JPH0460603A - Focus detector and observation device equipped with the same - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a focus detection device and an observation device equipped with the focus detection device, and in particular, the present invention relates to a focus detection device and an observation device equipped with the focus detection device. of the reflected light flux from the object and detects the incident position information on the detector surface of the light flux that passes through other areas of the imaging optical system. The present invention relates to a focus detection device that detects the focal position of a system and an R detection device equipped with the focus detection device.

(Prior Art) Various types of focus detection devices have been proposed for photoelectrically detecting the focal position of an imaging optical system.

For example, Japanese Patent Application Laid-Open No. 57-210308 proposes a so-called active type focus detection device in which a light beam is projected toward an object by a light projecting means and focus detection is performed using the light beam reflected from the object. Also, JP-A No. 57-72111 and JP-A No. 6
0-41013 and the like propose a passive focus detection device that performs focus detection using the imaging state of an object image formed by an imaging optical system. Also, JP-A-57-22
Publication No. 210 uses an active method, and at this time, the light flux is projected to the object side via an imaging optical system.
A focus detection device using a through-the-lens (through-the-lens) method has been proposed.

FIG. 9 is a schematic diagram of a main part of an optical system of a microscope equipped with a conventional active type focus detection device using a TTL type.

In the figure, reference numeral 1 denotes a light source for focusing, which is comprised of, for example, a laser diode, an LED (light emitting diode), or the like. A light beam from a light source 1 is condensed by a condenser lens 2. A part of the light beam condensed by the condenser lens 2 passes through the transmission surface 91a of the knife mirror 91, which has a reflection surface 91b on one side with respect to the optical axis and a transmission surface 91a on the other side. pass through. The light beam that has passed through the transmission surface 91a is reflected by the beam splitter 8 and enters the imaging optical system 9 as a light beam 18. The incident light flux to the imaging optical system 9 is a luminous flux whose principal ray is decentered with respect to the optical axis 114 of the imaging optical system 9 on the pupil plane 111, as shown in FIG. Area 112 (1
A light beam like 13 passes through the inside (formed by the shape of the transmitting/reflecting surface of the knife mirror 91).

The light beam 18 that has passed through the imaging optical system 9 is projected onto an object 92 and forms a spot image of the light emitting part of the light source 1 in the vicinity thereof. Of the luminous flux reflected by the object 92, the optical axis 11
The light beam 17 that returns to the optical path that is approximately symmetrical with respect to 4 and is reflected is
It passes through the imaging optical system 9 again. and beam splitter
8, reflected by the reflective surface 91b of the knife mirror 91, and condensed by the condenser lens 6 to form a spot image on the light receiving surface of the photoelectric conversion element 7 for focus detection.

In the figure, the light source 1 and the object 92, and the object 92 and the photoelectric conversion element 7 are each in a substantially conjugate relationship with each other.

Reference numeral 10 denotes a television camera of the microscope, which is located at a substantially conjugate position with the object 92 through the imaging optical system 9, and observes the object 92.

Now, when the object 92 is at the position (focus position) 11 shown in FIG. 9, light Ml as shown in FIG.
04 is imaged as a good spot light. At this time, a steep intensity distribution as shown by a curve 101 shown in FIG. 10 is obtained from the charging conversion element 7.

Further, when the object 92 is at the front pin (rear pin) position 12 (13), a light ray 106 (105) as shown in FIG. 10 is incident on the photoelectric conversion element 7. At this time, the light ray 106 (105) becomes a spot light that is wider than the light ray 101, and from the charge conversion element 7, it is wide as shown by the curve 103 in the same figure, and the light beam 17 reflected from the object 92 or the optical axis 1
Since it is eccentric with respect to 14, an intensity distribution that is shifted in the lateral direction with respect to the intensity distribution due to the light ray 104 is obtained.

