JP2001305420A - Automatic focusing device for microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an automatic focusing device for a microscope capable of surely performing an appropriate focusing control, irrespective of the surface shape of an object to be inspected. SOLUTION: As for automatic focusing device, an object to be inspected 2 is irradiated with a laser beam L1 through an objective lens 1 by taking a position deviated from optical axis K of the objective lens 1 as an incident position, and then, the laser light L2 guided through the objective lens 1 and a beam splitter 5 after being reflected by the object to be inspected 2 is received by a sensor array 10, and the focus displacement is detected based on the position of the received light spot formed on the light receiving surface, then, the focusing operation is performed based on the detection output, the object to be inspected 2 is irradiated with the laser light L1 in order at four incident points on the circumference around the optical axis K of the object lens by rotating the laser beam L1 by a wedge prism 12, and then, whenever the object 2 is irradiated with the laser beam L1 at each incident position, the focus displacement is detected so as to perform the focusing control.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an autofocus device for a microscope.

[0002]

2. Description of the Related Art When observing a test object with an optical microscope, a so-called focusing operation for adjusting the distance between the observation optical system of the microscope and the test object is required. Autofocusing devices that perform focusing have become widely used. Auto focus generally means automatically detecting a difference amount (defocus) from a focused position, and moving, for example, a stage on which an objective lens or a test object is mounted according to the difference amount, The automatic adjustment is performed so that a clear image can be obtained.

Referring to FIG. 14, an example of a conventional fine beam type auto focus (AF) control will be described.

This auto focus control is performed by
As shown in (a), a position deviated from the optical axis K of the objective lens 1 is set as a fixed incident point A, and the test object 2 is irradiated with the measurement beam L1 through the objective lens 1 so that the test object 2 The reflected light L2 of the measurement beam guided through the lens 1 is
As shown in FIG. 14B, light is received by an optical sensor 90 composed of two light receiving sections E and F, and the position of the light receiving spots SP, SPf, and SPb formed on the light receiving surface of the sensor 90 is used to determine the objective. A defocus of the test object 2 from the focal position of the lens 1 is detected. Then, based on the defocus detection signal, the distance between the objective lens 1 and the test object 2 is adjusted, and the focus of the objective lens 2 is adjusted to a target point on the test object 2.

Here, when the light receiving spot SP is at the proper focus position F, the light receiving spot SP becomes a point image at an intermediate position between the two light receiving portions E and F. When the front focus position is at the position F + ΔF, the light receiving spot SPf shifts from the intermediate position onto the light receiving portion E on the front focus side to form a blurred image, and the rear focus position F−ΔF
, The light receiving spot SPb is shifted from the intermediate position onto the light receiving section F on the rear focus side to form a blurred image. In addition,
“Front focus” refers to a state in which focus is achieved before the image plane, and “back focus” refers to a state in which focus is achieved before the image plane.

Accordingly, the control device for instructing the autofocusing performs the focusing based on the signals of the two light receiving units E and F as shown in the flowchart of FIG.

That is, the microprocessor, which is a main element of the control device, first reads A / D conversion values e and f of the output signals of the two light receiving units E and F in the first step 901. In the next step 902, it is determined whether or not focusing is performed based on the A / D conversion values e and f of the output signal. The focus is determined by determining whether “e = f”. If in focus, the motor is stopped in step 903 and the process returns to the first step.

If it is not in focus, it is determined in step 904 whether the focus is on the front or the back. The determination of the front focus or the rear focus is performed by determining whether “e> f”. If it is the front focus, the motor is turned to the rear focus side in step 905, and the distance between the objective lens 1 and the test object 2 is reduced. If it is the back focus, the motor is turned to the front focus side in step 906, and the distance between the objective lens 1 and the test object 2 is increased. It looks for a focal point. As a result, even if the focus position shifts, the focus automatically returns to the focal point F.

[0009]

In the above-described conventional fine beam type autofocus control, the point of incidence of the measurement beam L1 is fixed at one point A, and therefore, as shown in FIG. There is no particular problem when observing the planar test object 2 in FIG. 1, but there is unevenness on the surface of the test object 2 as shown in FIG. 16B (the convex portion 2a exists in the illustrated example). In such a case, as shown in FIG.
In some cases, blind spots N that cannot be reached can prevent proper autofocus control.

SUMMARY OF THE INVENTION An object of the present invention is to provide an autofocus device for a microscope capable of reliably performing appropriate autofocus control regardless of the surface shape of a test object in consideration of the above circumstances.

[0011]

According to a first aspect of the present invention, an observation optical system including an objective lens and a position deviating from the optical axis of the objective lens are set as a point of incidence, and a measurement beam is applied to a test object through the objective lens. A measuring beam irradiating mechanism for irradiating, and a reflected light of the measuring beam guided from the object through the objective lens is received, and a position of a light receiving spot formed on the light receiving surface is used to move the object from the focal position of the objective lens. A focus shift detecting means for detecting a focus shift, and a drive mechanism for adjusting a distance between the objective lens and the test object based on an output of the focus shift detecting means, thereby controlling the objective lens at a target point on the test object. And a control means for adjusting the focal point of the objective lens, wherein the light incident point is set at 90% on the circumference around the optical axis of the objective lens.
Four light incident points are set at a degree interval, and a measurement beam irradiation mechanism irradiates the test object with a measurement beam at the four light incident points in order. For each irradiation of the measurement beam at each light incident point,
The defocus detecting means detects the defocus of the object from the focal position of the objective lens, and the control means controls the driving mechanism based on the detected output.

