JP2006113198A - Focus detecting apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a focus detecting apparatus that realizes stable focusing with a fixed height on a rugged sample surface, even if the ruggedness has periodicity. <P>SOLUTION: The focus detector has a laser beam source, a collimating means of collimating a laser beam, a knife edge to intercept the half of the parallel beams to thereby make the parallel beams semicircular, an objective lens for projecting the beams made semicircular to the surface of an observation object to thereby form the image thereon and restore the reflected light to be parallel, a means of transmitting either the projected beam or the reflected beam and reflect the other, to thereby separate the beams to two optical axes, a means to make the beam from the separated reflected light form the image on a focal plane that is conjugate to the focal plane of the objective lens, and a means placed on the focal plane conjugate to the focal plane of the objective lens and outputing the luminance of the formed image, and the focus detector is equipped with a means arranged on a side where the laser beam is made incident on or emitted from the collimating means and to divide the laser beam made the parallel beams by the collimating means to a plurality of parallel beam groups, whose propagating directions are somewhat different from each other. When the parallel beam groups are projected to the sample surface by the objective lens, they form an images as a plurality of points arranged at unequal intervals. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a focus detection apparatus used in a microscope, for example, a focus detection apparatus for positioning a sample to be observed at a focal position of an optical system.

(First prior art)
FIG. 13 is a diagram illustrating an example of an optical path diagram of the focus detection apparatus according to the first conventional technique.
The focus detection apparatus shown in FIG. 13 is a knife edge method focus detection apparatus widely used in optical instruments such as a microscope.

  In FIG. 13, the laser light emitted from the laser light source 341 is converted into parallel light by the collimating lens 344, and half of the light beam is accurately shielded by the knife edge 345. The half-moon-shaped light beam that is not shielded passes through the half mirror 346, is changed in direction by the dichroic mirror 348, and forms an image on the sample surface 351 through the objective lens 350. If the sample surface 351 coincides with the focal plane of the objective lens 350, the reflected light returns to the objective lens 350 and becomes a parallel light beam. At this time, the incident light beam becomes a half-moon-shaped parallel light beam exactly on the opposite side across the optical axis.

  Then, the direction of the reflected light is changed by the dichroic mirror 348 and further changed by the half mirror 346, and enters the imaging lens 353 as a half-moon-shaped parallel light beam. The photodetector 354 is arranged so that the surface thereof is located at a position conjugate with the focal plane (sample surface 351) of the objective lens 350.

  As shown in FIG. 13, when the sample surface 351 to be observed coincides with the focal plane of the objective lens 350, a very small spot (point image 352) is formed at the center of the surface of the photodetector 354 conjugate with it. Image. However, if the sample surface 351 is in the near focus position, the reflected light beam that has passed through the imaging lens 353 attempts to form an image farther than the surface of the photodetector 354, so that the half of the photodetector 354 (the right half in the figure). ) A faint half-moon-shaped blur image appears on the surface. On the other hand, if the sample surface 351 is in the far focus position, the reflected light beam attempts to form an image in front of the surface of the photodetector 354, and the light half moon is on the surface of the other half (left half in the figure) of the photodetector 354. Represents a blurred image.

  Therefore, if the photodetector 354 is divided into two parts around the optical axis and the intensity of the output is compared, it can be evaluated how much the sample surface 351 is displaced with respect to the focal plane of the objective lens 350, and the sample surface 351. Can be automatically matched with the focal plane of the objective lens 350 (see, for example, Patent Document 1).

However, the laser beam spot projected onto the sample surface 351 is only one point (point image 352). Therefore, if the sample is rich in unevenness, such as a semiconductor wafer, and the unevenness is equal to or greater than the depth of field of the high-magnification objective lens, the alignment of the sample depends on where the single spot happens to be collected. The height at which the focus is controlled changes. In other words, if the spot is focused on the valley bottom of the projections and depressions, the focal point is focused on the valley bottom, and if the spot is focused on the projection, it is focused on the height of the projection. Alternatively, if the spot is condensed on the uneven boundary (gap), most of the reflected light is scattered and does not return to the objective lens 350, and the focal position cannot be detected in the first place.
(Second prior art)
Therefore, Patent Document 1 discloses a focus detection device that projects a linear line on a sample surface instead of a single spot.

FIG. 14 is a diagram illustrating an example of an optical path diagram of line projection according to the second conventional technique.
In FIG. 14, only differences from FIG. 13 will be described. The toric lens (cylindrical lens) 307 has an imaging function only in a direction orthogonal to the paper surface. The solid line optical path in the drawing explains the behavior of the light beam in the direction in which the toric lens 307 does not have an image forming action, and the laser light is imaged on the sample surface 311 by the action of the objective lens 310 as in FIG.

  A broken line optical path in the figure is an optical path in a direction having an image forming action, and originally represents an in-plane behavior perpendicular to the paper surface. In this direction, the light beam once formed at the upper focal position 309 of the objective lens 310 by the image forming action of the toric lens 307 enters the objective lens 310 and reaches the sample surface 311 as a parallel light beam. That is, since the laser beam is imaged by the objective lens 310 only in a specific direction and is irradiated onto the sample surface 311 as a parallel light beam in a direction orthogonal to the objective lens 310, a slit image 312 is formed (for example, (See Patent Document 1).

  According to the second prior art, since the sample surface 311 is irradiated with a linear image (slit image 312) instead of a spot-shaped image, the average height of the irregularities on the straight line is always focused. be able to. Also, even if irregular reflection occurs at a certain irregularity boundary surface, the reflected light returns from most other places, so that it is strong against irregular reflection due to irregularities.

  However, regardless of a commercially available standard product, a toric lens having a desired curvature in design is expensive because the mold cost is high, and the toric lens 307 is focused on the upper side of the objective lens 310 in assembly adjustment. Such a rational adjustment method is not established for matching with the focal position 309, and there is a problem that adjustment is difficult in a mass production site.

Furthermore, since the upper focal position 309 of the objective lens 310 varies depending on the magnification of the objective lens 310, the position of the toric lens 307 must be readjusted every time the objective lens 310 is replaced for precise operation. There is also.
(Third prior art)
Patent Document 2 proposes a focusing device that projects laser light in a line shape onto the sample surface as a technique similar to the second prior art described above.

FIG. 15 is a diagram showing an optical microscope according to the third prior art.
An integrated optical microscope 430 shown in FIG. 15 schematically includes a lens barrel 405 that includes an objective lens 402 and a CCD 409 and is disposed so as to face the sample 404, and illumination that irradiates illumination light. And an integrated device 431 having an autofocus device 407 for irradiating a unit 406 and a laser beam for focusing.

