JP2001318302A - Focus detecting device and autofocusing microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a focus detecting device and an autofocusing microscope by which the position of a sample surface is highly accurately and easily detected even though the sample has unevenness on its surface and which are easily assembled. SOLUTION: The detecting device and the microscope possess one-dimensional light sources 31, 32 and 33 whose point light sources are arrayed in one direction, focus detecting optical systems 15 and 16 to project the image of the one-dimensional light source on the sample surface and to project the image of the one-dimensional light source projected on the sample surface to an image formation surface and an aperture 35 arrayed in accordance with each point light source of the one-dimensional light source projected on the image formation surface, and are provided with a one-dimensional aperture 34 arranged so as to be tilted to the image formation surface, a one-dimensional photodetector 36 to detect light passing through each aperture of the one-dimensional aperture and a signal processor 37 to detect the position of the sample surface in the optical axis direction of the focus detecting optical system by processing the output of the one-dimensional photodetector.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus detecting device for detecting a surface position (displacement in a direction perpendicular to the surface) of a flat plate such as a wafer, and an automatic focus microscope using the same, and more particularly to a circuit pattern formed on the surface. The present invention relates to a focus detection device capable of detecting a surface position with high accuracy even on a surface having fine irregularities, such as a semiconductor wafer, and an automatic focus microscope using the same. 2. Description of the Related Art Various methods have been proposed for a focus detection device in an optical device such as an optical microscope and an automatic focusing device (autofocus mechanism: AF mechanism) using the same. For example, as an AF mechanism in an optical recording / reproducing device such as a CD player or an automatic focusing device of a microscope, an astigmatism method or a knife edge method is used. The present invention relates to a focus detection device using the principle of a confocal microscope.

[0002]

2. Description of the Related Art FIG. 1 is a diagram for explaining a focus detection device using the principle of a confocal microscope. As shown in FIG. 1A, the light source 11 illuminates the pinhole 13 of the aperture plate 12, so that the pinhole 13 becomes a point light source. Light radiated from the pinhole 13 is converged on the surface of the sample 100 by an optical system including a collimator lens 14, a half mirror 15, and a projection lens (objective lens) 16, as shown by a solid line.
3 is formed as a point image on the surface of the sample 100.
This point image has a size obtained by multiplying the size of the pinhole 13 by the projection magnification of the optical system in a focused state, and the light intensity at the center becomes large. When deviated from the focal position, the point image becomes blurred and large, and the light intensity at the center decreases.

When the surface of the sample 100 is rough, a point image on the surface of the sample 100 serves as a secondary light source, and the sample surface 10
A new point light source is formed on the surface of the sample 100. Here, it is assumed that the size of the point image on the surface of the sample 100 is sufficiently smaller than the roughness of the surface, and that a position symmetrical to or on the surface is assumed. The following description is based on the assumption that a point light source is formed. The light forming the point image is reflected by the surface of the sample 100 and is reflected by the projection lens 1.
6. The optical system constituted by the half mirror 15 and the converging lens 17 converges on the pinhole 19 of the aperture plate 18 to form a point image. In the focused state, the light reflected on the surface of the sample 100 is converged on the pinhole 19 as shown by the solid line, and most of the light passes through the pinhole 19 and enters the light receiving element 20. , The light receiving element 20 outputs a large detection signal. When the surface of the sample 100 shifts from the focal position, the light reflected on the surface of the sample 100 converges on the position shifted from the aperture plate 18. As shown by the broken line, when the sample 100 is shifted in a direction away from the optical system, the light reflected on the surface of the sample 100 is converged in front of the aperture plate 18 and then enters the aperture plate 18 in a spread state. When the sample 100 shifts in the direction approaching the optical system, the light reflected on the surface of the sample 100 is converged behind the aperture plate 18 and is incident on the aperture plate 18 before being converged.

In any case, since the light does not converge on the pinhole 19, the amount of light passing through the pinhole 19 and entering the light receiving element 20 decreases, and the detection signal of the light receiving element 20 decreases. The amount of light passing through the pinhole 19 decreases according to the deviation from the focal position on the surface of the sample 100, and changes as shown in FIG. Therefore, if the characteristics shown in FIG. 1B are measured and stored in advance, the amount of deviation from the focal position can be detected from the detection signal of the light receiving element 20. In FIGS. 1 and 2, light from the pinhole on the light source side is projected onto the sample surface via the collimator lens and the projection lens, and the reflected light is converged on the light receiving side pinhole by the projection lens and the converging lens. Although a configuration example is shown, a configuration that does not use a collimator lens and a converging lens is also used.