According to the present invention, since the measurement beam can be irradiated from four incident points, that is, the measurement beam can be irradiated on the surface of the object from four directions, the surface of the object can be uneven. Even if there is, the measurement beam from any of the light entry points can always reach the target point on the test object, and appropriate autofocus control can be performed based on the measurement beam. it can.

According to a second aspect of the present invention, in the first aspect, the measurement beam irradiation mechanism for sequentially irradiating the test object with the measurement beam at the four light incident points emits one measurement beam. An irradiation source, a wedge prism through which a measurement beam emitted from the irradiation source passes, and a rotation mechanism for rotating the wedge prism to rotate the measurement beam along a circular locus passing through the four light incident points. And characterized in that:

According to the present invention, by rotating one measurement beam by the wedge prism, the measurement object can be irradiated to the object to be measured from the four light incident points through the objective lens. Therefore, the effect of the first aspect can be obtained with a simple structure without increasing the number of irradiation sources of the measurement beam.

According to a third aspect of the present invention, in the first or second aspect, the defocus detecting means includes four light receiving portions arranged in a cross shape, and a combination of the two light receiving portions arranged in a straight line. One detecting means configured to receive reflected light when the measurement object is irradiated with the measurement beam at one light incident point, and the two light receiving units arranged on the straight line are two light receiving units at the time of focusing A light receiving spot is formed in the middle of the light receiving spot, a light receiving spot is formed on one light receiving part at the time of front focus, and a light receiving spot is formed on the other light receiving part at the time of rear focus, and the light receiving spot is formed on a straight line. The combination of the two light receiving units arranged in a row also serves as each detecting means for detecting a defocus when the measurement beam is irradiated at each of the two light incident points located at positions opposed by 180 degrees.

According to the present invention, when a measurement beam is made incident on an objective lens at a certain light incident point A, the light beams are aligned on a straight line.
Light receiving spots are formed on the two light receiving portions E and F. When the light receiving spot is in the front focus state, one of the light receiving portions E
It is formed on the other light receiving portion F in the rear focus state.

Therefore, when the camera is in the front focus state, the focusing is performed so as to be on the rear focus side (the distance between the objective lens and the test object is reduced), so that the light is formed on one of the light receiving portions E. The position of the light receiving spot moves toward the intermediate point O between the two light receiving units E and F. Then, when the light receiving spot reaches the intermediate point O, the focusing operation is stopped, and in this state, the object is focused on the test object.

Further, in the rear focus state, the focusing is performed so as to be on the front focus side (the distance between the objective lens and the object to be measured is increased), so that it is formed on one of the light receiving portions F. The position of the light receiving spot moves toward the intermediate point O between the two light receiving units E and F. Then, when the light receiving spot reaches the intermediate point O, the focusing operation is stopped, and in this state, the object is focused on the test object.
As described above, the light receiving spot moves on the straight line where the two light receiving units E and F are arranged due to the change of the focus position.

Next, a light incident point C at a position 180 degrees opposite
Considering the case where the measurement beam is made incident on the light receiving spot, light receiving spots are formed on the two light receiving portions E and F arranged on the same straight line as described above. However, in this case, two light receiving units E,
The role of F is reversed. That is, by switching to a position where the light incident point is inverted by 180 degrees, the light receiving unit E functioning for the front focus when the measurement beam is incident at the light incident point A now functions for the rear focus, The light receiving portion F functioning for the back focus now functions for the front focus. Thereby, the same focusing operation as described above is performed.

The same applies to the case where the measuring beams are irradiated at the light incident points B and D located at positions shifted by 90 degrees from the light incident points A and C.

In any case, by combining the light receiving portions arranged in a cross shape, all the defocuses in each case where the measurement beam is irradiated at the four light incident points in order are detected, so that the number of light receiving portions is reduced. Autofocus control without blind spots by irradiating measurement beams from four directions can be realized without increasing the power consumption.

According to a fourth aspect of the present invention, in the third aspect, the four light receiving portions are respectively divided into an inner light receiving sensor and an outer light receiving sensor, whereby the defocus detecting means is divided into eight. Characterized by comprising a sensor array of

According to the present invention, each light receiving portion arranged in a cross is divided into an inner light receiving sensor and an outer light receiving sensor. ) And when the degree of defocusing is small (that is, when the light receiving spot is on the inner light receiving sensor), it is possible to perform control separately.

For example, when the camera approaches the focal point while focusing is being performed based on the formation of a light receiving spot on one of the light receiving portions, a ghost image other than the regular light receiving spot is shifted to the opposite side. May be formed on the light receiving sensor outside the light receiving unit located at the position indicated by the arrow mark. In such a case,
Unless the effects of the ghost image are removed, proper autofocus control cannot be performed. Therefore, at the stage of approaching the focal point, the signal of the outer light receiving sensor is deliberately ignored (separated), and the focusing control is performed up to the focal point only by the signal of the inner light receiving sensor. By doing so, accurate autofocus control can be performed with high responsiveness.

According to a fifth aspect of the present invention, in any one of the first to fourth aspects, the control means determines the validity of the signal of the defocus detection means obtained by irradiating the measurement beam at one light incident point. If the signal is evaluated to be invalid, the signal is rejected and a control signal is sent to the measurement beam irradiation mechanism to move the light incident point of the measurement beam to the next light incident point in the next order. It is characterized by.

According to the present invention, the effectiveness of the detection signal is evaluated at the stage of irradiating the measurement beam at each light incident point when performing the autofocus control by irradiating the measurement object sequentially from four directions to the test object. However, in the case of an invalid signal, the signal is rejected and moved to the next light incident point.Therefore, the signal obtained by irradiating the measurement beam from the direction of the blind spot should be excluded as invalid data. Accordingly, appropriate autofocus control can be performed regardless of the surface shape of the test object.

