JPH0783844A - Defect inspection device - Google Patents

Abstract

PURPOSE:To accurately detect only defects irrespective of conditions such as the proper pattern density or the form of a subject for inspection. CONSTITUTION:Asubstrate 100 to be inspected is irradiated with illuminating light from a light source 105, and a Fourier-transformed image of the light reflected from the substrate 100 to be inspected is picked up by an image pickup element 114 via a half mirror 113, and the light of the Fourier-transformed image within an aperture 112 undergoes inverse Fourier transform via a lens 115 and its image is picked up by an image pickup element 116. The position and size of the apertufe with which the illuminance of the beam passing inside the aperture 112 is at a minimum are calculated from the image pickup signal of the image pickup element 114, and with the aperture 112 set to the position and the size, images of defects are picked up by the image pickup element 116.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a defect inspection apparatus,
In particular, for example, an exposure mask used when manufacturing a semiconductor device or the like using a photolithography technique, a reticle or a wafer after exposure, or a glass substrate such as an optical disk,
It is suitable for application when inspecting foreign matter, defects, etc. on an object having a regular (periodic) structure such as an iron plate or a mesh.

[0002]

2. Description of the Related Art For example, an exposure mask used for manufacturing a semiconductor device or the like, a reticle, or a wafer after exposure, which has a regular (periodic) structure, has foreign matter or defects on an object to be inspected. A defect inspection device is used when inspecting.
FIG. 9 shows a conventional defect inspection apparatus. In FIG.
The light beam L1 emitted from the light source 1 is deflected by a vibrating mirror (galvano scanner mirror or polygon scanner mirror) 2 and enters a scanning lens 3, and the light beam L2 emitted from the scanning lens 3 is an object to be inspected. Scan on the scan line 5 on the surface 4. At this time, the light beam L
When the surface to be inspected 4 is moved in the R direction perpendicular to the scanning line 5 at a speed slower than the scanning period of 2, the entire surface on the surface to be inspected 4 can be scanned by the light beam L2. In this case, when the light beam L2 is applied to the region where the defect 6 such as a foreign substance exists on the surface of the surface 4 to be inspected, scattered light L3 is generated. Further, a periodic structure (for example, a circuit pattern on a reticle, a circuit pattern on a wafer or a groove of an optical disk) different from a defect such as a foreign substance on the surface 4 to be inspected (hereinafter,
When the light beam L2 is applied to the area where the “pattern” is collectively) 7, the diffracted light L4 is emitted from the pattern 7.
Occurs.

However, the object to be detected by the defect inspection apparatus is not the pattern 7 originally existing on the surface 4 to be inspected, but the defect 6 that should not originally exist. Therefore, it is necessary to distinguish between the pattern and the defect and detect only the defect.
Therefore, in FIG. 9, the light receivers 8, 9 and 10 are arranged so as to face the scanning line 5 from different directions. The scattered light L3 generated from the defect 6 such as a foreign substance is isotropic scattered light generated in almost all directions.
The diffracted light L4 generated from the pattern 7 is light (light with strong directivity) emitted in spatially discrete directions because it is generated by diffraction. When light is detected by all of the light receivers 8, 9 and 10 using such a difference in properties, the light is scattered light from a defect and the light receivers 8, 9 and 10 are detected.
If there is a light receiver that does not detect even one of the light, it is determined that the light is diffracted light from the pattern.
As a result, only the defect 6 can be detected separately from the pattern 7.

[0004]

However, in the conventional defect inspection apparatus as described above, depending on the density and the shape of the pattern on the surface 4 to be inspected, all the light receivers even if the light is diffracted from the pattern. There is a problem that light may be incident on 8, 9 and 10 and may be erroneously determined as a defect.

In view of the above point, the present invention has an object to provide a defect inspection apparatus capable of detecting only defects without depending on conditions such as the density and shape of the original pattern of an object to be inspected. To do.

[0006]

A defect inspection apparatus according to the present invention is, for example, as shown in FIG. 5, a light irradiation means (105) for irradiating an inspection object (100) with inspection light, and the inspection object. A light-collecting optical system that collects light from an object and inspects a defect of the object to be inspected by the light thus condensed, in which the light from the object (100) is Fourier-transformed. The relative positional relationship between the first transform optical system (107 to 109) and the Fourier transform pattern of the subject (100) is variable on the Fourier transform surface of the subject (100) by the first transform optical system. And opening setting means (110A to 110D) for setting the opening (112) having a variable area.

