JP2003029130A - Optical microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical microscope, which makes autofocusing possible by a light source for observation of an object. SOLUTION: An aperture stop 21 and aperture stop 22 of a Koehler illumination optical system 5, and further a field stop 23 and a field stop 24 are changed over under the control of a control system 8, by which rays along an optical axis are used, when the object 2 is observed and the rays emitted form the same light source 17 and parted from the optical axis are used in autofocusing and therefore the difficulty in the achromatism of an objective lens 26 is eliminated, as compared with the case another light source is used for autofocusing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical microscope used for inspection of semiconductor patterns, for example, and more particularly to an optical microscope having an autofocus mechanism for adjusting the focus position of an object.

[0002]

2. Description of the Related Art Generally, in an inspection apparatus using an optical microscope, TTL (Thr
The "out the lenses" method has become widespread.

In this case, as a light source, a laser light source for autofocusing having good monochromaticity is often used. Further, the objective lens of the optical microscope is used as a part of the autofocus means, but this objective lens is generally achromatic by combining a plurality of glass materials in the wavelength region used. Further, in the objective lens which is achromatic, an antireflection coat is applied in the achromatic band.

On the other hand, in recent years, in microscopic observation of a semiconductor pattern represented by a semiconductor inspection process by an optical microscope, the wavelength of the light source used as a light source is determined to be ultraviolet because of the optical resolution required with the miniaturization of the semiconductor pattern. The wavelength is becoming shorter in the region.

[0005]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
In the ultraviolet region below nm, the optically transparent material is limited, and the optical aberration performance required for the optical microscope also requires the frequency response near the diffraction limit. Therefore, if the difference between the wavelength of the light source in the ultraviolet region used for microscopic observation and the wavelength of the light source for autofocus becomes large, it becomes difficult to achromatize the objective lens at the wavelength of the light source for autofocus. As a result, it is very expensive to manufacture the objective lens of the optical microscope, which has become a hindrance to the spread of the ultraviolet microscope.

For example, deep ultraviolet (DUV :) used as a light source in an automatic defect classifying device for semiconductor circuit patterns.
Deep Ultra Violet) light has a drawback in that it is necessary to use a lot of very expensive high-purity fluorite and quartz for achromatization of an objective lens for autofocusing, which is very expensive. .

Further, an ultraviolet transmissive adhesive is used to bond the two kinds of glass materials, but this adhesive has a drawback that it is damaged by deep ultraviolet light and its transmittance decreases with time. There is.

In addition, the light source wavelengths normally used for auto-focusing often use red to infrared wavelengths. Therefore, the depth of focus of the light source wavelength used for autofocus becomes deeper by the wavelength ratio than the depth of focus of the deep ultraviolet wavelength used as the light source for microscopic observation, and the autofocus accuracy naturally deteriorates accordingly.

On the other hand, an image autofocus method for obtaining an optimum image plane position from the contrast of a photographed image not based on an optical method, a distance measuring type autofocus method using a displacement sensor, and a triangulation method not based on the TTL (Through the Lens) method. An autofocus method based on the distance method and the like have been proposed, but all of them are inferior to the TTL method due to processing speed, measurement error, physical restrictions, and the like.

The present invention is made to solve such problems, and an object thereof is to provide an optical microscope capable of autofocusing by a light source for observing an object.

[0011]

In order to achieve the above object, an optical microscope according to a main aspect of the present invention has a first light beam for observation which is irradiated along an optical axis which is a first axis. And illuminating means for emitting a second light beam for autofocus, which is emitted along a second axis apart from the first axis,
An optical system that irradiates the object with a light beam emitted by the illumination unit, forms an image of reflected, diffracted, or scattered light of the object at an image forming position; and an image capturing unit arranged at the image forming position. The object is irradiated with the second light beam through the optical system, the reflected light of the object is imaged on the image capturing means, and the optical system in the optical system is based on a signal obtained by the image capturing means. And an autofocus unit for adjusting the focus position of the object.

In the present invention, the first light ray along the optical axis is used when observing an object, and when autofocusing, the same illumination means as the first light ray is used, and it is separated from the optical axis. Since the second light beam is used, the difficulty of achromatizing the objective lens in the case of autofocusing by the TTL method is eliminated and the focus control becomes extremely accurate.

According to one aspect of the present invention, the illumination means includes a light source for emitting the light beam, an aperture stop having an aperture on the optical axis of the light beam by the light source, and a light beam emitted from the aperture stop. And a Koehler illumination optical system having a field stop having an opening on the optical axis of the field stop, the position of the opening of the aperture stop can be changed, and the opening area of the opening of the field stop can be changed. It is characterized by Accordingly, the aperture stop can be an aperture stop that is deviated from the optical axis, and a light beam that is away from the optical axis can be emitted from the illumination means. Therefore, since the separated light beam can be used as the light beam for autofocusing, autofocusing in the optical microscope can be performed at low cost with a simple structure.