At this time, the amount of deviation of the incident light beam on the surface of the photoelectric conversion element 7 and the amount of day focus from the focus position 11 of the object 92 are in a constant relationship. In the apparatus shown in FIG. 9, the focus of the imaging optical system 9 is detected by detecting the amount of deviation of the light intensity center of the light beam incident on the surface of the charge conversion element 7 from a predetermined position. That is, when a two-split sensor is used as the charge conversion element 7, and the intensity distribution of the incident light beam is a curve 101, the output value from the left sensor 7a is A, ti'[ as shown in FIG.
The output value from the sensor 7b of 1 is set as B, and the difference signal between output value A and output value B is set so that A-B or A-B=0.

FIG. 13 is an explanatory diagram showing the relationship between the day focus amount of the object 92 and the difference signal AB from the charge conversion element 7. That is, when object 92 is at position 12, the difference signal is A
-B>0, when object 92 is at position 13, the difference signal is A
-B<O.

The focus detection device shown in FIG. 9 moves the imaging optical system 9 or the object 92 along the optical axis so that the difference signal A-B of the output signals from the photoelectric conversion element 7 becomes A-B=0. By moving the object 9, the object 9 is brought into focus on the imaging optical system 9.

(Problem to be solved by the invention) In the focus detection device shown in FIG. As shown in FIG. 10, the light beam 17 is at a distance β2 from the photoelectric conversion element 7.
An image is formed at a point 105a in the front by about 2·ΔX.

However, β is the paraxial lateral magnification when the object 92 is imaged onto the photoelectric conversion element 7 side via the imaging optical system 9.

Here, if the object 92 is far away from the imaging optical system 9,
That is, as the day focus amount ΔX increases, the first
The distance β2·2·ΔX in FIG. 1 increases, and as shown in FIG. As a result, all of the reflected light beam 17 from the object 92 passes through the transparent part 91a of the knife mirror 91,
The light is no longer reflected by the reflective surface 91b and no longer enters the charge conversion element 7. At this time, the difference signal AB from the photoelectric conversion element 7 becomes AB=O as shown in FIG.

That is, when the day focus amount ΔX increases by a certain value ΔX MAX or more, the difference signal AB becomes AB=O, resulting in a problem that focus detection becomes impossible.

In the present invention, even if the object is largely day-focused from the imaging optical system, the reflected light beam from the object always enters the light receiving surface of the photodetector, and a predetermined difference signal is output from the photodetector. It is an object of the present invention to provide a focus detection device capable of detecting day focus of an object with respect to an imaging optical system over a wide range.

(Means for Solving the Problems) A focus detection device of the present invention and an observation device equipped with the same include a light source, an objective optical system, and a light portion of the objective optical system that is blocked by blocking a portion of light from the light source. A light restriction member that directs a light beam eccentric with respect to the axis toward the objective optical system; and a light restriction member that directs the reflected light from the test surface illuminated through the objective optical system through the objective optical system and the light restriction member. In the focus detection device, the focus detection device has a photodetector and detects displacement of the surface to be inspected in the direction of the optical axis based on a signal from the photodetector, and a polarization splitter that directs a linearly polarized light beam as the light beam to the objective optical system, and the objective optical system converts the linearly polarized light beam into a circularly polarized light beam and also reflects the linearly polarized light beam. It is characterized in that it includes a polarization conversion member that converts light into a polarized light beam polarized in a direction perpendicular to the linearly polarized light beam, and the polarized light beam is reflected to the photodetector by the polarization splitting section and the reflecting section.

In addition, in the present invention, (a) the light source includes a light emitting diode, a lens system that collects light from the light emitting diode and makes it enter the light restricting member, and a polarization direction of the light from the light emitting diode; The light emitting diode is characterized in that it includes a polarizing plate provided between the light emitting diode and the light restricting member to make the polarization direction coincide with the polarization direction of the polarization splitting section.

(b) It is characterized by being equipped with a light source or a light emitting diode.

(c) The light limiting member includes a beam splitter in which a metal film forming the reflecting portion and a polarizing film forming the polarization splitting portion are formed on a bonded surface of a pair of prisms.

(d) The objective optical system includes an objective lens system that focuses the circularly polarized light beam on a predetermined position between the polarization conversion member and the test surface, and the photodetector is connected between the predetermined position and the test surface. It is characterized by outputting a signal according to a relative displacement with respect to the surface to be inspected in the optical axis direction.