Further, according to the present invention, the illuminance measuring means for obtaining the light quantity per unit area of the light flux passing through the opening (112), and the area of the opening are equal to or more than a predetermined minimum area determined from the smallest defect to be detected. Under such a condition that the light quantity passing through the aperture per unit area is minimized, the relative positional relationship between the aperture and the Fourier transform pattern through the aperture setting means and the area of the aperture. And a second conversion optical system (115) that forms a conjugate image of the object (100) by performing an inverse Fourier transform on the light that has passed through the opening, and the object (100). Observing means (116) for observing the conjugate image of (1).

In this case, an example of the illuminance measuring means is an image pickup means (113, 114) for picking up the Fourier transform pattern of the object (100), and an image pickup signal from the image pickup means for processing the aperture. It has an arithmetic means (130) for calculating the light quantity per unit area of the light flux passing through the aperture, when the relative positional relationship with the Fourier transform pattern and the area of the aperture are changed.

Another example of the illuminance measuring means is, for example, as shown in FIG. 7, photoelectric conversion means (124 to 12) for photoelectrically converting the light flux passing through the openings (121A, 121B).
6) and an arithmetic unit (132) for obtaining the light amount per unit area of the light flux passing through the aperture, based on the area of the aperture set by the aperture setting unit (120) and the photoelectric conversion signal from the photoelectric conversion unit. I have.

As the opening setting means, the area of the opening is set to an area selected from a plurality of preset areas, and the control means sets the opening within the preset plurality of areas. The area of the opening may be set to the area where the amount of light flux passing through the unit area is the minimum.

[0011]

The optical principle underlying the present invention will be described with reference to FIG. In FIG. 1, the surface 11 to be inspected is irradiated with the light beam L. However, in order to simplify the description here, it is assumed that the surface 11 to be inspected is the surface of an object that transmits light at least partially, and the light beam L is incident vertically from the back surface direction of the surface to be inspected 11. The present invention is also applicable to epi-illumination as well as transmitted illumination. Furthermore,
The present invention is applicable to both bright field and dark field illumination methods.

A light receiving lens 12 is arranged in a direction in which a light beam L is emitted from the surface 11 to be inspected, and a Fourier transform image of a pattern 13 on the surface to be inspected 11 is formed on a pupil plane P1 on the image side of the light receiving lens 12. 13F is formed. The pupil plane P1 of the light receiving lens 12 is also called a Fourier transform plane. Furthermore, the pupil plane P
The lens 14 is arranged in the direction in which the light beam is emitted from the first light source 1, and the lens 14 allows the second pupil surface P2 conjugate with the pupil surface P1.
A reduced image of the Fourier transform image 13F is formed on the top.
The light receiving surface of the light receiver 15 is arranged on the second pupil plane P2, and the reduced image on the second pupil plane P2 is photoelectrically converted by the light receiver 15. Therefore, the position 11C which is conjugate with the surface 11 to be inspected by the light receiving lens 12 and the lens 14 is the second pupil plane P.
Different from 2.

In FIG. 1, no optical element is placed at the position of the pupil plane P1, and the pupil plane P1 is a virtual plane. That is, in the configuration of FIG. 1, all the optical information on the surface 11 to be inspected is incident on the photodetector 15. Therefore, if it is left as it is, there is a defect along with the optical information of the original pattern 13 on the surface to be inspected 11. If so, the optical information of the defect also enters the light receiver 15. Therefore, it is difficult to distinguish the defect from the pattern and detect only the defect. Similarly, even at the position 11C, which is conjugate with the surface 11 to be inspected, the original pattern and the defect are observed as a mixture, and therefore only the defect cannot be observed.

Therefore, the present invention is configured as shown in FIG. In FIG. 2 in which the same parts as those in FIG. 1 are denoted by the same reference numerals, the optical positional relationship among the surface 11 to be inspected, the light receiving lens 12, the pupil surface P1, the lens 14, the second pupil surface P2, and the light receiver 15 is illustrated. Same as 1. In FIG. 2, a light shielding plate 17 having an opening 16 is further provided in the pupil plane P1. At this time, when the relative position between the Fourier transform image 13F (see FIG. 1) of the pattern 13 formed on the pupil plane P1 and the aperture 16 is changed, the light spot in the Fourier transform image 13F does not exist in the aperture 16. In some cases, even if a light spot exists in the opening 16, the light amount of the light spot is weak. On the other hand, the scattered light generated from a defect such as a foreign substance existing on the surface 11 to be inspected is isotropically generated as described above, and thus the Fourier transform image 1
Even if the relative position between the 3F and the opening 16 is changed, the opening 16
The increase or decrease in the amount of scattered light that passes through is slight, or the amount of scattered light that passes through the opening 16 hardly changes. By utilizing this characteristic, only the defect is detected by distinguishing the defect from the pattern.