However, in the signal shown in FIG. 1B, it is not possible to determine in the positive and negative directions, that is, whether the surface of the sample 100 has approached or separated from the optical system, and the surface state of the sample 100 on which a point image is formed. There is a problem that the amount of light reflected by the light varies. Therefore, as shown in FIG. 2A, a half mirror 21 is provided behind the converging lens 17 to divide the converged light beam into two, and an aperture plate having a pinhole 23 for one light beam. 22 is provided on the front side of the focal position, and for the other light beam, an aperture plate 25 having a pinhole 26 is provided on the rear side of the focal position.
The detection signal F of the light receiving element 24 for detecting the light passing through the pinhole 23 and the detection signal R of the light receiving element 27 for detecting the light passing through the pinhole 26 are shown in FIG. (B). Therefore, 2
While the two detection signals F and R reach their maximum values, 2
The ratio R / F between the two detection signals F and R simply increases as shown in FIG. Therefore, it can be seen from the ratio R / F in which direction and how much the focus position is shifted. Also, since the ratio of light reflected by the same part of the sample is determined,
It is less affected by the reflection state of the surface of the sample.

Various focus detecting devices using the principle of the confocal microscope as described above are disclosed in Japanese Patent Application Laid-Open No. Hei 4-3508.
No. 18, JP-A-5-232370, JP-A-Hei-6
-51206, JP-A-7-174962,
JP-A-8-43717, JP-A-8-178623
JP, JP-A-8-220418 and JP-A-9-220418
Since it is disclosed in -325277 and the like, further detailed description is omitted here.

[0007]

In the semiconductor manufacturing process,
Semiconductor chips are formed by forming various layers of various circuit patterns on the surface of a semiconductor wafer. In a process in the middle or the final process, quality control is performed by examining a defect or the like of a formed pattern and feeding back information on the defect. For this purpose, an optical microscope is widely used.
In such an optical microscope, an operator sometimes looks at an optical image with the naked eye. However, the optical image is converted into an image signal by a TV camera or a line sensor, and the image signal is processed to determine whether there is a defect or the like. Is common. In particular, a highly integrated semiconductor wafer needs to generate a high-resolution image signal, and a high-integration line sensor scans to obtain a high-resolution image signal. Scanning is usually performed by moving a sample placed on a stage at a constant speed.

In the focus detection devices shown in FIGS. 1 and 2 and the focus detection devices disclosed in the above-mentioned known examples, an image of a small pinhole is projected on the surface of the sample. There is one image. Further, JP-A-7-17496
In the automatic focusing device disclosed in Japanese Patent Application Laid-open No. 2 (1999) -1995, the shape of the pinhole on the light source side is made elliptical or rectangular, and by using a line sensor as a light receiving element, accurate and quick focusing can be achieved even if the imaging position shifts. Although a configuration for focusing is disclosed, the point image projected on the sample surface is elliptical or rectangular but one. FIG. 3 shows how a point image is projected when a semiconductor wafer is used as a sample.
01 indicates a light beam converged on the surface of the sample 100. In the case where the sample is a semiconductor wafer, as shown in the figure, the surface has irregularities of the same size as the point image, and the focus state changes greatly at the position where the point image is formed. For this reason, the convergence state of the point image, that is, the detection signal greatly changes only by moving the sample by a very small amount, and it is difficult to detect a stable focus position, and it is difficult to perform good focusing control accordingly. There was a problem.

In the configuration shown in FIG.
It is necessary to precisely arrange the two pinholes 23 and 26 so as to correspond to the same point on the sample surface. If the pinholes 23 and 26 deviate, the light intensity of a different portion of the converged point image will be detected, and a detection error will occur. . Therefore, there has been a problem that high-precision positioning is required, and assembly of the device is complicated. In the automatic focusing device disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 7-174962, the influence of the displacement is reduced, but two or four line sensors are used. It was necessary to adjust them one by one, and the assembly of the device was complicated.

The present invention is intended to solve such a problem. Even if the surface of the sample has irregularities, the position of the surface of the sample can be detected with high precision and easily, and the focus can be easily assembled. An object of the present invention is to realize a detection device and an autofocus microscope using the same.

[0011]

In order to achieve the above object, a focus detecting apparatus according to the present invention comprises a one-dimensional light source in which point light sources are arranged in one direction instead of a point light source, and a one-dimensional light source instead of a pinhole. Is used, and the one-dimensional light source and the one-dimensional aperture are arranged obliquely from the imaging plane. That is, the central point light source of the one-dimensional light source and the central aperture of the one-dimensional aperture have an imaging relationship when the sample surface is at the focal position, and the point light sources on both sides of the one-dimensional light source and the apertures on both sides of the one-dimensional aperture are formed. Are in an image forming relationship when the sample surface deviates from the focal position. One or both of the one-dimensional light source and the one-dimensional aperture are tilted.

