JPH1123953A - Microscope equipped with focus detector and displacement measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a microscope equipped with a focus detecting means whose focusing detectable range is wide and where the shape of a focus error signal is symmetric on the positive side and the negative side around a focal position as the center. SOLUTION: In this microscope equipped with a differential beam size system focus detecting means, a 1st detection part 18 of the focus detecting means is arranged at a position separate from a condensing optical system 16 by a distance L1 from a focal point 20 of the optical system 16 and a 2nd detection part 19 is arranged at a position near to the optical system 16 by a distance L2 from a focal point 21 of the optical system 16. At this time, the L1 and the L2 are set to be L1≠L2 by coinciding with the asymmetric displacement of the converging point of a luminous flux by the optical system 16.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microscope provided with a focus detecting device for automatic focusing, and a displacement measuring device for detecting a displacement of a surface of an object to be measured in a non-contact manner.

[0002]

2. Description of the Related Art Conventionally, focus detection methods include, for example,
A method called a differential beam size method is known.

FIG. 10 is a block diagram of a schematic configuration of a microscope and a focus detection device when a differential beam size type focus detection device is used for focus detection of a conventional epi-illumination type microscope. The apparatus shown in FIG. 10 includes an observation optical system, an illumination optical system, and an autofocus optical system of a microscope.

The observation optical system of the microscope includes a first objective lens 1
02, a second objective lens 103, and a bird's-eye view prism 104
And an eyepiece 105. First objective lens 10
A parallel optical path is formed between the second objective lens 103 and the second objective lens 103 along the optical axis 101. In this parallel optical path, a dichroic mirror 107 and a beam splitter 108 are installed at an angle of 45 degrees with respect to the optical axis 101, respectively. The dichroic mirror 107 has a characteristic of reflecting infrared light and transmitting visible light.

[0005] The illumination optical system of the microscope has an illumination light source 110 for emitting visible light and a condenser lens 111, and the illumination light beam is reflected by the beam splitter 108 and guided to the above-mentioned parallel optical path.

The autofocus optical system includes a light source 113 for emitting infrared light, a collimator lens 114, a beam splitter 115, a condenser lens 116, a beam splitter 117, a first photodetector 118, It has two photodetectors 119. The first photodetector 118 is provided at the convergence point 12 where the light flux transmitted through the beam splitter 117 converges.
It is arranged near zero. On the other hand, the second photodetector 119
Is arranged near the convergence point 120 where the light beam reflected by the beam splitter 117 converges. The distance between the first photodetector 118 and the condenser lens 116 is
6 is longer than the focal length of the second photodetector 11 by L0.
The distance between 9 and the condenser lens 116 is set shorter than the focal length of the condenser lens by L0.

The light detector of the first light detector 118 and the light detector of the second light detector 119 have circular light detectors 118a and 119a at the center as shown in FIG. It has surrounding photodetectors 118b and 119b. In addition, these light detection units 118a, 118b, 11
9a and 119b are connected to operational amplifiers 129 and 130, and operational amplifiers 129 and 130 are connected to operational amplifier 131.

[0008] The operational amplifiers 129, 130 and 131 are arranged in the control unit 126. The test object 124 is mounted on a moving stage 125 that can move in the direction of the optical axis 101. The control device 126 controls the operation of the moving stage 125.

In the configuration shown in FIG. 10, a light beam emitted from a light source 113 and having passed through a collimator lens 114 is reflected by a beam splitter 115, further reflected by a dichroic mirror 107, and
And forms an image on the test object 124. Test object 12
The light beam reflected from the test surface 123 passes through the objective lens 102, is reflected by the dichroic mirror 107, passes through the beam splitter 115, and enters the beam splitter 117.

As shown in FIG. 11, light spots 132 and 13 are provided on the photodetectors 118 and 119 by the first and second light beams split by the beam splitter 117.
3 are formed respectively. The light spot 132 formed on the first photodetector 118 increases when the objective lens 102 and the object 124 are separated from each other, and decreases when the object lens 102 and the object 124 approach each other. On the other hand, the light spot 133 formed on the second photodetector 119 becomes smaller when the objective lens 102 and the test object 124 are separated from each other, and becomes larger when they are closer to each other. (| 118a |-| 118b |)-(| 119a |) from the detection signals of both photodetectors 118 and 119 by operational amplifiers 129, 130 and 131.
− | 119b |), and if this signal is used as a focus error signal, a focus error signal having S-characteristics can be obtained. However, | 118a |, | 118b |, |
119a | and | 119b | are the light detection units 11 respectively.
8a, the outputs of the photodetector 118b, the photodetector 119a, and the photodetector 119b.

