JP2951361B2 - Automatic focusing device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic focusing device in an optical device such as a microscope.

[Conventional technology]

An automatic focusing device that automatically focuses on an object being observed by an optical device using a measuring light beam is disclosed in, for example, West German Patent No.
3219503 C2 and West German Patent Publication No. 2102922.

In these conventional automatic focusing devices, a light beam from a light source for measurement passes through one side of a pupil of an objective lens and is condensed on an object, and the spot image is received by a photodetector via the objective lens and is representatively represented. The position is detected, and the object or the objective lens is driven in the direction of the optical axis to perform automatic focusing according to the deviation between the representative position and the representative position of the spot image incident on the photodetector at the time of focusing. I have. That is, assuming that a representative position of the spot image incident on the photodetector at the time of focusing is X ₀ and a representative position of the spot image actually incident is X, X = X _{0 as} shown in FIG. An object or an objective lens is driven to automatically focus.

[Problems to be solved by the invention]

However, in the above-described conventional automatic focusing apparatus, an image of a spot formed on an object is received by a photodetector, and a representative position thereof is detected.
As shown in FIG. 9, if the surface of the object 1 has fine irregularities, even if the maximum gap depth of the irregularities is sufficiently small with respect to the focal depth of the objective lens 2, the irregularities may be reduced. In the case where the spot is smaller than the spot of the measurement light beam formed on the surface of 1 or the spot is located at the boundary of the uneven portion, the reflected light is scattered by the uneven portion, and therefore, even in the focused state. light amount distribution of the spot images formed on the photodetector becomes as shown by a curve b in FIG. 10, the representative (center of gravity) position X, the focus shift is different from the center-of-gravity position X ₀ during focusing There is a problem that arises. In FIG. 10, a curve B shows a light amount distribution at the time of focusing of a spot image formed on the photodetector when there is no fine unevenness on the surface of the object 1. In this case, the center of gravity is shown. and the position X and X ₀ matches.

As described above, in the conventional automatic focusing apparatus, if there is fine irregularities on the surface of the object, a focusing shift occurs,
For example, when observing an object having a continuous fine uneven pattern such as a baked wafer while scanning, an in-focus error occurs with the scanning, and accurate observation cannot be performed. There is a problem of getting tired.

The present invention has been made in view of such a conventional problem, and even when the surface of an object has minute irregularities, it is possible to appropriately perform focus control without always causing a focus shift. It is an object of the present invention to provide a configured automatic focusing device.

[Means and actions for solving the problem]

In order to achieve the above object, according to the present invention, a light beam from a measurement light source is projected on an object through one side of a pupil of an objective lens, and the spot image is received by a photodetector through the objective lens, and An automatic focusing device that controls focusing by driving one or both of the objective lens and the object in the optical axis direction of the objective lens based on an output, wherein the light detection is performed based on an output of the photodetector. Means for detecting the representative position and size of the spot image formed on the container, and providing one or both of the objective lens and the object based on the representative position and size of the spot image detected by the detecting means. The focus control is performed by driving the lens in the optical axis direction.

〔Example〕

FIG. 1 shows a first embodiment of the present invention. This embodiment is applied to an epi-illumination type microscope. After a light beam from a measurement light source 11 such as a semiconductor laser is converted into a parallel light beam by a collimator lens 12, the polarization beam splitter 1 is used.
The light is reflected by the dichroic mirror 15 through the 3/4 wavelength plate 14, and the measurement light flux is made incident on one side of the pupil of the objective lens 16 to be focused on the observation object 18 mounted on the sample stage 17. Let it.

The reflected light of the measurement light beam condensed on the observation object 18 is reflected by the dichroic mirror 15 through the objective lens 16, and the return light from the observation object 18 passes through the quarter-wave plate 14 and the polarization beam splitter 13. Incident on Here, return light from the observation object 18 that enters the polarization beam splitter 13 is
Since the light passes through the quarter-wave plate 14 twice in the forward path and the return path, the polarization plane of the return light differs from the polarization plane in the forward path by 90 °, and is reflected by the polarization beam splitter 13. The return light from the observation object 18 reflected by the polarization beam splitter 13 is received by the line sensor 20 via the imaging lens 19.

