WO2010015696A1

WO2010015696A1 - Inspection device and method for optical investigation of object surfaces, in particular a wafer notch

Info

Publication number: WO2010015696A1
Application number: PCT/EP2009/060255
Authority: WO
Inventors: Dietrich Drews; Manfred Guckes; Mladen Nikolov
Original assignee: Nanophotonics Ag
Priority date: 2008-08-08
Filing date: 2009-08-06
Publication date: 2010-02-11
Also published as: DE102008041135A1; DE102008041135B4

Abstract

The invention relates to an inspection device and an inspection method for optically investigating object surfaces in the area of a structural feature of an edge of the object, in particular for the optical investigation of the notch of a wafer. In the method according to the invention, a digital image of an object edge is taken at least in the area of a structural feature using a digital camera under dark field illumination, and at least one typical reflex of the structural feature is identified from pixel information of the dark field image under dark field illumination. According to another aspect of the invention, the digital image is taken in such a way that a main surface surrounding the edge is under bright field illumination, and the object edge is under dark field illumination. During photographing, a background illumination of the side of the object facing away from the digital camera is turned on, wherein the light of the background illumination radiates in the direction of the digital camera and is partially shaded by the object. At least the shape of the structural feature is identified from pixel information from the bright field image by way of a contrast difference between the main surface and the object edge and/or between the object edge and the background illumination.

Description

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

wafer notch

description

The invention relates to an inspection device and an inspection method for the optical examination of object surfaces in the region of a structural feature of an edge of the otherwise substantially planar object, in particular for the optical examination of the notch of an (unstructured) wafer.

The optical inspection process of semiconductor wafers for defects (breakouts, scratches, marks, particles, etc.) is an important part of the manufacturing process of computer chips. 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, which designates the entire surface of the object and in particular includes the following sections.

- "Main surface" refers to the flat, opposite upper or lower sides of the generally disk-shaped object (wafer).

- "edge" or "object edge" is the one hand on the main surface adjacent and on the other hand, the object on the outside circumferentially bounding surface section, which thus connects the main surfaces and usually both an upper and lower - -

oblique portion ("bevel") as well as an end-peripheral portion ("apex"). The "edge environment" describes a surface section that includes both the edge and a section of the main surface in the transition area to the edge. "Edge" or "object edge" refers to the transition line between the object edge and the environment that can be seen under the respective viewing angle.

- "Bevelline" refers to the transition line between the object's top and bottom sides and the bevel of the object's edge, which can be seen from the respective perspective.The "structural feature" is a deviation of the edge profile in the vertical projection onto the object plane Main surfaces defined by a given uniform or continuous contour. In the case of a circular wafer, such a structural feature is, for example, a radial notch (notch) or a straight edge section (circular chord).

Inspection devices for wafer edges often use an arrangement consisting of a digital camera, which faces the object surface and in particular can be focused on the object edge. Furthermore, one or more lighting devices are used in such inspection devices. There are known those which have a lighting device which is arranged relative to the digital camera and the object surface so that an image of the object surface can be generated under Dunkei field lighting, or those in which the arrangement of the illumination device relative to the digital camera and the object surface bright field illumination allowed. In dark-image illumination, the light emitted by the illumination device is reflected by the intact object surface in such a way that It does not come into the optics of the digital camera, so that the image of the object surface remains mostly dark. If there is a defect in the surface area (scratch, eruption) or in the form of an increase (dust grain, impurity), then part of the defect will usually catch one or the other reflex in the optics of the digital camera. This creates a bright image of defect fragments. In bright field illumination, the coating conditions are approximately inverted.

One or more of such images may be assembled into the image of the entire defect by means of a suitable image processing device. The digital image of the object surface taken under these illumination conditions is then usually fed to a manual or automatic evaluation, wherein 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.

From DE 103 13 202 B3, for example, such a device is known, in which the object edge of the wafer consisting of the upper Bevel (bevel), the apex and the lower Bevel are completely in the dark field of an LED light source, while that of the Wafer top or upper main surface reflected light directly into the camera, the wafer top is so in the bright field area. 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 - A -

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 mapped as a bright-field background mismatching to 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 lighting conditions 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 subsequent bright field image of the wafer top side on the one hand and the mirror on the other hand outshines the transition region to the edge, so that resolution losses can be expected here. It is not clear how the edge environment should be inspected in the area of the wafer slot (or any other structural feature of the object.

The utility model 20 2004 020 330 U1 relates to a generic per se device for the inspection of Glasplatten- edge areas. With the arrangement consisting of arranged in the glass plate plane and looking at the edge of the glass plate line or matrix camera, two arranged above and below the glass plate plane light sources and two arranged above and below the glass plate plane mirror for Umienkung the light rays of the profile profile is one under the camera monitored moving edge of the glass plate. EP 1 212 583 B1 deals with the inspection of the solder paste pressure on printed circuit boards. The core idea of the inspection described therein is to generate a three-dimensional image of the surface structure of the printed circuit board with the solder paste applied by the screen printing method and to compare this with a stored desired state and to display an error if tolerance ranges are exceeded.

