JP3279815B2 - Displacement / tilt detection method and automatic focusing device using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for detecting the displacement and inclination of a sample and an automatic focusing device using the same.
Displacement used in a sample appearance inspection device using a microscope, etc.
The present invention relates to a tilt detection method and an automatic focusing device using the same.

[0002]

2. Description of the Related Art Conventionally, since the appearance inspection of a thin film pattern or the like formed on a substrate or the like is generally a fine pattern, an enlarged and projected image is detected using a microscope or the like, and the inspection is performed. Had been done. The microscope has a wavelength λ of the illumination light, a numerical aperture (hereinafter, referred to as NA) of the objective lens, and a depth of focus ΔZ.
Is determined, and if the sample is set outside this range, a so-called blurred image will be detected. The depth of focus ΔZ is represented by the following equation (1).

(Equation 1)

Here, a description will be given, with reference to FIG. 12, of a detection error of the conventional displacement / tilt detection method caused by the inability to set the sample surface at the focal point of the objective lens. FIG.
FIG. 2 is an explanatory diagram of an optical system of a displacement / tilt detection method according to the related art. In FIG. 12, 1a is the sample surface, 1b
Is a low reflectance portion of the sample surface, 45 is a photoelectric conversion element for detecting height, 70 is incident light, 70 'is a light intensity distribution of incident light,
80 is the reflected light, 80 'is the light intensity distribution of the reflected light 80, 84
Is the reflected light after the sample surface has moved in the Z direction, 84a is the light intensity distribution of the reflected light 84, I is the light intensity, θ is the incident angle of light, z
Is the moving distance in the Z direction.

In FIG. 12, the light intensity I is 70 '
When the illumination light 70 illuminating the sample surface 1a at an incident angle θ, the reflected light 80 has the same light intensity I as the incident light 70 when the sample surface 1a has a uniform reflectance. Of 80 '. Now, when the sample is lowered in the Z direction, it is assumed that the surface at the position where light is reflected includes the low reflectance portion 1b. In this case, the reflected light 8
The light intensity distribution 84a of No. 4 is low in the low reflectance portion 1b and relatively high in other portions. Therefore, the image detected by the height detecting photoelectric conversion element 45 is asymmetric.

Therefore, despite the image interval before and after the sample surface 1a descends is 2z sin θ, the light intensity distribution 84 of the reflected light 84 over the low reflectance portion 1b
Since a has shifted its center of gravity by Δz, the interval between the detected images is 2z sin θ−Δz.

The aforementioned Δz becomes a position detection error of the sample surface 1a. If there is a pattern having a different reflectance on the sample surface 1a at the focal point, the sample surface 1a is moved to the objective lens 5
4 could not be set. For this reason, if a blurred image is detected, there is a possibility that the appearance inspection accuracy of the sample may be impaired. Therefore, means for setting the sample within the depth of focus has been indispensable.

Therefore, the height of the sample is automatically detected by giving a tilt angle to the sample, illuminating the sample from an oblique direction, and detecting the reflection position of the reflected light on the sample by the photoelectric conversion element. There is a technique for setting a sample within a depth of focus.
Also, if the sample is tilted with respect to the focal plane of the microscope,
Even if the sample is set within the depth of focus, there is a possibility that the sample is out of the depth of focus in a peripheral portion or the like, and a blurred image is also detected in this portion. For this reason, the appearance inspection accuracy of the sample may be impaired, and a means for detecting the inclination between the focal plane and the sample surface is indispensable.

Therefore, the sample is illuminated obliquely, and the tilt angle of the sample is detected by detecting the reflection angle of the light reflected on the sample by a photoelectric conversion element. There is a technique for automatically setting the sample within the depth of focus. For example, Japanese Patent Application Laid-Open No.
There is a technique described in Japanese Patent Publication No. 3 (JP-A) No. 3 (1994). The above technique is excellent in that the displacement detection optical system and the tilt detection optical system are configured independently by using coherent light for illumination, and the displacement and tilt of the sample can be measured independently and simultaneously. There are features.

[0009]

SUMMARY OF THE INVENTION The above-mentioned prior art displacement measuring method is characterized in that, at a position where illumination light is reflected on a sample, a pattern having a different reflectivity is formed on the sample. Has an intensity distribution corresponding to the reflectance at the position reflected on the sample. Therefore, the intensity distribution of the detected image becomes asymmetric depending on the reflectance at the reflected position, and the center position of the light beam and the center position of the waveform are different. The shift amount of this center position becomes a displacement detection error,
There is a problem that it becomes a major factor that deteriorates the focusing accuracy.

Further, when a transparent thin film is formed on a sample, both light reflected on the upper surface of the thin film and light transmitted and reflected on the underlying layer reach the photoelectric conversion element. Since the images are shifted and overlapped, there is a problem that the symmetry of the waveform is further impaired.

In addition, since coherent light is used as illumination light, if a transparent thin film is formed on a sample, multiple interference will occur strongly in the thin film, causing a loss of waveform symmetry. . Furthermore, since the displacement detection optical system and the tilt detection optical system are configured independently, there has been a problem that the optical system becomes complicated and the cost of the apparatus increases.