That is, the focus detection device of the present invention comprises a one-dimensional light source in which point light sources are arranged in one direction, an image of the one-dimensional light source projected on the sample surface, and a one-dimensional light source projected on the sample surface. It has a focus detection optical system that projects an image on the image plane, and apertures that are arranged corresponding to each point light source of the one-dimensional light source projected on the image plane, and are arranged inclined with respect to the image plane. A one-dimensional aperture, a one-dimensional photodetector that detects light passing through each of the one-dimensional apertures, and a position in the optical axis direction of the focus detection optical system on the sample surface by processing an output of the one-dimensional photodetector. And a signal processing device for detecting

According to the focus detecting device of the present invention, a one-dimensional light source is used instead of a point light source and a one-dimensional aperture is used instead of a pinhole. Therefore, if the detection signal output from the one-dimensional photodetector is processed, Focus positions for a plurality of positions on the sample are continuously determined. Further, the one-dimensional light source and the one-dimensional aperture are arranged at an angle from the image plane, and the point light sources and the apertures on both sides have an image-forming relationship when the sample surface is shifted from the focal position. Thus, when the sample surface is located between them, one of the point light sources and the aperture is in an image forming relationship, and the output thereof is increased. Therefore, if the position at which the output of the one-dimensional photodetector is maximized is detected, the focal position can be determined.

More specifically, the calculation in the signal processing device is performed, for example, by storing the waveform of the intensity signal group in a state in which the focus is in advance as a template, and comparing the correlation with the waveform of the intensity signal group at that time. Then, the shift amount having the highest correlation is calculated. In addition, calculating the envelope of the intensity signal of the light that has passed through each aperture output by the one-dimensional photodetector and detecting the position of the sample surface in the optical axis direction of the focus detection optical system from the maximum intensity position of the envelope. Is also possible. Furthermore, a low-pass filter process for extracting only low-frequency components of the intensity signal group may be performed to determine the maximum intensity position. The low-pass filter processing can be performed by digital processing or analog processing.

If each point light source of the one-dimensional light source is a slit group in which a plurality of slits extending in a direction perpendicular to the arrangement direction are arranged apart from each other, the alignment between the one-dimensional light source and the one-dimensional photodetector is extremely improved. It will be easier. It is also possible to arrange the point light sources of the one-dimensional light source very densely, that is, to make the one-dimensional light source a straight slit and illuminate the slit from the back.

It is also possible to use a one-dimensional image sensor as the one-dimensional light detector. In a one-dimensional image sensor, light receiving elements having fine light receiving areas are linearly arranged, and the light receiving areas of the respective light receiving elements function as apertures. It is also possible to use a two-dimensional image sensor as the one-dimensional photodetector. In this case, the light receiving area of each light receiving cell of the two-dimensional image sensor functions as each aperture of the one-dimensional aperture. By using a two-dimensional image sensor, the alignment between the one-dimensional light source and the image sensor becomes unnecessary.

The image of the one-dimensional light source projected on the two-dimensional image sensor has a narrow width at the portion corresponding to the focal position, and the central intensity increases, and the central intensity increases in both directions away from the focal position and decreases. . If the relationship between the position of the one-dimensional light source and the optical system is fixed, the line at which the intensity of the image of the one-dimensional light source projected on the two-dimensional image sensor becomes maximum is also fixed. Therefore, only the signal at this line position of the two-dimensional image sensor needs to be processed. If the line position is not detected and stored in advance, the line position is obtained from the output of the two-dimensional image sensor, and the output of the line position is processed.

If the above-described focus detection device is used for an autofocus mechanism of an autofocus microscope, the position of the sample surface can be easily detected with high accuracy even for a semiconductor wafer having an uneven surface. Focus adjustment can be performed appropriately.
That is, the autofocus microscope of the present invention includes a stage for holding a sample, an illuminating device, a half mirror, and irradiating the illumination light from the illuminating device onto the sample surface via the half mirror and half-shifting the image of the sample surface. An imaging optical system for projecting onto a projection surface via a mirror, an imaging device arranged so that the imaging surface is located on the projection surface, and an optical axis direction position of the imaging optical system with respect to the sample surface to detect the position of the sample surface. An autofocus microscope that includes a stage and an autofocus mechanism that adjusts a relative position of the imaging optical system in the optical axis direction so that an image is formed on a projection surface.The autofocus mechanism includes the focus detection device described above. The relative position of the stage and the imaging optical system in the optical axis direction is adjusted according to the position in the optical axis direction of the focus detection optical system on the sample surface detected by the focus detection device.

The optical coupling between the imaging optical system and the focus detection optical system of the autofocus mechanism is performed in the same manner as in the above-mentioned known example.
What is necessary is just to provide a 2nd half mirror further. Further, in the autofocus mechanism, a third optical path for separating an optical path for projecting the image of the one-dimensional light source on the sample surface and an optical path for imaging the image of the one-dimensional light source projected on the sample surface on the imaging surface is provided. A half mirror is provided. This makes it possible to project the image of the one-dimensional light source into the imaging range on the sample surface. In this case, it is desirable that the imaging device has no sensitivity to light emitted from the one-dimensional light source so that the image of the one-dimensional light source does not affect the image signal of the imaging device.