That is, at this time, the light passing through the aperture 16 is detected by the light receiver 15 at the pupil conjugate position. If the relative position between the Fourier transform image 13F and the aperture 16 is determined so that the photoelectric conversion signal S of the light receiver 15 becomes the smallest, then the light spot of the Fourier transform image 13F does not pass through the aperture 16 or if it passes through the aperture 16. Since the amount of light is small, relatively more optical information from the defect passes through the opening 16 than the Fourier transform image 13F. At this time, if the image of the surface 11 to be inspected is observed using the light that has passed through the opening 16 at the position 11C that is substantially conjugate with the surface 11 to be inspected, only the image of the defect can be observed. As the observation means, an image pickup means such as a charge-coupled image pickup device (CCD) may be used, or visual observation may be performed. The above is the principle of the present invention.

As described above, the relative position changing means for changing the relative position between the Fourier transform image 13F and the aperture 16 is roughly classified into two means. The first means is a driving means that moves the light shielding plate 17 in the plane of the pupil plane P1 to change the position of the opening 16. The second means is the incident vector of the light beam L, that is, the surface to be inspected 1 with the position of the opening 16 fixed.
The incident direction changing means changes the incident direction and the incident angle with respect to 1. The former will be described with reference to FIG. 3, and the latter will be described with reference to FIG.

FIG. 3A shows a state in which the pupil plane P1 shown in FIGS. 1 and 2 is viewed from a direction perpendicular to the pupil plane P1.
In (a), 13F is the Fourier transform image of the pattern 13 of FIG. 1, and the opening 16 is a part of the light shielding plate 17 of FIG. Aperture 1 for given origin PO on pupil plane P1
When the position vector representing the position of 6 is <C>, FIG.
The photoelectric conversion signal S of the light receiver 15 of the position vector <C>
Changes as shown in FIG. 3 (b). That is, when the light spot of the Fourier transform image 13F passes through the opening 16, the photoelectric conversion signal S becomes large, but otherwise, the defect information other than the pattern 13 passes through the opening 16, so that the photoelectric conversion signal S Is small.

Therefore, the photoelectric conversion signal S of FIG.
Minimum value S_minIt is possible to detect only defects by detecting
Wear. Specifically, a pair of thresholds S for a predetermined defect
_TH1And S_TH2(S_TH2> S_TH1> 0), and
Minimum position S of photoelectric conversion signal S of _minSatisfies the following equation
Is determined to have the defect. S_TH1≤ S_min≤ S_TH2 At this time, the minimum value S_minThe original surface 11
Pattern 13 has almost no effect, so that pattern
It is possible to detect only defects accurately without relying on
It

Next, a case where the incident vector of the light beam L changes will be described with reference to FIG. In FIG.
When the initial incident vector of the light beam L (vector of unit length parallel to the light beam L incident on the surface 11 to be inspected) is <e ₀ >, the 0th-order diffracted light of the pattern 13 is formed on the pupil plane P1. Spots 18 are formed. The position vector of the spot 18 with respect to the aperture 16 fixed on the pupil plane P1 is <C ₀ >.

Then, the surface to be inspected 1 of the incident light beam L
When the incident direction or the incident angle with respect to 1 is changed, the incident vector becomes <e '>. At this time, the 0th-order diffracted light on the pupil plane P1 becomes a spot 18 ', and the aperture 1 of the spot 18'
The position vector for 6 is <C '>, but <C ₀ >
≠ <C ′>. That is, as shown in FIG.
Since the position vector <C ₀ > changes in the same manner as when the position of is changed, it is possible to obtain only the optical information of the defect by changing the incident vector, that is, the incident direction.