SUMMARY OF THE INVENTION An object of the present invention is to solve all of the above-mentioned problems of the prior art, and even if illumination light is reflected on patterns formed on a sample and having different reflectivities, the detection is performed. Improves displacement detection accuracy by preventing image asymmetry and reducing image shift due to reflection at the interface between the transparent thin film surface and the substrate and image interference due to multiple interference in the transparent thin film. Another object of the present invention is to provide a low-cost displacement / tilt detection method and an automatic focusing apparatus using the same by sharing the displacement detection optical system and the tilt detection optical system.

[0013]

In order to solve the above-mentioned problems, a displacement / tilt detecting method according to the present invention comprises: an illuminating means for illuminating a sample at a tilt angle with respect to a normal to the sample;
In the method for detecting displacement / tilt of a sample, comprising: a projecting unit that projects reflected light from the sample, and a detecting unit that detects the projected sample image, the projecting unit includes an optical axis of the reflected light. A lens is provided on the top, a front focal position of the lens is a reflection position on the sample, a mirror is provided at a rear focus position of the lens, the reflected light is inverted by a mirror, turned back, and projected on the sample again. The detection means is configured to detect an oblique projection image on the sample by a photoelectric conversion element disposed at a position optically conjugate with the reflection position.

Further, another configuration of the displacement / tilt detecting method according to the present invention includes an illuminating means for illuminating the sample at an angle of inclination with respect to a normal line of the sample, and a projecting means for projecting reflected light from the sample. In the method for detecting displacement / inclination of a sample, the projection means includes a concave mirror on the optical axis of the reflected light, and a position twice as long as the focal length of the concave mirror is a reflection position on the sample. It is characterized by having such a configuration.

In any one of the displacement / tilt detection methods described in the preceding paragraph, the illuminating means arranges a slit pattern provided with a rectangular opening at a position optically conjugate with the reflection position, and The slit image projected onto the sample is configured to be parallel to the sample surface.
In the displacement detecting / tilting method described in the preceding paragraph, the illumination means is configured to project the slit pattern onto the sample by a telecentric optical system.

Further, still another configuration of the displacement / tilt detection method according to the present invention includes an illuminating means for illuminating the sample at an angle of inclination with respect to a normal line of the sample, and a projection for projecting reflected light from the sample. Means for detecting the displacement / inclination of the sample, comprising: a lens on the optical axis of the reflected light from the sample; and The front focal position is a reflection position on the sample, a semi-transparent mirror is provided at the rear focal position of the lens, a part of the reflected light is turned over by a semi-transparent mirror, turned back, and projected again on the sample, Another part of the reflected light is transmitted through the translucent mirror, projected on a photoelectric conversion element by the lens, and the detecting means is configured to detect a reflection angle of the illumination light having the tilt angle. Characterized by

In the displacement / tilt detecting method according to any one of the preceding items, the illuminating means is configured to use illuminating light of a P-polarized component and set the incident angle to the Brewster angle of the sample. It is characterized by. In the displacement / tilt detecting method according to any one of the preceding items, the illuminating means includes a slit pattern having a cross-shaped opening disposed at a position optically conjugate with a reflection position on the sample. Is
Consisting of one and the other detection unit, the one detection unit,
The image of the slit pattern projected onto the sample is reflected and guided by the translucent mirror so that the image of the slit pattern is parallel to the surface of the sample. It is characterized in that it is configured to transmit and guide light in orthogonal directions.

In the displacement / tilt detection method described in the preceding paragraph,
The slit pattern having a cross-shaped opening of the illuminating means is a polarizing plate that transmits one side of P-polarized light and another side perpendicular to the one side of S-polarized light, and the one detecting unit and It is characterized in that light guided to another detection detection unit is selected by the polarizing plate. In any of the sample displacement / tilt detection methods described in the preceding paragraph, the illumination means uses incoherent light having a wide wavelength width as the illumination light.

An automatic focusing apparatus characterized by using the displacement / tilt detection method according to the present invention comprises: an illuminating means for illuminating the sample at a tilt angle with respect to a normal line of the sample; An autofocusing device for projecting light and detecting means for detecting the projected sample image, detecting displacement / inclination of the sample, and adjusting focus; It is characterized in that any one of the above-described displacement / inclination detection methods is used for the detection of.

[0020]

The function of each of the above technical means is as follows.
According to the configuration of the present invention, the sample is obliquely illuminated, the light reflected from the mirror sample is inverted and turned back by the lens and the mirror, and the light is reflected again on the sample. Is conjugate between the forward path and the return path and is inverted, so that the image is necessarily symmetric and the center of gravity of the image can be kept constant regardless of the reflectance of the sample. In addition, since the photoelectric conversion element is disposed at a position optically conjugate with the position on the sample that has been reflected twice, even if patterns with different reflectivities are formed on the sample, the image remains symmetric. Is not impaired. Furthermore, even if a transparent thin film is formed on the sample, the symmetry of the image is not impaired because the influence of multiple interference generated in the thin film occurs symmetrically.