Further, the focus detection optical system and the imaging optical system can be used in common without providing the second half mirror, and the one-dimensional light source can be projected outside the imaging range of the imaging device on the sample surface. is there. In this case, the one-dimensional light source is realized by an illumination device for imaging that illuminates a pinhole row, a slit row, or a linear slit from the back. As a result, the focus detection optical system and the imaging optical system have the same wavelength characteristics.

[0021]

FIG. 4 is a diagram showing the configuration of a focus detection device according to a first embodiment of the present invention. This embodiment is different from the embodiment shown in FIG. 1 in that a collimator lens and a converging lens are not used. The illumination device 31 illuminates a first aperture plate 32 having a plurality of pinholes 33 arranged linearly. As a result, light is emitted from the plurality of pinholes 33 to form a one-dimensional light source in which point light sources are arranged in one direction. Although nine pinholes 33 are shown, it is assumed that a large number of pinholes are actually arranged. The first aperture plate 32 is arranged perpendicular to the optical axis. Light from each pinhole 33 is reflected by the half mirror 15, enters the objective lens 16, and is projected on the surface of the sample 100. The light reflected on the surface is converged by the objective lens 16, passes through the half mirror 15, and forms an image on the second aperture plate 34 having the plurality of pinholes 35. The images of the plurality of pinholes 33 are formed at positions corresponding to the plurality of pinholes 35, respectively.
It is arranged to be inclined. Here, when the surface of the sample 100 is at the focal position, the image of the center pinhole in the row of the plurality of pinholes 33 is formed on the central pinhole in the row of the plurality of pinholes 35. The pinholes on one side of the row of the plurality of pinholes 35
When the image of the corresponding pinholes in the row of the plurality of pinholes 33 is formed when the surface of the pinhole 00 approaches the objective lens, the pinhole on the other side of the row of the plurality of pinholes 35 is When the surface of the sample 100 is separated from the objective lens, it is arranged at a position where an image of the corresponding pinhole in the row of the plurality of pinholes 33 is formed. Multiple pinholes 3
Behind the fifth row, a plurality of light receiving elements 36 are arranged so as to respectively receive the light passing through each pinhole. The detection signal of each light receiving element 36 is sent to a signal processing circuit 37 for processing.

FIG. 5 is a diagram showing an output example of a plurality of light receiving elements 36 according to the positional relationship between the image of the surface of the sample 100 and the surface of the second aperture plate 34. As shown in FIG. 5A, there are two plane portions having different heights on the sample surface, and the surface of the second aperture plate 34 is inclined with respect to the plane to be projected as shown in FIG. The surface of the second aperture plate 34 coincides with one plane at the position P and coincides with the other plane at the position Q. Therefore, as shown in FIG. 5B, the outputs of the plurality of light receiving elements 36 have distributions in which the outputs increase at the positions corresponding to P and Q, respectively. When the sample surface moves in the optical axis direction, the center of this distribution moves to the positions of P 'and Q'.

As shown in FIG. 5C, it is assumed that the surface of the sample 100 has small periodic irregularities. It is assumed that the step of the unevenness is the same as the step of the two planes in FIG. In this case, the surface of the second aperture plate 34
At the position of P, the height of the concave portion of the sample surface coincides with the height, and at the position of Q, the height of the convex portion of the sample surface coincides with the height. Therefore, P and Q
The output of the light receiving element corresponding to the position is increased. However, the portion where the sample surface adjacent to P is convex and the portion where the sample surface adjacent to Q is concave are out of focus, so that the output of the corresponding light receiving element is small. As described above, the outputs of the plurality of light receiving elements 36 change drastically with the pitch of the unevenness,
If you capture the entire change in the signal, it will change smoothly. In order to capture the entire change of the signal, for example, the envelope may be taken, and if the envelope is taken, the distribution shown in FIG. 5B is obtained.

