then, the photoelectric detector 8 photoelectrically detects the defocus image of the slit in the rear focus state.

Here, the focus detection based on the photoelectric detector 8 is to balance two light amount signals respectively detected in the left and right light receiving regions 8a and 8b of the photoelectric detector 8, that is, to take a differential between the two light amount signals. Done in. For example, in FIG. 6A, the image is in focus, and in this case, the detection light is detected at the center of the light receiving surface of the photoelectric detector 8. Therefore, the outputs of the two light amount signals respectively detected in the left and right side regions 8a and 8b of the light receiving surface become equal, and the differential signal becomes zero.

FIG. 6 (b) shows the front focus state, and in this case, the detection light is mainly detected in the area 8a on the left side of the light receiving surface of the photoelectric detector 8. Therefore, the left and right side regions 8 of the light receiving surface
As the differential signal based on the two light amount signals respectively detected by a and 8b, an output signal of a certain positive level is obtained, for example. Further, in FIG. 6C, the rear focus state is set, and in this case, the detection light is mainly detected in the region 8b on the right side of the light receiving surface of the photoelectric detector 8. For this reason, the differential signal based on the two light amount signals respectively detected in the left and right side regions 8a and 8b of the light receiving surface is, for example, an output signal of a certain negative level.

In this way, the two obtained from the photoelectric detector 8
By taking the differential of two signals, the direction of defocus can be detected by the positive / negative of the differential signal, and the defocus amount can be detected by the output level of the differential signal.

[0010]

In recent years, the proportion of liquid crystal displays in displays and the like has been rapidly increasing. Therefore, inspection of a liquid crystal substrate, which is a source of liquid crystal display, has become important, and this liquid crystal substrate is mainly inspected by a microscope. However, when trying to focus on the surface of the liquid crystal substrate using the microscope equipped with the focus detection device described above, not only the reflected light from the surface of the liquid crystal substrate that should be originally detected, but also the reflected light from the back surface of the liquid crystal substrate. Even the light reaches the photoelectric detector, which has a great influence on the focus detection accuracy.

Therefore, since the surface of the liquid crystal substrate cannot be accurately inspected in a focused state, there is a problem that a defective product cannot be accurately discriminated. Therefore, the present invention has been made in view of the above problems, and a position that can detect the position of the front surface of the substrate with high accuracy even when reflected light from the back surface of the substrate including the liquid crystal substrate is generated. An object is to provide a detection device.

[0012]

In order to achieve the above object, the present invention provides an optical axis A of an objective lens 6 as shown in FIG.
A predetermined pattern of light is projected onto the front surface 7a of the substrate via one of the first regions divided into two with the surface including x as a boundary, and an image of the projection pattern light reflected from the front surface 7a of the substrate is formed. In a position detection device that detects the position of the substrate 7 by photoelectrically detecting with the detector 8 through the other second region that is divided into two by the surface including the optical axis of the objective lens 6 as a boundary,
A light blocking member 9 for blocking the reflected light from the back surface 7b of the substrate, which goes to the light receiving surface of the detector 8 through the second area, is arranged at a position separated from the light receiving area by a predetermined distance.

Based on the above basic structure, the light shielding member 9 is preferably provided so as to be movable in the optical axis direction of the objective lens 6 according to the thickness of the substrate 7.

[0014]

[Operation] Here, the principle of the present invention will be described with reference to FIGS. FIG. 5 is a diagram showing how reflected light from the back surface of the substrate is detected when the conventional focus detection device is focused on the front surface of the substrate. As shown in FIG. 5, the upper half L ₁ of the slit-shaped light flux formed by the light source 1, the condenser lens 2 and the slit plate 3 passes through the left half of the objective lens 6 and is condensed on the substrate 7. The light beam L ₂ reflected by the surface 7 a (test surface) of the substrate 7 and passing through the right half of the objective lens 6 is condensed on the photoelectric detector 8.

On the other hand, the slit-shaped light flux which passes through the left half of the objective lens 6 and is condensed on the substrate 7 is the surface 7 of the substrate.
The light passes through a and is reflected by the back surface 7b of the substrate. Then, the reflected light L ₃ from the back surface 7b passes through the right half of the objective lens 6, is then condensed before the light receiving surface 8a of the photoelectric detector 8, and is left side area 8a of the light receiving surface of the photoelectric detector 8. Is received by.