In FIG. 2, when the surface 11 to be inspected is rotated, the pattern 13 on the surface 11 to be inspected on the pupil plane P1.
The Fourier transform image 13F of is rotated. Therefore, by rotating the surface 11 to be inspected, the position vector <C> in FIG. 3 also changes, and only optical information of the defect can be obtained. However, in practice, the opening 16 is not often provided in the region between the light spots that are the Fourier transform image of the original pattern 13 as shown in FIG. 3. For example, when the periodic pitch of the pattern 13 is large, the Fourier transform is performed. Since the distance between the light spots on the surface becomes smaller in inverse proportion to the pitch of the pattern 13, the light spots passing through the openings 16 are present.

Therefore, the size of the opening 16 also depends on the pattern 13.
It is desirable to change it according to the state of the surface 11 to be inspected such as the cycle pitch of the above. However, of course, the smaller the opening 16 is, the smaller the amount of light passing through the opening 16 is.
When the amount of light passing through 6 is minimized, the aperture 16
Becomes too small to observe the defect image. Therefore, in the present invention, after converting the amount of light passing through the opening 16 into the amount of light (illuminance) per unit area, the size and position of the opening 16 are determined so that this illuminance is minimized. However, if the opening 16 becomes too small, the resolution of the defect becomes too poor, so the lower limit of the area of the opening 16 is set.

In this case, one method for measuring the illuminance in the opening 16 is to collectively capture the Fourier transform images on the pupil plane (Fourier transform plane) P1 and calculate from the light quantity distribution of the Fourier transform images. This is to obtain the position and size of the opening when the illuminance becomes the smallest. Also,
Another method for measuring the illuminance in the opening 16 is to actually set the position and size of the opening 16 variously and measure the amount of light passing through the opening 16, respectively, It is to calculate the illuminance from the area.

Further, it is desirable that the opening 16 can be set to an arbitrary size by a mechanism like a variable diaphragm. However, if the size of the opening 16 is arbitrary, it may take a long time until the optimum size and position of the opening 16 are obtained. Therefore, the optimum size of the opening 16 may only be approximately calculated. In this case, a plurality of openings having a plurality of sizes may be prepared in advance, and one having the smallest illuminance may be selected from the plurality of openings.
This reduces the inspection time.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the defect inspection apparatus according to the present invention will be described below with reference to FIGS. FIG. 5 shows the configuration of the defect inspection apparatus of this embodiment. In FIG.
A pattern 101 such as a periodic circuit pattern is formed on the surface of a substrate 100 to be inspected, which is a reticle or a wafer. A defect of the pattern 101 or a foreign substance attached to the surface of the substrate 100 to be inspected is a detection target. Test board 100 is X
It is mounted on the Y stage 102. Test board 100
The XY stage 102 is configured to be movable in the X direction and the Y direction by driving units 103 and 104, respectively, with an orthogonal coordinate system of a plane parallel to the surface of the X axis and the Y axis.

A light beam 106 emitted from a light source 105 is applied to an observation visual field of a predetermined area surrounding a point Q on the surface of the substrate 100 to be inspected. The diffracted light generated from the pattern 101 in the observation field surrounding the point Q and the scattered light generated from the defect (not shown) in the observation field are received by the light receiving lens 1.
After being focused by 07, the light passes through a field stop 108 provided on a surface conjugate with the surface of the substrate 100 to be inspected. The diffracted light and scattered light after the unnecessary light (outside the irradiation region of the light beam 106 or outside the observation visual field) is blocked by the field stop 108 are further Fourier transformed by the lens 109, and the pupil plane (Fourier transform) of the lens 109 is obtained. Surface) to be inspected substrate 10
A Fourier transform pattern of the zero surface is formed.

Four light shields 110A, 110B, 110C and 110D are movably arranged on the pupil surface of the lens 109 or on a surface in the vicinity of the pupil surface, and the light shields 110A, 11A are provided.
Rectangular opening 11 surrounded by 0B, 110C and 110D
The light flux of the Fourier transform pattern passes through the inside of 2. In this case, the light blocking plates 110A and 110B are respectively provided in the driving unit 11
The light shielding plates 110C and 110D can be independently moved in the X direction by 1A and 111B, and the light shielding plates 110C and 110D can be independently moved in the X direction by the driving units 111C and 111D, respectively. That is, the light shielding plates 110A to 110D are translationally driven through the driving units 111A to 111D, thereby setting the position and size of the rectangular opening 112 on the pupil plane to arbitrary positions and arbitrary sizes, respectively. be able to. The vertices of this rectangular opening 112 are denoted by A, B,
As C and D, the length of a pair of sides AB and CD parallel to the X axis is defined as ΔX, and the length of a pair of sides BC and DA parallel to the Y axis is defined as ΔY.