  This integrated device 431 has a configuration in which an illumination mirror 415 constituting the illumination unit 406 is arranged between a lens 419 and a mirror 420 constituting an autofocus device 407. In the integrated optical microscope 430 configured as described above, the optical axis of the illumination light emitted from the illumination light source 410 in the integrated apparatus 431 and the optical axis of the laser light in the autofocus apparatus 407 are overlapped to form a mirror. Enter the tube 405. The illumination light and the laser light are incident on the objective lens 402 and irradiated on the sample 404 in the lens barrel 405.

The third prior art is common to the second prior art in that a toric lens (cylindrical lens) 417 is used to project a linear object onto the sample surface. Therefore, the problem is also common.
(Fourth prior art)
Therefore, the present applicant has proposed a focus detection apparatus that can solve the above-mentioned problems. The main point is not to project laser light on a line but to project a plurality of spots simultaneously (see Patent Document 3).

FIG. 16 is a diagram showing a focus detection apparatus according to the fourth prior art.
In FIG. 16, laser light emitted from a laser light source 504 is collimated by a collimating lens 505 and then divided by a diffraction grating 506. Therefore, a plurality of spots arranged in a row are projected on the sample surface 500.

  According to this, even on an uneven sample surface, it is possible to focus on the average height of the positions where a plurality of spots are focused, so it is possible to always focus on a substantially constant height. In addition, even if the reflection is scattered at some of the plurality of spots, the reflection from other spots is returned, so that focusing is possible. Furthermore, in general, the diffraction grating is inexpensive, and adjustment is easy because only the diffraction direction needs to be adjusted during assembly.

  However, even with this focusing device, new problems were found while observing various samples. That is, if the unevenness of the sample has periodicity and the periodicity coincides with the spot interval, the following problems occur.

The problem will be described below with reference to FIGS.
FIG. 17 and FIG. 18 are diagrams showing images in a state of being focused on an observation image of a certain sample.
FIG. 18 shows a state in which the sample is moved by a small amount while the autofocus follow-up control is applied from the state of FIG.

  In the image shown in FIG. 18, it can be seen from the degree of blur of the image that the height of the sample surface is changed. Then, when the sample is further moved, the height of the image shown in FIG. 17 is restored, and thereafter the sample height periodically changes as shown in FIGS.

The cause of this phenomenon can be explained as follows.
In FIG. 17 and FIG. 18, the spot condensed on the sample surface is calculated and overlaid. In the drawing, spots that are focused on a pattern that appears white are shown in black, and spots that are focused between patterns are shown in white.

  In FIG. 17, three of the nine points are white, but in FIG. 18, six of the nine points are white. That is, among the nine points, more of the light is collected on the pattern, or more of the light is collected under the pattern.

19 is a diagram showing a cross section AA in FIG. 17, and FIG. 20 is a diagram showing a cross section AA in FIG. 18.
According to FIGS. 19 and 20, when there are many spots that focus on the pattern, it is possible to focus on a high place on average, and when there are many spots that focus on the pattern, on average You can see that you can focus on low places. The pattern period itself does not seem to coincide with the spot period, but considering that the pattern is bent in the shape of a bowl at the top of the screen, it is condensed on the pattern when the sample is finely moved. It can be explained that the ratio of the spot and the spot condensed under the pattern is periodically reversed. Considering this fact, it can be said that this phenomenon is caused by interference between the periodicity of the pattern and the periodicity of the arrangement of spots.

Patent Document 3 discloses a configuration in which the spot interval is variable.
FIG. 21 is a diagram showing multi-slits (multi-pinholes) that are moved in a direction perpendicular to the optical axis in the optical path to change the pattern irradiated on the sample.

The multi slit 567 is a rectangular parallel flat plate, and is provided with a plurality of opening rows 567A to 567E linearly from the top to the bottom (vertical direction).
The opening row 567A has three openings located at the left end of the multi-slit 567, and has one opening on the center line 569 and one opening close to the top and bottom. Yes. The opening row 567B is located on the right side of the opening row 567A and has three openings, one opening on the center line 569, and slightly above and below it (wider than the opening row 567A). It has one opening (at intervals).

  The opening row 567C has seven openings located on the left and right center lines, and has one opening on the center line 569 and three openings close to the top and bottom. . The opening row 567D has three openings positioned on the right side of the opening row 567C, and has three openings close to the center line 569. The opening row 567E is located at the right end of the multi slit 567 (on the right side of the opening row 567D) and has three openings, and has three openings close to the center line 569. .

  As described above, since the multi slit 567 includes a plurality of opening rows having different intervals and different numbers of openings at different lateral positions, the multi slit 567 can be moved in a direction perpendicular to the optical axis. The number and interval of light beams that can pass through the opening can be varied. As a result, it is possible to change the pattern (the number and interval of spot lights) irradiated on the sample.

FIG. 22 is a diagram for explaining a configuration in which the spot interval is variable.
21 is inserted into one of the image planes in the optical path as shown in FIG. 22 to block a part of the plurality of spots, and the rest is used for auto-slit. Focus.

According to this, the “multi slit” pattern can be selected depending on the state of the sample, and the number and interval of spots projected on the sample surface can be changed.
JP-A-8-254650 JP-A-10-161195 JP 2001-296469 A

  However, since the operator who operates the apparatus cannot see the spot of the laser beam, the operator cannot determine whether or not the interval of the spot row matches the interval of the pattern to be observed. Each time, trial and error, it is necessary to replace the multi-slit and look at the situation, and it is not possible to select a reasonably optimal spot row. In addition, an automatic machine in which the operator cannot attach to the apparatus is useless in the first place.

  That is, according to the conventional focus detection device, when the laser beam projected on the sample surface is a single spot, if the sample surface has irregularities, it can be focused according to the irregularities. There has been a problem that the height may fluctuate or focus may not be achieved due to irregular reflection of laser light.

  In addition, when the projected laser beam is projected onto a single line instead of a single spot, it is possible to focus on a certain height even on an uneven sample surface, and the influence of irregular reflection is reduced. However, there is a problem that the cost of the optical element to be used is high and the assembly adjustment is difficult.

  In addition, when projecting multiple spots on the sample surface using a diffraction grating, etc., even a sample surface with unevenness can be focused at a certain height, and there is little influence of diffuse reflection, and the cost is low. When the interval between the spots projected on the surface coincides with the periodicity of the unevenness of the sample by chance, there is a problem that the height at which focusing can be performed varies periodically.

  The present invention has been made in view of the above-mentioned drawbacks of the prior art. A focus detection device that stably focuses at a constant height on a sample surface with irregularities, even if the irregularities have periodicity. The purpose is to provide.