Therefore, when the focus error signal is positive, it is possible to determine the front focus state, when the focus error signal is negative, it is possible to determine the rear focus state, and when the focus error signal is zero, it is possible to determine the focus state. It is possible to determine the position of the surface to be inspected from the focus error signal and move the movable stage 125 up and down by the control device 126 to automatically adjust the position to the focused state.

Further, the displacement amount of the test object 124 can be measured from the focus error signal.

[0013]

In the above-mentioned microscope with a focus detecting device, in order to enable observation of various surface shapes of the object 124 to be inspected, it is necessary to widen the range in which the auto-focus optical system can detect the focus. desired. Since the focus detectable range increases as L0 in FIG. 10 increases, L0 needs to be increased in order to widen the focus detection range. However, when L0 is increased, conventionally, FIG.
As shown in (b), the shape of the focus error signal becomes asymmetric, and the focus detection range is different between the positive side and the negative side.

The present invention solves this problem and provides a microscope provided with a focus detection means having a wide focus detectable range and a shape of a focus error signal symmetrical on the positive side and the negative side with respect to the focus position as a center. The purpose is to provide.

[0015]

According to the present invention, there is provided a microscope provided with the following focus detecting means.

That is, a stage for mounting a test object, an observation optical system including an objective lens for observing the test object, and a displacement of the test object from a focal position of the objective lens. Focus detection means for detecting,
The focus detection unit, an illumination optical system for irradiating the test object with illumination light through the objective lens, and a condensing optical system for converging the reflected light flux of the illumination light from the test object, A dividing unit for dividing the reflected light beam into first and second light beams, a first and second detecting unit for detecting the first and second light beams, respectively, and a first and a second detecting unit. Calculating means for calculating a focus error signal by calculating a detection result, wherein the first and second detectors detect a light flux of an optical axis portion among the first and second light fluxes, respectively. And a second detection area for detecting a light beam outside the first detection area, and the calculating means is configured to output the first detection area with respect to the output of the first detection area for each of the first and second detection units. The difference from the output of the second detection area is And a difference between the difference result of the first detection unit and the difference result of the second detection unit. The first detection unit is more than the focal position of the light collecting optical system. The second detection unit is disposed at a position separated by L1 from the condensing optical system, and the second detection unit is disposed at a position closer to the condensing optical system by L2 than a focal position of the condensing optical system,
L1 is a microscope provided with focus detection means, which is set at a distance not equal to L2.

[0017]

Embodiments of the present invention will be described below.

In the focus detection device of the differential beam size system, when the distance L0 between the photodetector and the focal point of the condenser lens is increased in order to widen the focus detectable range, the focus error signal is changed as shown in FIG. The cause of asymmetry as in b) was studied. As a result, the following was found.

In a microscope equipped with a focus detection device having a configuration as shown in FIG. 1, the distance between the objective lens 2 and the test surface 23 is a, and the convergence point of light on the test surface 23 side of the objective lens 2 is The distance between the converging point of the light on the side of the condenser lens 16 and the objective lens 2 is b, the distance between the condenser lens 16 and the converging points 20 and 21 is c, and the distance between the objective lens 2 and the condenser lens 16 is L
3. Assuming that the focal lengths of the objective lens 2 and the condenser lens 16 are f1 and f2, respectively, these can be represented in a positional relationship as shown in FIG. Also, a, b, c, L3,
f1 and f2 have the following relations (Equation 1) and (Equation 2) from the lens formula. Furthermore, (Equation 1), (Equation 2)
Thus, c can be expressed as (Equation 3).

[0020]

(Equation 1)

[0021]

(Equation 2)

[0022]

(Equation 3)

FIG. 4 shows Equation 3 in a graph.
However, FIG. 4 shows that f1 = 20 mm, f2 = 40 mm, L
3 = 180 mm, and the pupil diameter of the objective lens 2 is 12 mm. In FIG. 4, the scale on the horizontal axis a represents 0 at the position of a = f1, and the scale on the vertical axis represents 0 at the position of c = f2. As can be seen from FIG. 4, when the test surface 23 is near the focal length f1 (for example, ± 250 μm), the relationship between a and c is almost linear. For this reason,
When the test surface 23 is near the focal length f1, even if a is shifted in the positive direction or the negative direction from the focal length f1, the shift amount of c from the focal length f2 is almost equal. Equal (about ± 2 mm). However, the test surface 23 has a focal length f1
A large deviation (for example, ± 1000 μm),
Is shifted in the negative direction, the shift amount of c is 5 mm, whereas when shifted in the positive direction, the shift amount of c is -2.
It reaches 0 mm, and the curve of the graph of FIG. 4 cannot be ignored. The fact that the shift amount of c becomes asymmetric in the positive and negative directions in this way means that the displacement of the convergence points 20 and 21 of the condenser lens becomes asymmetric in the positive and negative directions of the focal position in FIG. For this reason, the photodetector 1
When the mirrors 8 and 19 are arranged symmetrically with respect to the focal position, the actual displacement of the convergence points 20 and 21 is asymmetrical with respect to the focal position, so that the output of the detector is also asymmetrical and the focus error signal is shown in FIG. It is considered that it becomes asymmetric as shown in FIG.

