JP2002181727A - Optical inspection apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical inspection apparatus which can surely carry out a filtering process to a scattering light from a measuring object,, and has its efficiency of utilizing light improved. SOLUTION: The scattering light for inspection from a light irradiation device 10 after being diffracted and scattered by the measuring object S is imaged by an imaging lens 20 to an imaging face P2 at an imaging apparatus 40. At this time, the filtering process for emphasizing an image of an abnormal point such as a foreign matter, a defect or the like is carried out, in which a polarization state is modulated in accordance with a periodic pattern structure of the measuring object S by a reflecting type spatial optical modulator 30 arranged near a Fourier face P1, and moreover the polarization state is selected by a polarizing beam splitter 21 and a polarizing plate 22. In inspecting the abnormal point of the measuring object S, the efficiency of utilizing light to the scattering light and a shielding efficiency to light components from the pattern are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical inspection apparatus for inspecting an object to be measured, such as a semiconductor wafer having a predetermined pattern, by an optical measurement for an abnormal portion such as a foreign matter or a defect.

[0002]

2. Description of the Related Art As a method of inspecting a measurement target having a predetermined pattern, such as a semiconductor wafer having a circuit pattern formed thereon, for the presence or absence of an abnormal portion such as a foreign matter or a defect, conventionally, the measurement target is irradiated with inspection light. Optical measurement for measuring scattered light generated by diffraction, scattering, and the like at a measurement target is used.

That is, when Fourier transform is performed on scattered light from a measurement object having a periodic pattern structure such as a circuit pattern, the spectrum of the Fourier light image becomes a regular pattern such as a bright spot or a bright line corresponding to the pattern structure. The spectrum is as follows. On the other hand, when Fourier transform is performed on the scattered light from the abnormal portion of the measurement object, the spectrum in the Fourier light image becomes a spectrum based on a random pattern that spreads at a low light intensity over the entire light image.

On the other hand, instead of forming the scattered light as it is by an imaging lens, the scattered light is once subjected to a Fourier transform by a lens, and filtered at the stage of the Fourier light image to perform spectral component formation by a regular pattern. Is removed by shading. Then, if an image is formed as an imaging light image and imaged by an imaging device such as a CCD, an image such as a circuit pattern is removed as much as possible from the formed imaging light image, and abnormal portions such as foreign matter and defects are detected. Is obtained.

[0005]

In the above-described filtering of a Fourier light image composed of scattered light, a mask pattern corresponding to a pattern to be measured is formed by using a wire that physically shields the scattered light, A method of arranging this mask pattern on a Fourier surface on which a Fourier light image is formed can be used. Here, such a method using light shielding by a wire has a problem that a mask pattern using a wire has a small degree of freedom of a specific mask pattern configuration in addition to a small opening. Further, since it is necessary to control the mask pattern by mechanically moving the wire, the device is likely to be broken down.

As a spatial filter used for filtering a Fourier light image, a liquid crystal panel (LCD: Li
quid Crystal Display) and Spatial Light Modulator (SLM: Spat)
ialLight Modulator) is being considered.

For example, Japanese Patent Application Laid-Open No. 7-92236 discloses that
An optical inspection apparatus having a configuration using a photographic dry plate or a transmission type LCD as a spatial filter is described. However, when a photographic dry plate is used, there is no real-time filter processing, and there is a problem in terms of inspection work efficiency and the like. Further, when a transmissive LCD or transmissive SLM is used, the transmittance is reduced due to a circuit portion such as a pixel electrode.
Sufficient light use efficiency cannot be obtained for scattered light used for inspection.

On the other hand, JP-A-7-103907 discloses that
An optical inspection apparatus having a configuration using a reflection type SLM as a spatial filter is described. In this configuration, the measurement target and the reflection type SLM are used in order to achieve both the guide of the scattered light from the measurement target to the reflection type SLM and the guide of the modulated light reflected by the reflection type SLM to the imaging device. A half mirror is installed between the SLM and the SLM.

However, in such a configuration using the half mirror, the scattered light from the object to be measured passes through the half mirror twice before reaching the imaging device.
At this time, since the amount of light reaching the imaging device is １ ／ of the amount of scattered light generated in the measurement target, the light use efficiency is greatly reduced, and weak scattered light from the measurement target is efficiently measured. Can not do.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and it is possible to reliably perform a filtering process on scattered light from an object to be measured and improve the light use efficiency. It is an object to provide an optical inspection device.

