JPH0663982B2 - Foreign object detection method and apparatus - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method and an apparatus for detecting minute foreign matter on a sample, and particularly to a foreign matter suitable for detecting foreign matter on a product (patterned) wafer. The present invention relates to a detection method and its device.

[Conventional technology]

Taking a patterned wafer foreign matter inspection as an example, a conventional technique is represented by, for example, JP-A-54-57126. That is, the first
As shown in FIG. 1A, the wafer 1 is obliquely irradiated with the S-polarized beam emitted from the lasers 3a and 3b. As shown in FIG. 3B, foreign matters 401, 40 are formed on the wafer pattern 11.
When there is 2, polarization is eliminated, and S-polarized light and P-polarized light components are mixed in the scattered light from the foreign matter. On the other hand, in the pattern 11, the S-polarized component is stored as it is in the scattered light from the straight edge orthogonal to the optical axis of the laser beam. Therefore, if the polarizing plate 101 is arranged above the objective lens 4 so as to block the S-polarized component (shown by the solid line), the pattern information can be removed. To be detected. According to this method, 3 on the patterned wafer
It is possible to sufficiently detect the foreign substance 401 having a size of about 5 μm.
However, of the scattered light from the foreign matter, the P-polarized component is a small part of the total scattered light, so a minute foreign matter of about 1 to 2 μm
In the case of 402, the decrease in the amount of light detected by the polarizing plate is remarkable,
As shown in FIG. 7C, it may be difficult to distinguish the scattered light 103 from the pattern corner. That is, in the conventional method, the polarizing plate is used to remove the reflected light from the pattern, but as a result, most of the foreign substance scattered light is also removed. In addition, depending on the material and shape of the foreign matter, it may be difficult to eliminate polarized light.
In that case, the scattered light of the foreign matter contains almost no P-polarized component, and it becomes more difficult to detect.

On the other hand, in JP-A-59-65428, as shown in FIG. 12 (a), the exit pupil in the objective lens 4, that is, the spatial frequency domain (Fourier transform plane) 4a is formed by the field lens 5.
An image is formed at the position of 300, and a Fourier transform image 12 of the pattern 11 and the foreign matters 401 and 402 shown in FIG. Reference numeral 13 is a Fourier transform image of a straight edge portion of the pattern 11 which is orthogonal to the optical axis of the laser beam, and generally exists locally in the spatial frequency domain as shown in the figure. 14
Are Fourier-transformed images of the foreign matters 401 and 402, and generally exist over the entire spatial frequency domain as shown in the figure.
The spatial filter 104 having the light-shielding portion 104a shown in FIG. 3D is arranged at the position 300, and the Fourier transform image 13 of the straight edge is arranged.
When the light is blocked, the image formed on the photoelectric conversion element 8 by the field lens 7 is composed of foreign matters 401a and 402a and pattern corner portions as shown by 105 in FIG. Therefore,
In Japanese Patent Laid-Open No. 59-6536, the detected image 105 and the memory 9
Image of the adjacent chip stored in the same place at the same place 10
6 (the image obtained through the laser oblique illumination and the spatial filter 104) is compared in the comparison circuit 10, and the difference image 107 is used to detect the foreign matters 401a and 402a. However, in the foreign matter detection method using the spatial filter as described above,
Conventionally, the following problems have been pointed out. That is, as shown in FIG. 13A, the foreign matter 403 on the pattern 11 is
If the shape has some directionality, the Fourier transform image 110 does not spread so much and the Fourier transform image 13
In that case, the Fourier transform image of the foreign matter is shielded by the light shielding unit 104a of the spatial filter 104, and the foreign matter is not detected as indicated by 111. On the other hand, conversely, as shown in FIG. 13B, depending on the shape of the circuit pattern 120, the Fourier transform image 130 of the straight edge portion does not converge linearly but spreads, and the Fourier transform image 140 of the foreign substance 404. May overlap with. In that case, the spatial filter 121 having a large light shielding portion 121a for shielding the Fourier transform image 130.
If is used, the Fourier transform image 140 of the foreign matter is also shielded from light, and the foreign matter cannot be detected as in 122.

