WO2010015694A1

WO2010015694A1 - Inspection device and method for optical investigation of object surfaces, in particular wafer edges

Info

Publication number: WO2010015694A1
Application number: PCT/EP2009/060253
Authority: WO
Inventors: Dietrich Drews; Andreas Bodden; Ralph Schrauth
Original assignee: Nanophotonics Ag
Priority date: 2008-08-08
Filing date: 2009-08-06
Publication date: 2010-02-11
Also published as: DE112009001936A5; DE112009001936B4; WO2010015695A1

Abstract

The invention relates to an inspection device and an inspection method for optically investigating object surfaces surrounding an edge of an otherwise substantially flat object (10), in particular wafer edges. The inspection device comprises at least one digital camera (14) facing the object surface at an acute angle with respect to the object plane, said camera being able to be focused onto the object edge (18), and a plane illumination device (30) which is positioned relative to the digital camera (14) and to the object surface in such a way that an image of a flat main surface (22) of the object surface surrounding the edge proximate to the edge of the object can be produced under bright field illumination, wherein the plane illumination device (30) comprises a collimation device.

Description

Inspection device and method for the optical examination of object surfaces, in particular of wafer edges

description

The invention relates to an inspection apparatus for the optical examination of object surfaces in an edge environment of an otherwise substantially planar object, in particular edges of unstructured wafers, with at least one of the object surface at an oblique angle to the object plane and focusable on the object edge digitaikamera and a plane lighting device, the relative to the digital camera and to the object surface is arranged so that an image of an adjoining the object edge planar main surface of the object surface is generated in the edge environment under bright field illumination.

The optical inspection of semiconductor wafers for defects (breakouts, scratches, marks, particles, etc.) is an important part of the manufacturing process of computer chips. For this purpose, camera-based methods are frequently used in which the part of the wafer surface to be inspected is imaged into the sensor plane of a camera. The defect detection then takes place by evaluation of the image. Decisive for the performance is the quality of the image of the surface. The inspection usually includes both the planar object or wafer top and bottom side and its edge. The present invention particularly relates to the inspection of the edge.

The terms used herein to designate the inspected object are to be understood as follows:

"Object surface" is understood as a generic term that refers to the entire surface of the object and in particular the hereinafter defined major surfaces and object edges.

By "main surface" or "flat area" the flat, opposite upper or lower sides of the generally disk-shaped object (wafer) are referred to.

- "edge" or "object edge" is the one hand, on the main surface adjacent and on the other hand, the object peripherally delimiting surface portion, which thus connects the main surfaces and usually both an upper or lower oblique portion ("Bevel") and a front circumferential Share ("apex").

- The "edge surround" describes a surface section that includes both the edge and a section of the main surface in the transition region to the edge.

The term "edge" or "object edge" refers to the transition line between the object edge and the environment which can be recognized from the respective angle.

"Bevelline" refers to the transition line between the object's top and bottom sides and the bevel of the object's edge that can be seen from the respective angle.

A "structural feature" is understood to be a deviation of the edge profile in the vertical projection onto the object plane defined by the main surface (s) from a predetermined uniform or continuous contour profile. Notch) or a straight edge section (circle chord).

Inspection devices for wafer edges often use an arrangement consisting of a digital camera, which faces the object surface and in particular focused on the object edge is. Furthermore, one or more lighting devices are used in such inspection devices.

From DE 103 13 202 B3 a device of the type mentioned is known in which the object edge of the wafer consisting of the upper Beve! (Bevel), the apex and the lower Bevel are completely in the dark field of an LED light source, while the emanating from this and from the wafer top or upper main surface reflected light directly into the camera, the wafer top is in the bright field area is the camera thereby aligned with the object edge at an angle of 45 ° to the wafer top. Using a plane mirror arranged underneath the wafer and oriented parallel thereto, the lower image or lower main surface of the wafer is also recorded in the same image, which, insofar as can be seen, are also in the dark field region. The upper Bevel is thus illuminated under grazing light from the light source and the apex and the lower Bevel are completely in the shadow of the light source. The light that passes through the wafer is reflected by the mirror surface directly into the camera so that it is displayed as a bright field background following the bottom. As a result, the wafer edge is depicted as a narrow strip in the dark field area, on one side of which the direct reflection from the wafer top side and on the other side the direct reflection from the plane mirror join. The illumination ratios on the upper side and the lower side of the wafer edge are very different for the aforementioned reasons.

The disadvantage here is that the edge region of interest is partially imaged directly and partially reflected on the mirror. Since the wafer edge is in the dark field overall, it can not be located exactly in the image. In addition, the oblique orientation of the camera on the wafer edge causes different distances to the wafer. ferrand and to the wafer top, so that not the entire edge environment can be simultaneously sharply imaged.

DE 103 24474 A1 describes a device comprising an upright illumination device and a depiction device with which the surface of a wafer coated with photoresist is recorded in the bright field. In contrast to the present invention, this device is used to inspect a patterned wafer. Polarization of the light and camera-side analysis of the polarization state of the light reflected on the surface are used to investigate the stripping of the wafer in its edge region. In addition, a further illumination device is provided on the underside of the wafer, the light rays of which on the way to the camera are partially shaded by the wafer edge so that the edge of the wafer edge appears as a light-dark transition.