According to one aspect of the present invention, the aperture stop and the field stop are a liquid crystal element for an aperture stop and a liquid crystal element for a field stop, respectively. This further speeds up the off-axis aperture stop and eliminates mechanical wear.

According to one aspect of the present invention, the autofocus means has an actuator for moving an objective lens provided in the optical system in a focus direction. As a result, the objective lens can be electrically controlled extremely accurately and instantaneously.

According to one aspect of the present invention, a holding mechanism for holding the object is further provided, and the autofocus means has a moving means for moving the holding mechanism in a focus direction. . As a result, autofocusing can be performed with the objective lens fixed, so that autofocusing itself as an optical system is simple and an inexpensive device can be obtained.

According to one aspect of the present invention, the autofocus means includes the actuator for moving the objective lens provided in the optical system in a focus direction, and the movement for moving the holding mechanism in the focus direction. And means. As a result, since the objective lens can be moved in the focus direction at the same time as being moved by the holding mechanism in the focus direction, the autofocus can be further speeded up and highly accurate.

According to one embodiment of the present invention, a light source for detecting a distance, which is provided in the objective lens of the optical system and irradiates the object with a light beam, and a reflected light reflected by the object is detected. Further comprising a detection unit, wherein the autofocus means preliminarily adjusts the distance between the object and the detection unit according to a signal from the detection unit, and then the focus position of the object in the optical system. It is characterized by adjusting. Thereby, first, the focus position of the target object can be adjusted to the best position by performing the autofocus preliminarily by adjusting the distance between the target object and the distance detecting means. The efficiency of autofocus can be improved, and the autofocus can be made more precise.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of an optical system and a control system showing an optical microscope according to a first embodiment of the present invention.

As shown in FIG. 1, this optical microscope 1
Is an object 2 to be observed microscopically as a holding mechanism and moving means.
A movable stage 3 on which the object 2 is placed and moved, an optical system 4 for irradiating the object 2 with light rays and for forming an image of reflected, diffracted or scattered light from the object 2, and an optical system 4 as illumination means Light source 17 and light source 17 for emitting light rays
A Koehler illumination optical system 5 on which a light beam emitted from
Image capturing means 6 for capturing the image formed by the optical system 4.
And an image processing system 7 for processing the image obtained by the image capturing means 6, and a control system 8 for controlling the overall movement of the optical microscope.

For example, in the case of inspecting various defects existing in the semiconductor wafer 9 by the optical microscope 1 and inspecting and measuring the dimension, the overlay accuracy, etc. of the pattern formed on the semiconductor wafer 9 in the lithography step of the semiconductor process. , The semiconductor wafer 9 becomes the object 2 to be microscopically observed.

Here, FIG. 2 is a perspective view showing the movable stage 3, and FIG. 3 is a configuration diagram of an optical system and a control system showing an optical microscope when the focus of the object 2 is adjusted.

As shown in FIG. 2, the movable stage 3 includes an XY stage 10 for moving in the horizontal direction (XY direction), a Z stage 11 for moving the semiconductor wafer 9 in the vertical direction (Z direction), and a semiconductor wafer 9. A θ stage 12 that rotates in the XY plane (θ direction), and drive motors 13, 14, 15 and 16 for driving each stage.
And a suction plate (not shown) for sucking and fixing the semiconductor wafer 9 on the movable stage 3.

Further, the movable stage 3 drives the driving motors 13, 14 and 15 under the control of the control system 8 so that the semiconductor wafer 9 attracted by the attraction plate.
It is possible to move any point above to just below the optical system 4. As a result, the drive motors can be driven at the same time, so that the movement of the semiconductor wafer 9 is extremely speeded up.

Further, the focus position of the semiconductor wafer 9 can be adjusted by driving the drive motor 16 under the control of the control system 8. As a result, autofocus can be performed extremely easily and quickly.

As shown in FIG. 1, the light source 17 is, for example, an ultraviolet solid state laser. This ultraviolet solid-state laser performs wavelength conversion on a solid-state laser such as a YAG laser using a non-linear optical element. For example, the wavelength is 266 nm and 1
DUV laser light of about 93 nm to 213 nm is emitted.

Here, the resolution of the optical microscope 1 depends on the wavelength of the light beam irradiating the object and the numerical aperture (NA: numerical aperture) of the objective lens 26, and the wavelength of the illuminating light beam is a short wavelength. , The larger the NA, the higher the resolution.

