KR101332786B1 - Method and apparatus for detecting and/or classifying defects - Google Patents

Abstract

The present invention provides a defect detection apparatus, in particular as a defect detection apparatus on the workpiece surface, wherein the radiation is directed on the workpiece and is at least partially affected by the workpiece, preferably the defect.

Camera, defect, optical detector, lighting device, thin film substrate

Description

Fault detection and / or classification method and apparatus {METHOD AND APPARATUS FOR DETECTING AND / OR CLASSIFYING DEFECTS}

The present invention generally relates to quality control in workpiece production and / or processing processes, in particular optical detection and / or classification of workpiece surface or internal defects.

Particularly in the large scale production of integrated electronics or optoelectronic devices, there is a very strong demand for no defects in the surface quality of the substrates used and the volume of the substrates. In particular in the field there is also a need for particularly rapid mass production in order to be able to further lower production costs in order to survive the rampant competition. To lower production costs, wider substrates are used, for example, to increase the number of subcomponents produced simultaneously on one substrate. The time it takes to produce more sub-components on a board typically does not increase or only slightly increases, but this is usually a matter of quality control, as the corresponding larger surface or the larger number of sub-components must be inspected. It is true that it is not valid.

In addition to detecting defects, there are various kinds of defects, for example, particles on the glass surface or scratches on the glass, and various work cycles are possible in the further processing of these various kinds of defects. Classification is also given high value.

It is therefore an object of the present invention to be able to provide optical detection and classification of substrate defects which also meets the strong demand for quality assurance with a high defect detection rate.

This object has already been achieved in a surprisingly simple way by the invention described in the independent claims. Advantageous refinements and limitations of the invention have been specified in the dependent claims.

As a result, the present invention is particularly an apparatus and method for detecting surface defects of a plate-shaped workpiece, such as a workpiece, preferably a glass plate, in which radiation is directed towards the workpiece and at least partially affected by the workpiece, preferably the defect. It provides a defect detection apparatus and method characterized in that the receiving. In particular, it is provided to detect at least a portion of the radiation affected by a defect using an optical detector.

In addition, an improved invention of the invention, in particular, is a device and method for detecting and / or classifying defects on a workpiece surface, wherein radiation from at least one light source is directed towards the workpiece and at least partially affected by the workpiece, preferably a defect. And a first optical signal and a second optical signal are generated by the apparatus, and it is possible to distinguish a defect from the signals.

As a result, the invention is a device for detecting and / or classifying defects, in particular on the surface of a workpiece, wherein radiation from at least one light source is directed onto the workpiece and at least partially affected by the workpiece, preferably the defect, The apparatus provides a defect detection and / or classification apparatus, characterized in that a first optical signal and a second optical signal are generated by the apparatus and it is possible to distinguish a defect from the signals.

In the present invention, differentiating the type of defects, for example classifying the particles placed on the substrate from scratches placed on the substrate or bubbles inserted into the substrate, can have a very positive effect on subsequent further processing. .

For example, when particles are detected, the substrate can be put into a further cleaning process. In this process, the location of one or more detection particles and / or detection scratches may be stored in a downstream information processing system that controls further processing operations.

Thus, it is possible to carry out further cleaning of the substrate or precutting of the substrate so that the particulate coating is allowed and the scratched glass area is separated by precutting.

In this case the release of particles can be carried out both before and after precutting.

Particles with diameters in the range of 0.5 micrometers to 5 micrometers can be stably detected by the present inventive invention and can be distinguished from scratches and bubbles of glass. The particles can be externally mixed solids and residues of previous cleaning operations such as cleaning chemical residues or fine droplets on the glass surface, for example.

It is particularly preferred that the illumination comprises a bright field lighting device and a dark field lighting device. In particular, the optical detector or optical detectors are arranged to detect at least the dark field region.

As a powerful and especially controlled light source, for example lasers or multiple lasers are suitable.

The light source may in particular comprise a scanning system for scanning a workpiece, in particular with a line camera or other detector with parallel detection of multiple surface areas or with optical detection in synchronization with the scanning system. .

The optical detector preferably comprises a plurality of light detecting pixels, each detecting light originating from different substrate regions in order to be able to simultaneously inspect a relatively large surface area with high precision. The other substrate region does not necessarily mean a separate region, but rather may mean, for example, a partially overlapped region.

Also provided is a lighting device having a plurality of light source points arranged such that light is incident on each substrate region from at least two different incidence directions. This is advantageous for detecting extended structures such as, for example, scratches, since scattering of light in this structure is generally very closely related to the angle between the scratch and the incident light. In this way it is also possible to detect scratches that are too long to be detected stably extending along the surface. It is advantageous here that the direction of incidence comprises an angle of at least 45 °, preferably at least 90 °, particularly preferably at least 120 °. It is particularly advantageous if the angle between the two incidence directions is at least 120 ° when light is irradiated onto each surface area from two or more directions, ie when irradiated onto the surface from at least three directions. The light source point does not necessarily need to be a dedicated light source. Rather, the light of one or more light sources can also be split in a suitable manner.

It is particularly preferred that the optical detector comprises a line camera that can be used to inspect parallel regions of the inspection substrate extending along the surface. According to a further limitation of the invention, the optical detector comprises an imaging camera which can be used to detect the substrate in cross section along the surface or even to detect the entire substrate at once.

Particularly advantageously a 4F arrangement can be arranged upstream of the optical detector. The device is surprising in that it can particularly highlight the scattered light effect in the presence of substrate defects. This is especially true if the 4F device is arranged to filter out structures of a size that do not correspond to the size of the defect structure to be detected. Alternatively or in addition, the 4 F device can be arranged similarly to the downstream of the lighting device with the same advantages as above.

It is particularly preferred that the illumination comprises a dark field illumination device. In particular, the optical detector or detectors are arranged to detect at least the dark field area. By excluding the direct light signal, the dark field device is particularly suitable for accurately identifying small defects, ie meeting the most stringent requirements. According to a further refinement of the invention, the dark field illumination device is arranged to share the focal point with the optical axis of the optical detector to exclude the residual background signal in reflection. In this case, the dark field illumination device can be arranged to share the focal point with the optical axis of the optical detector in transmission.

In addition, the illumination may also include a phase contrast illumination device. With such a device, the smallest deviation in the surface structure or volume structure can be detected with a large contrast.

According to the present invention, illumination can be used for both transmission, reflection and combinations of transmission and reflection.