[Problems to be solved by the invention]

As described above, in the above-mentioned conventional technique, that is, in the method using the polarizing plate, the amount of scattered light from the foreign matter is reduced, and the foreign matter with less depolarization cannot be detected. However, there is a problem that the foreign matter detection capability is deteriorated due to the shape of the Fourier transform image.

An object of the present invention is to solve the above-mentioned problems of the prior art by irradiating a sample on which a circuit pattern is formed with highly directional linearly polarized illumination light obliquely with respect to the surface of the sample. The scattered light of the polarization component generated from the circular edge is selectively shielded so that the scattered light having various polarization components from the foreign matter is increased as much as possible to detect the minute foreign matter with high efficiency and with high sensitivity. Another object of the present invention is to provide a foreign matter detection method and an apparatus therefor.

[Means for solving problems]

The present invention, in order to achieve the above-mentioned object, irradiates a highly polarized linearly polarized illumination light on a sample on which a circuit pattern is formed from a diagonal direction at a desired angle with respect to the vertical direction of the sample surface, The scattered light from the irradiation area is detected by a detection optical system having an optical axis in a direction substantially perpendicular to the sample surface, and only the polarized component of the scattered light generated from the linear edge portion of the detected circuit pattern is detected. , Selectively shields light by a polarization spatial filter installed in the spatial frequency region of the detection optical system, receives scattered light from the foreign matter on the sample that has passed through the polarization spatial filter by photoelectric conversion means, and removes the foreign matter. It is a foreign matter detection method characterized by detecting the signal shown. Further, the present invention is characterized in that, in the foreign matter detecting method, the linearly polarized illumination light is light having a narrow wavelength width. Further, the present invention is an illumination optical system for irradiating a linearly polarized illumination light having high directivity on a sample on which a circuit pattern is formed, from an oblique direction inclined at a desired angle with respect to a vertical direction of the sample surface, and the sample surface. A detection optical system having an optical axis in a direction substantially perpendicular to the detection optical system for detecting scattered light from the irradiation region on the sample irradiated by the illumination optical system, and a circuit pattern detected by the detection optical system. A polarized light spatial filter installed in the spatial frequency region to selectively shield only the polarized light component of the scattered light generated from the linear edge portion, and scattered light from the foreign matter on the sample that has passed through the polarized spatial filter. A foreign matter detection device comprising: a photoelectric conversion unit that receives a light and detects a signal indicating the foreign matter. Further, the present invention is characterized in that, in the foreign matter detection device, the polarization spatial filter is configured by a partial polarization element. Further, the present invention is characterized in that, in the foreign matter detecting device, the polarization spatial filter is composed of an optical element that changes a polarization state of light only in a part thereof. Further, the present invention is characterized in that, in the foreign matter detecting device, the optical element is composed of a liquid crystal element. Further, the present invention is characterized in that, in the foreign matter detecting device, the optical element is constituted by a wave plate. Further, the present invention is characterized in that, in the foreign matter detection device, the linearly polarized illumination light with high directivity that is emitted by the illumination optical system light has a narrow wavelength width.

[Action]

With the above configuration, only the polarization component of the scattered light generated from the linear edge portion of the circuit pattern by the polarization spatial filter is affected without affecting the scattered light from the foreign matter existing on the sample on which the circuit pattern is formed. By selectively blocking the light, scattered light from the foreign matter can be detected with the highest possible efficiency, and minute foreign matter existing on the sample on which the circuit pattern is formed can be detected with high sensitivity. That is, linearly polarized illumination light having high directivity is irradiated onto a sample on which a circuit pattern is formed from an oblique direction inclined at a desired angle with respect to the vertical direction of the sample surface, and the light is irradiated in a direction substantially perpendicular to the sample surface. When detecting scattered light from the irradiation region with a detection optical system having an axis, a Fourier transform image from a linear edge portion of a circuit pattern in a spatial frequency region (Fourier transform surface) of the detection optical system and a Fourier from a foreign substance A polarization space composed of a partial polarization element installed in the spatial frequency domain (Fourier transform plane) or an optical element that changes only the polarization state of light by utilizing the difference in shape and polarization component from the converted image. Identification of the Fourier transform image of only the region corresponding to the Fourier transform image from the linear edge portion of the placement circuit pattern in the spatial frequency domain by the filter It can be detected efficiently foreign matter without significantly impairing by passing the scattered light from light polarization components composed of various directions of polarization components from foreign matter.