Therefore, in the present embodiment, by considering the asymmetry of the shift amount of c, the range in which the focus can be detected is wide, and the shape of the focus error signal is different from the positive side around the focal position. Provided is a microscope provided with focus detection means symmetrical on the negative side.

First, a microscope with a focus detection device according to a first embodiment of the present invention will be described with reference to FIG. The microscope shown in FIG. 1 includes an observation optical system, an illumination optical system, and an autofocus optical system.

The observation optical system has a first objective lens 2, a second objective lens 3, a depressed prism 4, and an eyepiece 5. A parallel optical path is formed along the optical axis 1 between the first objective lens 2 and the second objective lens 3. In this parallel optical path, a dichroic mirror 7 and a beam splitter 8 are installed at an angle of 45 degrees with respect to the optical axis 1 of the parallel optical path. The dichroic mirror 7 has a characteristic of reflecting infrared light and transmitting visible light.

The illumination optical system has an illumination light source 10 for emitting visible light and a condenser lens 11. The illumination light beam emitted from the illumination optical system is reflected by the beam splitter 8 and guided to the above-mentioned parallel optical path.

The autofocus optical system includes a light source 13 for emitting infrared light, a collimator lens 14, a beam splitter 15, a condenser lens 16, and a beam splitter 1.
7, a first light detector 18, and a second light detector 19. As the light source 13, a light emitting diode that emits infrared light was used. The first photodetector 18 is installed at a position separated from the focal length f2 of the condenser lens 16 by L1. On the other hand, the second photodetector 19 is installed at a position closer to the condenser lens 16 by L2 than the focal length f2 of the condenser lens 16. The convergence points 20 and 21 are points where the reflected light from the test object 24 is converged by the condenser lens 16. A method for determining the values of L1 and L2 will be described later.

The light detector of the first light detector 18 and the light detector of the second light detector 19 have circular light detectors 18a and 19a at the center as shown in FIG. I have. Light detectors 18b and 19b surrounding the light detectors 18a and 19a are formed on the outside. The diameter of the central circular light detecting portion 18a and the diameter of the light detecting portion 19a are determined so that their ratio is equal to the ratio between the distance L1 and the distance L2.

The light detection areas of the light detection sections 18a and 18b and the light detection sections 19a and 19b are formed by doping the semiconductor substrate with impurities. FIG.
In the drawing, adjacent light detection units are drawn so as to be in contact with each other. However, in practice, a dead area where light is not detected is formed between adjacent light detection units. This allows
Adjacent photodetectors are isolated from each other.

Light detectors 18a, 18b, 19a, 19b
Is connected to the operational amplifiers 29 and 30, and the operational amplifier 2
9 and 30 are connected to an operational amplifier 31. The operational amplifiers 29, 30, and 31 are amplifiers that subtract two input signals.

The operational amplifier 29 makes a difference between the output of the light detector 18a and the output of the light detector 18b. Operational amplifier 3
0 makes a difference between the output of the light detection unit 19a and the output of the light detection unit 19b. The operational amplifier 31 makes a difference between the output of the operational amplifier 29 and the output of the operational amplifier 30. Photodetector 18
a, 18b, 19a, and 19b are | 18
a |, | 18b |, | 19a |, | 19b |, the output of the operational amplifier 31 is (| 18a | − | 18b
|)-(| 19a |-| 19b |).

The operational amplifiers 29, 30, 31 are arranged in the control device 26. The test object 24 is mounted on a moving stage 25 that can move in the optical axis 1 direction. The control device 26 controls the operation of the moving stage 25.

Next, the operation of each part of the microscope with a focus detection device shown in FIG. 1 will be described.

