JP2006285154A - Focus detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a slit-projection system focus detector which is attained at a low cost, and easily adjustable. <P>SOLUTION: A diffusion plate 11 diffuses light in at least only one one-dimensional direction in a plane, and also, the diffusion angle on the diffusion is controlled. An objective lens 106 condenses the luminous flux of light emitted from the diffusion plate 11 when parallel light is made incident on the diffusion plate 11, and the lens 106 is used also as a part of an observation optical system. The light receiving surface of a photodetector 15 is arranged in the light condensing position of the objective lens 106, and the light receiving surface is irradiated with the luminous flux which returns from the objective lens 106 after being condensed by the objective lens 106 and reflected on the surface of a sample 100. A distance between the surface of the sample 100 and the objective lens 106 is controlled by a stage Z-axis control circuit 110 based on a signal outputted from the photodetector 15. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a technique of an imaging optical system for observing, measuring, and inspecting a specimen, and more particularly to a technique for detecting focus.

  When the light beam is half-shielded in the optical path for re-imaging the return light of the spot light projected on the specimen surface and focused on the photodetector, the WD (working distance) changes between the specimen and the objective lens. The position and size of the spot image focused on the photodetector changes. Then, since the signal output from the photodetector changes, it is possible to determine the in-focus / in-focus state. This method is well known as one of the active focus detection devices. Here, this focus detection method is referred to as a single spot method.

This single spot type focus detection apparatus will be further described.
FIG. 12 shows an optical system of a single spot type focus detection apparatus cut out from a microscope. This optical system includes a light source 101, a collimating lens 102, a shutter 103, a half mirror 104, a dichroic mirror 105, an objective lens 106, a condenser lens 107, and a photodetector 108.

As the light source 101, a semiconductor laser (LD) having an infrared wavelength is used.
The dichroic mirror 105 has a property of reflecting light in the infrared region while transmitting light in the visible region. Therefore, the objective lens 106 also serves as a part of the observation optical system.

The light receiving surface of the photodetector 108 is divided into two regions by a surface including the optical axis, and a signal output for each region is obtained separately.
Of the light rays emitted from the light source 101 and collimated by the collimator lens 102 to become parallel light, half of the light flux is shielded by the shutter 103. The remaining rays that are not shielded by the shutter 103 are transmitted through the half mirror 104, reflected by the dichroic mirror 105, passed through the optical path on the right side with respect to the optical axis, transmitted through the objective lens 106, and the sample surface of the sample 100. Projected in a spot shape.

  The reflected light from the sample surface passes through the optical path on the left side toward the optical axis after passing through the objective lens 106, is reflected by the dichroic mirror 105 and the half mirror 104, and is collected on the light receiving surface of the photodetector 108 by the condenser lens 107. Shine. The magnitude of the signal output from the photodetector 108 is output as a value corresponding to the amount of light irradiated on the light receiving surface.

Here, when the sample surface and the light receiving surface of the photodetector 108 have a conjugate positional relationship, the reflected light from the sample surface is collected on the boundary line of the light receiving surface of the photodetector 108.
On the other hand, a case where the conjugate positional relationship between the sample surface and the light receiving surface of the photodetector 108 is broken, that is, a case where the WD between the sample surface and the objective lens 106 is changed will be described with reference to FIG. In FIG. 13, a single lens system 120 in which the objective lens 106 and the condenser lens 107 are combined is shown and described.

  First, when the sample surface and the light receiving surface of the photodetector 108 are in a conjugate positional relationship, the reflected light from the sample surface is reflected on the light receiving surface of the photodetector 108 as shown in FIG. Concentrate on the boundary.

  Here, when the WD between the specimen surface and the objective lens 106 increases, the reflected light from the specimen surface is condensed before the light receiving surface of the photodetector 108, and the photodetector 108 is shown in FIG. ), The light is received while being defocused on the lower light receiving surface in the figure.

  On the other hand, when the WD between the sample surface and the objective lens 106 is decreased, the reflected light from the sample surface is collected deeper than the light receiving surface of the photodetector 108. As shown in (c), light is received in a state where it is defocused on the upper light-receiving surface in FIG.

  That is, the position and size of the spot image condensed on the photodetector 108 change according to the change in WD between the sample surface and the objective lens 106. As a result, since the signal output from the photodetector 107 changes, it is possible to determine the in-focus state or the out-of-focus state.