Further, the lens 109 and the light blocking plates 110A-1
The half mirror 113 is provided between the half mirror 113 and 10D, and the light flux reflected by the half mirror 113 forms a Fourier transform pattern on the surface of the test substrate 100. On the surface on which the Fourier transform pattern is formed, an image pickup device (hereinafter referred to as "pupil plane image pickup device") including a two-dimensional CCD for a Fourier transform image monitor.
Image pickup surface 114. The image pickup surface of the pupil plane image pickup element 114 is provided at a position optically equivalent to the light shielding plates 110A to 110D, that is, on the pupil plane (Fourier transform plane) of the lens 109, and the image pickup plane of the pupil plane image pickup element 114 is the lens 109. The size is such that an image having a size similar to the pupil diameter, that is, an image in a range equivalent to the range in the X and Y directions in which the rectangular opening 112 is formed can be captured.

The pupil plane image pickup element 114 supplies an image pickup signal obtained by picking up a Fourier transform image of the surface of the substrate 100 to be inspected to the arithmetic section 130. As will be described later, the calculation unit 130 obtains the position and size of the opening when the illuminance becomes the smallest in the Fourier transform image, and the control unit 131 receives the information of the position and size of the opening, as described later. Supply.
However, a predetermined lower limit is set for the size of the opening. The control unit 131 translationally drives the light blocking plates 110A to 110D via the driving units 111A to 111D to set the position and size of the opening 112 to the position and size determined by the calculation unit 130.

Then, the light flux passing through the rectangular aperture 112 is subjected to inverse Fourier transform by the lens 115, and the substrate 1
An image of the defect is formed on a plane conjugate with the surface of 00. An image pickup surface of an observation image pickup element (hereinafter, referred to as “image plane image pickup element”) 116 including a two-dimensional CCD or the like is arranged on a surface conjugate with the surface of the substrate 100 to be inspected. An image of the defect is taken. In addition, the image plane imaging device 116
Alternatively, an eyepiece lens may be provided so that the image of the defect can be visually observed.

Next, the operation for inspecting the surface of the substrate 100 to be inspected for defects will be described. In this case, a periodic Fourier transform image 117 shown in FIG. 6, which is a Fourier transform pattern of the pattern 101 on the test substrate 100, is formed on the image pickup surface of the pupil plane image pickup element 114 of FIG. The pupil plane image sensor 114 converts the entire Fourier transform image 117 of FIG. 6 into an image pickup signal.

In the following, a method for calculating the amount of light (illuminance) per unit area in the opening 112 in the calculation unit 130 from the image pickup signal of the pupil plane image pickup device 114 and a method for optimally controlling the size and position of the opening 112 will be described. explain. Figure 6
Fourier transform image 117 imaged by the pupil plane image sensor 114
2 shows a two-dimensional pixel configuration of the Fourier transform image 117 in FIG. 6 and is composed of M rows × N columns of pixels 118. Then, the light amount data of the pixel at an arbitrary m row and n column position is represented by I (m, n).

In this case, the position and size of the rectangular pattern 119 composed of pixels from the nth column to the (n + i) th column and from the mth row to the (m + j) th row are set to the position and the size of the rectangular opening 112 of FIG. The amount of light per unit area in the pattern 119 indicated by the thick solid line is calculated in correspondence with the size.
The integrated value I _T of the light quantity in the pattern 119 is as follows, where Σ _{a is} the sum from 0 to j regarding the subscript a and Σ _b is the sum from 0 to i regarding the subscript b.

[0034] _{I T = Σ a Σ b I} (m + a, n + b) Accordingly, the width in the column direction of the pixels 118 Delta] p, and the width of the row direction and [Delta] q, per unit area within the pattern 119 The light quantity f (i, j, m, n) of the pixel is as follows on the pixel. f (i, j, m, n) = I T / {(i + 1) Δp · (j + 1) Δq} = {Σ a Σ b I (m + a, n + b)} / {(i +1) Δp · (j + 1) Δq} (1) However, the rectangular pattern 119 must surely be a single pattern in the Fourier transform image 117 including all pixels, so (1) An integer i greater than or equal to 0 in the formula,
j, m, and n need to satisfy the following conditions.