The light emitted from the light source 13 and the collimator lens 1
The light beam passing through 4 is reflected by the beam splitter 15, further reflected by the dichroic mirror 7, enters the objective lens 2, and forms an image on the test object 24. The light beam reflected from the test surface 23 of the test object 24 passes through the objective lens 2, is reflected by the dichroic mirror 7, passes through the beam splitter 15,
And enters the beam splitter 17.

On the photodetectors 18 and 19, the first and second light beams split by the beam splitter 17 generate
As shown in FIG. 2, light spots 37 and 38 are respectively formed. The spot diameter of the light spot 37 formed on the first photodetector 18 increases when the objective lens 2 and the object 24 are separated from each other, and decreases when the object lens 2 and the object 24 approach each other. on the other hand,
Contrary to the light spot 37, the spot diameter of the light spot 38 formed on the second photodetector 19 becomes smaller when the objective lens 2 and the test object 24 are separated, and becomes larger when the object lens 2 comes closer. Therefore, the output of the operational amplifier 31 (| 18a |
− | 18b |) − (| 19a | − | 19b |) becomes an S-shaped curve as shown in FIG.
A focus error signal having an S-shaped characteristic is obtained.

Here, a method of determining the values of L1 and L2 will be specifically described. In the present embodiment, the test surface 2
L1 and L2 are determined as three focus detectable ranges so that 710 μm can be secured symmetrically in the positive direction and the negative direction with respect to the focus. Note that the focal length f1 of the object lens 2 is 20 as in the condition of the graph in FIG.
mm, the focal length f2 of the condenser lens 16 is 40 mm, and the distance L3 between the objective lens 2 and the condenser lens 16 is 180 mm.
mm, the pupil diameter of the objective lens 2 is 12 mm.

First, the relationship between the position c of the convergence points 20 and 21c and the position a of the surface 23 to be inspected is obtained by using Equation (3). Under the conditions of the present embodiment, the relationship between c and a is as shown in the graph of FIG. However, the scale on the horizontal axis a is represented by 0 at the position of a = f1, and the scale on the vertical axis is represented by 0 at the position of c = f2. Here, as described above, as the focus detectable range of the test surface 23, 710 μm is secured in each of the positive direction and the negative direction, so that the position a of the test surface 23 is f1−710 μm in the graph of FIG. f1 +
When the position c of the convergence points 20 and 21 at 710 μm is obtained, when a is f1 + 710 μm, c is f2−10000
μm, and when a is f1-710 μm, c is f2 +
It can be seen that the displacement is 4000 μm. This indicates that the convergence points 20 and 21 are asymmetrically displaced about the focal point f2.

As described above, the output of the operational amplifier 31 is (| 18a |-| 18b |)-(| 19a |-| 19b
|), The output (focus error signal) of the operational amplifier 31 becomes near the peak value when the beam diameter of the light spot incident on each of the first and second photodetectors 18 and 19 becomes the smallest. . Therefore, the first photodetector 18 is arranged at the position (f2 + 4000 μm) of the convergence point 20 when the test surface 23 is at f1−710 μm, and the second photodetector 19 is disposed when the test surface 23 is at f1 + 710 μm. At the position of the convergence point 21 (f2-10000 μm).
That is, in the present embodiment, the first photodetector 18 is disposed at a position separated by a distance L1 = 4000 μm from the focal length f2 of the condenser lens 16, and the distance L2 is greater than the focal length f2 of the condenser lens 16. It was set so that the second photodetector 19 was disposed at a position from the condenser lens 16 by 10000 μm.

Since L1 and L2 are set to unequal values, the focal point of the condenser lens 16 and the first
The distance between the first and second photodetectors 18 and 19 is asymmetric, and the size of the light spot on the first and second photodetectors 18 and 19 is different. Therefore, in the present embodiment,
The ratio of the size of the light detection unit 18a to the size of the light detection unit 19a is
The ratio between the distance L1 and the distance L2 is made equal, so that when the convergence points 20, 21 are at the focal length f2, (| 18
a |-| 18b |)-(| 19a |-| 19b |) is specifically set to 0. Specifically, the light detector 18a of the photodetector 18 is a circle having a diameter of 694 .mu.m.phi. Was made circular with a diameter of 1742 μmφ, and the ratio of the size of the light detection unit 18a to the size of the light detection unit 19a was made equal to the ratio of the distance L1 to the distance L2. Also, the light detection unit 1
The outer shapes of 8b and 19b were 6000 μm × 6000 μm.

