JP2018146239A - Defect inspection apparatus, and manufacturing method of defect inspection apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a defect inspection apparatus capable of stably exhibiting high defect detection power independent of defect directionality.SOLUTION: A defect inspection apparatus comprises an optical system 100 for defect inspection and illumination systems 31 and 32 for defect inspection. In the latter, ring illumination 31, 32 is constituted by a plurality of LEDs annularly arranged so that spot lights from a plurality of LEDs are gathered in an area centered on the focal position of the optical system 100. A ring illumination 31 installed on the side of the optical system 100 of the substrate 1 to be inspected and irradiated at an acute angle to the surface of the substrate 1 is a dark-field ring illumination 31 for reflection which is configured so that the reflected light does not directly enter the objective lens 11. A ring illumination 32 installed on the opposite side of the optical system 100 of the substrate 1 to be inspected and irradiated at an acute angle to the surface of the substrate 1 is a dark-field ring illumination 32 for transmission which prevents transmitted light transmitted through refraction inside the substrate 1 from directly entering the objective lens 11.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a defect inspection apparatus. In addition, the present invention is suitable for defect inspection of glass substrates, mask blanks (substrates with thin films), mask blanks with resists (substrates with resists), and the like, and is suitable for defect inspections of large substrates for display devices such as FPDs. About.

Usually, in a defect inspection apparatus, scattered light from a defect on the surface of a substrate or a defect in the glass is detected by illumination from a specific direction with a laser beam or the like.
For example, there is a defect inspection apparatus that irradiates a substrate surface with laser light and detects scattered light from defects on the substrate surface with a detection optical system.
Also, for example, a laser beam is irradiated (introduced) inside the glass substrate, and the entire area inside the glass is irradiated by repetition of total reflection inside the glass substrate, so that scattered light from defects on the surface of the glass substrate and defects inside the glass is emitted. There is a defect inspection device that detects with a detection optical system.

Japanese Patent No. 3422935

  For high-precision defect inspection, illumination that is not from a specific direction is essential. In the case of illumination from a specific direction, there is a possibility that a significant decrease in defect detection power may occur due to scratches having strong direction dependency. In high-accuracy defect inspection, a high defect detection capability for such defects such as scratches with strong direction dependency is desired.

  In addition, for thin-film defects of a type that generates little scattered light from the defects or very little scattered light, the inspection method that detects scattered light causes a significant decrease in defect detectability and inability to detect. there is a possibility. For example, there is a possibility that a significant decrease in defect detection power may occur for a half pinhole that does not have a clear edge and generates little scattered light. Further, for example, a gently curved depression (gradation) of a thin film cannot be detected because the generation of scattered light is extremely small. In high-accuracy defect inspection, a high defect detection capability is desired for such a type of thin film defect that generates little scattered light from the defect or generates very little scattered light.

  Furthermore, there is a problem of ensuring defect detection power for defects with low contrast such as thin scratches and white haze (white stain). In high-accuracy defect inspection, a high defect detection capability for these low-contrast defects is desired.

  In high-accuracy defect inspection, there are many types of defects with different scattered light characteristics as described above.

There is a problem that inspection time is required for highly accurate defect inspection. For example, in the detection of weak scattered light or the like, the inspection accuracy can be increased by increasing the sensitivity by increasing the exposure time (inspection time).
In high-precision defect inspection, a technique that does not sacrifice inspection speed (inspection time) is desired.

The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a defect inspection apparatus that can achieve a stable and high defect detection power that does not depend on the directionality of defects.
It is another object of the present invention to provide a defect inspection apparatus that can achieve a significant improvement in defect detection capability for a type of thin film defect that generates little scattered light from the defect or generates very little scattered light.
Furthermore, an object of the present invention is to provide a defect inspection apparatus that can achieve a high defect detection capability for defects with low contrast.

In order to solve the above-described problems, the present inventor has conducted earnest research and development. As a result, the application of ring illumination was examined. However, the ring illumination that is currently provided and the ring illumination that has been easily modified and improved can illuminate from various directions. However, even when applied to a defect inspection system, high defect detection power can be obtained. Therefore, it was found that the defect detection power was insufficient and the expected effect could not be obtained.
The present inventor has further conducted earnest research and development. As a result, we succeeded in developing a ring illumination that is much better than the ring illumination currently available. In addition, by using this exceptionally excellent ring illumination, it is possible to illuminate simultaneously from all directions of 360 °, and it is possible to detect defects independent of the directionality of the defects. Compared to the case of using ring illumination, it was found that the defect detection power was much more stable and the expected effect was obtained.

In addition to the above, in the present invention, both forward scattering and backward scattering are achieved by double-sided simultaneous dark field illumination (both reflection / transmission complex dark field ring illumination) including both reflection dark field ring illumination and transmission dark field ring illumination. Simultaneous detection is possible. Thereby, for example, it is possible to stably detect a defect of a type in which scattered light having bias in forward scattering or backward scattering is generated. For this reason, defect detection power improves compared with the case where either one of ring illumination is used.
In addition to this, the present invention can achieve a high defect detection power for defects with low contrast, such as thin scratches and white haze (white stain), by the configuration of the ring illumination and the double-sided dark field that are remarkably excellent.
In addition, when the reflective dark field ring illumination is compared with the transmission dark field ring illumination, the latter has higher defect detection power. This is because, from the scattering theory, in general, the forward scattering and the back scattering can provide higher intensity. Light that is incident from the back side of the substrate by the transmitted dark field ring illumination and transmitted through refraction becomes forward scattering.

The present inventor has found that a dent (concave part) of a film with very little generation of scattered light or a gently curved depression (gradation) of a thin film cannot be detected in a double-sided dark field because the generation of scattered light is extremely small. I found it. The present inventor has found that by using spot illumination from the back surface side, the indentation (concave portion) of the film that generates very little scattered light can be detected as a difference in transmittance. Furthermore, the present inventor uses a vertically transmissive illumination with good parallelism and high brightness (high illuminance) as spot illumination from the back side, so that the thin curved hollow of the thin film, which is particularly difficult to detect, is thin. It was ascertained that the location was seen as a difference in transmittance and that a stable and high defect detection capability could be exhibited against such defects.
In the present invention, the determination as to whether or not a defect is made is performed by differentiating the two-dimensional image, and leaving only a portion having a gradation of light and shade, and determining that portion as a defect. Even a thin film depression can be detected because the difference in brightness becomes a gradient of light and shade.
The same applies to thin film defects of a type that generate little scattered light from the defects or generate very little scattered light. For example, a significant improvement in defect detection can be achieved for half pinholes that do not have a clear edge and generate less scattered light, and dents (concaves) that generate less scattered light.

In the present invention, a configuration including both a reflection dark field ring illumination and a transmission dark field ring illumination (or a configuration in which spot illumination from the back side is further added) is used, and these illuminations are used simultaneously. It has been found that defects caused by (corresponding to) illumination can be detected at a time, and whether or not there is a defect can be efficiently inspected by one inspection. In the present invention, the above-mentioned different types of defects that are problematic in high-precision defect inspection can be detected at a time by one inspection. For this reason, the efficiency is high, and the total inspection time can be shortened as compared with the case of detecting different types of defects individually. In the present invention, it can be said that the inspection is highly accurate in that the types and number (opportunities) of defects that can be detected are relatively increased.
In the present invention, the greatest merit is that a defect can be inspected at high speed and with high accuracy. It is possible to inspect and introduce all methods capable of detecting any defect.

  The present invention has an effect of detecting a defect that cannot be detected over time. For example, scratches with strong direction dependence and gently curved depressions (gradations) of thin films are particularly good examples.

Note that an auto-focusing technology that maintains a focused (focused) state is different from a technology that performs illumination so that defects can be detected satisfactorily. No matter how good the illumination or its light source is, the performance you expect to be in a more out-of-focus condition is not possible. For this reason, it is most preferable to apply the ring illumination and the spot illumination from the back side according to the present invention in combination with the technique of continuously focusing (focusing) the focused position.
Further, in order to realize high-speed and high-precision inspection, a high-precision autofocusing technique is necessary, and a coaxial autofocus (AF) is a technique for doing so. Even if it is always in the state of focusing with coaxial AF, the expected effect cannot be obtained unless the illumination is excellent, so the ring illumination according to the present invention designed to obtain the expected effect and the back side Spot lighting is required.