While the investigation of the edge region in the last-mentioned document does not go beyond the control of paint stripping and therefore unsuitable for the investigation of an unstructured wafer on defects of the type mentioned, with the device known from DE 103 31 202 B3 no complete investigation of the Wafers of the main surface can be ensured over the entire edge area including bevel and apex with a setting.

Against this background, the inventors have made it their task to improve the inspection device or the inspection method in such a way that all types of defects on the object surface can be identified from the recorded image contents as completely as possible and with location accuracy. The object is achieved by an inspection device having the features of claim 1 and an inspection method having the features of claim 15. Advantageous developments of the invention are the subject of the dependent claims.

The inspection method according to the invention provides that the light emitted by the plane lighting device is light-colored.

Accordingly, in the inspection device according to the invention, the plane lighting device comprises a collimation device.

The camera arranged at an oblique angle (0 ° <viewing angle <90 °) to the plane of the wafer makes it possible, as in DE 103 13 202 B3, for the entire edge environment, ie the Bevel and the apex of the wafer edge, simultaneously with the flat area near the edge to capture a position.

However, a disadvantage of this arrangement is, as already mentioned, that the distance between the object points and the camera optics changes considerably in the entire flat area. If the optical system of the camera is set so that the wafer edge is sharply imaged, the points of the flat area run out of focus with increasing distance to the wafer edge and are correspondingly blurred. Typically, this problem is addressed by the lack of depth of field by greatly reducing the aperture of the lens. However, this option is ruled out for the present application, since this measure would also greatly reduce the throughput of light through the objective, which is disadvantageous for the defect inspection if one wants to use the same camera arrangement in combination with suitable illumination for the darkfield inspection of the wafer edge , The invention is based on the knowledge that a polished, flat surface reflects the light according to the law of reflection but does not scatter in different directions. At the same time, the acceptance angle of a conventional lens which is to be used for imaging the surface into the sensor plane of the camera is small compared to the half space above the surface. According to the set aperture only light rays pass through the lens in the image plane, which come from a direction that differs only slightly from the optical axis of the lens. In order to obtain a bright image of the polished surface, it is therefore necessary that the surface of a light source is illuminated so that its light is reflected exactly in the direction of the lens. It is sufficient if the light is reflected exactly parallel to the optical axis of the lens. The plane illumination device must therefore emit collimated light onto the object plane at the same angle (illumination angle) as the viewing angle under which the digital camera looks at the object surface. The above applies analogously when the beam path is deflected on the way from the plane lighting device to the object surface or from the object surface to the camera.

In the bright field image, the defect-free surface appears bright because it reflects the light directly into the camera lens. A surface defect reflects or scatters the light in other directions, so that the defect appears dark in the bright field image. According to the invention, illumination with collimated light containing exclusively light rays which after reflection at the surface is parallel to the optical axis of the objective results in an increase in contrast compared to a diffuse light source since even the slightest disturbance of the surface results in that the incident light from the light source is no longer reflected in the objective. The essence of an optical image is that all (also in different directions) emanating from an object point rays of light that go through the entrance pupil of the lens, are reunited at a point in the image plane. However, this condition is only met if the object point lies at a certain distance from the objective, which results from the focal length of the objective. If the object point lies at a different distance, the light rays emanating from it are not united at one point of the image plane but are scattered over an extended area. This creates a blurred image. However, if a collimated illumination is used in the sense of the invention, no bundle of light rays in different directions emanates from each object point (a specular surface), which must be brought together again in the image plane. Ideally, only one light beam (parallel to the optical axis of the camera) passes from each object point to the corresponding point in the image plane. The problem of lack of depth of field does not occur. Therefore, no telecentric lens is used on the camera side. Due to the collimated illumination, the aperture diaphragm in the focal plane which is usual with telecentric objectives becomes superfluous. Strictly speaking, there is an object-oriented center of division to this extent. If, preferably, a magnification of 1: 1 is selected, however, the beams also run parallel in the image plane, and thus the solution according to the invention also has the features of an image-side telescope, that is, two-sided telecentricity.

Embodiments of the collimation device according to the invention comprise, for example, a sufficiently small ("punctiform") illumination source, for example an LED, at a sufficiently great distance from the objective, a sufficiently small ("punctiform") illumination source, eg an LED, together with collimation optics, in the simplest manner Trap a convergent lens, at the focal point of which is the illumination is arranged, or a laser whose beam has been expanded sufficiently to achieve a homogeneous illumination of the object field. A collimated laser beam ideally fulfills the requirement of parallelism of the light beams. However, the high coherence of the laser light can have a disadvantage, as a result of which interference phenomena (speckle) can lead to undesired patterns in the image, which can adversely affect the image evaluation.

Preferably, the inspection device has a backlight device which is arranged on the side facing away from the digital camera side of the object so that its light is emitted in the direction of the digital camera, wherein the light emitted in the direction of the digital camera is partially shaded by the object.

Thus, unlike in DE 103 13 202 B3, the inspection device or the inspection method according to the invention thus provides a separate background illumination which illuminates directly into the digital camera, provided that it is not shadowed by the object and thus a contrast between the directly recorded object edge and the background creates. This makes it possible for the first time to establish a clear relationship between the envelope line identified on the basis of the contrast between the object edge and the main surface and the edge identified on the basis of the contrast between the object edge and the background light.