The same function as described above is produced by providing a concave mirror instead of the lens and the mirror so that the reflection position on the sample is twice as long as the focal length of the concave mirror. Also, in the present invention, even if a thin film is formed on the sample, the light reflected on the surface of the thin film is set by setting the incident angle to the Brewster angle of the sample using the illumination light of the P-polarized component. However, since all of the light is reflected by the underlayer of the thin film, amplitude division on the surface of the thin film is eliminated, and a symmetric image can be detected.

Further, in the present invention, the use of incoherent light having a wide wavelength width as illumination light reduces coherence, thereby reducing the effect of an image becoming asymmetric due to multiple interference in the transparent thin film. Further, in the present invention, by using a translucent mirror as the turning mirror of the light beam, the light is divided into reflection and transmission, and the reflected light is reflected again on the sample, guided to an optical path for detecting displacement, and transmitted. The reflected light is enlarged and projected by a lens on the image of the translucent mirror onto a photoelectric conversion element for detecting tilt, and guided to a tilt detection optical path for detecting a reflection angle of the oblique illumination light. Accordingly, the displacement and tilt detection optical system shares the return optical system with the illumination optical system, and the size and cost of the device can be reduced.

In an automatic focusing optical apparatus for inspecting the surface shape and the like of a sample using a microscope or the like, since the focusing accuracy is improved, a stable inspection is performed without lowering the inspection performance due to defocusing. be able to. In addition, even if the defect size to be inspected becomes finer and the depth of focus of the microscope becomes shallow, the height and inclination can be detected by the same optical system, so that the entire field of view of the microscope can be set within the depth of focus. The false alarm rate of the inspection result due to blur can be reduced, and a stable inspection can be performed in a short time.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to FIGS. [Embodiment 1] In the present embodiment, a visual inspection apparatus equipped with an automatic focusing device using the displacement / tilt detection method of the present invention will be described. FIG. 1 is an explanatory diagram of a visual inspection device provided with an automatic focusing device using a displacement and tilt detection method according to an embodiment of the present invention. In the figure, the same reference numerals as those in FIG. 12 denote the same parts, and a detailed description thereof will be omitted.

In FIG. 1, 1 is a sample to be inspected, 2 is a chuck for sucking the sample 1, 3 is a θ stage that rotates and moves in a horizontal plane, and 4 is a Z that moves vertically.
Stage 5 is an XY stage that moves two-dimensionally on a horizontal plane.
Reference numeral 10 denotes an auto-focusing optical system (indicated by a two-dot chain line in the figure), 50 denotes an appearance inspection optical system (indicated by a two-dot chain line in the figure), 55 denotes a photoelectric conversion element for sample imaging, Reference numeral 60 denotes a movement distance calculation unit for the Z stage 4, and reference numeral 100 denotes a Z stage driver for moving the Z stage up and down. The dashed line indicates the optical path system, and the dotted line indicates the electric system.

Further, the auto-focusing optical system 10 includes a light source 11 for emitting a wide wavelength band light 70, a collimator lens 12 for collimating the wide wavelength band light, a slit 13 for transmitting the parallel light, A half mirror 14 for receiving the light transmitted through the slit 13, an imaging lens 20 for forming an image of the transmitted light of the half mirror 14, and a reflected light 8 from the sample 1.
The light receiving lens 30 receives the light transmitted through the lens 30 and a mirror 35 that receives light transmitted through the lens 30.

The appearance inspection optical system 50 includes a light source 51 for emitting illumination light and a condenser lens 5 for condensing the illumination light.
2, a half mirror 53 receiving the collected illumination light.
And an objective lens 54 for receiving the reflected light of the half mirror 53, and a sample imaging photoelectric conversion element 55 for receiving the transmitted light of the half mirror 53. The appearance inspection optical system 50 is configured above the sample 1, and
This is a so-called epi-illumination type optical system.

The sample 1 to be inspected is adsorbed and fixed on the chuck 2 and is placed on the XY stage 5, the Z stage 4, and the θ stage 3. .
The Z stage is moved up and down by the Z stage driver 100, and the moving distance z is measured by the height detecting photoelectric element 45. The moving distance z is calculated by the moving distance calculating unit 6.
It is calculated with 0. Note that X, Y, and Z each represent a three-dimensional movement direction.

Next, the operation of the appearance inspection apparatus according to this embodiment will be described. First, the illumination light emitted from the light source 51 is condensed by a condenser lens 52, and a part of the light is reflected by a half mirror 53 to reach an objective lens 54, and illuminates the sample 1 by incident light. Reflection from the sample 1,
The diffracted and scattered light is again taken into the objective lens 54, passes through the half mirror 54, and forms the image of the sample 1 on the sample imaging photoelectric conversion element 55.