The present invention has the following configuration.
(Configuration 1)
It has an optical system for defect inspection and an illumination system for defect inspection.
The illumination system is a ring illumination in which a plurality of LEDs are arranged in an annular shape, and spot lights from the plurality of LEDs are gathered in a region centered on a focal position of the optical system,
In the ring illumination installed on the optical system side of the substrate to be inspected, each of the spot lights from the plurality of LEDs is irradiated at an acute angle with respect to the substrate surface, and the reflected light is the objective lens Reflective dark field ring illumination configured to prevent direct entry into
The ring illumination installed on the opposite side of the substrate from the optical system, wherein each of the spot lights from the plurality of LEDs is irradiated at an acute angle with respect to the back surface of the substrate and transmitted through the substrate through refraction. A transmitted dark field ring illumination that prevents transmitted light from directly entering the objective lens;
A defect inspection apparatus comprising:

(Configuration 2)
It has an optical system for defect inspection and an illumination system for defect inspection.
The illumination system is a ring illumination in which a plurality of LEDs are arranged in an annular shape, and spot lights from the plurality of LEDs are gathered in a region centered on a focal position of the optical system,
In the ring illumination installed on the optical system side of the substrate to be inspected, each of the spot lights from the plurality of LEDs is irradiated at an acute angle with respect to the substrate surface, and the reflected light is the objective lens Reflective dark field ring illumination configured to prevent direct entry into
The ring illumination installed on the opposite side of the substrate from the optical system, wherein each of the spot lights from the plurality of LEDs is irradiated at an acute angle with respect to the back surface of the substrate and transmitted through the substrate through refraction. A transmitted dark field ring illumination that prevents transmitted light from directly entering the objective lens;
Illumination installed on the side of the substrate opposite to the optical system, and a spot illumination that is coaxial with the optical axis of the optical system;
A defect inspection apparatus comprising:

(Configuration 3)
3. The defect inspection apparatus according to Configuration 1 or 2, wherein an optical axis of the optical system and a central axis of a ring in the ring illumination are made coincident and coaxial.

(Configuration 4)
An imaging optical system including an objective lens, an imaging lens, and an imaging device;
The imaging device is a TDI sensor;
The imaging optical system includes a TDI camera,
Means for relatively moving the substrate and the TDI camera in a constant direction at a constant speed;
It has means for repeatedly exposing and photographing the imaging area by the number of vertical stages of the CCD by matching the moving direction and speed of the imaging area on the substrate with the charge transfer direction and speed of the CCD in the TDI sensor. The defect inspection apparatus according to any one of configurations 1 to 3.

(Configuration 5)
The defect inspection apparatus according to any one of configurations 1 to 4, wherein the defect inspection apparatus includes a high-precision imaging optical system having a focal likelihood smaller than ± 0.1 mm.

(Configuration 6)
Using the objective lens and using a laser beam to construct an autofocus means,
6. The defect inspection apparatus according to claim 4, further comprising means for avoiding reflection of the laser beam used for the autofocus means on the image pickup device.

(Configuration 7)
It has an optical system for defect inspection and an illumination system for defect inspection.
The illumination system is a ring illumination in which a plurality of LEDs are arranged in an annular shape, and spot lights from the plurality of LEDs are gathered in a region centered on a focal position of the optical system,
The ring illumination is installed on the optical system side of the substrate to be inspected,
The distance from the tip on the substrate side to the substrate surface in the ring illumination is the working distance d of the ring illumination,
Let the radius of the ring illumination be r,
From the viewpoint of mechanical size limitation, the range of d and r is defined,
When the light beam of the LED is incident on the substrate, an angle formed by the light beam and the substrate surface is set as an irradiation angle α of the ring illumination, and a dark field request is made so that illumination light does not enter the objective lens directly. From the viewpoint, the range of α is defined,
From the viewpoint that the irradiation density by the ring illumination is p, the viewpoint of increasing the irradiation density p and the upper limit of the irradiation angle α from the dark field requirement, the range of the p is defined,
Defect characterized by determining the values of d, r, and α from numerical formula d = rTan (α) determined from the positional relationship, taking irradiation density p into account, and manufacturing the device based on these values Manufacturing method of inspection device.

(Configuration 8)
It has an optical system for defect inspection and an illumination system for defect inspection.
The illumination system is a ring illumination in which a plurality of LEDs are arranged in an annular shape, and spot lights from the plurality of LEDs are gathered in a region centered on a focal position of the optical system,
The ring illumination is installed on the opposite side of the optical system of the substrate to be inspected,
The distance from the tip on the substrate side to the substrate back surface in the ring illumination is the working distance d of the ring illumination,
Let the radius of the ring illumination be r,
From the viewpoint of mechanical size limitation, the range of d and r is defined,
When the light beam of the LED is incident on the substrate, an angle formed by the light beam and the back surface of the substrate is an irradiation angle α of the ring illumination, and a dark field request is made so that illumination light does not enter the objective lens directly. From the viewpoint and from the viewpoint of the request for incidence near the Brewster angle, the range of α is defined,
From the viewpoint that the irradiation density due to the ring illumination is p, the upper limit of the irradiation angle α is limited by the viewpoint of increasing the irradiation density p and the dark field requirement and the incidence request in the vicinity of the Brewster angle. Define the scope,
The glass thickness is g,
Defect inspection apparatus characterized in that the values of d, r and α are determined from the following mathematical formula (3) determined from the positional relationship in consideration of the irradiation density p, and the apparatus is manufactured based on these values. Manufacturing method.

ADVANTAGE OF THE INVENTION According to this invention, the defect inspection apparatus which can achieve the stable high defect detection power independent of the directionality of a defect can be provided.
Furthermore, according to the present invention, it is possible to provide a defect inspection apparatus that can achieve a significant improvement in defect detection power for a thin film defect of a type that generates little scattered light from a defect or generates very little scattered light.
Furthermore, according to the present invention, it is possible to provide a defect inspection apparatus that can achieve a high defect detection capability for defects with low contrast.

It is a schematic diagram for demonstrating the principal part of the defect inspection apparatus of this invention. It is a schematic diagram for demonstrating ring illumination. It is a figure for demonstrating the housing of ring illumination. It is a figure for demonstrating the relational expression of the working distance d of ring illumination, the radius r of ring illumination, and the irradiation angle (alpha) of ring illumination. It is a figure for demonstrating the optimal design of surface side ring illumination. It is a figure for demonstrating the optimal design of back surface side ring illumination. It is a figure for demonstrating the XYZ drive system of the defect inspection apparatus of this invention. It is a schematic diagram for demonstrating the astigmatism method. It is a figure which shows the structure of a coaxial autofocus module. It is a figure for demonstrating the means to avoid the reflection to the imaging device of the laser beam used for an autofocus function.

FIG. 1 is a schematic diagram for explaining the main part of the defect inspection apparatus of the present invention.
In FIG. 1, the direction perpendicular to the paper surface is the X axis, the vertical direction of the paper surface is the Y axis, and the left and right direction of the paper surface is the Z axis.
An imaging optical system 100 is disposed on the surface side (right side of the drawing) of the inspection object 1. The imaging optical system 100 is configured to be driven in the X-axis, Y-axis, and Z-axis directions by XYZ driving means.
The imaging optical system 100 includes an objective lens 11, an imaging lens 12 and an imaging device 13 (for example, a TDI camera) 10, and an autofocus module (coaxial AF module) disposed between the objective lens and the imaging lens. 20 and illumination means 31. The illumination means 31 is attached to the objective lens 11.
An illumination system 101 having illumination means 32 and spot illumination means 33 is disposed on the back side (left side of the drawing) of the device under test 1. The illumination system 101 is configured to be integrated with the imaging optical system 100 (or integrated with complete synchronization) and can be driven in the X-axis, Y-axis, and Z-axis directions by XYZ driving means.