[0027]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of a microscope including an autofocus device according to an embodiment, FIG. 2 is a diagram illustrating a position of a light incident point of a measurement beam on an incident surface of an objective lens, and FIG.
FIG. 3 is a plan view of a sensor array as a defocus detecting unit.

The observation optical system of this microscope includes an objective lens 1
, An eyepiece 9, and first and second beam splitters 5 and 7 for guiding an optical image passing through the objective lens 1 to the eyepiece 9.
And a camera 20 set on the eyepiece 9. The first beam splitter 5 has an optical axis K of the objective lens 1.
Is set at an inclination of 45 degrees.

The observation illumination system comprises an optical fiber 30 for guiding light from an illumination light source (not shown), and a third beam splitter 8 for reflecting illumination light emitted from the optical fiber 30.
And The illumination light reflected by the third beam splitter 8 is transmitted through the second beam splitter 7, reflected by the first beam splitter 5, and radiated to the object 2 through the objective lens 1.

On the first beam splitter 5, a fourth beam splitter 6 is disposed, on which a wedge prism 12 is disposed, and on the wedge prism 12,
1 as a measurement beam for performing autofocus control
A laser light source (measurement beam irradiation source) 15 for emitting the laser light is arranged. As the laser light source 15,
A red semiconductor laser or a HeNe laser can be used.

In this auto-focusing device, a laser beam L1 for focusing is applied to the test object 2 through the objective lens 1 with a position deviating from the optical axis K of the objective lens 1 as a light incident point. I have. In this case, the laser light L1 emitted from the laser light source 15 passes through the wedge prism 12 and the fourth beam splitter 6, and reaches the incident surface 1A of the objective lens 1. Then, the laser beam L1 applied to the test object 2 from the light incident point on the objective lens 1 through the objective lens 1 is reflected on the test object 2, and the reflected light L2 is reflected by the objective lens 1 and the first beam. The light beam travels backward through the splitter 5 and is reflected by the fourth beam splitter 6 in a direction orthogonal to the optical axis K of the objective lens 1 so that the sensor array 10
To form a laser spot on the light receiving surface of the sensor array 10.

In particular, in this autofocusing device, as shown in FIG. 2, four points are formed on the same circumference M around the optical axis K of the entrance surface 1A of the objective lens 1 at intervals of 90 degrees in the circumferential direction.
Auto-focus control is performed by sequentially irradiating the object 2 with the laser beam L1 at the four light-entering points A, B, C, and D at these four light-entering points A, B, C, and D. It is supposed to do.

In this case, the four incident points A, B, C, and D
Is virtually set on the incident surface 1A of the objective lens 1,
It is defined as the intersection of the XY axis with the optical axis K as the orthogonal point and the circumference M. Accordingly, a pair of light incident points A and C are located on the X axis, and another pair of light incident points B and D are located on the Y axis.

The wedge prism 12 is used in this autofocus device as a method for sequentially irradiating the laser light L1 to the four light incident points A, B, C and D. When the wedge prism 12 is rotated by the rotation mechanism 31, the laser light L1 rotates around the optical axis K. Therefore, by rotating the laser beam L1 by the wedge prism 12, the laser beam L1 traces the four incident points A, B, C, and D in this order. Also,
In order to detect the timing at which the laser light L1 passes through the four light incident points A, B, C and D, the wedge prism 12 is provided with a rotation position sensor (= rotation angle sensor) 32 for detecting the rotation position thereof. ing.

Here, the wedge prism 12, a rotation mechanism 31 for rotating the wedge prism 12, and a laser light source 15 for emitting a laser beam L1 as a measurement beam are provided at four light incident points A, B, C, and D. In order laser light L
1 constitutes a measurement beam irradiation mechanism for irradiating the object 1 to the test object 2.

On the other hand, the sensor array 10 receives the laser reflected light L2 guided from the test object 2 through the objective lens 1 and determines the position of the light receiving spot formed on the light receiving surface from the focal position of the objective lens 1 based on the position of the light receiving spot. It constitutes a defocus detecting means for detecting a defocus of the test object 2.

As shown in FIG. 3, the sensor array 10 includes four light receiving portions E, F, G, and H arranged in a cross shape, and two light receiving portions E, F, or The combination of G and H receives the reflected light L2 when the test object 2 is irradiated with the laser light L1 at one incident point.
It performs the function of two detection means. That is, the first light incident point A
When measuring at the second light receiving point B, the combination of the light receiving sections E and F performs the detection function.
When the combination of H performs the detection function, and the measurement is performed at the third light incident point C, the combination of the light receiving units E and F performs the detection function. When the measurement is performed at the fourth light incident point D, the light receiving unit G, H
Perform the detection function. Therefore, the combination of the two light receiving units E and F or G and H arranged on a straight line is 1
It also serves as each detecting means for detecting the defocus when the laser light L1 is irradiated at the two light incident points A and C or B and D located at positions facing each other by 80 degrees.

An XY axis corresponding to the XY axis set on the incident surface 1A of the objective lens 1 is virtually set on the sensor array 10, and a cruciform is set on the XY axis. To 4
The two light receiving units E, F, G, and H are arranged. To form these pairs, two light receiving units E and F (or G and H) arranged on a straight line (on the X axis or the Y axis) are 2
A light receiving spot is formed at an intermediate point (origin O of the XY axis) between the two light receiving portions E and F (or G and H), a light receiving spot is formed on one light receiving portion at the time of front focus, and the other at the time of rear focus. Are arranged in a positional relationship such that a light-receiving spot is formed on the light-receiving portion.