In this case, the photoelectric signal obtained by the photoelectric detector 8 will be examined. As shown in FIG. 5, since the surface 7a of the substrate is in focus, the light quantity signal obtained in the left and right light receiving regions of the photoelectric detector with the optical axis Ax of the objective lens 6 sandwiched by the reflected light from the surface 7a of the substrate. However, since the reflected light from the back surface 7b of the substrate is incident on the light receiving area on the left side of the photoelectric detector, defocusing (the surface 7a of the substrate is below the in-focus position) by an amount corresponding to this incident light amount. ) Is also detected as.

Therefore, in the present invention, as shown in FIG. 4, the light blocking member 9 for blocking the reflected light from the back surface 7b of the substrate is separated by a predetermined distance from the light receiving surface 8a of the photoelectric detector Ax.
It is provided on the left side of the border. Thereby, only the reflected light from the front surface 7a of the substrate can be extracted, so that the front surface 7a of the substrate can be detected with extremely high accuracy.

Here, the light shielding member 9 receives light from the photoelectric detector 8 at the position A where the reflected light from the back surface 7b of the substrate is focused by the objective lens 6 when the front surface 7a of the substrate is in focus. It is preferably arranged between the surfaces. In the above, the detection of the position of the substrate surface where the thickness t of the substrate is constant has been described, but in order to detect the position of the substrate surface having a different thickness, the light shielding member 9 is moved in the optical axis Ax direction. It is good to install it as much as possible.

[0019]

1 shows an example in which the present invention is applied as a focus detecting device for a microscope. As shown in FIG. 1, the luminous flux in the visible range from the epi-illumination system 12 is reflected by the half mirror 11, and passes through the dichroic mirror 10, the half mirror 5, and the objective lens 6 that transmit visible light and reflect infrared light. Illuminate 7. This substrate 7 is a stage 16
The stage 16 is mounted on the top of the stage 16. The stage 16 is two-dimensionally moved in the XY directions and is movable in the Z direction (vertical direction) by a driving unit (not shown) provided inside. ..

By illuminating the substrate 7 under visible light, the light reflected from the surface 7a of the substrate 7 is the objective lens 6, the half mirror 5, the dichroic mirror 1.
After forming an image through 0 and the half mirror 11, it passes through the eyepiece lens 13. Here, a spatial image I of the surface 7a of the substrate is formed at the position where the image is formed by the objective lens 6, and when observed through the eyepiece lens 13, the spatial image I of the substrate surface 7a is enlarged and observed. The objective lens 6
And the eyepiece lens 13 constitute an observation optical system.

On the other hand, the infrared light from the light source 1 is condensed by the condenser lens 2 and then illuminates the slit plate 3 having a predetermined slit-shaped opening.
A slit-shaped light beam is formed on the top. Of the light beams passing through the slit plate 3 which is divided into two by the surface including the optical axis Ax of the condenser lens 2 (the surface perpendicular to the paper surface in the figure), half of one light beam (lower light beam) is a light shielding plate. Half of the other light flux (upper light flux) L ₁ is shielded by 4, and is reflected by the half mirror 5. Then, the light flux reflected by the half mirror 5 passes through the left half of the objective lens 6 (the left half of the pupil of the objective lens 5), and on the surface 7a of the substrate, strictly speaking, the object plane (reference plane) of the objective lens 5. It is focused on P ₀ .

Here, the slit plate 3 is provided at a position conjugate with the object plane (reference plane) P ₀ of the objective lens 6 with respect to the objective lens 6, and on the object plane of the objective lens 6, An image of the opening of the slit plate 3 is formed. Therefore, on the substrate surface 7a of the test surface, substantially slit-like light is projected, thereby the light beam L ₂ reflected on the substrate surface 7a is the right half of the objective lens 6 (the objective lens 5 After passing through the right half of the pupil and the half mirror 5, the light is reflected by the dichroic mirror 10 and condensed on the light receiving surface of the photoelectric detector 8 such as a line sensor.

The light receiving surface of the photoelectric detector 8 is provided at a position conjugate with the object plane (reference surface) P ₀ of the objective lens 5 with respect to the objective lens 5, and the position where the optical axis Ax intersects the light receiving surface. The first detection area 8a and the second detection area 8a
Detection area 8b. Then, at a position apart from the side corresponding to the second detection area 8b by a predetermined distance, a light shielding plate that shields unnecessary reflected light from the back surface 7b of the substrate passing under the optical axis Ax. 9 is provided. As a result, the reflected light L ₂ from the substrate surface 7a that passes through the first detection region 8a side where the light shielding plate 9 is not arranged is provided.
Only can be extracted. Instead of the light blocking plate 9, a partial light blocking plate having a transmissive portion and a light blocking portion may be used to block light only in a necessary area.