The illumination means 31 is ring illumination. In the ring illumination, a plurality of LEDs are arranged in an annular shape, and spot light from each of the plurality of LEDs is an area (image acquisition area, inspection area, imaging area) centered on the focal position of the imaging camera (for example, TDI camera) 10. ), The directivity and the optical axis of the plurality of LEDs are adjusted, and then fixed to an annular member. The ring illumination that is the illumination means 31 is coaxial with the center axis of the ring in the ring illumination and the optical axis O of the imaging optical system 100.
The ring illumination as the illumination means 31 has a configuration in which LEDs are arranged in a triple (three rows) in an annular shape along each of three concentric circles (see FIG. 2). Blue LEDs are used for the outer and inner LED rings, and yellow or orange LEDs are used for the middle LED rings. When inspecting a glass substrate and a mask blank (substrate with a thin film), all three rows (blue LED and yellow LED) are usually used. When inspecting a mask blank with a resist, the middle LED ring array (only yellow LED) is used. This is to avoid exposure of the resist.

On the back side (the left side in the drawing) of the device under test 1, there are illumination means 32 and spot illumination means 33.
The illumination means 32 is ring illumination.
The ring illumination as the illumination means 32 has a configuration in which LEDs are arranged in a triple (three rows) in an annular shape along each of three concentric circles (see FIG. 2). Blue LEDs are used for each of the outer, middle, and inner LED circles. When inspecting a glass substrate and a mask blank (a substrate with a thin film), all three rows (blue LEDs) are usually used. The ring illumination as the illumination means 32 is coaxial with the center axis of the ring in the ring illumination and the optical axis O of the imaging optical system 100.
As the spot illumination means 33, a transparent spot illumination (for example, a parallel light spotlight) is used, and a blue LED is used. The spot illumination means 33 is a pinhole in a mask blank (substrate with a thin film), a half pinhole that does not have a clear edge and generates less scattered light, a dent (concave portion) in a film that generates less scattered light, or scattering. It is effective for detecting gently curved depressions (gradations) in thin films that generate very little light. The spot illumination means 33 is coaxial with the center axis of the spot illumination (the optical axis of the LED) and the optical axis O of the imaging optical system 100.
The spot illuminating means 33 includes an aspect of vertical transmission illumination using a LED light source or a lamp light source having good parallelism and high luminance (high illuminance), a surface emitting light source, and the like.

In the present invention, the LED includes an aspect in which the LED is multiplexed in a single ring (one row), double (two rows), four (four rows) or more.
Further, the present invention includes a mode in which the center of the illumination area formed on the substrate by ring illumination does not coincide with the central axis of the ring in ring illumination (mode of eccentric illumination by ring illumination). .

  The working distance d (working distance: WD) of the ring illumination that is the illumination means 32 can be adjusted according to the plate thickness of the device under test 1. The working distance is the installation distance of the ring illumination with respect to the substrate surface, and more specifically the distance from the tip of the ring illumination on the substrate side to the substrate surface.

When inspecting the glass substrate, the illumination means 31 and the illumination means 32 are preferably used, and both of these illuminations are preferably used simultaneously. This is because defects caused by (corresponding to) both illuminations can be detected at a time, and it is possible to efficiently inspect whether there is a defect in one inspection. In the inspection of the glass substrate, optical defects such as scratches, foreign matter, foreign matter inside the glass and striae are detected.
When inspecting a mask blank (substrate with a thin film), it is preferable to use the illuminating means 31, the illuminating means 32, and the spot illuminating means 33, and it is preferable to use all of these illuminations simultaneously. This is because defects caused by (corresponding to) all the illuminations can be detected at a time, and it is possible to efficiently inspect whether there is a defect in one inspection. In the inspection of the mask blank (substrate with a thin film), pinholes, half pinholes, foreign matters, etc. are detected.
When the mask blank with resist is inspected, the middle LED ring array (only yellow LEDs) in the illumination means 31 is used. This is to avoid exposure of the resist. In the inspection of the mask blank with resist, in addition to the substrate defect, a resist pinhole, a resist half pinhole, and a foreign substance are detected.

  Examples of the inspection object 1 include a glass substrate, a mask blank (a substrate with a thin film), a mask blank with a resist, and the like. Examples of the mask blank include mask blanks used for manufacturing a binary mask, a gray tone mask (tone mask), a phase shift mask, and the like.

  The inspection of the mask blank includes an aspect of inspecting in a state of a single layer film, and an aspect of inspecting in a state of a two-layer film or a laminated film of three or more layers. In addition, the mask blank inspection includes an aspect of inspecting each time a film is formed in the case of a two-layer film or a laminated film of three or more layers.

The inspected object 1 includes a large substrate for a display device such as an FPD, and a medium / small substrate.
In the present invention, typical display devices (display devices) such as FPD (flat panel display) include liquid crystal display devices, plasma display devices, EL display devices, organic EL display devices, LED display devices, and DMD display devices. It is.

The light shielding mask 40 is inserted into the optical system as a countermeasure against stray light. The light shielding mask 40 cuts light (stray light) that does not contribute to the formation of a defect image. The light shielding mask 40 may be installed in a size suitable for a position suitable for stray light countermeasures while changing the size. The light shielding mask 40 may use a light shielding plate or a diaphragm.
For example, the light shielding mask 40 is disposed between the objective lens 11 and the imaging lens 12. The light shielding mask 40 is installed, for example, between the objective lens 11 and the inspection object 1, between the inspection object 1 and the illumination means 31, between the inspection object 1 and the illumination means 32, and the like. The light shielding mask 40 can be installed at all these locations, can be installed at any of these locations, and can be installed at any location on the optical path other than those described above.

In the present invention, the image pickup device 13 is typically a solid-state image pickup device such as a CCD, TDI, CMOS, or VMIS.
The gantry 200 is a vibration isolation table. The anti-vibration table has a function of locking the anti-vibration function. When the substrate is attached to and detached from the apparatus by the robot, the spatial position of the apparatus can be fixed by locking the anti-vibration function.

  Next, the LED illumination according to the present invention will be described.

In the ring illumination, the LED wavelength, LED spreading angle, LED diameter (dimension), LED irradiation angle, and the like are designed. These values are determined from the viewpoint of improving the defect detection power.
The wavelength of the LED is designed in the visible range, for example. For example, the wavelength of the LED is designed to be blue (465 nm), yellow (592 nm), orange (610 nm), and the like.
The LED spread angle can be selected from, for example, a narrow irradiation angle type (half-value angle ± 5 degrees), a normal type (half-value angle ± 20 degrees), a power LED type (half-value angle ± 60 degrees), and the like.
The diameter (dimension) of the LED is designed in a range of several mm, for example. For example, the diameter (size) of the LED is designed to have a narrow angle of 5.0 mm, an ultra narrow angle of 3.1 mm, or the like.
The irradiation angle of the LED is designed in a range of 10 degrees to 40 degrees, for example.

The housing of the ring illumination is designed with an inner diameter R1, an outer diameter R2, a thickness t, etc. (see FIG. 3). These values are determined from the viewpoint of improving the defect detection power. The housing of the ring illumination has an annular shape, and an inclined portion 35 for attaching the LED is formed on the inner peripheral surface of the annular shape. The housing dimension R3 (the thickness of the body) is designed in consideration of strength (see FIG. 3).
In the ring illumination housing, chamfering (not shown), light shielding plate mounting holes (not shown), and the like can be designed. These can be formed, for example, on the surface of the inclined portion 35 on the inspection substrate side.

In the ring illumination, the optical axis of each LED of the number determined by design is positioned (direction control is performed) and fixed to the housing. For example, each LED 37 is embedded in a flexible printed circuit board 36 attached to the inclined portion 35 on the inner peripheral surface of the housing 34 (see FIG. 3).
Since the directivity (expansion range) of the LED is larger than the positioning accuracy, the positioning accuracy may be adjusted in consideration of this.

In the present invention, the directivity characteristic (expansion range) of the LED differs depending on the diameter (size) of the LED. The diameter (size) of the LED itself is not a very important parameter, and it is preferable to design with a focus on the directivity.
For example, when the irradiation angle of the LED is an ultra narrow angle: ± 5.5 °, ± 4.0 °, etc., it is possible to control the light so as to shine only at the target position.
The diameter (size) of a narrow-angle or ultra-small-angle type LED is, for example, 5.5 mm and 3.8 mm, but when designed with an emphasis on directional characteristics, for example, a narrow angle of 5.0 mm or It is designed to have an ultra narrow angle of 3.1 mm.