  Returning to the description of FIG. 12, the signal output from each region of the light receiving surface divided into two in the photodetector 108 is input to the difference circuit 109 and subtracted or normalized by a normalization circuit (not shown). It is output as a signal of the selected value. This output signal is input to the stage Z-axis control circuit 110 to determine the in-focus direction. Based on the determination result, the Z-axis stage 111 is moved up and down at a constant speed to move the sample surface of the sample 100 to the in-focus position. Thus, automatic focusing is realized.

  As a technique similar to the focus detection technique using the single spot method, for example, Patent Document 1 discloses a technique in which a diffraction grating is arranged between a collimating lens and a shutter to increase the number of spots projected on a specimen surface. Has been.

  In addition, for example, in Patent Document 2, a cylindrical lens is disposed between a collimating lens and a shutter so that only a light beam having a curvature direction component is condensed at the rear focal position of the objective lens and projected onto a specimen surface. A technique for making a slit is disclosed.

  Further, for example, in Patent Document 3, by arranging a cylindrical lens between a dichroic mirror and a half mirror, only a light beam having a curvature direction component is condensed at the rear focal position of the objective lens and projected onto the specimen surface. A technique for slitting a spot is disclosed.

In the case of various techniques as described above, the in-focus position is the average position of the steps in the range projected on the sample surface.
In the following description, the focus detection method related to the technique disclosed in Patent Document 1 will be referred to as a multi-spot method, and the focus related to the techniques disclosed in Patent Document 2 and Patent Document 3 will be referred to. The detection method is called a slit projection method.
JP 2001-296469 A JP-A-10-161195 JP-A-8-254650

  In the focus detection by the single spot method, when the step pattern is formed on the sample surface and the spot light is projected onto the edge portion, the return light may be rapidly reduced. In addition, the scattered light may form an image on the light receiving portion of the photodetector as stray light. In such a case, as a result of adding noise to the signal output from the photodetector, the focusing accuracy is lowered.

Further, when the level difference of the sample surface exceeds the object-side focal depth of the objective lens, the following phenomenon may occur in the focus detection by the single spot method.
FIG. 14 shows the positional relationship between the objective lens and the sample. Here, it is assumed that the surface above the step formed on the specimen surface of the specimen 100 placed on the Z-axis stage 111 is to be observed.

FIG. 14A shows that focus detection is performed on the upper surface of the step 100a of the sample surface of the sample 100, and at this time, a desired surface can be observed.
However, in the focus detection by the single spot method, since the focus detection area is always one point, if the position of the sample 100 is moved in the plane to the state shown in FIG. The lower surface of 100a becomes a focus detection region. In this case, the surface on the upper side of the step 100a, which is the part that is originally desired to be observed, is defocused.

As described above, when single spot type focus detection is used in an optical system that captures images by automatic control, the focus detection result may deviate from a desired observation position.
On the other hand, the above-mentioned focus detection by the multi-spot method or the slit projection method was introduced in order to solve the above-described problem of focus detection by the single spot method, and the range in which the in-focus position is projected on the sample surface. Since it becomes the average position of the height of the inner step, instability of the in-focus position can be eliminated.

However, the focus position may not be stable even with focus detection in the case of the multi-spot method. Such a case will be described with reference to FIG.
FIG. 15 shows an example of the relationship between the multi-spot 200a projected on the sample 100 and the interval between the steps 100a of the sample 100. When the pitch of the step 100a of the sample 100 coincides with the spot interval as in the case of FIG. 15, or when the pitch and the spot interval have an integer multiple of the pitch. As in the case of the single spot method, if the spot 200a reaches the boundary of the step 100a when the position of the sample 100 is moved in the plane, the same behavior as in FIG. 14 occurs, and the in-focus position changes. As a result, the desired observation position is defocused, so that the surface to be originally observed cannot be observed.

  On the other hand, as shown in FIG. 16, in the case of focus detection by the slit projection method in which the detection spot is the slit 200b, the above phenomenon does not occur. However, the cylindrical lens itself is expensive and has a high degree of difficulty in position adjustment when assembling the apparatus, so that a complicated adjustment mechanism is required. Further, when a high-magnification objective lens is used, since such an objective lens has a short focal length, it is difficult to accurately match the condensing position of the cylindrical lens with the rear focal position of the objective lens.

  The present invention has been made in view of the above-described problems, and a problem to be solved is to provide a low-cost and easy-to-adjust focus detection apparatus using a slit projection method.