[0011]

In order to achieve the above object, an optical inspection apparatus according to the present invention is an optical inspection apparatus for inspecting an object to be measured having a predetermined pattern for an abnormal portion by optical measurement. (1) a light irradiating means for irradiating a predetermined inspection light to a measurement object;
(2) image forming means for forming an image of scattered light generated by the inspection light being diffracted and scattered by the object to be measured; and (3) arranged near the Fourier plane formed by the image forming means and incident from the image forming means. A reflection-type spatial light modulator that modulates and reflects a Fourier light image composed of scattered light in accordance with a pattern to be measured and emits the modulated light, and (4) a vicinity of an image plane formed by the image forming means. An imaging unit arranged to capture an imaging light image composed of modulated light incident from a spatial light modulator; and (5) a light component in a first polarization state of scattered light from the imaging unit is spatial light. A polarizing beam splitter that is transmitted or reflected to the modulator, and of the modulated light from the spatial light modulator, a polarization beam splitter disposed at a position where a light component in the second polarization state is transmitted or reflected to the imaging unit; (6) Modulation light from the spatial light modulator Chi, light components in the second polarization state, characterized in that it comprises a polarizing means disposed at a position which is passed to the imaging means.

In the above-mentioned optical inspection apparatus, as a spatial filter used for filtering the Fourier light image of the scattered light, the polarization state of the scattered light is modulated by the reflection type spatial light modulator and the polarization state of the scattered light is modulated by the polarization beam splitter. It is used in combination with selection. Here, the reflection type spatial light modulator can realize a high reflectance close to 100%. Therefore, the light use efficiency of the scattered light in the inspection of the abnormal portion is improved as compared with the transmission type spatial light modulator in which the transmittance is limited by the circuit portion.

Further, both the light guide of the scattered light from the imaging means (measurement object) to the spatial light modulator and the light guide of the modulated light modulated and reflected by the spatial light modulator to the image pickup means are compatible. For this purpose, a polarization beam splitter that also selects the polarization state is used instead of a half mirror in which the amount of light decreases separately from the selection of the polarization state for each pass. Thereby, the light use efficiency of the scattered light is further improved.

As for the selection of the polarization state for shielding the scattered light from the pattern to be measured to emphasize an abnormal portion, a sufficient extinction ratio cannot be obtained with a polarization beam splitter, and the light-shielding ability is reduced. May be. On the other hand, in the above configuration, a polarizing means is further provided in addition to the polarizing beam splitter, and the polarization state is selected by both of them. Thereby, the ability to block the light component from the pattern in the scattered light is improved, and the polarization state can be reliably selected.

As described above, in the inspection of an abnormal part by optical measurement using the scattered light from the measurement object, the light use efficiency for the scattered light and the light shielding ability for the light component from the pattern of the measurement object are improved. Therefore, it is possible to realize an optical inspection apparatus that can surely perform the filtering process on the scattered light from the measurement target and improve the light use efficiency.

Here, the polarizing means is preferably arranged at a position between the polarizing beam splitter and the image pickup means.

In the polarization means for compensating for the selection of the polarization state by the polarization beam splitter, when the scattered light (modulated light) passes through the polarization means (transmitted or reflected, etc.), a phase distortion of the light occurs, thereby causing an image plane. In some cases, the resolving power of the imaging light image formed in the image may be reduced. On the other hand, this polarizing means is provided on the imaging means side of the polarizing beam splitter,
By disposing it at a position closer to the imaging means, the influence of phase distortion on the formed optical image is suppressed, and a high resolution can be maintained.

Further, the spatial light modulator is an optical writing type spatial light modulator, and a mask pattern image for modulating a Fourier light image according to a pattern to be measured with respect to the spatial light modulator. It is characterized by comprising pattern writing means for writing. This makes it possible to efficiently perform modulation on the Fourier light image according to the pattern to be measured. As a mask pattern image to be written, it is preferable to obtain a Fourier light image of a pattern to be measured in advance and use a mask pattern image created based on the light image.

Further, the polarization beam splitter transmits the first polarization state light component of the scattered light from the imaging means to the spatial light modulator at a position between the imaging means and the spatial light modulator. And the light component in the second polarization state of the modulated light from the spatial light modulator is arranged to be reflected to the imaging means.

In a polarizing beam splitter, the extinction ratio in reflection is usually lower than that in transmission, so that the polarization state may not be sufficiently selected. On the other hand, by using the reflection by the polarization beam splitter to select the polarization state of the modulated light guided from the spatial light modulator to the imaging means, and by using the polarization means in combination, the extinction ratio can be sufficiently increased. A high light-shielding ability can be obtained.

Alternatively, the polarization beam splitter reflects the first polarization state light component of the scattered light from the imaging means at a position between the spatial light modulator and the imaging means, and reflects the light component to the spatial light modulator. In addition, it is characterized in that, of the modulated light from the spatial light modulator, the light component in the second polarization state is arranged to be transmitted to the imaging means.