  For example, when the diameter (size) of the LED is an ultra narrow angle of 3.1 mm, the LED elements are arranged in a close-packed manner and the pitch b is 4 mm (see FIG. 3). The number of LED elements arranged is approximately 120 elements. This makes it possible to illuminate simultaneously from all directions of 360 °.

  In the present invention, by combining the above-described various designs and various adjustments, the present inventors have succeeded in developing a ring illumination that is significantly superior to the ring illumination currently provided. This ring illumination is an illumination system capable of handling the next generation, the second generation, the third generation, and the subsequent generations. It was confirmed that this ring illumination had no problems with respect to heat generation problems, lifetime problems, and durability problems.

  In the present invention, an ideal arrangement of dark field illumination obtained from the light collection characteristics of the imaging optical system and the light emission characteristics of a plurality of LED elements serving as light sources is formulated. In the present invention, the optimum design has been successfully achieved due to mechanical size limitation and lighting efficiency.

  In the present invention, a limit range and an inequality are defined from three requirements (limitation factors), a mechanical requirement, a dark field requirement (optical requirement), and an efficiency requirement (irradiation density), and the LED design is determined. At this time, in consideration of ease of production, production cost, etc., the design of the LED is determined within the limits and inequality. Each value described below varies depending on the individual machine, but an example of each value will be described.

(Surface: Reflected dark field ring illumination)
The first point of the mechanical requirement (dimension limitation) is the working distance d (working distance: WD) of the ring illumination, which is the installation distance of the ring illumination with respect to the substrate surface, and more specifically the substrate side of the ring illumination. The distance from the tip of the substrate to the substrate surface. In order to ensure a clearance with the substrate holder, the working distance of ring illumination is d> 15 mm.
The second point of the mechanical requirement (size limitation) is the outer shape (radius) of the ring illumination. Since the arrangement pitch when three TDI cameras are continuously arranged in contact with each other is set to 130 mm, the outer shape of the ring illumination is limited to 128 mm. This is because when the imaging optical system equipped with ring illumination is scanned for inspection from end to end of the substrate, the outer peripheral portion of the ring illumination is disposed on the substrate holding mechanism (especially usually on the back side) of the substrate end. This is a requirement from the necessity of keeping the outer dimensions of the ring illumination within a predetermined range so that collision or contact with the rotary substrate holding unit) or the frame of the apparatus does not occur. The radius of the ring illumination is r <62 mm.

The dark field request (optical request) is the irradiation angle α of the ring illumination. The irradiation angle α of the ring illumination is an angle formed between the light beam and the substrate surface when the LED light beam is incident (irradiated) on the substrate. In dark field illumination, illumination light is prevented from entering the objective lens directly.
Realization of dark field illumination requires illumination design including an imaging lens system. Since a high numerical aperture (NA) lens is used as the imaging lens, it is necessary to irradiate the substrate surface with an acute angle for dark field illumination. Therefore, in order to ensure the working distance, it is necessary to increase the ring outer diameter. The upper limit of the irradiation angle α is determined by the magnification and NA of the objective lens in the imaging optical system. For example, when the magnification of the objective lens is 1 and the NA is 0.5, the upper limit of the irradiation angle α is 50 °. In order to reduce stray light, the upper limit of the irradiation angle α is preferably 30 ° or less from the viewpoint of setting the irradiation angle to a safer angle.

  The efficiency request is the irradiation density p by ring illumination. As the irradiation density is increased (the illumination is brightened), the defect detection time can be shortened and the inspection efficiency is increased. Therefore, the higher the irradiation density, the better. From the viewpoint of increasing the irradiation density, the larger the irradiation angle α, the better. However, the upper limit of the irradiation angle α is limited because of the dark field requirement. Thereby, the irradiation density p is also limited. From the viewpoint of the irradiation density p, the irradiation angle α is preferably 20 ° or more.

From the positional relationship shown in FIG. 4, in the surface side ring illumination, there is a relationship of d = rTan (α) (Equation 1). FIG. 5 (1) shows Formula 1. Since the irradiation density p is inversely proportional to the square of the distance from the LED light source, there is a relationship of (Equation 2) in FIG. This 3D graph is shown in FIG. These 3D graphs are superimposed and shown in FIG. In FIG. 5 (3), the dark color graph (curved surface) represents Equation 1, and the light color graph (curved surface) represents Equation 2.
From the 3D diagram of r, d, and α shown in FIG. 5 (3), considering the irradiation density p, considering the ease of production, production cost, etc., as shown in FIG. 5 (4), r: 54.0 mm , Α: 25.5 °, d: 25.0 mm.
In order to maintain the dark field requirement in the surface-side reflection ring illumination, the reflection ring illumination needs to be interlocked with the objective lens.

(Back side: Transparent dark field ring illumination)
In the transmission side ring illumination on the back side, the relational expressions (inequality) of the mechanical requirement, dark field requirement (optical requirement) and efficiency requirement (irradiation density) are the same as the above-mentioned reflection side ring illumination. .
In the transmission ring illumination, the formula of d is different from the reflection ring illumination in that the thickness g of the glass and the refracted light from the back surface are different, and thus the formula of d also changes. From the positional relationship shown in FIG. 4, the transmission ring illumination has the relationship of (Equation 3) in FIG. This 3D graph is shown in FIG. In FIG. 6 (2), the dark color graph (curved surface) represents Formula 3, and the light color graph (curved surface) represents Formula 2. FIG. 6 (3) is an enlarged view of FIG. 6 (2).
In transmitted illumination, a request for incidence near the Brewster angle, that is, a request for α: 33.0 ° is added. The Brewster angle is an incident angle at which the reflectance of P-polarized light becomes zero. By utilizing the Brewster angle phenomenon, the reflection loss for effective illumination reaching the glass surface can be made extremely small.
From the 3D diagram of r, d, and α shown in FIG. 6 (2), taking into account the irradiation density p, the ease of production, production costs, etc. are taken into consideration, and as shown in FIG. 6 (3), r: 50.0 mm , Α: 33.0 °, d: 20.0 mm.
It should be noted that the transmission-side dark field ring illumination on the back side needs to be interlocked with the magnification of the imaging lens. Due to the necessity of such interlocking, a transmission dark field by back side illumination is not common in a microscope or the like. For the same reason, there is no example of both the reflection and transmission simultaneous dark fields.

In the present invention, based on the values determined in the above design (with some numerical changes), for example, the surface side (reflective side) ring illumination has an irradiation angle α of 25 °, an outer diameter R2 of the housing of 128 mm, The final design is such that the thickness t is 22 mm or 20 mm.
The back side (transmission side) ring illumination is finally designed such that the irradiation angle α is 31 °, the outer diameter R2 of the housing is 125 mm, and the thickness t of the housing is 22 mm or 19 mm.

  In the present invention, the working distance d (working distance: WD) of the ring illumination is changed to, for example, 18 mm, 20 mm, 22 mm, 25 mm, 27 mm, etc., for the above-described specific surface side reflection dark field ring illumination. The optimum working distance d of the ring illumination can be obtained by examining the luminance distribution (the brighter the better) and the light amount profile (the flatter the higher the light amount) in the illumination area having a radius on the substrate. . Thereby, uniform illumination can be created within the field of view of the imaging camera. The same applies to the transmission dark field ring illumination on the back side.

In the present invention, as can be seen from FIG. 3, an illumination area having a certain radius on the substrate is formed by a collection of spot lights by a plurality of LEDs. This is the same as a spotlight, and only the spot-struck part is illuminated brightly, and the surrounding area is not illuminated and becomes dark. The same applies to a collection of spot lights by a plurality of LEDs (a spot light collection area formed by overlapping a plurality of spot lights).
In the present invention, it is preferable that the radius of the illumination area formed on the substrate by the collection of spot lights by the plurality of LEDs is in the range of, for example, 1 mm to 20 mm (for example, 10 mm). This range preferably corresponds to an area (image acquisition area, inspection area, imaging area) centered on the focal position of the imaging camera (eg, TDI camera).

