WO2006087213A2

WO2006087213A2 - Method and device for detecting and/or classifying defects

Info

Publication number: WO2006087213A2
Application number: PCT/EP2006/001465
Authority: WO
Inventors: Klaus Gerstner; Clemens Ottermann; Bernhard Hunzinger
Original assignee: Schott Ag
Priority date: 2005-02-18
Filing date: 2006-02-17
Publication date: 2006-08-24
Also published as: KR20070107773A; TW200636230A; WO2006087213A3; KR101332786B1

Abstract

The invention relates to a device for detecting defects, more particularly in the surfaces of workpieces, wherein radiation is directed at a workpiece and is at least partially influenced by the workpiece, preferably by the defect.

Description

Method and device for detecting and / or classifying defects

description

The invention generally relates to the quality control in the production and / or processing of workpieces, in particular the optical detection and / or

Classification of errors on or in workpieces.

In particular, in the production of highly integrated electronic or optoelectronic devices very high demands are placed on the substrates used both on the surface quality, as well as the freedom from defects of the substrate volume. Especially in this area, a particularly rapid mass production is desirable in order to reduce the production costs so far that the manufacturers can prevail in the prevailing strong competition here. For example, to reduce production costs, ever larger substrates are used to increase the number of components produced in parallel on the substrate. Although the production time for producing a larger number of components on a substrate generally does not increase or only slightly, this is generally not true for quality control, since correspondingly larger areas or a larger number of components must be controlled. Since various types of defects exist, such as particles on or scratches in the glass, and for these different types of defects in further processing different workflows may be useful, in addition to the detection of defects and their classification of high value.

The invention is therefore based on the object to be able to provide an optical error detection and classification of errors of substrates, which even at high speed error detection meets the highest quality assurance requirements.

This object is already achieved in a surprisingly simple manner by the subject matter of the independent claims. Advantageous developments and refinements of the invention are specified in the subclaims.

Accordingly, the invention provides an apparatus and a method for detecting defects, in particular on surfaces of workpieces, preferably plate-shaped workpieces, such as glass plates, in which radiation is directed to a workpiece and is at least partially influenced by the workpiece, preferably by the defect. In particular, it is provided to detect at least part of the radiation influenced by the defect from an optical detector.

According to one embodiment of the invention is also an apparatus and a method for detecting and / or classification of defects, especially on surfaces of workpieces, in which radiation at least one light source is directed to a workpiece and is at least partially influenced by the workpiece, preferably by the defect , in which a first and a second optical signal is generated and from these signals a distinction of the defect is possible.

Accordingly, the invention provides a device for detecting and / or classifying defects, in particular on surfaces of workpieces, wherein radiation of at least one light source is directed to a workpiece and is at least partially influenced by the workpiece, preferably by the defect, in which a first and a second optical signal is generated and from these signals a distinction of the defect is possible.

By a classification, which includes in the inventive sense, for example, the distinction of types of defects, for example, the distinction of lying on the substrate of particles located in the substrate scratches or embedded air bubbles in the substrate, the subsequent processing can be influenced very positively.

Upon detection of particles, a substrate may be supplied for further purification, for example. In this case, a ^' storage of the ^' location of one or more detected particles and / or detected scratches in a subsequent data processing system can be carried out, which controls the further processing operations.

This can either cause further cleaning or the cutting of substrates are made so that particulate coating tolerated and glass areas with ^' scratches through the blank are discarded. The liberation of particles can be done both before and after cutting.

With the method according to the invention, particles with diameters in a range of one-half to five micrometers are still reliably detectable and distinguishable from scratches and bubbles in the glass. These particles can be both externally introduced solids and remaining residues of a previous cleaning process, such as detergent residues or very fine droplets on the glass surface.

Particularly preferably, the illumination comprises a bright field and a dark field illumination arrangement. In particular, the or the optical detectors are arranged so that they detect at least areas of the dark field.

As an intense and specially directed light source, for example, one or more lasers are suitable.

Among other things, the light source may comprise a scanning system for scanning the workpiece, in particular in conjunction with a line scan camera or another detector with parallel detection of multiple surface areas or with the scanning system synchronized optical detection.

The optical detector preferably comprises a plurality of light-detecting pixels, each. detect light originating from different substrate areas in order to be able to examine large surface areas simultaneously with high accuracy. Different areas of the substrate do not necessarily mean disjoint areas here, but rather the areas may partially overlap, for example. Furthermore, a lighting device is provided which has a plurality of light source points, which are arranged so that falls on each of the substrate regions light from at least two different directions of incidence. This is advantageous for being able to detect elongated structures, such as scratches, since the light scattering on such structures is generally strongly dependent on the angle between scratch and incident light. In this way it is also possible to reliably detect any scratches along the surface and only slight scratches. It is advantageous if the directions of incidence include an angle of at least 45 °, preferably of at least 90 °, particularly preferably of at least 120 °. An angle between two directions of incidence of at least 120 ° is particularly favorable when the light from more than two directions on the respective surface area, so for example from at least three directions on the surface falls. A light source does not necessarily have to be a separate light source. Rather, the light of one or more light sources can be divided in a suitable manner.

Particularly preferably, the optical detector comprises a line camera, with which along the surface elongated regions of the substrate to be tested are verifiable in parallel. According to a further embodiment, the optical detector comprises an imaging camera, with which the substrate along the surface sections, or even can be detected at once.

The optical detector can be particularly advantageously preceded by a 4f arrangement. It has surprisingly been found that such an arrangement is able to emphasize light scattering effects on defects of the substrate particularly. This is especially the case when the 4F Anor.dnung is arranged such that it performs a filtering of structure sizes, which does not correspond to the structure size of the defects to be detected. Likewise, with the same advantages, alternatively or additionally, the illumination device can be followed by a 4F arrangement.

Particularly preferably, the lighting comprises a

Darkfield lighting arrangement. In particular, the or the optical detectors are arranged so that they detect at least areas of the dark field. A dark field arrangement is just by the elimination of the direct light signal for detecting particularly small errors, so suitable for the highest requirements. According to yet another embodiment of the invention is the

Dark field illumination arrangement confocal to the optical axis of the optical detector arranged in reflection to turn off remaining background signal. In this case, the dark field illumination arrangement can be arranged confocal to the optical axis of the optical detector in transmission.

The illumination may further include a phase contrast illumination arrangement. Even with such an arrangement, the smallest deviations in surface or volume structure can be detected with high contrast.

The illumination can be made according to the invention both in transmission, as well as in reflection, as well as in combination of transmission and reflection.

In particular, for the detection of surface defects, it is also advantageous if the illumination is made with obliquely incident light. It becomes oblique incidentally in the sense of the invention as incident obliquely to the illuminated surface of the substrate understood. The obliquely incident light may advantageously comprise a narrow light beam which illuminates only one of the two main surfaces of a substrate to be tested in the field of view of the camera.

According to a particularly preferred embodiment, the light is focused and irradiated at an oblique incidence on the substrate, wherein the optical axis of the

Detector is arranged at an angle α to the light beam, for which applies:

α> arcsin (n _s • sin (aretan (b / d)), preferably

α> 1.2 • arcsin (n _s • sin (aretan (b / d)).