Therefore, the signal processing circuit 37 is connected to each light receiving element 3
The surface position of the sample 100 can be calculated by calculating the envelope of the intensity from the detection signal of No. 6 and calculating the center position.
As described above, according to the present invention, it is possible to accurately determine the focal position even if the surface of the sample has fine irregularities. FIG. 6 is a diagram showing the configuration of the automatic focusing microscope according to the second embodiment of the present invention. As shown, this embodiment also does not use a collimator lens and a converging lens. In the automatic focusing microscope of this embodiment, the sample 100 is placed on a stage 102 that can move in three XYZ directions and that can rotate the mounting surface. The stage controller 95 controls the stage 10
2 movement in the XY plane and movement in the Z-axis direction (focus adjustment)
I do. The portion including the illumination device 83, the half mirror 82, the objective lens 81, and the imaging device 87 is an optical microscope similar to the conventional one. In FIG. 6, reference numeral 84 is an area corresponding to an imaging range on a conjugate plane on the illumination side of the imaging plane. This area is projected on the surface of the sample 100 at a position indicated by reference numeral 90. In the second embodiment, an aperture plate 91 having a slit row 92 is arranged outside the region 84. The aperture plate 91 is illuminated by the illumination device 83, and an image of the slit row 92 is projected on an area indicated by reference numeral 97 on the sample surface, and the image is projected beside the imaging device 87. One-dimensional image sensor 93 in which this image is inclined by θ with respect to the imaging surface
Caught in As described later, the one-dimensional image sensor 9
Since each light receiving element of No. 3 has a predetermined small light receiving area,
It functions in the same way as the pinhole 35 in FIG. 4 and the light receiving element 36 that converts light passing through each pinhole into an electric signal. The one-dimensional image sensor 93 continuously outputs the output of each light receiving element at a predetermined cycle. This continuous output is called a channel output. The channel output of the one-dimensional image sensor 93 is sent to a signal processing device 94 for processing.
A focus state is detected.

FIG. 7 is a view showing a slit row 92 according to the second embodiment. As shown, a plurality of slits 92A extending in one direction are arranged apart. When deviating from the focus state, the image of each slit is blurred, and the degree of the blur is detected by the one-dimensional image sensor 93. Therefore, in order to improve the detection accuracy of the focus state, when the deviation from the focus state is within a predetermined range, the slits are distorted. It is necessary that the images do not affect each other.
The one-dimensional image sensor 93 has such a slit array 9.
Since two images are detected, a similar output can be obtained even if the position is shifted by the length of each slit 92A. Therefore, the allowable range of the alignment between the slit row 92 and the one-dimensional image sensor 93 is the length of each slit 92A, and the alignment is very easy.

Next, processing of the channel output of the one-dimensional image sensor 93 in the signal processing device 94 of the second embodiment will be described. In the first embodiment, the central position of the output envelope of each light receiving element is calculated by calculating the envelope. In the second embodiment, it is also possible to detect the focus state by calculating the envelope in the same manner. Here, the reference channel output in the focused state is detected in advance and stored as template data. The channel output at the time is compared with the template data to calculate the difference between the center positions. FIG. 8 is a diagram illustrating this calculation process.

As shown in FIG. 8A, the channel output of the one-dimensional image sensor 93 is stored as template data in a focused state. In order to perform such storage, after the channel output is A / D converted,
Store in memory. Next, it is assumed that the channel output is shifted as shown in FIG. Here, when the correlation value C (x) is calculated based on the equation as shown in FIG. 8C, the correlation value C (x) changes as shown in FIG. 8D. Therefore, the correlation value C
If xmax that maximizes (x) is obtained, it corresponds to a shift of the focal position.

Various modifications of the channel output processing in the signal processing device 94 are possible. FIG. 9 is a diagram illustrating a modified example. As shown in FIG.
A low-pass filter 98 for removing high-frequency components of the channel output of the one-dimensional image sensor 93 is provided, and the output is input to a signal processing circuit 94. The channel output is shown in FIG.
As shown in (B) of FIG.
In the portion corresponding to No. 2, the height is high, and in the portion between them, it is low, and so on, at a period corresponding to the arrangement pitch of the slits 92. When high-frequency components are removed by filtering with the low-pass filter 98, the channel output becomes a signal that changes smoothly. The peak of this signal corresponds to the focal position.

In the second embodiment, since the same light is used in the imaging system and the focus detection system, no detection error occurs due to different wavelengths of the light used. However, detecting the focal position is outside the imaging range. For example, in a microscope that converts an optical image into an electrical image signal and outputs it, in order to obtain a high-resolution image signal, a one-dimensional image sensor is used to move the sample on the stage in the direction in which the one-dimensional image sensor extends. Generally, a two-dimensional image signal is generated by moving the image signal in a vertical direction. In this case, since the width of the imaging range is narrow, it is possible to project a slit for focus detection at a position near the optical axis of the sample surface outside the imaging range.

FIG. 10 is a diagram showing a configuration of an automatic focusing microscope according to a third embodiment of the present invention. As shown, this embodiment uses a collimator lens and a converging lens. In the autofocus microscope of this embodiment, the sample 100 is an XYZ 3
Stage 1 that can move in the axial direction and that can rotate the load surface
02. Illumination light from the light source 41 enters the objective lens 44 through the collimator lens 42 and the half mirror 43 and illuminates the imaging range on the surface of the sample 100 uniformly. The light reflected on the sample surface is
4. The image is projected onto the imaging surface of the imaging device 48 through the half mirrors 43 and 45, the return mirror 46, and the projection lens 47, and an image of the sample surface is formed on the imaging surface. Imaging device 48
Converts an image of the sample surface into an electric signal and outputs it as an image signal.