In this respect, since the optical microscope 1 uses the deep ultraviolet solid state laser as the light source 17 and uses the objective lens 26 having a higher NA, a fine pattern on the semiconductor wafer 9 produced in the semiconductor lithography process. Can be inspected.

Further, the deep ultraviolet solid state laser as the light source 17 in the optical microscope 1 has a small apparatus itself,
Wavelength stability, monochromaticity, beam profile, compared to excimer lasers that are widely used in lithography processes
Excellent in cooling, gas replenishment, laser safety and handling.

The Koehler illumination optical system 5 includes an optical fiber 18 that guides the light beam emitted from the light source 17, an emitting unit 19 that emits the light beam guided by the optical fiber 18, and an emitting unit 1.
An auxiliary condenser lens 20 for condensing the light rays emitted from 9;
Aperture stops 21 and 22 to which the light rays emitted from the auxiliary condenser lens 20 are incident, field diaphragms 23 and 24 to which light rays emitted from the aperture diaphragms 21 and 22 are incident, and field diaphragms 23 and 24.
A condenser 25 to which a light beam emitted from the camera enters, and a diaphragm driving unit 27 that drives the aperture diaphragms 21 and 22 and the field diaphragms 23 and 24.

The aperture stop 21 of the aperture stops 21 and 22
Is used when microscopically observing the object 2,
For example, an opening is provided at the center of the aperture stop 21 so that the opening is on the optical axis of the light beam emitted from the auxiliary condenser lens 20 having a plate shape.

The aperture stop 22 is used when adjusting the focal position of the object 2, so that the Koehler illumination optical system 5 can emit a light beam distant from the optical axis of the light beam for microscopic observation. Therefore, for example, the aperture stop has a plate shape and is off-axis from the optical axis. That is, the aperture stop 22 is provided with the opening above the center of the aperture stop 22.

Further, the off-axis amount of the aperture stop 22 is determined by the aperture stop 2
Since the magnification of 2 and the objective lens pupil diameter are equal, the maximum is the objective lens pupil diameter.

Here, the upper end of the aperture stop 22 is lowered below the light beam so as not to block the light beam emitted from the opening part of the aperture stop 21 when the object 2 is observed microscopically. .

Of the field diaphragms 23 and 24, the field diaphragm 23
Is used when microscopically observing the object 2,
For example, an aperture is provided in the center of the field stop 23 so that the aperture is on the optical axis of the light beam emitted from the auxiliary condenser lens 20 having a plate shape.

The field stop 24 is used when adjusting the focus position of the object 2. The field stop 24 has, for example, a plate-like field stop 24 so as to connect a spot to the image pickup means 6. In the central portion of the, an opening portion that is sufficiently smaller than the image pickup range of the image pickup means 6 is provided. This opening is not limited to a round hole, and may be a slit.

Further, when the object 2 is observed microscopically, the field stop 24 has its upper end lowered below the light beam so as not to block the light beam emitted from the opening of the field stop 23. There is.

As a result, the aperture stop 21 and the field stop 23 can be used as a Koehler illumination optical system when emitting a light beam for observing the object 2, and when viewed from the object surface, all of the aperture stop 21 can be used. It serves as a light source and provides uniform illumination.

Further, as shown in FIG. 3, when the light beam for adjusting the focus position of the object 2 is emitted, the aperture driving means 27 can replace the aperture stop 21 and the aperture stop 22 and the field stop 23 and the field of view. The diaphragm 24 can also be replaced. At this time, the aperture stop 21 and the field of view are prevented so that the light beam entering the aperture stop 22 and the light beam exiting the aperture stop 22 away from the optical axis of the microscopic observation light beam are not blocked. The diaphragm 23 will be lowered.

As a result, a light beam is emitted from the Koehler illumination optical system along the optical axis of the condenser 25 when observing the object 2, and the light of the condenser 25 is adjusted when the focus position of the object 2 is adjusted. A ray that is off axis will be emitted.

The diaphragm driving means 27 replaces the aperture diaphragm 21 with the aperture diaphragm 22 and the field diaphragm 23 with the field diaphragm 24 under the control of the control system 8 by, for example, a driving motor or an electromagnet.

As a result, the same light source 17, Koehler illumination optical system 5 and optical system 4 can be used quickly and easily to perform microscopic observation of the object 2 and also autofocus the object 2.

Further, as shown in FIG. 1, the optical system 4 includes a beam splitter 28 on which the light beam emitted from the Koehler illumination optical system 5 enters, and an objective lens 26 on which the light beam reflected by the beam splitter 28 enters. An actuator 30 is provided with an imaging lens 29 on which the light rays reflected from the object 2 and returned and which have passed through the objective lens 26 and the beam splitter 28 are incident.