(E) The photodetector includes a lens system that collects the reflected light from the light restriction member, and a sensor that photoelectrically converts the light from the lens system and outputs a signal corresponding to the incident position of the light. The object optical system is characterized in that the objective optical system is arranged so that the sensor and the predetermined position are optically conjugate.

(f) The objective optical system is arranged so that the light emitting part of the light source and the predetermined position are optically conjugate.

(Embodiment) FIG. 1 is a schematic diagram of the main parts of an optical system according to a first embodiment of the present invention, and shows a microscope (observation device) equipped with a focus detection device.

In the figure, reference numeral 1 denotes a light source, which is composed of an LED and has a wavelength λ. Monochromatic light or wavelength λ. It emits a light beam (quasi-chromic light with a center wavelength λ) that spreads around . 2
is a condenser lens, which condenses the light beam from the light source 1. The condenser lens 2 is provided to effectively utilize the luminous flux from the light source 1, and by appropriately determining the configuration and arrangement of the lens system that constitutes the lens 2, the light emitting portion of the light source 1 toward the object 92 can be reduced. It is also possible to change the imaging magnification.

A linear polarizer (polarizing plate) 3 converts the light beam from the condenser lens 2 into a linearly polarized light beam 14 that vibrates within the plane of the paper. Reference numeral 4 denotes a light restricting member, which forms a light beam decentered with respect to the optical axis.

FIG. 2 shows an enlarged view. As shown in FIG. 2, the member 4 is constructed by bonding two right-angled prisms 21 and 22 together. And on these bonded surfaces,
Light source 1 is placed in the area (reflection part) 23 on one side near the optical axis 114.
The wavelength λ from A1, Au which reflects most of the luminous flux of
, Cu, etc., and the region 24 (polarized light splitting section) on the other side from the vicinity of the optical axis 114 has characteristics of transmittance and reflectance for P and S polarized light as shown in FIG. A polarizing film is applied. The polarization axis of this polarizing film coincides with the polarization direction of the linearly polarized light beam 14, so the linearly polarized light beam 14 incident on the member 4 passes through the region 24 on one side of the optical axis 114, and the linearly polarized light beam 14 passes through the region 24 on one side of the optical axis 114. The light beam 14 is emitted as a linearly polarized light beam 15 polarized in the same direction as the light beam 14.

In addition, in FIG. 3, curves 31 and 32 indicate the wavelength λ from the light source 1. Curves 33 and 34 show the reflectance for both the s and p polarization components of the light beam of wavelength λ0 from the light source 1.

Returning to FIG. 1, reference numeral 5 denotes a λ/4 plate (polarization conversion member), which is arranged with its main axis inclined at 45 degrees with respect to the polarization axis of the linear polarizer 3. The λ/4 plate 5 converts the incident linearly polarized light beam 15 into a circularly polarized light beam 16 and emits the circularly polarized light beam 16. 8 is a beam splitter, which has no polarization characteristics, reflects the light beam (circularly polarized light) from the λ/4 plate 5, and directs it toward the optical axis (center ray).
The decentered light beam 18 is incident on a part of the area on one side of the optical axis 114 of the imaging optical system 9, which is made up of an objective lens. An objective lens is an assembly of multiple lenses arranged side by side. 92 is an object, 6 is a condenser lens, 7
has a photoelectric conversion element and consists of a two-part sensor.

The light entrance surface 21a of the prism 21 and the light exit surface 22a of the prism 22 of the light restriction member 4 are each formed of a plane, and the member 4 is arranged so that these surfaces 21a, 22a are perpendicular to the optical axis 114. It is. Also, the bonding surfaces of the prism 21 and the prism 22, that is, the area 23 and the area 24
The formed surface is set to form an angle of 450 with respect to the optical axis 114.

10 is a television camera, and when the surface to be measured on the object 92 is focused on the imaging optical system 9, its imaging surface is approximately conjugate with the surface to be measured on the object 92 via the imaging optical system 9. and is observing object 92.