The present invention employs the following configuration in order to solve the above problems.
That is, according to one aspect of the present invention, the focus detection apparatus of the present invention has a laser light source, collimating means for converting the laser light output from the laser light source into a parallel light beam, and parallel light beams by the collimating means. A knife edge that shields half of the laser beam and forms a half-moon-shaped parallel light beam, and a parallel light beam that becomes a half-moon shape by the knife edge is projected onto the surface of the observation object, and the reflected light from the image is collimated. An objective lens for returning the light beam, separation means for transmitting one of the projected light beam and reflected light beam and reflecting the other to separate the two optical axes, and reflected light separated by the separation means Imaging means for forming an image on the focal plane of the objective lens and the conjugate focal plane, and the focal plane of the objective lens and the conjugate focal plane, and outputting the luminance of the imaged image Detection means In the focus detection device, the laser light from the laser light source is disposed on the side where the laser light is incident on the collimating means or on the side where the laser light is emitted through the collimating means, and the collimating means slightly propagates the laser beams that become parallel light beams. A beam splitting means for splitting into a plurality of parallel beam groups having different directions is provided, and when these are projected onto the sample surface by the objective lens, they are imaged as a plurality of points arranged at unequal intervals. Features.

  Further, in the focus detection apparatus of the present invention, the light beam splitting unit is configured by a combination of a transparent plate and a diffraction grating disposed on the side emitted through the collimating unit, and the transparent plate has a slightly non-front and back side. Parallel and separates the light flux into slightly different angles by multiple reflection inside the transparent plate, and the diffraction grating further separates into an angle different from the angle separated by the transparent plate, and the parallel light flux group as a whole It is desirable that the propagation directions of the pitches are unequal pitches.

  Further, in the focus detection apparatus of the present invention, the light beam splitting means is a diffraction grating disposed on the side emitted through the collimating means, and the diffraction grating is a surface of a transparent plate whose front and back are slightly non-parallel. The light beam is separated into slightly different angles by the multiple reflection inside the transparent plate, and further separated to a different angle by the diffraction grating on the surface of the face plate, so that the propagation direction of the parallel light beam group as a whole can be changed. It is desirable to have unequal pitches.

  Further, in the focus detection apparatus of the present invention, the light beam splitting means includes a quarter λ plate disposed on the side incident on the collimating means, a birefringent element following the quarter λ plate, and the collimating means. A combination with a diffraction grating arranged on the exit side, and the laser beam, which is linearly polarized light, is split into light having two different polarization planes and optical axes using anomalous refraction, and the 1 / 4λ plate By making circularly polarized light through, it is made coherent, and when passing through the collimating means, the optical axis is slightly shifted to form a plurality of parallel light beams that are slightly non-parallel, and separated by a diffraction grating. It is desirable that the propagation directions of the parallel light beam groups become unequal pitches as a whole by further separating them at a uniform angle.

  Further, in the focus detection apparatus of the present invention, the light beam splitting means is a combination of a plurality of birefringent elements arranged on the side incident on the collimating means and a 1 / 4λ plate, and the thickness of each birefringent element. The laser beam, which has been changed in material or crystal axis and is linearly polarized, is split into light having two different polarization planes and optical axes using anomalous refraction, and is circularly polarized through a 1 / 4λ plate. After repeating this multiple times, a group of light beams whose optical axes are shifted at unequal pitches are formed, and the optical axis is slightly shifted when passing through collimating means. Therefore, it is desirable to form a plurality of parallel light flux groups whose propagation directions are shifted at unequal pitches.

  According to the present invention, since the intervals of the spots projected onto the surface of the sample to be observed are made unequal, even when the unevenness of the sample surface has periodicity, it is stably near the average of the unevenness You can focus on the height of.

  In addition, according to the present invention, since the light beam splitting means is a combination of a transparent plate and a diffraction grating arranged on the side emitted through the collimating means, the surface irregularities have periodicity due to an inexpensive configuration. Even a sample can be focused without changing the focus height.

  Further, according to the present invention, the light beam splitting means is a diffraction grating arranged on the side emitted from the collimating means, and the diffraction grating is formed on the surface of the transparent plate slightly non-parallel on the front and back sides. The light flux is separated into slightly different angles by multiple reflections inside the transparent plate, and further separated to a different angle by the diffraction grating on the surface of the face plate, so that the propagation direction of the parallel light flux group becomes an unequal pitch as a whole. As a result, the number of parts does not increase at all, and it is not necessary to adjust the direction of the non-parallel plate to the diffraction direction of the diffraction grating, and the cost is reduced particularly in mass production.

  Further, according to the present invention, the light beam splitting means is arranged on the side incident on the collimating means, the birefringent element following the quarter λ plate and the side exiting through the collimating means. The laser beam, which is linearly polarized light, is split into light having two different polarization planes and optical axes using anomalous refraction, and is converted into circularly polarized light through a 1 / 4λ plate. When the light passes through the collimating means, the optical axis is slightly deviated to form a plurality of light beams that are slightly non-parallel, and further separated at a different angle by the diffraction grating. . As a result, the propagation direction of the parallel light flux group becomes an unequal pitch as a whole, so that, in principle, a high-order multiple reflection does not occur, and only the light beam intended by design is generated. There is no waste in the amount of light.

  According to the present invention, the light beam splitting means is a combination of a birefringent element arranged on the side incident on the collimating means and a ¼λ plate. The laser beam, which has been changed in thickness, material, or crystal axis and is linearly polarized, is split into light having two different polarization planes and optical axes using anomalous refraction, and converted into circularly polarized light through a 1 / 4λ plate. After repeating this several times, a group of luminous fluxes whose optical axes are shifted at unequal pitches is formed, and the optical axis is slightly shifted when passing through the collimating means. As a result, a group of parallel light beams whose propagation directions are shifted at unequal pitches can be formed, so that a row of spots having almost no periodicity can be projected onto the sample surface. No matter what Without being affected by this, it is always possible to focus on the vicinity of the average surface height.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a diagram showing a configuration of a focus detection apparatus according to a first embodiment to which the present invention is applied.

In FIG. 1, a light source 4 supplies a light beam used by the focus detection apparatus according to the first embodiment. A light source, a projection system, and an imaging system for forming an observation image are not shown.
The laser driving unit 20 is for driving the light source 4 and blinks the light source 4 or changes the light emission amount in accordance with a command from the control unit 23.

The collimating lens 5 turns the light from the light source 4 into a parallel light flux.
The non-parallel plate 101 is made of an optically transparent material such as quartz glass, and the front and back surfaces are optically sufficiently flat. The parallelism of the front and back is intentionally slightly non-parallel, and multiple reflection occurs, but the direction of the multiple reflected light is attached so as to coincide with the diffraction direction of a diffraction grating described later. Note that, from the relationship between the reflectances of the front and back surfaces of the non-parallel plate 101, it is sufficient to focus only on the first-order multiple reflected light, and the intensity of the second-order or higher multiple reflected light can be ignored.