Apart from the already mentioned DE 103 24 474 A1, further prior art is known, which describes a background light source on the side of the wafer facing away from an optical sensor. For example, Japanese Patent Laid-Open No. 59125627 A discloses a device in which a bundle of parallel light beams is irradiated perpendicularly to the wafer surface in the edge region and the unshaded portion of this light beam by means of a light source on the is located on the opposite side of the wafer arranged planar photosensor, while the wafer is rotated. In principle, the same arrangement is known from US Pat. No. 5,438,209 A, which uses a camera line instead of the photo sensor. Both devices are devices for determining the position of a Notch and not the generic inspection device for receiving a dark field image of the wafer surface. The lighting is a pure backlight, so that a dark field recording is not possible. The accuracy of the position determination of Notch is ensured only by the parallelism of the light beams, which ensures a sharp shadow.

Another device for determining the notch position in a wafer is known from the publication JP 2000031245 A. This has a camera whose optical axis is aligned perpendicular to the top of the wafer and on its center and which receives a two-dimensional overall image of the wafer surface, without the wafer is rotated thereby. The Beieuchtungseinrichtung is swung away for this purpose from the optical axis of the camera, so that no direct reflection of the light from the wafer surface falls into the camera. The immediate vicinity of the wafer is lightened by the fact that the light of the illumination device is the material of the wafer support (diffused) scattered. In this way, a contrast arises between the wafer support and the wafer, so that the edge of the printer is imaged as a dark edge in front of the lighter support. This device allows the identification of the wafer edge and in particular a Notch. However, it is not intended and suitable for identifying and localizing defects on the wafer surface with sufficient accuracy. This is also a device for determining the Notch position. Also, the asymmetrical arrangement of the lighting device with respect to the central axis of the wafer for a shadow, which makes it difficult to localize the wafer edge with high accuracy, since not the light emitted in the direction of the digital camera is partially shaded by the object edge, but already the light on the way to the wafer support. Finally, the contrast is dependent on the material and the nature of the wafer surface on the one hand and the overlay on the other hand and can not be influenced.

In contrast, the invention relates to an inspection device for the detection of surface defects, which allows an improved localization of these surface defects and at the same time a recognition of the surface defects up to the outermost object edge ie to the object edge.

Since the focus of the digital camera in the inspection device according to the invention lies on the object edge, in particular the edge of the object is sharply imaged, which enables a precise localization of the object. Furthermore, this has the advantage that the background illumination device, which is located farther away, is displayed blurred and therefore no artifacts of the background interfere with the image impression, in particular can serve as a backlight device a simple lamp, which mapped due to the fuzziness as an extended light spot on the sensor of the digital camera becomes. Of course, as a backlight device, a direct or indirect and / or diffuse emitting surface light source can be selected.

According to the invention, the inspection of the object edge also includes that of the transition to the main surface of the object. Here, the Bevelline is of particular interest. In addition to the aforementioned defects in the form of scratches, eruptions, dust grains, imprints or the like, Bevel can also cause defects in the form of processing errors. lends polishing defects. The wafer edge usually receives a rumpled surface. If the polishing process of the edge is done properly, the Bevelline and the wafer edge must always be parallel, deviations from this are polishing defects. Such Poiierfehler do not lead to contrasting Streichichtrefiexen or dark spots, as do the aforementioned defects under light or dark field illumination. Polishing errors thus lead to more or less pronounced deviations of the bevel from their soil position on the wafer. Fluctuations in the Bevelline due to buffing are, however, overlaid with artefacts of the measurements, such as vibrations or eccentricity of the wafer during the measurements, so that a statement about their actual position can not be easily made. Therefore, it is provided according to an advantageous development, by means of an image processing device having an edge detection means, from the pixel information of the image generated with the digital camera based on a contrast between the object edge and the main surface a transition line to identify the Bevelline. Particularly preferably, the edge detection means is also set up to identify the edge of the object in addition to the bevel at the same time also on the basis of a contrast between the object edge and the backlight.

Preferably, the image processing device further comprises an edge analysis means, which is set up to monitor the relative position of the bees to the edge.

The edge detection center! detects by means of a simple algorithm a non-round run of the wafer (horizontal oscillation in the wafer plane) as a consequence of centering inaccuracy or fluttering of the wafer (vertical oscillation perpendicular to the wafer plane) due to unevenness or resonant excitation. So far one endeavored the mentioned error sources by active and partly mechanically very to minimize costly centering and damping measures. In contrast to any defects, however, horizontal or vertical vibrations provide a periodic, low-frequency course of the wafer edge in the image and can therefore be easily identified. The exact edge detection of the device according to the invention therefore allows to dispense with complex active centering and damping measures and to correct any errors in the context of image processing by means of suitable correction means or routines.

Monitoring the relative position of the bevelline to the edge, on this basis, by identifying the population and boundary line from the contrast differences in the image, then determining the distance of both lines in the image along an approximately perpendicular line to the edge. If the wafer is not well centered, so the distance wafer edge - camera changes, can be closed taking into account the imaging geometry on the real distance bevel line - wafer edge. This distance must always be constant within certain tolerances on the normal wafer edge.

In a preferred development, the edge detection means comprises a structure recognition means which is set up to identify a structural feature of the object edge from pixel information of the dark field image on the basis of the contrast difference between the object edge and the background illumination.