Designates _s ή the refractive index of ^'the substrate, b is the smallest dimension of the focus of the light beam and d is the thickness of the substrate. In this sense, the focus is understood to be the area of smallest expansion perpendicular to the direction of light propagation, at which the intensity of the boundary has dropped to 1 / e relative to the maximum intensity. The focus is particularly preferably within the substrate. In this way, a dark field view is made possible, in which the illuminated by light beam surfaces are adjacent to each other so that they do not overlap from the perspective of the detector. At the same time, the focusing achieves a high light intensity at the substrate surfaces. In this case, the distance between the areas illuminated on the surfaces in projection onto the viewing direction of the optical detector is preferably in the range from 100 μm to 500 μm. In this case, the detector can in particular also be directed perpendicular to the substrate surface. In this case, ie with the optical axis directed perpendicular to the workpiece surface, the angle α then corresponds to the light incidence angle.

Preferably, in particular in the above embodiment of the invention, the detector is further arranged on the light exit side of the substrate and views the illuminated area at an acute angle to the emergent beam. However, the angle is preferably more than 5 ° and more preferably less than 50 ° to the light-out direction, more preferably in the range of 10 ° to 35 °. More than 5 ° have proven to be beneficial to direct posts

Exclude lighting. Too large angles, such as a right angle, however, are also less favorable, since it has been found that the scattering of the small structures to be detected, such as weak scratches, is generally at least partially Mie-like. Mie scattering gives preference to forward scattering. Accordingly, the scattering intensity in directions around the light-out direction is higher than in other directions.

In order to detect the two illuminated areas, according to one embodiment of the invention, the optical detector may comprise a camera with at least two lines. It is positioned with respect to the light source and the substrate so that one of the lines detects the surface area illuminated by the light striking the substrate and the other line detects the surface area illuminated by the light exiting the substrate. A further general improvement of the invention for detecting extremely weak scatterers on the surfaces consists in the use of a signal amplifier for the optical detector, in particular a photomultiplier or a multi-channel plate. The optical detector can then be used in particular in conjunction with a scanning light beam. In particular, the light beam can be focused to increase the light intensity and spatial resolution. Particularly suitable is focused laser radiation, which is scanned with a scanning system over the surface of the workpiece.

In an imaging detector, in particular a multi-channel plate can be used, which is the

It has surprisingly been found that conventional optical methods for the determination of defects on glass substrates are not sufficiently sensitive, even for large areas

To be able to quickly and completely check substrates for defects which, in particular in the production of TFT displays on such substrates, still have a disadvantageous effect up to a scrap. For example, such errors can be scratches of microscopic width far below the wavelength of the light.

However, the inventors have recognized that with the use of high intensity light sources in the dark field such for the production of TFT displays still disturbing structures are still recognizable. According to a special. According to a preferred embodiment of the invention, a light source with an irradiance on the substrate of at least 2.5 × 10 ⁶ watts per square meter and a scattered light detection is used used. Such light intensities can be achieved in particular by means of focused light sources. For this purpose, according to a development of the invention, provision is made for a focused light source having a focus with a minimum extension of at most 200 μm, preferably at most 150 μm.

By means of the invention, it is thus still possible to reliably detect defects having a structure width of 100 nanometers, such as scratches having a width of the order of 100 nanometers.

The obliquely incident light can also be s-polarized in an advantageous manner. Thus, the reflection at defect-free areas of the surface of the substrate to be tested is reduced, so that an improved signal-to-noise ratio of the originating from surface defects scattered light signal is achieved. It is particularly advantageous if the obliquely incident light is irradiated relative to the workpiece under the Brewster angle.

Additionally or alternatively, the optical detector having a similar effect may comprise a polarizer which polarizes the light substantially perpendicular to the polarization of the light reflected from the workpiece. For the purposes of the invention, the term "essentially" means in particular that this applies to the main surface, but not to the defect, for example, In other words, the polarizer is adjusted so that light reflected from defect-free regions of the surface is blocked.

In order to enable a clean separation of light reflected by defects and reflected light on defect-free surface areas, it is particularly advantageous if the illumination comprises a laterally arranged from the optical detector lighting, which lower or no light components perpendicular to the substrate surface.

The illumination means may comprise in vorteilha ^'fter further also mirror for beam shaping.

According to a further development, it is provided in this regard that the illumination device comprises faceted mirrors for defining a plurality of foci on the workpiece, from which spherical waves emanate. Another way to provide illumination with a variety of individual light sources is. a

Lighting device with at least one holographic optical element for defining a plurality of foci on the workpiece. A portion of such holographic optical elements may comprise a phase hologram, which preferably includes vapor deposition glass. Accordingly, the structures holographically effective structures can be prepared by structured vapor deposition of a vapor-deposited glass. The holographic optical element may be arranged in particular on a refractive element, such that the desired illumination of the substrate can be performed by one or more light sources which irradiate the holographic ^'optical element. According to another embodiment of the invention, the holographic optical element is arranged on a reflective element. The light source may advantageously also comprise a holographic optical element and a cylindrical lens in order to achieve the desired angular distribution of the light incident on the workpiece.

The one or more light sources used can advantageously also be limited in their bandwidth. The scattering intensity is generally dependent on both the shape and the size of the scattering elements. To be able to detect the smallest possible defects is In this regard, for example, the use of a light source whose spectrum is at wavelengths less than 300 nm, advantageous.

Also, the light source can advantageously emit light at a wavelength at which. the workpiece to be tested has only low transmission, in particular a transmission of less than 50%, preferably less than 25%, most preferably less than 15%. In this way, it can also be easily distinguished on detection of a surface defect or a surface contamination on which side of the workpiece the defect found. When using further light sources, in which the workpiece is transparent, it is then also possible to distinguish between surface and volume defects. '

Particularly advantageous is the use of several simultaneously operated light sources, or light sources with simultaneously emitting light source points, in order to achieve a high light intensity and thus a high sensitivity of the arrangement according to the invention. Suitable for this purpose is, for example, a laser diode array. In this case, a linear laser diode array is preferably used. According to yet another embodiment, a laser diode array is used, which For example, includes a collimator assembly which generates a single light beam. Such a light source is advantageous, inter alia, in conjunction with a line scan camera as an optical detector. A laser or laser diode array may further be defined to adapt the longitudinal coherence to a plurality of longitudinal. Emit fads. It is further contemplated that the laser or laser diode array may be short pulsed, or operable to define desired longitudinal coherence characteristics.

According to another embodiment of the invention, the laser diode array may comprise at least one FAC and preferably additionally at least one SAC lens which generates at least one focus on the workpiece. This makes it possible to produce a linear focus on the workpiece, which in turn is outstandingly suitable in combination with a line scan camera arranged parallel to the focus for detecting scattered light from defects in the workpiece. The light source may also include a phase framer to define desired transverse coherence. This makes it possible, in particular, to switch off unwanted interference effects that cause false signals.

According to a further embodiment of the invention, the light source may also comprise a fluorescent or fluorescent tube. With such a light source, a plurality of surface areas can be illuminated in particular in an arrangement parallel to the surface of the workpiece so that the respective surface areas are illuminated in each case by light from different directions. For further analysis of the workpiece, a fluorescent tube with several spectral emission bands can also be used. Thus, for example, at the same time fluorescence and Stray light measurements are performed. Preferably, a fluorescent or fluorescent tube is arranged parallel to a line scan camera as part of the optical detector.