(N + i) ≦ N (2A) (m + j) ≦ M (2B) In actual processing, the Fourier transform image obtained when the surface of the substrate 100 to be inspected is irradiated with the light beam 106 is used as the pupil plane image pickup element 122. Then, the image is captured and stored as two-dimensional pixel data in the address of M rows × N columns of the storage unit (memory) in the arithmetic unit 130. Then, under the conditions of the expressions (2A) and (2B),
The values of the integers i, j, m, and n when the light quantity f (i, j, m, n) per unit area in the equation (1) becomes the minimum value are obtained. However, the integers i and j have lower limit values α and β determined according to the resolution of the defect to be detected, respectively.

After the values of the integers i, j, m, and n are determined in this way, the control unit 131 of FIG.
Through 111D, the light shielding plates 110A to 110D are translationally driven to set the position and size of the rectangular opening 112 to an integer i,
Set to the state corresponding to the values of j, m, and n. Specifically,
The vertices AP, BP, CP of the rectangular pattern 119 of FIG.
DP is respectively the vertices A, B, and A of the rectangular opening 112 of FIG.
Corresponding to C and D, the size of the Fourier transform image on the arrangement surface of the light shielding plates 110A to 110D and the pupil plane image pickup element 114
It is assumed that the size of the Fourier transform image on the image pickup surface of 1 is 1: 1 (same magnification). At this time, sides AP to BP or sides CP to D of the pattern 119 on the image pickup surface of the pupil plane image pickup device 114.
Pixel pitch in the P direction (column direction) is Δp, sides BP to C
Since the pixel pitch in the direction of P or in the direction of the sides DP to AP (row direction) is Δq, the width ΔX of the rectangular opening 112 in the X direction,
And the width ΔY in the Y direction is as follows.

ΔX = (i + 1) Δp (3A) ΔY = (j + 1) Δq (3B) and on the arrangement surface of the shading plates 110A to 110D of FIG. 5 corresponding to the pixels in the first row and first column of FIG. From the position n in the X direction
-Drive units 111A to 111D so that a rectangular opening 112 is formed at a position that is moved by Δp and m · Δq in the Y direction.
The light blocking plates 110A to 110D are moved via the.

In this state, the image pickup from the image plane image pickup device 116 is performed.
A monitor obtained by supplying the signal to a TV monitor (not shown).
On the monitor screen or visually with the eyepieces mentioned above
When observed, from the pattern 101 on the substrate 100 to be inspected
Only the defects can be inspected by removing the diffracted light of
It Next, as another processing method, the rectangular opening 11 of FIG.
The widths ΔX and ΔY indicating the size of 2 are, for example, a set of three stages.
Matching (ΔX₁, ΔY₁), (ΔX₂, ΔY₂), (ΔX ₃, Δ
Y₃). To do this,
In the above configuration, the control sequence of the drive units 111A to 111D is
To the size of one of these three combinations
Please limit the size of the opening 112 only.
Or you can prepare three types of rectangular openings in advance.
Therefore, it may be configured to be switchable or replaceable.

In this case, (ΔX ₁ , ΔY ₁ ), (ΔX ₂ , ΔY)
₂ ), corresponding to the size of the aperture of (ΔX ₃ , ΔY ₃ ), the integers i and j indicating the size of the pattern 119 on the pupil plane image sensor 114 of FIG. 6 are also three combinations (i ₁ , j ₁ ), (i
_{It is} only necessary to consider ( ₂ , j ₂ ), (i ₃ , j ₃ ). However, (ΔX _k , ΔY _k ) and (i _k , j _k ) are (k = 1 to 3),
_{ΔX k = (i k +1)} · Δp, are related by _{ΔY k = (j k +1)} · Δq. Under this condition, if the combination of the integers i and j when the expression (1) takes the minimum value and the values of the integers m and n are obtained, the position and size of the rectangular opening 112 are calculated. The time required to do this can be shortened.

Next, a second embodiment of the present invention will be described with reference to FIG. 7, the same members as those in FIG. 5 are designated by the same reference numerals, and detailed description thereof will be omitted. Figure 7
In the above, a plurality of (two types in FIG. 7) rectangular openings 121A and 121B having different sizes are provided on the Fourier transform surface of the lens 109 on the surface of the substrate 100 to be inspected or a surface in the vicinity thereof. The light shielding plate 120 is arranged. The light shielding plate 120 is supported by a drive unit 122 and a drive unit 123 so as to be freely driven in the Y direction and the X direction, respectively, and the drive unit 123 also serves to perform switching (moving in and out of the optical path) of the rectangular openings 121A and 121B. To do.