Reference numerals 51 to 57 are parts constituting a focus detection device, and the stage 102 is moved in the Z-axis (optical axis) direction in accordance with a detection signal of the focus detection device, and a good image signal is always obtained. An auto-focus mechanism for performing adjustment is configured. The illumination device 51 of the focus detection device illuminates an aperture plate 52 having a linear slit 58 as shown in FIG. This forms a one-dimensional light source that extends linearly in one direction. The aperture plate 52
Is provided perpendicular to the optical axis. The light emitted from the slit 58 is converged on the surface of the sample 100 via the collimator lens 53, the half mirror 54, the half mirrors 45 and 43, and the objective lens 44,
The image of the slit 58 is projected on the surface of the 00. In addition,
The imaging device 48 emits the sample 100
Is insensitive to the wavelength of the light projected on the surface of the half mirror 45, and the half mirror 45 has such a characteristic that the wavelength of the light radiated from the slit 58 is transmitted but the other wavelengths are reflected. . A half mirror having such characteristics is realized by, for example, a multilayer coating.

The light projected from the slit 58 onto the surface of the sample 100 passes through the objective lens 44, the half mirrors 43, 45 and 54, and the projection lens 55 as shown in FIG. Converges to
An image 59 of the slit 58 is formed in this portion. As described above, since the aperture plate 52 is provided perpendicular to the optical axis, the image 59 of the slit 58 formed is perpendicular to the optical axis. As shown in FIG. 11, the one-dimensional image sensor 56 is arranged such that the rows 61 of the arranged light receiving elements 62 coincide with the image 59 of the slit 58 and the light receiving surface is inclined by θ with respect to the optical axis. .

The slit 58 can be regarded as a continuous arrangement of point light sources. Each of the light receiving elements 62 of the one-dimensional image sensor 56 has a predetermined small light receiving area as shown in FIG. Having. (Here, the light receiving area is a square light receiving area.) This light receiving area operates in the same manner as a pinhole, and the output of the light receiving element becomes large when the focus is in focus, but the output of the light receiving element becomes out of focus. Since the output decreases, an output as shown in FIGS. 5B and 5C is obtained. The output of the one-dimensional image sensor 56 is sent to the signal processing device 57, and the center position of the channel output is calculated as in the first embodiment or the second embodiment.

FIG. 13 is a diagram showing a configuration of a portion constituting a focus detecting device of an automatic focusing microscope according to a fourth embodiment of the present invention, and other portions are the same as those of the third embodiment. In the focus detection device according to the fourth embodiment, an aperture plate 71 having a slit 72 is arranged to be inclined with respect to the optical axis. The illumination device for the slit 72 is not shown. Further, instead of the one-dimensional image sensor 56 of the second embodiment, a two-dimensional image sensor 73 is arranged so that the imaging surface is perpendicular to the optical axis. Since the aperture plate 71 is arranged to be inclined with respect to the optical axis, as shown in FIG. 13, the image 74 of the slit 72 is formed to be inclined with respect to the optical axis.

FIG. 14A is a perspective view showing an image 74 of the slit 72 projected on the imaging surface of the two-dimensional image sensor 73, and FIG. 14B is a top view, and FIG.
4 (C) is an output signal Si of the two-dimensional image sensor 73.
FIG. As shown in FIGS. 14A and 14B, the slit image 74 is inclined with respect to the optical axis, and any part thereof coincides with the imaging surface of the two-dimensional image sensor 73. Here, it is assumed that the center portions match. Accordingly, the image 74 of the slit has the width of the slit at the center portion 77 and the light intensity is large, but the width gradually increases and shifts from the imaging surface toward the both ends, and the light intensity gradually decreases.

Here, as shown in FIG. 14B, when the position of the imaging surface of the two-dimensional image sensor 73 is represented by XY orthogonal coordinates, a line 75 in the Y-axis direction passing through the central portion 77 of the image 74 is obtained. The upper output changes as indicated by reference numeral 78 in FIG. When the position of the sample surface in the Z-axis direction is shifted and the value of the slit image 74 corresponding to the imaging surface of the two-dimensional image sensor 73 changes, the output on the line 75 of the two-dimensional image sensor 73 is denoted by reference numeral 79. Move as shown. Therefore, by detecting the movement amount of the position where the light intensity becomes the highest, the position shift of the sample surface can be detected.
The signal processing device performs this processing by processing the output of the two-dimensional image sensor.

FIG. 14 shows a case where the sample surface is flat. If the sample surface has irregularities, the output of the two-dimensional image sensor 73 changes accordingly. As in the example, the two-dimensional image sensor 7
Then, the envelope and the correlation value of the output of No. 3 are calculated, and then the center position is calculated. If the relationship between the position of the slit 72, the optical system, and the two-dimensional image sensor 73 is fixed, the center 77 of the slit image 73 projected on the two-dimensional image sensor is always located on the line 75. Therefore, the position (Y coordinate) of the line 75 is detected and stored in advance,
During operation of the apparatus, only the signal at this line position of the two-dimensional image sensor 73 is read and processed. This allows
As compared with the case where the X coordinate of the two-dimensional image sensor 73 is changed as usual and the image signal of the entire image pickup surface is read, the cycle of reading the image signal on the line 75 can be greatly shortened.