When the extinction ratio is lower in transmission than in reflection in the polarization beam splitter, the transmission by the polarization beam splitter is used to select the polarization state for the modulated light, and the polarization means is used. By increasing the extinction ratio in combination, a sufficient light-shielding ability can be obtained similarly.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the optical inspection apparatus according to the present invention will be described below in detail with reference to the drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description. Also, the dimensional ratios in the drawings do not always match those described.

FIG. 1 shows a first embodiment of an optical inspection apparatus according to the present invention.
1 is a configuration diagram schematically showing an embodiment of FIG. In FIG. 1, reference symbol S denotes a measurement target having a predetermined pattern and being a target to be inspected for the presence or absence of an abnormal portion due to a foreign substance, a defect, or the like. Specifically, the measurement target S includes, for example, a semiconductor wafer on which a circuit pattern is formed in a periodic pattern structure. In addition, this measurement target S
Is mounted on a mounting table 11 that can be driven to an arbitrary position on XYZ coordinates.

The present optical inspection apparatus performs
A light irradiation device 10 for irradiating predetermined inspection light, an imaging lens 20 for forming an image of scattered light generated by the inspection light being diffracted and scattered by the measurement target S, and a scattered light incident from the imaging lens 20 The spatial light modulator 30 includes a reflective spatial light modulator 30 that performs necessary modulation, and an imaging device 40 that images modulated light incident from the spatial light modulator 30. Further, on the optical path where scattered light or modulated light is guided from the imaging lens 20 to the spatial light modulator 30 and the imaging device 40,
A polarizing beam splitter 21 and a polarizing plate 22 are provided.

The light irradiation device 10 is, for example, an SHG-YAG
A laser light source such as a laser light source is used, and is installed so that inspection light such as laser light is irradiated on the measurement target S at a small irradiation angle θ. On the other hand, an imaging lens 20 for imaging scattered light from the measurement target S
Is located at a position facing the measurement target S deviating from the optical paths of the inspection light and the reflected light to the measurement target S, and is disposed above the measurement target S in FIG. Further, at the subsequent stage (upper part in FIG. 1) of the imaging lens 20, the imaging lens 2 is provided.
The polarization beam splitter 21 and the spatial light modulator 30 are arranged in series along the 0 optical axis.

The scattered light from the measuring object S is transmitted to the imaging lens 2
The light is incident on the polarization beam splitter 21 via the light beam 0.
In the polarization beam splitter 21, when monochromatic light is incident, a P-polarized light component is transmitted in an emission direction parallel to the incident direction. Also, in the emission direction perpendicular to the incident direction,
The S-polarized light component is reflected. In the configuration shown in FIG. 1, of the scattered light from the measurement target S and the imaging lens 20, the P-polarized light component in the first polarization state is transmitted through the polarization beam splitter 21 to form a spatial light modulator. The light is guided to 30.

The spatial light modulator 30 is a reflective spatial light modulator that reflects the scattered light that has entered, and for example, uses a light-writing type PAL-SLM. The spatial light modulator 30 is arranged near the Fourier plane P1 formed by the imaging of the scattered light by the imaging lens 20, and is combined with the selection of the polarization state by the polarizing beam splitter 21 and the polarizing plate 22, which will be described later. , Functions as a spatial filter that performs a filtering process on a Fourier light image composed of scattered light. That is, the spatial light modulator 30 applies the measurement target S to the Fourier light image of the scattered light formed on the Fourier plane P1.
In accordance with the periodic pattern structure, modulation is performed such that the image of the pattern is removed and the image of an abnormal portion such as a foreign substance or a defect is emphasized.

More specifically, in the configuration shown in FIG. 1, the Fourier light image composed of the P-polarized scattered light transmitted through the polarization beam splitter 21 and scattered by the pattern of the measurement target S is scattered. The polarization state is modulated so that the polarization state of the regular spectral component is preserved and the polarization state of the random spectral component scattered at the abnormal location is not preserved. Then, the obtained modulated light is reflected and emitted to the polarization beam splitter 21.
In addition, about the structure and function of the spatial light modulator 30,
This will be specifically described later.

The modulated light from the spatial light modulator 30 enters the polarization beam splitter 21 again. Then, of the modulated light from the spatial light modulator 30, the S-polarized light component in the second polarization state is reflected by the polarization beam splitter 21 and guided to the imaging device 40.