According to a particularly preferred embodiment of the invention, the workpiece comprises glass, or glass is examined as a workpiece. In particular, can be examined with the invention thin glass. The invention is suitable in this respect for checking the quality of floated thin glass, downdraw thin glass, downdraw fusion thin glass, in particular overfiow downdraw glass.

Even remaining surface defects of surface-treated, in particular polished workpieces can still be detected and / or distinguished. For example, even extremely weak polishing scratches can be detected.

It is intended, in particular, for the invention

Glass inspection apparatus for a display, in particular a TFT display. With respect to the surface finish, such glasses are subject to particularly stringent requirements, since even the smallest scratches, which can occur during polishing or during handling in the production process, can adversely affect the coatings applied to the glass.

It is assumed that even large-scale

Substrates, such as thin glass with a width of more than 1.8 meters and / or a length of more than 2.0 meters according to the invention can be checked so quickly that the production process in the production of TFT displays such substrates is not or only slightly slowed down.

Thin glass, which has been tested with a device according to the invention and sorted using the test results, has in this way a significantly reduced error concentration or number of errors. For example, in a batch of tested thin glass, the concentration itself of scratches having a depth of 3 ^' to 30 nanometers should be less than 5, preferably less than 3, more preferably less than 1 per square meter.

Significant increases in yield are also due to the distinction, or the classification of the

Fault types achieved, which then leads to waste or waste only to the smallest extent necessary.

In ^'The invention is based on

Embodiments and with reference to the drawings explained in more detail, wherein the same and similar elements are provided with the same reference numerals and the features of various embodiments can be combined.

Show it:

Fig. ^'L in a schematic view a device for detecting flaws on thin glass according to an embodiment of the invention,

2 shows a variant of the device shown in Fig. 1, 3A, 3B parts of developments of devices according to the invention,

Fig. 4 shows a further embodiment of the invention with

Phase contrast detection of defects,

5 shows the optical beam path according to a

Development of the invention,

Fig. 6 shows an embodiment with straightening

Means for generating a plurality of foci on the substrate surface,

7 shows an embodiment with illumination by means of focused laser radiation,

Fig. 8 shows a variant of that shown in Fig. 7

Embodiment with photomultipliers and a scanning system,

Fig. 9 shows a development of the invention with a plurality of juxtaposed optical

detectors,

A receptacle with an optical detector, such as can be obtained with a device according to Fig. 7 Fig. 10 ^■.

Fig. 11 is a greatly simplified schematic

Representation of a flat glass substrate from the side on which a particle and in which there is a scratch, Fig. 12 is a greatly simplified schematic

Illustration of a. Flat glass substrate from obliquely above, on which there are two scratches and their optical signal in the bright field and in the dark field,

Fig. 13 shows a preferred embodiment of the device according to the invention.

1 shows a schematic view of a device for detecting defects on and / or in workpieces 3. With the apparatus of this exemplary embodiment designated as a whole by the reference numeral 1, in particular thin-glass substrates 3 are checked for the presence of defects. Typical errors can be detected, such as those caused by the manufacturing process, for example with downdraw thin glass, downdraw fusion thin glass, in particular overflow downdraw glass or float glass, as well as due to postprocessing. In particular, the device is also surprisingly suitable for rapid testing of very large substrates, such as thin glass with a width of more than 1.8 m. and / or a length of more than 2, 0 m.

Such imperfections may be, for example, polishing scratches on the surface 31 of the thin glass substrate 3, as they may remain in the surface treatment. With the device 1 for detecting defects, radiation is directed by means of a lighting device 11 on the workpiece and at least partially influenced by the workpiece, in particular by the defect. At least part of the radiation influenced by the defect is then detected by an optical detector 5. In the embodiment shown in Fig. 1, the optical detector comprises in particular a line camera 7. A Focusing optics of the line scan camera is designed so that each pixel of the camera 7 detects a different surface area of the thin-glass substrate 3, or from this outgoing light. The totality of the detected surface areas gives an elongated

Surface area 20, which is illustrated in Fig. 1 by dashed lines. The surface region 20 extends in particular along the entire width of the substrate 3, so that the entire surface 31 or the entire substrate 3 can be detected by a single pass from the substrate at the optical detector 5. For this purpose, both the substrate 3, and the detector can be moved.

The illumination device 11 is formed so as to form a plurality of light source spots arranged so that light from at least two different directions of incidence falls on each of the substrate regions which detect the individual pixels of the line scan camera.

In the example shown in FIG. 1, this is achieved by the light source comprising a fluorescent tube 13. This extends parallel to the line scan camera. And is suitably collimated and focused by means of a cylindrical lens 15, so that substantially only the narrow surface area 20 is illuminated. In addition, the illumination is made with obliquely incident light, while the line scan camera looks substantially perpendicular to the surface, so that no directly reflected light can enter the line scan camera 7. The fluorescent tube emits its light isotropically, so that any longitudinal section of the fluorescent tube forms a light source. In this way, light falls from many different directions on each of the detected substrate areas. For example, in the case of the arrangement shown in FIG. 1, an area at the very edge of the substrate 3 is covered by light under all possible directions of incidence, which differ at most by an angle .alpha. The length of the fluorescent tube and its distance to the region 20 can then be chosen so that the different directions of incidence make an angle of at least 45 °, preferably at least 90 °, more preferably even at least 120 °. In this way, scratches that run along any direction of the surface can be reliably detected. Furthermore, as can be seen with reference to FIG. 1, which is arranged laterally from the optical detector, wherein the illumination by the illumination device 11 has lower or, in particular, no light components perpendicular to the substrate surface 31.

To gain further information regarding the nature of defects, the fluorescent tube can have multiple spectral emission bands. In this way, for example, in conjunction with appropriate

Filtering the Optical Detector Fluorescence signals and / or scattering signals at different wavelengths are detected.

Due to the arrangement with oblique incidence of light and vertical detection of scattered light is detected by the optical detector. Accordingly, the illumination of this embodiment particularly represents a dark field illumination arrangement.

FIG. 2 shows a variant of the device 1 shown in FIG. In this variant of the invention, the optical detector 5 comprises, in a modification of the embodiment shown in Fig. 1, an image-recording camera 17, the pixels of a grasp square or rectangular area 20 on the surface. In addition, in this example, the illumination device 11 comprises a plurality of fluorescent tubes 13 configured in accordance with the exemplary embodiment shown in FIG. 1, which are also arranged to illuminate the surface 31 of the substrate 3, in particular the surface area 20 covered by the pixels, under oblique incidence of light Achieve dark field illumination.

Also in this embodiment, the light source points are arranged along the fluorescent tubes so that light falls from at least two different directions of incidence on each of the substrate regions, the directions of incidence for each of the surface regions within the region 20 detected by the respective pixels being at an angle α of at least 45 °, preferably at least 90 °, more preferably at least 120 °.

In both embodiments, the thin glass substrate 3 is guided along a feed direction 100 by means of a feed device, not shown, so that the substrate 3 is checked its length.