In particular, illumination by inclined incident light is more advantageous in order to detect surface defects. In this case, inclined incidence in the present invention means incidence inclined with respect to the substrate surface to be irradiated. The oblique incident light may advantageously comprise a narrow light bundle that irradiates only one major surface of the two major surfaces of the substrate to be inspected in the camera's image field.

According to a particularly preferred development of the invention, the light is irradiated onto the substrate in the form of its focal point adjusted and oblique incidence, and the optical axis of the detector is arranged at an angle α with respect to the light beam satisfying the following equation.

α> arcsin (n _s * sin (arctan (b / d))), preferably

α> 1.2 * arcsin (n _s * sin (arctan (b / d))).

Where n _s denotes the refractive index of the substrate, b denotes the minimum range of the light beam focus, and d denotes the thickness of the substrate. In this sense, the focal point is understood as the smallest range of surfaces perpendicular to the direction of light transmission where the luminous intensity to maximum luminous intensity at the boundary of the surface falls to 1 / e. In this case, it is particularly preferable that the focal point is inside the substrate. This allows for dark field viewing when the surfaces irradiated by the light rays are laid side by side so that they do not overlap when viewed from the detector side. At the same time, the light intensity at the surface of the substrate is obtained by focusing. In this case, the interval of the surface irradiation area is preferably in the range of 100 micrometers to 500 micrometers in projecting onto the sight line of the optical detector.

Here, the detector may in particular also be oriented in a direction perpendicular to the substrate surface. In this case, that is, when the optical axis faces a direction perpendicular to the workpiece surface, the angle α coincides with the incident angle.

In particular, in the previous embodiment of the present invention, it is more preferable that the detector is disposed on the light emitting surface of the substrate and the irradiation surface is seen forming an acute angle with the emerging beam. However, the angle is preferably 5 ° or more and preferably 50 ° or less with respect to the emerging light beam direction, particularly preferably in the range of 10 ° to 35 °. Being more than 5 ° has proved advantageous in excluding the effects of direct illumination. However, excessively large angles, such as, for example, right angles, are less advantageous because scattering in small structures, such as weak scratches, has generally been found to be at least partially still a Mie type. In scattering, forward scattering is preferred. As a result, the scattering intensity in the direction near the light emission direction is higher than in the other directions.

In order to be able to detect two irradiation regions, according to one embodiment of the invention it is possible for the optical detector to comprise a camera with at least two lines. The detector is arranged in relation to the light source and the substrate such that one of the lines detects the surface area irradiated by the light irradiating the substrate and the other line detects the surface area irradiated by the light emitted from the substrate. do.

A further general refinement of the present invention for also detecting very weak scattering of surfaces uses signal amplifiers, especially for optical detectors such as photomultipliers or multichannel plates. Thus, the optical detector can be used in particular with irradiation light. The light beam can in particular be focused in this case to increase the luminosity and spatial resolution. Laser radiation scanning the workpiece surface by the scanning system is particularly suitable for adjusting the focus.

In the case of an image detector, it is possible in particular to use multichannel plates.

Conventional optical methods for determining defects in glass substrates, in particular when producing TFT displays with such substrates, allow for the rapid and complete inspection of defects that cause adverse effects that may dispose of substrates in large area substrates. Not sensitive enough. The defect can be, for example, a scratch with a fine width that is much smaller than the wavelength of the light.

However, the inventors have found that structures having a detrimental effect in the production of TFT displays can be identified using a high brightness light source in the dark field. According to a particularly preferred embodiment of the present invention, light sources and scattered light detection with an irradiation intensity of at least 2.5 * 10 ⁶ watts per square meter (watt / m ² ) are used to achieve the above object. The brightness can in particular be reached by adjusting the focus of the light sources. To this end, one development of the present invention provides a focusing light source with a focus having a minimum range of up to 200 micrometers, preferably up to 150 micrometers.

Thus, the present invention can be used for the stable detection of defects having a width of 100 nanometers in structure, such as, for example, scratches having a width of 100 nanometers in size.

Inclined incident light may advantageously be s-polarized. Reflection in the defect-free inspection substrate surface area is reduced so that the signal-to-noise ratio of the scattered light signal resulting from the surface defect is improved. In this case, it is particularly preferable that the oblique incident light is irradiated at the Brewster angle with respect to the workpiece. Additionally or alternatively, the optical detector can include a polarizer having a similar effect that polarizes light substantially perpendicular to the polarization of light reflected by the workpiece. In this regard, the term “substantially” means especially for the main surface in the present invention and does not mean for example defects. That is, the polarizer is set to block light reflected from the defect-free surface area.

In order to enable reliable separation of the scattered light reflected from the defect and the reflected light in the defect free surface area, the illumination is in particular provided with a small light element disposed on the optical detector side and perpendicular to the substrate surface or on the substrate surface. It is advantageous to include lighting in which nothing is vertical.

In an advantageous refinement, the lighting device may also be provided with a mirror for adjusting the beam shape. According to one refined invention, in this connection the lighting device comprises a faceted mirror from which square waves are emitted to form a plurality of foci of the workpiece. As illumination with a plurality of individual light sources, it is possible to further provide an illumination device with holographically optical elements for forming a plurality of focal points on the workpiece. The member with the holographic optical element may preferably comprise a phase hologram comprising evaporation-coating glass. As a result, the holographic dynamic pattern can be generated by the patterned vapor precipitation of the evaporation-coated glass. The holographic optical element can be arranged in particular in a refracting element such that the illumination of the required substrate can be performed by one or more light sources passing through the holographic optical element. According to another embodiment of the invention, the holographic optical element is arranged in the reflective element. The light source may advantageously also comprise a holographic optical element and a cylindrical lens so that light incident on the workpiece can be distributed at the required angle.

One or more light sources used may advantageously also have a limited bandwidth. Scattering intensity is generally a function of the shape and size of the scattering elements. For example, it is advantageous to use a light source whose spectrum lies at a wavelength of 300 nanometers or less so that even small defects can be detected.

It is also possible for the light source to advantageously emit light at a wavelength in which the workpiece to be inspected comprises a low transmission, in particular a transmission of 50% or less, preferably 25% or less, most preferably 15% or less. . When detecting surface defects or surface contamination, it is also possible in this way to easily distinguish which side the found defect is on the workpiece. If the workpiece is transparent and uses additional light sources, it is also possible to distinguish between surface defects and volumetric defects.

As an intensive especially directional light source, for example, a laser or a plurality of lasers are suitable.