In the present invention, a region (image acquisition region, inspection region, imaging region) centered on the focal position of an imaging camera (for example, a TDI camera) is relatively narrowed in order to increase inspection accuracy (imaging). Correspondingly, the radius of the illumination area formed on the substrate by the collection of spot light from a plurality of LEDs is also made relatively small. Can continue.
For example, by making the inclined portion 35 on the inner peripheral surface of the housing 34 a curved surface (or a part of a polygon inscribed in a circle that approximates the curved surface) that improves the light collection characteristics, the radius of the illumination area is also relatively Can be made narrower.
Furthermore, the inclined portion 35 on the inner peripheral surface of the housing 34 is inscribed in a curved surface having a condensing characteristic or a circle that approximates the curved surface so that spot light from a plurality of LEDs overlaps at almost one point (one spot region). It can also be part of a polygon.

In the present invention, the working distance d (working distance: WD) of the ring illumination is configured to be finely adjustable. For example, when assembling the apparatus, it has a fine adjustment mechanism that is first fixed at a determined value and finely adjusted (for example, finely adjusted in units of ± 1 mm) and fixed. The fine adjustment mechanism is also used during use of the device. In these cases, adjustment is made so that the illumination effect is maximized. The illumination effect is good when the illuminance is uniform within the field of view and the irradiation density is high (bright). In particular, it is preferable that the illuminance is uniform and the irradiation density is high (bright) within the range of the field of view of TDI (field of view corresponding to the longitudinal direction of TDI).
The working distance d of the ring illumination is naturally determined at the optimum position on the front side (reflection side) in combination with the imaging lens, but on the back side (transmission side), the glass thickness (for example, 8 mm to 13.5 mm) is set. Since the optimal position changes accordingly, the mechanism can change dynamically on the stage.

In the present invention, as a countermeasure against stray light, a light shielding mask for cutting illumination light that does not contribute to image formation may be provided on the front surface side (reflection side) ring illumination and the back surface side (transmission side) ring illumination.
As for the stray light by the illumination system, the stray light reflected from the substrate is considered in the surface side (reflection side) ring illumination. In the back side (transmission side) ring illumination, the reflected light on the back side of the substrate is considered, the refraction inside the glass substrate is taken into consideration, and the stray light of the transmitted light from the inside of the glass substrate is taken into consideration.

  The defect inspection apparatus of the present invention preferably uses a TDI camera.

The defect inspection apparatus of the present invention has an imaging optical system including an objective lens, an imaging lens, and an imaging device, the imaging device is a TDI sensor, and the imaging optical system includes a TDI camera,
Means for relatively moving the substrate and the TDI camera in a constant direction at a constant speed;
By matching the moving direction and speed of the imaging area (imaging object) on the substrate with the charge transfer direction and speed of the CCD in the TDI sensor, the imaging area (imaging object) is repeated by the number of CCD vertical stages. It is preferable to have means for exposing and photographing.
Here, by combining the moving direction and speed of the imaging area on the substrate with the charge transfer direction and speed of the CCD in the TDI sensor, means for repeatedly exposing and imaging the imaging area by the number of CCD vertical stages is, for example, It can be performed by a control device (control circuit, CPU, software, etc.) built in the TDI camera.

A normal line sensor has CCDs arranged in a line. In a TDI (Time Delay Integration) sensor (element), a plurality of CCDs (one row) arranged on a line are arranged in a direction perpendicular to the direction along the line. By performing integral exposure on images obtained by a plurality of rows of CCDs, an image with high sensitivity can be obtained.
If the object to be imaged moves at a constant speed and in a certain direction, the object (one column's worth) corresponds to the number of vertical stages of the CCD by combining the moving direction / speed of the object to be imaged and the direction / speed of charge transfer of the CCD. The same area on the object corresponding to the CCD) is repeatedly exposed and photographed.
The image obtained by the first row CCD is transferred to the second row CCD as it is. In the CCD in the second row, the image obtained from the CCD in the second row is added to the image picked up from the previous row, accumulated, and further transferred to the CCD in the third row. In the CCD in the n-th column, the image obtained by the CCD in the n-th column is added to the images accumulated up to the (n−1) th column and transferred to the (n + 1) th column. That is, in a TDI sensor in which x rows of CCDs are arranged, the obtained imaging is accumulated x times. When performing integral exposure of x rows, it is possible to expect x times the light amount and noise reduction of √x (root x).
As a result, remarkably high sensitivity can be obtained, and both high speed and high sensitivity can be achieved.
With a conventional CCD, only a low-brightness image with insufficient sensitivity due to its high resolution can be obtained. However, by performing integral exposure, a bright and clear image can be obtained with high resolution. Compared to the conventional method in which the moving speed of the object to be photographed is reduced or stopped in order to compensate for the lack of brightness, processing can be performed at high speed and in a short time.
In TDI, not only the camera technology but also the nature of shooting an object while moving. Total solution power including optical technology and transport technology is required.

  TDI can perform panning like a copier. Unlike a normal area sensor, it is not a step-and-repeat method that repeats the steps of imaging a certain area in a stopped state, moving to an adjacent area, and imaging in a stopped state. With TDI, the total throughput can be 3 to 4 times. In the step-and-repeat method, driving and stopping (acceleration and deceleration) of the heavy imaging optical system are repeated at high speed, so that vibration occurs. However, in TDI, such vibration is difficult to occur.

The TDI sensor is, for example, vertically long (24 mm × 1.5 mm (128 steps)) and 1.5 mm wide.
The present invention is also applicable to line sensors. The line sensor can perform panning like the TDI. The TDI sensor has 128 stages and can take 128 times the amount of light as the line sensor. The inspection speed can be increased 128 times as much as the amount of light can be taken.
In the case of a CCD area sensor, for example, it is 15 mm square. Panning is not possible. The sensitivity is not good.
In the present invention, a TDI sensor is preferred. In line sensors and area sensors, it is difficult to inspect defects for two generations ahead.

FIG. 7 is a diagram for explaining an XYZ drive system and the like of the defect inspection apparatus of the present invention. (Holding means) (not shown, will be described later) for mounting and fixing an object (substrate) 1 to be inspected for defect inspection vertically in a main body frame 201 installed on the gantry 200; A head unit 300 including an imaging optical system 100 (an optical system for performing defect inspection) and an observation optical system (an optical system for performing magnified observation of defects), and for moving the head unit 300 in three directions XYZ The X-axis, Y-axis, and Z-axis stages 211, 212, and 213 are arranged.
The X-axis stage 211 drives the head unit 300 in the X-axis direction by moving the Y-axis stage 212 in the X-axis direction (left and right direction on the paper surface).
The Y-axis stage 212 drives the head unit 300 in the Y-axis direction by moving the Z-axis stage 213 in the Y-axis direction (vertical direction on the paper surface).
The Z-axis stage 213 drives the head unit 300 in the Z-axis direction by moving the head unit 300 in the Z-axis direction (direction perpendicular to the paper surface).

In the defect inspection apparatus of the present invention, in the head unit 300, for example, three TDI cameras are preferably arranged in contact with each other continuously, for example, in the Y-axis direction of FIG. Thereby, it is possible to scan (scan) with three (triple) TDI cameras in the X-axis direction, and to inspect the region for three at a time. Compared to a single TDI camera, the inspection speed is three times (the inspection time is 1/3). The number of TDI cameras can be appropriately increased or decreased to an arbitrary number.
In the apparatus of the present invention, in the head unit 300, for example, a TDI camera and an observation optical system (microscope) can be arranged adjacent to each other in the X-axis direction of FIG.

  Each of the X-axis, Y-axis, and Z-axis stages 211, 212, and 213 preferably has a linear lock mechanism that acts on a moving direction during scanning by an imaging optical system (for example, a TDI camera). This is a mechanism for high-precision observation, and when an image is viewed with a microscope, the image is shaken if very fine vibration remains. Therefore, the very fine vibration is eliminated by locking the stage.

In the apparatus of the present invention, it is preferable to employ a material having high rigidity for the base (base) of the main body. The gantry preferably has a vibration isolation function that reduces the influence of vibration.
In the apparatus of the present invention, it is preferable that the inspection object (substrate) 1 is fixed and the defect inspection is performed by moving the imaging optical system 100 to a desired position on the inspection object (substrate) 1. In the case of a structure in which the object to be inspected (substrate) 1 is moved, a corresponding movement space is required. In addition, since the object to be inspected (substrate) 1 is very heavy, vibration tends to occur when the object to be inspected (substrate) 1 is moved, reversed, or stopped.