As described above, L1 and L2 are set asymmetrically in accordance with the asymmetry of the displacement of the convergence point, and the sizes of the photodetectors 18a and 18b are set in proportion to L1 and L2. As shown in FIG. 3A, a focus detectable range of the test surface 23 can be secured in a wide range of about ± 710 μm, and a focus error signal having a symmetric shape on the positive side and the negative side of the focus position can be obtained. I got it.

Therefore, in the apparatus shown in FIG. 1, when the focus error signal shown in FIG. 3A is positive, it is possible to determine the front focus state, when the focus error signal is negative, the rear focus state, and when the focus error signal is zero, it is possible to determine the focus state. It is. The position of the test surface is determined from the differential signal,
It is possible to move the moving stage 25 up and down by the control device 26 to automatically adjust the position to the focused state. In this state, by observing the light emitted from the illumination light source 10 to the object 24 with the observation optical system, the image of the object 24 can be observed in a focused state. Further, the displacement amount of the test object 24 can be accurately measured from the magnitude of the focus error signal.

On the other hand, in the above configuration, the distance L1 between the convergence point 20 and the photodetector 18 is set to 60
The distance L2 between the convergence point 21 and the photodetector 19 is set to 6000 μm, the distances L1 and L2 are made equal, and the size of the photodetector 18a of the photodetector 18 is set at 104 μm.
8 μmφ, the size of the light detection unit 18b is 6000 μm × 60
00 μm, and the size of the photodetector 19 a of the photodetector 19 is 10
48 μmφ, dimensions of the photodetector 19b are 6000 μm × 6
When the objective lens 2 of the microscope is 000 μm and the objective lens 2 has a focal length of 20 mm and a pupil diameter of 12 mm, the focus error signal is as shown in FIG.

The focus error signal shown in FIG. 3B has an asymmetric shape with different focus detectable ranges on the positive side and the negative side of the focal position. Therefore, even if the focus error signal has the same magnitude, the amount of deviation of the surface to be detected from the focal point differs between the positive side and the negative side, making it difficult to perform focusing control. Also, when detecting the displacement amount of the test object 24 from the magnitude of the focus error signal, the asymmetry of the focus error signal must be considered.

In the above-described first embodiment, L for providing a range of ± 710 μm as the focus detection range is used.
Although the values of L1 and L2 are set, L1 and L2 are not limited to the values described above, and the values of L1 and L2 are not limited to the desired focus detection range.
The values of L1 and L2 determined using the relationship between c and a can be used. Specifically, as in the first embodiment, desired values of a may be taken in the positive and negative directions, respectively, and L1 and L2 may be set to the corresponding values of c. Further, the value of c for determining L1 and L2 does not have to be strictly a point on the curve of FIG. 4, and a value near the curve of FIG. 4 can be used.

In the first embodiment described above, a quarter-wave plate is provided between the dichroic mirror 7 and the beam splitter 15, and the light source 13 is used as a light source for emitting linearly polarized light. By using a configuration in which 15 is a polarization beam splitter, the test surface 23
Can be detected by the photodetectors 18 and 19, and the amount of light received by the photodetectors 18 and 19 increases, so that a focus error signal can be obtained with higher sensitivity even with a sample having a low reflectance. .

Next, a microscope with a focus detection device according to a second embodiment of the present invention will be described with reference to FIG.

The configuration of FIG. 5 is substantially the same as the configuration of FIG. 1 of the first embodiment, except that a slit 80 is disposed between the light source 13 and the collimator lens 14, The form is different from FIG.

The autofocus optical system having the configuration shown in FIG.
A light source 13 for emitting infrared light, a slit 80, a collimator lens 14, a beam splitter 15, a condenser lens 16, a beam splitter 17, and a first photodetector 8
1 and a second photodetector 82. A light emitting diode was used as the light source 13. FIG. 7 shows the slit 80 as viewed from the front. The first photodetector 81 is installed at a distance L1 from the focal length f2 of the condenser lens 16.
On the other hand, the second photodetector 82 is installed at a position closer to the condenser lens 16 by L2 than the focal length f2 of the condenser lens 16.

As shown in FIG. 6, the photodetector of the first photodetector 81 and the photodetector of the second photodetector 82 are vertically divided into three sections. 81a, 82
a is a photodetector 81b, 81c and 82b, respectively.
82c sandwiched from above and below.

These light detectors 81b, 81c, 82
b and 82c are connected to operational amplifiers 83 and 84, photodetectors 81a and 82a, operational amplifiers 83 and 84 are connected to operational amplifiers 85 and 86, and operational amplifiers 85 and 86 are connected to operational amplifier 87. I have. Operational amplifiers 83, 84
Is an amplifier that adds two input signals, and operational amplifiers 85, 86, and 87 are amplifiers that subtract the two input signals.