The light source may in particular comprise a scanning system for scanning the workpiece, in particular with a line camera or other detector with parallel detection of multiple surface areas or with optical detection in synchronization with the scanning system.

In order to achieve high luminosity, and therefore high sensitivity, in the device according to the invention, it is particularly advantageous to use a light source having a plurality of light sources operating simultaneously or light source points emitted simultaneously. Laser diode arrays are suitable for this purpose. In this case, it is preferable to use linear laser diode rows. According to another refined invention, laser diode heat is used which comprises, for example, a collimator arrangement for generating a single bundle of light. The light source is particularly advantageous as an optical detector in addition to a line camera. In addition, the laser or laser diode heat may emit in a limited number of longitudinal modes to harmonize with longitudinal coherence. In addition, the laser or laser diode train can be activated or operated with a short timed pulse to form the required longitudinal coherence.

According to another embodiment of the invention, the laser diode heat is at least one fast-axis collimation lens, preferably additionally at least one SAC lens AC lens (Slow) which generates at least one focus on the workpiece. An Axis Collimation lens). Thus, it is possible to generate a linear focus on the workpiece, which is very suitable with line cameras arranged in sequence parallel to the focus to detect scattered light from the workpiece defect. The light source may include a phase front scrambler to form the required transverse coherence. Therefore, it is possible to exclude unnecessary interference effects that produce a particularly obvious signal.

According to a further embodiment of the invention, the light source may also comprise a fluorescent tube. The light source can be used in particular in a device parallel to the workpiece surface to irradiate multiple surface areas in such a way that each surface area is in each case irradiated with light from a different direction. To further analyze the workpiece, it is also possible to use fluorescent tubes with multiple spectral emission bands. Thus, for example, fluorescence and scattered light can be measured. The fluorescent tube is preferably arranged parallel to the line camera as an element of the optical detector.

According to a particularly preferred embodiment of the invention, the workpiece comprises glass or the glass is inspected as a workpiece. In particular, the present invention can be used to inspect thin film glass. In this regard, the present invention relates to float thin glass, downdraw thin glass, downdraw fusion thin glass, in particular overflow downdraw glass. It is suitable for checking the quality.

Residual surface defects, particularly polished workpieces, of the treated surfaces may still be identified and / or identified. For example, extremely fine abrasive scratches can still be identified.

The inventive device is used to inspect glass for displays, in particular TFT displays. Since even the smallest scratches that can occur during polishing operations or handling in the production process can adversely affect the coating applied to the glass, the glass requires particularly stringent conditions for its surface condition.

Even large area substrates such as thin film glass having a width of 1.8 meters or more and / or a length of 2.0 meters or more can be quickly inspected by the present invention, thus delaying the production cycle for producing TFT displays using such substrates. They are not supported or are only delayed very impractically.

The thin film glass inspected by the present progressive device and aligned using the results of this manner clearly reduces the concentration of defects or the number of defects. For example, in inspected thin film glass, the concentration of scratches having a depth of 3 to 30 nanometers is 5 or less per square meter, preferably 3 or less per square meter, particularly preferably 1 or less per square meter.

Substantial increases in yield can also be achieved by identification and / or classification of defect types, such that scrap or blanking waste occurs only to the minimum extent necessary.

The invention is described in more detail below with reference to representative embodiments and figures, the same and similar elements are given the same reference numerals, and the characteristics of the various representative embodiments can be combined with each other.

1 is a schematic diagram of an apparatus for detecting thin film glass defects according to an exemplary embodiment of the present invention.

2 shows a variant of the apparatus shown in FIG. 1.

3A and 3B show an improved part of the progressive device.

4 illustrates a further embodiment of the present invention with a phase contrast detection function of a defect.

5 is a view showing a light path according to an improved invention of the present invention.

FIG. 6 shows a representative embodiment with a beam shaping device for forming multiple foci at the substrate surface. FIG.

FIG. 7 shows an embodiment with illumination by laser radiation in which focus is adjusted.

8 shows a variant of the exemplary embodiment shown in FIG. 7 with a photomultiplier and scanning system.

9 shows an improved invention of the invention with a plurality of optical detectors arranged side by side.

FIG. 10 shows the recording by an optical detector obtainable by the apparatus according to FIG. 7.

FIG. 11 is a schematic illustration of a very simplified surface where particles and scratches are placed on a flat glass substrate.

FIG. 12 is a schematic illustration of a very simplified view of a flat glass substrate with two scratches positioned by each optical signal in the bright field and dark field so as to look obliquely from the top.

13 shows a preferred embodiment of the inventive device.

1 is a schematic view of a workpiece 3 surface and / or internal defect detection device. The apparatus according to this exemplary embodiment, which is generally given the reference number 1, is used in particular for checking the presence of defects in the thin film glass substrate 3. Defects occurring during operation can be identified as well as typical defects resulting from the production of downdraw thin film glass, downdraw molten thin film glass, in particular overflow downdraw glass or float glass. In particular, the apparatus is also well suited for the rapid inspection of very wide substrates, for example thin films having a width of at least 1.8 meters and / or a length of at least 2.0 meters.

The defect may be, for example, an abrasive scratch of the surface 31 of the thin glass substrate 3 such as may remain in the surface treatment operation. The defect detection device 1 is used in particular to direct the radiation of the lighting device 11, which is at least partly affected by a defect, to the workpiece. Thus, at least a portion of the radiation affected by the defect is detected by the optical detector 5. In the representative embodiment shown in FIG. 1, the optical detector comprises a line camera 7. The optical focusing system of the line camera is designed such that each pixel of the camera 7 detects another surface area of the thin glass substrate 3 or detects light emitted from the surface area of the thin glass substrate. The detected surface area as a whole forms an extended surface area 20, shown by dashed lines in FIG. 1. The surface area 20 extends especially along the entire width of the substrate 3 so that the entire surface 31 or the entire substrate 3 can be detected by moving the substrate through the optical detector 5 only once. For this purpose, both the substrate 3 and the detector can move.

The lighting device 11 is designed such that a plurality of light source points are arranged so that light from at least two different incidence directions is irradiated over each substrate region detected by each pixel of the line camera.