The beam splitter 28 reflects the light beam emitted from the Koehler illumination optical system 5 to the objective lens 26, and transmits the light beam reflected from the object 2 and transmitted through the objective lens 26 to the imaging lens 29. .

The objective lens 26 is a beam splitter 28.
The object 2 is irradiated with the light beam emitted from the Koehler illumination optical system 5 and emitted from the object. In addition, the objective lens 26
Are provided so as to emit reflected light from the object 2 and the like to the imaging lens 29 via the beam splitter 28.

The imaging lens 29 is for further enlarging the image formed by the objective lens 26 and forming an image on the image pickup means 6, whereby the minute object 2 can be microscopically observed. For example, various defects existing on the semiconductor wafer 9 can be inspected, and in the lithography process of the semiconductor process, the dimensions of the pattern formed on the semiconductor wafer 9 and the overlay accuracy can be inspected and measured.

FIG. 4 shows a Koehler illumination optical system 5 and an optical system 4 showing off-axis autofocus.

Here, when the focus position of the object 2 is adjusted, a light ray distant from the optical axis of the condenser 25 is emitted, and this light ray is, for example, in the optical system 4 as shown in FIG. , Is parallel to the optical axis of the condenser 25 in the Koehler illumination optical system 5 and enters the beam splitter 28 at a distance, and is reflected by the beam splitter 28 to the objective lens 26.

Here, in the object space plane of the objective lens 26,
Since the light ray is emitted from a position away from the optical axis of the objective lens 26, the light ray obliquely advances to the focal position on the optical axis.

Therefore, the light ray reflected from the object 2 is reflected at the same angle θ ₁ as the incident angle and enters the object space surface of the objective lens 26.

The light beam incident on the objective lens 26 at the angle θ ₁ forms an image on the spot position of the image pickup means 6 via the beam splitter 28 and the image forming lens 29.

Here, when the object 2 is separated from the objective lens 26 by Δd _{1, the} reflection position of the reflected light from the object 2 is laterally displaced by h _1, so that the beam splitter 28 and the connecting unit are connected. The position where an image is formed on the image pickup means 6 via the image lens 29 is Δd ₂ from the optical axis image pickup means 6.
It will connect the spot just in front. That is, the light receiving surface of the image pickup means 6 is laterally displaced by h ₂ .

The horizontal displacement h ₂ is determined by the optical microscope 1
If the magnification is 100 times, it is 100 times as large as the displacement h ₁ of the reflection position on the object 2, and very high precision autofocus is possible.

At this time, the deviation Δ from the focus position of the object 2
d ₁ is the reflection angle θ ₁ , the lateral shift h _{2 on} the light receiving surface of the image pickup means 6, and the focal length f of the objective lens 26.
_The method of performing autofocus by utilizing the fact that it is determined by ₁ and the focal length f ₂ of the imaging lens 29 is called the off-axis autofocus method.

The off-axis autofocus method will be described below by using mathematical expressions.

The off-axis autofocusing method uses the characteristic that the vertical magnification according to the image formation formula is expressed by the square of the horizontal magnification, and the image plane on the image plane due to defocusing of the semiconductor wafer 9 as the object surface is used. The property that the lateral displacement amount is proportional to the incident angle tangent due to the off axis of the vertical magnification, the enlargement magnification, and the defocus amount is used.

That is, as shown in FIG. 3, the off-axis amount from the optical axis of the aperture stop 22 in the Koehler illumination optical system 5 is
The incident angle from the objective lens 26 to the object surface is determined.

The incident angle θ ₁ (degrees) of the off-axis light depends on the numerical aperture N of the objective lens 26, the diameter ratio σ between the objective lens pupil diameter and the aperture stop, the off-axis amount R and the aperture stop diameter A. The incident angle of light θ ₁ (degree) = sin ⁻¹ (N × σ × R) / 2A.

Now, as shown in FIG. 4, when the semiconductor wafer 9 which is the object surface has a defocus of Δd ₁ , the defocus amount on the image surface of the image pickup means 6 under observation is It is expressed by Δd ₂ = (f ₂ / f ₁ ) ² × Δd ₁ by the image formula.

At this time, the incident angle si to the image pickup means 6 is
nθ_TwoIs the angle of incidence sin θ on the image pickup means 6._Two= (F₁
/ F_Two) × sin θ₁So f₁<< f_TwoThat is,
Lateral displacement h on the target surface₁And in the image pickup means 6
Lateral displacement h_TwoBetween and h ₁<< h_TwoWithin the range
Displacement h_TwoIs h_Two= Δd_Two× sin θ_TwoBecomes

Organizing this, h ₂ = (f ₂ / f ₁ ) ×
It can be expressed as sin θ ₁ × Δd _1, and it is possible to grasp the focus state by correctly measuring the lateral displacement amount h ₂ .

