JP3237023B2 - Position detection device - Google Patents

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 a test object, and more particularly to a position detecting 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 U.S. Pat. No. 3,721,827. Therefore, a focus detection device disclosed in U.S. Pat. No. 3,721,827 will be specifically described with reference to FIG.

In FIG. 6, (a) is a focused state, (b)
Indicates a front focus state, and (c) indicates a rear focus state. First, as shown in FIG. 6A, light from a light source 1 is condensed by a condenser lens 2, and a slit plate 3 having a slit-shaped opening is illuminated to form a slit-shaped light source. One half (lower light beam) of one of the light beams passing through the slit plate 3 divided by a surface including the optical axis of the condenser lens 2 (a surface perpendicular to the paper surface in the figure) is blocked. Half of the other light beam (upper light beam) L
₁ reflects the half mirror 5. Thereafter, the light beam 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
(Object surface of the objective lens 6).

[0004] On the test surface 70, the slit plate 3
The light flux L ₂ formed on the surface to be inspected 70 after the image of the opening is formed passes through the right half of the objective lens 6 (the right half of the pupil of the objective lens 5) and then passes through the half mirror 5. The light is condensed on the light receiving surface of the photoelectric detector 8, where an image of the opening of the slit plate 3 is formed. The light receiving surface of the photoelectric detector 8 has light receiving regions 8a and 8b on the left and right sides of a region intersecting the optical axis Ax of the objective lens 6, and the image forming state of the opening of the slit plate 3 is indicated by the photoelectric. Detection.

Further, as shown in FIG.
Is located at a position P ₁ below the position P ₀ of the object plane (reference plane) of the objective lens 6, the light flux L ₂ reflected by the test surface 70 and passing through the right half of the objective lens 6 is The light is condensed just before the light receiving surface of the photoelectric detector 8 and reaches the left area 8a of the light receiving surface. Here, since a 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 a defocused image of the slit in the front focus state.

Further, as shown in FIG.
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 test surface 70 and passing through the right half of the objective lens 6 is photoelectrically detected. Table 8
To the right side area 8b of the light receiving surface so as to be focused behind the light receiving surface of the light receiving surface. Then, the photoelectric detector 8 photoelectrically detects the defocus image of the slit in the back focus state.

Here, the focus detection based on the photoelectric detector 8 is to balance two light quantity signals detected in the left and right light receiving areas 8a and 8b of the photoelectric detector 8, ie, to take a difference between the two light quantity signals. Done in For example, FIG. 6A shows a state in which the subject is in focus. In this case, the detection light is detected at the center of the light receiving surface of the photoelectric detector 8. For this reason, the outputs of the two light amount signals 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. 6B shows the front focus state. In this case, the detection light is mainly detected in the left area 8 a of the light receiving surface of the photoelectric detector 8. For this reason, the left and right side regions 8 of the light receiving surface
As the differential signal based on the two light quantity signals detected at a and 8b, for example, an output signal having a certain positive level is obtained. FIG. 6C shows a rear focus state. In this case, the detection light is mainly detected in an area 8 b on the right side of the light receiving surface of the photoelectric detector 8. Therefore, as a differential signal based on the two light amount signals detected in the left and right side regions 8a and 8b of the light receiving surface, for example, an output signal having a certain negative level is obtained.

As described above, 2 obtained from the photoelectric detector 8
By taking the difference between the two signals, the direction of defocus can be detected by the positive / negative of the differential signal, and the amount of defocus can be detected by the output level of the differential signal.

[0010]

In recent years, the ratio of liquid crystal displays in displays and the like has been rapidly increasing. For this reason, inspection of a liquid crystal substrate, which is a source of liquid crystal display, is becoming 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 to be detected but also the reflected light from the back surface of the liquid crystal substrate Even the light reaches the photoelectric detector, which greatly affects the focus detection accuracy.

Therefore, since the surface of the liquid crystal substrate cannot be inspected accurately in a focused state, there is a problem that a defective product cannot be accurately determined. Therefore, the present invention has been made in view of the above-described problems, and a position where the position of the front surface of the substrate can be detected with high accuracy even when reflected light from the back surface of the substrate such as a liquid crystal substrate occurs. It is intended to provide a detection device.

[0012]

According to the present invention, an optical axis A of an objective lens 6 is provided as shown in FIG.
A predetermined pattern of light is projected onto the surface 7a of the substrate through one of the first regions divided by the surface including x, and an image of the projected pattern light reflected from the surface 7a of the substrate is projected. In a position detection device that detects the position of the substrate 7 by photoelectrically detecting with the detector 8 via the other second region divided into two by the surface including the optical axis of the objective lens 6,
A light-blocking member 9 that blocks light reflected from the back surface 7b of the substrate toward the light-receiving surface of the detector 8 via the second region is disposed at a position separated by a predetermined distance from the light-receiving region.