When a two-dimensional sensor such as a TV camera is used as the photoelectric conversion element 55, each stage performs a so-called step-and-repeat movement.
When all the stages are stopped, the image of the sample 1 is captured by the photoelectric conversion element 55. When the stage 5 is moved, the stage 5 may be displaced in the Z direction, and may be out of the depth of focus determined by the objective lens 54 of the visual inspection optical system 50.

In this case, since the image of the sample 1 taken in by the photoelectric conversion element 55 becomes a blurred image, the contrast is lowered, and it becomes impossible to detect a fine defect. For this reason, the appearance inspection accuracy is reduced, and erroneous determination of determining a normal portion as a defect is increased.

Therefore, before detecting the image of the sample 1 by the photoelectric conversion element 55, the height of the sample 1 with respect to the in-focus position of the objective lens 54 is determined by the automatic focusing optical system 10 for detecting the height of the sample 1. The shift amount in the vertical direction is obtained. When capturing an image of the sample 1 by moving the Z stage 4 up and down by this amount of displacement, the sample 1 is always positioned within the depth of focus of the objective lens 54. .

When the photoelectric conversion element 55 is a one-dimensional linear sensor or the like, the XY stage 5 is moved at a constant speed to capture an image.
The height of the sample 1 is detected by using 0, and the Z stage 4 is moved up and down so that the sample 1 does not deviate from the depth of focus of the objective lens 54. The auto-focusing optical system 10 emits a wide wavelength light 70 from a light source 11, becomes parallel light by a collimator lens 12, and forms a slit 13 with a so-called cage.
Light up the lights.

The light transmitted through the slit 13 forms an image of the slit 13 on the sample 1 by the imaging lens 20. As for the reflected light 80 from above the sample 1, light having the same reflection angle is arranged at the rear focal position of the lens 30 by the light receiving lens 30 disposed at a position where the reflection position on the sample 1 is matched with the front focal position. Light is condensed on one point of Mirror-35. Mira-3
The light that has reached 5 is specularly reflected, and is again reflected on the sample 1 by the lens 35.

At this time, the distance of the light receiving lens 30 from the reflection position on the sample 1 and the distance from the lens 30 to the mirror 35
By matching the distance to the focal length of the light receiving lens 30, the forward and backward light fluxes are inverted symmetrically with respect to the optical axis,
The slit image reflected on the sample 1 is conjugate. The light beam reflected twice on the sample 1 is taken into the imaging lens 20 again, reflected by the half mirror 14, and the magnifying lens 40 forms a slit image on the photoelectric conversion element 45 for height detection. .

Accordingly, the four locations of the slit 13 and the forward and backward slit images reflecting on the sample 1 and the photoelectric conversion element 45 for detecting the height have an optically conjugate positional relationship with each other. The position of the light reaching the element 45 is
Since the height information of the sample 1 is included, the position in the Z direction can be detected from the slit position reaching the photoelectric conversion element 45.

From the distance between the detected position in the Z direction and the in-focus position of the objective lens 54, that is, the so-called defocus amount, the moving distance of the Z stage is calculated by a Z-stage moving distance calculating section 6.
0, and sends a command to the Z stage driver 100 to
The stage 4 is driven. As a result, the surface of the sample 1 is always located within the depth of focus of the objective lens 54, and the focused image of the sample 1 is focused on the photoelectric conversion element 5 for sample imaging.
5 can be detected.

Next, the Z-direction position detection in the displacement / inclination detection method will be described in detail with reference to FIG. FIG.
FIG. 3 is an explanatory diagram of position detection in the Z direction in the displacement / inclination detection method according to the embodiment of FIG. 1. FIG. 2 is an enlarged view of the surface portion of the sample 1 in FIG. In FIG. 2, 1a is the sample surface, 70 is the irradiation light passing through the slit 13, 80 is the reflected light from the sample surface 1a, 85 is the reflected light from the sample surface 1a after moving, θ is the incident angle of the irradiation light 70, z
Is the moving distance in the Z direction.

The irradiation light 70 passing through the slit 13 projected on the sample surface 1a illuminates the sample surface 1a at an incident angle θ. At this time, the interval between the reflected light 80 reflected on the sample surface 1a and the reflected light 85 from the sample surface 1a after the movement of the sample surface 1a by z in the Z direction is 2z.
sin θ. The distance between the light reaching the height detecting photoelectric conversion element 45 of the automatic focusing optical system 10 before and after the sample surface 1a descends in the Z direction is 2zsi.
The distance is obtained by multiplying nθ by the magnification magnified by the magnifying lens 40.

Therefore, the movement of the sample surface 1a in the Z direction and the movement of the image on the photoelectric conversion element 45 have a linear relationship. Here, if the focal position of the objective lens 54 shown in FIG. 1 is calibrated, the defocus amount of the sample surface 1a can be obtained. Note that, for simplicity of description, only the outward rays are described, but the above relationship is the same even if the rays reciprocate.