The actuator 30 is composed of a focus coil, a focus magnet and the like (not shown) provided inside, and is provided so as to perform a focus operation when a voltage is applied to the focus coil by the control system 8. There is.

When the light source 17 of the optical microscope 1 is a deep ultraviolet solid state laser or the like, the image pickup means 6 forms an image forming lens 29.
Since the image formed by is not directly visible to the naked eye, it is provided at a place where an image is formed by the image forming lens 29 so as to be imaged by a CCD or the like.

The image processing system 7 processes the information picked up by the image pick-up means 6 so that it can be viewed on a monitor television or the like.

The control system 8 comprises a light source 17 and an aperture driving means 2
7. The motors 13 to 16 for driving the movable stage 3 and the actuator 30 are provided so as to control the entire optical microscope 1.

Next, the operation of the optical microscope 1 configured as described above will be described.

For example, in the case of inspecting various defects of the semiconductor wafer 9, first, the semiconductor wafer 9 to be inspected is placed on the XY stage 10 of the movable stage 3, and when the power of the control system 8 is turned on, the light source 17 emits light. The light beam is emitted, and the semiconductor wafer 9 is attracted by the attraction plate and fixed on the XY stage 10. by this,
The semiconductor wafer 9 can be prevented from being displaced during the inspection, and the semiconductor wafer 9 can be prevented from being damaged.

Next, under the control of the control system 8, the drive motor 1
3 moves the XY stage 10 in the horizontal X direction, and the drive motor 14 moves the XY stage 10 in the horizontal Y direction. As a result, the position of the semiconductor wafer 9 to be inspected can be moved directly below the optical system 4.

Next, autofocus is performed. For example, when the autofocus start switch is turned on, first, the diaphragm drive means 27 is turned on under the control of the control system 8 and the upper end portion of the aperture diaphragm 21. Lowers the light beam that has passed through the auxiliary condenser lens 20 so as not to be blocked.

The aperture stop 22 rises so that the aperture of the aperture stop 22 is separated from the optical axis of the auxiliary condenser lens 20.

Further, the field stop 23 descends so that the upper end of the field stop 23 does not block the light beam emitted from the opening of the aperture stop 22. The field stop 24
Rises so that the opening of the field stop 24 is on the optical axis of the auxiliary condenser lens 20.

Next, the light beam emitted from the light source 17 is guided to the emission unit 19 by the optical fiber 18, and the light beam emitted from the emission unit 19 passes through the aperture stop 22 and the field stop 24.
The light beam separated from the optical axis from the condenser 25 is emitted to the beam splitter 28 of the optical system 4. This makes it possible to perform autofocus extremely easily and accurately using the off-axis light beam.

That is, when the off-axis light beam enters the beam splitter 28 of the optical system 4, it is reflected by the objective lens 26, and the semiconductor wafer 9 from the object space surface of the objective lens 26.
Is irradiated obliquely to the position to be inspected.

Further, the irradiated light beam is reflected from the semiconductor wafer 9 at the position to be inspected and obliquely enters the objective lens 26, and is imaged on the image pickup means 6 such as CCD through the beam splitter 28 and the imaging lens 29. Will be tied together. At this time, as shown in FIG. 4, when the focus of the semiconductor wafer 9 at the position to be inspected is deviated by Δd ₁ , at the imaging position by the imaging lens 29, the expanded Δ
It will be offset by d ₂ and will be offset by h _{2 in the} horizontal direction.

The deviation of h ₂ is converted into electronic information by the image pickup means 6, whereby a voltage is applied from the control system 8 to the focus coil provided in the actuator 30. As a result, the objective lens 26 is moved in the focus direction and a proper focus position is secured. That is, the image pickup means 6 cannot recognize the shift of h _{2 and} the autofocus ends.

Next, under the control of the control system 8, various defects of the ordinary semiconductor wafer 9 are inspected at the specified inspection position.

That is, the diaphragm driving means 27 is powered on under the control of the control system 8, and the aperture diaphragm 21 is raised so that the aperture of the aperture diaphragm 21 is on the optical axis of the auxiliary condenser lens 20. The upper end of the aperture stop 22 drops below the light beam so that the light beam emitted from the aperture stop 21 is not blocked.

Further, the field stop 23 is raised so that the opening of the field stop 23 is on the optical axis of the auxiliary condenser lens 20. Further, the field stop 24 lowers the upper end of the field stop 24 below the light beam so as not to block the light beam emitted from the field stop 23.

As a result, a light beam along the optical axis is emitted from the condenser 25 to the beam splitter 28 of the optical system 4. Further, it is reflected by the beam splitter 28,
The semiconductor wafer 9 to be inspected and emitted to the objective lens 26 is irradiated with a light beam along the optical axis.