In this embodiment, when the imaging optical system 9 focuses on the surface to be measured of the object 92, the light emitting part of the light source 1 and the surface to be measured of the object 92,
The device is configured such that the surface to be detected of the object 92 and the light receiving surface of the charge conversion element 7 are in a substantially conjugate relationship with each other.

In this embodiment, a diverging light beam from a light source 1 is condensed by a condenser lens 2, and is made to enter a light restriction member 4 as a linearly polarized (P-polarized) light beam 14 that vibrates within the plane of the paper by a linear polarizer 3. As shown in FIG. 2, among the linearly polarized light beams 14 incident on the member 4, the light beams incident on the region 23 on one side with respect to the boundary line near the optical axis 114 are reflected by the metal film, and are reflected by the imaging optical system. The system 9 is shielded from light. On the other hand, the optical axis 11
The polarizing film applied to the area 24 on the other side of the boundary line near 4 transmits nearly 100% of the P-polarized light, as shown by the curve 31 in FIG. Most of the light beam incident on this region 24 passes through the region 24 and enters the λ/4 plate 5.

The linearly polarized light beam 15 incident on the ^/4 plate 5 exits from the λ/4 plate 5 as a circularly polarized light beam 16, and is passed through the λ/4 plate 5.
8 and enters the imaging optical system 9 as a light beam 18 decentered with respect to the optical axis 114.

At this time, as shown in FIG. 11, the light beam 18 passes through a region 112 on the pupil plane 111 of the imaging optical system 9 that is eccentric from the light l1lII1114. The shape of this region 112 changes depending on the shapes of the regions 23 and 24 of the light restriction member 4 and the cross-sectional shape of the light beam 14 incident thereon. Therefore,
For example, if the shape of the area 24 is circular, the area 24 is surrounded by the area 24.
4, the area 112 on the pupil plane 111 of the imaging optical system 9
is as shown in FIG.

The imaging optical system 9 focuses the light beam 18 on a position substantially conjugate with the imaging surface of the television camera, and forms a light spot (image of the light source 11) on the test surface of an object 92 located at a position 11, for example.

The light beam 18 projected onto the object 92 is reflected by the test surface of the object 92 and becomes a light beam 17 that travels in the opposite direction along an optical path that is approximately symmetrical to the optical path at the time of projection with respect to the optical axis 114.
The beam enters the imaging optical system 9, passes through another area located symmetrically to the area through which the light beam 18 passes, with respect to the optical axis 114 of the imaging optical system 9, and is directed to the beam splitter 8. It is reflected by the splitter 8 and enters the λ/4 plate 5.

The light beam 17 incident on the λ/4 plate 5 becomes a linearly polarized (S-polarized) light beam polarized in a direction perpendicular to the plane of the paper and perpendicular to the polarization direction of the linearly polarized light beam 15 by the λ/4 plate 5. incident.

Among the linearly polarized light beams incident on the light restriction member 4 , the light beams incident on the region 23 of the member 4 are reflected by the metal film and enter the condenser lens 6 . In addition, the polarizing film applied to the region 24 of the member 4 polarizes the S-polarized light to 1 as shown by the curve 33 in FIG.
Since nearly 00% is reflected, the linearly polarized (S-polarized) light beam incident on this region 24 is also reflected by the polarizing film of the region 24 and enters the condenser lens 6. The condenser lens 6 condenses the incident light flux to form a light spot on the light receiving surface of the photoelectric conversion element 7. The photoelectric conversion element 7 charges and converts the incident light flux, and generates signals A and B corresponding to the displacement of the surface to be measured of the object 72.
Output.

Output signals A and B from the charging conversion element 7 are input to the controller 100 via signal lines, and the controller 100 receives the difference signal A-
A signal corresponding to B is generated, and the drive device 101 is controlled based on this signal.

The driving device 101 moves the object 92 up and down in the optical axis direction of the imaging optical system 9 in response to a command signal from the controller 100 so that the light beam from the imaging optical system 9 focuses on the surface to be inspected of the object 92. urge The controller 101 also controls the light emission operation of the light source 1 (ONloFF).