It can be arranged side by side and transverse to the feed direction 33 in the embodiments shown in FIGS. 1 and 2 also several optical detectors. In general, an arrangement with a plurality of transverse to the feed direction optical detectors, which detect the substrate in its entire width across the feed direction, in particular. Preferred, in particular for wide substrates 3 in order to check their surface with high resolution can. Fig. 3A and 3B parts of developments of inventive devices. 3A shows an optical detector 5 with a line scan camera 7, wherein the optical detector 5 is preceded by a 4F arrangement 25. The 4F arrangement comprises two cylindrical lenses 26, 27, in whose common focal plane a diaphragm 30 is arranged.

In an analogous manner, in the example shown in FIG. 3B, the illumination device 1 1 with a collimated and focused fluorescent tube 13 is followed by a structure corresponding to a 4F arrangement. Such lighting devices and optical detectors with subsequent or upstream 4F arrangement can be used for example in the embodiments shown in FIG. 1 or 2.

By means of the diaphragm 30 of the 4F arrangement, the 4F arrangement 25 can effect a filtering of structure sizes which do not correspond to the structure size of the defects to be detected.

FIG. 4 shows a further exemplary embodiment of a device 1 according to the invention for detecting defects. This embodiment of the

The invention is based on phase contrast detection of defects, such as, in particular, scratches on the surface 31 of a thin glass substrate for TFT displays.

The basic structure is similar to the example shown in FIG. 1, however, the optical detector is constructed so that its optical axis lies in the light beam of the illumination arrangement reflected by the surface 31. In front of the illumination device 11, a slit diaphragm and a cylindrical lens is arranged, which focuses the light of the slit diaphragm 30 onto the substrate surface 31. In the reflected beam, a further cylindrical lens 36 and a phase plate 38 having a linear light-attenuating region 39 are arranged in front of the line camera 7 of the optical detector 5. The phase plate 38 is arranged so that the directly reflected light is attenuated by the line-shaped region 39. If there are defects or even soiling on the surface 31 or even in the volume of the thin-glass substrate 3, these lead to light scattering. The scattered light then has a direction deviating from the mirror beam and passes laterally past the line-shaped attenuating region 39 of the plate 38 into the line scan camera. On the respective pixels of the line scan camera 7 there is then an interference of the scattered with the attenuated direct light beam, so that defects due to the occurring

Interference phenomena can be easily detected. Again, any arbitrary longitudinal portion of the aperture 30 forms again a light source point, so that each illuminated through the slot of the aperture 30 surface area is illuminated from several different directions. In order to be able to detect, for example, scratches running in any direction, it is particularly advantageous if the directions of incidence include an angle of at least 45 °, preferably of at least 90 °, particularly preferably of at least 120 °.

In all of the embodiments illustrated in FIGS. 1 to 4, advantageously polarized light can also be used. Is, as measured in these embodiments in reflection, it offers It is also intended to use a lighting device 11 which emits s-polarized light with respect to the surface 31. Thus, the reflection is suppressed at error-free surface areas and achieved an improved signal-to-background ratio. With all these

Arrangements, the illumination device 11 can then be advantageously arranged so that the light falls in or around the Brewster angle on the surface.

Furthermore, in all these Ausführngsbeispielen the lighting devices on the side 31 opposite side 32 of the substrate 3 can be arranged so that the light is not reflected, but is transmitted through the substrate 3. The position of the illumination adjustment 11 is mirrored in each case on the substrate 3 with respect to the position shown in FIGS. 1, 2, 4.

Furthermore, in the embodiments shown in FIGS. 1 and 4, the areas illuminated by the illumination device linear areas can be kept so narrow by means of appropriate collimation and / or focusing at oblique incidence that in the field detected by the line camera 20, or in the image field only one of both main surfaces, so one of the surfaces 31, 32 is illuminated. Such an arrangement is outlined in Fig. 5, which illustrates the beam path according to this embodiment of the invention. The arrangement of the optical detector 5 and the illumination device, not shown here, can correspond, for example, to the example shown in FIG. The obliquely incident light beam 40 illuminates a region 41 on the surface 31 and a region 42 on the opposite surface 32. The refraction of the light beam was not considered in the illustration. The one of the Line detector 7 of the optical detector 5 detected area 20 is within the range 41, but outside the range 42. Accordingly, in the field of view of the camera 7 only one of the two. Illuminated surfaces. This is particularly useful because in this way signals due to stray light from defects on the surface 32 are suppressed. For example, a substrate 3 for the manufacture of TFT displays may still be used if there are no scratches on the coating side, although there may possibly be a scratch on the opposite side which would cause the coatings to be contaminated but optically completely inconspicuous is. By an arrangement, as shown in FIG. 5, therefore, the committee ^ can be considerably reduced.

There are still further measures conceivable to avoid the detection of defects on the opposite side 32. If, for example, when checking the workpieces, only surface defects such as scratches occur, it is also possible to use light of a suitable wavelength, which does not penetrate the substrate 3. Thus, for float glass, for example, a bandwidth-limited light source having a spectrum of wavelengths smaller than 300 nm can be used. Light of these short wavelengths is no longer transmitted, so that only superficial or possibly near-surface defects are detected. Generally, to distinguish flaws on the top and bottom of the workpiece, or even to exclude the detection of flaws on the opposite side, it may be advantageous to use a light source that emits light at a wavelength at which the workpiece transmits only little, in particular a transmission less than 50%, preferably less than 25%, most preferably less than 15%.

If, as mentioned above, polarized light, preferably incident at the Brewster angle, is used, according to a further development of the invention, an optical detector 5 as shown in FIG. 5 can be provided with a polarizer 45 which transmits the light essentially perpendicular to the polarization of the reflected light from the substrate 3 polarized. Accordingly, using s-polarized light, one would adjust the polarizer so that reflected s-polarized light is blocked by the polarizer 45.

FIG. 6 shows a further variant of the example shown in FIG. 1. In this example, instead of the fluorescent tube, a laser, in particular a laser bar 50, for example a laser diode array with a plurality of linearly arranged in the direction parallel to the surface 31 laser diodes used. The laser diode array may comprise at least one FAC, and preferably additionally at least one SAC lens, which generate at least one focus on the workpiece. In order to avoid undesired interference effects, a phase framer scrambler may additionally be provided. The ^"laser diode array may continue to adjust the longitudinal coherence at multiple longitudinal modes defined emit and / or desirable to define the longitudinal coherence properties kurzzeitgepulst be operated.

Although lasers are particularly advantageous because they emit intense, highly parallel light, but this effect is just annoying, if according to the invention for each of the pixels of the line scan 7 detected surface area light from different Would like to use directions of incidence. To achieve this, the laser is a. corresponding jet-forming device downstream. In the example shown in FIG. 6, the illumination device 11 comprises holographic optical elements for defining a plurality of foci on the substrate. In particular, the holographic optical element comprises a phase hologram. Specifically, a phase hologram plate 52 is disposed in front of the laser bar 50.

The phase hologram can advantageously be produced by structured deposition of vapor-deposited glass on a glass plate as a refractive element. With the phase hologram, the light beams are also deflected and focused in the direction of the surface, so that again falls on each of the detected surface areas of the pixels light from different directions of incidence. Instead of a glass plate can be used as a refractive element and a cylindrical lens. Thus, for example, the focusing in the lateral direction through the cylindrical lens and the focusing under different directions of incidence along the surface 31 can be effected by the phase hologram.