  A focus detection apparatus according to one aspect of the present invention includes a diffusing element that diffuses light only in at least one one-dimensional direction in a plane and a diffusion angle in the diffusion is controlled, and a parallel light A condensing optical system that condenses the light beam emitted from the diffusing element when incident on the condensing element and also serves as a part of the observation optical system; A light detector in which a light receiving surface is arranged at a light position, and the light beam condensed by the light collecting optical system is reflected on the sample surface, and then returns to the light collecting optical system to be irradiated to the light receiving surface. And a distance control unit that controls a distance between the sample surface and the condensing optical system based on a signal output from the photodetector. Yes, this feature solves the aforementioned problems.

  The focus detection apparatus according to the present invention described above further includes a light shielding member that shields a part of the light incident on the diffusion element or the light emitted from the diffusion element, and the distance control unit includes the light detection unit. The distance may be controlled so that the light beam applied to the light receiving surface of the device forms an image at a predetermined position on the light receiving surface.

  At this time, the diffusion element diffuses the light emitted from the light source only in one one-dimensional direction, the light shielding member shields half of the incident light flux, and the light detector The light receiving surface is divided into two regions on the surface including the optical axis of the light beam irradiated to the light receiving surface, and a signal corresponding to the amount of light irradiated to the region is output for each region. The distance control unit may be configured to control the distance so that the difference in the amount of light applied to each of the areas is small.

  Alternatively, at this time, the diffusing element diffuses the light emitted from the light source only in two one-dimensional directions, and the light shielding member shields a three-quarter region of the light flux, and the light detector The light receiving surface is divided into four regions on the surface including the optical axis of the luminous flux irradiated to the light receiving surface, and a signal corresponding to the amount of light irradiated to the region is output for each region. And a selection unit that selects two signals from the signals for each region output from the photodetector, and the distance control unit reduces a difference between the two signals selected by the selection unit. The distance may be controlled as described above.

  Alternatively, at this time, a determination unit that determines whether or not the distance obtained as a result of control by the distance control unit is appropriate as a detection result of the focal position, and determination that the determination unit is inappropriate And a selection control unit that controls the selection unit to switch the selection of the signal by the selection unit.

  At this time, the determination unit is configured to perform the determination based on the degree of change in the difference between the two signals selected by the selection unit, which changes according to the control by the distance control unit. May be.

  At this time, the determination unit is configured to determine that the difference is incorrect when the degree of change in the difference between the two signals selected by the selection unit is less than a preset value. May be.

  According to the present invention, it is possible to provide a low-cost and easy-to-adjust focus detection apparatus using the slit projection method in which the spot projected onto the specimen is formed into a slit shape.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows a configuration of an optical system of a focus detection apparatus that implements the present invention. In the figure, components having the same functions as those shown in FIG. 12 are denoted by the same reference numerals, and detailed description thereof will be omitted.

  The focus detection apparatus shown in FIG. 1 is used for a microscope, and includes a light source 101, a collimating lens 102, a diffuser plate 11, a light projection side shutter 12, a half mirror 104, a relay lens system 13, a dichroic mirror 105, an objective. The lens 106, the light-receiving side shutter 14, the condensing lens 107, and the photodetector 15 constitute the optical system.

  As the light source 101, a semiconductor laser (LD) having an infrared wavelength is used. At this time, the coherence may be destroyed by changing the wavelength of the laser light minutely in units of several nm by periodically changing the current value applied to the semiconductor laser.

The dichroic mirror 105 has a property of reflecting light in the infrared region and transmitting light in the visible region. Therefore, the objective lens 106 also serves as a part of the observation optical system.
The diffusing plate 11 is a diffusing element that diffuses light only in at least one one-dimensional direction in the plane, and the diffusion angle in the diffusion is controlled. In this embodiment, the diffusion order is limited. The diffraction grating is designed to have a diffraction angle sufficiently small so that the diffracted light cannot be separated.

  In this embodiment, the light beam is diffused only in the one-dimensional direction on the surface, that is, the incident light beam 20a and the outgoing light beam schematically shown in FIG. As in the relationship with 20b, a light that diffuses and emits incident light in a line segment is used. As the diffusion plate 11 that causes such diffusion, for example, LSD (trade name), which is a beam shaping diffuser manufactured by Physical Optics Corporation, can be used.