Next, the feature of inverting light again in the projection means of the displacement / tilt detection method according to the present invention will be described in detail. FIG. 3 is a partially enlarged view of the automatic focusing optical system of the displacement / tilt detection method according to the embodiment of FIG. FIG. 3 is an explanatory view of the folding optical system of the automatic focusing optical system in the displacement / tilt detection method according to the embodiment of FIG. In the drawings, the same reference numerals as those in FIGS. 1 and 12 denote the same parts, and a detailed description thereof will be omitted. Only new codes will be described. 83 is the outward reflected light, 8
3a is the light intensity I distribution of the outward reflection light, 85 is the return reflection light, 85a is the light intensity I distribution of the return reflection light, and f is the focal length of the light receiving lens 30.

As shown in FIG. 3, the irradiation light 70 has a light intensity I
Illuminates the sample surface 1a with the distribution 70a shown,
The low-reflectance portion 1b is present at the reflection position, and the outgoing-path reflected light 83 of the reflected light has a light intensity I having a distribution of 83a in the drawing according to the reflectance of the sample surface 1a. When the light flux of the outward reflected light 83 is reversed and turned back by the action of the mirror 35 and the light receiving lens 30, the phases of the asymmetric distributions are reversed, and they compensate each other. For this reason, the distribution 85a of the light intensity I of the return path reflected light 85 detected by the height detecting photoelectric conversion element 45 becomes symmetric, and the position detection error Δz caused by the change in the reflectance of the sample surface 1a is corrected. You.

This is because the focal length f of the light receiving lens 30 is
By arranging the sample surface 1a at the front focal position and the mirror 35 at the rear focal position, the slit image once projected on the sample surface 1a is reflected and axially symmetric. This is based on the fact that the image is inverted and is projected again on the sample surface 1a. In this way,
The center of the light coincides with the center of the image, the image is targeted, and a displacement detection error can be eliminated.

Embodiment 2 Next, another embodiment of the present invention will be described with reference to FIG. FIG. 4 is an explanatory view of a folding optical system of an automatic focusing optical system in a displacement / tilt detecting method according to another embodiment of the present invention. The return optical system of the displacement / tilt detection method shown in FIG.
5 is folded using a concave mirror instead of 5. In the drawings, the same reference numerals as those in FIGS. 1 and 3 denote the same parts, and a description thereof will not be repeated. 16, the first telecentric lens, 17, the second telecentric lens, 33 is a concave mirror, f ₄ is the focal length of the concave mirror.

In FIG. 4, when the illumination light 70 having a light intensity I having a distribution of 70a shown in the drawing is illuminated on the sample surface 1a in a so-called telecentric manner using the first and second telecentric lenses 16 and 17, Sample surface 1a
The concave mirror 33 is arranged at a position 2f ₄ from the reflection position of the above.
At this time, the reflected light of the concave mirror 33 reverses the light flux, reflects again on the sample, and is enlarged and projected on the photoelectric conversion element 45 by the magnifying lens 40. Also in this case, the slit image projected on the sample surface 1a is reflected, the image is inverted symmetrically with respect to the axis, and projected again on the sample surface 1a. A symmetrical slit image can be obtained regardless of the ratio.

Embodiment 3 Next, still another embodiment of the present invention will be described with reference to FIG. FIG. 5 is an explanatory view of a folding optical system of an automatic focusing optical system in a displacement / tilt detecting method according to still another embodiment of the present invention. In the drawings, the same reference numerals as those in FIGS. 1, 3, and 4 denote the same parts, and a description thereof will be omitted. f ₁ is the focal length of the first telecentric lens 16, f ₂ is the focal length of the second telecentric lens 17, f ₃ is the focal length of the light receiving lens 30.

As shown in FIG. 5, the light emitted from the light source 11 passes through the slit 13 by the collector lens 12 so as to form a color.
Light up. Here, the distance from the slit 13 to the lens 16 is defined as the focal length f _{1 of the} lens 16. The distance from the lens 16 to the lens 17 is defined as the sum f ₁ + f ₂ of the respective focal lengths. The distance from the lens 17 to the sample surface 1a to the focal length f ₂ of the lens 17.

In this telecentric optical system, so-called parallel perspective is used.
The principal ray projected on a is parallel to the optical axis. Further, also in the folded optical path, the light receiving lens 30 from the sample surface 1a.
Distance focal length f ₃ of the light receiving lens 30 to respectively set the distance from the light receiving lens 30 to mirror -35 to f _3. In this optical system, when the image of the slit 13 is projected onto the sample surface 1a again, the principal ray becomes parallel to the optical axis. Therefore, all the images of the slit 13 projected on the sample surface 1a are projected by the telecentric optical system.

For this reason, the slit image enlarged and projected on the height detecting photoelectric conversion element 45 by the magnifying lens 40 is:
2 mz even if the sample surface 1a is lowered by z in the Z direction
Only the distance represented by sin θ moves. Therefore, the movement of the sample surface 1a and the movement of the image detected by the height detecting photoelectric conversion element 45 have a linear relationship. Therefore, no magnification error occurs due to the defocus on the sample surface 1a. In the above 2 mz sin θ, m indicates the magnification at which the image of the slit 13 is enlarged by the height detecting magnifying lens 40.