Each of the light receiving sections E, F, G, H is divided into two parts: an outer light receiving sensor E1, F1, G1, H1 and an inner light receiving sensor E2, F2, G2, H2. , The sensor array 10 is configured as an eight-segment type. In this case, the inner light receiving sensors E2, F2,
G2 and H2 have triangular tips so that they are as close to each other as possible.

The auto-focusing device also has a drive mechanism 33 for driving the objective lens 1 in focus (to move the objective lens 1 closer to or away from the test object 2). This drive mechanism is composed of a DC servo motor or a stepping motor, a precision screw, a precision gear, and the like (not shown).

This autofocus device controls the driving mechanism 33 based on the signal of the sensor array 10,
Accordingly, a control device (control means) 35 for focusing the objective lens 1 on a target point on the test object 2 is provided.

The control unit 35 controls the light incident points A, B,
The signal of the wedge prism rotational position sensor 32 is monitored so as to capture the signal of the sensor array 10 every time the laser beam L1 is irradiated in C and D. The control device 35 evaluates the validity of the signal of the sensor array 10 obtained by irradiating the laser beam L1 at one incident point, and when the signal is evaluated to be invalid, the signal is evaluated. Is not adopted, a drive control signal is sent to the wedge prism rotating mechanism 31 to perform the function of moving the light incident point of the laser beam L1 to the next light incident point. The order of moving the light incident point is A → B → C
→ The order is D.

Next, the principle of the auto focus control executed by the control device 35 will be described with reference to FIG. First, a control method when the test object 2 is irradiated with the laser beam L1 at the first light incident point A will be described. In this case, the reflected light L2 of the beam splitter 6 is transmitted to the sensor array 1
Four light receiving sensors E arranged on the X-axis because 0 is received
1, E2, F1, and F2 are valid.

When the laser beam L1 is incident on the objective lens 1 at the light incident point A, four light receiving sensors E1 arranged on the X axis,
The light receiving spot SP (SPf, S) is placed on E2, F1, F2.
Pb) is formed. The light receiving spot is formed on one of the light receiving sensors E1 and E2 when the front focus state is set,
In the rear focus state, it is formed on the light receiving sensors F1 and F2 on the other side.

That is, as shown in FIG. 4, when the objective lens 1 is at an appropriate focus position F (see FIG. 14A), the light receiving spot SP is divided into two light receiving portions E (light receiving sensors E
1, E2) and F (light receiving sensors F1 and F2) form a point image at an intermediate point O. When the front focus position is F + ΔF (see FIG. 14A), the light receiving spot SPf is at the intermediate point O.
14 is shifted to the light receiving section E (light receiving sensors E1 and E2) on the front pin side to form a blurred image, and the rear focus position F-ΔF [FIG.
(Refer to (a))], the light receiving spot SPb is
The light receiving section F (light receiving sensors F1, F
2) The image is shifted upward and becomes a blurred image.

Therefore, in the front focus state, focusing is performed so as to be on the rear focus side, so that the light receiving spot SPf formed on the light receiving portion E (light receiving sensors E1, E2) on one side is focused. The position is two light receiving sections E,
It moves toward the middle point O of F. And the midpoint O
Is reached, the focusing operation is stopped, and in this state, the object 2 is focused on the test object 2. Also, in the rear focus state, focusing is performed so as to be on the front focus side, so that the position of the light receiving spot SPb formed on the light receiving unit F (light receiving sensors F1 and F2) on the other side is changed. It moves toward the intermediate point O between the two light receiving units E and F. When the light receiving spot SP reaches the intermediate point O, the focusing operation is stopped, and the object 2 is focused on the object 2 in that state. As described above, the light receiving spot SP becomes 2 due to the change of the focus position.
It moves on a straight line where the two light receiving units E and F are arranged.

Next, let us consider a case where the laser beam L1 is incident at the third light incident point C located at a position facing 180 degrees.
Also in this case, the four light receiving sensors E1, E2, F1, and F2 arranged on the X axis become effective because the reflected light L2 of the beam splitter 6 is received by the sensor array 10, and these light receiving sensors E1, E2, and F1 are effective. , F2, light receiving spots are formed. That is, the same sensor as that used for measurement at the first light incident point A is used. However, in this case, the roles of the two light receiving units E (light receiving sensors E1, E2) and F (light receiving sensors F1, F2) are reversed. That is, the light incident point is switched to a position that is inverted by 180 degrees, so that the light incident point A
When the laser beam L1 is incident on the light receiving unit E (light receiving sensors E1 and E2) functioning for the front focus, the light receiving unit F (functioning for the rear focus this time and functioning for the rear focus) is used. The light receiving sensors F1 and F2) now function for the front focus. Thereby, the same focusing operation as described above is performed.

The same applies to the case where the laser light L1 is irradiated at the second and fourth light incident points B and D, which are at positions shifted by 90 degrees from the first and third light incident points A and C. It is.

In this case, the four light receiving sensors G1, G2, H1, H2 arranged on the Y axis become effective, and when the laser beam L1 is incident on the objective lens 1 at the second light incident point B,
Light receiving spots are formed on these four light receiving sensors G1, G2, H1, and H2. The light receiving spot is formed on one of the light receiving sensors G1 and G2 when in the front focus state, and is formed on the other light receiving sensor H1 and H2 when in the rear focus state.
Formed on top.

When the objective lens 1 is at an appropriate focus position, the light receiving spot becomes a point image at an intermediate point O between the two light receiving portions G (light receiving sensors G1 and G2) and H (light receiving sensors H1 and H2). When at the front focus position, the light receiving spot is shifted from the intermediate point O onto the front light receiving portion G (light receiving sensors G1 and G2) on the front focus side and becomes a blurred image. The image is shifted from the point O onto the light receiving portion H (light receiving sensors H1 and H2) on the rear focus side to form a blurred image.