Further, a half mirror 124 is provided between the light shielding plate 120 and the lens 115, and the luminous flux reflected by the half mirror 124 is passed through the condenser lens 125 to the photoelectric detector 1.
The light is condensed on the light receiving surface of 26. As the photoelectric detector 126,
A silicon photodiode, a photomultiplier, or the like is used, and the photoelectric detector 126 photoelectrically converts the amount of light that is proportional to the amount of light that has passed through the rectangular opening 121A or 121B (opening 121A in the state of FIG. 7). The photoelectric signal is supplied to the arithmetic unit 132. Calculation unit 13
2 is also supplied with the information of the aperture 121A or 121B currently set on the Fourier transform pattern from the light shielding plate 120, and the calculation unit 132 calculates the illuminance of the light passing through the aperture 121A or 121B and causes the control unit 133 to calculate the illuminance. Supply. The controller 133 controls the opening 1 via the drivers 122 and 123.
The light shielding plate 120 is positioned so that the illuminance of the light flux passing through 21A or 121B is minimized. Other configurations are the same as those in FIG.

The operation in the case of performing the defect inspection of the surface of the substrate 100 to be inspected will be described with reference to FIG. First, the rectangular opening 12
With 1A entering the light flux (Fourier transform pattern) that has passed through the lens 109, the light shielding plate 120 is moved in the X direction and the Y direction on the pupil plane through the driving units 122 and 123, and the photoelectric detector 126 is used. XY coordinates of the light shielding plate 120 when the photoelectric signal (in proportion to the amount of received light) is minimized, and the XY coordinates are stored in a storage unit such as a memory inside the control unit 133.
The coordinates and the data of the amount of light per unit area at that time are stored. Then, the rectangular opening 12 is formed by the driving unit 123.
Light-shielding plate 12 so that 1B is included in the Fourier transform pattern
After 0 is largely moved in the X direction, exactly the same operation as in the case of the opening 121A is repeated to store the data in the storage unit inside the control unit 133.

If the area ratio between the openings 121A and 121B is 1: 4, the calculation unit 132 opens the openings 121.
The photoelectric signal of the photoelectric detector 126 at A and the opening 121
A value obtained by dividing the photoelectric signal of the photoelectric detector 126 in the case of B by a coefficient having a ratio of 1: 4 is obtained as light amount data per unit area. Therefore, the opening 121A,
121B determines which of the light amounts passing through the opening per unit area is small, and uses the data of the lower illuminance (that is, the XY coordinates of the light shielding plate 120) to switch to the opening of the lower illuminance. Set the position of 120.

In the arithmetic unit 133, instead of dividing the photoelectric signal of the photoelectric detector 126 by a coefficient determined by the aperture area ratio, for example, rectangular apertures 121A, 121.
In association with the switching operation of B, the transmittance of the filter plate 127 arranged in front of the photoelectric detector 126 may be switched by the driving unit 128 as shown in FIG. That is, the filter plate 127 is a combination of glass plates 129A and 129B having different transmittances in parallel, and when the area ratio of the rectangular openings 121A and 121B is 1: 4, the transmission of the glass plates 129A and 129B is reduced. The rates are 100% and 25%, respectively. When the opening 121A is in the optical path, the glass plate 129A
Is arranged immediately before the photoelectric detector 126, and the glass plate 129B is arranged immediately before the photoelectric detector 126 when the opening 121B is in the optical path. As a result, the photoelectric signal from the photoelectric detector 126 is transmitted to which of the openings 121A and 121A.
Even when B is used, the amount of light transmitted through the aperture per unit area is represented as it is, so that only a simple numerical comparison is required.

When this embodiment is further developed, a glass plate (filter) having the same transmittance as that of the glass plates 129A and 129B of FIG. 8 is directly attached to each of the rectangular openings 121A and 121B of FIG. That is, it can be seen that the amount of light passing through the large aperture may be reduced by a filter having a low transmittance by that area and received by the photoelectric detector 126. In this case, the calculation unit 1 of FIG.
32 can be omitted.

As described above, the present invention is not limited to the above-described embodiments, and various configurations can be adopted without departing from the gist of the present invention.

[0047]

According to the present invention, the illuminance measurement for measuring the illuminance of the light flux passing through the aperture, and the size and position of the aperture for removing the original periodic pattern light spot from the Fourier transform pattern. Since the optimization is performed according to the measurement result of the means, there is an advantage that only the defect can be detected without depending on the conditions such as the density and shape of the original pattern of the test object.