  The diffuser plate 11 is disposed in the vicinity of a position conjugate with the pupil of the objective lens 106, but the light incident on the diffuser plate 11 is collimated by the collimator lens 102, and the diffuser plate 11 has a cylindrical lens or the like. Since there is no light collecting action, the setting of the arrangement in the optical axis direction is relatively easy.

  In the present embodiment, the photodetector 15 has a light receiving surface that is divided in two by a surface including the optical axis, and can obtain a signal output corresponding to the amount of received light for each of the divided light receiving surfaces. use. This output signal is input to the difference circuit 109, subtracted or normalized, and input to the stage Z-axis control circuit 110. The stage Z-axis control circuit 110 determines the in-focus direction based on this signal, and moves the Z-axis stage 111 up and down based on the determination result to move the sample surface of the sample 100 to the in-focus position.

  In FIG. 1, when a light beam emitted from the light source 101 and collimated by the collimator lens 102 to become parallel light passes through the diffusion plate 11, it diffuses in one direction as shown in FIG.

  Half of the luminous flux of this diffused light is shielded by the light projection side shutter 12 provided beside the diffuser plate 11. If the position of the light projection side shutter 12 is near the diffusion plate 11, it is arranged on the collimator lens 102 side instead of being arranged on the half mirror 104 side as shown in FIG. 1, that is, incident on the diffusion plate 11. You may make it light-shield half of the light beam to perform.

  The remaining light that has not been blocked by the light-projecting shutter 12 passes through the half mirror 104 and the relay lens system 13, is reflected by the dichroic mirror 105, and passes through the left optical path toward the optical axis. Then, the light is guided to the objective lens 106 and condensed on the surface of the specimen 100 in a slit shape.

  At this time, the light beam reflected by the sample surface passes through the objective lens 106, and then returns to the dichroic mirror 105 through the optical path on the right side with respect to the optical axis. And reflected by the half mirror 104. The light beam reflected here is condensed on the light receiving surface of the photodetector 15 by the condenser lens 107 after the noise light is cut by the light receiving side shutter 14.

Here, FIG. 3 will be described. This figure shows the state of light collection on the light receiving surface of the photodetector 15 at this time.
When the sample surface of the sample 100 and the light receiving surface of the photodetector 15 are in a conjugate positional relationship, the reflected light from the sample surface is condensed in a slit shape on the boundary line of the light receiving surface, and FIG. An image as shown in FIG.

  On the other hand, when the conjugate positional relationship between the sample surface of the sample 100 and the light receiving surface of the photodetector 15 is broken, the image on the light receiving surface changes. Here, when the WD increases, the reflected light from the sample surface is collected before the light receiving surface, so that the image on the light receiving surface is on the left side as shown in FIG. The light receiving surface is defocused. Conversely, when the WD decreases, the reflected light from the sample surface is collected deeper than the light receiving surface, so that it is defocused toward the right light receiving surface as shown in FIG. It becomes a state.

  That is, the position and size of the slit image condensed on the photodetector 15 change according to the change in WD between the specimen 100 and the objective lens 106. The behavior in which the image on the light receiving surface changes due to the change in WD is the same as in the case of the single spot method.

  The difference circuit 109 obtains a difference between signals output for each of the two light receiving surfaces of the photodetector 15. The stage Z-axis control circuit 110 determines the in-focus direction (the direction in which the absolute value of the difference signal becomes smaller) based on the difference signal, and moves the Z-axis stage 111 up and down based on the determination result to move the specimen 100 The sample surface is moved to change the WD. Then, automatic focusing is realized by stopping the Z-axis stage 111 when the absolute value of the difference signal is minimized.

  Note that, instead of obtaining the difference signal between the two signals output from the photodetector 15 in the difference circuit 109, the difference signal is obtained as a normalized value, that is, the 2 for the sum of the two signals. Even if the signal indicating the ratio of the difference between the two signals is obtained and the stage Z-axis control circuit 110 performs the above-described operation based on this signal, automatic focusing can be performed.

  In the present embodiment, even if the sample surface has a stepped shape, the signal output from the photodetector 15 is spatially integrated in the light receiving surface by an image obtained according to the shape of the step. Is output as Accordingly, the detected focus position is the average position of the steps in the range projected on the sample surface. That is, the focus detection apparatus of the present embodiment can perform focus detection similar to the case of focus detection by the conventional slit projection method.