In the case of the example shown in FIG. 1, this is achieved by having a light source comprising a fluorescent tube 13. The fluorescent tube extends parallel to the line camera, is aimed in a suitable manner, and its focus is adjusted by the cylindrical lens 15 so that the substantially narrow surface area 20 is irradiated. In addition, irradiation is performed by inclined incident light, and the line cameras face the surface substantially vertically so that the directly reflected light does not reach the line camera 7. The fluorescent tube emits light isotropically such that any arbitrary longitudinal portion of the fluorescent tube forms a light source point. In this manner, a plurality of lights from different directions are irradiated to each detection substrate region. Thus, in the case of the device shown in FIG. 1, light is irradiated from the edge of the substrate 3 to the right area from all possible incidence directions which differ from each other by the maximum angle α. Thus, the length of the fluorescent tube and the distance from the region 20 to the fluorescent tube can be selected such that the various incidence directions include an angle of at least 45 °, preferably at least 90 °, particularly preferably at least 120 °. In this way, scratches formed along any direction of the surface can be stably detected. In addition, as shown in FIG. 1, illumination by means of an illumination device 11 with a small optical component perpendicular to the substrate surface 31 or in particular without such a component is arranged on the optical detector side.

To obtain additional information regarding defect characteristics, the fluorescent tube can be equipped with multiple spectral emission bands. Fluorescent signals and / or control signals can be detected in this manner, for example at various wavelengths with a suitable optical detector filter.

By the device with the inclined light incidence and the vertical detection function, only scattered light is detected by the optical detector. As a result, the illumination of the present exemplary embodiment also constitutes a particularly dark field illumination device.

A variant of the device 1 shown in FIG. 1 is shown in FIG. 2. In a variant of the exemplary embodiment shown in FIG. 1, the optical detector 5 comprises an image camera 17 in which the pixel detects a square or rectangular area 20 of the surface. Further, in this example the lighting device 11 is constructed according to the representative embodiment shown in FIG. 1 and similarly to the surface 31 of the substrate 3, in particular the surface area 20 detected by the pixel. And a plurality of fluorescent tubes 13 arranged to irradiate by oblique light incidence and to implement darkfield illumination.

In the present exemplary embodiment, the light source point is also disposed along the fluorescent tube such that light from at least two different incidence directions is irradiated to each substrate region, and the incidence direction for each surface region detected by the individual pixels is the region 20. ) An angle α of at least 45 °, preferably at least 90 °, particularly preferably at least 120 °.

In all of the above exemplary embodiments, the thin glass substrate 3 is guided along the feeding direction 33 by a feeding device (not shown) so that its length is inspected.

In the exemplary embodiment shown in FIGS. 1 and 2, multiple optical detectors may be arranged to intersect the supply direction 33 next to each other. In general, mention is made of a device having a plurality of optical detectors arranged to intersect the feeding direction, which intersects the feeding direction, particularly for wide substrates 3, in order to be able to inspect the surface of the substrate in high resolution. In a manner that detects the substrate as a whole over its full width.

3A and 3B show some of the refinements of the progressive device. Here, FIG. 3A shows an optical detector 5 having a line camera 7 and a four F device 25 disposed upstream of the optical detector 5. The four F device comprises two cylindrical lenses 26, 27 with a diaphragm 30 disposed on a common focal plane.

In the example of the lighting device 11 with the aimed and focused fluorescent tube 13 as shown in FIG. 3B, a similarly designed four F device is arranged downstream in a similar manner. Illumination devices and optical detectors with four F devices disposed downstream and upstream, respectively, are used, for example, in the exemplary embodiment shown in FIG. 1 or FIG. 2.

By means of the diaphragm 30 of the four F device, the four F device 25 may filter the structural size which does not correspond to the structural size of the defect to be detected.

4 shows a further representative embodiment of the progressive defect detection device 1. Embodiments of the present invention are based on detection of defects, in particular phase contrast, of scratches on the surface 31 of thin glass substrates for TFT displays.

The basic design is similar to the example shown in FIG. 1, but the optical detector is designed such that its optical axis lies in the light beam of the lighting device reflected by the surface 31.

Upstream of the lighting device 11 is arranged a slit diaphragm 30 and a cylindrical lens for focusing the light of the slit diaphragm 30 to the substrate surface 31. In the upstream reflection beam of the line camera 7 of the optical detector 5, a phase plate 38 having an additional cylindrical lens 36 and a linear light attenuation region 39 is arranged. In this case, the phase plate 38 is arranged such that the direct reflected light is attenuated by the linear region 39. If defects or other contaminants are present on or within the surface 31 of the thin glass substrate 3, this will lead to scattering of light. The scattered light then represents a direction deviating from the reflected light and laterally passes through the linear attenuation region 39 of the plate 38 to reach the line camera. Thus, this creates an interference between the scattered light beam and the attenuated direct light beam for each pixel of the line camera 7 so that the defect can be easily identified by the occurrence of the interference phenomenon. Here, each arbitrary longitudinal region of the diaphragm 30 forms a light source point so that each surface region irradiated by the slit of the diaphragm 30 is irradiated from a plurality of different directions. For example, in order to be able to detect scratches formed in any direction, it is particularly advantageous in this case for the incident direction to include an angle of at least 45 °, preferably at least 90 °, particularly preferably at least 120 °. .

In addition, in all the embodiments shown in FIGS. 1 to 4, it is advantageous to use polarized light. If the measurement is made in reflection as in the representative embodiments above, it is also clear that in this case it is necessary to use an illumination device 11 which emits S-polarized light against the surface 31. This suppresses reflections in the defect free surface area and creates an improved signal-to-noise ratio. In all of these devices, the lighting device 11 can advantageously also be arranged such that light is irradiated to the surface at a Brewster angle or similar angle.

In addition, in all of the above exemplary embodiments, the lighting device may also be arranged on the substrate 3 face 32 located opposite the face 31 such that light is transmitted through the substrate 3 without being reflected. As for the position of the lighting device 11, the position shown in FIG. 1, FIG. 2, FIG. 4 is reflected in the board | substrate 3, respectively.

In addition, in the exemplary embodiment shown in Figs. 1 and 4, since the area linearly irradiated by the lighting device can be kept narrow by proper focusing and / or focus adjustment associated with inclined light incidence, Only in one of the two major surfaces, ie one of the surfaces 31, 32, is irradiated in the area 20 detected or in the image field of view. The device is schematically illustrated in FIG. 5, which shows a ray path according to an improvement of the invention. The arrangement of the optical detector 5 and the illumination device (not shown) may be, for example, consistent with the example shown in FIG. 1. The oblique incident light bundle 40 irradiates an area 41 of the surface 31 and an area 42 of the opposite surface 32. Refraction of light bundles is not considered in the figures. The area 20 detected by the line camera 7 of the optical detector 5 is located inside the area 41 but outside the area 42.