〔Example〕

 An embodiment of the present invention will be described with reference to FIGS.

First, the basic principle of the present invention will be described. Once again, based on FIGS. 2 (a)-(e), the pattern 11 and the foreign matter 401, on the wafer 1 illuminated by the S-polarized laser beam,
The behavior of scattered light from the 402 will be described. Fig. 2 (a)
In, the spatial frequency region in the objective lens 4, that is, the Fourier transform surface (corresponding to the exit pupil) 4 a is imaged at the position 300 by the field lens 5. Therefore, at the position of 300, a Fourier transform image 13 of a straight edge portion orthogonal to the optical axis of the laser beam in the pattern 11 shown in FIG. 11B and a Fourier transform image 14 of the foreign matter are obtained (FIG. 11C). Now, let us focus not only on the difference in the shapes of the Fourier transform images of the two, but also on the polarization state thereof. As shown in FIG.
The Fourier transform image 13 of the straight edge portion is composed of almost the same S-polarized component 18 as the incident laser beam. On the other hand, as shown in FIG. 6E, the Fourier transform image 14 of the foreign matter 401, 402 is composed of polarized components 19 in various directions.

Here, if the polarizing plate 20 shown in FIG. 3 (a) is arranged at the position of 300 and the S-polarized component is shielded, all the light passing through the polarizing plate 20 is P as shown in FIG. 3 (b). Becomes the polarization component 30,
The Fourier transform image 13 of the linear edge portion of the pattern 11 including the S polarization component is completely removed, and only the P polarization component of the Fourier transform image 14 of the foreign matters 401 and 402 can be obtained.
However, comparing 19 in Fig. 2 with 30 in Fig. 3 (b),
Obviously, the light amount of the foreign matters 401 and 402 is greatly reduced.

On the other hand, when the spatial filter 21 shown in FIG. 3 (c) is similarly arranged at the position 300 of FIG. 2, the Fourier transform image 13 of the straight edge portion is removed as shown in FIG. 3 (d). However, at the same time, a part of the Fourier transform image 14 of the foreign matters 401 and 402 is also removed. Further, when the light-shielding portion 22a of the spatial filter 22 is large as shown in FIG. 6E, the Fourier transform image 14 of the foreign matters 401 and 402 is also greatly damaged as shown in FIG.

The present invention focuses on the difference in the shapes of the Fourier transform image of the direct edge portion of the pattern and the Fourier transform image of the foreign matter in the spatial frequency domain, and the difference in the polarization states of the two, and detects the foreign matter by the polarizing plate and the spatial filter. By combining the methods, the advantages of both methods are tried to be utilized. That is, as shown in FIG. 4 (a), a portion corresponding to the Fourier transform image 13 of the linear edge portion of the pattern 11 is arranged so as to block the S-polarized component or the polarization state of the incident light is changed. A spatial filter 23 (23a is a light-shielding portion) formed of an optical material 23c, which is formed of an optical material 23c that allows the polarization state of the incident light to pass therethrough while maintaining the polarization state of the incident light, is arranged at the position 300 in FIG. To do. As a result, FIG. 4 (b)
As shown in, the S-polarized component is shielded only in the region corresponding to the Fourier transform image 13 of the straight edge portion, and all the polarized components can pass through the other regions. Therefore, the Fourier transform image 13 of the linear edge portion including the S-polarized component and the foreign matter 401,
Of the Fourier transform image 14 of 402, only the S-polarized component within the region of the polarizing plate 23c is shielded, and the amount of foreign matter detection light is significantly increased as compared with the conventional method shown in FIG.
Further, even when the area corresponding to the Fourier transform image 13 of the straight edge portion is large, the foreign substance detection light amount is increased as compared with the conventional method (FIG. 3 (f)) as shown in FIG. 4 (d).
In the following, the spatial filter will be referred to as a polarized spatial filter in order to distinguish it from the conventional spatial filter.

Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. In addition, in order to have versatility in the following, S
The terms "polarized light" and "p-polarized light" will not be used, but the terms "x-direction polarized light" and "y-direction polarized light" will be unified with reference to the x, y coordinates in the figure.

FIG. 1 (a) is a diagram showing a foreign matter detecting optical system in the first embodiment of the present invention. This optical system consists of an xy stage 2,
The lasers 3a and 3b, the objective lens 4, the relay lens 5, the polarization spatial filter 6, the relay lens 7, and the two-dimensional solid-state imaging device 8 are included. In the figure, the sample is a product wafer on which a circuit pattern is formed. The wafer 1 is imaged on the xy stage 2 on the two-dimensional solid-state imaging device 8 by the objective lens 4, the relay lenses 5 and 7. On the other hand, the Fourier transform surface (spatial frequency domain) 4 a of the objective lens 4 is imaged at the position of 300 by the relay lens 5. The wafer 1 is obliquely illuminated from two directions by the y-direction polarized (S-polarized) beams emitted from the lasers 3a and 3b facing each other. FIG. 2B shows an example of the circuit pattern 11 and the foreign matters 601 and 602. As a result of the laser oblique illumination, the Fourier transform image 12 of the circuit pattern 11 and the foreign matters 601, 602 is obtained at the position 300, that is, the image forming position of the Fourier transform surface 4a of the objective lens 4, as shown in FIG. . Reference numeral 13 is a Fourier transform image of a linear edge portion of the circuit pattern 11 which is orthogonal to the optical axes of the laser beams in the two directions, and is substantially composed of the same y-direction polarization component as the incident laser beam. Reference numeral 14 is a Fourier transform image of the foreign matter 601, 602, which is composed of polarized components in various directions. Therefore, the polarization spatial filter 6 shown in FIG.
To place. This polarization spatial filter 6 has the following configuration. That is, the portion corresponding to the Fourier transform image 13 of the linear edge portion of the pattern 11 is formed by the polarizing plate 6c arranged so as to shield the y-direction polarized light component, and the other portion is kept the polarization state of the incident light. Ordinary glass plate 6b to pass
Is formed by. Incidentally, 6a is a light shielding portion formed of a chrome film for shielding stray light and the like. Shading space filter 6
By arranging at the position of 300, as shown in FIG. 4 (b), the Fourier transform image 13 of the linear edge portion composed of the y-direction polarization portion and the Fourier transform image 14 of the foreign matters 601 and 602 are polarized plate 6c. Only the y-direction polarized light component existing in the example region is blocked. As a result, as shown in the detection image 15 of FIG. 1, the foreign substance scattered light is detected in the two-dimensional solid-state imaging device 8 with almost no loss. On the other hand, since the scattered light from the pattern corner has the same scattering and polarization characteristics as the foreign matter scattered light, it passes through the polarization spatial filter 6 and is detected as indicated by 351. In this regard, the detected image 15
And the stored image 16 (image obtained through the laser oblique illumination and the spatial filter 6) at the same location of the adjacent chip stored in the preliminary memory 9 are compared in the comparison circuit 10, and the difference is obtained. By obtaining the image 17, the pattern corner information 351 can be removed and only the foreign substance information 601a and 602a can be extracted.

As described above, according to the present embodiment, only the y-direction component existing in the region of the polarizing plate 6c is blocked by the polarization spatial filter 6 in the foreign substance scattered light, as described in the section “Operation”. Yes, it is a small part of the total scattered light from foreign matter. Therefore, compared to the conventional method of using a polarizing plate to shield all the y-direction components and the method of using a spatial filter to shield all the foreign matter scattered light existing in the light blocking portion, the detected light amount of the foreign matter is smaller. Since the foreign matter detection capacity is increased and the foreign matter detection ability is not influenced by the pattern or the shape of the foreign matter, it is possible to detect a finer foreign matter.

A second embodiment of the present invention will be described with reference to FIGS. In the following, as in the first embodiment, the directions of light polarization are referred to as x-direction polarization and y-direction polarization with reference to the xy coordinate in the drawing.

FIG. 5 (a) is a diagram showing a foreign matter detecting optical system in the second embodiment of the present invention. In the foreign matter detection optical system according to the first embodiment shown in FIG. 1A, two lasers 3a and 3b facing each other are used and oblique illumination is performed from two directions. Two sets of four lasers 3a, 3b, 3c, 3d facing each other are used to obliquely illuminate from four directions,
The configuration of the polarization spatial filter is changed accordingly.
The configuration and functions of the other parts are all the same as in the first embodiment. First, the linearly polarized beams emitted from the lasers 3a, 3b, 3c and 3d (y-directional polarized beams are emitted from the lasers 3a and 3b, and x-directional polarized beams are emitted from the lasers 3c and 3d) on the wafer 1. Is obliquely illuminated from four directions. FIG. 2B shows an example of the circuit pattern 11 and the foreign matters 601 and 602.
As a result of the laser oblique illumination, the Fourier transform image 150 of the circuit pattern 11 and the foreign matters 601, 602 is obtained at the position 300, that is, the image forming position of the Fourier transform surface 4a of the objective lens 4, as shown in FIG. . 37a is a Fourier transform image of a linear edge portion of the circuit pattern 11 which is orthogonal to the optical axis of the laser beams emitted from the lasers 3a and 3b, and is substantially composed of the same y-direction polarization component as the incident laser beam. Reference numeral 37b is a Fourier transform image of a straight edge portion of the circuit pattern 11 which is orthogonal to the optical axis of the laser beams emitted from the lasers 3c and 3d, and is composed of the x-direction polarized component like the broken incident laser beam. 38 is a Fourier transform image of the foreign matter 601 and 602, and is composed of polarized components in various directions. Therefore, the polarization spatial filter 36 shown in FIG. The polarization spatial filter 36 has the following configuration. That is, the portion corresponding to the Fourier transform image 37a of the linear edge portion shown in FIG. 7C is formed by the polarizing plate 36c arranged so as to shield the y-direction polarized light component, while it is orthogonal to the linear edge portion. A portion of the straight edge portion corresponding to the Fourier transform image 37b is a polarizing plate 36d arranged to block the x-direction polarized component.
Is formed by. Incidentally, the polarization components in the x and y directions are shielded at the portions where the two polarizing plates 36c and 36d intersect. On the other hand, the other part is formed of a normal glass plate 36b that allows the incident light to pass therethrough while preserving its polarization state. 36a is a light-shielding portion formed of a chrome film to shield stray light and the like. By disposing the polarization spatial filter 36 at the position of 300, similar to the first embodiment, the Fourier transform images 37a and 37b of the linear edge portions orthogonal to each other and the foreign matter 601 and 602 are formed.
In the Fourier transform image 38, the y-direction polarization component is shielded in the region of the polarizing plate 36c, and only the x-direction polarization component is shielded in the region of the polarizing plate 36d. As a result, the detected image 40 of FIG.
As shown in (2), in the two-dimensional solid-state imaging device 8, the foreign substance scattered light is detected with almost no loss. Regarding the information 351 of the pattern corner portion, as in the first embodiment, the detected image 40 and the stored image 41 of the adjacent chip are compared in the comparison circuit 10, and this is removed by obtaining the difference image 42, Only the foreign substance information 601a and 602a can be extracted.

As described above, according to this embodiment, not only the same effects as those of the first embodiment are obtained, but also the following effects are newly obtained. That is, some foreign matter has a certain direction in its shape. When the incident direction of the illumination light is limited, the directivity of the scattered light from the foreign matter becomes high, and in the worst case, the foreign matter scattered light is the objective. It may not enter the lens. In the present embodiment, since the wafer is obliquely illuminated from four directions by four lasers, even in the above case, it is possible to reduce the directivity of the foreign substance scattered light and prevent the foreign substance detection light amount from decreasing. . Further, even for a foreign matter that is attached to the vicinity of the pattern step portion and is difficult to detect due to the shadow of the step in the two-direction illumination, a sufficient illumination light amount can be obtained by the four-direction illumination, and the foreign matter can be prevented from being overlooked.

A third embodiment of the present invention will be described with reference to FIGS. In the above-mentioned two embodiments, the polarization spatial filter formed of the polarizing plate and the glass plate is used to remove the information of the circuit pattern, but in the present embodiment, it is formed by using the liquid crystal element. It is characterized in that the above-mentioned object is achieved by using a polarization spatial filter. Before specifically describing the present embodiment, the function of the liquid crystal element will be described in detail with reference to FIGS. 7 to 9.

As shown in FIG. 7, the liquid crystal element has a structure in which liquid crystal 72 is filled between two parallel glass plates 70, 70 'printed with transparent electrodes 73, 73' and seals 71, 71 '. The AC voltage generated from the AC power supply 74 can be applied to the ‘′’ by the switch 75. As shown in FIG.
When the linearly polarized light is incident on the liquid crystal element 80, the liquid crystal element 80 functions as a polarizer and rotates the polarization direction of the incident light by 90 ° when the AC power supply 74 is turned off by the switch 75. On the other hand, in the ON state, as shown in FIG. 9, linearly polarized light passes through as it is. Therefore, by disposing a polarizing plate behind the liquid crystal element 80, it is possible to block or transmit arbitrary linearly polarized light by turning on / off the switch 75. By providing a plurality of the liquid crystal elements and combining them with a polarizing plate, it is possible to configure a flexible polarization spatial filter capable of blocking or transmitting arbitrary linearly polarized light in an arbitrary region.

Hereinafter, with reference to FIG. 6, the present embodiment in which the polarization spatial filter using this liquid crystal element is adopted will be specifically described.
In the following, as in the first and second embodiments, the directions of light polarization are referred to as x-direction polarization and y-direction polarization with reference to the xy coordinates in the drawing.

FIG. 6A is a diagram showing the foreign matter detection optical system in this embodiment. This optical system consists of an xy stage 2, lasers 3a, 3b,
3c, 3d, objective lens 4, relay lens 45, polarization beam splitter 46, polarization spatial filters 47, 4 using liquid crystal elements
7 ', polarizing plates 48, 48', polarizing beam splitter 50, relay lens 52, and two-dimensional solid-state image sensor 8. The wafer 1 on the xy stage 2 has an objective lens 4 and a relay lens.
An image is formed on the two-dimensional solid-state image sensor 8 by 45 and 52. On the other hand, the Fourier transform plane (spatial frequency domain) 4a of the objective lens 4 is imaged at the positions 301 and 302 by the relay lens 45. The polarization beam splitter 46 has a function of reflecting the y-direction polarization component and passing the x-direction polarization component as it is. On the other hand, the polarization beam splitter 50 has a function of conversely reflecting the x-direction polarization component and passing the y-direction polarization component as it is. Therefore, as shown in FIG. 6 (a), by combining the two, it is possible to combine again the lights that have been separated into the x-direction polarization component and the y-direction polarization component.
First, two sets of lasers 3a, 3b, 3c and 3d facing each other emit linearly polarized beams (y-direction polarized beams are emitted from the lasers 3a and 3b, and x-direction polarized beams are emitted from the lasers 3c and 3d). ), And obliquely illuminate the wafer 1 from four directions. FIG. 1A shows an example of the circuit pattern 11 and the foreign matters 601 and 602. By the laser oblique illumination, the Fourier transform image 55 of the circuit pattern 11 and the foreign matters 601, 602 is obtained at the position of 301, that is, the image forming position of the Fourier transform surface 4a of the objective lens 4, as shown in FIG. Reference numeral 56 is a Fourier transform image of a linear edge portion of the circuit pattern 11 which is orthogonal to the optical axes of the laser beams emitted from the lasers 3a and 3b, and is substantially composed of the y-direction polarization component 53 like the incident laser beam. 57
Is a Fourier transform image of the foreign matter 601 and 602, which is originally composed of polarization components in various directions, but is obtained by separating only the y-direction polarization component 54 of the polarization components by the polarization beam splitter 46. At the position of 301, a polarization spatial filter 47 using the liquid crystal element shown in FIG. 7 is arranged. 10th
The figure shows an enlarged plane of the polarization spatial filter 47. As shown in the figure, a plurality of transparent electrodes 82, 83 are formed on the parallel glass plate 550, and the application of the AC voltage 74 to them is selectively performed by the switch 75 corresponding to each transparent electrode 82, 83. It has become a thing. In the case of this embodiment, the switch 75 is turned off only on the transparent electrode 83 'corresponding to the Fourier transform image 56 of the straight edge portion, so that the y-direction polarization component 53 is formed as shown in FIG. 6 (c). The Fourier transform image 56 of the straight line edge portion and the Fourier transform image 57 of the foreign matters 601 and 602 are rotated by 90 ° in the polarization direction of the y-direction polarization component existing in the region of the transparent electrode 83 ′, respectively, and the result is shown in FIG.
It is possible to change the polarization component in the x direction as shown by 58 and 59 as shown in FIG. Therefore, if the polarizing plate 48 is arranged behind the polarization spatial filter 47 so as to shield this x-direction polarization component, as shown by 60 and 61 in FIG. Fourier transform image 56 of the part and foreign matter 60
The portion of the 1,602 Fourier transform image 57 that has changed to the x-direction polarization component is removed.