Based on the above basic configuration, 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]

The principle of the present invention will now be described with reference to FIGS. FIG. 5 is a diagram illustrating a state in which reflected light from the back surface of the substrate is detected when the conventional focus detection device is focused on the substrate surface. As shown in FIG. 5, the light source 1, the upper half L ₁ of the slit-shaped light fluxes formed by the condenser lens 2 and the slit plate 3 is condensed on the substrate 7 through the left half of the objective lens 6, 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 collected on the photoelectric detector 8.

On the other hand, a slit-like light beam which passes through the left half of the objective lens 6 and is condensed on the substrate 7 is applied to the surface 7 of the substrate.
a and is reflected by the back surface 7b of the substrate. Then, the reflected light L ₃ from the back surface 7 b passes through the right half of the objective lens 6 and is condensed in front of the light receiving surface 8 a of the photoelectric detector 8 to be collected on the left side region 8 a of the light receiving surface of the photoelectric detector 8. Is received at.

In this case, the photoelectric signal obtained by the photoelectric detector 8 will be described. As shown in FIG. 5, since the surface 7a of the substrate is in a focused state, the light amount signal obtained by the reflected light from the substrate surface 7a in the left and right light receiving areas of the photoelectric detector with the optical axis Ax of the objective lens 6 interposed therebetween. However, since the reflected light from the back surface 7b of the substrate is incident on the light receiving region on the left side of the photoelectric detector, the defocus (the front surface 7a of the substrate is lower than the in-focus position) by an amount corresponding to the amount of incident light. ) Is also detected.

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

Here, when the front surface 7a of the substrate is in focus, the light-shielding member 9 is positioned between the position A where the reflected light from the rear surface 7b of the substrate is condensed by the objective lens 6 and the light receiving position of the photoelectric detector 8. Preferably, it is arranged between the surface and the surface. In the above description, the detection of the position of the substrate surface having a constant thickness t of the substrate has been described. However, 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 provide as possible.

[0019]

FIG. 1 shows an example in which the present invention is applied to a focus detection device for a microscope. As shown in FIG. 1, a light beam in the visible range from the epi-illumination system 12 is reflected by a half mirror 11 and passes through a dichroic mirror 10, a half mirror 5, and an objective lens 6 that transmit visible light and reflect infrared light. Illuminate 7. The substrate 7 is mounted on a stage 16
The stage 16 is mounted on the top, and is provided so as to be two-dimensionally movable in the X and Y directions and movable in the Z direction (up and down directions) by a driving unit (not shown) provided therein. .

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

On the other hand, the infrared light from the light source 1 is condensed by a condenser lens 2 and then illuminates a slit plate 3 having a predetermined slit-shaped opening.
A slit-shaped light beam is formed on the upper side. Half of one light beam (lower light beam) of the light beam passing through the slit plate 3 divided by a surface including the optical axis Ax of the condenser lens 2 (a surface perpendicular to the paper surface in the drawing) is a light shielding plate. The half (upper light beam) L ₁ of the other light beam is reflected by the half mirror 5. The light beam 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 6 ), and on the surface 7a of the substrate, more precisely, the object plane (reference plane) of the objective lens 6 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. 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 6 After passing through the right half of the pupil 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 a 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 plane) P ₀ of the objective lens 6 with respect to the objective lens 6 , and a position where the optical axis Ax intersects with the light receiving surface. The first detection area 8a and the second detection area
And a detection area 8b. A light-shielding plate that shields unnecessary reflected light from the back surface 7b of the substrate that passes below the optical axis Ax at a position separated by a predetermined distance from the side corresponding to the second detection area 8b. 9 are provided. Thus, the reflected light L ₂ from the substrate surface 7a passing through the first detection area 8a side where the light shielding plate 9 is not disposed
Only can be extracted. Instead of the light-shielding plate 9, a partial light-shielding plate having a transmission part and a light-shielding part may be used to shield only a necessary region from light.

The first light-receiving surface of the photoelectric detector 8 will now be described.
The 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 surface detection unit 14 includes a differential signal processing circuit for obtaining a differential signal between two photoelectric signals. When the objective lens 6 is focused on the substrate surface 7a, the differential signal becomes zero, and If the focus is achieved, a certain differential signal corresponding to the defocus amount can be obtained. Therefore, the position of the substrate surface 7a with respect to the object plane (reference plane) of the objective lens 6 is detected by the object plane detection unit 14.

Thereafter, the focus detection information from the object plane detection unit 14 is input to the control unit 15, and the stage 16 is moved in the vertical direction (Z direction) by a predetermined amount based on the input information to perform focusing. . Substrate now to consider the optimum position of the light shielding plate 9, in order to have a function of removing the reflected light (unnecessary infrared light) L ₃ of the substrate of the back surface 7b in the light shielding plate 9, the in-focus state position a and the photoelectric detector 8 which is reflected light L ₃ from the back surface 7b is condensed by the objective lens 6 of
It can be seen that it is preferable to dispose it between.