As a result, only one of the two surfaces in the image field of view of the camera 7 is irradiated. This is particularly useful because the signal caused by the light scattered from the surface 32 defect is suppressed in this manner. Thus, for example, the substrate 3 for TFT display production may in some cases, even if it is recognized that the coating is certainly damaged, may have scratches on the opposite side of the coating side that are not optically visible at all. It can be used without scratch. Thus, scrap can be significantly reduced by the apparatus as shown in FIG. 5.

However, additional arrangements can be considered to prevent defect detection of the opposite side 32. For example, if the defect is only a surface defect such as a scratch that is still important in workpiece inspection, it is also possible to use light of a suitable wavelength that does not penetrate the substrate 3. Thus, for example, light sources with a limited bandwidth and spectrum of wavelengths shorter than 300 nanometers can be used in the float glass. As described above, light of short wavelengths are no longer transmitted, so only defects on the surface or at most near the surface are identified. In general, in order to distinguish between defects on the top and inside of the workpiece or to exclude detection of opposite side defects, the workpiece has a low transmittance, in particular a transmittance of up to 50%, preferably up to 25%, most preferably It may be advantageous to use a light source that emits light at a wavelength that exhibits a transmission of 15% or less.

As mentioned above, if polarized light is preferably used that is incident at Brewster's angle, according to another refined invention of the invention, the light is directed substantially perpendicular to the polarization of the light reflected by the substrate 3. It is possible to provide an optical detector 5 as shown in FIG. 5 with a polarizer 45 to polarize. As a result, if using the S-polarized light, the polarizer will be set so that the S-polarized reflected light is blocked by the polarizer 45.

6 shows another variant of the example shown in FIG. 1. In this example, a laser diode row is used instead of a fluorescent tube, in particular a laser diode 50 with a plurality of laser diodes arranged linearly in a direction parallel to the surface 31. The laser diode array may comprise at least one fast-axis collimation lens (FAC) that forms at least one focal point on the workpiece, and preferably additionally at least one slow-axis collimation lens. . In order to prevent unwanted interference effects, an in-phase wavefront scrambler may be further provided. In addition, the laser diode train can emit in a limited number of longitudinal modes to harmonize with longitudinal interference, and / or can be operated with a single pulse to form the desired longitudinal interference characteristics.

Although the laser is particularly advantageous because it emits strong and high quality parallel light, nevertheless the effect uses light of various incidence directions for each surface area detected by the pixels of the line camera 7 according to the invention. If you do, it is strictly a hindrance. To achieve this, a suitable beam shaping device is arranged downstream of the laser. In the example shown in FIG. 6, the illumination device comprises a holographic optical element for forming a plurality of foci on the substrate for this purpose. In particular, the holographic optical element comprises a phase hologram. In particular, the phase hologram plate 52 is disposed upstream of the laser bar 50.

The phase hologram can advantageously be formed by the standard deposition of the evaporation-coated glass as the refractive element of the glass plate. The phase hologram also refracts and adjusts the light beam in the surface direction so that light is irradiated to each surface area detected by the pixel in various incident directions. Instead of glass plates, it is also possible to use cylindrical lenses as refractive elements. Thus, for example, the focusing operation in the lateral direction may be performed by the cylindrical lens, and the focusing operation in various incidence directions along the surface 31 may be performed by the phase hologram.

In this example, the lighting device further comprises a beam shaping mirror. In particular, in this example, a faceted mirror 54 is provided with concave mirror facets that contribute to forming a plurality of focal points on the workpiece similarly to the above. It is placed in the reflected beam so that the light is reflected back accurately precisely to increase the brightness of the surface area to be irradiated.

In addition to or in addition to the concave mirror surface, it is also possible to configure the mirror 54 as a support for reflective elements and holographic optical elements in order to reflect light back into the detection surface area in various incidence directions.

7 shows a further exemplary embodiment of the present invention when a focused laser light is used to detect a defect. The light bundle 40 incident toward the surface 32 of the thin glass substrate 3 is focused by the lens 56 such that the focal point F is placed inside the substrate 3. In this case the light is focused by the lens 56 such that the focus is in the range of at most 200 micrometers, preferably at most 150 micrometers. In particular in this case, the goal is to have the smallest possible focus in the range of about 50 micrometers to 100 micrometers. A laser or laser bar with multiple laser light sources is used as the light source (not shown in FIG. 7 for clarity). As a result, a high luminous intensity of at least 2.5 * 10 ⁶ watts per square meter (watt / m ² ) of irradiation intensity of the substrate can be obtained by focusing.

Regions 41 and 42 irradiated by the light source and scattered light at the defects appear on the surfaces 31 and 32. As in the case of the representative embodiment shown in FIG. 5, the detector 7 is arranged on the side opposite to the incident light direction with respect to the substrate 3, so that the light scattered in the surface area 42 is transmitted to the detector 5. Is detected. However, the detector is arranged such that the region 41 of the substrate 3 face 31 facing the detector 5 is also detected by the detector 5. In addition, the optical axis 58 and the intermediate ray 60 of the newly generated light bundle are arranged to form an acute angle α. The angle α is selected so that the two regions 41, 42 do not overlap when viewed from the detector 5 side. This is ensured when the angle α is as follows.

α> arcsin (n _s * sin (arctan (b / d)))

n _s is the refractive index of the substrate, b is the minimum range of light focus, and d is the thickness of the substrate. In this relationship, the refraction of light at the substrate (not shown in FIG. 7) is further described. The angle is at least 5 ° in the example shown. The lower limit has the meaning of preventing the detection of direct sunlight from the edge region of the light bundle when the focus is adjusted with a short focal length. The angle α here preferably has a value within the range of at least 10 °, particularly preferably from 10 ° to 30 °.

Due to the refraction, the light beam is deflected in a direction perpendicular to the substrate surface while moving the substrate. As a result, for a given angle α, the regions 41, 42 move closer to each other in the projection when viewed from the detector 5 side with a relatively high refractive index. However, if the angle is selected by this particular relationship, the areas 41 and 42 for the detector can be detected independently. It is therefore also possible to check on which side 31, 32 of the substrate 3 the identified defects lie.

Since the optical axis 58 of the detector is directed in a direction perpendicular to the surface 31 of the substrate 3, the angle α also corresponds here to the incident angle of light.