A polarizing plate 22 is disposed at a position between the polarizing beam splitter 21 and the image pickup device 40. Like the reflection of the modulated light by the polarization beam splitter 21, the polarizing plate 22 transmits the second polarization state light component of the modulated light from the spatial light modulator 30 and the polarization beam splitter 21. is set up. The polarization state of the modulated light from the spatial light modulator 30 is selected by the polarizing beam splitter 21 and the polarizing plate 22.

The image pickup device 40 uses, for example, a CCD camera, and is arranged near an image forming plane P2 formed by forming an image of scattered light (modulated light) by the image forming lens 20.
The imaging device 40 captures an imaging light image composed of modulated light incident from the spatial light modulator 30 via the polarization beam splitter 21 and the polarizing plate 22.

Further, in this embodiment, pattern writing for writing a mask pattern image for modulating a Fourier light image in accordance with the pattern of the measurement target S is performed on the optical writing type spatial light modulator 30 described above. A unit 50 is provided. The pattern writing unit 50 includes a writing light source 5 such as a laser diode for supplying writing light to the spatial light modulator 30.
1, a liquid crystal panel (LCD) 52 for displaying a mask pattern image to be written to the spatial light modulator 30, and a liquid crystal panel 5
2 and an imaging lens 53 for imaging the writing light from the writing light source 51 on which the mask pattern image is formed by transmitting the light through the spatial light modulator 30.

The operations of the spatial light modulator (SLM) 30 and the liquid crystal panel (LCD) 52 are controlled by an SLM controller 61, respectively.
And an inspection control unit 60 via the LCD control unit 62. The SLM control unit 61 applies, for example, a necessary voltage to the spatial light modulator 30. In addition, the LCD control unit 62 instructs the liquid crystal panel 52 to display a mask pattern image, for example.

In the above configuration, when the inspection object S is irradiated with the inspection light from the light irradiation device 10, the inspection light is diffracted and scattered by the measurement object S to generate scattered light. Then, the scattered light scattered upward from the measurement target S at a scattering angle within a predetermined angle range enters the reflection type spatial light modulator 30 via the imaging lens 20 and the polarization beam splitter 21. You. At this time, a Fourier light image (Fourier image) of the scattered light is formed on the Fourier plane P1.

The spatial light modulator 30 includes a pattern writing unit 50
As described above, the polarization state of each spectral component (each optical image portion) of the Fourier light image is modulated based on the mask pattern image written by. The modulation of the polarization state of the Fourier light image by the spatial light modulator 30 and the polarization beam splitter 21 for the modulated light
And the selection of the polarization state by the polarizing plate 22, filtering of the Fourier light image by intensity modulation according to the pattern of the measurement target S is performed.

At this time, in the imaging light image (imaging image) of the scattered light from the measuring object S formed on the imaging plane P2, the image of the pattern of the measuring object S among the scattered light images is removed as much as possible. (Shielded). Thus, an imaging light image in which an image due to an abnormal portion such as a foreign substance or a defect is emphasized is captured by the imaging device 40. Using the imaging light image obtained by the above optical measurement, the presence or absence of an abnormal portion such as a foreign matter or a defect in the measurement target S is inspected.

Next, the effects of the optical inspection apparatus according to the present embodiment will be described.

Generally, in the inspection of an abnormal portion such as a foreign matter or a defect by optical measurement using the scattered light from the measuring object S, the scattered light from the abnormal portion is very weak. For this reason, in the inspection for the presence or absence of such an abnormal portion, it is required to sufficiently increase the light use efficiency with respect to the scattered light and the light shielding ability with respect to the light component from the pattern of the measurement target S other than the abnormal portion.

On the other hand, in the optical inspection apparatus shown in FIG. 1, the Fourier plane P1 of the scattered light from the measuring object S
As a spatial filter used for filtering processing to enhance anomalous portions in the Fourier light image in the above, modulation of the polarization state of the scattered light by the reflection type spatial light modulator 30 and selection of the polarization state by the polarization beam splitter 21 Are used in combination. Here, the reflection type spatial light modulator 30
Can achieve a high reflectance close to 100%. Therefore, the light use efficiency with respect to the scattered light can be improved as compared with a transmission type spatial light modulator or a liquid crystal panel whose transmittance is limited by the circuit portion.

Further, the scattered light from the imaging lens 20 (measurement object S) is guided to the spatial light modulator 30 and the modulated light modulated and reflected by the spatial light modulator 30 is transmitted to the imaging device 40. In order to achieve both light guide and polarization, a polarization beam splitter 21 that also selects the polarization state is used instead of a half mirror in which the amount of light decreases separately from the selection of the polarization state for each passage. Thereby, extra loss of scattered light is prevented, so that the light use efficiency for scattered light is further improved.