Therefore, in the front focus state, the focusing is performed so as to be on the rear focus side, so that the position of the light receiving spot formed on the light receiving portion G (light receiving sensor G1, G2) on one side. Moves toward the intermediate point O between the two light receiving units G and H. When the light receiving spot reaches the intermediate point O, the focusing operation is stopped, and in this state, the object 2 is focused on the test object 2. Also,
In the rear focus state, focusing is performed so as to be on the front focus side, so that the positions of the light receiving spots formed on the light receiving portions H (light receiving sensors H1 and H2) on the other side are two light receiving spots. It moves toward the intermediate point O between the parts G and H. When the light receiving spot reaches the intermediate point O, the focusing operation is stopped, and in this state, the object 2 is focused on the test object 2. As described above, the light receiving spot moves on the straight line on which the two light receiving sections G and H are arranged due to the change of the focus position.

Similarly, when the laser beam L1 is incident on the fourth light incident point D, the two light receiving portions G (light receiving sensors G1, G
2), the roles of H (light-receiving sensors H1 and H2) are reversed, light-receiving portion G (light-receiving sensors G1 and G2) now functions for rear focus, and light-receiving portion H (light-receiving sensors H1 and H2) is now It functions for the front focus, thereby performing the same focusing operation as described above.

In any case, the light receiving portions E arranged in a cross shape,
By the combination of F, G, and H, four light incident points A, B,
It is possible to detect all the defocuses in each case where the laser light L1 is irradiated in order at C and D.

In this sensor array 10, the light receiving units E, F, G, and H arranged in a cross form the outer light receiving sensors E1, F1, G1, and H1, and the inner light receiving sensor E, respectively.
2, F2, G2, and H2, the image is largely out of focus (that is, the light receiving spot is on the outer light receiving sensors E1, F1, G1, and H1);
Different control can be performed when the degree of defocusing is reduced (that is, when the light receiving spot is on the inner light receiving sensors E2, F2, G2, and H2).

For example, as shown in FIG. 5, when the camera approaches the focal point O during focusing while the light receiving spot SP is formed on one of the light receiving portions F, a regular Ghost image SP other than light receiving spot SP
g may be formed on the outer light receiving sensor E1 of the light receiving units E and F located on the same side or the opposite side.

In such a case, since the ghost image SPg is naturally included in the light receiving signal of the sensor, proper autofocus control cannot be performed unless the influence is removed.

In the illustrated example, the light receiving spot SP is about to be driven from the light receiving portion F side to the intermediate position (focus position) O, but a ghost image SPg appears on the light receiving portion E side in some cases. The ghost image SPg moves from the light receiving unit E side toward the intermediate position O, and the ghost image SPg is also included in the sensor value, so that appropriate control cannot be performed.

Therefore, at the stage of approaching the focal point, that is, at the stage when the light receiving spot SP moves on the inner light receiving sensor, the signal of the outer light receiving sensor is deliberately ignored, and the signal of the inner light receiving sensor is ignored. Only signals are used to control until focusing. By doing so, accurate autofocus control can be performed with high responsiveness. In addition, the influence of the ghost cannot be ignored especially when observing the test object to which the coating is applied.

Next, the electrical configuration of the autofocus device and the control contents thereof will be described.

FIG. 8 is a block diagram showing an electrical configuration. The control device 35 of the autofocus device includes a microprocessor 51 and A / D
A / D converter 52 for conversion and output interface 5
3 are included. The signal of the sensor array 10 and the signal of the rotational position sensor 32 of the wedge prism are input to the microprocessor 51 via the A / D converter 52 in real time.

The microprocessor 51 operates the motor 5 of the auto focus driving mechanism 33 based on these signals.
6 as well as the motor 57 of the wedge prism rotation mechanism 31 to execute necessary autofocus control.

Next, the control operation of the microprocessor 51 will be described with reference to a flowchart. The microprocessor 51 includes an AF (auto focus) shown in FIG.
The main routine of control is executed. In this main routine, four subroutines 100, 200, 30
Steps 0 and 400 are repeatedly executed in order. In these subroutines 100, 200, 300, and 400, auto focus control is performed for each of the four light incident points A, B, C, and D.

The auto focus control at the point A is shown in FIG.
Is executed according to the flowchart shown in FIG. First, in the first step 101, the wedge prism 12 is rotated, and while watching the signal of the wedge prism rotation position sensor 32,
The light incident point is set to point A. Next, in step 102, the signal of the sensor array 10 when the laser beam L1 is incident at the point A is read. In this case, the effective light receiving sensor is E
1, E2, F1, F2, their signals e1,
Read e2, f1, f2. And step 103
Calculate the values of "e1 + e2" and "f1 + f2".

Next, the read signals e1, e2, f1, f
It is determined whether 2 is valid or invalid (step 104). For example, when the measurement target point is in a blind spot from the irradiated laser beam L1, these signals e1, e2, f1, f2
Deviates from the normal range (a normal range is determined by comparison with other data, etc.). In that case, it is determined that those data are invalid and the data e1, e2, f
1, f2 is discarded (step 105), and the process returns to the main routine. Then, in the main routine, the light incident point is moved to the next point (that is, the process proceeds to the “AF at point B” subroutine).

If it is determined that the data e1, e2, f1, and f2 are valid, it is determined whether or not the image is in focus based on the data (step 10).
6). The focus is determined based on whether “e1 + e2 = f1 + f2”. In the case of focusing, the motor for focusing is stopped (step 107), and the process returns to the main routine.