  In addition, the diffuser plate 11 used in the present embodiment is less expensive than a cylindrical lens used in focus detection by the conventional slit projection method, so that the cost of the apparatus is reduced. Furthermore, complicated and highly difficult adjustment operations such as adjusting the center of the cylindrical lens and accurately matching the condensing position of the cylindrical lens with the rear focal position of the objective lens 10 are not required.

  The configuration of the optical system of the focus detection apparatus according to the present embodiment is the same as that shown in FIG. In addition, the configurations of the photodetector 15 and the difference circuit 109 are different from those in the first embodiment.

  The diffuser plate 11 is the same as the first embodiment in that it is a diffraction grating that has a diffraction order that is designed to have a diffraction angle that is sufficiently small so that the diffraction order is not limited and the diffracted light cannot be separated. The diffuser plate 11 diffuses light only in two one-dimensional directions on the surface, that is, as shown by the relationship between the incident light beam 20c and the emitted light beam 20d schematically shown in FIG. What diffuses and radiate | emits light in the shape of a line segment of two directions is used. As the diffusion plate 11 that causes such diffusion, for example, LSD (trade name), which is a beam shaping diffuser manufactured by Physical Optics Corporation, also used in the first embodiment, can be used in this embodiment.

Further, in the present embodiment, the light projection side shutter 12 and the light receiving side shutter 14 are configured to shield a three-quarter region of the luminous flux as in the light shielding unit 21 shown in FIG.
Further, in the present embodiment, the photodetector 15 has a light receiving surface that is divided into four by a surface including the optical axis, and a signal output corresponding to the amount of light received can be obtained for each of the divided light receiving surfaces. Use what you can.

  In this embodiment, instead of the differential circuit 109, the terminal configuration is shown in FIG. 6A and the internal configuration is shown in FIG. 6B. That is, the selection circuit 22 and the selection control of the selection circuit 22 are selected. A difference circuit unit 23 formed by combining the terminal 22a and the difference circuit 109 is used. This selection circuit 22 gives a control signal to the selection control terminal 22a from the outside, so that two of the four signals output from the photodetector 15 whose light receiving surface is divided into four are subjected to difference calculation. The signal is selected.

  In the present embodiment, similarly to the first embodiment, when a semiconductor laser is used as the light source 101, the wavelength of the laser beam is changed in units of several nm by periodically changing the current value applied to the semiconductor laser. The coherence may be destroyed by changing it extremely minutely.

  In the configuration shown in FIG. 1, when the diffusing plate 11, the light emitting side shutter 12 and the light receiving side shutter 14, the photodetector 15, and the difference circuit unit 23 are provided, the collimating lens is emitted after being emitted from the light source 101. When the light beam collimated by 102 and becomes parallel light passes through the diffusion plate 11, it diffuses in two directions as shown in FIG.

  The diffused light is shielded from three-quarters of the luminous flux by the light-projecting shutter 12 provided near the diffuser plate 11. If the position of the light projection side shutter 12 is near the diffuser plate 11, it may be arranged on the collimating lens 102 side instead of being arranged on the half mirror 104 side as shown in FIG.

  The remaining light that has not been blocked by the light-projecting shutter 12 passes through the half mirror 104 and the relay lens system 13, is then reflected by the dichroic mirror 105, and passes through the left optical path toward the optical axis. Then, the light is guided to the objective lens 106 and condensed into a cross-shaped slit shape on the surface of the specimen 100 as in the line projection light 200c shown in FIG.

  At this time, the light beam reflected by the specimen surface passes through the objective lens 100, and then returns to the dichroic mirror 105 through the optical path on the right side with respect to the optical axis. And reflected by the half mirror 104. The light beam reflected here is condensed on the light receiving surface of the photodetector 15 by the condenser lens 107 after the noise light is cut by the light receiving side shutter 14.

Here, FIG. 8 will be described. This figure shows the state of light collection on the light receiving surface of the photodetector 15 at this time.
When the sample surface of the sample 100 and the light receiving surface of the photodetector 15 are in a conjugate positional relationship, the reflected light from the sample surface is collected in a cross slit shape on the boundary line of the light receiving surface, and FIG. An image as shown in FIG.

  On the other hand, when the conjugate positional relationship between the sample surface of the sample 100 and the light receiving surface of the photodetector 15 is broken, the image on the light receiving surface changes. Here, when the WD increases, the reflected light from the specimen surface is collected in front of the light receiving surface, so that the image on the light receiving surface is on the left side as shown in FIG. And it will be in the state defocused by the upper light-receiving surface. On the contrary, when the WD decreases, the reflected light from the specimen surface is collected deeper than the light receiving surface, and therefore, as shown in FIG. It will be in the focused state. The behavior in which the image on the light receiving surface changes due to the change in WD is the same as in the case of the single spot method.