The illumination device also includes mirrors for beam shaping in this example. In particular, in this example, a faceted mirror 54 with concave facets is provided which also serves to define a plurality of foci on the workpiece. This is arranged in the mirror beam so that the light is just reflected back to increase the light intensity on the illuminated surface area. - Instead of or in addition to concave mirror facets, the mirror 54 may also be designed as a reflective element and support for holographic optical elements in order to reflect back light onto the detected surface area under different directions of incidence.

Fig. 7 shows a further embodiment of the invention, in which focused laser light is used for the detection of defects. By means of a lens 56, a light beam 40 incident in the direction of the surface 32 of the thin-glass substrate 3 is focused so that the focus F lies within the substrate 3. The light is focused by means of the lens 56 so that the focus has an extension of at most 200 microns, preferably at most 150 microns. The aim is in particular a minimum extension of the focus in the range of about 50 microns to 100 microns. As a light source - this is not shown in Fig. 7 for clarity - preferably a laser or a laser bar is used with a plurality of laser sources. As a result, high intensities with irradiation intensities on the substrate of at least 2.5 × 10 ⁶ watts per square meter can be achieved by focusing. On the surfaces 31, 32 arise from the light source illuminated areas 41 _f 42, at which light is scattered at defects.

Similarly to the embodiment shown in FIG. 5, the detector 7 is disposed opposite to the light incident direction with respect to the substrate 3, so that the light scattered on the surface region 42 is detected by the detector 5 in transmission. The detector is also arranged so that ^' the area 41 on the detector 5 side facing 31 of the substrate 3 from Detector 5 is detected. The optical axis 58 and the center beam 60 of the emergent light beam are also arranged at an acute angle α. This angle α is chosen so that the two areas 41, 42 do not overlap from the perspective of the detector 5. This is guaranteed if the angle α is:

α> aresine (n _s • sin (aretane (b / d)),

where n _{s is} the refractive index of the substrate, b is the smallest dimension of the focus of the light beam and d is the thickness of the substrate. In this respect, the refraction of the light in the substrate, which is not shown in FIG. 7, is also taken into account. The angle is more than 5 ° in the example shown. This lower limit is useful in order to avoid the detection of direct light from the peripheral areas of the light bundle during short focal length focusing. In particular, the angle α is preferably at least 10 °, particularly preferably in the range of 10 ° to 30 °.

Due to the refraction of the light beam is deflected when passing through the substrate in the direction perpendicular to the surface thereof. As a result, the regions 41, 42 at a given angle α in the projection move closer together as viewed from the detector 5 with a higher refractive index. However, if the angle is selected in accordance with the above-mentioned relationship, the regions 41, 42 for the detector can be detected separately. Thus, it is also possible to detect on which of the sides 31, 32 of the substrate 3 a detected defect lies. Since the optical axis 58 of the detector is directed perpendicular to the surface 31 of the substrate 3, the angle α here also corresponds to the light incident angle.

In order to detect the two illuminated areas, according ^• 71 and 71 comprise a line camera 7 with at least two lines of an embodiment of the invention, the optical detector. This is arranged with respect to the light source and the substrate 3 so that by means of the optics 63 of the detector 5 one of the rows 72 illuminated surface area 42 illuminated by the substrate on the substrate and the other line 71 the surface area illuminated by the light emerging from the substrate 41 recorded.

The arrangement with a measurement in transmission, or with a detector arranged opposite to the incident light beam, as shown in FIG. 7, is preferred to an arrangement in which the detector is arranged on the light incident side.

The arrangement shown in Fig. 7 allows observation of the surface portions 41, 42 at acute angles without causing problems with the arrangement of the light source and the detector 5 due to their dimensions. Such problems may arise in particular because of the preferred short focal length lens or lenses for focusing. Short focal length lenses are advantageous for producing small foci and thus high light intensities on the surfaces 31, 32 of the substrate. This is accompanied by the fact that the focusing lens 56 is to be arranged very close to the substrate surface 32 in order to achieve a position of the focus in the region of the substrate, preferably within the substrate. In addition, in many scattering structures, the forward scattering predominates, resulting in a better signal-to-noise ratio. Under certain circumstances, however, a configuration with a detector on the light incidence side also makes sense, for example if the signal of particularly small scattering structures is to be emphasized in comparison to the scatter signals of larger structures. For very small defects, for example well below 100 nanometers structure size, the intensities of forward and in this case the detector detected backward scattering are similar according to the intensity distribution of the Rayleigh scattering.

The detector can also include a signal amplifier to detect individual scattered photons with the highest sensitivity and security for the detection of the smallest defects. In question come here, for example, photomultipliers or multi-channel plates. An exemplary embodiment is shown in FIG. 8. In the

Fig. 8 shown device 1 is a variant of the embodiment shown in Fig. 7. Again, the substrate portions 41, 42 are detected separately, so that it is distinguishable on which of the substrate sides 31, 32 is a defect. Unlike the in

In the embodiment shown in FIG. 7, in the device 1 shown in FIG. 8, photomultipliers 61, 62 are provided as components of the optical detector. The optics 63 of the detector, similar to the embodiment shown in Fig. 7 is formed so that each of one of the areas 41, 42 outgoing light beams are each focused on one of the photomultipliers 61, 62. In order to obtain spatially resolved information about the position of a defect, in this embodiment a scanning system with a scan Unit 65 is used with which the substrate 3 is scanned across the feed direction 33 by means of a laser beam. The scanning unit 65 may be, for example, a Galvo scanner. In addition, by moving the substrate 3 along the feed direction 33 by means of a feed device, the entire substrate surface can be detected in this way.

Around the entire surface of the substrate 3, or at least a large part to detect it and to check, the substrate is moved past the device 1 as in the examples shown in FIGS. 1 and ^'2 embodiments, along the feed direction 33. In this way, the detected regions 41, 42 extending across the width transversely to the feed direction cover the entire surfaces 31, 32 or at least the regions of the thin-glass substrate to be checked.

If, for example, an edge region of the substrate is not used for the production of display glass, this region does not necessarily have to be scanned with it. However, it is preferred to test at least 80% of the area even of large-area substrates, in particular thin-glass substrates with a width of more than 1.8 meters and / or a length of more than 2.0 meters, in order to achieve as complete a characterization as possible to maintain the glass quality. Of course, this also applies to all other embodiments described here. In the case of such large substrates, it is also advantageous to use a plurality of detectors 5 arranged next to one another, as shown in the development of the exemplary embodiment of FIG. 7 shown in FIG. The detectors are arranged side by side along the width of the thin-glass substrate 3 perpendicular to the feed direction 33. On the opposite side are several likewise juxtaposed lighting devices. In the example shown, laser bars 50 are used for illumination. Also shown on the side facing the detectors 5 side 31 of the substrate 3 each detected, transverse to the feed direction and along the entire width of the substrate 3 extending surface region 41, which is illuminated by the exiting, perpendicular to the feed direction 33 laser light.

In order to hold the substrate in its intended for the measurement position and to move the substrate along the feed direction, an advancing and holding device is provided. In the example shown, this comprises rollers 55 on which the substrate 3 rests and is moved along the feed direction 33 by the rotation of the rollers. Of course, a feed and holding device can also be provided in the other embodiments shown in order to keep the substrate in the intended position.