The light beam applied to the semiconductor wafer 9 is reflected and returned to the objective lens 26 again, and passes through the beam splitter 28 and the image forming lens 29 to pick up the image pickup means 6.
The image will be connected to.

Further, the electronic information of the image formed on the image pickup means 6 is processed by the image processing system 7 so that it can be seen on a monitor television or the like, and is inspected on the monitor television or the like.

As described above, according to the present embodiment, the aperture stop 21 and the aperture stop 22 of the Koehler illumination optical system 5 and the field stop 23 and the field stop 24 are switched under the control of the control system 8. A light ray along the optical axis is used when observing the object 2, and a light ray emitted from the same light source 17 and decentered from the optical axis is used when autofocusing. Compared to the case of using another light source, the difficulty of achromatization of the objective lens 26 is solved, and the structure is simple and can be manufactured at low cost.

Further, since the lateral displacement amount in the image pickup means 6 is measured by the incident angle to the objective lens 26 by using the light beam deviated from the optical axis, and the focus situation is grasped, it is extremely precise and accurate. Autofocus is now possible. Furthermore, because signal processing can be performed at extremely high speed,
The convergence speed is extremely high as compared with the image contrast method which is widely used as the same-color autofocus method.

Therefore, by using deep ultraviolet rays, for example, various defects existing in the semiconductor wafer 9 and the dimension, overlay accuracy, etc. of the pattern formed on the semiconductor wafer 9 are inspected and measured in the lithography process of the semiconductor process. Great for use on purpose.

Next, FIG. 5 is a block diagram of an optical system and a control system showing an optical microscope according to a second embodiment of the present invention, and FIG. 6 shows an optical microscope when the focus of an object is adjusted. It is a block diagram of an optical system and a control system. 5 and 6, the same components as those in FIGS. 1 and 3 shown in the first embodiment are designated by the same reference numerals, and the description thereof will be omitted.

As shown in FIG. 5, the Koehler illumination optical system 5
The aperture stop liquid crystal element 31 is provided in place of the aperture stops 21 and 22, and the field stop liquid crystal element 32 is provided in place of the field stop 23 and 24, and is controlled by the control system 8.

The operation of this embodiment will be described with reference to FIGS. Here, it is the same as the case of the first embodiment until the position of the semiconductor wafer 9 to be inspected is moved to directly below the optical system 4.

Next, autofocus is performed. When the autofocus start switch is turned on, the liquid crystal element 31 for the aperture stop is controlled by the control system 8.
A voltage is applied so that a portion for transmitting light rays is formed at a position off the optical axis of the auxiliary condenser lens 20.

Further, a voltage is applied to the field stop liquid crystal element 32 so that a portion for transmitting light rays is formed on the optical axis of the auxiliary condenser lens 20. Further, this transmission portion is sufficiently smaller than the image pickup range of the image pickup means 6 so that the light beam emitted from the imaging lens 29 forms a spot on the image pickup means 6.

As a result, as in the first embodiment, the condenser 25 emits a light beam away from the optical axis toward the beam splitter 28 of the optical system 4, and the optical system 4 forms an image on the image pickup means 6. An image is formed, and a voltage is applied to the actuator 30 under the control of the control system 8 based on this information to perform autofocus.

Next, under the control of the control system 8, various defects of the ordinary semiconductor wafer 9 are inspected at the specified inspection position.

That is, under the control of the control system 8, a voltage is applied to the liquid crystal element 31 for the aperture stop so that a portion for transmitting light rays is formed on the optical axis of the auxiliary condenser lens 20.

A voltage is also applied to the field stop liquid crystal element 32 so that a portion for transmitting light rays is formed on the optical axis of the auxiliary condenser lens 20.

As a result, similarly to the first embodiment, a light beam along the optical axis is emitted from the condenser 25 toward the beam splitter 28 of the optical system 4, and the optical system 4
Thus, an image is formed on the image pickup means 6. Further, the electronic information of the image formed on the image pickup means 6 is processed by the image processing system 7 so that it can be seen on a monitor television or the like, and the pattern or the like of the semiconductor wafer 9 is inspected on the monitor television or the like.

As described above, according to the present embodiment, the aperture diaphragm liquid crystal element 31 and the field diaphragm liquid crystal element 32 are used instead of the aperture diaphragms 21 and 22 and the field diaphragms 23 and 24. There is no need for a mechanism to drive to eliminate mechanical wear. Moreover, since the number of parts can be reduced, the space can be made compact.

Next, FIG. 7 is a block diagram of an optical system and a control system showing an optical microscope according to a third embodiment of the present invention, and FIG. 8 shows an optical microscope when the focus of an object is adjusted. FIG. 9 is a flow chart showing the operation of the optical microscope 1 when autofocusing is performed. In addition, in FIGS. 7 and 8, the same components as those in FIGS. 1 and 3 shown in the first embodiment will be denoted by the same reference numerals, and the description thereof will be omitted.