Such a structural feature is, for example, the contour of a notch in the wafer edge. This has a known shape and can therefore be easily identified by an algorithm or a comparison of the recorded edge image with stored in a memory forms. However, in this way not only a notch but also any other structural features, for example in the form of a straight edge section (at an otherwise circular wafers). All regular structural features can thus be easily identified and, in particular, distinguished from an irregular outbreak. As a result, a simple inspection of the structural feature itself is made possible. In particular, defects in the structural feature, the complete absence of the structural feature, a shape deviation of the Strukturmerkmais of a desired geometry to the presence of several structural features along the Waferkaπte be automatically detected and displayed. It is also possible to monitor the relative position between the Bevel line and the edge along such a feature. This also applies if no constant distance is expected here but another profile of the bevelline following the outline of the structural feature (nominal geometry).

Preferably, the image processing device is also set up to determine a coordinate system on the basis of the identified edge and / or the identified structural feature.

By way of example, a reference point for the azimuthal angle (ie the angle of rotation of the wafer) can be determined unambiguously on the basis of the identified structural feature. For example, the center of a notch may be taken as the coordinate zero point of the azimuthal angle, allowing accurate angular position indication of each identified surface defect (or defect fragment).

Furthermore, with the aid of such an image processing device, it is possible to deduce the course of the true physical object edge from the identified edge in the case of a known shaping of the edge profile. The center of the apex, which forms the radially outermost edge of the object, is determined in the simplest case by keeping a constant distance of the middle of the apex to the identi- fied shape of the edge profile and the viewing angle at which the camera looks at the edge of the object. fied edge is adopted. This distance can be stored as a system- and / or profile-specific setting in a memory of the image processing device and subtracted from the position of the identified edge when the position of the true object edge is calculated. As the coordinate zero point of the radial component of the coordinate system, the true object edge, ie, the center of the apex, is then preferably selected. This and the coordinate zero point of the azimuthal angle preferably form the origin of a two-dimensional coordinate system.

If the coordinate system is defined in two dimensions, the position of the bevelline with respect to the coordinate system can preferably be determined by means of the image processing device.

This allows Poiierfehler also with respect to their angular position relative to the structural feature, the Wafernotch to determine.

If the object is inspected obliquely from its top and bottom, you get a complete picture of the edge environment. The two halves of the image can thus be joined together in the center of the apex in the coordinate point of the radial component, whereby the coordinates of the azimuthal angle determined in both partial images are superimposed. Thus, all defects can be represented in a common coordinate system.

The digital camera is preferably a zebra camera arranged so that the single image line taken with the line scan camera lies in a plane which is perpendicular to the plane of the object. The viewing direction from which the image is taken from the edge of the object by means of a digital camera can, viewed in the projection on the object plane, be perpendicular to the object edge or a tangent and the object edge. That is, the optical axis of the camera is oriented (possibly after deflection) according to this embodiment so as to define together with the image line an optical plane coincident with a radial plane of the wafer. The advantage of this embodiment is that fewer image distortions occur.

Preferably, a first edge lighting device is provided, which is arranged relative to the digital camera and the object edge so that an image of the object edge can be generated under dark field illumination.

In dark field illumination, the light emitted by the illumination device is reflected by the intact object surface so that it does not enter the optics of the digital camera, so that the image of the object surface remains predominantly dark. If a defect in the surface area is in the form of a depression (scratch, eruption) or in the form of an increase (dust grain, impurity), then part or all of the defect will usually invade the optics of the digital camera. This results in a perfect image of defect fragments.

The inventors have also recognized that, depending on the lighting situation, different sections of the defects are illuminated, that is to say that different fragments are displayed under different light-incidence directions. In order to obtain a more complete picture of the entire defect, therefore, advantageously, alternatively or additionally, a second edge illumination device is provided which is arranged relative to the digital camera and to the object edge such that an image of the object edge can be generated under bright field illumination.

In bright field illumination, the light emitted by the illumination device is reflected by the intact object surface directly into the optics of the digital camera, so that the image of the object surface appears predominantly bright. If a defect in the surface area is in the form of a depression (scratch, eruption) or in the form of an increase (dust grain, impurity), the light is scattered in other directions and does not fall into the optics of the majority of the defects the digital camera. This creates a dark image of defect fragments.

Especially in the case of Helifeldbeleuchtung the optical axis of the camera is preferably oriented so that the defined together with the Biidzeile optical plane of the line scan camera is pivoted out of the radial plane. Admittedly, this will lead to more image distortions. However, this arrangement allows the bright field image of the wafer edge to be realized in a simple manner by inserting the bright field illumination device in a mirror-image arrangement relative to the camera arrangement relative to the radial plane through the focal point on the wafer surface. In this embodiment, the background illumination device is preferably swiveled out of the radial plane by the same amount and in the same direction, so that it lies on the optical axis of the camera.

Preferably, the second Kantenbeieuchtungseinrichtung is designed in the form of a ring segment, which partially spans the object edge. As a result, the profile of the edge profile (Bevel Apex Bevel) is approximately taken into account. Particularly preferably, the ring segment is circular segment-shaped and adjustable so that its center falls in the region of the object edge. This ensures a sufficiently good condition for bright field illumination over a wide profile section of the object edge.

Most preferably, the ring segment is adjustable so that the radial light beam emanating from an outermost end extends parallel to the coincident light of the plane lighting device.