  Next, of the signals output from each of the divided light receiving surfaces of the photodetector 15, a signal input to the difference circuit 109 is selected by the selection circuit 22. Specifically, as shown in FIG. 8, among the cross-crossed slit images collected on the light receiving surface of the photodetector 15, the selection control terminal 22 a is selected according to the slit image used for focus detection. Switch the applied signal.

  For example, in FIG. 8, when focusing detection is performed by focusing only on the slit image condensed in the horizontal direction in FIG. 8, signals output from the regions A and D are input to the difference circuit 109. Alternatively, the selection circuit 22 is switched, or the selection circuit 22 is switched so that signals output from the regions B and C are input to the difference circuit 109, respectively.

  For example, in FIG. 8, when focusing detection is performed by focusing only on the slit image condensed in the vertical direction in FIG. 8, signals output from the regions A and B are respectively sent to the difference circuit 109. The selection circuit 22 is switched so as to be input, or the selection circuit 22 is switched so that signals output from the region D and the region C are respectively input to the difference circuit 109.

  Further, for example, in FIG. 8, when focus detection is performed by paying attention to both the vertical and horizontal slit images that intersect and intersect the cross in FIG. 8, signals output as region B and region D The selection circuit 22 is switched so that each is input to the difference circuit 109.

  The difference circuit 109 of the difference circuit unit 23 obtains a difference between two signals selected from signals output for each of the four light receiving surfaces of the photodetector 15. The stage Z-axis control circuit 110 determines the in-focus direction (the direction in which the absolute value of the difference signal becomes smaller) based on the difference signal, and moves the Z-axis stage 111 up and down based on the determination result to move the sample 100. The sample surface is moved to change the WD. Then, automatic focusing is realized by stopping the Z-axis stage 111 when the absolute value of the difference signal is minimized.

  Note that, instead of obtaining the difference signal between the two selected signals output from the photodetector 15 in the difference circuit 109, the difference signal is obtained as a normalized value, that is, the two selected signals. A signal indicating the ratio of the difference between the two selected signals with respect to the sum of the signals is obtained, and automatic focusing is performed even if the stage Z-axis control circuit 110 performs the above-described operation based on this signal. Can do.

  As described above, in this embodiment, at least one slit image advantageous for focus detection is selected from the cross-crossed slit images collected on the light receiving surface of the photodetector 15, that is, the sample 10. At least one of the cross-crossed slit images projected onto the specimen surface is selected. According to the focus detection apparatus of this embodiment, for example, as shown in FIG. 9, when the shape of the step 100a on the sample surface of the sample 100 is parallel to one of the projected line projection light 200c. Even so, by using the line projection light 200c having a direction component orthogonal to the shape of the step 100a, appropriate focus detection can be performed.

  That is, according to the present embodiment, even in the case of FIG. 9, the average position of the steps within the range projected on the sample surface is adjusted without depending on the shape of the step 100 a of the sample 100. The focal position can be stabilized.

  The method of selecting the signal to be input to the difference circuit 109 among the signals output from each of the divided light receiving surfaces of the photodetector 15 may be manually selected by the user or automatically. It can also be made possible.

  When this selection is manually performed by the user, for example, a switch for switching a signal applied to the selection control terminal 22a is provided outside, and the user operates the switch to input a desired signal to the difference circuit 109. You can do so. In addition, a signal corresponding to a desired selection result may be applied to the selection control terminal 22a by operating a button for selecting a command.

Next, a method for automatically performing this selection will be described. At this time, an external control device such as a PC or a sequencer is added to the configuration shown in FIG.
As shown in FIG. 10, the external control device 30 is connected to the selection control terminal 22 a of the difference circuit unit 23 and the external control terminal 110 a of the stage Z-axis control circuit 110. In addition, an allowable range of the tilt amount of the focus error signal in the vicinity of the in-focus determination (degree of change per unit time) is registered in advance in a storage unit (not shown) provided in the external control device 30. .

  Here, FIG. 11 will be described. This figure is a flowchart showing the contents of control processing performed by a central processing unit (not shown) of the external control device 30. This process is realized by the central processing unit reading and executing a predetermined control program stored in advance in a storage unit (not shown) of the external control device 30, and the external control device 30 performs a focus detection operation. It starts when information indicating the start instruction is acquired.