In order to be able to detect two irradiation areas, according to one embodiment of the invention, it is possible for the optical detector to comprise a line camera 7 with at least two lines 71, 72. The optical system 63 of the detector 5 detects the surface area 42 irradiated by one of the lines 72 by the light irradiating the substrate and the remaining lines 71 by the light generated from the substrate. The camera is arranged in relation to the light source and the substrate 3 to detect the surface area 41 irradiated by it.

It is preferable that the device having the transmission measuring device or the detector arranged opposite to the incident light as shown in Fig. 7 is a device in which the detector is arranged on the light incident side.

The apparatus shown in FIG. 7 allows the surface areas 41 and 42 to be viewed at an oblique angle without problems that arise on the basis of their dimensions in the arrangement of the light source and the detector 5. In this case, the problem may arise in particular on the basis of basic short focal length lenses or focus adjusting lenses. Short focal length lenses are advantageous for generating high brightness at the surfaces 31, 32 of the substrate. However, it should be noted that the focusing lens 56 should be placed very close to the substrate surface 32 such that the focus is located in the substrate region, preferably inside the substrate.

In addition, forward scattering is most prevalent in many scattering structures, and thus better signal-to-noise ratios can be obtained. However, the arrangement with a detector on the light incident side is also meaningful in some situations, for example, in the case of emphasizing a signal of small scattering structure, in contrast to a scattering signal of a relatively wide structure. For very small defects, for example defects whose structure size is clearly 100 nanometers or less, the forward scattering intensity and the backscattering intensity detected by the detector in this case will be consistent with the Rayleigh scattering intensity distribution.

However, the detector may further comprise a signal amplifier to enable detection of the individual scattered photons with the highest sensitivity and reliability for the purpose of detecting the minimum size defect. Here, for example, a photomultiplier tube or a multichannel plate is considered. Representative embodiments are shown in FIG. 8. The device 1 shown in FIG. 8 is a variant of the exemplary embodiment shown in FIG. 7. Here, the substrate regions 41 and 42 are also independently detected in order to be able to distinguish which side 31 and 32 the defect is located on. Starting from the representative embodiment shown in FIG. 7, in the case of the device 1 shown in FIG. 8, photomultipliers 61, 62 are provided as part of the optical detector. In a manner similar to the representative embodiment shown in FIG. 7, the optical system 63 of the detector is such that in each case the light emitted from one of the regions 41, 42 is respectively photomultiplied by the photomultiplier 61, 62. It is designed to be focused into one photomultiplier tube. In order to obtain spatially resolved defect position information, in the present exemplary embodiment, a scanning system having a scanning unit 65 capable of scanning the substrate by light rays in a manner crossing the supply direction 33 is used. For example, the scan unit 65 may be a galvanometer scanner. Considering that the substrate 3 is further moved along the supply direction 33 by the supply device, it is possible to detect the entire substrate surface in this manner.

As in the case of the representative embodiment shown in FIGS. 1 and 2, the substrate is moved past the device 1 along the feeding direction 33 to detect and inspect the entire surface or at least a wide portion thereof. do. As a result, the detection regions 41, 42 extending along the width across the feeding direction pass through the entire surface 31, 32 or at least the thin glass substrate region to be inspected.

For example, if the edge area of the substrate is not used for display glass production, there is no need to scan that area. However, in order to obtain the maximum possible glass quality properties, it is desirable to inspect at least 80% of the substrate surface of large areas, in particular thin film substrates having a width of 1.8 m or more and / or a length of 2.0 m or more. Of course, this is also valid for all other embodiments described herein. In the case of such a wide substrate, it is also advantageous to use a plurality of detectors 5 arranged side by side, as shown in FIG. 9, as an improved invention of the representative embodiment of FIG. 7. The detectors are arranged side by side along the width of the thin glass substrate 3 perpendicular to the feed direction 33. Similarly, a number of lighting devices arranged next to each other are arranged on the opposite side. In the example shown, a laser bar 50 is used for irradiation. The surface of the substrate 3 facing the detector 5, which is irradiated by an emerging laser light that extends along the entire width of the substrate 3 across the feed direction and is focused to be perpendicular to the feed direction 33. Surface areas 41 respectively detected at 31 are similarly shown.

A feeding and holding device is provided to hold the substrate in the position provided for measurement and to move along the feeding direction. In the example shown, the apparatus comprises a roller 55 on which the substrate 3 is placed and which moves along the feeding direction 33 as the roller rotates. Of course, a feeding and holding device may also be provided for the other representative embodiments shown to hold the substrate in position.

FIG. 10 shows a record that can be obtained by the apparatus corresponding to FIG. 7 or 8. However, the recording was made by a matrix camera rather than a line camera or photomultiplier coupled with the scanning system. The image is shown in reverse, and the location of emitting scattered light in FIG. 10 appears black. The dashed lines indicate the strip-shaped surface areas 41 and 42 which were irradiated. Scatter structures in the form of some dots are shown in the surface region 41. This is due to the surface particles 66. The opposite side of the substrate 3, with the irradiation area 42, has a fine scratch 67 which is clearly identified on the record.

The concentration of scratches can be substantially lowered by removing the glass identified as defective in the thin film glass inspected by the apparatus according to the exemplary embodiment described above. In the thin film glass thus inspected, it is possible to lower the concentration of scratches having a depth of 3 to 30 nanometers to 5 or less per square meter, preferably 3 or less per square meter, particularly preferably 1 or less per square meter. Thus, the production line, especially for the production of TFT displays, including the advanced devices, can quickly provide high quality final products.

Once again, for example in the case of production lines for glass production, it is also possible to feed back the results obtained by the advanced device to the production process online. The production process can therefore be directly controlled and optimized by using a device for detecting defects.

In the following detailed description, the content of German Patent Application No. 10 2005 07715.3, filed with the German Patent Office on February 18, 2005 entitled "Method and Apparatus for Defect Detection", is incorporated in its entirety into the specification of the present application. In particular, the device thus combined may be supplemented by a device described below or a device that can be combined with it.

FIG. 11 is a simplified representation of the surface of the flat glass substrate 3 on which the particles 162 and scratches 160 are located.

Particles 162, typically having a size of 0.5 micrometers or more, for example 5 micrometers or more, in diameter may be viewed from above when viewed from above by a brightfield device as described in more detail below. All can be effectively identified when viewed with a dark field device as described similarly below.

However, FIG. 12 shows how the optical signal in the bright field differs from the optical signal in the dark field. Reference numeral 164 denotes a scratch, thus a line defect, which is identified as a good contrast in the dark field.