Next, still another embodiment of the present invention will be described with reference to FIGS. FIG. 6 is a perspective view of a folded optical system of an automatic focusing optical system in a displacement / tilt detection method according to still another embodiment of the present invention, and FIG. 7 is a diagram illustrating a thin film of the displacement / tilt detection method according to the embodiment of FIG. FIG. 8 is an explanatory view of a detection error, FIG. 8 is an explanatory view of a method of correcting a detection error by the thin film of FIG. 7, and FIG. 9 is a graph showing the relationship between light reflectance, transmittance, and incident angle in the detection error correction method of FIG. FIG. In the drawings, the same reference numerals as those in FIGS. 1, 3, and 4 denote the same parts, and a description thereof will be omitted.

In FIG. 6, the light transmitted through the slit 13 reaches the sample 1 by the telecentric lens lenses 16 and 17, and forms a slit image 13a. At this time, the slit image 13a is projected so as to be parallel to the plane of the sample 1. Thereby, the projected image of the slit 13 formed on the height detecting photoelectric conversion element 45 can detect the average position of the position reflected on the sample 1, Even if there is a local step, it is possible to reduce the variation in the detection value.

In the thin film manufacturing process in which the present invention is frequently used, a step frequently occurs because a protective film or the like is formed on the pattern formed on the sample 1. A detection error when a protective film is formed on the sample 1 will be described.
Now, for the sake of simplicity, FIG. 7 shows a configuration in which the reflected light of the illumination light 70 is reflected and then directly incident on the height detecting photoelectric conversion element 45 without being incident on the photoelectric conversion element 45. This is because the return optical system is irrelevant to the correction of the detection error by the protective film.

In FIG. 7, 7 is a protective film, and d is the thickness of the protective film. As shown in FIG. 7, the oblique illumination light 70 transmits the light reflected on the surface of the protective film 7 and the protective film 7, and reflects the light reflected on the surface of the sample 1 and the light reflected multiple times in the protective film 7. Amplitude division occurs. Since these light rays are shifted by Δz ₁ by passing through the protective film 7, the slit image detected on the height detecting photoelectric conversion element 45 becomes asymmetric.

The shift amount Δz1 of the light beam is as follows: when the incident angle is θ, the refraction angle is θ ₁ , the refractive index of air is n0, the refractive index of the protective film 7 is n ₁ , and the film thickness of the protective film 7 is d. It is expressed by the following equations (2) and (3).

(Equation 2)

(Equation 3)

The image asymmetry caused by the amplitude division by the protective film 7 can be prevented by making the incident angle θ of the illumination light 70 incident at a so-called Brewster angle. This will be described with reference to FIGS. In FIG. 8, if incident light 70 is illuminated at an incident angle θ on a substance having a refractive index of n ₁ to n ₂ , if the light reflectance is R, and the transmittance is T, the incident angle θ, the reflectance R, the transmission The relationship with the rate T is shown in FIG.
The diagram shown in FIG. In FIG. 9, Rs is S
The reflectance of polarized light, Rp is the reflectance of P-polarized light, and Rs + p is S
The reflectance is a mixture of polarized light and p-polarized light, and n ₁ = 1.
0, n ₂ = 1.5.

At this time, the P-polarized light has a Brewster angle at which the light is entirely transmitted at the incident angle θp. Note that the Brewster angle θp is expressed by equation (4).

(Equation 4) By setting the Brewster angle θp as the incident angle,
Even if the protective film 7 or the like is formed, amplitude division does not occur, and a symmetric image is detected.

[Embodiment 5] Next, detection of the inclination α of the sample surface 1a according to the present invention will be described. FIG. 10 is an explanatory diagram of a tilt detection optical system of the displacement / tilt detection method according to one embodiment of the present invention. In the figure, the same reference numerals as those in FIG. 1 denote the same parts, and a description thereof will be omitted. α is a tilt angle, 37 is a half mirror, 90 is a tilt detection optical system,
95 skew detection magnifying projection lens, f ₅ is the focal length of the lens 95, 97 is a photoelectric conversion element for tilt detection. In FIG. 10, the light beam reflected from the sample surface 1a is:
The light is condensed on a half mirror 37 disposed at the rear focal position of the light receiving lens 30 according to the angle component incident on the light receiving lens 30 having the sample surface 1a as the front focal position.

Therefore, the surface 1a of the sample has an angle α
When tilted, the angle of incidence on the light receiving lens 30 changes,
The position of the light focused on the half mirror 37 changes.
If the light condensed on the half mirror 37 is enlarged and projected onto the tilt detecting photoelectric conversion element 97 by the tilt detecting magnifying projection lens 95, the tilt angle α of the sample surface 1a can be detected. .

When the sample surface 1a is inclined by α degrees, the light that converges on the half mirror 37 converges on a position separated by f ₃ tan α when the focal length of the light receiving lens 30 is f ₃ . Of the light condensed on the half mirror 37, the transmitted light is enlarged and projected on the photoelectric conversion element 97 by the lens 95. At this time, when the sample surface 1a is inclined by α degrees,
The position of the light focused on the tilt detection photoelectric conversion element 97 is
As shown in distribution 99 of light intensity I, m ₁ f ₃ tan α
Just move.