When the illuminance measuring means has an image pickup means for picking up a Fourier transform pattern and an arithmetic means for image-processing the image pickup signal from the image pickup means to calculate the illuminance of the light flux passing through the aperture. Since the number of mechanical operations is small, the aperture can be optimized at high speed. on the other hand,
The illuminance measuring means, photoelectric conversion means for photoelectrically converting the light flux passing through the opening, and an operation means for obtaining the illuminance of the light flux passing through the opening based on the area of the opening and the photoelectric conversion signal from the photoelectric conversion means. When it has, the actual illuminance can be accurately measured.

Further, when the size of the opening is set to an area selected from a plurality of areas set in advance, the opening can be optimized at a higher speed, although it is approximate.

[Brief description of drawings]

FIG. 1 is a perspective view for explaining the principle of defect detection of the present invention.

FIG. 2 is an explanatory diagram of a defect detection principle of the present invention, and is a perspective view showing a case where a light shielding plate having an opening is arranged on a pupil plane P1.

3A is a front view showing a positional relationship between an aperture 16 and a Fourier transform image 13F on the pupil plane P1, and FIG. 3B is a diagram showing a case where the positional relationship between the aperture 16 and the Fourier transform image 13F is changed. 5 is a waveform diagram showing an example of a change in photoelectric conversion signal S of the light receiver 15 of FIG.

FIG. 4 is an explanatory view of a defect detection principle of the present invention, and is a perspective view showing a case where the incident vector of the light beam L on the surface to be inspected changes.

FIG. 5 is a perspective view showing the configuration of the defect inspection apparatus according to the first embodiment of the present invention.

FIG. 6 is a diagram for explaining a method of processing image pickup data of the image pickup device 114 according to the first embodiment.

FIG. 7 is a perspective view showing a configuration of a second exemplary embodiment of the present invention.

FIG. 8 is a perspective view showing a main part of a modified example of the second embodiment.

FIG. 9 is a perspective view showing a configuration of a conventional defect inspection apparatus.

[Explanation of symbols]

 100 substrate to be inspected 101 pattern 102 XY stage 107 light receiving lens 108 field stop 109 lens for Fourier transform 110A to 110D light blocking plate 111A to 111D drive unit 112 aperture 113 half mirror 114 pupil surface image sensor 115 lens for inverse Fourier transform 116 image Area image sensor 126 Photoelectric detector

Claims (4)

[Claims] 1. A light irradiating means for irradiating a test object with inspection light, and a condensing optical system for condensing light from the test object. In a device for inspecting a defect of an inspection object, a first conversion optical system for Fourier-transforming light from the inspection object, and the inspection object on the Fourier transform surface of the inspection object by the first conversion optical system. Of the Fourier transform pattern of the relative positional relationship is variable, the aperture setting means for setting the aperture of the variable area, the illuminance measuring means for obtaining the light amount per unit area of the light flux passing through the opening, the area of the opening Under the condition that it is equal to or larger than a predetermined minimum area determined from the smallest defect to be detected, the light amount per unit area of the light flux passing through the opening is minimized through the opening setting means. Relative between the aperture and the Fourier transform pattern Control means for setting the positional relationship and the area of the aperture, a second conversion optical system for forming a conjugate image of the subject by performing an inverse Fourier transform on the light passing through the aperture, and a conjugate of the subject A defect inspection apparatus comprising: an observation means for observing an image. 2. The illuminance measuring means, an image pickup means for picking up a Fourier transform pattern of the object to be examined, and a relative positional relationship between the aperture and the Fourier transform pattern by processing an image pickup signal from the image pickup means. 2. The defect inspection apparatus according to claim 1, further comprising a calculation unit that calculates a light amount per unit area of a light flux that passes through each of the openings when the area of the opening is changed. 3. The illuminance measuring means uses the photoelectric conversion means for photoelectrically converting the light flux passing through the opening, the area of the opening set by the opening setting means, and the photoelectric conversion signal from the photoelectric conversion means. 2. The defect inspection apparatus according to claim 1, further comprising a calculation unit that obtains a light amount per unit area of a light flux passing through the opening. 4. The opening setting means sets the area of the opening to an area selected from a plurality of preset areas, and the control means sets the opening within the plurality of preset areas. The defect inspection apparatus according to claim 1, 2, or 3, wherein the area of the opening is set to an area at which a light amount per unit area of a passing light flux is minimized.