On the other hand, similarly, at another image forming position 302 on the Fourier transform surface 4a of the objective lens 4, a Fourier transform image 92 of the circuit pattern 11 and the foreign matters 601, 602 is obtained as shown in FIG. Reference numeral 93 is a Fourier transform image of a linear edge portion of the circuit pattern 11 which is orthogonal to the optical axis of the laser beams emitted from the lasers 3c and 3d, and is substantially the same as the incident laser beam in the x-direction polarization component 90. Reference numeral 94 is a Fourier transform image of the foreign matters 601, 602, which originally consists of polarization components in various directions as described above, but only the x-direction polarization component 91 is separated by the polarization beam splitter and obtained. This 302
At the position of, the polarization spatial filter 4 arranged at the position of 301
A polarization spatial filter 47 'obtained by rotating 7 by 90 ° is arranged. In addition, a polarizing plate is provided behind the polarization spatial filter 47 '.
The 48 'is also rotated by 90 ° and arranged. The functions of both are exactly the same as those arranged at the position of 301.
First, the polarization spatial filter 47 'causes the x-direction polarization component 90
Fourier transform image 93 of the straight edge portion consisting of
The polarization direction of the x-direction polarization component existing in the region of the transparent electrode 83 'of the Fourier transform image 94 of 602 is rotated by 90 °, and the y-polarized light is polarized as shown by 95 and 96 in FIG. 6 (g). Change to ingredients. Next, using the polarizing plate 48 ', 97, 9
As shown by 8, the Fourier transform image 93 of the linear edge portion changed to the y-direction polarization component and the portion of the Fourier transform image 94 of the foreign matters 601 and 602 changed to the y-direction polarization component are removed. By combining the y-direction polarization component 61 (FIG. 6 (e)) and the x-direction polarization component 98 (FIG. 6 (h)) of the foreign substance scattered light obtained as described above by the polarization beam splitter 50, As indicated by 99 and 100 in FIG. 6 (i), only the scattered light of the foreign matter can be detected without much loss of the polarization component. Incidentally, the removal of the residual information in the pattern corner portion is exactly the same as in the above-mentioned two embodiments, and therefore its explanation is omitted. In this embodiment, the polarized beam splitter 46 separates the scattered light from the pattern 11 and the foreign substances 601 and 602 into two polarization components. A major feature is that foreign matter scattered light is prevented from being greatly impaired by removing the information and then combining the two again. Of course, according to this embodiment, the same effects as those of the above-described two embodiments are obtained, and at the same time, the polarization spatial filter using the liquid crystal element shown in FIG.
Even if the size of the Fourier transform images 56 and 93 changes, the pattern information of an arbitrary area can be reliably removed by changing the off area of the switch 75 accordingly, and high foreign matter detection capability can be maintained. Also, instead of the liquid crystal element, 1 /
The same effects as those of the first and second embodiments can be obtained also by the polarization spatial filter configured by using the two-wave plate.

Although a semiconductor wafer is used as a sample in the above embodiments, the present invention can be sufficiently applied to detection of foreign matter on a reticle, a mask or other semiconductor elements or a substrate.