The line sensor 20 is disposed so as to extend in the direction of displacement of light incident on the line sensor 20 due to a change in the relative distance between the objective lens 16 and the observation target 18, and the observation target 18 is positioned with respect to the objective lens 16. Line sensor when in focus position
Arrange them so that a minimum spot image is formed on the approximately central element 20. The output of the line sensor 20 is supplied to an arithmetic and control unit 21, where a representative position X and a size l of a spot image formed on the line sensor 20 are obtained.
The sample stage 17 is driven in the direction of the optical axis of the objective lens 16 via a driving device 22 having a stepping motor or the like based on (1) and (2) to automatically perform focusing control.

Note that the image of the observation target 18 is formed at an imaging position 24 by the observation imaging lens 23 via the objective lens 16 and the dichroic mirror 15, and can be observed visually or by a TV camera or the like.

Hereinafter, the operation of this embodiment will be described with reference to the flowchart shown in FIG.

First, in the arithmetic and control unit 21, the representative position X and the size l of the spot image projected on the line sensor 20 are obtained based on the output of the line sensor 20 (block 3).
1).

Here, in a front focus state in which the focal point of the objective lens 16 is located in front of the observation target 18 (on the side of the objective lens 16), the return light from the observation target 18 becomes convergent light, as shown in FIG. The spot image 25 formed on the line sensor 20 is
On one side from the representative positions X ₀ upon focusing, the size of the spot moves with increases in other words according to the focus shift is increased according to the front focus state. Further, in the back focus state in which the focal point of the objective lens 16 is located behind the observation target 18, the return light from the observation target 18 is divergent light,
Spot image 25 which is formed on the line sensor 20, on the other side from the representative position X ₀ of the in-focus state, the size of the spot moves while increases as the focus shift is increased.
Therefore, the light quantity distribution of the spot image formed on the line sensor 20 becomes as shown in FIG. 3B according to the focus state.

As the representative position X of the spot image 25 formed on the line sensor 20, the position of the center of gravity or the median position is obtained. Here, assuming that the number of elements of the line sensor 20 is n and the photoelectric output of each element is y _i , the center of gravity position X is And the median position X is Can be obtained by interpolation from x and x + 1.

The size l of the spot image 25 formed on the line sensor 20 is determined by providing a threshold level as shown in FIG. 3 and counting the number of elements whose output exceeds the threshold level.

After determining the representative position X and size l of the spot image projected on the line sensor 20, then, obtains the absolute value of the difference between the representative position X ₀ during focusing a preset representative position X, its It is determined whether or not | X−X ₀ | ≦ ΔX with respect to a certain allowable value ΔX whose absolute value is within a preset depth of focus of the objective lens 16 (block 32).

Here, when | X−X ₀ | ≦ ΔX, the observation object 18
Is determined to be at the in-focus position with respect to the objective lens 16, the current position is maintained without supplying a drive signal to the drive device 22, and the process returns to the block 31. On the other hand, | X−X ₀ |>
In the case of ΔX, it is determined that the focus is not at the in-focus position, the front focus and the rear focus are determined based on the polarity of the calculation result of X−X ₀ , and a drive signal is supplied to the drive device 22 accordingly, and Is driven one step in the direction of correcting the focus shift (block 33),
The representative position X 'and size l' of the spot image 25 after the driving are obtained (block 34). Thereafter, the size l of the spot image 25 before the one-step drive is compared with the size l 'after the drive (block 35). If l'≤l, it is determined that the drive is truly in the focusing direction. Judgment is made, X = X ', l = l' (block 36), and the flow returns to block 32 to repeat the above operation. On the other hand, when l ′> l, it is determined that the sample table 17 has not been driven in the focusing direction, that is, it has been affected by the scattered light.
That is, it returns to the position before the one-step drive (Block 3
7). The amount of one-step drive by the step drive is set in advance so as to be smaller than the range of the depth of focus.