As shown in FIG. 7, the actuator 30 of the optical system 4 is provided with the distance detecting light source 33 and the detecting section 34, and is controlled by the control system 8. Here, for example, a laser diode is used as the distance detection light source 33,
A photo detector is used as the detection unit 34.

The operation of this embodiment will be described with reference to FIGS. 7, 8 and 9. Semiconductor wafer 9
Until the position to be inspected of is moved directly below the optical system 4,
This is the same as the case of the first embodiment.

Next, autofocus is performed. When the autofocus start switch is turned on (step 101), first, the distance detection light source 33 is moved to the object 2 under the control of the control system 8. A light beam is emitted to a position on the semiconductor wafer 9 to be observed.

Further, the light beam emitted from the distance detecting light source 33 is reflected by the semiconductor wafer 9 and enters the detecting portion (step 102). The light beam incident on the detection unit becomes an electric signal, and the Z stage 11 of the movable stage 3 is moved in the focus direction by the drive motor 16 under the control of the control system 8 (step 103).

As a result, the distance between the semiconductor wafer 9 and the detector 34 is adjusted, and preliminary rough adjustment of the focal position of the semiconductor wafer 9 is performed (step 104).

Next, under the control of the control system 8, the diaphragm driving means 2
The aperture stop 21 is moved down by the optical axis 7 and the aperture of the aperture stop 22 is lifted away from the optical axis. Further, the field stop 23 is lowered below the optical axis, and the field stop 24 is raised so that the opening is on the optical axis (step 105).

As a result, the light beam emitted from the light source is treated as a light beam separated from the optical axis by the beam splitter 2 of the optical system 4.
8 and is obliquely irradiated to the semiconductor wafer 9 through the objective lens 26. Further, the reflected light from the semiconductor wafer 9 forms an image on the image pickup means 6 via the objective lens 26, the beam splitter 28, and the imaging lens 29.

At this time, the amount of lateral displacement on the light receiving surface of the image pickup means 6 due to the defocus still remaining in the preliminary autofocus is detected (step 10).
6).

Next, under the control of the control system 8, the objective lens 26
A voltage is applied to the actuator 30 provided in the (step 107), and the objective lens 26 is moved in the focus direction.

As a result, the focal position of the semiconductor wafer 9 becomes the best position, and the autofocus is completed (step 108).

After that, various defects of the ordinary semiconductor wafer 9 are inspected at the specified inspection position under the control of the control system 8, which is the same as in the case of the first embodiment.

As described above, according to this embodiment, since the distance detection light source 33 and the detection unit 34 separately provided before the off-axis type autofocusing preliminarily perform autofocusing, the actuator 30 is used. When the dynamic range of autofocus due to is narrow, high-precision autofocus can be reliably performed.

The present invention is not limited to any of the above-mentioned embodiments, and can be carried out by appropriately modifying it within the scope of the technical idea of the present invention.

For example, in the above-described embodiment, the image pickup means 6 for autofocus and the image pickup means 6 for microscope observation are used in common, but a beam splitter or the like is provided in the middle of the optical path to provide an optical element for autofocus. A system and image capturing means may be provided. In this case, as the optical system for autofocus, the focal length of the optical system may be determined by the required autofocus accuracy.

The optical system for autofocus may be combined with the optical system for microscope observation.

Furthermore, the image pickup means for autofocus need not be a two-dimensional image pickup means,
It may be a one-dimensional photoelectric conversion element having sensitivity and modulation in the off-axis direction, such as a split detector and a line CCD. In this case, the field stop 24 may determine the area according to the light receiving area of the light receiving element such as the two-divided detector.

This eliminates the need for control or the like for using the image pickup means 6 for microscope observation as the image pickup means 6 for autofocusing, and makes the control system 8 and the like more efficient and quicker processing. Is possible.

Further, in the above-described embodiment, the actuator 30 is moved in the focus direction in the off-axis type auto focus, but the present invention is not limited to this. For example, the Z stage 11 of the movable stage 3 may be moved in the focus direction by the drive motor 16 without moving the actuator 30 in the focus direction.

As a result, the structure of the objective lens 26 is simplified and the device can be made inexpensive.

Further, the movement of the objective lens 26 in the focus direction by the actuator 30 and the driving motor 16
Both the movement of the Z stage 11 in the focus direction by the above may be performed.

As a result, since the objective lens can be moved in the focus direction at the same time as being moved by the Z stage 11 in the focus direction, the autofocus is further speeded up and the accuracy is increased.