The operational amplifier 83 adds the output of the light detector 81b and the output of the light detector 81c. Operational amplifier 8
4 adds the output of the light detection unit 82b and the output of the light detection unit 82c. The operational amplifier 85 makes a difference between the output of the photodetector 81a and the output of the operational amplifier 83. Operational amplifier 8
6 makes a difference between the output of the photodetector 82a and the output of the operational amplifier 84. The operational amplifier 87 makes a difference between the output of the operational amplifier 85 and the output of the operational amplifier 86.

Therefore, the photodetectors 81a, 81b, 81
c, 82a, 82b, and 82c are | 81
a |, | 81b |, | 81c |, | 82a |, | 82b
And | 82c |, the output of the operational amplifier 87 is also (| 81a |-(| 81b | + | 81c |))-(| 8
2a |-(| 82b | + | 82c |)).

The operational amplifiers 83, 84, 85, 8
6, 87 are arranged in the control device 26.

In the configuration of FIG. 5 of the second embodiment, a linear slit image is formed on the surface 23 to be measured. That is, part of the light emitted from the light source 13 passes through the slit 80,
The light beam that has passed through the collimator lens 14 is reflected by the beam splitter 15, further reflected by the dichroic mirror 7, enters the objective lens 2, and is movable by the control device 26 in the direction of the optical axis 1.
A slit image is formed on the test surface 23 of the test object 24 placed thereon. The light beam reflected from the test surface 23 of the test object 24 passes through the objective lens 2, is reflected by the dichroic mirror 7, passes through the beam splitter 15, passes through the condenser lens 16, and enters the beam splitter 17.
Then, a slit image is formed on each of the photodetectors 81 and 82 by the first and second light beams split by the beam splitter 17. At this time, the slit 80 is arranged such that the longitudinal direction of the slit image on the photodetectors 81 and 82 is parallel to the width direction of the photodetectors 81 and 82.

The method of focus detection is the same as in the first embodiment, and a description thereof will be omitted.

In the second embodiment, an apparatus was manufactured under the following conditions, an experiment was performed, and a focus error signal was obtained.

The focal length of the condenser lens 16 is 40 mm, and the distance L3 between the objective lens 2 and the condenser lens 16 is 180 m
m. L1 is 4000 μm, L2 is 10,000 μm
The distances L1 and L2 were set to unequal values. Further, the dimensions of the light detecting portion 81a of the light detector 81 are set to be 170 μm in length in the vertical direction in FIG.
The dimensions of b and 81c are set to a vertical length of 2915 μm and a width of 6
000 μm, the size of the photodetector 82 a of the photodetector 82 is 432 μm in length in the vertical direction, 6000 μm in width,
The dimensions of 2b and 82c are 2784 μm in length in the vertical direction and 6000 μm in width, and the ratio between the length in the vertical direction of the light detection unit 81a and the length in the vertical direction of the light detection unit 82a is equal to the ratio of the distance L1 to the distance L2. I let it.

FIG. 8A shows a focus error signal when an objective lens having a focal length of 20 mm and a pupil diameter of 12 mm is used as the objective lens 2 of the microscope at this time. FIG.
In (a), the horizontal axis indicates the position of the test object surface 23 and the focal position is 0, and the vertical axis indicates the intensity of the focus error signal.

On the other hand, in the above configuration, as in the prior art,
L1 is 6000 μm, L2 is 6000 μm, and the distance L
1 and L2 are made equal to each other, and the light detector 81a of the light detector 81 is
The dimensions of the vertical direction length 262μm, width 6000μm,
The length of the vertical direction of the light detecting portions 81b and 81c is 286.
9 μm, width 6000 μm, photodetector 82 of photodetector 82
The dimension of a is 262 μm in length in the vertical direction and 6000 μm in width.
m, the size of the light detection units 82b and 82c is
869 μm and 6000 μm in width, the photodetectors 81a,
FIG. 8B shows a focus error signal when the length of the vertical direction 82a is made equal. Note that an objective lens having a focal length of 20 mm and a pupil diameter of 12 mm was used as the objective lens 2.

The focus error signal shown in FIG. 8B has an asymmetric shape with a different focusing range between the positive side and the negative side of the focal position, whereas the focus error signal shown in FIG. It can be seen that the focusing range is the same on the negative side and the symmetrical shape.

The above L1 was 4000 μm and L2 was 100
The reason why the thickness is set to 00 μm is the same as that in the first embodiment, and a description thereof will be omitted.