The tilt detection magnifying lens 95
Has a role of setting the half mirror 37 and the photoelectric conversion element 97 in a conjugate relationship, and the positional relationship is arranged at a position that satisfies the following equation (5).

(Equation 5) In the above formula, a is ha - half mirror -37 and skew detection expanded length between the projection lens 95, b is skew detection magnifying projection lens 95 and the inclination detecting photoelectric length between transducers 97, f ₅
Is the focal length of the lens 95.

The magnification at which the image on the half mirror 37 is enlarged and projected onto the photoelectric conversion element 97 by the lens 95 is m ₁ . The magnification m ₁ is represented by the following equation (6).

(Equation 6)

[Embodiment 6] Next, detection of displacement / inclination of a sample surface according to the present invention will be described. FIG. 11 is an explanatory view of a displacement / tilt detection optical system of a displacement / tilt detection method according to another embodiment of the present invention. In the figure, the same reference numerals as those in FIGS. FIG. 11 illustrates the optical system for detecting the height and inclination of the sample surface 1a.

In FIG. 11, the light emitted from the light source 11 passes through a slit 13 by a collimator lens 12.
The image of the slit 13 is projected on the sample surface 1a by the lenses 16 and 17 of the telecentric optical system. Now, the above optical system is hereinafter referred to as an illumination optical system 18.

The light projected on the sample surface 1a is converged on a half mirror 37 in accordance with the angle component reflected on the sample surface 1a by the light receiving lens 30. This optical system is hereinafter referred to as a folding optical system 36. The light transmitted through the half mirror 37 of the folding optical system 36 is enlarged on the half mirror 37 to the photoelectric conversion element 97 by the tilt detection enlargement projection lens 95 arranged in the tilt detection optical system 90. Projected. For this reason, the amount of inclination of the sample surface 1a can be detected by obtaining the position of the image formed on the inclination detecting photoelectric conversion element 97.

Also, the half mirror of the folding optical system 36 is used.
The light reflected by 37 is projected on the sample surface 1a with the image of the slit 13 inverted in optical axis symmetry, and then enters the illumination optical system 18 again. These lights are transmitted to the half mirror 14
, And is guided to the height detecting optical system 47, and the image of the slit 13 projected on the sample surface 1 a by the lens 40 is enlarged and projected on the photoelectric conversion element 45. For this reason, the height of the sample surface 1a can be detected by obtaining the position of the slit image formed on the photoelectric conversion element 45.

[0066]

As described above in detail, according to the structure of the present invention, patterns formed on a sample and having different reflectivities are obtained.
Even if illumination light is reflected on the surface, the asymmetry of the detected image is prevented, and the image is displaced due to reflection at the interface between the transparent thin film surface and the base, and the image is distorted due to multiple interference in the transparent thin film. By reducing the asymmetry, the displacement detection accuracy is improved, and by sharing the displacement detection optical system and the tilt detection optical system, a low-cost displacement / tilt detection method and an automatic focusing device using the same are provided. can do.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an automatic focusing device using a displacement / tilt detection method according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of position detection in a Z direction in a displacement / tilt detection method according to the embodiment of FIG. 1;

FIG. 3 is an explanatory diagram of a folding optical system of an automatic focusing optical system in the displacement / tilt detection method according to the embodiment of FIG. 1;

FIG. 4 is an explanatory view of a folding optical system of an automatic focusing optical system in a displacement detection method according to another embodiment of the present invention.

FIG. 5 is an explanatory view of a folding optical system of an automatic focusing optical system in a displacement / tilt detection method according to still another embodiment of the present invention.

FIG. 6 is a perspective view of a folding optical system of an automatic focusing optical system in a displacement / tilt detection method according to still another embodiment of the present invention.

FIG. 7 is an explanatory diagram of a detection error due to a thin film in the displacement / tilt detection method according to the embodiment of FIG. 6;

FIG. 8 is an explanatory diagram of a method for correcting a detection error by the thin film of FIG. 7;

FIG. 9 is a diagram showing the relationship among the reflectance, the transmittance, and the incident angle of light in the detection error correction method of FIG.

FIG. 10 is an explanatory diagram of a tilt detection optical system in a displacement / tilt detection method according to one embodiment of the present invention.

FIG. 11 is an explanatory diagram of a displacement / tilt detection optical system in a displacement / tilt detection method according to an embodiment of the present invention.