Thereafter, the representative position X ″ and the size l ″ of the spot image 25 are obtained again (block 38), and | X ″ −X | ≦ is obtained by using the representative position X ″ and the representative position X previously obtained at the step drive position. ΔX is determined (block 39), and | X ″ −X |
When ≦ ΔX, it is determined that the observation object 18 is at the in-focus position with respect to the objective lens 16, and the current position is maintained without supplying a drive signal to the drive device 22, and the process returns to the block 38. When | X ″ −X |> ΔX, it is determined that the subject is not at the in-focus position, and X = X ″, l = l ″ (block 40) and the block 32 is set.
And the above operation is repeated.

Therefore, according to this embodiment, for example, as shown in FIG. 4, a specimen having a flat region a, a lower flat region b, and a region c having fine irregularities substantially flush with the region b. When the scanning is performed by moving 45 in the direction indicated by the arrow, the following operation is performed.

First, in the area a, when the representative position X and the size l are detected in the block 31 first, then X ≒ X ₀ (| X−X ₀ | ≦ ΔX) as shown in FIG. 5A. In such a manner, the loop of the blocks 32 → 33 → 34 → 35 → 36 → 32 is repeated several times to control the focus, and then the focus state is maintained by the loop of the blocks 32 → 31. That is, when the sample surface is flat, it is impossible that l ′> l in the block 35, so that the above blocks 32 → 33 → 34 → 35 → 36
→ Focusing is controlled by the loop of 32.

Thereafter, when scanning of the area b starts, the front focus state is initially set due to a step with the area a. Therefore, as shown in FIG. 5B, X ≠ X ₀ (| X−X ₀ |> ΔX). together becomes, but also increases the size of the spot image, then the same operation as in the region a, the size of the spot image is focused controlled so as to minimize in X ≒ X _0.

Next, when entering the area c, scattered light due to minute irregularities on the specimen surface causes the specimen to be in focus, despite being in focus, as shown in FIG.
As shown in (2), X ≠ X ₀ (| X−X ₀ |> ΔX), and the size l of the spot image also increases. In this case, first, the sample stage 17 is driven by one step in the block 33. Since the one-step drive is in the direction of the focus shift from the in-focus position, the size l 'of the spot image is necessarily larger than that before the drive. growing. Therefore, after that, in block 37, it is returned to the step position before driving, that is, the in-focus position,
When the absolute value | X ″ −X | of the difference between the representative positions before and after the step driving at the same step position is | X ″ −X | ≦ ΔX, it is determined that the object is in focus, and the block 38 → 39 is driven by the loop. Device 22
Maintains the stopped state, and the focused state is maintained. Note that |
If X ″ −X |> ΔX, the process goes through block 40 to block 32
And the focusing operation is performed according to the determination of | X−X ₀ | ≦ ΔX.

As described above, according to this embodiment, the size of the spot image 25 before and after the step drive is compared (l ′ ≦ l) to determine whether the drive direction is correct, and when the drive direction is not correct, Returning to the previous step position, the representative position X ″ of the spot image 25 at that position is obtained again, and the absolute value | X ″ − of the difference between the representative position before and after the step driving at the same step position is obtained.
When X | is | X ″ −X | ≦ ΔX, focus is determined and the current position is maintained. Therefore, even if there are minute irregularities on the surface of the observation object 18, the same height is maintained to some extent. If scanning is performed after focusing on a flat surface, focusing control can always be performed accurately without being affected by minute irregularities.
Since the representative position X and the size l of the spot image 25 are obtained based on the output of one line sensor 20, the configuration of the optical system can be simplified and the cost can be reduced.

FIG. 6 shows a second embodiment of the present invention. This embodiment is different from the configuration shown in FIG.
Return light from the observation object 18 having passed through the
The light is divided into two parts, one of which is received by the line sensor 20 and the other is received by the semiconductor position detector (PSD) 52, and the size of the spot image is determined based on the output of the line sensor 20.
The representative position of the spot image is detected based on the output of D52, and the other configuration is the same as that of the first embodiment. As described above, if the size and the representative position of the spot image are detected based on the outputs of the independent detectors, the calculation speed can be increased, so that quick focusing control can be performed.