Further, regarding the selection of the polarization state for shielding the scattered light from the pattern of the measurement target S to emphasize the abnormal portion, a sufficient extinction ratio cannot be obtained with the polarization beam splitter 21 alone. The ability may decrease. In other words, a single spatial light modulator such as a PAL-SLM has an extinction capability of about 1000. However, if the extinction capability of the polarizing beam splitter 21 is not sufficient, the extinction capability as a whole decreases, In some cases, the ability to block light components from light cannot be sufficiently obtained.

On the other hand, in the configuration described above, a polarizing plate 22 is further provided in addition to the polarizing beam splitter 21, and the polarization state is selected by both of them. Thereby, the selection of the polarization state can be performed more reliably, and the ability to block the light component from the pattern of the scattered light is improved. At this time, in the imaging light image picked up by the image pickup device 40, it is possible to obtain a light image in which an abnormal portion is sufficiently emphasized.

As described above, in the inspection of an abnormal portion by optical measurement using the scattered light from the measurement target S, the light use efficiency with respect to the scattered light and the light shielding ability with respect to the light component from the pattern of the measurement target are improved. Therefore, it is possible to realize an optical inspection apparatus that can surely perform the filtering process on the scattered light from the measurement target and improve the light use efficiency.

In this embodiment, the polarization beam splitter 21 is connected to the imaging lens 20 and the spatial light modulator 30.
And are arranged at the position sandwiched between them. And the imaging lens 20
The light component of P-polarized light (first polarization state) is transmitted to the spatial light modulator 30 among the scattered light from the light, and the S-polarized light (second light) of the modulated light from the spatial light modulator 30 is transmitted. The optical path through which the scattered light and the modulated light are guided is set so that the light component in the (polarized state) is reflected to the imaging device 40.

In a polarizing beam splitter, usually,
Since the extinction ratio is lower in reflection than in transmission, the polarization state may not be sufficiently selected in some cases.
As an example of such an extinction ratio, the transmittance for S-polarized light is Ts, and the reflectance is Rs, and the extinction ratio Ts /
(Ts + Rs) is about 1/400, and the extinction ratio Rp / (Tp + Rp) is about 1/50, where Tp is the transmittance for P-polarized light and Rp is the reflectance. At this time, in the reflection of the S-polarized light component, the P-polarized light component that is originally removed by being transmitted remains.

On the other hand, the polarization state of the modulated light guided from the spatial light modulator 30 to the image pickup device 40 is selected by using the reflection by the polarization beam splitter 21 and using the polarizing plate 22 together. By increasing the extinction ability as described above, it is possible to sufficiently obtain the ability to block light components from the scattered light pattern.

The arrangement of the polarizing plate 22 is shown in FIG.
As shown in the figure, the polarization beam splitter 21 and the imaging device 4
It is preferable that the position be sandwiched by 0. It is also possible to adopt a configuration in which a polarizing plate is installed on each of the front and rear sides of the polarization beam splitter 21. However, the above configuration simplifies the configuration of the optical inspection apparatus except for extra optical elements. Can be.

Further, by setting the position of the polarizing plate 22 at a position where the polarizing beam splitter 21 and the image pickup device 40 are interposed, it is possible to improve the resolving power of the imaging light image of the measurement target S imaged by the image pickup device 40. Can be. In semiconductor wafers and the like in recent years, circuit patterns to be formed have become very fine, and when inspecting such an abnormal part in the measurement target S, it is important to increase the resolving power in the imaging light image. It is.

That is, since the image of the scattered light by the imaging lens 20 can be resolved to the diffraction limit, the resolution is sufficient. On the other hand, if an optical element such as the polarizing plate 22 is installed in the optical path from the imaging lens 20 to the imaging device 40, when scattered light (modulated light) passes through the optical element, a phase distortion of light is generated. This causes a problem in that the resolution is reduced in the imaging light image due to the above.

On the other hand, the polarizing plate 22 is arranged at a position closer to the image pickup device 40 on the image pickup device 40 side than the polarization beam splitter 21, preferably at a position immediately before the image pickup device 40. At this time, the distance that the light is guided to the imaging device 40 after the phase distortion occurs in the polarizing plate 22 is reduced as much as possible, so that the influence of the phase distortion on the imaging light image captured by the imaging device 40 is suppressed, and The resolution can be maintained. In addition, regarding the reduction of the resolving power due to such a polarizing plate, the resolving power was compared using a USAF chart while changing the distance from the polarizing plate to the CCD camera. As the polarizing plate was closer to the CCD camera, a higher resolving power was obtained. Was confirmed.