At this time, if the surface to be examined of the object 92 is at position 11, that is, at the in-focus position, the light beam 17 will be as shown in FIG.
It is mainly reflected by the area 23 of the light limiting member 4, and the photoelectric conversion element 7
A light beam 104 shown in FIG. 10 is incident on the light receiving surface of the light receiving surface, forming a clear light spot on the light receiving surface.

If the object 92 is at the position 12 (front focus), the light beam 17 is reflected by the region 23 of the light restriction member 4, as shown in FIG. The light beam 106 enters the light beam and forms a spread optical beam on the light receiving surface.

On the other hand, the object 92 is at position 13 (rear focus), and at this time the day focus amount ΔX is large, that is, as shown in FIG. As the light becomes larger, the light beam 17 reaches a point 17b in front of the light limiting member 4, as shown in FIG.
After being imaged, most of the light is incident on the area 23 and then on the area 24.

At this time, the light beam 17 is S-polarized as described above, so it is reflected by the area 24 coated with the polarizing film,
As shown in FIG. 10, the light beam 105 enters the light receiving surface of the photoelectric conversion element 7 and forms a spread light spot on the light receiving surface.

In this manner, in this embodiment, even if the object 92 is largely defocused in the front focus direction and the rear focus direction, the light beam 17 can be made incident on the photoelectric conversion element 7.

As a result, when a two-split sensor similar to the conventional one shown in FIG. 9 is used as the charging conversion element 7, a difference signal A between the output signal A from the sensor A and the output signal B from the sensor B with respect to the day focus amount is obtained. -B, as shown in FIG. 14, can be detected even if the object 92 is in more day focus than the conventional maximum detectable day focus amount ΔX MAX.

As described above, according to this embodiment, even if the object 92 is day-focused over a wide range, the focal position can be detected with high precision.

In the above embodiment, an LED was used as the light source 1, but
A laser diode (semiconductor laser) may be used as the light source 1. In this case, the polarizer 3 can be removed by arranging the laser diode and the light limiting member so that the polarization direction of the laser light emitted from the laser diode matches the polarization axis of the polarizing film of the light limiting member. I'll come.

Furthermore, if the intensity of the luminous flux from the light source 1 is large, the condenser lens 2 can be removed, but even in this case, it is necessary to ensure that the image of the light emitting part of the light source 1 is formed near the object 92. be.

Further, depending on the case, the device may be configured with the condenser lens 6 removed.

In the above embodiment, a two-split sensor was used as the light source conversion element 7, but as the light source conversion element 7, a one-dimensional CCD,
Two-dimensional CCD or PSD (Position 5e
nsitive Detector) etc. can be used.

Further, the structure of the light restricting member 4 is not limited to a block-like member as in the above embodiment, but may be, for example, a structure in which a metal film and a polarizing film are formed adjacent to each other on a transparent parallel plate.

Furthermore, when focusing the inspection surface of the object 92 on the imaging optical system 9, instead of moving the object 92 up and down, the entire microscope or a part of the optical system (for example, the optical system 9) may be moved. method will also be adopted.

Further, when the focus detection device of the present invention is mounted on an observation device such as a microscope, it is preferable to arrange the person/4 plate 5 between the member 4 and the beam splitter 8 as in the above embodiment. When mounted on another optical device, it can be provided at any position between the member 4 and the surface to be inspected.

In the above embodiment, the shape of one of the right-angled prisms 22 of the light limiting member 4 is changed, and the bottom surface 73a as shown in FIG. Also good.

In this way, the bottom surface 73a of the prism 73 or the photoelectric conversion element 7
By setting the optical axis so as not to be perpendicular to the optical axis, the light beam 14 reflected by the metal film in the area 23 is emitted to the opposite side in a direction away from the area 24. This prevents the light beams reflected by the area 23 from being reflected by the bottom surface 73a of the prism 73 and entering the areas 23 and 24 again, and prevents these light beams from entering the charge conversion element 7 as flare or ghost light. can be effectively prevented.

In addition, in the above embodiment, as shown in FIG.
The members 3 and 4.5 may be integrated by bonding the linear polarizer 3 and the man/4 plate 5 to the light restricting member 4. This is preferable because the assembly mechanism can be simplified.