  The diffraction grating 102 divides the incident light beam into a plurality of parallel light beam groups. All the divided outgoing beam groups are in a single plane including the optical axis of the incident beam. In addition, the angles formed by adjacent light beams are the same, as in the fan bones that are spread out. In addition, since the primary multiple reflected light by the non-parallel plate 101 is also divided in the same manner, the situation is such that two sets of spread fan bones are slightly shifted and overlapped.

  The light shielding plate 7 shields exactly half of the outgoing light flux group. The light shielding direction is set so that the edge of the light shielding plate 7 includes the optical axis of all light beams. Therefore, all the luminous fluxes are shielded in a half-moon shape, and the strings of the half-moon are placed on the same straight line, that is, on the edge of the light-shielding plate 7. The direction in which the non-parallel plate 101 and the diffraction grating 102 shown in FIG. 1 divide the light beam is parallel to the paper surface, but this is a figurative expression for helping understanding, and the edges are actually perpendicular to the paper surface. ing.

  The polarizing beam splitter 8 reflects the half-moon shaped light beam group that has passed through the light shielding plate 7 and bends the propagation direction. However, a light beam group reflected from the sample surface and returned to a parallel light beam group by objective lenses 3a and 3b described later has a different polarization plane when returned to linearly polarized light by a quarter λ plate 11 described later. Therefore, it passes through the polarization beam splitter 8.

  The relay optical systems 9 and 10 have an intermediate imaging position 6 therebetween. The intermediate imaging position 6 is a focal plane conjugate with the focal plane of objective lenses 3a and 3b described later. The 1 / 4λ plate 11 converts linearly polarized light into circularly polarized light. The dichroic mirror 12 bends the light beam group. Note that observation light (not shown) is transmitted.

The objective lens 3a and the objective lens 3b have different magnifications. The sample stage 1 is a stage for placing the sample S to be observed.
The projection lens 13 forms an image of the light flux group returned from the sample surface. Since the position of the light detector 14 is conjugate with the focal plane of the objective lens 3a, when the light beam group forms an image on the sample S, the light image is also formed on the light detector 14 and becomes a minimal spot on a straight line. line up. However, the photodetector 14 is divided into two regions A and B. When the spot group forms an image on the surface of the photodetector 14, it is aligned in a straight line, but the boundary line of the division is positioned so as to exactly match this straight line.

  The preamplifier 21 receives the output of the photodetector 14, and the AD converter 22 converts the output of the preamplifier 21 into digital data, and the digital data corresponding to the amount of light received by the optical converter 14 is controlled by the control unit. 23. Note that the preamplifier 21 and the AD converter 22 have two channels, and separately process outputs from the two divided regions of the photodetector 14.

  The semi-focusing motor 16 is for moving the sample stage 1 to change the distance to the objective lens 3a so that the surface of the sample S to be observed coincides with the focal point of the objective lens 3a. The motor drive unit 18 supplies a drive signal corresponding to the amount by which the semi-focusing motor 16 is to be driven in accordance with a command from the control unit 23.

  The revolver 2 is attached with a plurality of objective lenses 3a and 3b having different magnifications. The revolver driving motor 15 rotates the revolver 2 to insert desired objective lenses 3a and 3b into the optical path. The motor drive unit 17 supplies a drive signal corresponding to the amount by which the revolver drive motor 15 is to be driven in accordance with a command from the control unit 23. The hole detection unit 19 notifies the control unit which hole of the revolver 2, that is, which objective lenses 3a and 3b are currently inserted in the optical path.

  The control unit 23 includes a CPU 27, a ROM 28, a RAM 29, and an I / O port 30. These are connected to each other via a data bus 31, and data is exchanged via the data bus 31. The ROM 28 stores programs for performing various controls such as autofocus operation, movement of the sample stage 1, and rotation of the revolver 2. The RAM 29 stores, for example, digital data from the above-described AD converter 22. The I / O port 30 inputs and outputs control signals for various driving units.

Next, the operation of the focus detection apparatus according to the first embodiment to which the present invention is applied will be described.
2 and 3 are diagrams for explaining the operation of the focus detection apparatus according to the first embodiment to which the present invention is applied.

  In response to a command from the control unit 23, the laser driving unit 20 drives the light source 4 to emit laser light. The laser light is converted into a parallel light beam by the collimating lens 5. The parallel light flux passes through the non-parallel plate 101 as shown in FIG. At this time, multiple reflection occurs on the front and back of the non-parallel plate 101, and primary multiple reflected light 202 having a slightly different angle from the 0th order light 201 is emitted. Note that the second-order or higher-order multiple reflected light has a low intensity due to the reflectance, and the action can be ignored.

  These pass through the diffraction grating 102. As shown in FIG. 2, the optical axis of the 0th order light 201 is divided as the first order diffracted light 203. Further, the primary multiple reflected light 202 of the non-parallel plate 101 is also diffracted, and the optical axis is divided and emitted as with the primary diffracted light 204. At this time, the angle between adjacent primary diffraction lights 203 is constant. Further, the angles between the adjacent first-order diffracted beams 204 are also the same.

  However, the front and back angles of the non-parallel plate 101 are set so that the angle formed between the 0th-order light and the primary multiple reflected light is different from this. Further, the direction of the diffraction grating 102 is adjusted and installed so that the direction of diffraction is the same as the deviation of the optical axis due to multiple reflection. Then, as shown in FIG. 2, diffracted light is arranged at two different angles in a plane including the paper surface of FIG.

  As shown in FIG. 1, half of the light is accurately shielded by the light shielding plate 7. The light shielding direction is set so that the edge of the light shielding plate 7 includes the optical axes of all the light beams (0th-order light 201, first-order multiple reflected light 202, first-order diffracted light 203, and first-order diffracted light 204). Accordingly, all the light beams (the 0th order light 201, the first order multiple reflected light 202, the first order diffracted light 203, and the first order diffracted light 204) are shielded in a half moon shape, and their half moon strings are on the same straight line, that is, on the edge of the light shielding plate 7. It is on.

  These light beams are bent by a polarization beam splitter 8 and pass through relay optical systems 9 and 10. Then, when passing through the ¼λ plate 11, it is made circularly polarized light. Further, it is bent by the dichroic mirror 12, superimposed on an observation beam (not shown), and condensed through the objective lens 3a. If the surface of the sample S coincides with the focal plane of the objective lens 3a, a plurality of minimal spots are imaged in a line on the surface of the sample S. At this time, as shown in FIG. 2, reflecting the fact that two kinds of angular relationships are mixed in the optical axes of the light beams 201 to 204, the spots are alternately spaced by two kinds as shown in FIG. Lined up with.