  First, in S101, processing for setting the initial value of the variable n to “0” is performed. The variable n is used as a parameter for selecting a signal to be input to the difference circuit 109 among signals output from each of the divided light receiving surfaces of the photodetector 15.

In S102, processing for reading the allowable tilt amount range of the focus error signal in the vicinity of the focus determination described above is performed.
In S103, a signal for switching the selection circuit 22 so that signals output from the region B and the region C (see FIG. 8) of the divided light receiving surfaces of the photodetector 15 are input to the difference circuit 109, respectively. Processing to output to the selection control terminal 22a is performed.

  In S104, a process of giving a control signal for starting the focusing operation from the external control device 30 to the stage Z-axis control circuit 110 is performed. In S105, the signal output from the difference circuit 109 at this time (focus error) Signal) is received by the external control device 30.

  Thereafter, when the focusing operation is completed, a signal indicating completion of the focus detection operation is output from the stage Z-axis control circuit 110, and therefore, processing for receiving this signal by the external control device 30 is performed in S106.

  In S107, processing for calculating the tilt amount of the focus error signal in the vicinity of the in-focus position in the most recently performed focus detection operation is performed. Then, in subsequent S108, a process of determining whether or not the calculated inclination amount is equal to or greater than a specified value of the inclination amount indicated by the allowable range read out in the process of S102 is performed. Here, when it is determined that the calculated tilt amount is equal to or greater than the specified value (when the determination result is Yes), it is considered that the focus detection has been properly performed, and the focus detection operation is completed in S109. The control process in FIG. 11 is terminated. On the other hand, when it is determined in S108 that the calculated tilt amount is smaller than the specified value (when the determination result is No), the focus detection is regarded as inappropriate and the process proceeds to S110.

In S110, a process for determining the current value of the variable n described above is performed.
In the process of S110, when the value of the variable n is determined to be “0”, focus detection based on signals output from the areas B and C of the divided light receiving surface of the photodetector 15 is performed. In S111, signals output from the regions B and A (see FIG. 8) of the divided light receiving surfaces of the photodetector 15 are input to the difference circuit 109, respectively. Thus, a process of outputting a signal for switching the selection circuit 22 to the selection control terminal 22a is performed, and thereafter, the process proceeds to S114.

  Further, when the value of the variable n is determined to be “1” in the processing of S110, focusing based on signals output from the regions B and A of the divided light receiving surfaces of the photodetector 15 is performed. It is assumed that the detection is also improper, and in S112, signals output from regions B and D (see FIG. 8) of the divided light receiving surfaces of the photodetector 15 are input to the difference circuit 109, respectively. As described above, a process of outputting a signal for switching the selection circuit 22 to the selection control terminal 22a is performed, and thereafter, the process proceeds to S114.

  On the other hand, when the value of the variable n is determined to be “2” in the processing of S110, focusing based on signals output from the regions B and D of the divided light receiving surfaces of the photodetector 15 is performed. In S113, it is assumed that the detection is also improper, and in S113, for example, a display indicating that the focus detection is improper is displayed on the display unit (not shown) of the external control device 30. The control process of FIG. 11 is terminated thereafter.

In S114, a process of adding “1” to the current value of the variable n and substituting the value into the variable n is performed. Thereafter, the process returns to S104 and the above-described processes are repeated.
By performing the above processing, a signal input to the difference circuit 109 is automatically selected from signals output from each of the divided light receiving surfaces of the photodetector 15.

As mentioned above, although embodiment of this invention was described, this invention is not limited to each embodiment mentioned above, A various improvement and change are possible within the range which does not deviate from the summary of this invention.
For example, in the configuration common to Embodiment 1 and Embodiment 2 described above (FIG. 1), slit light is projected on the specimen surface of the specimen 100 by providing a slit at the position of the intermediate image formed by the relay lens system 13. The projection width may be limited. By doing so, it is possible to arbitrarily set the focus detection range, and it is possible to exclude noise that is reflected from the back surface of the specimen 100.

  Further, at this time, such a slit may be provided near the light receiving surface of the photodetector 15. Also by doing this, it is possible to exclude light that becomes noise reflected from the back surface of the specimen 100.