Therefore, if the arrangement condition of the light shielding plate 9 is expressed by a mathematical expression, the distance between the photoelectric detector 8 and the light shielding plate 9 in the optical axis direction 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} a focal length on the detection side (image side) of the objective lens 6 and f ₁₂ is as follows.

[0027]

(Equation 1)

Further, while removing unnecessary reflected light L ₃ reflected from the substrate backside 7b, to equalize the detection range of the front focus and the rear focus, it is preferable to satisfy Equation 2 below.

[0029]

(Equation 2)

As described above, in this embodiment, the back surface 7 of the substrate
for unnecessary reflection light L ₃ from the b can be shielded by the light shielding plate 9 can detect the position of the substrate surface 7a with respect to the object plane of the objective lens 6 in very high accuracy original. 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, components having the same functions as those shown in FIG. 1 are denoted by the same reference numerals.

In the above-described first embodiment, an example has been described in which the position of the surface 7a of the substrate 7 having a constant thickness is accurately detected. However, in the second embodiment, the position of the surface 7a of the substrate 7 having a different thickness is described. An example of detecting the position with high accuracy will be described. Now, when the thickness is to be detected different substrate surface 7a, focusing position A of the reflected light L ₃ from the back surface 7b of the substrate by the objective lens 6 is moved along the optical axis Ax direction. Therefore, to remove unwanted reflected light L ₃ from the rear surface 7a, it is necessary to adjust the light shielding plate 9 with a change in thickness of the substrate 7 is moved along the optical axis Ax direction.

Therefore, in this embodiment, as shown in FIG.
The light shielding plate 9 is driven by the driving unit 18 along the Ax direction (arrow direction a).
Is provided so as to be movable. 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 an end of the substrate surface, and the mark has a thickness of the substrate 7. Information such as t and the refractive index n of the substrate 7 is included. A bar code reader 17 is provided at the end of the stage 16 as mark detection means for reading the bar code BC. When the barcode reader 17 reads the barcode BC on the substrate 7, the barcode reader 17
, Where a predetermined operation is performed.

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

With the above arrangement, even when the thickness t of the substrate as the test object changes, the light-shielding plate 9 can be set at an optimum position.
The position a can always be detected with high accuracy. Therefore, the substrate surface 7a can be inspected with higher accuracy by the observation optical system (6, 13). Next, a third embodiment in which the apparatus according to the present invention is applied to a microscope will be described with reference to FIG. 3, components having the same functions as those shown in FIG. 1 are denoted by the same reference numerals.

The third embodiment is particularly different from the above-described first embodiment in that a spatial image I 'of a surface to be inspected is formed once in a focus detection optical system, and reconstructed by a relay optical system 20. The point is that the aerial image I ′ to be formed is detected by the photoelectric detector 8. The present embodiment will be described specifically.
a (first object 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 a spatial image I of the surface 7a to be inspected, constitutes an objective optical system. Then, the aerial image I of the surface to be inspected is formed by the two objective lenses 61 and 62, and the aerial image I is magnified and observed through the eyepiece 13.

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

With respect to the infrared light from the light source 1 through the condenser lens 2, the light beam on the right side of the optical axis Ax is shielded by the light shielding plate 4 through the slit plate 3, and the light beam L on the left side of the optical axis Ax.
Only ₁ reflects the half mirror 21. The reflected light is transmitted to the lower half of the third objective lens 63 (the lower half of the pupil of the third objective lens 63), the dichroic mirror 10 and the left half of the first objective lens (the left half of the pupil of the first objective lens 63). (Half) on the substrate surface 7a. Here, with respect to the first and third objective lenses, the slit plate 3 has an object plane (reference plane) P by the first and second objective lenses.
It is provided at a position conjugate with _0, and an image of the opening of the slit plate 3 is formed substantially on the substrate surface 7a as the surface to be inspected.

[0038] Therefore, on the substrate surface 7a of the test surface is substantially slit-like infrared light is projected, thereby the infrared light L ₂ reflected on the substrate surface 7a is first 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 an aerial image I '. In this embodiment, a relay optical system 20 for relaying the aerial image I ′ is provided, and the reflected light L ₂ from the substrate surface 7 a passing through the lower half of the relay optical system 20 is applied to the photoelectric detector 8. The light is focused 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. The device 8 photoelectrically detects the image forming 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.