  The light beam group imaged and reflected by the sample surface returns to the objective lens 3a and is returned to the parallel light beam group. These return in a half-moon shape on the opposite side of the outward path across the central axis of the objective lens 3a. Then, the path is bent by the dichroic mirror 12 to be separated from the observation beam (not shown), and is linearly polarized by the ¼λ plate 11. At this time, since the quarter-wave plate 11 is counted twice from the forward linearly polarized light, the polarization plane is orthogonal to the forward polarization plane. Then, after passing through the relay optical system 10, 9, it passes through the polarization beam splitter 8, but the outgoing light beam is reflected, but the plane of polarization is different from that by 90 °. Is separated into the projection lens 13 and collected.

  Since the photodetector 14 is placed on the focal plane of the projection lens 13 and this is conjugate with the focal plane of the objective lens 3a, when the light beam group forms an image on the sample S, it is also connected to the photodetector 14. Image and form a tiny spot on a straight line. The photodetector 14 is divided into two regions, and the position of the boundary line of the division is adjusted so as to exactly coincide with the arrangement of spots when the image is formed.

  As shown in FIG. 3, when the surface of the sample S to be observed coincides with the focal plane of the objective lens 3a, a very small spot forms an image at the center of the surface of the photodetector 14 conjugate with it. . However, if the surface of the sample S is in the near focus position, the reflected light flux that has passed through the projection lens 13 tends to form an image farther than the surface of the photodetector 14, so that the half of the photodetector 14 (FIG. A plurality of thin and bright half-moon-shaped blur images appear on the surface of the upper half in 1 (B region).

  On the other hand, if the surface of the sample S is in the far focus position, the reflected light beam attempts to form an image in front of the surface of the light detector 14 and is half of the light detector 14 (lower half in FIG. 1: area A). ) Multiple thin and bright half-moon-shaped blur images.

  Since the surface of the photodetector 14 is divided into two along the above-mentioned spot group, the intensity of the output of the two areas is taken out, amplified by the preamplifier 21, and converted into digital data by the AD converter 22. Then, if the comparison is made by the control unit 23, it can be evaluated how much the surface of the sample S is deviated from the focal plane of the objective lens 3a, and the position of the surface of the sample S is automatically set to the focal plane of the objective lens 3a. Can be matched to each other.

4 and 5 are diagrams for explaining the relationship between the arrangement of spots on the sample surface and the periodicity of the pattern on the sample surface.
4 and 5, the spot focused on the white pattern is represented in black, the spot focused on the black portion is represented in white, and the sample S is compared with the white 9 vs. black 9 in FIG. 4. In FIG. 5 in which a small amount is moved, white 11 vs. black 7 is obtained, and even when the sample S is moved, the fluctuation of the black and white ratio is small. Therefore, there is little fluctuation in the height at which focusing can be achieved.

  When the signals from the two areas of the photodetector 14 are called A and B, the control unit 23 uses, for example, (A−B) / (A + B) from the digital data of the A and B intensities obtained from the AD converter 22. ) Can be calculated. This is a two-dimensional value, for example, always takes a negative value during near focus, takes a positive value during far focus, and passes 0 only at the in-focus point.

  Therefore, the control unit 23 always monitors the value of (A−B) / (A + B), issues a drive command to the motor drive unit 18, and performs feedback control so that this value becomes 0, so that the sample is automatically obtained. The surface of S can be focused on the focal plane of the objective lens 3a.

  The control unit 23 can give a command to the motor driving unit 17 to rotate the revolver 2 and switch the types of the objective lenses 3a and 3b. The drive amount command to be determined and given to the motor drive unit 18 can be given an optimum value for each type of objective lens.

  Further, the focus detection device can be operated manually by an operator sending various commands from the operation unit 26. For example, the operator manually performs initialization of the focus detection device, forced movement of the sample stage 1, display of the current position of the sample stage 1, switching of autofocus operation / stop, switching of the objective lenses 3a and 3b, and the like. be able to. Further, when the operator operates the focusing motor 16, the use of the operation becomes a pulse and is sent to the pulse counter 24, and the pulse counter transmits this to the control unit 23 as the amount of movement command. Thus, the operator can stop the autofocus operation and manually operate the height of the sample stage 1.

  As described above, according to the first embodiment, since only the non-parallel plate 101 is added, the in-focus height varies even with a sample having periodic surface irregularities due to an inexpensive configuration. You can observe without having to do it, and there is no need to manually insert and remove the multi slit.

Next, a second embodiment to which the present invention is applied will be described.
FIG. 6 is a diagram showing a configuration of a focus detection apparatus according to a second embodiment to which the present invention is applied.

In FIG. 6, the same elements as those in the focus detection apparatus according to the first embodiment shown in FIG. 1 are denoted by the same reference numerals, description thereof is omitted, and different components are mainly described.
First, the second embodiment differs from the first embodiment in that a diffraction grating 103 is provided instead of the non-parallel plate 101 and the diffraction grating 102, and the diffraction grating 103 also functions as a non-parallel plate. It is that. That is, the substrate such as glass constituting the diffraction grating 103 is configured so that the front and back surfaces are slightly non-parallel, and the inclination direction is the same as the diffraction direction. Note that, from the relationship between the reflectances of the front and back surfaces, it is only necessary to focus on the first-order multiple reflected light, and the intensity of the second-order or higher multiple reflected light can be ignored.

  The diffraction grating 103 divides the incident light beam into a plurality of parallel light beam groups. All the divided outgoing light beam groups are in a single plane including the optical axis of the incident light beam, and the angles formed by the adjacent light beams are the same, as in the spread fan bone. Since the above-described primary multiple reflected light is also divided in the same manner, the situation is such that two sets of spread fan bones are slightly shifted and overlapped.

Next, the operation of the focus detection apparatus according to the second embodiment to which the present invention is applied will be described focusing on differences from the operation of the focus detection apparatus according to the first embodiment.
7 and 3 are diagrams for explaining the operation of the focus detection apparatus according to the second embodiment to which the present invention is applied.

  When the laser light is converted into a parallel light beam by the collimator lens 5, the parallel light beam passes through the diffraction grating 103 as shown in FIG. At this time, multiple reflection occurs on the front and back of the diffraction grating 103, and primary multiple reflected light 202 having a slightly different angle from the 0th order light 201 is emitted. Note that the second-order or higher-order multiple reflected light has a low intensity due to the reflectance, and the action can be ignored.

  Next, as shown in FIG. 7, the zero-order light 201 passes through the diffraction grating 103 and the optical axis is divided as the first-order diffracted light 203. Further, the primary multiple reflected light 202 is also diffracted and emitted with the optical axis divided as in the primary diffracted light 204. At this time, the angle between adjacent primary diffraction lights 203 is constant. Further, the angles between the adjacent first-order diffracted beams 204 are also the same.