In FIG. 5 of the second embodiment, the object 2
4 irradiates a linear image that is long in one direction on the surface 23 to be inspected, so that even if a part of the linear image is applied to a step portion of the surface to be inspected, a normal focus error occurs in other portions. A signal can be obtained. Therefore, even when there is a step on the surface 23 to be inspected, the focus error signal is less likely to be affected by the step, so that the focus error signal is suitable as an autofocus optical system of a microscope for observing the object 24 having a step.

Further, in the configuration of FIG.
Although a linear image is formed by 0, the light emitted from the light source 13 is condensed by a cylindrical lens,
Similar effects can be obtained by forming a linear image at the position of the slit 80 in FIG. In this case, the slit 80 becomes unnecessary.

Next, a third embodiment of the present invention will be described with reference to FIG. The third embodiment is an embodiment using the present invention for a displacement measuring device.

In the displacement measuring apparatus shown in FIG. 9 according to the third embodiment, the illumination optical system, the observation optical system, the dichroic mirror 7, and the stage 25 are removed from the microscope equipped with the focus detection device according to the first embodiment. Things. Other configurations are the same as those of the focus detection device according to the first embodiment.

In FIG. 9, the same parts as those in FIG. 1 are denoted by the same reference numerals.

The displacement measuring apparatus shown in FIG. 9 can measure the displacement of the surface 23 of the object 24 in the direction of the optical axis 1 from the magnitude of the focus error signal. The operation of each unit is the same as the focus detection operation of the first embodiment, and a description thereof will be omitted.

The displacement measuring apparatus shown in FIG. 9 can obtain a symmetrical focus error signal similarly to the autofocus optical system of the microscope shown in FIG. 1, and therefore can accurately detect the displacement.

In the first, second and third embodiments described above, a light emitting diode is used as the light source 13, but a semiconductor laser may be used.

Although a light source that emits infrared light is used as the light source 13, a visible light source may be used. When using a visible light source, a beam splitter is used instead of a dichroic mirror.

In the first embodiment, as the photodetectors 18, 19, etc., a semiconductor substrate having a detection region formed by doping impurities is used, but the photodetectors 18, 19 are used. For example, a CCD can be used. In that case, an appropriate signal processing circuit is required.

In the first embodiment, since the shape of the light spot is circular, the ratio of the diameter of the light detecting portion 18a to the diameter of the light detecting portion 19a is determined by the ratio of L1 to L2. However, the shape of the light detection unit can be freely set according to the light spot diameter. In this case, the ratio between the area of the light receiving surface of the light detecting unit 18a and the area of the light receiving surface of the light detecting unit 18b is set to be equal to the ratio between L1 and L2.

[0074]

As described above, according to the present invention, there is provided focus detection means which has a wide range in which focus can be detected and which has a symmetrical shape of the focus error signal on the positive side and the negative side with respect to the focus position. Can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a schematic configuration of a microscope with a focus detection device according to a first embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of a photodetector of a photodetector of the microscope with a focus detection device according to the first embodiment of the present invention.

FIG. 3A is a graph showing a focus error signal obtained by a microscope with a focus detection device according to the first embodiment of the present invention. (B) A graph showing a focus error signal when L1 and L2 are set to conventional settings in the microscope with a focus detection device according to the first embodiment.

FIG. 4 is a graph showing a relationship between a position of a test surface and a position of a converging point of a condenser lens of the microscope with a focus detection device according to the first embodiment of the present invention.

FIG. 5 is a block diagram illustrating a schematic configuration of a microscope with a focus detection device according to a second embodiment of the present invention.

FIG. 6 is a block diagram illustrating a configuration of a photodetector of a photodetector of a microscope with a focus detection device according to a second embodiment of the present invention.

FIG. 7 is a front view of a slit used in a microscope with a focus detection device according to a second embodiment of the present invention.

FIG. 8A is a graph showing a focus error signal obtained by a microscope with a focus detection device according to the second embodiment of the present invention. (B) is a graph showing a focus error signal when L1 and L2 are set to conventional settings in the microscope with a focus detection device according to the second embodiment.

FIG. 9 is a block diagram showing a schematic configuration of a displacement measuring device according to a third embodiment of the present invention.

FIG. 10 is a block diagram showing a schematic configuration of a conventional microscope with a focus detection device.

FIG. 11 is a block diagram showing a configuration of a photodetector of a photodetector of a conventional microscope with a focus detection device.

FIG. 12 is a test surface 2 of the microscope with the focus detection device of FIG. 1;
3, objective lens 2, condenser lens 16, convergence points 20, 21
Explanatory drawing which shows the positional relationship of.