In the case of using a one-dimensional image sensor in which light receiving elements are linearly arranged as in the first and second embodiments, it is necessary to align the position of the one-dimensional image sensor with the image of the slit and tilt the image sensor. Yes, alignment work was required. On the other hand, in the third embodiment, after the two-dimensional image sensor 73 is disposed, the image of the slit is projected, and the center position is obtained from the image signal of the entire surface of the two-dimensional image sensor 73 and stored. Alignment work is unnecessary.

When there is a possibility that the position of the line 75 may change, the processing device detects the position of the line 75 from the output of the two-dimensional image sensor, processes the output of the line, and processes the output of the line to determine the center position. Detect the amount of movement. The detection of the position of the line 75 is performed, for example, by calculating the sum of the signal intensities for each line and determining the line having the maximum signal intensity. In addition, since the calculation time is long when the calculation is performed for all the lines, for example, only the first line is checked, the line including the center position is calculated, and the next line is calculated only for a few lines in the X-axis direction of the previous line. Read and process image signals.

In the third and fourth embodiments, the image pickup apparatus has no sensitivity to light forming an image of the slit irradiated on the sample surface for focus detection, and the image pickup range of the sample surface is adjusted. By projecting the image of the slit substantially at the center, the focus at the substantially center of the imaging range is detected. FIG. 15 is a diagram showing a configuration of an automatic focusing microscope according to a fifth embodiment of the present invention.
The portion including the illumination device 83, the half mirror 82, the objective lens 81, and the imaging device 87 is an optical microscope similar to the conventional one. The stage is not shown. In FIG. 15, reference numeral 84 is an area corresponding to an imaging range on a conjugate plane on the illumination side of the imaging plane. This area is Sample 1
The image is projected onto the surface of the surface 00 at a position indicated by reference numeral 90. In the fifth embodiment, an aperture plate 85 having a slit 86 is arranged outside a region 84. The aperture plate 85 is illuminated by the illumination device 83, and an image of the slit 86 is projected on an area indicated by reference numeral 91 on the sample surface, and the image is projected beside the imaging device 87.

The image pickup device 87 actually occupies an area around the image pickup surface, and it is not possible to arrange a one-dimensional image sensor in that area. Therefore, as shown in the figure, a folding mirror 88 is arranged in the middle of the optical path where the area 91 is projected, and the position where the area 91 is projected is moved to a place different from the imaging surface, and the one-dimensional image sensor is 89 is inclined with respect to the optical axis by θ. The rest is the same as in the other embodiments.

In the third and fourth embodiments, there is a problem that a detection error occurs because the wavelengths of light used in the imaging system and the focus detection system are different. In the fifth embodiment, the same light is used in the imaging system and the focus detection system as in the second embodiment, so that no detection error occurs due to different wavelengths of light used. However, detecting the focal position is outside the imaging range.

[0043]

As described above, according to the present invention,
Even with a sample having an uneven surface, a focus detection device that can easily and accurately detect the position of the sample surface and can be easily assembled, and an autofocus microscope using the same can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a focus detection device using the principle of a confocal microscope.

FIG. 2 is a diagram illustrating another example of a focus detection device using the principle of a confocal microscope.

FIG. 3 is a diagram for explaining a state in which a beam for focus detection is irradiated on a surface having irregularities such as a semiconductor wafer.

FIG. 4 is a diagram illustrating a configuration of a focus detection device according to a first embodiment of the present invention.

FIG. 5 is a diagram illustrating a change in an output signal of a light receiving element according to a focus state in the first embodiment.

FIG. 6 is a diagram showing a configuration of an automatic focusing microscope according to a second embodiment of the present invention.

FIG. 7 is a diagram showing a slit array for focus detection in a second embodiment.

FIG. 8 is a diagram illustrating signal processing of a one-dimensional image sensor according to a second embodiment.

FIG. 9 is a diagram illustrating another example of signal processing of the one-dimensional image sensor.

FIG. 10 is a diagram showing a configuration of an automatic focusing microscope according to a third embodiment of the present invention.

FIG. 11 is a diagram showing a positional relationship between an aperture on a one-dimensional light source side and a one-dimensional image sensor in a third embodiment.

FIG. 12 is a diagram illustrating a one-dimensional image sensor according to a third embodiment.

FIG. 13 is a diagram showing a positional relationship between an aperture on a one-dimensional light source side and a one-dimensional image sensor in an automatic focusing microscope according to a fourth embodiment of the present invention.

FIG. 14 is a diagram showing a sensor output of a slit image projected on a two-dimensional image sensor in a fourth embodiment.