Now, the first on the light receiving surface of the photoelectric detector 8
Two photoelectric signals obtained from both the detection area 8a and the second detection area 8b are output to the object plane detection unit (focus position detection unit) 14. The object plane detection unit 14 includes a differential signal processing circuit for obtaining a differential signal of two photoelectric signals, and when the objective lens 6 is focused on the substrate surface 7a, the differential signal becomes zero, and the differential signal becomes zero. When in focus, a certain differential signal corresponding to the defocus amount can be obtained. Therefore, the object plane detection unit 14 detects the position of the substrate surface 7a with respect to the object plane (reference plane) of the objective lens 6.

Thereafter, the focus detection information from the object plane detection unit 14 is input to the control unit 15, and based on this input information, the stage 16 is moved in the vertical direction (Z direction) by a predetermined amount for focusing. .. Next, considering the optimum position of the light shielding plate 9, in order to give the light shielding plate 9 a function of removing the reflected light (unnecessary infrared light) L ₃ from the back surface 7b of the substrate, the substrate should be focused at the time of focusing. Position A at which the reflected light L ₃ from the back surface 7b of the light is condensed by the objective lens 6 and the photoelectric detector 8
It can be seen that it is preferable to dispose between and.

Therefore, if the arrangement condition of the light shielding plate 9 is expressed as a mathematical expression, the distance in the optical axis direction from the photoelectric detector 8 to the light shielding plate 9 is d, and the substrate 7 with respect to the wavelength of the focus detection light.
Is n, the lateral magnification of the objective lens 6 when the substrate surface is at the object plane (reference position) P ₀ of the objective lens 6 is β ₁ , and the focal length of the objective lens 6 on the test surface side (object side) Where f _{11 is} the focal length on the detection side (image side) of the objective lens 6 is f ₁₂ , the following formula 1 is obtained.

[0027]

[Equation 1]

Further, in order to eliminate the unnecessary reflected light L ₃ reflected from the back surface 7b of the substrate and equalize the detection ranges of the front pin and the rear pin, it is preferable to satisfy the following formula 2.

[0029]

[Equation 2]

As described above, in this embodiment, the back surface 7 of the substrate is
Since the unnecessary reflected light L ₃ from b can be blocked by the light blocking plate 9, the position of the substrate surface 7a with respect to the object plane of the objective lens 6 can always be detected with high accuracy. Therefore, the substrate surface 7a can be inspected with high accuracy by the observation optical system (6, 13). Next, a second embodiment according to the present invention will be described with reference to FIG. In FIG. 2, members having the same functions as the members shown in FIG. 1 are designated by the same reference numerals.

In the above-described first embodiment, an example in which the position of the surface 7a of the substrate 7 whose thickness is always constant is detected accurately has been described, but in the second embodiment, the surface 7a of the substrate 7 having a different thickness is detected. An example of accurately detecting the position will be described. Now, when trying to detect the substrate front surface 7a having a different thickness, the condensing position A of the reflected light L ₃ from the rear surface 7b of the substrate by the objective lens 6 moves along the optical axis Ax direction. Therefore, in order to remove the unnecessary reflected light L ₃ from the back surface 7a, it is necessary to move the light shielding plate 9 along the optical axis Ax direction for adjustment as the thickness of the substrate 7 changes.

Therefore, in this embodiment, as shown in FIG.
The light shielding plate 9 is driven by the drive unit 18 along the Ax direction (arrow direction a).
It is provided so that it can be moved. Therefore, the setting of the position of the light shielding plate 9 in the present embodiment will be specifically described. First, a mark, for example, a bar code BC is provided at the end of the substrate surface, and the thickness of the substrate 7 is provided at this mark. Information such as t and the refractive index n of the substrate 7 is included. A bar code reader 17 as a mark detecting means for reading the bar code BC is provided at the end of the stage 16. When the bar code reader 17 reads the bar code BC on the board 7, this information is calculated by the calculation unit 18
And the predetermined calculation is performed here.