FIG. 12 is an explanatory diagram of an optical system of a displacement / tilt detection method according to the related art.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Sample 1a, 1b ... Sample surface 2 ... Chuck 3 ... Rotation stage 4 ... Z stage 5 ... XY stage 10 ... Autofocus optical system 11 ... Light source 12 ... Collimator lens 13 ... Slit 14 ... C -Fumila 16 ... First telecentric lens 17 ... Second telecentric lens 18 ... Illumination optical system 20 ... Imaging lens 30 ... Lens 33 ... Concave mirror 35 ... Mirror 36 ... Folding optical system 37 ... Half mirror 40 ... Height detecting magnifying lens 45 ... Height detecting photoelectric conversion element 47 ... Height detecting optical system 50 ... Appearance inspection optical system 51 ... Illumination light source 52 ... Illumination light condenser lens 52,53 ... Illumination light -Fumilla 54 -Objective lens 55 -Photoelectric conversion element for sample imaging 60 -Z stage movement distance calculation unit 80 -Reflected light 83 -Outward reflected light 84 -Stage descent position Reflected light 85 ... return reflected light 90 ... inclination detecting optical system 95 ... for detecting inclination magnifying projection lens 97 ... inclination detecting photoelectric conversion element 100 ... Z stearate in - Jidoraiba -

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-138403 (JP, A) JP-A-58-113706 (JP, A) JP-A-2-6709 (JP, A) JP-A 62-113 293103 (JP, A) JP-A-63-275912 (JP, A) JP-A-59-188931 (JP, A) JP-A-5-182896 (JP, A) (58) Fields investigated (Int. ^7, DB name) G01B 11/00 G01B 11/26 G01C 3/06

Claims (10)

(57) [Claims] An illumination unit configured to illuminate the sample at an inclination angle with respect to a normal line of the sample; a projection unit configured to project light reflected from the sample; and a detection unit configured to detect the projected sample image. In the method for detecting displacement / tilt of a sample provided, the projecting means includes a lens provided on an optical axis of the reflected light, a front focus position of the lens being a reflection position on the sample, and a rear focus of the lens. A mirror is provided at a position, the reflected light is inverted by the mirror, turned back, and projected again on the sample, and the detecting means is provided by a photoelectric conversion element disposed at a position optically conjugate with the reflection position. A displacement / tilt detection method characterized by detecting an upper oblique projection image. 2. Illumination means for illuminating the sample at an inclination angle with respect to the normal line of the sample, projection means for projecting reflected light from the sample, and detection means for detecting the projected sample image In the method for detecting displacement / tilt of the sample provided, the projecting unit is provided with a concave mirror on an optical axis of the reflected light,
A displacement / tilt detection method, wherein a position twice as long as the focal length of the concave mirror is a reflection position on the sample. 3. The displacement / inclination detection method according to claim 1, wherein the illuminating means sets a slit pattern having a rectangular opening at a position optically conjugate with the reflection position. A displacement / tilt detection method, wherein the slit image to be arranged and projected on the sample is configured to be parallel to the sample surface. 4. The displacement detection / tilt method according to claim 3, wherein said illumination means is configured to project said slit pattern onto said sample by a telecentric optical system. Method. 5. An illumination unit for illuminating the sample at an angle of inclination with respect to a normal line of the sample, a projection unit for projecting light reflected from the sample, and a detection unit for detecting the projected sample image. In the method for detecting displacement / inclination of a sample provided, the projection unit includes a lens on an optical axis of reflected light from the sample, a front focal position of the lens being a reflection position on the sample, A translucent mirror is provided at the rear focal position, a part of the reflected light is inverted by the translucent mirror and turned back, projected again on the sample, and another part of the reflected light is transmitted through the translucent mirror. A displacement / tilt detection method, wherein the projection is performed on the photoelectric conversion element by the lens, and the detection means detects a reflection angle of the illumination light having the tilt angle. 6. The displacement / inclination detection method according to claim 4, wherein said illumination means uses illumination light of a P-polarized component, and sets an incident angle to a Brewster angle of said sample. A displacement / inclination detection method, characterized in that: 7. The displacement / inclination detection method according to claim 5, wherein the illumination means optically conjugates a slit pattern provided with a cross-shaped opening with a reflection position on the sample. And the detecting means comprises one and another detecting unit, wherein the one detecting unit has an image of the slit pattern projected onto the sample parallel to the surface of the sample. Reflected by the translucent mirror so as to be guided, and the other detection unit is configured to transmit and guide light in a direction orthogonal to the reflected light of the translucent mirror. Displacement / tilt detection method. 8. The displacement / inclination detection method according to claim 7, wherein the slit pattern of the illumination means having a cross-shaped opening has one side of P-polarized light and the other side perpendicular to the one side of S. Displacement / polarization, characterized in that the polarization plate transmits light, and light guided to the one detection unit or the other detection unit is selected by the polarization plate.
Tilt detection method. 9. A method according to claim 3, wherein said illumination means uses incoherent light having a wide wavelength width as said illumination light. For detecting the displacement and inclination of 10. Illumination means for illuminating the sample at an inclination angle with respect to the normal line of the sample, projection means for projecting reflected light from the sample, and detection means for detecting the projected sample image 10. An automatic focusing device comprising: a displacement / inclination detection unit for detecting a displacement / inclination of a sample to adjust a focus; and detecting the displacement / inclination of the sample in accordance with any one of claims 1 to 9. An automatic focusing device characterized by using: