JPH0695036A - Optical element - Google Patents

Abstract

PURPOSE:To enable the observation of Fourier spectra possessed by fine objects in a wide frequency region by bundling plural light transmitting elements which are aligned with light incident ends on a spherical surface and aligned with the exit ends thereof to a grid form, thereby constituting the optical element. CONSTITUTION:This optical element is constituted by bundling the plural light transmitting elements 11-i, 11-j which are aligned with the respective light incident ends of the spherical surface S in different positions and are aligned with the light exit ends thereof to the two-dimensional grid form. The alignment obtd. by orthogonal projection of the light incident end faces to the plane running the center 0 of the spherical surface S are resembled to the alignment of the light exit ends of the plural light transmitting elements. Then, the light emitted at a prescribed angle from an object to be observed, etc., is made incident on the incident end of the corresponding light transmitting element on the spherical surface S when this object is disposed near the center 0 of the spherical surface S and is illuminated. If the exit ends of these light transmitting elements are aligned according to the conversion rule of, for example, Fourier transform lenses, ftheta lenses, etc., according to the angle of the incident light, the same optical conversion as the optical conversion of these Fourier transform lenses and ftheta lenses is executed by these optical elements.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical element suitable for application to various inspection devices or various measurement devices to which optical Fourier transform is applied.

[0002]

2. Description of the Related Art For example, when manufacturing a semiconductor device or the like using a photolithography technique, a photomask on which a circuit pattern is drawn is used. In such a photomask defect detection apparatus, there is a case where the presence or absence of a defect in the pattern is classified or the defect is classified based on the pattern of the spatial frequency space obtained by Fourier-transforming the light from the pattern on the photomask. . When the light from the object is thus optically Fourier-transformed, the Fourier-transform optical element is used.

Generally, when diffracted light when a plane wave is incident on a two-dimensional aperture is measured at an observation point at infinity from the aperture, a Fraunhofer diffraction pattern is obtained, and this diffraction pattern is the aperture. Is an optical Fourier transform of. In order to express this mathematically, the plane where the two-dimensional aperture exists is called the aperture plane,
The x and y orthogonal axes are taken. The amplitude distribution of the incident plane wave on the aperture plane is F (x, y). If an observation point at infinity from the aperture is represented by spatial frequencies u and v, and the amplitude distribution of the diffraction pattern at this observation point is f (u, v), the amplitude distribution F (x, y) and the amplitude distribution f Between (u, v), there is a Fourier transform relationship shown in the following equation (1). f (u, v) = C∬F (x, y) exp [-2πi (ux + vy)] dxdy (1)

In this equation (1), C is a constant,
The integral symbol ∬ represents the integral from −∞ to + ∞ for the variables x and y. Further, there is a relation of the formula (2) between the coordinates x and y of the position of the aperture plane and the coordinates u and v of the spatial frequency space of the observation point at infinity. (1−l ₀ ) / λ = u, (m−m ₀ ) / λ = v (2) where λ is the wavelength of the incident plane wave, and l ₀ and m ₀ are respectively when the incident plane wave is incident on the aperture plane. The x-axis and y-axis direction cosine, and l and m are the x-axis and y-axis direction cosine of the light traveling from the aperture plane to the observation point at coordinates (u, v) at infinity.

Conventionally, a lens (Fourier transform lens) has been used as such a Fourier transform optical element.
The condition of the Fourier transform lens will be described by taking a one-dimensional case as an example. FIG. 6 shows an optical system in the case of performing one-dimensional Fourier transform. In FIG. 6, in an orthogonal coordinate system in which the normal line of the aperture plane P1 coincides with the z axis, x, y orthogonality is present on the aperture plane P1. An opening 1 having a width ξ in the x direction is formed on the opening plane P1 so as to include the origin of the coordinate system on the axis P1.
This aperture 1 is illuminated with a plane wave I incident from the left direction. Also, 2 has a focal length of f whose optical axis coincides with the z-axis and f
Of the Fourier transform lens, the aperture plane P1 is arranged in the object focal plane of the lens 2, and an observation plane P2 perpendicular to the optical axis is formed in the image focal plane of the lens 2. On the observation plane P2, U and V axes are taken in parallel with the x and y axes. The Fourier transform lens 2 has the following two conditions.

Condition In order to obtain an observation result equivalent to the observation result at the point at infinity, it is necessary to focus diffracted light having the same direction cosine (for example, diffracted lights i ₁ and i ₂ having a diffraction angle θ) at one point. For that purpose, the aperture plane P1 must be aligned with the front focal plane of the Fourier transform lens 2 and the observation plane P2 must be aligned with the rear focal plane. If this condition is not satisfied, the spatial frequency and the direction cosine do not have a one-to-one correspondence.

Condition In order to observe the Fourier transform pattern on the UV plane by the U and V axes which are orthogonal coordinates having the optical axis of the rear focal plane of the Fourier transform lens 2 as the origin,
The Fourier transform lens 2 has the characteristics of the following expressions (3) and (4). U = fsin θ _x = fl (3), V = f sin θ _y = fm (4) where f is the focal length of the lens 2, θ _x is the x component of the viewing angle, and θ _y is the y component of the viewing angle. By the way, the Fourier transform information is usually shown on the orthogonal coordinates of the spatial frequencies u and v, and the following relationship is established by the definition of the Fourier transform. u = (l−l ₀ ) / λ (5), v = (m−m ₀ ) / λ (6) However, the meaning of each variable is as follows. l: direction cosine of diffracted light (component parallel to x axis), l ₀ : direction cosine of 0th order diffracted light (component parallel to x axis), m: direction cosine of diffracted light (component parallel to y axis), m ₀ : Direction cosine of 0th-order diffracted light (component parallel to y-axis)

Next, using the direction cosines l ₀ and m ₀ , the following coordinates U ₀ and V ₀ are introduced. U ₀ = fl ₀ (7), V ₀ = fm ₀ (8) This is because the position of the 0th-order diffracted light on the UV plane is (U ₀ , V ₀ ) in the equations (7) and (8). Means to be represented.
From the expressions (3) to (8), the following relationships are established. u = {1 / (λf)} (U−U ₀ ) (9), v = {1 / (λf)} (V−V ₀ ) (10) Equations (9) and (10) are UV planes. It is shown that the spectrum distribution obtained by performing the similarity transformation on the Cartesian coordinates of the spatial frequencies u and v with the coefficient of λf is observed with the point (U ₀ , V ₀ ) as the origin. Hereinafter, the UV plane that is the observation surface of the spectrum will be referred to as the Fourier transform surface.

Under the above conditions, a diffraction image of the amplitude distribution 3 is formed on the observation plane P2, which is the rear focal plane of the Fourier transform lens 2. The orthogonal coordinates in the spatial frequency space of the observation plane P2 are (u, v), and corresponding to the equation (1), the aperture plane P
The amplitude distribution of the incident plane wave I at the aperture 1 of No. 1 is F (x,
y), the amplitude distribution of the diffraction image on the observation plane P2 is f (u,
v). The intensity of the diffraction image is | f (u,
v) | ² , but this intensity distribution becomes distribution 4.

[0010]

However, in the optical system using the conventional Fourier transform lens 2 as shown in FIG.
In order to perform the Fourier transform in a wide range of spatial frequencies, the lens diameter becomes large. Further, in consideration of the thickness of the lens in the optical axis direction, it is very difficult in practice to perform Fourier transform on the diffracted light having a diffraction angle θ of about 90 ° by the Fourier transform lens 2. In this regard, such a large diffraction angle θ is when the structure of the object illuminated by the incident plane wave is fine.

Further, for example, the fθ lens is a lens that focuses a light beam emitted at an angle θ to a position proportional to the angle θ. In such a case, when the angle θ becomes large, The diameter must be quite large, but there are limits.

In view of the above point, the present invention, when converging light emitted from a predetermined area on a plane according to a predetermined conversion rule, even if the emission angle is large as it approaches 90 °, the conversion rule is large. According to the present invention, an optical element capable of focusing the light on the plane is provided. Another object of the present invention is to provide an optical element capable of observing the Fourier spectrum of a fine object in a wider frequency range than ever before.

[0013]

In the first optical element according to the present invention, for example, as shown in FIG. 1, the respective light incident ends are arranged at different positions on the spherical surface S, and the respective light emitting ends are arranged. Is a bundle of a plurality of light transmitting elements (11-i, 11-j) arranged in a two-dimensional lattice. Further, the second optical element is the same as the first optical element, except that the incident ends of the light of the plurality of light transmitting elements (11-i, 11-j) are orthographically projected onto a plane passing through the center O of the spherical surface S. The obtained array is similar to the array of light emitting ends of the plurality of light transmitting elements.

In this case, the plurality of light transmitting elements (11
It is desirable that each of -i and 11-j) is a light guide. Further, it is desirable that the light incident ends of the plurality of light transmitting elements are substantially perpendicular to the spherical surface S, as shown by the incident ends (14-1a, 14-2a) in FIG. 4, for example. Further, in the second optical element, an array obtained by orthographically projecting the light incident ends of the plurality of light transmitting elements (11-i, 11-j) onto a plane passing through the center O of the spherical surface S and those It is desirable that the arrangement of the light emitting ends of the plurality of light transmitting elements is an arrangement on orthogonal coordinates.

[0015]

According to the first optical element of the present invention, the light incident ends of the plurality of light transmitting elements are arranged on the spherical surface S. Therefore, when an observation object or the like is placed near the center O of the spherical surface S and is illuminated with, for example, a plane wave, the light emitted from the observation object at a predetermined angle is incident on the spherical surface S of the corresponding light transmitting element. Incident on. Therefore, by arranging the exit end of the light transmitting element according to the conversion rule of, for example, a Fourier transform lens, an fθ lens or a normal lens according to the angle of the incident light, the Fourier transform lens can be used in the optical element. , Fθ lens or an ordinary lens can be used for optical conversion.

The second optical element of the present invention is an element for performing an optical Fourier transform. The second optical element is proposed by paying attention to the following two points. First,
First, the optical Fourier transform is applied to an inspection device or the like that inspects fine defects. For example, in the defect inspection device, the defect can be illuminated with a sufficient amount of light to photoelectrically convert the amount of light scattered by the defect. It is necessary to have a good level. Therefore, in many defect inspection apparatuses, the illumination light is condensed by the optical system, and only a minute area of the inspection object is illuminated,
The amount of illumination light to the defective part is secured.

Secondly, when the information on the Fourier transform plane is processed in real time, generally the information on the intensity distribution of the Fourier transform image is used. Therefore, in most cases, a one-dimensional or two-dimensional image sensor is installed on the Fourier transform plane,
The image sensor converts the intensity distribution of light into an electric signal.

The above first and second aspects will be supplementarily described. Regarding the first aspect, as shown in the conventional example of FIG. 6, the existence range (aperture 1 of width ξ) of the object to be Fourier-transformed on the aperture plane P1 which is the front focal plane of the Fourier transform lens 2 is sufficient. When it is small, it is possible to obtain a light amount distribution equivalent to the light amount distribution at the observation point at infinity, which is the condition of Fraun-Hofer diffraction, without using the focusing effect by the lens.

Specifically, when the object to be Fourier-transformed is limited to ± xe in the x direction and ± ye in the y direction (direction perpendicular to the paper surface of FIG. 6), the following equation (11) is used. When satisfied, the diffracted lights i ₁ and i ₂ in FIG. 6 can no longer be separated, and the observation plane P2 of the rear focal plane of the Fourier transform lens 2 is observed.
The Fourier transform lens 2 is not required to have the characteristic of converging the light flux. f >> {2 (xe ² + ye ² )} / λ (11) For example, λ = 633 [nm], xe = ye = 0.1 [m
m], f >> 60 [mm]. In other words, due to the balance between the existence ranges xe and ye of the conversion target and the focal length f, the above-mentioned "focusing condition" which is the first condition of the optical element for Fourier transform is unnecessary.

Regarding the second aspect, in the Fourier transform lens 2 shown in FIG. 6, the amplitude distribution 3 of the Fourier transform image including the phase information on the observation plane P2 which is the Fourier transform plane.
However, phase information is not necessary if only the intensity distribution of the Fourier transform image is focused. In addition, recently, one-dimensional or two-dimensional image sensors are used to observe the intensity distribution of light, but since the pixels of these one-dimensional or two-dimensional image sensors have a finite size, No continuous Fourier spectrum is obtained. However,
Actually, a continuous Fourier spectrum is not necessary, and it is sufficient to obtain a discrete spectrum corresponding to the pixels of the image sensor. As described above, the present invention has a relatively small existence range of an object to be Fourier transformed,
The present invention also relates to a Fourier transform optical element that is optimal for observing the intensity distribution of an image on the Fourier transform plane when a one-dimensional or two-dimensional image sensor (an array of photoelectric conversion elements) is arranged on the Fourier transform plane. .

Next, the basic principle of the second optical element of the present invention will be described with reference to FIG. 7, parts corresponding to those in FIG. 6 are designated by the same reference numerals, and detailed description thereof will be omitted. In FIG. 7, it is assumed that a circle 5 having a radius f is centered on the opening 1 having a width ξ in the x direction on the opening surface P1. Substituting the radius f into the focal length f of the equation (11), ye = 0, 2xe
When> ξ, the radius f is determined so that the condition of the equation (11) is satisfied.

Next, the incident end face 6a of the light transmitting element 6 is arranged on the circumference 5 so that the second condition "image height condition" of the optical element for Fourier transform described above is satisfied, and its light transmission is performed. The exit end face 6b of the element 7 is arranged on the Fourier transform plane P3 of the coordinate system (U, V). That is, in the plane wave I that has entered the opening 1 from the left direction, the incident end surface 6a from the opening 1
Letting θ be the angle formed by the light traveling toward the lens and the normal to the aperture plane P1, the light transmitting element 6 changes the light so that the image height H ₁ becomes f · sin θ in order to satisfy the “condition of image height”. Just send it. Therefore, the exit end surface 6b may be arranged on the Fourier transform surface P3 so that the light exiting from the exit end surface 6b of the light transmitting element 6 becomes a point image of the image height H ₁ on the Fourier transform surface P3.

In the example of FIG. 7, the light transmitting element 6 has a shape parallel to the normal line direction of the opening surface P1, the incident end surface 6a coincides with the circular arc of the circumference 5, and the exit end surface 6b is parallel to the opening surface P1. Since it is an end face, the Fourier transform plane P3 is formed parallel to the aperture plane P1. The resolution of the Fourier spectrum depends on the size of the incident end surface 6a of the light transmission element 6. That is, the light from the opening 1 incident on the incident end face 6a is shown as light having an angle θ in FIG. 7, but the incident end face 6a is actually not a point but an angular width δ when viewed from the opening 1. Have a width of. Therefore, the resolution of the Fourier spectrum is on the order of the angular width δ.

In addition, in the necessary part of the Fourier spectrum
Correspondingly, the angle θ on the circumference 5₁ , Θ ₂ , Θ₃ Enter in the direction of
The shooting end surfaces 6-1a, 6-2a, 6-3a,
Emission end surfaces 6-1b, 6-2b, 6-3b on the conversion surface P3
Optical transmission elements 6-1, 6-2, 6-3 having
, The image heights ha, hb, and hc are ha = f · s
in θ₁ , Hb = f · sin θ₂ , Hc = f · sin θ
₃ The angle on the circumference 5 of the incident end face of each light transmitting element
Just set the degree.

In this way, the Fourier transform plane P3 is
An intensity distribution of the Fourier spectrum is formed. By increasing the resolution by reducing the incident end face of each light transmitting element, a substantially continuous intensity distribution of the Fourier spectrum as shown by distribution 7 in FIG. 7 can be obtained. When photoelectrically converting the intensity distribution of the Fourier transform plane P3, for example, the pixels g ₁ , g ₂ , ... Of light receiving elements having a width d _{2 at} a predetermined pitch in the u direction.
.., g _n are formed on the Fourier transform plane P3.

When considering the use of a commercially available image sensor, the degree of freedom of the pixel size and the number of pixels is not so large, so the size of the Fourier transform plane is reduced or expanded according to the image sensor. There is a need.
A simple example in this case is shown in FIG. In FIG. 8, a series of light transmitting elements 9-1 to 9-n each having an incident end face are bundled on a circumference 5 centered on the opening 1 on the opening face P1. In addition, the Fourier transform plane P parallel to the opening plane P1
U is the coordinate that any light-transmitting element 9-i (i = 1 to n) passes on 3 and the coordinate that the light-transmitting element 9-i passes on the conversion surface P3 to the right of the conversion surface P3. U '
By reducing the diameter of the emitting portion of each of the light transmitting elements 9-1 to 9-n, the relationship of U '= kU (k is a constant smaller than 1) is established.

In the light transmitting elements of FIGS. 7 and 8, the light incident end faces of the plurality of light transmitting elements (6-1, 9-1, etc.) are orthographically projected onto a plane passing through the center O of the circumference 5. The obtained array is similar to the array on the Fourier transform plane P3 or P4 of the light emitting end faces of the plurality of light transmitting elements.

Next, the case of epi-illumination will be described with reference to FIG. In FIG. 9, a reflection type pattern 10 having a width of ξ in the x direction is arranged as an object to be Fourier transformed on the opening surface P1. The incident plane wave I of wavelength λ is
The opening surface P1 is illuminated so that the reflection angle in the regular reflection direction with respect to the normal line of the opening surface P1 is θ ₀ . in this case,
Due to the effect of oblique incidence on the aperture plane P1, the incident plane wave I has a phase distribution that changes sinusoidally along the x-axis on the aperture plane P1, and the intensity distribution of the Fourier spectrum is laterally offset.

Assuming that the image height when the reflected light of the reflection angle θ ₀ intersects the circumference 5 is H ₀ , the intensity distribution of the Fourier spectrum on the Fourier transform plane P3 is on the U axis as compared with the case of FIG. The shift is made by U _{0 in} equation (7) along. However, by arranging the light transmission element 6 so that the incident end face is in contact with the circumference 5, the intensity distribution in which the Fourier spectrum is shifted laterally is obtained on the Fourier transform plane P3 as in the case of FIG.

Further, the light transmitting elements (6-1, 9-1)
Etc.) is configured by an optical fiber or a light guide such as a cylindrical mirror whose inner surface is mirror-finished, so that light is efficiently guided from the incident surface to the exit surface. Furthermore,
When the light incident ends of the plurality of light transmitting elements are substantially perpendicular to the spherical surface S as shown in FIG. 4, the light from the vicinity of the center of the spherical surface S is efficiently taken into each light transmitting element.

In the second optical element, an array obtained by orthographically projecting the light incident ends of the plurality of light transmitting elements onto a plane passing through the center of the spherical surface S and the light emission of the plurality of light transmitting elements. When the array of the ends is an array on the orthogonal coordinates, the intensity distribution of light on the Fourier transform plane is obtained on the orthogonal coordinates, and the subsequent processing is facilitated.

[0032]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the optical element according to the present invention will be described below with reference to FIGS. The optical element of this example optically performs a Fourier transform. Figure 1 is the first
2 is a transparent perspective view of the optical element of the example, and in FIG. 1, a hemispherical surface S having a predetermined radius with an origin O on an orthogonal coordinate system composed of an x axis and ay axis as a center is assumed. Further, assuming an orthogonal coordinate system composed of the U axis and the V axis at a position separated by a distance L from a plane composed of the x axis and the y axis (xy plane), the x axis and the U axis are parallel to each other, and the y axis is parallel to the y axis. And make the V axis parallel.
Further, straight lines passing through the origin O of the xy plane and the origin of the plane (UV plane) composed of the U axis and the V axis are perpendicular to the xy plane and the UV plane, respectively.

Then, a large number of square columnar optical fibers each having a bottom whose width in the U direction is Du and whose width in the V direction is Dv are densely bundled. Two representative ones of the quadrangular prism-shaped optical fibers are represented by 11-i and 11-j, and the main bodies of the other quadrangular prism-shaped optical fibers are omitted. In this case, on the UV plane, one end face (for example, the shaded end faces 11-ib and 11-jb) of each of the large number of rectangular column-shaped optical fibers is located in each grid-shaped square. On the other hand, the other end faces (for example, the shaded end faces 11-ia and 11-ja) of the large number of the square pole-shaped optical fibers each form a part of the hemispherical surface S. Also, the other end surface is a hemispherical surface S
The square column optical fiber not on the top is deleted.

FIG. 2 is a schematic sectional view taken along a plane passing through the center of the hemispherical surface S of FIG. 1. In FIG. 2, the hemispherical surface S is shown.
From the end of the rectangular prism optical fiber 11-1, 11-2, 1
1-3, ... Are closely arranged. In addition, each of the quadrangular prism-shaped optical fibers has a core 11-1c, 11-2c, 1
1-3c, ... and clads 11-1d, 11-2d,
11-3d, ... In this case, for example, the other end surface 11-6a of the square pole optical fiber 11-6 is used.
Of the light from the center of the surface S of the hemisphere, the light having an emission angle of θ ₁ to θ ₂ is incident on the core portion of, and the light is emitted from one end face 11-6b. Similarly, a square pole optical fiber 11
The exit angle is θ _{3 at} the core portion of the other end surface 11-2a of −2.
The light near the point of incidence enters and the light exits from the one end face 11-2b.

When the radius of the surface S of the hemisphere is f, for example, with respect to the square pole optical fiber 11-2, the exit angle θ _{3 of the} light incident on the other (incident side) end face 11-2a is As shown in FIG. 2, the following relationship exists between the coordinate (u ₃ ) on the U axis of the one (exit side) end face 11-2b. u ₃ = f · sin θ ₃ Other square column optical fibers 11-k (k = 1, 3, 4, ...
...) has the same relationship. From this, it can be seen that the optical element configured by bundling the rectangular column-shaped optical fibers acts as an optical element for Fourier transform.

In this example, the light emitted from the vicinity of the center of the surface S of the hemisphere at an angle of about 90 ° with respect to the optical axis is efficiently propagated to the UV plane by, for example, the rectangular column optical fiber 11-1. The Fourier spectrum in a wide frequency band can be observed with a good SN ratio. An ordinary column-shaped optical fiber may be used instead of the rectangular column-shaped optical fiber 11-i. A cylindrical optical fiber is slightly inferior in light collection efficiency, but is easy to manufacture.

Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 3A is a schematic cross-sectional view of the optical element of the second embodiment. In FIG. 3A, the square pole optical fiber 11-i (i = 1, 2, ...) Of FIG. Each is replaced by a hollow quadrangular prismatic pipe 12-i. The other structure is similar to that of the first embodiment. Figure 3
(B) shows a quadrangular prismatic pipe 12 representative of the quadrangular prismatic pipe 12-i.
It is surrounded by 3, and four inner surfaces are configured by mirror surfaces 12d, and light passes through the hollow portion 12c.

Therefore, in FIG. 3A, the hemispherical surface S
The light emitted from the inside is reflected by each of the mirror surfaces 12-1c, 12-2c, 12-3c, ... Of the rectangular column pipe 12-i, and each of the hollow portions 12-1d, 12-2d, 12-3.
It passes through d, ... And reaches the UV plane which is the Fourier transform plane. Also in this embodiment, the rectangular column pipe 12-i is used.
One end face 12-1b, 12-2b, 12
-3b, ... Are arranged in the UV plane, and the other end faces 12-1a, 12-2a, 12-3a, ... Are arranged so as to contact the surface S of the hemisphere.

Next, a third embodiment of the present invention will be described with reference to FIG. In the third embodiment, as in the first embodiment of FIG. 2, each light transmission element is composed of an optical fiber, and the positional relationship between the center of the end face on the incident side and the center of the end face on the exit side of each optical fiber. Is the same as in the first embodiment. However, in this embodiment, the light propagation efficiency is higher than that in the first embodiment. That is, since the optical fiber has a unique opening angle, in the example of FIG. 2, the average exit angle θ ₃ is larger than that inside the rectangular column-shaped optical fiber 11-6 that enters at the exit angles θ _{1 to} θ _2. Incident square pole optical fiber 11-2
The efficiency of light propagation inside is generally low. This can be eliminated by making the incident angle of the light beam on the incident side end surface of the optical fiber close to vertical.

FIG. 4 is a schematic sectional view of the optical element of this example. In FIG. 4, a hemispherical surface S centered on the origin O is shown.
From the end of the optical fiber 14-1, 14-2, 14-
3, ... are arranged. Further, each optical fiber has cores 14-1c, 14-2c, 14-3c, ... And clads 14-1d, 14-2d, 14-3d ,.
It is composed of Furthermore, within those optical fibers,
The closer to the end of the surface S of the hemisphere, the shape of the end on the incident side is deformed so that each end on the incident side is in contact with the surface S of the hemisphere substantially perpendicularly. For example, the optical axes of the optical fibers themselves in the vicinity of the end faces 14-1a, 14-2a, 14-3a, ... On the incident side of the optical fibers are each perpendicular to the surface S of the hemisphere. In addition, the end face 14-1b on the exit side of the optical fiber,
14-2b, 14-3b, ... Are arranged in the UV plane.

Thus, for example, light incident on the end face 14-3a of the optical fiber at the exit angle θ ₃ also propagates efficiently through the core 14-3c and reaches the end face 14-3b. Thus, according to this embodiment, the light emitted from the inside of the surface S of the hemisphere is efficiently supplied to the UV plane which is the Fourier transform surface. The above-described first to third embodiments are examples along the formulas (3) and (4) for explaining the principle. However, as shown in FIG. It may be reduced or enlarged.

Next, a fourth embodiment of the present invention will be described with reference to FIG. This embodiment is an example of a reflection type optical system.
FIG. 5 shows a schematic sectional view of the fourth embodiment. In FIG. 5, a hemispherical surface 15 having a radius f ₁ centering on the origin on the opening surface P1 is assumed. Further, on the opening surface P1, the width in the x direction as the measurement target of the Fourier spectrum is ξ ₁
And ξ ₂ reflective pattern 10A and reflective pattern 10
B and are arranged. Now, assuming that the incident plane wave I passes through a part of the hemispherical surface 15 and obliquely enters the opening surface P1, observe the Fourier spectrum corresponding to the observation direction from the angle θ ₁ to the angle θ ₂ in FIG. think of.

When only the reflection type pattern 10A exists in the illumination area of the plane wave I from the oblique direction, a Fourier spectrum having the same distribution as the Fourier spectrum on the plane P3 of FIG. 9 mentioned in the explanation of the principle should be obtained. is there. This Fourier spectrum is also shown by the distribution 16 on the plane P3 in FIG.
In the case of FIG. 5, since the reflection type pattern 10B is also present in the plane wave I, a Fourier spectrum obtained by combining the Fourier spectra of the reflection type patterns 10A and 10B is observed. In this embodiment, a lens 17 and a slit plate 18 are further added in order to obtain a Fourier spectrum in an arbitrary region from the incident plane wave I.

That is, the reflective pattern 10A on the opening surface P1
The light reflected from the lens 17 is applied to the slit plate 1 on the surface P5.
Focusing in the slit in the center of 8, the reflective pattern 1
The slit plate 18 blocks the reflected light from the object around 0A. For example, when the optical system of FIG. 5 is actually used by incorporating it into a defect inspection apparatus, there is an advantage that unnecessary stray light or the like generated from other than the inspection object is cut by the slit plate 18.

In FIG. 5, the image on the aperture plane P1 is the lens 1
An image is formed on the surface P5 by 7, and an image 10AI of the reflective pattern 10A is formed in the slit of the slit plate 18. That is, the light around the image 10AI is transmitted to the slit plate 18
The light is shielded by, and only the spectrum of the light rays forming the image 10AI is extracted. Then, assuming a hemispherical surface 19 having a radius f ₂ with the slit of the slit plate 18 as the center,
The light transmitting elements 20-1, 20-2, 20-3, ... Are arranged so that the end surface on the incident side is in contact with the surface 19 of the hemisphere, and the end surfaces on the emitting side of these light transmitting elements are parallel to the surface P5. It is arranged on the Fourier transform plane P6. The coordinate system of the plane P5 is x '
Axis and y'-axis, and the coordinate system of the Fourier transform plane P6 is represented by U'-axis and V'-axis.

In this case, the radius f ₂ is determined so as to satisfy the above equation (11), and the image 1 of the reflection type pattern on the surface P5 is determined.
Light from 0AI is transmitted to the light transmitting elements 20-1, 20-, respectively.
2, and so on, are guided onto the Fourier transform plane P6. On the Fourier transform plane P6, an intensity distribution of the Fourier spectrum corresponding to the resolution of the light transmission element is obtained as indicated by the distribution 21.

In this embodiment, the reflective pattern 10 is used.
Although the case where A is minute has been described, whether an object to be Fourier-transformed on the aperture plane P1 is reflective or transmissive and an attempt is made to obtain a Fourier spectrum for measuring objects of various sizes, It is difficult to always satisfy equation (11). There are the following two methods for obtaining the Fourier spectrum of a measurement target of arbitrary size.

The first method is to make the gap of the slit of the slit plate 18 in the fourth embodiment shown in FIG. 5 minute so as to satisfy the equation (11). Further, the second method is the same as the fourth embodiment shown in FIG.
In the configuration shown in FIG. 9, the illumination area of the incident plane wave I on the aperture plane P1 is made minute so as to satisfy the expression (11). As described above, the second method can be easily realized by the illumination optical system generally used in the inspection device for inspecting fine defects. That is, in such a defect inspection apparatus, a laser beam that is narrowed down is normally applied to the inspection object.

Further, the Fourier spectrum obtained by using the first method is measured as the Fourier spectrum of the void of the slit of the slit plate 18 which is convolution integrated (convolution), and the second method thereof. The Fourier spectrum obtained when is used is measured as a convolution of the Fourier spectrum of the illumination region. Function f in real space
The Fourier transform of (x, y) is represented by F [f (x, y)], and two functions f ₁ (u, v) and f in the spatial frequency space are represented.
The convolution integral of ₂ (u, v) is f ₁ (u, v) * f ₂
Expressed by (u, v), the Fourier spectrum obtained by the first method and the Fourier spectrum obtained by the second method can be expressed by the following equations (12) and (13), respectively.