In this embodiment, as in the previous embodiment, the light-shielding 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. the reflected light L ₃ from the back surface 7b is disposed between the position a and the photoelectric detector 8 which is condensed in. Here, when the arrangement condition of the light-shielding plate 9 is expressed by a mathematical expression, the distance in the optical axis direction from the light receiving surface 8a of the photoelectric detector to the light-shielding plate 9 is d, and the substrate 7 with respect to the wavelength of the light for focus detection. Is n, and the substrate surface is an objective optical system (61, 6).
The lateral magnification of the objective optical system (61, 63) at the object plane (reference position) P ₀ of 3) is β ₁ , and the objective optical system (61, 6)
3) The focal length on the surface to be inspected (object side) is f ₁₁ , the focal length on 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). ) Is the object plane (reference position) P ₀ , the lateral magnification of the relay optical system 20 is β ₂ ,
Assuming that the focal length of the relay optical system 20 on the surface to be inspected (object side) is f ₂₁ and the focal length of the relay optical system 20 on the detection side (image side) is f ₂₂ , Equation 3 below is obtained.

[0041]

(Equation 3)

In order to make the detection ranges of the front focus and the rear focus equal in this embodiment, it is desirable to satisfy the following expression (4).

[0043]

(Equation 4)

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

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 displacement of the test surface (substrate surface) from the object surface of the objective optical system (61, 63). However, as shown in FIG. 3, the focusing may be performed by moving the first objective lens 61 for making the light from the surface to be measured parallel in the direction of the optical axis Ax. In this case, focusing can be performed only by moving the first objective lens 61 without moving the substrate as the test surface.

Further, in each of the embodiments described above, examples in which the present invention is applied to focus detection of a microscope are shown. However, it is needless to say that the present invention can be applied to focus detection or a position of another device. .

[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 with only a slight improvement in the conventional device.

[Brief description of the 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 view showing the principle of the present invention.

FIG. 5 is a diagram illustrating a state where reflected light from the back surface of a substrate is detected by a conventional focus detection device.

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

[Description of Signs of Main Parts]

DESCRIPTION OF SYMBOLS 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 lens, 14 focus detection unit, 15 control unit, 16 stage

Claims (4)

(57) [Claims] 1. A predetermined pattern of light is projected onto a surface of a substrate via one first region divided by a surface including an optical axis of an objective lens, and is reflected from the surface of the substrate. Detecting the position of the substrate by photoelectrically detecting the image of the projection pattern light with a detector via the other second area divided into two parts by the plane including the optical axis of the objective lens A light-shielding member that shields light reflected from the back surface of the substrate via the second region toward the light-receiving surface of the detector, wherein the reflected light from the back surface is condensed by the objective lens. Between the position and the light receiving surface, and disposed on the side where the reflected light from the back surface passes with the optical axis of the objective lens as a boundary,
The following conditions are satisfied: The distance in the optical axis direction from the light receiving surface of the detector to the light blocking member is d, the refractive index of the substrate with respect to the wavelength of the focus detection light is n, and the substrate surface is the objective lens. When the objective lens is at the object plane (reference position), the lateral magnification of the objective lens is β1, the focal length of the objective lens on the test surface side (object side) is f11, and the focal length of the objective lens on the detection side (image side). To f12 ,
When the thickness of the plate is t , the following formula 1 A position detection device characterized by satisfying the following. 2. The method according to claim 1, wherein a spatial image of the surface to be detected is once formed in the position detecting optical system, and the spatial image re-imaged by the relay optical system is detected by a detector. 3. The position detecting device according to claim 1. 3. The position detecting device according to claim 1, wherein the light shielding member is provided so as to be movable in an optical axis direction of the objective lens according to a thickness of the substrate. 4. A predetermined pattern of light is projected onto the surface of the substrate through one of the first regions divided by the surface including the optical axis of the objective lens, and is reflected from the surface of the substrate. Detecting the position of the substrate by photoelectrically detecting the image of the projection pattern light with a detector via the other second area divided into two parts by the plane including the optical axis of the objective lens In the position detecting device, a light-shielding member that shields reflected light from the back surface of the substrate toward the light-receiving surface of the detector via the second region is provided so as to be movable in the optical axis direction of the objective lens . Further light shielding
The member reflects light from the back surface by the objective lens.
Between the light-collecting position and the light-receiving surface, and
Reflected light from the back surface passes through the optical axis of the object lens
Side, satisfying the following conditions, in the optical axis direction from the light receiving surface of the detector to the light shielding member
Is the distance of d, the refraction of the substrate with respect to the wavelength of the focus detection light.
Rate is n and the substrate surface is the object plane of the objective lens (reference
Position), the lateral magnification of the objective lens is β1,
The focal length of the objective lens on the object side (object side) is f11,
The focal length on the detection side (image side) of the objective lens is f12,
When the thickness of the plate is t, equation 1 Equation 1] below A position detection device characterized by satisfying the following .