If it is not in focus, it is determined in step 108 whether the focus is on the front or the back. Judgment of front focus or rear focus is
The determination is made based on whether “e1 + e2> f1 + f2”. In the case of AF at point A, if “e1 + e2> f1 + f2”, it is determined to be the front focus, and if “e1 + e2 <f1 + f2”, it is determined to be the back focus.

In the case of the previous pin, step 109
Is used to determine whether the state is large or small.
The determination is made based on whether or not “e1> e2”. If the out-of-focus is large, the process proceeds to step 110, in which the motor is rotated to the rear focus side at full speed to approach the focal point (this operation is referred to as coarse AF). On the other hand, when the defocus is small or when the defocus becomes small, the process proceeds to step 111, and the motor is slowly rotated to the rear focus side to search for a focal point (this operation is called fine movement AF).

Following steps 110 and 111, step 1
Returning to 02, the motor is controlled and brought to the focal point while repeatedly watching the sensor signals e1, e2, f1, and f2 so as to gradually approach the focal point.

At the stage where the process has proceeded to step 111, the data e1, F1 of the outer light receiving sensors E1, F1
If f1 is set to "0" and ignored, autofocus control excluding the effect of the ghost image can be performed.

In the case of rear focus, the process proceeds from step 108 to step 112 to determine whether the state of defocus is large or small. The judgment is “f1> f2”
Whether to do. If the defocus is large, the process proceeds to step 113, in which the motor is turned to the front focus side at full speed to approach the focal point (coarse movement AF). On the other hand, when the out-of-focus is small or when the out-of-focus is small, the process proceeds to step 114, and the motor is slowly rotated to the front focus side to search for a focal point (fine movement AF).

Following steps 113 and 114, step 1
Returning to 02, the motor is controlled and brought to the focal point while repeatedly watching the signals e1, e2, f1, and f2 of the sensor so as to gradually approach the focal point.

As described above, when the process proceeds to step 114, the outer light receiving sensors E1, F1
If the data e1 and f1 are set to "0" and ignored, it is possible to perform autofocus control excluding the influence of the ghost image.

Next, the auto focus control at the point B is as follows.
It is executed according to the flowchart shown in FIG. The control at the point B is almost the same as the control at the point A, but uses a different sensor signal.

First, in a first step 201, the wedge prism 12 is rotated, and the light incident point is set to the point B while watching the signal of the wedge prism rotation position sensor 32. Next, in step 202, the signal of the sensor array 10 when the laser beam L1 is incident at the point B is read. In this case, since the effective light receiving sensors are G1, G2, H1, and H2, the signals g1, g2, h1, and h2 are read. Then, in step 203, “g1 + g2”, “h1
+ H2 "is calculated.

Next, the read signals g1, g2, h1, h
It is determined whether 2 is valid or invalid (step 204). For example, when the measurement target point is in a blind spot from the irradiated laser beam L1, these signals g1, g2, h1, h2
Deviates from the normal range (a normal range is determined by comparison with other data, etc.). In that case, it is determined that those data are invalid and the data g1, g2, h
1, h2 is discarded (step 205), and the process returns to the main routine. Then, in the main routine, the light incident point is moved to the next point (that is, the process proceeds to the “AF at point C” subroutine).

If it is determined that the data g1, g2, h1, and h2 are valid, it is determined whether or not the image is in focus based on the data (step 20).
6). The focus is determined based on whether “g1 + g2 = h1 + h2”. In the case of focusing, the motor for focusing is stopped (step 207), and the process returns to the main routine.

If not in focus, it is determined in step 208 whether the focus is on the front or the back. Judgment of front focus or rear focus is
The determination is performed based on whether “g1 + g2> h1 + h2”. In the case of AF at the point B, if “g1 + g2> h1 + h2”, it is determined to be the front focus, and if “g1 + g2 <h1 + h2”, it is determined to be the back focus.

In the case of the previous pin, step 209
Is used to determine whether the state is large or small.
The determination is made based on whether “g1> g2”. If the defocus is large, the process proceeds to step 210, in which the motor is rotated to the rear focus side at full speed to approach the focal point (coarse movement A
F). On the other hand, when the defocus is small, or
When the defocus becomes small, the process proceeds to step 211, and the motor is slowly rotated to the rear focus side to search for a focal point (fine movement AF).

Following steps 210 and 211, step 2
Returning to 02, the motor is controlled and brought to the focal point while repeatedly watching the signals g1, g2, h1, and h2 of the sensor so as to gradually approach the focal point.

At the stage where the process proceeds to step 211, the data g1 of the outer light receiving sensors G1 and H1,
If g1 is set to “0” and set to be ignored, it is possible to perform autofocus control excluding the influence of the ghost image.

In the case of back focus, the process proceeds from step 208 to step 212 to determine whether the out-of-focus state is large or small. The judgment is “g1> g2”
Whether to do. If the defocus is large, the process proceeds to step 213, in which the motor is turned to the front focus side at full speed to approach the focal point (coarse AF). On the other hand, when the out-of-focus is small or when the out-of-focus is small, the process proceeds to step 214, and the motor is slowly rotated to the front focus side to search for a focal point (fine movement AF).

Steps 213 and 214 are followed by step 2
Returning to 02, the motor is controlled and brought to the focal point while repeatedly watching the signals g1, g2, h1, and h2 of the sensor so as to gradually approach the focal point.

As described above, when the process proceeds to step 214, the outer light receiving sensors G1, H1
If the data g1 and h1 are set to "0" and ignored, autofocus control excluding the influence of the ghost image can be performed.