  However, the front and back angles of the diffraction grating 103 are set so that the angle formed between the 0th-order light 201 and the primary multiple reflected light 202 is different from this. Further, the non-parallel directions on the front and back sides are adjusted so that the direction of diffraction is the same as the deviation of the optical axis due to multiple reflection. Then, as shown in FIG. 7, the diffracted light is arranged at two different angles in the plane including the paper surface of FIG.

  If the surface of the sample S coincides with the focal plane of the objective lens 3a, a plurality of minimal spots are imaged in a line on the surface of the sample S. At this time, as shown in FIG. 7, reflecting the fact that two kinds of angular relationships are mixed in the optical axes of the light beams 201 to 204, the spots alternately have two kinds of intervals as shown in FIG. Are arranged in the same manner as in the first embodiment.

  Further, since the photodetector 14 is placed on the focal plane of the projection lens 13 and this is conjugate with the focal plane of the objective lens 3a, when the light beam group forms an image on the sample S, it is placed on the photodetector 14. Also form an image and form a tiny spot on a straight line. The photodetector 14 is divided into two regions. The boundary line of the division is adjusted so that the position of the boundary line is exactly coincident with the arrangement of spots when imaged. This is the same as the embodiment.

  Also, as shown in FIGS. 4 and 5, when considering the relationship between the arrangement of spots on the sample surface and the periodicity of the pattern on the sample surface, the spots focused on the white pattern are represented in black, 4 represents white 9 vs. black 9 in FIG. 4 and white 11 vs. black 7 in FIG. 5 where the sample S is moved by a small amount. There is little change in the ratio. Therefore, the effect that there is little fluctuation in the height at which focusing can be achieved is the same as in the first embodiment.

  As described above, according to the second embodiment, it is necessary to manufacture the diffraction grating 103 having a slightly special specification, but the number of parts does not increase at all, and the direction of the non-parallel plate is changed to the diffraction grating 103. There is no need to make adjustments to match the direction, which reduces the cost especially for mass production.

Next, a third embodiment to which the present invention is applied will be described.
FIG. 8 is a diagram showing a configuration of a focus detection apparatus according to a third embodiment to which the present invention is applied.

In FIG. 8, the same components as those in the focus detection apparatus according to the first embodiment shown in FIG. 1 are denoted by the same reference numerals, description thereof is omitted, and different components are mainly described.
First, the third embodiment is different from the first embodiment in that a combination of the birefringent element 104 and the ¼λ plate 105 is arranged on the side incident on the collimation lens 5 instead of the non-parallel plate 101. It is that.

  In FIG. 8, the birefringent optical element 104 is formed of a uniaxial crystal plate such as quartz and the optical axis is the incident optical axis so that incident linearly polarized light can be separated into an ordinary ray Lo and an extraordinary ray Le. Is cut out in a slanting direction. Note that the direction in which the extraordinary ray Le is separated from the ordinary ray Lo is adjusted and installed so as to coincide with the diffraction direction of a diffraction grating described later.

  The quarter-λ plate 105 is for converting two linearly polarized light emitted from the birefringent element 104 into circularly polarized light and equalizing coherence in the diffraction grating 102 described later. May be omitted. Although these two light beams pass through the collimation lens 5, the axes are shifted when exiting from the birefringent element 104, so that when passing through the collimation lens 5, the propagation directions of these two light beams are slightly different from each other.

  The diffraction grating 102 divides the incident light beam into a plurality of parallel light beam groups. All the divided outgoing light beam groups are in a single plane including the optical axis of the incident light beam, and the angles formed by the adjacent light beams are the same, as in the spread fan bone. Since the above-described primary multiple reflected light is also divided in the same manner, the situation is such that two sets of spread fan bones are slightly shifted and overlapped.

Next, the operation of the focus detection apparatus according to the third embodiment to which the present invention is applied will be described focusing on differences from the operation of the focus detection apparatus according to the first embodiment.
9 and 3 are diagrams for explaining the operation of the focus detection apparatus according to the third embodiment to which the present invention is applied.

  The light incident on the birefringent element 104 is divided into an ordinary ray Lo and an extraordinary ray Le and is emitted. Then, it is converted into circularly polarized light by the ¼λ plate 105. The 0th order light 201 derived from the ordinary light Lo passes through the diffraction grating 102 and has its optical axis divided as the first order diffracted light 203. Also, the primary multiple reflected light 202 derived from the extraordinary ray Le is also diffracted, and the optical axis is divided and emitted as in the primary diffracted light 204. At this time, the angle between adjacent primary diffraction lights 203 is constant. Further, the angles between the adjacent first-order diffracted beams 204 are also the same.

  However, the thickness of the birefringent element 104 is set so that the angle formed between the 0th-order light 201 and the primary multiple reflected light 202 is different from this. Further, the directions of the birefringent element 104 and the diffraction grating 102 are adjusted so that the direction of diffraction is the same as the deviation of the optical axis due to birefringence. Then, as shown in FIG. 9, the diffracted light is arranged at two different angles in the plane including the paper surface of FIG.

  If the surface of the sample S coincides with the focal plane of the objective lens 3a, a plurality of minimal spots are imaged in a line on the surface of the sample S. At this time, as shown in FIG. 9, reflecting the fact that two kinds of angular relationships are mixed in the optical axes of the light beams 201 to 204, as shown in FIG. 3, the spots alternately have two kinds of intervals. Are arranged in the same manner as in the first and second embodiments.

  Since the photodetector 14 is placed on the focal plane of the projection lens 13 and this is conjugate with the focal plane of the objective lens 3a, when the light beam group forms an image on the sample S, it is also connected to the photodetector 14. Image and form a tiny spot on a straight line. The photodetector 14 is divided into two regions, and the boundary line of the division is adjusted so that the position of the boundary line exactly coincides with the arrangement of the spots when imaged. This is the same as in the second embodiment.

  Also, as shown in FIGS. 4 and 5, when considering the relationship between the arrangement of spots on the sample surface and the periodicity of the pattern on the sample surface, the spots focused on the white pattern are represented in black, 4 represents white 9 vs. black 9 in FIG. 4 and white 11 vs. black 7 in FIG. 5 where the sample S is moved by a small amount. There is little change in the ratio. Therefore, the effect that there is little fluctuation in the height at which focusing can be achieved is the same as in the first embodiment.

  As described above, according to the third embodiment, the birefringent element 104 is somewhat expensive, but in principle, such a high-order multiple reflection does not occur, and the light beam intended by design. Only occurs, so there is no waste in the amount of light.