[Explanation of symbols]

2, 102 Objective lens 7, 107 Dichroic mirror 13, 113 Light source 14, 114 Collimator lens 16, 116 Condenser lens 15, 17, 115, 117 Beam splitter 18, 19, 81, 82, 118, 119 Photodetector 18a, 18b, 19a, 19b, 81a, 81b, 8
1c, 82a, 82b, 82c, 118a, 118b,
119a, 119b Photodetector 23, 123 Surface 24, 124 Object 25, 125 Stage 26, 126 Controller 29, 30, 31, 83, 84, 85, 86, 87, 1
29, 130, 131 Operational amplifier 37, 38, 132, 133 Light spot 80 Slit

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI G03B 3/00 A

Claims (6)

[Claims] A stage for mounting a test object; an observation optical system including an objective lens for observing the test object; and a position shift of the test object from a focal position of the objective lens. A focus detection means for detecting, the focus detection means, an illumination optical system for irradiating the test object with illumination light through the objective lens, and reflected light flux of the illumination light from the test object A condensing optical system for converging, a splitting unit for splitting the reflected light beam into first and second light beams, and first and second detection units for detecting the first and second light beams, respectively. Calculating means for calculating a focus error signal by calculating detection results of the first and second detection units, wherein the first and second detection units are respectively configured to output the first and second light beams. Of which, the luminous flux of the optical axis A first detection region for emitting light, and a second detection region for detecting a light beam outside the first detection region, wherein the calculating means includes a first detection region for the first detection region and a second detection region for detecting the light beam outside the first detection region. Calculating a difference between an output and an output of the second detection area, and further calculating a difference between a difference result of the first detection unit and a difference result of the second detection unit; The second detection unit is disposed at a position L1 away from the focusing optical system than the focusing position of the focusing optical system, and the second detection unit is closer to the focusing optical system by L2 than the focusing position of the focusing optical system. A microscope provided with focus detection means, wherein the distance L1 is set to be not equal to the distance L2. 2. A microscope provided with a focus detecting means according to claim 1, wherein the ratio of the area of the first detection area of the first detection section to the area of the first detection area of the second detection section is: Said L
A microscope equipped with focus detection means, wherein the ratio is equal to the ratio of 1 to L2. 3. In the microscope provided with the focus detecting means according to claim 1, when the focal length of the objective lens is f1, the first detecting unit determines that the object to be measured is f1-A (where When A is at a position of A> 0), the condensing optical system is disposed at a position of a convergence point at which the first light flux converges, and the second detection unit is configured to detect the target object. Is f
A microscope equipped with focus detection means, wherein the focusing optical system is arranged at a position of a convergence point where the second light flux converges at a position of 1 + A. 4. A microscope provided with a focus detecting means according to claim 1, wherein a distance between said objective lens and said object is a, and a distance between said converging optical system and its convergence point is c. The relationship between c and a obtained is c = G (a), the focal length of the objective lens is f1, and the focal length of the condensing optical system is f
When L2 is 2, L1 and L2 are f2 + L1 = G (f1-A), f2-L2 = G (f1 + A), where A is set to a value satisfying an arbitrary value of A> 0. A microscope provided with a focus detection means. 5. A microscope provided with a focus detecting means according to claim 1, wherein said illumination optical system irradiates light in which a light spot on said test object has a linear shape. The second detection unit includes a focus detection unit, wherein the first region has a linear shape. 6. An objective lens disposed at a position facing the object to be inspected, an illumination optical system for irradiating the object to be illuminated with illumination light through the objective lens, and the illumination light from the object to be inspected A converging optical system for converging the reflected light beam of
A dividing unit for dividing the reflected light beam into first and second light beams, a first and second detecting unit for detecting the first and second light beams, respectively, and a first and a second detecting unit. Calculating means for calculating a focus error signal by calculating a detection result, wherein the first and second detectors respectively detect a light flux of an optical axis portion among the first and second light fluxes And a second detection area for detecting a light beam outside the first detection area for the first and second detection units, wherein the calculation unit outputs an output of the first detection area for each of the first and second detection units. A means for obtaining a difference from an output of the second detection area, and further obtaining a difference between a difference result of the first detection unit and a difference result of the second detection unit; The focus position of the optical system rather than the focal position of the optical system L2, the second detection unit is disposed at a position closer to the light-collecting optical system by L2 than the focal position of the light-collecting optical system, and L1 is not equal to L2. A displacement measuring device characterized by being set to a distance.