FIG. 10 shows a receptacle as can be obtained with an arrangement according to FIG. 7 or FIG. 8. However, the image was not taken with a line camera or photomultipliers in conjunction with a scanning system, but with a matrix camera. The image is shown in negative so that spots emitting stray light appear dark in FIG. The illuminated strip-shaped surface regions 41, 42 are identified by dashed lines. In the surface area 41, some punctiform scattering structures can be recognized. These are due to particles 66 on the surface. The opposite surface of the substrate 3 with the Illuminated area 42 has a fine scratch 67, which is clearly visible in the recording.

When tested with a device according to the described embodiments thin glass, the

Concentration of scratches can be significantly reduced by sorting out as defective detected glasses. For tested thin glass, the concentration of scratches having a depth of 3 to 30 nanometers can be reduced to less than 5, preferably less than 3, more preferably less than 1 per square meter. A production line, in particular for the production of TFT displays, which comprises such device according to the invention is thus able to quickly provide high-quality end products.

Also, in manufacturing lines, for example, for glass production, an online feedback of the results obtained with the device according to the invention in the manufacturing process can be made. This can be the

Manufacturing process can be controlled and optimized directly using the device for detecting defects.

In the following detailed description, the content of the filed on 18 February 2005 German Patent and Trademark Office German patent application 10 2005 007715.3 entitled "Method and apparatus for detecting defects" fully made the content of the disclosure of this application. In particular, the incorporated arrangement can be supplemented or combined with the device described below.

11 shows a greatly simplified schematic representation of a flat glass substrate 3 from the side, on which a particle 162 and in which a scratch 162 is located.

The particle 162, which typically has a size of 0.5 μm and more, for example, up to 5 μm or more

Diameter, both in viewing the ^" substrate from above with a bright field arrangement, as will be described in more detail below as well as when viewed with a dark field arrangement, as will also be described below, ^' good to see.

From Fig. 12, however, it can be seen how optical signals differ in the bright field of optical signals in the dark field. The reference numeral 164 shows a scratch, thus a line defect, as this can be seen in the dark field with good contrast.

Reference numeral 166 schematically indicates the optical signal, thus the image of a line-shaped defect, ie one

Scratcher when viewed in a bright field arrangement again. This optical signal has much less contrast in the bright field than in the dark field, and it can thus by subtracting the locally resolved optical signals of a bright field array of the locally resolved

Signals of a dark field arrangement of the particulate portion of the defects of scratches or bubbles in the glass can be distinguished.

If one subtracts the spatially resolved optical signals point by point from each other, arise at those points where low contrasts on high contrasts meet clear difference signal components, which are essentially scratches and bubbles in the glass. The contrast of the difference signal image now allowed to distinguish the scratches or bubbles from the particles, since they have much less contrast in the difference signal.

For this difference signal formation, the maximum or average intensity of the respective image can be normalized so that a value in the vicinity of the intensity zero value results for areas which are without defects. ,

FIG. 13 shows a schematic view of the device for detecting defects on and / or in workpieces 3.

With the designated as a whole by the reference numeral 1

Device of this embodiment, in particular thin glass substrates 3 are checked for the presence of defects.

Typical defects can be detected, such as those caused by the manufacturing process, for example with downdraw thin glass, downdraw fusion thin glass, in particular overflow downdraw glass or float glass, as well as due to post-processing. In particular, the device is suitable in a surprising manner and in a rapid testing of even very large substrates, ^'as thin glass with a width of more than 1.8 m and / or a length of more than 2.0 m.

Such defects, for example, again

Polishing scratches on the surface 31 of the thin glass substrate 3, as in the surface treatment. remain behind or can arise. With the device 1 for detecting defects, radiation by means of a lighting device, in particular a laser 170 on directed the workpiece and at least partially influenced by the workpiece, in particular by the defect.

In the device 1 for detection and / or classification of defects, in particular to

Surfaces of workpieces 3, radiation is directed at least one light source, in particular a laser 170 to a workpiece 3 and is at least partially influenced by the workpiece 3, preferably by the defect 160, 162, 164, 166, wherein a first and a second optical signal generated which is detected in each case with an optical detector 180, 188 and wherein, _v from these signals, a distinction of the defect is possible.

The first optical signal is a bright field signal which is obtained in a bright field arrangement. This bright-field arrangement comprises a laser 170, of which at least one light beam passes through a beam splitter 172 onto a galvanometer scanner 182, which detects it

Reflects light beam at an angle θ relative to the optical axis of a subsequent converging lens 84. A galvanometer scanner does not necessarily mean a galvanically operated scanner, but generally a scanner for deflecting light rays.

Such scanners are also known to the person skilled in the art under the term "Galvoscanner".

The pivot point of the galvanometer scanner 182 from which the reflected laser beam propagates lies approximately in the left-side focal point of the converging lens 184, which is also referred to as F-Θ lens. Consequently, the right side ^'emerging from the condenser lens 184, light rays are substantially parallel to each other and spread upon a pivotal movement of the mirror of the galvanometer scanner 182 on the surface 31 of the workpiece. 3

If now the Wertkstück 3 and / or the device 1 is moved, there is a linear sweeping the entire surface of the workpiece. 3

On the way from the galvanometer scanner 182 to the convex lens 184, the laser beams pass through a beam splitter 174, which is substantially of the below-described detailed Dunkelfeldan order assigned ^'.

As an alternative to a galvanometer scanner 182, it is also possible to use a rotating, mirrored polygon whose rotation in this case then defines the deflection angle θ of the laser beam.

Since the angle θ and the relative movement of the device 1 relative to the workpiece 3 in a downstream, not shown in the figures ^' data processing system is detected and this associated location on the substrate 3 thus ^{' is} known, the optical signals described below can be resolved resolved and be further processed.

From the workpiece 3 is either from the front or. also reflects back light from the back and passes through the galavanometer scanner 182 in the beam splitter 172, from which this is directed into the photodetector 180. The intensity or the spatially resolved contrast of this optical signal light reflected into the photodetector 180 depends on the surface contrast of the workpiece 3, which in the bright field is regularly higher for particles than for scratches or line-shaped defects.

The photodetector 180 preferably comprises a PIN diode or a photodiode with a high cutoff frequency.

The second optical signal is a dark field signal which is obtained in the dark field arrangement described below.

This dark-field arrangement comprises, in addition to the converging lens 184, the beam splitter 174, a line-shaped aperture 186, the further converging lens 178 and the photodetector 188.

The light reflected by the workpiece 3 is directed, after passing through the converging lens 184 through the beam splitter 174, not only into the bright field arrangement but also to the aperture 186 of the dark field arrangement.

At the stop 186, which is substantially line-shaped, those portions of light of the reflected light which originate from a plane surface are masked out.

If a surface 31 of the item of value 3 or the interior of the workpiece 3 has scattering centers, these produce in reflection portions of light that do not run (anti) parallel to the illuminating beams.

These beam components no longer fall on the diaphragm after passing through the converging lens 184 and the beam splitter 174 186 and reach the further converging lens 178, which focuses these beam portions on a photodetector 188.

The scattered light which contains the information of the second optical signal has a higher contrast with respect to the bright field optical signal, even with scratches or line-shaped defects, this means greater brightness differences.