〔The invention's effect〕

According to the present invention, a highly polarized linearly polarized illumination light is radiated from a diagonal direction at a desired angle with respect to the vertical direction of the sample surface onto the sample on which the circuit pattern is formed, to the sample surface. A circuit pattern detected by a polarization spatial filter installed in the spatial frequency region (Fourier transform plane) of the detection optical system when detecting scattered light from the irradiation region with a detection optical system having an optical axis in a substantially vertical direction. Since only the polarization component of the scattered light generated from the linear edge part of is selectively shielded, foreign matter scattering that is lost when the polarization component based on the scattered light generated from the linear edge of the circuit pattern is removed Since only a small part of the polarized light is emitted, it is possible to significantly increase the amount of foreign matter detection light, and it is possible to detect even smaller foreign matter with high sensitivity, thus improving the reliability of products such as semiconductors. An effect that can contribute to the upper and yield.

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention, FIG. 2 is a diagram showing a Fourier transform image and a polarization state of a pattern and a foreign substance in a spatial frequency domain, and FIG. 3 is pattern information by a polarizing plate and a spatial filter. FIG. 4 is a principle diagram showing removal, FIG. 4 is a principle diagram showing pattern information removal by a polarization spatial filter, FIG.
FIG. 6 is a diagram showing a second embodiment of the present invention, FIG. 6 is a diagram showing a third embodiment of the present invention, and FIGS. 7, 8 and 9 are the constitutions of liquid crystal elements and the element operation principles. FIG. 10 is an enlarged plan view of a polarization spatial filter formed by using a liquid crystal element.
Figure 11 is a diagram showing a conventional foreign matter detection method using a polarizing plate.
FIG. 12 is a diagram showing a conventional foreign matter detection method using a spatial filter and adjacent chip comparison, and FIG. 13 is a diagram showing how foreign matter information is damaged by the spatial filter. 1 …… Wafer 3a, 3b, 3c, 3d …… Laser 4 …… Objective lens 4a, 300,301,302 …… Fourier transform surface 11,120 …… Pattern 401,402,403,404,601,602 …… Foreign matter 13,37a, 37b, 56,93,130 …… Linear edge part Fourier transform image 14,38,57,94,110,140 …… Fourier transform image of foreign material 6,23,24,36 …… Polarization spatial filter 47,47 ′ …… Polarization spatial filter using liquid crystal element 20,48,48 ′, 81,101 …… Polarizer 8 …… Two-dimensional solid-state image sensor.

Claims (8)

[Claims] 1. A sample on which a circuit pattern is formed is irradiated with linearly polarized illumination light having high directivity from an oblique direction which is inclined at a desired angle with respect to the vertical direction of the sample surface, and the sample surface is almost illuminated. The scattered light from the irradiation area is detected by a detection optical system having an optical axis in the vertical direction, and only the polarization component of the scattered light generated from the linear edge portion of the detected circuit pattern is detected in the space of the detection optical system. Selectively shield the light by a polarization spatial filter installed in the frequency domain, and detect scattered light from the foreign matter on the sample that has passed through the polarization spatial filter by photoelectric conversion means to detect a signal indicating the foreign matter. Characteristic foreign matter detection method. 2. The foreign matter detecting method according to claim 1, wherein the linearly polarized illumination light is light having a narrow wavelength width. 3. An illumination optical system for irradiating a sample on which a circuit pattern is formed with linearly polarized illumination light having high directivity from an oblique direction inclined at a desired angle with respect to a vertical direction of the sample surface, and the sample surface. Has an optical axis almost perpendicular to
A detection optical system that detects scattered light from the irradiation region on the sample that is irradiated by the illumination optical system, and only the polarization component of the scattered light that is generated from the linear edge portion of the circuit pattern that is detected by the detection optical system. And a photoelectric conversion means for detecting scattered light from the foreign matter on the sample that has passed through the polarization spatial filter to detect a signal indicating the foreign matter. And a foreign matter detecting device. 4. The foreign matter detecting device according to claim 3, wherein the polarization spatial filter is composed of a partial polarization element. 5. The foreign matter detecting device according to claim 3, wherein the polarization spatial filter is composed of an optical element that changes the polarization state of light only in a part thereof. 6. The foreign matter detecting apparatus according to claim 5, wherein the optical element is a liquid crystal element. 7. The foreign matter detecting device according to claim 5, wherein the optical element is composed of a wavelength plate. 8. The foreign matter detection device according to claim 3, wherein the linearly polarized illumination light with high directivity emitted by the illumination optical system has a narrow wavelength width.