The arithmetic unit 18 stores the arithmetic expression of the above-mentioned formula 1 or formula 2 in advance, and the bar code reader 1
The calculation is performed based on the information output from 7 and the calculation result is output to the drive unit 19. Based on the calculation result, the drive unit 19 moves the light blocking plate 9 in the optical axis Ax direction (arrow direction a) and sets the light blocking plate 9 at the optimum position according to the thickness of the substrate 7.

With the above configuration, the light-shielding plate 9 can be set at the optimum position even when the thickness t of the substrate as the test object changes, so that the substrate surface 7 with respect to the object plane of the objective lens 6 can be set.
The position of a can always be detected with high accuracy. Therefore, the observation optical system (6, 13) can inspect the substrate surface 7a with higher accuracy. Next, a second embodiment in which the apparatus according to the present invention is applied to a microscope will be described with reference to FIG. In FIG. 3, members having the same functions as those shown in FIG. 1 are designated by the same reference numerals.

The third embodiment is particularly different from the above-described first embodiment in that the aerial image I'of the surface to be inspected is once formed in the focus detection optical system, and is recombined by the relay optical system 20. This is the point where the photoelectric detector 8 detects the aerial image I ′ to be imaged. This example will be specifically described. The substrate surface 7
a first objective lens 6 for converting light from a (surface to be inspected) into parallel light
1 and a second objective lens 62 that collects the parallel light from the first objective lens 61 to form an aerial image I of the surface 7a to be inspected. Then, a space image I of the surface to be inspected is formed by both of the objective lenses 61 and 62, and the space image I is magnified and observed through the eyepiece lens 13.

On the other hand, a dichroic mirror 10 having a function of transmitting visible light and reflecting infrared light is obliquely provided between the first objective lens 61 and the second objective lens 62, and this dichroic mirror 10 is provided. A third objective lens 63 for focus detection is provided in the reflection direction of. Here, the first objective lens 61 and the third objective lens 63 form an objective optical system for focus detection (position detection).

The infrared light from the light source 1 passing through the condenser lens 2 passes through the slit plate 3 by the light shielding plate 4 so that the light flux on the right side of the optical axis Ax is shielded and the light flux L on the left side of the optical axis Ax.
Only ₁ reflects off the half mirror 21. The reflected light is reflected by the lower half of the third objective lens 63 (lower half of the pupil of the third objective lens 63), the dichroic mirror 10 and the left half of the first objective lens (left of the pupil of the first objective lens 63). Light is focused on the substrate surface 7a via the (half). Here, the slit plate 3 has an object plane (reference plane) P formed by the first and second objective lenses with respect to the first and third objective lenses.
An image of the opening of the slit plate 3 is substantially formed on the substrate surface 7a as a surface to be inspected, which is provided at a position conjugate with ₀ .

Therefore, substantially slit-shaped infrared light is projected on the substrate surface 7a as the surface to be inspected, and the infrared light L ₂ reflected on the substrate surface 7a by this is the first infrared light. The right half of the objective lens (the right half of the pupil of the first objective lens 63), the dichroic mirror 10 and the third objective lens 6
After passing through the upper half of 3 (the upper half of the pupil of the third objective lens 63), the light passes through the half mirror 21 and is condensed to form a spatial image I ′. In this embodiment, a relay optical system 20 that relays this aerial image I ′ is provided, and the reflected light L ₂ from the substrate surface 7a that passes through the lower half of this relay optical system 20 is reflected by the photoelectric detector 8. It is condensed on the light receiving surface.

The light receiving surface of the photoelectric detector 8 is provided at a position conjugate with the object plane (reference plane) P ₀ of the objective optical system (61, 63), that is, the focal plane of the objective lens 61, and photoelectric detection is performed. The device 8 photoelectrically detects the image formation state of the image of the opening of the slit plate 3. The object plane detection unit 14 detects the in-focus state based on the signal output from the photoelectric detector 8, and the control unit 15 controls the vertical position of the stage 16 based on the detection result.