Preferably, the photodetector 188 is a photomultiplier.

Thus, the first optical signal includes spatially resolved information about defects containing particles, and the second optical signal comprises spatially resolved information about defects including scratches, particles, glass defects.

Classification into particles or scratches or bubbles can thus be carried out by subtracting the two optical signals, wherein the

Subtraction of the optical signals takes place after their detection by detectors and conversion into electrical signals by electronic means in a downstream data processing system.

If the diaphragm 186 and the further converging lens 178 and the photodetector 188 are arranged on the right-hand side of the workpiece 3 in the case of a transparent workpiece 3, a dark-field illumination arrangement can be provided confocal to the optical axis of the optical detector 88, which is arranged in transmission.

If the aperture 186 is replaced by a phase-shifting element, which shifts the phase of the light passing through by about half a wavelength, is from the dark field arrangement described above, a phase contrast illumination arrangement with respect to the photodetector 188th

Further, the laser 170 or a laser diode array may emit for adjusting the longitudinal coherence to a defined plurality of longitudinal modes.

To define desired longitudinal coherence properties, laser 170 or the laser diode array may be pulsed short-term.

For the definition of desired transverse coherence light source, in particular, the laser 170 may include a ^■ Phasenfrontscrambler.

With thin glass inspected as described above, the concentration of scratches can be significantly reduced by sorting out glasses identified as defective. For tested thin-glass, the concentration of scratches with a depth of 3 to 30 nanometers can thus be reduced to less than 5, preferably less than 3, more preferably less than. 1 per square meter be lowered. A production line, in particular for the production of TFT displays, which comprises such device according to the invention is thus able to quickly provide high-quality end products.

Furthermore, by distinguishing a particulate coating on the substrate from scratches and / or bubbles in the substrate by a more appropriate cutting in the further processing of the waste can be significantly reduced.

Also, in production lines, for example, for glass production also online feedback with the According to the invention obtained results are made in the manufacturing process. Thus, the manufacturing process can be controlled and optimized directly using the device for detecting defects.

It will be apparent to those skilled in the art that the invention is not limited to the exemplary embodiments described above, but rather may be varied in many ways. In particular, the features of the individual embodiments can also be combined with each other.

LIST OF REFERENCE NUMBERS

1 Device for detecting defects

3 thin glass substrate

5 optical detector

7 line camera

9 focusing optics of 7

11 lighting device

13 fluorescent tube

15 cylindrical lens

17 imaging camera

20 of 11 illuminated surface area 5 4F arrangement 6, 27 lenses of 25 0 aperture 1, 32 surface of 3. 5, ^'36 lenses 8 • phase plate 9 partially transmitting range 0 incident Lichtbünd'el 1 of 40 illuminated area 31 2 illuminated by 40 area 32 5 polarizer 0 laser bar 2 phase hologram plate 4 mirror 5 ^■ matrix camera with image intensifier 6 lens 0 Center beam of 40 1, 62 photomultiplier 3 optics of 5 5 scan unit 6 particles 7 scratches 160 scratches

162. particle

164, 166 line defects

170 ^• Laser

172, 174 beam splitters

176, ^■ 178 lens

180 photodiode

182 galvanometer scanner

184 f-θ lens

186 line panel

188 photomultiplier

Claims

claims

1.Vorrichtung for detecting defects, in particular on surfaces of workpieces, preferably plate-shaped workpieces, in which radiation is directed to a workpiece and is at least partially influenced by the workpiece, preferably by the defect.

2.Vorrichtung according to claim 1, characterized in that at least a part of the beeeinflußt by the flaw radiation is detected by an optical detector.

3.Vorrichtung according to any one of the preceding claims, characterized in that the optical detector comprises a plurality of light-detecting pixels, each detecting light originating from different substrate areas, wherein a

Lighting device is provided which has a plurality of light source points, which are arranged so that falls on each of the substrate regions light from at least two different directions of incidence.

4.Vorrichtung according to claim 3, characterized in that the directions of incidence an angle of at least 45 °, preferably of at least 90 °, more preferably of. include at least 120 °.

5.Vorrichtung according to claim 1 or 2, characterized in that the optical detector comprises a line scan camera. β. Device according to one of the preceding claims, characterized in that the optical detector comprises a picture-taking camera.

7.Vorrichtung according to any one of the preceding claims, characterized in 'that the optical detector upstream of a 4f arrangement or the lighting device is connected downstream.

8.Vorrichtung according to one of the preceding claims, characterized in that the 4F arrangement performs a filtering of structure sizes, which does not correspond to the structure size of the defects to be detected.

9.Vorrichtung according to one of the preceding claims, characterized in that the illumination comprises a dark field illumination arrangement.

10.Vorrichtung according to any one of the preceding claims, characterized in that the

Dark field illumination arrangement is arranged confocal to the optical axis of the optical detector in reflection. , ^■

11.Vorrichtung according to any one of the preceding claims, characterized in that the

Dark field illumination arrangement confocal to the optical axis of the optical detector arranged in transmission • is.

12.Vorrichtung according to one of the preceding claims, characterized in that the illumination comprises a phase contrast illumination arrangement. 13.Vorrichtung according to any one of the preceding claims, characterized in that the illumination is made in transmission.

14.Vorrichtung according to one of the preceding claims, characterized in that the illumination is made in reflection.

15.Vorrichtung according to any one of the preceding claims, characterized in that the illumination is made with obliquely incident light.

16.Vorrichtung according to any one of the preceding claims, characterized in that the light source is focused and wherein the light source and the optical detector are arranged so that the optical axis of the detector is arranged at an angle α to the light beam, for the following applies:

α> aresine (n _s • sin (aretane (b / d)),

where n _{s is} the refractive index of the substrate, b is the smallest dimension of the focus of the light beam and d is the thickness of the substrate.

17. Device according to the preceding claim, characterized in that the light source is arranged so that the focus lies within the substrate.

18.Vorrichtung according to one of the two preceding

Claims, characterized in that the angle α more than 5 °, preferably less than 50 ° to the direction of light emission, particularly preferably in the range of 10 ° to 35 °.

19.Vorrichtung according to any one of the three preceding claims, characterized in that ^' the optical detector comprises a camera having at least two lines, one of which lines illuminated by the incident on the substrate light surface area and the other line emerging from the substrate Light illuminated surface area captured.

20.Vorrichtung according to one of the preceding claims, characterized by a light source with an irradiance on the substrate of at least 2.5 • 10 ⁶ watts per square meter.

21.Vorrichtung according to any one of the preceding claims, characterized by a focused light source with a focus with a minimum extension of at most 200 microns, preferably at most 150 microns.

22.Vorrichtung according to any one of the preceding claims, characterized in that the optical detector comprises a signal amplifier, in particular a photomultiplier or a multi-channel plate.

23.Vorrichtung according to any one of the preceding claims, characterized in that the obliquely incident light comprises a narrow light beam, which in the image field of the Kame _. ra lit only one of the two main surfaces. ^•

24.Vorrichtung according to any one of the preceding claims, characterized in that the obliquely incident light is s-polarized. 25.Vorrichtung according to any one of the preceding claims, characterized in that the obliquely incident light is irradiated relative to the workpiece under the Brewster angle.