Next, the configuration of the reflection type spatial light modulator 30 used in the optical inspection apparatus of the embodiment shown in FIG. 1 and the function of modulating the Fourier light image and performing the filtering process will be specifically described. I do. FIG. 2 is a configuration diagram illustrating an example of the spatial light modulator used in the optical inspection device. Note that the left and right directions in FIG. 2 correspond to the lower and upper directions in FIG. 1, respectively.

The spatial light modulator 30 is an optical writing type spatial light modulator, and has a pair of transparent substrates 31 made of glass or the like having anti-reflection coats (AR coats) 31a and 32a formed on the outer side surfaces. , 32. As shown in FIG. 2, the transparent substrates 31 and 32 constitute a scattered light incident end (modulated light emitting end) and the transparent substrate 32 constitutes a writing light incident end, respectively, as shown in FIG.

Between the transparent substrates 31 and 32, a transparent electrode 33, a liquid crystal layer 35, a dielectric multilayer mirror 37, a photoconductor layer 36, and a transparent electrode 34 are sequentially laminated from the transparent substrate 31 side. I have. The transparent electrodes 33 and 34 are preferably made of indium tin oxide (ITO), and a necessary voltage such as an AC voltage of several volts is applied between the transparent electrodes 33 and 34 by the SLM control unit 61. .

A liquid crystal layer 3 made of a light modulating material such as a nematic liquid crystal is provided inside the transparent electrode 33 on the scattered light incident end side.
5 are provided. This liquid crystal layer 35 has an alignment layer 35a.
And the liquid crystal molecules are uniformly aligned so as to be parallel to the surfaces of the transparent electrodes 33 and 34.

On the other hand, a photoconductor layer 36 made of a photoconductive material such as amorphous silicon is provided inside the transparent electrode 34 on the write light incident end side. This photoconductor layer 3
Numeral 6 indicates that when a writing light having a wavelength within a predetermined wavelength range is incident from the pattern writing unit 50, the crystal structure at each part reversibly changes according to the light intensity distribution of the writing light. In addition, it has photoconductivity, which indicates conductivity due to change in electric resistance.

Further, between the liquid crystal layer 35 and the photoconductor layer 36, a dielectric multilayer mirror 37 is provided. As the dielectric multilayer mirror 37, one having a multilayer film formed so as to reflect light in a predetermined wavelength range including the wavelength of scattered light (the wavelength of inspection light supplied from the light irradiation device 10) is used. .

In the configuration of the spatial light modulator 30 described above,
When the writing light is incident from the transparent substrate 32 side, the electrical impedance changes at each part of the photoconductor layer 36 according to the light intensity at each part of the mask pattern image due to the writing light. Thereby, the transparent electrode 3 is formed together with the photoconductor layer 36.
The voltage (partial voltage) applied to the liquid crystal layer 35 interposed between the photoconductor layers 3 and 34 is changed at each portion thereof.
It changes in accordance with the change in the electric resistance at.

At this time, the direction of the liquid crystal molecules in each part of the liquid crystal layer 35 changes according to the applied voltage. That is, a birefringence distribution corresponding to the light intensity distribution of the mask pattern image due to the writing light is induced in the liquid crystal layer 35. In this state, when scattered light enters from the transparent substrate 31 side, the modulation of the polarization state of the scattered light received by the liquid crystal layer 35 depends on the birefringence in each part of the liquid crystal layer 35. For example, when the scattered light is incident such that the polarization direction of the scattered light forms an angle of 45 ° with the orientation direction of the liquid crystal molecules, the polarization state of the scattered light is modulated and changes upon emission.

Therefore, according to this structure, the spectrum of the Fourier light image formed from the scattered light incident on the spatial light modulator 30 is determined by the birefringence distribution of the liquid crystal layer 35 corresponding to the mask pattern image. Partial modulation will be performed. The modulated scattered light is reflected by the dielectric multilayer mirror 37 and becomes modulated light as the transparent substrate 3.
It is emitted again from one side.

An example of a Fourier light image formed by a periodic pattern such as a circuit pattern on the measurement target S and an example of a light-shielding pattern image corresponding to the mask pattern image are shown in FIG.
(A) and (b) schematically show each.

In the scattered light from the measurement object S such as a memory wafer, the scattered light component from a pattern having a periodic pattern structure such as a circuit pattern is converted into a scattered light Fourier light image FP formed on the Fourier plane P1. , As illustrated by the light image portion A in FIG.
The spectrum is a regular pattern of bright spots and bright lines. On the other hand, a scattered light component from an abnormal portion such as a foreign object or a defect to be measured is included in the Fourier light image FP in FIG.
As illustrated by the light image portion B, the spectrum is a random pattern that spreads at a low light intensity over the entire light image.