At the same time, the ring light is preferably arranged so that its outermost light source is as close as possible to the mechanical end of the ring light body. The entire arrangement can then be adjusted so that collimated light of the plane illumination falls just past the ring illumination and onto the flat area near the edge. As a result, the illumination of the flat area which is as homogeneous as possible is achieved, resulting in a gapless healing field image of the wafer edge and the flat area near the edge.

The image processing device is furthermore preferably configured to identify surface defects in the edge environment from the pixel information of the dark field image and / or the bright field image of the object edge on the basis of the contrasts generated as described above.

The detected defect fragments are first identified by the image processing device separately in the sub-images of the dark field recording and the bright field recording. This is preferably done by first assigning contiguous pixels whose contents (intensity, gray or color values) lie within a predetermined value range (intensity, gray or color value interval) to the same defect fragment. The defect fragments determined in this way are subsequently determined by means of an algorithm associated with the same defect. From two (or more) partial images of the object surface, a virtual surface image is thus generated, so that the entirety of the information from the bright field image and the dark field image allows a more comprehensive image of the entire defect to be produced.

The generated digital image of the object surface is then usually fed to a manual or automatic evaluation, the results of the evaluation are used to decide according to the specifications of the chip manufacturer on the usability of the wafer and perform a sorting according to quality criteria.

The second edge illumination device, the background illumination device and the plane illumination device can be controlled separately from one another by means of a suitable control unit.

In this way, it is possible to ensure that in each recording mode there is sufficient or optimum contrast between the main area in the helicopter field, the wafer edge in the bright or dark field and the background illumination, the simultaneous detection of the population, the wafer edge and defects in the bright field or darkfield allowed. For example, if there are defects in the form of eruptions directly at the edge of the wafer, then these too can easily be identified as a deviation from the continuous boundary curve. The information about the shape of the contour of the wafer thus offers (in addition to the one described above) an additional possibility for the detection of defects. In this case, the separate backlighting allows a contrast adjustment, which of the contrast center of gravity or of the intensity, gray or color value center of gravity in the dark field or Bright field lying defect deviates. Outbreaks are thus easily distinguishable from a surface defect of another kind. Due to the separate illumination control, the method according to the invention is furthermore independent of the refiectivity of the wafer surface, for example due to different coatings and / or structures,

If the coordinate system is defined in two dimensions, the position of the surface defect (s) found in relation to this coordinate system can be determined in the inspection method according to the invention. The position determination can include, for example, both the extent of the defect or defect fragment and its center of gravity and orientation, overall, the accuracy and reproducibility of the information about each defect are increased by the identification of the object edge and the feature of the invention.

Deviations from this can easily be detected with the method according to the invention and the device according to the invention if the image processing device is set up to determine the position of the bevelling with respect to the coordinate system and / or the identified wafer edge.

If the inspection device has a motor-driven turntable for rotatably supporting the object, wherein the digital camera is set up to record a digital image of the object edge synchronously with the rotation of the turntable, such a line camera can sequentially acquire a plurality of image lines of the object edge while the object is being combined turns with the turntable. For this purpose, the triggering of the camera can follow, for example, by means of a synchronization pulse by the drive motor (eg stepping motor). The sequentially recorded image lines of the object edge in different angular position of the object are then joined together to form a (panoramic) image of the object edge.

The method steps of the image processing, in particular the identification of the edge, the Bevelline or the structural features, the determination of a coordinate or reference system and the determination of the position of defects and Bevelline in the reference system, individually or collectively both as software and as Hardware or in combination of software and hardware.

Other objects, features and advantages of the invention will be explained in more detail using an exemplary embodiment with the aid of the drawings. Show it:

Fig. 1 is a side view of an embodiment of the inspection device according to the invention;

Fig. 2 is a side view of a Helifeldbeleuchtung the

Object edge extended embodiment of the inventive inspection device;

Fig. 3 is a plan view of the embodiment of FIG. 2;

4 is a plan view of an extension of the embodiment to a dark field illumination of the object edge.

Fig. 5 is a side view of the embodiment of FIG. 4 and

Fig. 6 is a histogram of the brightness curve of a Biidzeile.

FIG. 1 shows an embodiment of the inspection device according to the invention for inspecting an upper edge environment of a Semiconductor wafer 10 shown in side view. The inspection device has a digital camera 14, which is aligned with its optical axis 15 by means of an optical system 16 to the surroundings of the edge 18 of the wafer 10 and focused. The digital camera 14 is specially designed for edge inspection of the wafer 10 by tilting at an oblique angle, ie> 0 ° and <90 °, preferably between 30 ° and 60 ° and more preferably below about 45 ° to the object plane or top 22 of the The digital camera 14 thereby detects an edge environment that includes a portion of the top surface or major surface 22 of the wafer 10, its top, slightly oblique edge region or bevel 24, and at least a portion of the end edge region or apex 26, see. Fig. 5.

The inspection device furthermore has a plane illumination device 30. The plane illumination device 30 is arranged such that its light beams 31 are reflected directly from the upper main surface 22 of the wafer 10 into the camera optics 16. As a result, a bright field image of the main surface 22 is generated, as far as the angle of view of the camera and the beam spot of the plane lighting device 30 detects it. The planar illumination device 30 is shown in simplified form as a box. According to the invention, this device has a collimation device, not shown in FIG. 1, which generates a bundle of parallel light beams 31.