Also in this embodiment, as in the above-described embodiments, the shading plate 9 for removing unnecessary infrared light reflected from the back surface 7b of the substrate is provided by the objective lenses 61 and 63 during focusing. It is arranged between the photoelectric detector 8 and the position A where the reflected light L ₃ from the back surface 7b is condensed. Here, when the arrangement condition of the light shielding plate 9 is expressed as a mathematical expression, the distance from the light receiving surface 8a of the photoelectric detector to the light shielding plate 9 in the optical axis direction is d, and the substrate 7 with respect to the wavelength of the light for focus detection is Of the objective optical system (61, 6
When the lateral magnification of the objective optical system (61, 63) at the object plane (reference position) P ₀ of 3) is β ₁ , the objective optical system (61, 6) is
3) the focal length of the surface to be inspected (object side) is f ₁₁ , the focal length of the detection side (image side) of the objective optical system (61, 63) is f ₁₂ , and the substrate surface is the objective optical system (61, 63). ), The lateral magnification of the relay optical system 20 when the object plane (reference position) P ₀ is β ₂ ,
When the focal length on the surface to be inspected (object side) of the relay optical system 20 is f ₂₁ , and the focal length on the detection side (image side) of the relay optical system 20 is f ₂₂ , the following formula 3 is obtained.

[0041]

[Equation 3]

In order to make the detection ranges of the front pin and the rear pin equal in this embodiment, it is desirable to satisfy the following formula 4.

[0043]

[Equation 4]

As described above, the back surface 7 of the substrate is also used in this embodiment.
Since the unnecessary reflected light from b can be blocked by the light blocking plate 9, the position of the substrate surface 7a with respect to the object planes of the objective lenses 61 and 63 (or the focal plane of the objective lens 61) can always be detected with high accuracy. As a result, the substrate surface 7a
Can be inspected with higher accuracy. In this embodiment as well, as in the second embodiment shown in FIG. 2, a mark such as a bar code is provided at the end of the substrate surface 7a, and the calculation of the formula 3 or formula 4 is performed based on the detection information of this mark. The light shielding plate 9 may be moved in the direction of the optical axis based on the result of this calculation to set the light shielding plate 9 at the optimum position.

Further, in each of the embodiments described above, the stage 16 is provided so as to be movable in the Z direction in order to correct the deviation of the surface to be detected (substrate surface) from the object plane of the objective optical system (61, 63). However, as shown in FIG. 3, the first objective lens 61 for collimating the light from the surface to be inspected may be moved in the optical axis Ax direction for focusing. In this case, focusing can be performed by moving only the first objective lens 61 without moving the substrate as the surface to be inspected.

Furthermore, in each of the above-described embodiments, an example in which the present invention is applied to focus detection of a microscope has been shown, but it is needless to say that the present invention is not limited to this and can be applied to focus detection or position of other devices. ..

[0047]

As described above, according to the present invention, a position detecting device capable of detecting the surface of a substrate with higher accuracy can be achieved. Moreover, a great effect can be expected by adding a slight improvement to the conventional device.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of a first embodiment in which the present invention is applied to a microscope.

FIG. 2 is a diagram showing a schematic configuration of a second embodiment in which the present invention is applied to a microscope.

FIG. 3 is a diagram showing a schematic configuration of a third embodiment in which the present invention is applied to a microscope.

FIG. 4 is a principle diagram showing the principle of the present invention.

FIG. 5 is a diagram showing how reflected light from the back surface of a substrate is detected in a conventional focus detection device.

FIG. 6 is a diagram showing a schematic configuration of a conventional focus detection device.

[Explanation of symbols for main parts]

1 ... Light source, 2 ... Condensing lens, 3 ... Slit plate,
4, 9 ... Light-shielding plate 5, 11 ... Half mirror, 6 ... Objective lens, 7 ...
Substrate, 8 ... Light source detector 10 ... Dichroic mirror, 12 ... Epi-illumination system,
13 ... Eyepiece, 14 ... Focus detection unit, 15 ... Control unit, 16 ... Stage

Claims (2)

[Claims] 1. A light having a predetermined pattern is projected onto the surface of the substrate through one of the first regions which are divided into two parts with the surface including the optical axis of the objective lens as a boundary, and the light is reflected from the surface of the substrate. The position of the substrate is determined by photoelectrically detecting an image of the projection pattern light by a detector through the other second region that is divided into two parts with the surface including the optical axis of the objective lens as a boundary. In the position detecting device for detecting, a light blocking member for blocking the reflected light from the back surface of the substrate toward the light receiving surface of the detector through the second region is arranged at a position separated from the light receiving surface by a predetermined distance. A position detecting device characterized by: 2. The position detecting device according to claim 1, wherein the light shielding member is provided so as to be movable in the optical axis direction of the objective lens according to the thickness of the substrate.