Therefore, if the Fourier light image FP is subjected to a filtering process so that the light image portion A corresponding to the spectrum of the regular pattern is shielded, the image of the pattern is removed as much as possible, and the abnormal portion is removed. An imaging light image in which the image is enhanced can be obtained.

FIG. 3B shows an example of a light-shielding pattern image capable of performing such a filtering process. The light-shielding pattern image SP is a light-shielded Fourier light image formed by modulating scattered light by the spatial light modulator 30 and selecting a polarization state by the polarizing beam splitter 21 and the polarizing plate 22. This is schematically shown as

In the light-shielding pattern image SP shown in FIG. 3B, a pattern portion C substantially corresponding to the light image portion A in the Fourier light image FP is set as a light-shielding pattern, while a pattern substantially corresponding to the light image portion B is used. Portion D is a transmission pattern. Thereby, the spectral components of the regular pattern due to the scattered light from the pattern of the measurement target S are selectively shielded.

For realizing such a light shielding pattern image SP, for example, a Fourier light image FP based on the pattern of the measurement target S is obtained in advance. Then, it is preferable to use a mask pattern image corresponding to the light shielding pattern image SP created based on the light image.

Specifically, the light-shielding pattern image SP is determined from the Fourier light image FP acquired in advance, and the polarization state of the scattered light incident on the spatial light modulator 30 and the polarization state of the emitted modulated light are determined. In consideration of the polarization state selected by the beam splitter 21 and the polarizing plate 22, a mask pattern image from which the light shielding pattern image SP is obtained is created. The obtained mask pattern image is displayed on the liquid crystal panel 52 by the LCD control unit 62, and the pattern writing unit 50
To write to the spatial light modulator 30 to modulate the scattered light.

FIG. 4 shows a second embodiment of the optical inspection apparatus according to the present invention.
1 is a configuration diagram schematically showing an embodiment of FIG. In the present embodiment, the configuration of each component, except for its arrangement and the like,
This is the same as the first embodiment shown in FIG. FIG.
In FIG. 2, for simplicity, the illustration of the inspection control unit 60, the SLM control unit 61, and the LCD control unit 62 is omitted.

On the other hand, with respect to the arrangement, in the first embodiment shown in FIG.
Is arranged at a position sandwiching the imaging lens 20 and the spatial light modulator 30, whereas in the second embodiment shown in FIG. 4, the spatial light modulator 30 and the imaging device 40 are The polarizing beam splitter 21 is disposed at the position between the polarizing beam splitters. Then, of the scattered light from the imaging lens 20, the S-polarized (first polarization state) light component is reflected to the spatial light modulator 30 and the modulated light from the spatial light modulator 30
The optical paths through which the scattered light and the modulated light are guided are set such that the light component of the P-polarized light (second polarization state) is transmitted to the imaging device 40.

When the polarization beam splitter 21 has a lower extinction ratio in transmission than in reflection, the transmission by the polarization beam splitter 21 is used to select the polarization state for the modulated light. Board 2
By increasing the extinction ratio in combination with 2, it is possible to obtain a sufficient light blocking ability.

The optical inspection apparatus according to the present invention is not limited to the above embodiment, and various modifications and changes in the configuration are possible. For example, the reflection type spatial light modulator used for modulating the scattered light is not limited to the configuration shown in FIG. 2 and various types may be used. For writing the mask pattern image into the spatial light modulator, a suitable method may be used as appropriate according to the configuration of the spatial light modulator.

In the above embodiment, the polarizing plate is disposed between the polarizing beam splitter and the image pickup apparatus. However, depending on conditions such as the resolution required for an imaged light image, spatial light is disposed. It may be installed at various positions on the optical path from the modulator to the imaging device.

The polarization state of the inspection light applied to the object to be measured is not particularly limited in the above-described embodiment. However, depending on the arrangement of the polarization beam splitter, conditions for selecting the polarization state, and the like, It is preferable to set appropriately.

For example, in the optical inspection apparatus having the configuration shown in FIG. 1, it is preferable that the polarization state of the inspection light be S-polarized light. In other words, the polarization state of the inspection light is relatively preserved by scattered light from a circuit pattern or the like, whereas the polarization state of the inspection light is hardly preserved by scattered light from an abnormal portion such as a foreign substance or a defect. Therefore, if the inspection light is S-polarized light, it is possible to emphasize the light component from the abnormal part to some extent at the stage where the scattered light is transmitted through the polarization beam splitter and enters the spatial light modulator.