All light rays 31, which enter the optics 16 parallel to the optical axis 15 after reflection at the wafer top side 22, are combined in the rear focal point of their lens system 17 and then hit an image plane 19 in the camera, in which an optical sensor is arranged. The decisive factor for the location in the image plane 19 where the rays impinge is, however, the distance of the rays from the optical central axis in front of the objective. As a result, each object point A, B, C on the object surface is unique with a BÜdpunkt A ', B', C in the Image plane 19 of the camera connected. In particular, this relationship is independent of the distance of the object point from the lens, ie, regardless of whether the object point is in the focal plane of the lens or not.

The embodiment according to FIG. 2 differs from that according to FIG. 1 on the one hand in that the collimated light 31 of the plane illumination device 30 ', which is shown schematically as a point light source 32 with a lens arrangement 34 as a collocation device, by means of a mirror 36 on the flat area 22 near the edge of the wafer 10 is thrown. The mirror to be assigned to the plane lighting device 30 'is not absolutely necessary, as has been made clear with reference to FIG. 1, but facilitates the adjustment of the inspection device since it can be displaced in a simple manner, in particular in the direction of the incident light rays 31', and tiltable is.

The embodiment according to FIG. 2 also differs from that according to FIG. 1 by a second edge illumination device 29, which is arranged relative to the digital camera 14 and the object edge 18 such that an image of the object edge 18 is generated at least in the partial profile under bright field illumination. The second edge lighting device 29 is designed as a circular segment-shaped ring segment (in short: ring light), which is adjusted so that its center lies in the region of the object edge 18. The ring light has, for example, a dense arrangement of light sources, preferably LEDs, on a ring-segment-shaped holder. It illuminates the upper Bevef, the Apex and at least partially the lower level of the wafer edge 18. The holder of the ring light (not shown) also has a Justa- possibility, which makes it possible to rotate the ring light in the ring plane around the center point. It is preferably adjusted in such a way that the outermost upper (or lower) beam just does not affect the flat rich 22 of the wafer 10 falls and the radial light beam emanating from an outermost end is parallel to the collimated light of the plane illumination device 30 '. The ring light is further designed so that the outermost light source is as close as possible to the end of the ring light body.

At the same time, the mirror 36 is adjusted so that the light beams 31 of the planar illumination device 30 'at an angle equal to the angle 14 of the camera falls just past the edge illumination device 29 on the edge near flat edge region 22 and a homogeneous as possible illumination of the flat area to the transition into the upper Bevel is achieved. In order to avoid shadowing at this point, it is necessary for the edge illumination device 29 not to project into the beam path of the plane illumination device 30 '.

With correct J ustage of both lighting devices 29, 30 'and 36 results in a gapless bright field image of the edge environment of the wafer edge 18 to the upper edge near flat area 22nd

Both lighting devices 29, 30 'and 36 are independently controllable. In particular, the second edge illumination device 29 is adjusted to a different brightness value as the Fiachbe- so that at the transition line flat area / edge results in a brightness difference in the image, which makes it possible to identify the Bevelline (automatically), as with reference to FIG will be explained.

Figure 3 shows in isolation and greatly simplified the relative arrangement of the camera 14 and the second Kantenbeleuchtunsgeinrichtung 29 for generating a bright field image of the edge 18 of the wafer 10 in the plan view, the position of the camera 14 is at a first angle α from the Radial level 20 of the circular wafer 10 herausgeschweπkt, while the second Kantenbeieuchtungseinrichtung 29 is pivoted out at an equal angle ß from this. Of course, the opposite and not shown here level illumination device 30 'is swung out by the same angle α together with the camera from the radial plane 20, so that the light passes after reflection on the wafer top along the optical axis of the camera.

Figures 4 and 5 show in an isolated and simplified representation of how the inspection device according to the invention can be combined with a dark field illumination and a backlight for the object edge. The wafer 10 rests on a turntable 12, which is driven by a motor, preferably by means of a stepping motor, and sets the wafer 10 in rotation during the measurement. An engine control (not shown) may be provided, which outputs a control pulse which is used, on the one hand, to control the rotational movement and, on the other hand, to synchronize the recording of the object edge with the rotational movement.

The digital camera 14 is, as in the previous exemplary embodiments, preferably a line scan camera. The image line is in this example and in contrast to Figure 3 in the radial plane shown as a dashed line 20.

Furthermore, a first edge illumination device 28 is provided which, in this example, is designed in the form of a focused light gun of high intensity on both sides of the digital camera. The number of light sources and their arrangement are not relevant to the invention as long as no direct reflections of the light source at the wafer edge into the camera optics 16 occur. Therefore, a single light source may suffice or several may be provided to a quasi-flat, arcuate light source, in the center or focus of the object edge is located. While such a planar light source illuminates the edge region uniformly irrespective of its geometry due to its large angle spectrum, the individual light source has the advantage of being easy to focus and thus of generating a light spot of high intensity on the object surface.

With the shown arrangement of the digital camera 14 and the illumination device 28, a dark field image of the wafer edge 18 can be generated, since the optical axis of the camera 14 is perpendicular to the wafer edge and the illumination device 28 are swung out of the radial plane 20. Therefore, the light beams reflected at an intact object edge 18 under the tilt angle [alpha] with respect to the radial plane 20 do not fall into the lens of the camera. The object edge 18 is thus normally in the dark field.