Here, the definitions of the functions used in the equations (12) and (13) are shown below. A (x, y): Amplitude reflectance (or transmittance) distribution on the aperture surface of the measurement target, a (u, v): Fourier spectrum of A (x, y), B ₁ (x, y): Slit B ₂ (x, y): amplitude distribution in the illumination region of the incident beam, b ₁ (u, v): Fourier spectrum of B ₁ (x, y), b ₂ (u , V): Fourier spectrum of B ₂ (x, y).

F [A (x, y) · B ₁ (x, y)] = a (u, v) * b ₁ (u, v) (12) F [A (x, y) · B ₂ ( x, y)] = a (u, v) * b ₂ (u, v) (13) In this case, in order to extract only the Fourier spectrum of the measurement object, the left side of expression (12) or expression (13) On the left side of the function (b ₁ (u, v)) ⁻¹ or the function (b ₂
(U, v)) ^-1 may be convolved and integrated.

The present invention is not limited to the above embodiment,
Needless to say, various configurations can be adopted without departing from the scope of the present invention, for example, application to an fθ lens or a normal lens.

[0053]

According to the first optical element of the present invention, even light emitted with a large inclination can be guided to the exit end side by the light transmitting element. Therefore, the closer the exit angle is to 90 °, the closer. Even if it is large, there is an advantage that the light can be focused on a predetermined plane according to a predetermined conversion rule. Further, according to the second optical element, since the Fourier transform is accurately performed even for the light having a large emission angle, there is an advantage that the Fourier spectrum of a particularly fine object can be observed in a wider frequency range than before. . This second optical element is particularly applied to an apparatus such as a defect inspection apparatus for a substrate using intensity distribution information of a Fourier transform surface, or an apparatus based on the principle of breaking the intensity distribution of a Fourier transform surface in real time. Suitable for

Further, when the light transmitting element is constituted by a light guide or the incident end of the light transmitting element is made substantially perpendicular to the spherical surface, the light propagation efficiency is further improved. Further, the array obtained by orthographically projecting the light incident ends of the plurality of light transmitting elements onto a plane passing through the center of the spherical surface and the array of the light emitting ends of the plurality of light transmitting elements are arrays on orthogonal coordinates. In this case, subsequent image processing and the like are easy.

[Brief description of drawings]

FIG. 1 is a partially omitted perspective view showing a first embodiment of an optical element according to the present invention.

FIG. 2 is a schematic cross-sectional view of the first embodiment.

FIG. 3 is a schematic sectional view of a second embodiment of the present invention.

FIG. 4 is a schematic sectional view of a third embodiment of the present invention.

FIG. 5 is an optical path diagram including a partial cross-sectional view showing the configuration of a fourth embodiment of the present invention.

FIG. 6 is a diagram illustrating the principle of a conventional Fourier transform lens.

FIG. 7 is a diagram illustrating the principle of transmitted illumination of the optical element of the present invention.

FIG. 8 is an explanatory view of the principle when FIG. 7 is modified.

FIG. 9 is an explanatory view of the principle of reflected illumination of the optical element of the present invention.

[Explanation of symbols]

1 Aperture 10 Reflective Pattern S Hemispherical Surface 11-1, 11-2, 11-3, ... Square Column Optical Fiber 11-1c, 11-2c, 11-3c, ... Core 11-1d, 11-2d , 11-3d, clad 12-1, 12-2, 12-3, ... square columnar pipe 13 partition walls 14-1, 14-2, 14-3, ... optical fiber 18 slit plate 15, 19 hemisphere Face of

Claims (5)

[Claims] 1. The light incident ends are arranged at different positions on a spherical surface, and the light emitting ends are formed by bundling a plurality of light transmitting elements arranged in a two-dimensional lattice shape. Characteristic optical element. 2. The arrangement obtained by orthographically projecting the light incident ends of the plurality of light transmitting elements onto a plane passing through the center of the spherical surface and the arrangement of light emitting ends of the plurality of light transmitting elements are similar to each other. The optical element according to claim 1, wherein the optical element is present. 3. The optical element according to claim 1, wherein each of the plurality of light transmitting elements is a light guide. 4. The optical element according to claim 1, wherein the light incident ends of the plurality of light transmission elements are substantially perpendicular to the spherical surface. 5. An array obtained by orthographically projecting the light incident ends of the plurality of light transmitting elements onto a plane passing through the center of the spherical surface and an array of light emitting ends of the plurality of light transmitting elements are orthogonal to each other. The optical element according to claim 2, wherein the optical element is a coordinate array.