FIG. 15 is a diagram showing a configuration of an automatic focusing microscope according to a fifth embodiment of the present invention.

[Explanation of symbols]

 15 Half mirror 16 Objective lens 31 Illumination device 32 First aperture plate 33 Pinhole array 34 Second aperture plate 35 Pinhole array 36 Light receiving element 37 Signal processing device

Claims (14)

[Claims] 1. A one-dimensional light source in which point light sources are arranged in one direction, an image of the one-dimensional light source is projected on a sample surface, and an image of the one-dimensional light source projected on the sample surface is formed. A focus detection optical system that projects onto a surface, and an aperture that is arranged corresponding to each point light source of the one-dimensional light source that is projected onto the imaging surface, and is arranged to be inclined with respect to the imaging surface A one-dimensional aperture; a one-dimensional photodetector that detects light passing through each of the one-dimensional apertures; processing an output of the one-dimensional photodetector to generate light of the focus detection optical system on the sample surface. A focus detection device comprising: a signal processing device that detects an axial position. 2. The focus detection device according to claim 1, wherein the one-dimensional light source includes a linear slit and a slit illumination device that illuminates the slit from behind. 3. The focus detection device according to claim 1, wherein the one-dimensional light source includes a plurality of slits extending in a direction perpendicular to the arrangement direction of the one-dimensional light sources in the arrangement direction of the one-dimensional light sources. A focus detection device comprising: a slit group arranged at a distance; and a slit illumination device for illuminating the slit from the back. 4. The focus detection device according to claim 1, wherein the one-dimensional photodetector is a one-dimensional image sensor, and a light-receiving cell of each light-receiving cell of the one-dimensional image sensor. The light receiving area is
A focus detection device serving as each of the one-dimensional apertures. 5. The focus detection device according to claim 1, wherein the one-dimensional photodetector is a two-dimensional image sensor, and the one-dimensional photodetector is a light-receiving cell of the two-dimensional image sensor. The light receiving area is
A focus detection device serving as each of the one-dimensional apertures. 6. The focus detection device according to claim 5, wherein a line position of the projected one-dimensional light source on the two-dimensional image sensor is detected and stored in advance, and the signal processing device includes: A focus detection device that processes an image signal of the line position of the two-dimensional image sensor. 7. The focus detection device according to claim 5, wherein the signal processing device is configured to output a center line of the one-dimensional light source projected on the two-dimensional image sensor from an output of the two-dimensional image sensor. A focus detection device that detects a position, processes an output of the center line position of the two-dimensional image sensor, and detects a position of the focus detection optical system on the sample surface in an optical axis direction. 8. A stage for holding a sample, an illuminating device, a half mirror, and illuminating light from the illuminating device is irradiated onto the sample surface via the half mirror, and an image of the sample surface is halved. An imaging optical system for projecting onto a projection surface via a mirror, an imaging device arranged such that the imaging surface is located on the projection surface, and detecting a position of the imaging optical system in the optical axis direction with respect to the sample surface. An autofocus microscope comprising: an autofocus mechanism that adjusts a relative position of the imaging optical system in an optical axis direction so that an image of the sample surface is formed on the projection surface. Is provided with the focus detection device according to any one of claims 1 to 7, the stage and the stage according to the position of the focus detection optical system in the optical axis direction of the focus detection optical system detected by the focus detection device Autofocus microscope and adjusting the relative position of the optical axis of the image optical system. 9. The autofocus microscope according to claim 8, further comprising a second half mirror that optically couples the imaging optical system and the focus detection optical system of the autofocus mechanism. An autofocus mechanism configured to separate an optical path for projecting the image of the one-dimensional light source onto a sample surface and an optical path for forming an image of the one-dimensional light source projected on the sample surface on an image forming surface; Autofocus microscope equipped with a half mirror. 10. The autofocus microscope according to claim 9, wherein the imaging device has no sensitivity to light emitted from the one-dimensional light source of the autofocus mechanism. 11. The autofocus microscope according to claim 10, wherein the one-dimensional light source of the autofocus mechanism is projected within an imaging range of the imaging device on the sample surface. 12. The autofocus microscope according to claim 8, wherein a part of the focus detection optical system and a part of the imaging optical system are common, and the one-dimensional light source of the autofocus mechanism is the sample surface. An autofocus microscope projected outside the imaging range of the imaging device above. 13. The autofocus microscope according to claim 12, wherein the one-dimensional light source includes a linear slit, and the illumination device illuminates the slit from behind. 14. The autofocus microscope according to claim 12, wherein the one-dimensional light source has a plurality of slits extending in a direction perpendicular to the direction in which the one-dimensional light sources are arranged in the direction in which the one-dimensional light sources are arranged. An autofocus microscope comprising a group of slits arranged at a distance, wherein the illumination device illuminates the slits from behind.