FIG. 7 shows a third embodiment of the present invention. In this embodiment, in the configuration shown in FIG. 6, the return light from the observation object 18 reflected by the polarization beam splitter 13 is divided into two by a half mirror 51, and one of the two is passed through an imaging lens 55 to a line sensor 20. And the other through the imaging lens 56
The light is received by the PSD 52, and the other configuration is the same as that of the second embodiment. With this configuration, the same effects as those of the second embodiment can be obtained, and the imaging lens can be formed.
By decreasing the focal length of the 55, the rate of change of the spot image size can be increased, and by increasing the focal length of the imaging lens 56, the projection magnification can be increased to increase the sensitivity of the spot image displacement. Can be.

It should be noted that the present invention is not limited to the above-described embodiment, and various modifications or changes can be made. For example, in the above-described embodiment, the focus control is performed by driving the sample stage 17, but the focus control is performed by driving the objective lens 16 or by driving both the objective lens 16 and the sample stage 17. It can also be configured as follows. In the above-described embodiment, the distance between the objective lens and the object is changed by the step driving. Therefore, the driving amount of one step is set in advance so as to be smaller than the depth of focus range. and position X, rather than the second view of the block 33 step driving according to the difference between the representative position X ₀ of the time of focusing, may be driven at a time. In this way, more rapid focusing control is possible. Further, the present invention can be effectively applied not only to the epi-illumination type microscope but also to automatic focusing of another microscope or optical equipment other than the microscope.

〔The invention's effect〕

As described above, according to the present invention, the image of the spot projected on the object through one side of the pupil of the objective lens is received by the photodetector, and the representative position and size of the spot image are determined based on the output. And focus control is performed by driving one or both of the objective lens and the object in the optical axis direction of the objective lens based on the detected representative position and size of the spot image. Even when the surface has fine irregularities, focus control can always be performed accurately without causing a focus shift.

[Brief description of the drawings]

FIG. 1 is a view showing a first embodiment of the present invention, FIG. 2 is a flowchart showing the operation thereof, and FIGS. 3A and 3B are representative positions and sizes of spot images on the line sensor shown in FIG. FIG. 4 is a diagram showing the manner of scanning the sample, FIGS. 5A, 5B and 5C are diagrams for explaining the focusing operation on the sample shown in FIG. 4, and FIG. FIG. 7 is a view showing a second embodiment of the present invention, FIG. 7 is a view showing the same third embodiment, and FIGS. 8, 9 and 10 are views for explaining the prior art. 11 Light source for measurement, 12 Collimator lens 13 Polarizing beam splitter 14 Quarter-wave plate, 15 Dichroic mirror 16 Objective lens 17, Sample table 18 Object to be observed, 19 ... imaging lens 20 ... line sensor, 21 ... arithmetic and control unit 22 ... driving device, 23 ... observation imaging lens 24 ... imaging position, 25 ... spot image 45 ... sample, 51 … Half mirror 52 Semiconductor position detector (PSD) 55, 56 Imaging lens

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-71810 (JP, A) JP-A-62-62208 (JP, A) JP-A-60-61608 (JP, A) JP-A-63-61208 199311 (JP, A) JP-A-60-118814 (JP, A) JP-A-59-18913 (JP, A) JP-A-54-40649 (JP, A) (58) Fields investigated (Int. ⁶ , DB name) G02B 7/28-7/40 G03B 3/00-3/12

Claims (3)

(57) [Claims] 1. A light beam from a measurement light source is projected on an object through one side of a pupil of an objective lens, and a spot image is received by a photodetector through the objective lens, and the spot image is received based on an output of the object. An automatic focusing device that drives one or both of a lens and an object in an optical axis direction of an objective lens to perform focusing control, and is formed on the photodetector based on an output of the photodetector. A means for detecting the representative position and size of the spot image is provided, and one or both of the objective lens and the object are moved in the optical axis direction of the objective lens based on the representative position and size of the spot image detected by the detecting means. An automatic focusing device, which is configured to be driven to perform focusing control. 2. A line sensor is used as the light detector.
2. The automatic focusing apparatus according to claim 1, wherein a representative position and a size of the spot image are detected based on the output. 3. A line sensor and a semiconductor position detector are used as the photodetector, and the line image and the semiconductor position detector receive the spot image, respectively, based on an output of the line sensor. 2. The automatic focusing apparatus according to claim 1, wherein a size of the image is detected, and a representative position of the spot image is detected based on an output of the semiconductor position detector.