(Effects of the Invention) According to the present invention, when detecting the focal position of the imaging optical system, a linear polarizer and an optical element are used as a means for making an eccentric light beam incident on the imaging optical system. By appropriately setting each element such as the four plates, it is possible to achieve a focus detection device that can detect the focus position with high precision over a wide dayfocus range with a large dayfocus amount.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the main parts of an optical system according to a first embodiment of the present invention, and FIG. 4th. Fifth. 6 is an explanatory diagram of the light flux incident on the optical element of FIG. 1, FIG. 3 is an explanatory diagram of the optical characteristics of the region 24 of the optical element of FIG. 2, and FIGS. 7 and 8 are respectively related to the present invention. FIG. 9 is a schematic diagram of the main part of an optical system of a conventional focus detection device; FIG. 10 is an explanatory diagram of the light beam incident on the detector of FIG. 9; Figures 11 and 15 are explanatory diagrams of the light flux on the pupil plane of the imaging optical system in Figure 9, Figure 12 is an explanatory diagram of a part of Figure 9, and Figures 13 and 14 are diagrams showing the amount of day focus. FIG. 3 is an explanatory diagram showing a relationship with a difference signal. In the figure, 1 is a light source, 2.6 is a condenser lens, 3 is a linear polarizer, 4 is an optical element, 5 is a person/4 plate, 7 is a photoelectric conversion element, 8 is a musburi-tsuta-19 is an image forming Optical system, 1
0 is a television camera, 92 is an object, 111 is a pupil plane of the imaging optical system, 114 is an optical axis, 14.15 is linearly polarized light, 16 is circularly polarized light, 17.18 is a light flux, 100 is a controller, 101 is a drive It is a device.

Claims (10)

[Claims] (1) A light source, an objective optical system, a light restriction member that blocks part of the light from the light source and directs a light beam decentered with respect to the optical axis of the objective optical system toward the objective optical system, and the objective optical system. a photodetector that detects reflected light from a surface to be inspected illuminated via the optical system via the objective optical system and the light restriction member; In a focus detection device that detects a displacement of a surface to be inspected in the direction of the optical axis, the light limiting member includes a reflecting portion that blocks part of the light from the light source and a linearly polarized light flux as the light flux to the objective optical system. and a polarization conversion member that causes the objective optical system to convert the linearly polarized light beam into a circularly polarized light beam and convert the reflected light into a polarized light beam polarized in a direction orthogonal to the linearly polarized light beam. . A focus detection device, characterized in that the polarized light beam is reflected to the photodetector by the polarization splitting section and the reflection section. (2) The focus detection device according to claim 1, wherein the light source includes a light emitting diode. (3) The light source includes a lens system that collects the light from the light emitting diode and makes it enter the light restriction member, and a lens system that makes the polarization direction of the light from the light emitting diode match the polarization direction of the polarization splitting section. The focus detection device according to claim 2, further comprising a polarizing plate provided between the light emitting diode and the light limiting member. (4) The focus detection device according to claim 1, wherein the light source includes a laser diode. (5) The light limiting member includes a beam splitter in which a metal film forming the reflecting portion and a polarizing film forming the polarization splitting portion are formed on a bonding surface of a pair of prisms. focus detection device. (6) The objective optical system includes an objective lens system that focuses the circularly polarized light beam on a predetermined position between the polarization conversion member and the test surface, and the photodetector is arranged between the predetermined position and the test surface. 2. The focus detection device according to claim 1, wherein the focus detection device outputs a signal corresponding to a relative displacement in the optical axis direction with respect to the surface to be detected. (7) The photodetector includes a lens system that collects the reflected light from the light restriction member, and a sensor that photoelectrically converts the light from the lens system and outputs a signal according to the incident position of the light. The focus detection device according to claim 6, characterized in that: (8) The focus detection device according to claim 7, wherein the objective optical system is arranged so that the sensor and the predetermined position are optically conjugate. (9) The focus detection device according to claim 8, wherein the objective optical system is arranged so that the light emitting section of the light source and the predetermined position are optically conjugate. (10) An observation device comprising the focus detection device according to any one of claims 1 to 9.