  In addition, the observation optical system and the imaging optical system 100 include an illumination device for illuminating the defect position and its periphery during the defect inspection. Defects such as actual foreign matter defects and scratches may be difficult to observe depending on the type of illumination due to their shape and material, so the illumination is reflected epiaxial illumination, reflective dark field ring illumination, differential interference Equipped with illumination, transmission illumination (for example, coaxial vertical transmission illumination) and transmission dark field ring illumination, and color filters and polarization filters to change the quality of light so that various defects can be observed more clearly It is desirable to equip.

Further, in the observation optical system and the imaging optical system 100, in order to carry out defect inspection with a good field of view in which the focus is correctly adjusted, the distance between the inspection object (substrate) 1 and the lens tip is kept constant. It is desirable to provide a focusing means. For example, types of autofocus include those using laser reflection and those using image contrast on the focus surface. However, in the case of the object to be inspected (substrate) 1, there is no portion having contrast. Therefore, those utilizing laser reflection are preferred for the present invention.
In the autofocus means, a knife edge method or the like can be used in addition to the astigmatism method.

In addition, an observation optical system (not shown, provided in the head unit 300) for observing a defective part, for example, a low-magnification lens for grasping a rough position of the defective part, and a micro defect are observed. And high-power lenses and some medium-power lenses that are used in between. For these optical lenses, a method of switching a plurality of single lenses using a revolver or the like is suitable.
In the present invention, it is preferable that the optical lens used in the optical system has a working distance as long as possible in the space between the optical system and the object to be inspected (substrate) 1. A working distance (lens working distance) of at least several mm, preferably 4 mm or more is preferable.

  The wavelength of the light source used in the illumination device in the observation optical system is preferably in the range of 380 to 800 nm. When light in the ultraviolet region having a wavelength smaller than 380 nm is included, an optical component corresponding to the ultraviolet region is required, which is expensive. In addition, if infrared light greater than 800 nm is included, it has heat, and there is a risk of adversely affecting the object to be inspected and the observation apparatus. The wavelength of the light source is more preferably 400 to 750 nm from the same viewpoint. The wavelength band is preferably selected by providing a wavelength filter in the light source device.

  In addition, when it is desired to further select the wavelength or wavelength band of light due to the fact that the defect may be easily manifested depending on the type of defect depending on the wavelength or wavelength band to be used, or between the light source and the object to be inspected, or A wavelength filter may be provided between the object to be inspected and the observation apparatus.

  By using a light source having good parallelism as the light source, it becomes possible to make defects appear more stable. In addition, by using a light source with high brightness (high illuminance), the amount of light received by the light receiving optical system increases, so that the size of the pinhole that can be observed is expanded. In addition, observable defects extend to defects such as half pin holes and thin film recesses.

  The present invention is suitable for a defect inspection apparatus including a high-precision imaging optical system. This is because high-precision defect inspection requires inspection with a high-precision imaging optical system. The defect inspection apparatus of the present invention is suitable for a defect inspection apparatus including a high-precision imaging optical system with a focus likelihood smaller than ± 0.1 mm, and a high-precision imaging optical system with a focus likelihood smaller than ± 0.05 mm. Suitable for a defect inspection apparatus including a high-precision imaging optical system having a focus likelihood smaller than ± 0.03 mm, and a high-precision imaging optical system having a focus likelihood smaller than ± 0.02 mm Suitable for defect inspection equipment with

  For high-precision defect inspection, high-precision focus adjustment is essential. Large substrates are difficult to hold vertically with high accuracy, and a tilt of about 0.05 ° occurs. This inclination is shifted by about 0.9 mm when the length is 1000 mm. If the optical axis of the laser displacement meter and the imaging optical system are 100 mm apart, a measurement error of about 0.09 mm occurs. In a high-precision imaging optical system, the focus likelihood is about ± 0.03 mm, so it is possible to acquire an image in a defocused state (a state where the focus likelihood is exceeded), which can cause a significant decrease in defect detection power. There is sex. This problem can be addressed with the autofocus function described below.

  The defect inspection apparatus of the present invention preferably has an autofocus function using an astigmatism method.

FIG. 8 is a schematic diagram for explaining the astigmatism method.
In the astigmatism method, a cylindrical lens (cylindrical lens, kamaboko-shaped lens) is generally used. When a cylindrical lens is inserted in the return optical path reflected to the surface of the inspected object 1 and returned to the quadrant photodetector (PD), the cylindrical lens has a lens effect only in the X-axis direction in the figure, and thus the focal position in the X-axis direction. Astigmatism occurs due to a shift of the focal position in the Y-axis direction, and the shape of the beam changes as 1 (vertically long ellipse) → 2 (circular) → 3 (laterally long ellipse) depending on the distance on the optical axis ( (Upper view of FIG. 8).
Here, when the beam is received by the photodetector divided into four parts A, B, C, and D clockwise from above, the balance of the incident light amounts A to D changes in each of cases 1 to 3.
In the case of 1, the incident light amounts of A and C are large (the diagram below 1 in FIG. 8).
In case of 2, A. B. C. The four incident light amounts of D are equal.
In the case of 3, the incident light amounts of B and D are large.

If the optical system is adjusted so that the four incident light amounts are equal and the beam shape is circular when the surface of the inspection object 1 is in focus, (A + C)-(B + D ), The position of the imaging optical system 100 is controlled so that (A + C)-(B + D) = 0, so that the laser beam is always focused on the surface of the inspection object 1. Can keep. (A + C)-(B + D) is referred to as a focus error signal (FE). The position of the imaging optical system 100 can be moved by a drive mechanism (for example, a linear motor stage), and can be controlled at high speed and accurately.
When FE> 0, the focus is shifted toward the front (the object to be inspected 1 is close).
When FE = 0, the focus is in focus (focusing).
In the case of FE <0, the focus is shifted to the back side (inspection object 1 is far).

FIG. 9 is a diagram showing the configuration of the coaxial autofocus module.
The coaxial autofocus module includes a laser light source (laser diode) 21, a diaphragm 22, a polarizing beam splitter (PBS) 23, a ¼ wavelength plate 24, a reflecting element (prism mirror) 25, a condenser lens 26, a cylindrical lens 27, 4. A split photo detector (light detector) 28 is used.

  A laser beam emitted from a laser light source (laser diode) 21 is incident on a polarization beam splitter (PBS) 23 through a diaphragm 22, and the transmitted light is transmitted through a quarter-wave plate 24 to be reflected by a reflection element ( Is incident on the prism mirror) 25, reflected by the reflecting element (prism mirror) 25, transmitted through the objective lens 11 along the optical axis O of the imaging optical system 100, incident on the surface of the object 1 to be inspected, and reflected. Is done. The reflected light passes through the objective lens 11 along the optical axis O of the imaging optical system 100 and enters the reflecting element (prism mirror) 25. The reflected light passes through the quarter-wave plate 24, The light enters the polarization beam splitter (PBS) 23, and the reflected light sequentially passes through the condenser lens 26 and the cylindrical lens 27 and enters the quadrant photodetector 28.

The present invention provides a defect inspection apparatus that has an autofocus function using an astigmatism method coaxial with an imaging optical system and avoids reflection of a laser beam (reference light) used for the autofocus function on an image sensor. It is preferable to apply.
FIG. 10 is a diagram for explaining means for avoiding the reflection of the laser beam used for the autofocus function on the image sensor.
Specifically, FIG. 10A shows the positional relationship between the image acquisition region on the substrate to be inspected by the imaging optical system (objective lens) of the imaging camera (for example, TDI camera) and the spot of the laser beam on the substrate to be inspected. It is a figure for demonstrating. FIG. 10 (1) is a view of the image acquisition region as viewed from the front (viewed through the objective lens).
FIG. 10 (2) shows an image sensor (for example, TDI sensor) region on a light receiving plane including an image sensor (for example, a TDI sensor) and a laser beam reflected by a substrate to be inspected, and the reflected light passes through an imaging optical system. FIG. 6 is a diagram for explaining a positional relationship with a position where an image is formed on a light receiving plane including an imaging element (for example, a TDI sensor). FIG. 10B is a view of the light receiving plane as seen from the back.
The TDI sensor has CCDs arranged in a row in the horizontal direction and a plurality of CCDs arranged in the vertical direction. By performing integral exposure on images obtained by a plurality of rows of CCDs, an image with high sensitivity can be obtained.