[0075]

As described in detail above, the optical inspection apparatus according to the present invention has the following effects. That is,
According to the above-described optical inspection apparatus, which uses a reflection-type spatial light modulator to modulate a polarization state and a polarization beam splitter and a polarization plate to select a polarization state in a filtering process on a Fourier light image of scattered light, In this inspection, the light use efficiency of the scattered light in the inspection and the light blocking ability by selecting the polarization state are improved. Therefore, it is possible to reliably perform the filtering process on the scattered light from the measurement object,
An optical inspection device whose light use efficiency is improved is realized.

In the optical inspection apparatus having such a configuration, the mask pattern image to be written into the spatial light modulator may be changed for each inspection of the measurement object, so that the degree of freedom in the configuration of the mask pattern is high. Therefore, it is possible to efficiently cope with inspection of a semiconductor wafer having various circuit patterns. Further, since the light use efficiency and the light blocking ability are improved, it is possible to determine even a fine pattern structure or a small abnormal portion, and the inspection capability of the abnormal portion is enhanced.

[Brief description of the drawings]

FIG. 1 is a configuration diagram schematically showing a first embodiment of an optical inspection device.

FIG. 2 is a configuration diagram showing an example of a spatial light modulator used in the optical inspection device shown in FIG.

FIG. 3 is a diagram schematically showing a filtering process of a Fourier light image by a spatial light modulator.

FIG. 4 is a configuration diagram schematically showing a second embodiment of the optical inspection device.

[Explanation of symbols]

10: light irradiation device, 11: mounting table, 20: imaging lens,
DESCRIPTION OF SYMBOLS 21 ... polarization beam splitter, 22 ... polarizing plate, 30 ... reflection type spatial light modulator, 40 ... imaging device, 50 ... pattern writing part, 51 ... writing light source, 52 ... liquid crystal panel, 53 ...
Imaging lens, 60: inspection control unit, 61: SLM control unit,
62: LCD control unit, 31, 32: transparent substrate, 31a,
32a: anti-reflection coating, 33, 34: transparent electrode, 35
... a liquid crystal layer, 36 ... a photoconductor layer, 37 ... a dielectric multilayer mirror.

Continued on front page F term (reference) 2F065 AA49 BB02 BB18 CC19 FF41 FF49 GG04 HH12 JJ03 JJ09 JJ26 LL04 LL20 LL21 LL33 LL37 NN08 PP12 2G051 AA51 AB01 AB07 BA10 BA11 CA03 CB06 CC07 CC11 CC20 BA01 CA01 2 BB05 BB63 BC23

Claims (5)

[Claims] 1. An optical inspection device for inspecting, by optical measurement, the presence or absence of an abnormal portion in a measurement target having a predetermined pattern, comprising: a light irradiation unit configured to irradiate the measurement target with predetermined inspection light; Imaging means for forming an image of scattered light generated by the inspection light being diffracted and scattered by the measurement object; and a scattered light which is arranged near a Fourier plane formed by the imaging means and is incident from the imaging means. A reflection-type spatial light modulator that modulates and reflects a Fourier light image composed of light in accordance with the pattern of the measurement target and emits the modulated light, and disposed near an imaging plane formed by the imaging unit. Imaging means for imaging an imaging light image composed of the modulated light incident from the spatial light modulator; and a light component in a first polarization state of the scattered light from the imaging means is the sky component. While being transmitted or reflected to the optical modulator, of the modulated light from the spatial light modulator,
A polarization beam splitter disposed at a position where a light component in a second polarization state is transmitted or reflected to the imaging unit; and the light in the second polarization state among the modulated lights from the spatial light modulator. An optical inspection device, comprising: a polarizing unit disposed at a position where a component passes through the imaging unit. 2. The optical inspection apparatus according to claim 1, wherein the polarization unit is disposed at a position between the polarization beam splitter and the imaging unit. 3. The spatial light modulator is an optical writing type spatial light modulator, and modulates the Fourier light image with respect to the spatial light modulator according to the pattern to be measured. 2. The optical inspection apparatus according to claim 1, further comprising a pattern writing unit for writing the mask pattern image. 4. The polarization beam splitter according to claim 1, wherein the light component in the first polarization state of the scattered light from the imaging unit is located at a position between the imaging unit and the spatial light modulator. While being transmitted to the spatial light modulator, of the modulated light from the spatial light modulator, the light component in the second polarization state is arranged to be reflected to the imaging unit. The optical inspection device according to any one of claims 1 to 3, wherein the inspection device is an optical inspection device. 5. The polarization beam splitter according to claim 1, wherein the light component in the first polarization state of the scattered light from the imaging unit is located at a position between the spatial light modulator and the imaging unit. The modulated light from the spatial light modulator is reflected by the light modulator, and the light component in the second polarization state is transmitted through the imaging unit. The optical inspection apparatus according to claim 1, wherein