Next, a fourth embodiment to which the present invention is applied will be described.
FIG. 10 is a diagram illustrating a configuration of a focus detection apparatus according to a fourth embodiment to which the present invention is applied. FIGS. 11 and 12 illustrate focus detection according to the fourth embodiment to which the present invention is applied. It is a figure for demonstrating operation | movement of an apparatus.

10, the same elements as those in the focus detection apparatus according to the first embodiment shown in FIG. 1 are denoted by the same reference numerals, description thereof is omitted, and different components will be mainly described.
First, the fourth embodiment is different from the first embodiment in that neither the diffraction grating 102 nor the non-parallel plate 101 is used, and the birefringence elements 106, 108, 110 and the quarter λ plates 107, 109, 111 are used. That is, only the set of the above is arranged on the side incident on the collimation lens 5.

  In FIG. 10, birefringent optical elements 106, 108, and 110 emit incident linearly polarized light separately into an ordinary ray Lo and an extraordinary ray Le, and 1 / 4λ plates 107, 109, It is the same as that of the above-mentioned 3rd Embodiment that 111 makes two linearly polarized light emitted from the birefringent element circularly polarized light. However, in the fourth embodiment, there are a plurality of, typically three, combinations of the birefringent elements and the ¼λ plate. The directions of the crystal axes of all the birefringent elements are the same, and birefringence occurs in the same direction in any element. Furthermore, the thickness of the birefringent elements 106, 108, 110 is increased toward the downstream. The ratio of the thickness is based on a power of 2, such as 1: 2: 4, and is intentionally slightly deviated from the ratio of the power of 2. Then, when the light passes through the combination of all the birefringent elements and the ¼λ plate, the light flux becomes a set of light flux groups separated at unequal intervals as shown in FIG. If the thickness ratio of the birefringent elements is completely raised to a power of 2, the light beam groups are arranged at equal intervals. The most downstream ¼λ plate 111 may be omitted depending on circumstances, but the others are optically essential.

Next, the operation of the focus detection apparatus according to the fourth embodiment to which the present invention is applied will be described focusing on differences from the operation of the focus detection apparatus according to the first embodiment.
In FIG. 11, the light incident on the birefringence element 106 is divided into an ordinary ray Lo and an extraordinary ray Le and emitted. Then, it is converted into circularly polarized light by the ¼λ plate 107. A plurality of sets (a set of birefringence element 108 and 1 / 4λ plate 109 and a set of birefringence element 110 and 1 / 4λ plate 111 in addition to birefringence element 106 and 1 / 4λ plate 107) are passed. Each set is aligned in the direction in which extraordinary rays are generated, and the thickness is deliberately deviated from the power-of-two ratio, so that after passing through all of the sets, a set of light flux groups with non-constant spacing is obtained.

  If the surface of the sample S coincides with the focal plane of the objective lens 3a, a plurality of minimal spots are imaged in a line on the surface of the sample S. At this time, the spots are arranged at regular intervals. Further, they are not arranged with two kinds of intervals alternately as in the first to third embodiments, but are arranged with more complicated combinations as shown in FIG.

  Since the photodetector 14 is placed on the focal plane of the projection lens 13 and this is conjugate with the focal plane of the objective lens 3a, when the light beam group forms an image on the sample S, it is also connected to the photodetector 14. Image and form a tiny spot on a straight line. The photodetector 14 is divided into two regions, and the position of the boundary line of the division is adjusted so as to exactly match the arrangement of the spots when imaged. This is the same as in the third embodiment.

  Further, when considering the relationship between the arrangement of spots on the sample surface and the periodicity of the pattern on the sample surface, the spots are focused on the sample surface in an arrangement close to a random number. Therefore, regardless of the periodicity of the irregularities of the sample surface, it is possible to always focus on the vicinity of the average of the height of the surface without being affected at all.

  As described above, according to the fourth embodiment, the birefringent elements 106, 108, and 110 are slightly expensive, but a row of spots with little periodicity can be projected onto the sample surface. Regardless of the periodicity of the unevenness of the sample surface, it is possible to always focus on the vicinity of the average of the surface height without being affected at all.

  As described above, the embodiments of the present invention have been described with reference to the drawings. However, the focus detection apparatus to which the present invention is applied can be applied to the above-described embodiments as long as the function is executed. Without limitation, it goes without saying that a single device, a system composed of a plurality of devices or an integrated device may be used, or a system in which processing is performed via a network such as a LAN or WAN. Yes.

  It can also be realized by a system comprising a CPU, ROM or RAM memory connected to the bus, input device, output device, external recording device, medium driving device, portable recording medium, and network connection device. That is, a ROM or RAM memory, an external recording device, and a portable recording medium that record software program codes for realizing the systems of the above-described embodiments are supplied to the focus detection device, and the computer of the focus detection device Needless to say, this can also be achieved by reading and executing the program code.

  In this case, the program code itself read from the portable recording medium or the like realizes the novel function of the present invention, and the portable recording medium or the like on which the program code is recorded constitutes the present invention. .

  Examples of portable recording media for supplying program codes include flexible disks, hard disks, optical disks, magneto-optical disks, CD-ROMs, CD-Rs, DVD-ROMs, DVD-RAMs, magnetic tapes, and non-volatile memories. Various recording media recorded through a network connection device (in other words, a communication line) such as a card, a ROM card, electronic mail or personal computer communication can be used.

  In addition, the functions of the above-described embodiments are realized by executing the program code read out on the memory by the computer, and the OS running on the computer is actually executed based on the instruction of the program code. The functions of the above-described embodiments are also realized by performing part or all of the process.

  Furthermore, a program code read from a portable recording medium or a program (data) provided by a program (data) provider is provided in a function expansion board inserted into a computer or a function expansion unit connected to a computer. The CPU of the function expansion board or function expansion unit performs part or all of the actual processing based on the instruction of the program code, and the functions of the above-described embodiments are also performed by the processing. Can be realized.

  That is, the present invention is not limited to the embodiments described above, and can take various configurations or shapes without departing from the gist of the present invention.