Next, the auto focus control at the point C is as follows.
This is executed according to the flowchart shown in FIG. The control at the point C is almost the same as the control at the point A, and the signal of the sensor to be used is the same, but the role of the sensor is reversed.

First, in the first step 301, the wedge prism 12 is rotated, and the light incident point is set to the point C while watching the signal of the wedge prism rotation position sensor 32. The processing from the next step 302 to step 307 is A
The description is omitted because it is the same as the processing in the point.

The difference is in the determination of the front focus or the rear focus in step 308. In the case of the processing at the point A, "e1
+ E2> f1 + f2 ”, the previous pin,“ e1 + e2 <f
1 + f2 ”, it is determined that the back focus has occurred. However, in the case of the processing at the point C, the process is reversed, and“ e1 + e2 <f1 + f2 ”.
Is determined as a front focus, and when "e1 + e2> f1 + f2", it is determined as a rear focus.

Then, in the case of the previous pin, step 309
It is determined whether or not "f1>f2" indicates that the defocus is large or small. If the defocus is large, proceed to step 310, rotate the motor to the rear focus side at full speed to approach the focal point. If the defocus is small, proceed to step 311 and slowly rotate the motor to the rear focus side. Search for the focal point.

In the case of rear focus, it is determined in step 308 whether "e1>e2" indicates whether the defocus state is large or small. If the defocus is large, proceed to step 313, rotate the motor to the rear focus side at full speed to approach the focal point, and if the defocus is small, proceed to step 314 and slowly rotate the motor to the rear focus side. Search for the focal point. Other points are the same as the processing of the point A.

Next, the auto focus control at the point D is as follows.
This is executed according to the flowchart shown in FIG. The control at the point D is almost the same as the control at the point B, and the signal of the sensor to be used is the same, but the role of the sensor is reversed.

First, in the first step 401, the wedge prism 12 is rotated, and the light incident point is set to the point D while observing the signal of the wedge prism rotation position sensor 32. The processing from the next step 402 to step 407 is B
The description is omitted because it is the same as the processing in the point.

The difference is in the determination of the front focus or the rear focus in step 408. In the case of processing at the point B, “g1
+ G2> h1 + h2 ”, the front focus,“ g1 + g2 <h ”
1 + h2 ”, the rear focus is determined. However, in the case of the processing at the point D, the process is reversed and“ g1 + g2 <h1 + h2 ”.
Is determined as a front focus, and when "g1 + g2> h1 + h2", it is determined as a rear focus.

In the case of the previous pin, step 409
It is determined whether or not "h1>h2" indicates that the defocus state is large or small. If the defocus is large, proceed to step 410, rotate the motor to the rear focus side at full speed to bring it closer to the focal point. If the defocus is small, proceed to step 411 and slowly rotate the motor to the rear focus side Search for the focal point.

In the case of back focus, it is determined in step 408 whether "g1>g2" indicates whether the defocus state is large or small. If the defocus is large, proceed to step 413, rotate the motor to the rear focus side at full speed to approach the focal point, and if the defocus is small, proceed to step 414 and slowly rotate the motor to the rear focus side. Search for the focal point. Other points are the same as the processing of the point B.

As described above, if the data at point A is invalid, switch to point B, and if the data at point B is invalid, C is used.
Switch to point, switch to point D if data at point C is invalid, return to point A if data at point D is invalid, and irradiate laser light L1 sequentially from four directions. Irrespective of the shape of the test object 2, the laser light L1 irradiating an arbitrary measurement target position from any direction
, So you can focus without making a blind spot.

For example, as shown in FIGS. 6A and 6B, even when the object 2 has the convex portion 2a, the points A, B, C, and D Laser light L1A, L1B, L1C,
By irradiating L1D, as shown in FIGS. 7A and 7B, the laser light L1A from one direction is projected to the convex portion 2a.
Of the laser beam L1B, L1C, L1D from other directions even if it does not reach the target point MQ
Reaches the target point MQ, the objective lens 1 can be surely focused on the target point MQ.

As described above, the outer and inner light receiving sensors E1, E2, F1, F2, G1, G2, H
The autofocus control (wide control) is performed in accordance with the flowcharts shown in FIGS. 9 to 13 using all the signals of H1 and H2. If the range of the focus shift is limited to a narrow range, the sensor to be used is used. Is limited to the light receiving sensors E2, F2, G2, and H2 on the inner side, and autofocus control (narrow control) can be performed. In that case, for example, the signals e1, f1, g1, and h1 of the outer light receiving sensors E1, F1, G1, and H1 may be fixed to “0”.

If the stage or the like on which the test object is mounted is driven while the auto-focus control is continuously performed, the light receiving spot may deviate from the light receiving portion of the sensor array 10 due to the influence of scattering, holes, and the like. However, in such a case, a threshold may be set in advance for the signal of the sensor, and when the signal exceeds the threshold, the autofocus control may be interrupted.

In the above embodiment, the sensor array 1
Although the case where the number of divisions of the light receiving units E, F, G and H of 0 is divided into two inside and outside is shown, the number of divisions is not limited to this and may be set arbitrarily.

[0099]

As described above, according to the present invention,
Since the measurement beam can be irradiated to the surface of the test object from four directions through the objective lens, even if the surface of the test object has irregularities, the measurement beam from any of the light incident points can be irradiated. Can always reach the target point on the test object,
Appropriate autofocus control can be performed based on the measurement beam. Therefore, irrespective of the shape of the object to be inspected, much more accurate focusing can be performed as compared with the conventional method.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a schematic configuration of a microscope including an autofocus device according to an embodiment of the present invention.