On the side facing away from the digital camera 14 of the wafer 10 is a backlight device 40, here as a nearly point-like, non-collimated radiating light source. This is arranged with respect to the edge of the wafer 10 and the digital camera 14 so that the light emanating from it is emitted at least in part in the direction of the digital camera. At the same time, however, the light emitted in the direction of the digital camera is shadowed by the wafer 10 approximately halfway through the image window (the wafer edge does not have to run centrally in the image, as in this case). Since the digital camera is focused on the object edge 18, the more distant background illumination device 40 is imaged as a blurred area light spot on the sensor of the camera. In contrast to such a surface-healing background, the object surface and in particular the wafer edge lying in the dark field are imaged as a dark surface with a sharp edge. In the figure 5, the plane lighting device 30 is additionally shown again. The contrast between the main surface 22 in the bright field image and the oblique edge 24, which lies in the dark field of both illumination devices 28, 30, is particularly large, so that the Bevelline, so the linear transition from Bevel 24 to the main surface 22, can be well recognized In connection with the exact edge recognition according to the invention, the width of the Bevel and thus the polishing accuracy of the object edge can be detected over the entire circumference of the wafer with particularly high precision.

The first and second edge illuminators 28, 29 and the backlight 40 also combine with each other in an inspection device. The different directions of illumination then have to be operated alternately and / or in combination for the different lighting purposes in order to enable the most efficient and high-contrast image acquisition.

In this case, a modified arrangement is to be noted that the backlight device 40 and the first edge illumination device 28 together with the camera 14 are also pivoted by the same angle α so that the respective conditions described above for the beam path are met.

It should also be noted that the ring light does not protrude into the backlight even on the opposite underside of the wafer. On the other hand, there is a gap in the illumination that leads to a dark bar being visible below the apex center in the brightfield image, followed by the illuminated background, cf. Figure 6. This behavior can be tolerated as this black bar disappears in the image after merging the top and bottom camera images at the apex center. In the Raw data also makes it easier to find the edge of the wafer in the dark area

FIG. 6 shows an idealized histogram of the brightness progression of an image line from the edge environment of a wafer without defect. H1 denotes therein the brightness value of the direct reflection of the main plane lying in the bright field of the plane illumination device, H2 the brightness value of the edge lying in the bright field of the second edge illumination device and H3 the likewise independently adjustable brightness value of the light incident directly into the camera from the background illumination device. In addition to the illustrated case H1 <H2 <H3, other relationships are possible as long as a sufficient contrast remains, which makes the transitions of the areas of main surface, edge and background distinguishable.

The edge in this illustration includes the upper bevel, the apex, and a portion of the bottom bevel. This is due to the previously described oblique camera position, which is also outside the projection of the wafer on the main plane. The lower Bevel runs out of the bright field of the second edge illumination device, which is why the sanctity of the edge drops to the value 0 even before the wafer edge.

This is followed (radially outward) by the image of the backlight, whose intensity value is set even lower than that of the bright field edge, so that even under a different angle from which the entire imaged edge is in brightfield, sufficient contrast to Identification of the wafer edge is present. LIST OF REFERENCE NUMBERS

10 wafers

12 turntable

14 digital camera

15 optical camera axis

16 optics

17 lens system

18 wafer edge

19 image plane

20 radii sieves

22 main surface, top of the wafer

24 upper edge area, Bevel

26 frontal edge area, apex

28 first edge lighting device

29 second edge lighting device 30, 30 'level lighting device

31, 31 'light beams of the plane lighting device

32 Spot source of the plane lighting device

34 lens arrangement of the plane lighting device

36 mirrors of the plane lighting device

40 backlight device

A, B, C object points

A ', B \ C pixels H1. H2. H3 brightness value α first angle ß second angle

Claims

- Patent claims

1. Inspection device for the optical examination of object surfaces in an edge environment of an otherwise substantially planar object (10), in particular wafer edges, with at least one of the object surface at an oblique angle to the object plane and focusable on the object edge (18) digital camera ( 14) and a planar illumination device (30) which is arranged relative to the digital camera (14) and to the object surface such that an image of a planar main surface (22) of the object surface adjoining the object edge can be generated in the edge environment under bright field illumination, characterized in that the plane illumination device (30) comprises a co-ordination device.

2. Inspection device according to claim 1, characterized by a backlight device (40) which is arranged on the side of the object (10) facing away from the digital camera (14) in such a way that its light is radiated in the direction of the digital camera (14) in the direction of the digital camera (14) radiated light is partially shadowed by the object (10).

3. Inspection device according to claim 1 or 2, characterized by an image processing device having an edge detection means which is set up from the pixel information of the image generated with the digital camera (14) on the basis of a contrast between the object edge (18) and the main surface ( 22) to identify a transition line (Beveliine).

4. Inspection device according to claim 2 or 3, characterized in that the edge detection means is adapted to identify from pixel information of the digital camera (14) generated image based on a contrast between the object edge (18) and the backlight, the edge of the object (10) ,

5. Inspection device according to claim 3 and 4, characterized in that the image processing means comprises an edge analysis means which is adapted to monitor the distance between the velline and the edge.

6. Inspection device according to one of claims 2 to 5, characterized in that the image processing means comprises a structure recognition means which is arranged, a structural feature of the object edge (18) of pixel information of the image generated with the digital camera (14) based on the contrast between the object edge ( 18) and to identify the background lighting.