Reference numeral 166 schematically represents an image of the optical signal and thus the linear defect, that is, the image of the scratch when seen from the bright field device. The optical signal has substantially less contrast in the bright field than the dark field and thus scratches or removes the particulate component of the defect in the glass by removing the spatially resolved bright field device optical signal from the spatially resolved dark field device signal. It is possible to distinguish it from air bubbles.

By removing the spatially resolved optical signals point by point from one another, a clear distinction is made that essentially marks the scratches and bubbles of the glass where the low and high contrasts meet.

Since particles exhibit a substantially low contrast difference in the discrimination signal, the contrast difference in the discrimination signal image makes it possible to distinguish between the particles and scratches or bubbles.

The maximum intensity or average intensity of each image can be normalized to make the distinguishing signal information the value near that when the intensity of the defect free area is zero.

FIG. 13 is a view schematically showing a workpiece 3 surface and / or a defect detection device of the workpiece.

In particular, the presence of a defect in the thin glass substrate 3 is inspected by the apparatus of the present exemplary embodiment as indicated by reference numeral 1 as a whole.

For example, it is possible to identify typical defects such as those which occur as a result of the production of downdraw thin film glass, downdraw molten thin glass, in particular overflow downdraw glass or float glass, as well as by rework. In particular, the apparatus is also very suitable for quickly inspecting very wide substrates, for example thin film glass having a width of 1.8 m or more and / or a length of 2.0 m or more.

The defect may be, for example, an abrasive scratch of the surface 31 of the thin glass substrate 3 which may remain or occur by a surface treatment operation. The defect detection device 1 can be used to direct radiation onto a workpiece using an illumination device, in particular a laser 170, which radiation can be at least partially affected by the workpiece, in particular a defect. have.

In particular in the apparatus for detecting and / or classifying defects on the surface of the workpiece 3, the radiation from at least one light source, in particular the laser 170, is directed onto the workpiece 3 and the workpiece 3, preferably Preferably at least partially affected by defects 160, 162, 164, and 166, generating first and second optical signals detected by optical detectors 180, 188, respectively, and distinguishing the defects from the signals. It is possible to.

The first optical signal is a bright field signal obtained from a bright field device. The bright field device comprises a laser for irradiating through the beam splitter 172 with a galvanometer scanner 182 which deflects the light beam by an angle θ with respect to the optical axis of the downstream positive lens 84 170). The galvanometer scanner does not necessarily need to be understood as an electrically operated scanner, but generally as a beam deflection scanner. The scanner is also known to those skilled in the art as a "galvanoscanner".

The base point of the galvanometer scanner 182, which delivers the reflected laser beam further away, is located approximately at the left focal point of the positive lens 184, also indicated by the F-θ lens.

As a result, the light rays emitted from the right side of the positive lens 184 are substantially parallel to each other and pass over the surface 31 of the workpiece 3 when pivoting the mirror of the galvanometer scanner 182.

If the workpiece 3 and / or the device 1 move, it will pass linearly across the entire surface of the workpiece 3.

In the path from the galvanometer scanner 182 to the positive lens 184, the laser beam passes through a beam splitter 174 that is originally assigned to the dark field device, which is described in more detail below.

As an alternative to galvanometer scanner 182, rotatable, aluminum plated polygons may also be used, in which case the rotation is defined by the deflection angle θ of the laser beam.

Because the angle θ and the relative movement of the device 1 with respect to the workpiece 3 are detected in the downstream information processing system (not shown in the drawing) and thus the position of the substrate 3 assigned thereto, The optical signal described can be detected and further processed in a spatially resolved manner.

On the front side or on the rear side of the workpiece, the workpiece 3 retroreflects light passing through the galvanometer scanner 182 to the beam splitter 172, which emits the light to a photodetector ( 180).

The contrast or spatially resolved contrast difference of the optical signal reflected by the photodetector 180 is a function of the contrast contrast of the workpiece 3 surface, which is relatively higher in the particles than in scratches or linear defects in the bright field.

Photodetector 180 preferably includes a pin diode or photodiode with a high cutoff frequency.

The second optical signal is a dark field signal obtained from the dark field device described below.

In addition to the positive lens 184, the dark field device includes a beam splitter 174, a linear diaphragm 186, an additional positive lens 178, and a photodetector 188.

After passing through the positive lens 184, the light reflected by the workpiece 3 is guided by the light splitter 174 into the diaphragm 186 of the dark field device as well as into the bright field device.

Light components of the reflected light generated at the plate surface are blocked at the substantially linear diaphragm 186.

If the surface 31 or interior of the workpiece 3 has scattering centers, the scattering centers generate elements which are not (reverse) in the reflected light in the reflected light.

After passing through the positive lens 184 and the beam splitter 174, the beam element is no longer irradiated with the diaphragm 186 and further positive to adjust the beam element so that its focus is on the photodetector 188. Reach lens 178.

Compared with the optical bright field signal, the scattered light including the second optical signal information also has a high contrast difference in scratches and linear defects, which means a distinct difference in brightness.

Photodetector 188 is preferably a photomultiplier tube.

As a result, the first optical signal includes spatially resolved information about a defect including particles, and the second optical signal includes spatially resolved information about defects including scratches, particles, and glass defects.

Sorting into particles or scratches and / or bubbles may be performed by removing two optical signals as a result, wherein the removal of the optical signals is preferably detected by a detector and electrically transferred in a downstream information processing system. Performed after conversion to a signal.

If the diaphragm 186 is disposed on the right side of the workpiece 3 together with the additional positive lens 178 and the photodetector 188 for the transparent workpiece 3, the optical detector 88 optical axis disposed in the transmission process. It is possible to provide a dark field illumination device that shares the focus with.

If the diaphragm 186 is replaced by a phase shifting element that shifts the phase of the light passing by about half a wavelength, the dark field device described above is directed to the phase contrast illumination device in connection with the photodetector 188. Is changed.

For purposes of harmonizing with longitudinal coherence, laser 170 or laser diode heat may emit in a limited number of longitudinal modes.

In order to form the required longitudinal interference properties, the laser 170 or laser diode train can work with short axis pulses.

The light source, in particular the laser 170, may comprise an in-phase wavefront scrambler for the purpose of forming the required transverse coherence.

In the case of the thin film glass inspected by the above-described apparatus, the concentration of scratches can be substantially lowered by removing the glass identified as defective. Thus, in the case of inspected thin film glass, the concentration of scratches having a depth of 3 to 30 nanometers can be lowered to 5 or less per square meter, preferably 3 or less per square meter, particularly preferably 1 or less per square meter. Therefore, production lines, especially for TFT display production, including these advanced devices can quickly provide high quality final products.