It is a figure which shows the structure of the focus detection apparatus optical system which implements this invention. It is a figure showing the effect | action of the diffusion plate used in Example 1. FIG. It is a figure which shows the mode of condensing in the light-receiving surface of the photodetector in Example 1. FIG. It is a figure showing the effect | action of the diffusion plate used in Example 2. FIG. It is a figure which shows the form of the light projection side shutter and light reception side shutter which are used in Example 2. FIG. It is a figure which shows the terminal structure of a difference circuit part. It is a figure which shows the internal structure of a difference circuit part. FIG. 6 is a diagram illustrating a state of light collection on a sample surface in Example 2. It is a figure which shows the mode of condensing in the light-receiving surface of the photodetector in Example 2. FIG. It is a figure explaining the effect in Example 2. FIG. It is a figure which shows the mode of the connection of an external connection apparatus. It is a flowchart which shows the processing content of the control processing performed with an external control apparatus. It is a figure which shows the optical system of the focus detection apparatus by a single spot system. It is a figure explaining the method of focus detection by a single spot system. It is a figure which shows the positional relationship of an objective lens and a sample. It is a figure explaining the problem of the focus detection in the case of a multi spot system. It is a figure explaining the focus detection by a slit projection system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Diffuser 12 Light emission side shutter 13 Relay lens system 14 Light reception side shutter 15 Photodetector 20a, 20c Incident light beam 20b, 20d Output light beam 21 Light-shielding part 22 Selection circuit 22a Selection control terminal 23 Difference circuit part 30 External control device 100 Sample 100a Step 101 Light source 102 Collimating lens 103 Shutter 104 Half mirror 105 Dichroic mirror 106 Objective lens 107 Condensing lens 108 Photo detector 109 Difference circuit 110 Stage Z-axis control circuit 110a External control terminal 111 Z-axis stage 120 Composite lens system 200a Spot 200b Slit 200c Line projection light

Claims (7)

A diffusing element that diffuses light only in at least one one-dimensional direction in the plane and whose diffusion angle is controlled in the diffusion;
A condensing optical system that condenses the luminous flux of light emitted from the diffusing element when parallel light is incident on the diffusing element, and the condensing optical system that also serves as a part of the observation optical system;
A photodetector in which a light receiving surface is disposed at a condensing position of the condensing optical system, and the light collected by the condensing optical system is reflected on the sample surface and then returned to the condensing optical system. And the light detector irradiated on the light receiving surface,
A distance control unit that controls a distance between the sample surface and the condensing optical system based on a signal output from the photodetector;
A focus detection apparatus comprising: A light shielding member that shields part of the light incident on the diffusion element or the light emitted from the diffusion element;
The distance control unit controls the distance so that the light beam applied to the light receiving surface of the photodetector forms an image at a predetermined position on the light receiving surface;
The focus detection apparatus according to claim 1. The diffusion element diffuses light emitted from the light source only in one one-dimensional direction,
The light shielding member shields half of the incident light flux,
The light detector includes a surface including an optical axis of the light beam irradiated to the light receiving surface, the light receiving surface is divided into two regions, and a signal corresponding to the amount of light irradiated to the region is Output for each area,
The distance control unit controls the distance so that a difference in the amount of light applied to each of the regions is reduced.
The focus detection apparatus according to claim 2. The diffusion element diffuses light emitted from the light source only in two one-dimensional directions,
The light shielding member shields a three-quarter region of the luminous flux;
The photodetector has a surface including the optical axis of the light beam irradiated to the light receiving surface, the light receiving surface is divided into four regions, and a signal corresponding to the amount of light irradiated to the region is Output for each area,
A selection unit that selects two signals from the signals for each of the regions output from the photodetector;
The distance control unit controls the distance so that a difference between the two signals selected by the selection unit is small.
The focus detection apparatus according to claim 2. A determination unit that determines whether or not the distance obtained as a result of control by the distance control unit is appropriate as a detection result of a focal position;
A selection control unit that controls the selection unit to switch the selection of the signal by the selection unit when the determination unit determines that it is inappropriate;
The focus detection apparatus according to claim 4, further comprising:   6. The determination unit according to claim 5, wherein the determination unit performs the determination based on a degree of change in a difference between two signals selected by the selection unit, which changes according to the control by the distance control unit. The focus detection apparatus described in 1. 7. The determination unit according to claim 6, wherein when the degree of change in the difference between the two signals selected by the selection unit is less than a preset value, the determination unit determines that the signal is inappropriate. The focus detection apparatus described in 1.

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