7. Inspection device according to claim 3 and 4 6, characterized in that the image processing device is adapted to determine a coordinate system based on the identified edge and the identified structural feature.

8. Inspection device according to claim 7, characterized in that in that the image processing device is set up to determine the position of the bevelline in relation to the coordinate system.

9. Inspection device according to one of the preceding claims, characterized by a first edge illumination device (28) which is arranged relative to the digital camera (14) and the object edge (18) so that an image of the object edge (18) can be generated under dark field illumination.

10. Inspection device according to one of the preceding claims, characterized by a second edge illumination device which is arranged relative to the digital camera (14) and the object edge (18) so that an image of the object edge (18) can be generated under bright field illumination.

11. Inspection device according to claim 10, characterized in that the second edge lighting device is designed in the form of a ring segment, which partially spans the object edge.

12. Inspection device according to claim 11, characterized in that the ring segment is circular segment-shaped and adjustable so that its center lies in the region of the object edge.

13. Inspection device according to claim 11 or 12, characterized that the ring segment is adjustable so that the radial light beam emanating from an outermost end is parallel to the collimated light of the Ebebenbeieuchtungseinrichtung (30).

14. Inspection device according to one of claims 9 to 13, characterized in that the image processing device is adapted to identify surface defects in the edge region from the pixel information of the dark field image and / or the HeII felbildes the object edge (18) based on reflections and / or scattered light.

Inspection device according to claim 14 in conjunction with claim 7, characterized in that the image processing means is arranged to determine the position of the surface defects with respect to the coordinate system.

16. Inspection device according to claim 2 and 10, characterized in that the second edge illumination device, the backlight device (40) and the Ebenebeieuchtung- device (30) are controlled separately from each other.

17. Inspection method for the optical examination of object surfaces in an edge environment of an otherwise substantially planar object (10), in particular of wafer edges (18), with the steps

Taking a digital image from an object edge (18) of the object surface by means of a digital camera (14),

- Illuminating a plane adjacent to the object edge planar main surface (22) of the object surface in the edge environment mitteis a level lighting device (30), so that the light emanating from the plane illumination device (30) and reflected at the main surface (22) is incident on the digital camera (14) and a bright field image of the main surface (22) is generated, characterized in that the light emitted by the plane illumination device ( 30) outgoing light is collimated.

18. Inspection method according to claim 17, characterized in that it further comprises

Illuminating the background while taking the edge image by means of a on the digital camera (14) facing away from the object (10) arranged backlight (40) whose light emits in the direction of the digital camera (14), wherein in the direction of the digital camera (14 ) emitted light is partially shaded by the object (10),

19. Inspection method according to claim 17 or 18, characterized in that it further comprises

- determining in a transition line (Bevelline) pixel information of the image generated by the digital camera (14) based on a contrast between the object edge (18) and the main surface (22).

20. Inspection method according to claim 18 or 19, characterized in that it further comprises

- Detecting an edge of the object (10) from pixel information of the image generated with the digital camera (14) based on a contrast between the object edge (18) and the background.

21. Inspection method according to claim 19 and 20, characterized in that the distance between the Bevelline and the edge is monitored.

22. Inspection method according to one of claims 18 to 21, characterized in that a structural feature of the object edge (18) from pixel information of the image generated by the digital camera (14) is identified based on the contrast between the object edge (18) and the backlight.

23. Inspection method according to claim 22, characterized in that a coordinate system is determined on the basis of the determined edge and the identified structural feature.

24. Inspection method according to claim 23, characterized in that the position of the Bevelline is determined with respect to the coordinate system.

25. Inspection method according to one of claims 17 to 24, characterized in that it further comprises

Illumination of the object edge (18) by means of a first edge illumination device (28), so that the light emanating from the edge illumination device (28) and reflected at the object edge (18) does not enter the digital camera (14) and a dark field image of the object edge (18) is generated.

26. Inspection method according to one of claims 17 to 24, characterized in that it further comprises

Illumination of the object edge (18) by means of a second edge illumination device (29) so that the light emanating from the edge illumination device (29) and reflected at the object edge (18) is incident into the digital camera (14) and a bright field image of the object cells (18 ) is produced.

27 inspection method according to claim 26, characterized in that the object edge is illuminated by a this partially spanning ring segment.

28. Inspection method according to claim 27, characterized in that the ring segment is adjusted so that its center lies in the region of the object edge.

29. Inspection method according to claim 27 or 28, characterized in that the outgoing from an outermost end of the ring segment radial light beam is parallel to the koliimierten light of the plane lighting device (30).

30. Inspection method according to one of claims 25 to 29, characterized that surface defects in the edge region from the pixel information of the dark field image and / or the Heilfeibildes the object edge (18) are identified by means of reflections and / or scattered light.

31. Inspection method according to claim 30 in conjunction with claim 21, characterized in that the position of the surface defects with respect to the coordinate system is determined.

32. Inspection method according to claim 26, characterized in that the second edge illumination device (29), the background illumination device (40) and the plane illumination device (30) are separately controlled so that simultaneously a bright field image of the object edge (18) and a bright field image of Main surface (22) is generated and there is sufficient contrast between the object edge (18) and the background and between the object edge (18) and the main surface (22).