Further, in the above embodiment, the aperture stop 2
For setting the opening areas of the apertures 1 and 22 and the field diaphragms 23 and 24, for example, a plate-like one is used by appropriately forming holes, or in the liquid crystal element, a transmission part is appropriately provided by the control system 8. It is also possible to use a diaphragm in which a plurality of plates are used in one diaphragm and the aperture area is made variable. As a result, the number of parts is small and the device is inexpensive.

Further, in the above embodiment, the aperture stop 21
However, it is also possible to change the position of the aperture by moving one aperture stop so that the aperture is on the optical axis or at a position away from the optical axis. . This further simplifies the structure and makes the device less expensive.

[0121]

As described above, according to the present invention,
It can be auto-focused by the light source for observing the object.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an optical system and a control system showing an optical microscope according to an embodiment of the present invention.

FIG. 2 is a perspective view showing a movable stage according to the embodiment of the present invention.

FIG. 3 is a configuration diagram of an optical system and a control system showing an optical microscope in the case of adjusting the focus of an object according to the embodiment of the present invention.

FIG. 4 is a Koehler illumination system and an optical system showing off-axis autofocus according to an embodiment of the present invention.

FIG. 5 is a configuration diagram of an optical system and a control system showing an optical microscope according to a second embodiment of the present invention.

FIG. 6 is a configuration diagram of an optical system and a control system showing an optical microscope in the case of adjusting the focus of an object according to the second embodiment of the present invention.

FIG. 7 is a configuration diagram of an optical system and a control system showing an optical microscope according to a third embodiment of the present invention.

FIG. 8 is a configuration diagram of an optical system and a control system showing an optical microscope in the case of adjusting a focus of an object according to a third embodiment of the present invention.

FIG. 9 is a flowchart showing an operation in the optical microscope 1 when performing autofocus according to the third embodiment of the present invention.

[Explanation of symbols]

1 Optical microscope 2 object 4 Optical system 5 Koehler illumination optical system 6 Image capturing means 17 Light source 21,22 aperture stop 23, 24 Field stop 26 Objective Lens 30 actuators 31 Liquid crystal element for aperture stop 32 Liquid crystal element for field stop 33 Light source for distance detection 34 Detector

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G02B 21/06 G02B 7/11 J 21/24 D B F term (reference) 2H044 DA01 DB00 DC02 2H051 AA10 AA11 BA47 BA72 BB11 CB06 CC03 CC04 CC13 DA02 DD10 FA47 2H052 AC02 AC04 AC12 AC18 AC26 AC34 AD09 AD19 AD21 AD35

Claims (7)

[Claims] 1. A first ray for observation emitted along an optical axis which is a first axis, and a first ray for autofocus emitted along a second axis apart from the first axis. An illuminating unit that emits two light rays; an optical system that irradiates the object with the light beam emitted by the illuminating unit and forms an image of reflected, diffracted, or scattered light of the object at an imaging position; Image pickup means arranged at a position, and irradiating the object with the second light beam through the optical system, and forming an image of reflected light of the object on the image pickup means. An optical microscope, comprising: an autofocus unit that adjusts a focus position of the object in the optical system based on a signal obtained. 2. The optical microscope according to claim 1, wherein the illumination unit includes a light source that emits the light beam, an aperture stop having an opening on the optical axis of the light beam from the light source, and the aperture stop. A Koehler illumination optical system having a field stop having an opening on the optical axis of the emitted light beam is provided, the position of the opening of the aperture stop is changeable, and the opening area of the opening of the field stop is changed. An optical microscope characterized by being able to change. 3. The optical microscope according to claim 2, wherein the aperture stop and the field stop are a liquid crystal element for an aperture stop and a liquid crystal element for a field stop, respectively. 4. Any one of claims 1 to 3
Item 5. The optical microscope according to Item 4, wherein the autofocus unit has an actuator that moves an objective lens provided in the optical system in a focus direction. 5. Any one of claims 1 to 3
Item 5. The optical microscope according to Item 4, further comprising a holding mechanism that holds the object, wherein the autofocus means has a moving means that moves the holding mechanism in a focus direction. 6. Any one of claims 1 to 3
In the optical microscope according to the item 1, the autofocus unit includes the actuator that moves the objective lens provided in the optical system in a focus direction, and the moving unit that moves the holding mechanism in the focus direction. An optical microscope characterized by: 7. Any one of claims 4 to 6
In the optical microscope according to the item 1, provided in the objective lens of the optical system, a light source for distance detection that irradiates the object with light rays, and a detection unit that detects reflected light reflected by the object. The autofocus means further preliminarily adjusts a distance between the object and the detection unit by a signal from the detection unit, and then adjusts a focus position of the object in the optical system. An optical microscope characterized in that