FIG. 2 is a view taken in the direction of arrows II-II in FIG. 1 and shows a position of a light incident point of a laser beam (measurement beam) on an incident surface of the objective lens.

3 is a view taken in the direction of arrows III-III in FIG. 1 and shows a configuration of a sensor array.

FIG. 4 is a diagram showing an example of a light receiving spot formed on the sensor array.

FIG. 5 is a diagram showing how a ghost image of a light receiving spot formed on the sensor array appears.

6A and 6B are principle diagrams showing a state in which a laser beam is irradiated on a test object by the autofocus device of the present invention, and FIG.
Is a side view, and (b) is a perspective view.

7A and 7B are diagrams for explaining the effectiveness of the autofocus device of the present invention, wherein FIG. 7A is a side view, and FIG. 7B is a plan view.

FIG. 8 is a block diagram illustrating an electrical configuration of the autofocus device according to the embodiment of the present invention.

FIG. 9 is a flowchart showing processing contents of the microprocessor of FIG. 8;

FIG. 10 is a flowchart showing the contents of a first subroutine in the flowchart of FIG. 9;

FIG. 11 is a flowchart showing the contents of a second subroutine in the flowchart of FIG. 9;

FIG. 12 is a flowchart showing the contents of a third subroutine in the flowchart of FIG. 9;

FIG. 13 is a flowchart showing the contents of a fourth subroutine in the flowchart of FIG. 9;

14A and 14B are diagrams for explaining the content of conventional fine beam type autofocus control, where FIG. 14A is a side view showing a relationship between an objective lens and a measurement beam, and FIG. 14B is a diagram showing how light is received on an optical sensor. It is a top view of the optical sensor which shows whether a spot is formed.

FIG. 15 is a flowchart showing processing content of conventional auto focus control.

16A and 16B are diagrams for explaining a problem of the conventional autofocus control, in which FIG. 16A is a side view showing a state where a measurement beam is irradiated on a planar test object, and FIG. FIG. 7C is a side view showing a state in which the measurement object is irradiated with the measurement beam, and FIG. 9C is an enlarged side view showing that a blind spot where the measurement beam does not reach is formed by the convex portion.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Objective lens 2 Object to be measured 5, 6 Beam splitter 10 Sensor array (Defocus detection means) 12 Wedge prism 15 Laser light source (Measurement beam irradiation source) K Optical axis L1, L1A, L1B, L1C, L1D Laser light (Measurement beam ) L2 laser reflected light (reflected light of measurement beam) E, F, G, H light receiving section E1, E2, F1, F2, G1, G2, H1, H2 light receiving sensor SP, SPf, SPb light receiving spot

Claims (5)

[Claims] 1. An observation optical system including an objective lens, a measurement beam irradiation mechanism configured to irradiate a measurement beam to an object to be measured through the objective lens with a position deviating from an optical axis of the objective lens as a light incident point, and A focus shift detecting means for receiving reflected light of the measurement beam guided from the object through the objective lens, and detecting a focus shift of the test object from a focus position of the objective lens by a position of a light receiving spot formed on the light receiving surface; Control means for controlling a drive mechanism for adjusting the distance between the objective lens and the test object based on the output of the defocus detection means, thereby controlling the focus of the objective lens on a target point on the test object. In the autofocus device for a microscope provided with, as the light incident points, four light incident points are set on the circumference around the optical axis of the objective lens at intervals of 90 degrees in the circumferential direction,
The measurement beam irradiating mechanism irradiates the object to be measured with the measurement beam at the four light-entering points in order, and for each irradiation of the measurement beam at each light-irradiation point, the focal position of the objective lens is detected by the defocus detecting means. An autofocus device for a microscope, wherein the control means controls the drive mechanism based on the detection output of the defocus of the object to be detected. 2. A measurement beam irradiation mechanism for sequentially irradiating a test object with a measurement beam at the four light incident points, a measurement beam irradiation source for emitting one measurement beam, and a measurement beam irradiation source emitted from the irradiation source. A wedge prism through which the measured beam passes,
2. The microscope according to claim 1, further comprising: a rotation mechanism configured to rotate the wedge prism to rotate the measurement beam along a circular locus passing through the four light incident points. Focus device. 3. The defocus detecting means includes four light receiving units arranged in a cross, and a combination of two light receiving units arranged on a straight line allows a light incident point to be applied to a test object at one light incident point. One detecting unit configured to receive the reflected light when the measurement beam is irradiated is configured, and the two light receiving units arranged on the straight line include:
Positional relationship such that a light-receiving spot is formed between two light-receiving parts during focusing, a light-receiving spot is formed on one light-receiving part at the time of front focus, and a light-receiving spot is formed on the other light-receiving part at the time of rear focus. And a combination of two light receiving sections arranged on a straight line also serves as each detecting means for detecting a defocus when the measurement beam is irradiated at each of the two light incident points located at positions opposed by 180 degrees. 3. The autofocus device for a microscope according to claim 1, wherein: 4. The four light receiving sections arranged in a cross,
4. An autofocus apparatus for a microscope according to claim 3, wherein each of said plurality of light receiving sensors is divided into an inner light receiving sensor and an outer light receiving sensor, and said defocus detecting means comprises an eight-divided sensor array. 5. The control means evaluates the validity of the signal of the defocus detection means obtained by irradiating the measurement beam at one light incident point, and when the control means evaluates that the signal is invalid, The signal according to any one of claims 1 to 4, wherein the signal is not adopted, a control signal is sent to the measurement beam irradiation mechanism, and a light incident point of the measurement beam is moved to a light incident point in the next order. Autofocus device for microscope.