It is a figure which shows the structure of the focus detection apparatus concerning 1st Embodiment to which this invention is applied. It is FIG. (1) for demonstrating operation | movement of the focus detection apparatus concerning 1st Embodiment to which this invention is applied. It is FIG. (2) for demonstrating operation | movement of the focus detection apparatus concerning 1st Embodiment to which this invention is applied. FIG. 6 is a diagram (part 1) for explaining the relationship between the arrangement of spots on the sample surface and the periodicity of the pattern on the sample surface. FIG. 6 is a diagram (part 2) for explaining the relationship between the arrangement of spots on the sample surface and the periodicity of the pattern on the sample surface. It is a figure which shows the structure of the focus detection apparatus concerning 2nd Embodiment to which this invention is applied. It is FIG. (1) for demonstrating operation | movement of the focus detection apparatus concerning 2nd Embodiment to which this invention is applied. It is a figure which shows the structure of the focus detection apparatus concerning 3rd Embodiment to which this invention is applied. It is FIG. (1) for demonstrating operation | movement of the focus detection apparatus concerning 3rd Embodiment to which this invention is applied. It is a figure which shows the structure of the focus detection apparatus concerning 4th Embodiment to which this invention is applied. It is FIG. (1) for demonstrating operation | movement of the focus detection apparatus concerning 4th Embodiment to which this invention is applied. It is FIG. (2) for demonstrating operation | movement of the focus detection apparatus concerning 4th Embodiment to which this invention is applied. It is a figure which shows an example of the optical path figure of the focus detection apparatus concerning 1st prior art. It is a figure which shows an example of the optical path figure of the line projection concerning 2nd prior art. It is a figure which shows the optical microscope concerning 3rd prior art. It is a figure which shows the focus detection apparatus which concerns on a 4th prior art. It is a figure (the 1) which shows the image of the state focused on the observation image of a certain sample. It is FIG. (2) which shows the image of the state focused on the observation image of a certain sample. It is a figure which shows the AA cross section of FIG. It is a figure which shows the AA cross section of FIG. It is a figure which shows the multi slit (multi pinhole) which moves to the direction perpendicular | vertical to an optical axis in an optical path, and changes the pattern irradiated on a sample. It is a figure for demonstrating the structure which makes the space | interval of a spot variable.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sample stand 2 Revolver 3a, 3b Objective lens 4 Light source 5 Collimating lens 6 Intermediate imaging position 7 Light-shielding plate 8 Polarizing beam splitter 9 Relay optical system 10 Relay optical system 11 1 / 4λ plate 12 Dichroic mirror 13 Projection lens 14 Light detection 15 Revolver drive motor 16 Semi-focusing motor 17 Motor drive unit 18 Motor drive unit 19 Hole detection unit 20 Laser drive unit 21 Preamplifier 22 AD converter 23 Control unit 24 Pulse counter 26 Operation unit 27 CPU
28 ROM
29 RAM
30 I / O port 31 Data bus 101 Non-parallel plate 102 Diffraction grating 103 Diffraction grating 104 Birefringence element 105 1 / 4λ plate 106 Birefringence element 107 1 / 4λ plate 108 Birefringence element 109 1 / 4λ plate 110 Birefringence element 111 1 / 4λ plate 201 0th order light 202 First order multiple reflected light 203 First order diffracted light 204 First order diffracted light 307 Toric lens (cylindrical lens)
309 Upper focal position 310 Objective lens 311 Focal plane 312 Slit image 341 Laser light source 344 Collimate lens 345 Knife edge 346 Half mirror 348 Dichroic mirror 350 Objective lens 351 Sample plane (focal plane)
352 Point image 353 Imaging lens 354 Photo detector 402 Objective lens 404 Sample 405 Lens barrel 406 Illumination unit 407 Autofocus device 409 CCD
410 Illumination light source 415 Illumination mirror 417 Toric lens (cylindrical lens)
419 Lens 420 Mirror 430 Integrated optical microscope 431 Integrated device 500 Sample surface 504 Laser light source 505 Collimating lens 506 Diffraction grating 567 Multi slit 567A Opening row 567B Opening row 567C Opening row 567D Opening row 567E Opening row 567E Line A area B area S Sample

Claims (5)

A laser light source;
Collimating means for collimating the laser beam output from the laser light source;
A knife edge that shields half of the laser light that has been collimated by the collimating means and produces a half-moon-shaped parallel beam;
An objective lens that projects and images a parallel light beam having a half-moon shape by the knife edge onto the surface of the observation object, and returns reflected light from the image to the parallel light beam;
Separating means for transmitting one of the projected light flux and the reflected light flux and reflecting the other to separate the two optical axes;
An imaging unit that forms an image of a parallel light beam from the reflected light separated by the separating unit on a focal plane conjugate with a focal plane of the objective lens;
A detecting means placed on the focal plane conjugate with the focal plane of the objective lens and outputting the brightness of the image formed;
In a focus detection apparatus having
The laser light from the laser light source is disposed on the side where the laser light is incident on the collimating means or the side emitted through the collimating means. A beam splitting means for splitting into parallel beam groups,
A focus detection apparatus characterized in that when these are projected onto the sample surface by the objective lens, images are formed as a plurality of points arranged at unequal intervals. The beam splitting means is constituted by a combination of a transparent plate and a diffraction grating arranged on the side emitted through the collimating means,
The transparent plate is slightly non-parallel on the front and back sides, and separates the light flux at slightly different angles by multiple reflection inside the transparent plate,
2. The diffraction grating according to claim 1, wherein the diffraction grating is further separated at an angle different from the angle separated by the transparent plate so that the propagation directions of the parallel light flux groups become unequal pitches as a whole. Focus detection device. The beam splitting means is a diffraction grating disposed on the side emitted through the collimating means,
The diffraction grating is formed on the surface of a transparent plate whose front and back are slightly non-parallel, separates the light flux at slightly different angles by multiple reflection inside the transparent plate, and is separated from the angle by the diffraction grating on the surface of the face plate. The focus detection apparatus according to claim 1, wherein the propagation directions of the parallel light flux groups are made to be unequal pitches as a whole by further separating the light beams.   The beam splitting means includes a quarter λ plate disposed on the side incident on the collimating means, a birefringent element following the quarter λ plate, and a diffraction grating disposed on the side emitted through the collimating means. The laser beam, which is linearly polarized light, is divided into light having two different polarization planes and optical axes using anomalous refraction, and is made coherent by making circularly polarized light through the 1 / 4λ plate. When passing through the collimating means, the optical axis is slightly shifted to form a plurality of parallel light flux groups that are slightly non-parallel, and further separated by a diffraction grating at a different angle from the whole. The focus detection apparatus according to claim 1, wherein the propagation directions of the parallel light flux groups are unequal pitches. The beam splitting means is a plurality of combinations of a birefringent element arranged on the side incident on the collimating means and a ¼λ plate, and the thickness, material or crystal axis of each birefringent element is changed. ,
The laser beam, which is linearly polarized, is split into light having two different polarization planes and optical axes using anomalous refraction, and is made to be coherent by making it circularly polarized through a 1 / 4λ plate. After repeating a plurality of times, a group of light beams whose optical axes are shifted at unequal pitches is formed, and when passing through the collimating means, the optical axis is shifted slightly so that the propagation directions are shifted at unequal pitches. The focus detection device according to claim 1, wherein the focus detection device is a group of parallel light beams.