As shown in FIG. 10, there is an image acquisition area A on the inspected substrate captured by the objective lens (FIG. 10 (1)) and a corresponding area B projected by the imaging lens (FIG. 10 (2)). )). These regions are regions of the visual field of the imaging optical system 100.
In the present invention, as shown in FIG. 10 (2), an image sensor T that uses a part of the region B projected by the imaging lens is used.
In the present invention, as shown in FIG. 10 (1), the laser beam is applied to a region excluding the image acquisition region T ′ corresponding to the imaging element in the image acquisition region A on the inspected substrate captured by the objective lens. The spot S is positioned. Thereby, as shown in FIG. 10B, the image S ′ of the spot of the laser beam is positioned in the region excluding the image sensor T.
Thus, for example, as shown in FIG. 10A, the position of the laser beam spot S (condensing position of the laser beam) is slightly shifted from the optical axis O (on the surface of the image acquisition region A). ) To avoid the reflection of the image S ′ of the laser beam spot on the image sensor T.

For this purpose, for example, in the coaxial autofocus module shown in FIG. 9, the laser light source (laser diode) 21 or the reflecting element (prism mirror) 25 is slightly tilted from the state where the laser beam passes through the optical axis O. .
Note that “slightly” means that the spot image S ′ of the laser beam can be prevented from being reflected on the image sensor T. The laser beam spot image S ′ is enlarged in accordance with the focus shift, so that it is possible to avoid reflection on the image sensor and influence on the image sensor (for example, noise). . In addition, the image S ′ of the laser beam spot changes depending on the position where the laser light source (laser diode) is placed and the thickness of the laser light source (beam diameter). The arrangement of the laser light source (laser diode) and the diaphragm 22 are adjusted so as to avoid reflection and influence (for example, noise) on the image sensor.

In the present invention, a high defect detection power can be obtained due to a synergistic effect such as application of the illumination system according to the present invention, application of a high NA optical system, application of a TDI camera, and application of real-time autofocus.
In the present invention, as described above, by using ring illumination that is remarkably excellent, it is possible to illuminate simultaneously from all directions of 360 ° and in addition to enable defect detection independent of the directionality of defects, Compared to the case where the ring illumination currently provided is used, the defect detection power that is remarkably stable can be exhibited, and the expected effect can be obtained.
In the present invention, by using a high-precision imaging optical system (high NA, bright and high resolution, and minimum focus likelihood), the accuracy of defect detection is high compared to the case where such an optical system is not used. It is highly accurate in that the detectable defect size is relatively small.
Furthermore, in the present invention, it is possible to cope with high-sensitivity inspection by applying a TDI camera. In addition, the present invention can cope with high-sensitivity inspection by applying extremely accurate focus adjustment at the image acquisition position.
In the present invention, the accuracy of a two-dimensional image produced by the TDI sensor is improved by acquiring data with the TDI sensor while always focusing while illuminating with the illumination system according to the present invention. Thereby, it is possible to further improve the accuracy of defect detection.
Further, in the present invention, it is possible to cope with high-speed inspection by applying a TDI camera. In addition, in the present invention, high-speed inspection can be supported by real-time autofocus control.
The present invention eliminates the above-described focus likelihood problem in an inspection using a high-precision imaging optical system (high NA, bright and high resolution, and minimal focus likelihood). The accuracy of defect detection is higher than when the system is used but the real-time autofocus of the present invention is not used (in this case, focus may not be achieved due to the above-mentioned focus likelihood problem).
In the present invention, by applying real-time autofocus, extremely accurate focus adjustment at an image acquisition position is possible, and stable high defect detection power independent of the substrate posture can be exhibited.

Hereinafter, the present invention will be described more specifically with reference to examples.
Example 1
[Manufacture of defect inspection equipment]

The coaxial autofocus module shown in FIG. 9 is incorporated into the defect inspection apparatus shown in FIG. 1 using a TDI camera with a focus likelihood of ± 0.02 mm. The magnification of the objective lens of the TDI camera was 1 and the NA was 0.3.
The inclination of the substrate is 0.05 degrees in the X-axis direction of FIG. 1, and if it is 100 mm apart in the X-axis direction of FIG. 1, a deviation of about 0.09 mm in the Z-axis direction occurs. The scanning direction of the TDI camera is the X-axis direction.

  The illumination means is the ring illumination that is the illumination means 31 and the illumination means 32 described with reference to FIG. 2, and the dark field ring illumination with reflection on the front side described with reference to FIG. 5 and the transmission darkness with the back side described with reference to FIG. 6. All of the field ring illumination and the spot illumination means 33 described in FIG.

The reflection dark field ring illumination (surface side) which is the illumination means 31 has a configuration in which LEDs are arranged in an annular form (three rows) along each of three concentric circles (see FIG. 2). . The outer and inner LED ring arrays used blue LEDs (wavelength 465 nm), and the middle LED ring array used orange LEDs (wavelength 610 nm).
The diameter (size) of the LED was set to an ultra narrow angle of 3.1 mm. The number of LED elements arranged was 120 elements.
The housing shown in FIG. 3 was used. The irradiation angle α was 25 ° (dark field illumination), the housing outer diameter R2 was 128 mm, and the housing thickness t was 20 mm.
The working distance d of the reflection dark field ring illumination (surface side) which is the illumination means 31 was 25.0 mm. The working distance d is a distance from the tip of the LED lighting on the substrate side to the substrate surface.

The transmission dark field ring illumination (rear surface side) as the illumination means 32 has a configuration in which LEDs are arranged in an annular form (three rows) along each of three concentric circles (see FIG. 2). . Blue LEDs (wavelength 465 nm) were all used for the outer, middle, and inner LED ring arrays.
The diameter (size) of the LED was set to an ultra narrow angle of 3.1 mm. The number of LED elements arranged was 120 elements.
The housing shown in FIG. 3 was used. The irradiation angle α was 31 ° (dark field illumination), the housing outer diameter R2 was 125 mm, and the housing thickness t was 19 mm.
The working distance d of the transmission dark field ring illumination (back side) as the illumination means 32 was set to 20.0 mm. The working distance d is a distance from the tip of the LED lighting on the substrate side to the substrate surface.

  As the spot illumination means 33, a parallel light spotlight (high luminance (high illuminance) LED light source) was used, and a blue LED was used (see FIG. 1).

(Comparative Example 1)
In the comparative example 1, the commercially available ring illumination currently provided was used. A general spot illumination means was used. Other than that was the same as Example 1.
The diameter (size) of the LED was 120 mm. The number of LED elements arranged was 120 elements. The irradiation angle α was approximately 30 °. The combined illumination includes bright field light and dark field light, and the contrast of the defective portion is reduced.
As the spot illumination means 33, a spotlight (blue LED) which is not parallel light and does not have high luminance (high illuminance) was used.

(Comparative Example 2)
In Comparative Example 1, a ring illumination that was simply manufactured by improving the ring illumination currently provided was used. A general spot illumination means was used. Other than that was the same as Example 1.
The diameter (size) of the LED was 120 mm. The number of LED elements arranged was 120 elements. The irradiation angle α was approximately 25 °. The combined illumination includes bright field light and dark field light, and the contrast of the defective portion is reduced.
In Comparative Example 2, more defects were overlooked than in Example 1.
As the spot illumination means 33, a spotlight (blue LED) that has high luminance (high illuminance) but is not parallel light was used.

[Defect inspection]
Defect inspection was performed using the defect inspection apparatuses of Example 1, Comparative Example 1, and Comparative Example 2.
When inspecting the glass substrate, both the illumination means 31 and the illumination means 32 were used at the same time.
When inspecting a mask blank (substrate with a thin film), all of the illumination means 31, the illumination means 32, and the spot illumination means 33 were used simultaneously.
When inspecting the mask blank with resist, the middle LED ring array (only orange LED) in the illumination means 31 was used.