In addition, meaningless waste can be significantly reduced by distinguishing the particle coating of the substrate from scratches and / or bubbles of the substrate by proper pre-cutting in future processes.

In other words, for example in the case of a production line for glass production, it is possible to feed back the results obtained by the advanced device to the production process online. This allows the production process to be controlled by the use of defect detection devices and directly optimized.

It is apparent to those skilled in the art that the present invention is not limited to the exemplary embodiments described above but may be modified in various ways. In particular, the features of each representative embodiment may also be combined with each other.

*** REFERENCE LIST ***

1: defect detection device

3: thin film glass substrate

5: optical detector

7: line camera

9: optical focusing system of the line camera 7

11: lighting device

13: fluorescent tube

15: cylindrical lens

17: image camera

20: surface area irradiated by the lighting device 11

25: 4F device

26, 27: lens of 4F device

30: diaphragm

31, 32: surface of thin glass substrate

35, 36: Lens

38: phase plate

39: translucent area

40: bundle of incident light

41: region of thin film glass substrate surface 31 irradiated with a bundle of incident light

42: region of thin film glass substrate surface 32 irradiated with a bundle of incident light

45: polarizer

50: laser bar

52: phase hologram plate

54 mirror

55 matrix camera with image intensifier

56 lens

60: center ray of the incident light bundle

61, 62: photomultiplier

63: Optical system of optical detector

65: scan unit

66 particles

67: scratch

160: scratch

162: Particles

164, 166 line defect

170: laser

172, 174: Ray Splitter

176, 178: Lens

180: optical diode

182: Galvanometer Scanner

184: F-θ lens

186: line diaphragm

188: photomultiplier tube

Claims (77)

A defect detection device for detecting a defect on a surface of a workpiece, comprising a light source directed at the workpiece and at least partially affected by the defect of the workpiece and an optical detector for detecting at least a portion of the radiation affected by the defect as, The minimum range of the light source is out of focus adjustment, the light source and the optical detector is a refractive index of doedoe the optical axis of the detector disposed so as to be arranged at an angle α to the beam, said angle α is n _s substrate, b the beam focus, an d so as to satisfy the _{α> arcsin (n s * sin} (arctan (b / d))) indicate when the thickness of the substrate, in the defect detection apparatus for detecting defects in a workpiece surface, The optical detector has at least two lines, one of which detects the surface area irradiated by the light irradiating the substrate and the other of which detects the surface area irradiated by the light emitted from the substrate. And a camera comprising a camera. The method of claim 1, And the workpiece is a plate-shaped workpiece. The method of claim 1, The optical detector includes a plurality of light detection pixels each detecting light generated in different substrate regions, and a plurality of light source points disposed so that light is irradiated onto each substrate region from at least two different incidence directions. The defect detection apparatus provided with. The method of claim 3, And said incident direction comprises at least 45 degrees angle. 5. The method of claim 4, And said incidence direction comprises at least a 90 [deg.] Angle. The method of claim 5, And the incident direction comprises at least a 120 ° angle. The method according to claim 1 or 3, And the optical detector comprises a line camera. The method according to claim 1 or 3, And the optical detector comprises an image camera. The method according to claim 1 or 3, And the light source is arranged such that its focus is always placed inside the substrate. The method according to claim 1 or 3, And the angle α is 5 ° or more with respect to the direction of light generation. The method of claim 10, And said angle α is 50 degrees or less with respect to the direction of light generation. 12. The method of claim 11, The angle α is in the range of 10 ° to 35 ° with respect to the direction of light generation. delete The method according to claim 1 or 3, And the light source has a radiation intensity of at least 2.5 * 10 ⁶ watts per square meter of the substrate. The method according to claim 1 or 3, And wherein the focused light source has a focus with a minimum range of at most 200 micrometers. 16. The method of claim 15, And the light source has a focal point with a minimum range of at most 150 micrometers. The method of claim 3, The illuminating device comprises a polyhedral mirror for forming a plurality of focal points on a workpiece in which square waves are generated. The method of claim 3, The illumination device comprises a holographic optical element for forming a plurality of focal points on a workpiece. 19. The method of claim 18, And the holographic optical element comprises a phase hologram. 20. The method of claim 19, And said phase hologram comprises an evaporated-coated glass. The method of claim 18 or 19, And the holographic optical element is disposed in the refractive element. The method of claim 18 or 19, And the holographic optical element is disposed in the reflective element. The method of claim 1, And the light source comprises a laser diode array having at least one fast-axis collimation lens forming at least one focal point on the workpiece. 24. The method of claim 23, And the laser diode row further comprises at least one slow-axis collimation lens. The method of claim 1, And the light source comprises a holographic optical element and a cylindrical lens. A production line for a TFT display comprising the defect detection device according to claim 1. A defect detection method for detecting a defect on a surface of a workpiece, the radiation of which is directed by the defect detection device according to claim 1 and at least partially affected by the defect of the workpiece, the focus of the light source being adjusted, optical detector, α a refractive index of doedoe the optical axis of the detector disposed so as to be arranged at an angle α to the beam, said angle α is n _s substrate, b is the minimum range of the light-focusing, when d indicates the thickness of the substrate> In the defect detection method for detecting a defect on the surface of the workpiece to satisfy the arcsin (n _s * sin (arctan (b / d))), At least two lines of light emitted by the defect, one of which detects the surface area irradiated by the light irradiating the substrate and the other of which detects the surface area irradiated by the light emitted from the substrate It is detected by a camera provided with a defect detection method. 28. The method of claim 27, And the workpiece is a plate-shaped workpiece. 28. The method of claim 27, And the angle α is 5 ° or more with respect to the direction of light generation. 30. The method of claim 29, And the angle α is 50 ° or less with respect to the direction of light generation. 30. The method of claim 29, The angle α is in the range of 10 ° to 35 ° with respect to the direction of light generation, characterized in that the defect detection method. delete 30. The method of claim 27 or 29, And the light source is focused so that the focus is within the substrate. 30. The method of claim 27 or 29, Wherein the substrate is irradiated with an irradiation intensity of at least 2.5 * 10 ⁶ watts per square meter. 30. The method of claim 27 or 29, And the focus of the light source is adjusted to a focus having a minimum range of 200 micrometers. 36. The method of claim 35 wherein And the light source has a focal point with a minimum range of at most 150 micrometers. delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete

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