26. Device according to one of the preceding claims, characterized in that the optical detector comprises a polarizer, which polarizes the light substantially perpendicular to the polarization of the light reflected from the workpiece.

27.Vorrichtung according to any one of the preceding claims, characterized in that the illumination comprises a laterally arranged by the optical detector illumination, which has less or no light components perpendicular to the substrate surface.

28.Vorrichtung according to any one of the preceding claims, characterized in that the illumination device comprises mirrors for beam shaping.

29.Device according to one of the preceding claims, characterized in that the illumination device comprises faceted mirrors for defining a plurality of foci on the workpiece, from which spherical waves emanate.

30.Vorrichtung according to any one of the preceding claims, characterized in that the illumination device holographically optical elements for defining a. Variety of foci on the workpiece includes.

31. Device according to one of the preceding claims, characterized in that the holographic optical Element comprises a phase hologram, which preferably contains vapor deposition glass.

32.Vorrichtung according to any one of the preceding claims, characterized in that the holographic optical element is arranged on a refractive element.

33.Vorrichtung according to any one of the preceding claims, characterized in that the holographic optical element is arranged on a reflective element.

34.Vorrichtung according to any one of the preceding claims, characterized in that the light source is limited in the bandwidth.

35.Vorrichtung according to any one of the preceding claims, characterized in that the spectrum of the light source at wavelengths is less than 300 nm.

36.Vorrichtung according to any one of the preceding claims, characterized in that the light source emits light at a wavelength at which the workpiece only low transmission, in particular a transmission less than 50%, preferably less than 25%, most preferably less than .15% includes.

37.Vorrichtung according to any one of the preceding claims, characterized in that the light source comprises a laser.

38.Vorrichtung according to any one of the preceding claims, characterized in that the light source a

Scanning system includes. 39.Vorrichtung according to any one of the preceding claims, characterized in that the light source comprises a laser diode array.

40.Vorrichtung according to one of the preceding claims, characterized in that the light source comprises a linear laser diode array.

41.Vorrichtung according to any one of the preceding claims, characterized in that the laser or the

Laser diode array for adjusting the longitudinal coherence on defined a plurality of longitudinal modes emitted.

42.Vorrichtung according to one of the preceding claims, characterized in that the laser or the laser diode array is operated short-pulse to define desired longitudinal coherence properties.

43.Vorrichtung according to one of the preceding claims, characterized in that the laser diode array comprises at least one FAC and preferably additionally at least one SAC lens which generates at least one focus on the workpiece.

44.Vorrichtung according to one of the preceding claims, characterized in that the light source for defining desired transverse coherence comprises a phase frontscrambler.

45.Vorrichtung according to any one of the preceding claims, characterized in that the light source comprises a fluorescent tube. 46. Device according to one of the preceding claims, characterized in that the fluorescent tube has a plurality of spectral emission bands.

47.Vorrichtung according to one of the preceding claims, characterized in that the light source comprises a holographic optical element and a cylindrical lens.

48.Vorrichtung according to any one of the preceding claims, characterized in that the workpiece comprises glass, in particular a glass plate.

49.Vorrichtung according to any one of the preceding claims, characterized in that the workpiece comprises thin glass.

50.Vorrichtung according to any one of the preceding claims, characterized in that the workpiece comprises floated thin glass.

51.Vorrichtung according to any one of the preceding claims, characterized in that the workpiece comprises downdraw thin glass.

52.Vorrichtung according to one of the preceding claims, characterized in that the workpiece downdraw fusion thin glass, in particular overflow downdraw glass comprises.

53.Vorrichtung according to a. of the preceding claims, characterized in that the workpiece comprises a surface-treated, in particular polished workpiece ^' . 54.Vorrichtung according to any one of the preceding claims, characterized in that the workpiece is glass for a display, in particular a TFT display. , ^''

55.Vorrichtung according to any one of the preceding claims, characterized in that the thin glass has a width of more than 1.8 m.

56.Vorrichtung according to one of the preceding claims, characterized in that the thin glass has a length of more than 2.0 m.

57.Vorrichtung for detecting and / or classification of defects, in particular on surfaces of workpieces, in particular according to one of the preceding claims, in which radiation at least one light source is directed to a workpiece and is at least partially influenced by the workpiece, preferably by the defect in which a first and a second optical signal is generated and from these signals a distinction of the defect is possible.

58. Device according to the preceding claim, characterized in that the first optical signal is a bright field signal.

59.Vorrichtung according to one of the two preceding

Claims, characterized in that the second optical signal is a dark field or phase contrast signal.

60. Device according to one of the preceding claims, characterized in that the first optical signal substantially spatially resolved information about defects, include the particles includes.

61.Vorrichtung according to any one of the preceding claims, characterized in that the second optical signal substantially spatially resolved information about

Defects that include scratches, particles, glass defects, includes.

62.Vorrichtung according to any one of the preceding claims, characterized in that the spatially resolved

Information comprises a line signal which is associated with a deflection angle of a galvanometer scanner or a light emitting diode from a light emitting diode array includes.

63.Vorrichtung according to any one of the preceding claims, characterized in that a classification is carried out in particles or scratches by subtracting the two optical signals.

64.Vorrichtung according to any one of the preceding claims, characterized in that the subtraction of the. optical signals after their detection by detectors and conversion into electrical signals by electronic means.

65.Vorrichtung according to one of the preceding claims, characterized in that the illumination comprises a bright field and a dark field illumination arrangement.

66. Thin glass, tested with a device according to one of the preceding claims. 67. A thin glass comprising a concentration of scratches having a depth of 3 to 30 nanometers of less than 5, preferably less than 3, more preferably less than 1 per square meter.

68.Production line, in particular for the production of TFT displays, comprising a device according to one of the preceding claims.

69. Lighting device for a device according to one of the preceding claims.

70.A method for detecting defects, in particular on surfaces of workpieces, preferably plate-shaped workpieces, in which by means of a device according to one of the preceding claims radiation is directed to a workpiece and is at least partially influenced by the workpiece, preferably by the defect.

71.Method according to one of the preceding claims, characterized in that the light source is focused, wherein light source and optical detector are arranged so that the optical axis of the detector is arranged at an angle α to the light beam, for which applies:

α> aresine (n _s • sin (aretane (b / d)),

72.Method according to one of the two preceding claims, wherein the angle α more than 5 °, preferably ^• Less than 50 ° to the direction of light emission, particularly preferably in the range of 10 ° to 35 °.

73.Method according to one of the three preceding claims, characterized in that flare light emitted by flaws is detected by a camera having at least two lines, of which one of the lines -the surface illuminated by the light incident on the substrate and the other line of the detected from the substrate emerging light illuminated surface area.

74. The method according to any one of the preceding claims, characterized in that the light source is focused so that the focus lies within the substrate.

75. The method according to any one of the preceding claims, characterized in that the substrate is illuminated with an irradiance of at least 2.5 ^■ 10 ⁶ watts per square meter.

76. The method according to any one of the preceding claims, characterized in that the light source is focused with a focus with a minimum extension of at most 200 μrα, preferably at most 150 microns.

77.Verfahren according to any one of the preceding claims, characterized in that the signal is amplified in the optical detector with a signal amplifier, in particular a photomultiplier or a multi-channel plate.