In Example 1, in the inspection of the glass substrate, optical defects such as scratches, foreign matter, foreign matter inside the glass and striae could be detected very well, and high defect detection power was obtained.
In Comparative Example 1, almost no defects could be detected.
In Comparative Example 2, high defect detection power was confirmed in the region near the optical axis of the imaging lens system, but high defect detection power was not obtained in the other visual field regions, and the expected effect was that the defect detection power was insufficient. It was not obtained.

In Example 1, in the inspection of a mask blank (substrate with a thin film), pinholes, half pinholes that do not have a clear edge and generate less scattered light, and film dents (concaves) that generate less scattered light In addition, it was possible to detect a gently curved depression (gradation) in a thin film with very little generation of scattered light.
In Comparative Example 1, almost no defects could be detected.
In Comparative Example 2, high defect detection power was confirmed in the region near the optical axis of the imaging lens system, but high defect detection power was not obtained in the other visual field regions, and the expected effect was that the defect detection power was insufficient. It was not obtained.

For the foreign matter on the thin film, in Example 1, a high defect detection power was obtained.
In Comparative Example 1, almost no defects could be detected.
In Comparative Example 2, a high defect detection power was not obtained, and the expected effect was not obtained because the defect detection power was insufficient.

  In Example 1, in the inspection of the mask blank with resist, defects such as foreign matters could be detected very well, and high defect detection power was obtained. In Comparative Example 2, a high defect detection power was not obtained, and the expected effect was not obtained because the defect detection power was insufficient.

(Example 2)
In Example 2, the coaxial autofocus module in Example 1 was not operated. Other than that was the same as Example 1.
As a result, the difference between the part where the defect could be detected and the part where the defect could not be detected was large.

(Example 3)
In Example 2, the coaxial autofocus module in Example 1 was not operated. In Example 1, a line sensor was used instead of the TDI camera. The inspection time was 20 times that of Example 1. Other than that was the same as Example 1.
As a result, defect detection could hardly be performed.

(Example 4)
In Example 4, only the transparent dark field ring illumination on the back surface side in Example 1 was turned on.
In Example 4, the detection of foreign matters was inferior to that in Example 1.

(Example 5)
In Example 5, only the reflective dark field ring illumination on the surface side in Example 1 was turned on.
In Example 5, compared to Example 1, the detection of scratches and pinholes was inferior.

In addition, in Example 4, compared with Example 5, there was a difference in the type of defect that he is good at.
This is because, in terms of scattering theory, the forward scattering and the back scattering generally have higher intensity in the forward scattering, and the light is incident from the back side of the substrate by the transmission dark field ring illumination and transmitted. This is because the emitted light becomes forward scattering.

(Example 6)
In Example 6, only the spot illumination means in Example 1 was turned on.
In Example 6, the detection of foreign matter and half pinholes was inferior to that in Example 1.

1 Substrate to be inspected 10 Imaging camera (for example, TDI camera)
DESCRIPTION OF SYMBOLS 11 Objective lens 12 Imaging lens 13 Image pick-up element 20 Autofocus module 31 Illumination means 32 Illumination means 33 Illumination means 100 Imaging optical system 200 Base 300 Head part

Claims (8)

It has an optical system for defect inspection and an illumination system for defect inspection.
The illumination system is a ring illumination in which a plurality of LEDs are arranged in an annular shape, and spot lights from the plurality of LEDs are gathered in a region centered on a focal position of the optical system,
In the ring illumination installed on the optical system side of the substrate to be inspected, each of the spot lights from the plurality of LEDs is irradiated at an acute angle with respect to the substrate surface, and the reflected light is the objective lens Reflective dark field ring illumination configured to prevent direct entry into
The ring illumination installed on the opposite side of the substrate from the optical system, wherein each of the spot lights from the plurality of LEDs is irradiated at an acute angle with respect to the back surface of the substrate and transmitted through the substrate through refraction. A transmitted dark field ring illumination that prevents transmitted light from directly entering the objective lens;
A defect inspection apparatus comprising: It has an optical system for defect inspection and an illumination system for defect inspection.
The illumination system is a ring illumination in which a plurality of LEDs are arranged in an annular shape, and spot lights from the plurality of LEDs are gathered in a region centered on a focal position of the optical system,
In the ring illumination installed on the optical system side of the substrate to be inspected, each of the spot lights from the plurality of LEDs is irradiated at an acute angle with respect to the substrate surface, and the reflected light is the objective lens Reflective dark field ring illumination configured to prevent direct entry into
The ring illumination installed on the opposite side of the substrate from the optical system, wherein each of the spot lights from the plurality of LEDs is irradiated at an acute angle with respect to the back surface of the substrate and transmitted through the substrate through refraction. A transmitted dark field ring illumination that prevents transmitted light from directly entering the objective lens;
Illumination installed on the side of the substrate opposite to the optical system, and a spot illumination that is coaxial with the optical axis of the optical system;
A defect inspection apparatus comprising:   The defect inspection apparatus according to claim 1, wherein an optical axis of the optical system and a central axis of a ring in the ring illumination are made coincident and coaxial. An imaging optical system including an objective lens, an imaging lens, and an imaging device;
The imaging device is a TDI sensor;
The imaging optical system includes a TDI camera,
Means for relatively moving the substrate and the TDI camera in a constant direction at a constant speed;
It has means for repeatedly exposing and photographing the imaging area by the number of vertical stages of the CCD by matching the moving direction and speed of the imaging area on the substrate with the charge transfer direction and speed of the CCD in the TDI sensor. The defect inspection apparatus according to any one of claims 1 to 3.   The defect inspection apparatus according to any one of claims 1 to 4, wherein the defect inspection apparatus includes a high-precision imaging optical system having a focal likelihood smaller than ± 0.1 mm. Using the objective lens and using a laser beam to construct an autofocus means,
6. The defect inspection apparatus according to claim 4, further comprising means for avoiding reflection of the laser beam used for the autofocus means on the image sensor. It has an optical system for defect inspection and an illumination system for defect inspection.
The illumination system is a ring illumination in which a plurality of LEDs are arranged in an annular shape, and spot lights from the plurality of LEDs are gathered in a region centered on a focal position of the optical system,
The ring illumination is installed on the optical system side of the substrate to be inspected,
The distance from the tip on the substrate side to the substrate surface in the ring illumination is the working distance d of the ring illumination,
Let the radius of the ring illumination be r,
From the viewpoint of mechanical size limitation, the range of d and r is defined,
When the light beam of the LED is incident on the substrate, an angle formed by the light beam and the substrate surface is set as an irradiation angle α of the ring illumination, and a dark field request is made so that illumination light does not enter the objective lens directly. From the viewpoint, the range of α is defined,
From the viewpoint that the irradiation density by the ring illumination is p, the viewpoint of increasing the irradiation density p and the upper limit of the irradiation angle α from the dark field requirement, the range of the p is defined,
The values of d, r and α are determined from the mathematical formula d = rTan (α) determined from the positional relationship while taking the irradiation density p into account, and the apparatus is manufactured based on these values. Manufacturing method of defect inspection apparatus. It has an optical system for defect inspection and an illumination system for defect inspection.
The illumination system is a ring illumination in which a plurality of LEDs are arranged in an annular shape, and spot lights from the plurality of LEDs are gathered in a region centered on a focal position of the optical system,
The ring illumination is installed on the opposite side of the optical system of the substrate to be inspected,
The distance from the tip on the substrate side to the substrate surface in the ring illumination is the working distance d of the ring illumination,
Let the radius of the ring illumination be r,
From the viewpoint of mechanical size limitation, the range of d and r is defined,
When the light beam of the LED is incident on the substrate, an angle formed by the light beam and the back surface of the substrate is an irradiation angle α of the ring illumination, and a dark field request is made so that illumination light does not enter the objective lens directly. From the viewpoint and from the viewpoint of the request for incidence near the Brewster angle, the range of α is defined,
From the viewpoint that the irradiation density due to the ring illumination is p, the upper limit of the irradiation angle α is limited by the viewpoint of increasing the irradiation density p and the dark field requirement and the incidence request in the vicinity of the Brewster angle. Define the scope,
The glass thickness is g,
Defect inspection, wherein the values of d, r, and α are determined from the following mathematical formula (3) determined from the positional relationship in consideration of the irradiation density p, and the apparatus is manufactured based on these values. Device manufacturing method.