In the published patent application DE 10 2005 014 595 A1, a method for the visual inspection of a edge release edge of a disk-shaped object is shown, in which an image of the edge region of the disk-shaped object in the dark field is recorded with a line camera and displayed on a display in several views. In other words, this involves the inspection of so-called structured wafers on which a lacquer layer has been applied which has been removed in the edge area of the wafer and on which a multiplicity of structural elements (Dies) are furthermore arranged.

DE 103 30 006 B4 likewise deals with the inspection of structured wafers for lithographic defects. The claimed apparatus includes a pair of reflected-light illuminating means, which radiate obliquely to the substantially planar surface of the wafer, a camera in dark field arrangement which is perpendicular to the surface of the wafer, the illumination axes of the two illuminating means being perpendicular to each other and perpendicular to line-shaped structures are aligned on the surface of the wafer.

Furthermore, devices are known in the art which use a background light source on the side of the wafer remote from an optical sensor. For example, from the Japanese Laid-open JP 59125627 A discloses a device in which a bundle of parallel light beams is irradiated perpendicular to the wafer surface in the edge region and the unshaded portion of this light beam is detected by means of a flat photosensor arranged on the opposite side of the wafer while the wafer is being rotated. In principle, the same arrangement is known from the Offenlegungsschrift US 5,438,209 A, but which uses a camera line instead of the photo sensor. Both devices are devices for determining the position of a notch without defect inspection of the wafer surface. The lighting is a pure backlight, so that, for example, a dark field recording hereby 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 Offenlegungschrift 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 Waferoberfiäche without the wafer is rotated thereby. The Beleuchtungseinrichtuπg is pivoted 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 wafer edge 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 defects on the wafer surface or even on the wafer edge to identify and locate with sufficient accuracy. This is also a device for determining the Notch position. Also, the asymmetrical arrangement of the illumination 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 addition, in note inspection, it may be desirable collectively to determine the exact position of the notch for establishing a frame of reference and / or to check the shape, basic presence or excess presence of the notch and / or scan the notch for defects ,

Against this background, the inventors have set themselves the task of providing an improved inspection device or method that provides more accurate and extensive information about the nature of the notch or similar feature features of the object edge.

The object is achieved by inspection devices having the features of claims 1 and 3 and inspection methods having the features of claims 12 and 14. Advantageous developments of the invention are the subject of the dependent claims.

The inspection method according to the invention provides that a digital image of an object edge, in particular of the edge of a unstructured wafer, at least in the range of a structural feature by means of a digital camera under dark field illumination is taken and from pixel information of the dark field image at least a typical reflection of the structural feature under dark field illumination is identified.

This is preferably achieved by comparing a target information to at least one typical reflex with the pixel information of the dark field image and concluding from the comparison on the presence of a structural feature and / or the presence of a defect.

According to another aspect of the inspection method according to the invention, a digital image is taken of an edge environment of the object at least in the region of a structural feature by means of a digital camera, wherein a major surface in the edge environment is recorded under bright field illumination (bright field image) and the object edge lies in the dark field and wherein during the recording a backlight on the side facing away from the digital camera of the object is switched on, the light 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, and from pixel information of the bright field image based on a contrast difference between the main surface and the object edge and / or identified by means of a contrast difference between the object edge and the backlight at least one typical shape of the feature.

This is preferably achieved in that a soil information for at least one typical shape is compared with the pixel information of the bright field image and from the comparison to the presence a structural feature and / or the presence of a defect is closed.

In this way, a note, which usually has the shape of a sharp notch or any other structural feature, for example in the form of a straight edge portion (on an otherwise circular wafer), are recognized. All regular structural features can thus be easily identified and, in particular, distinguished from an irregular outbreak.

Accordingly, in the inventive inspection device, at least one digital camera facing the object surface and focusable on the object edge, a first illumination device which is arranged relative to the digital camera and the object edge such that an image of the object edge can be generated under dark field illumination, and an image processing device with a structure recognition means provided that is configured to identify from pixel information of the dark field image at least one typical reflection of the feature under dark field illumination.

Preferably, a memory device is further provided, on which a desired information is stored for at least one typical reflection of the structural feature, wherein the structure recognition means is arranged by comparing the desired information to the at least one typical reflex with the pixel information of the dark field image, the presence of a structural feature and / or Identify a defect.

According to this aspect of the invention, an image of the object edge in the region of the feature is under dark-field illumination taken, wherein the same first Beieuchtungseinrichtung preferably also for receiving a dark field image of the remaining object edge is used in the course of edge inspection. Under these circumstances, very bright areas will appear in the image caused by direct reflection of the light of the dark field illumination on the feature in the camera. Especially in the case of strongly curved surface geometries in the region of the structural feature in all spatial directions, such reflections can not or only with difficulty be avoided. In conventional dark field inspection, such reflections are perceived to be detrimental because they are easily recognized as defects in automatic processing. According to the present invention, these reflections are used for the automatic defect inspection. The exact shape and location of the reflections depends on the design of the dark field illumination device, the camera arrangement and the nature of the feature surface. If the first two are kept constant, any change in the shape and / or position of the reflections will reveal a change in the structure feature surface and surfaces.

This change is detected by the structure recognition means by creating a "model" of the appearance of the structural feature reflections, which is expected with a defect-free structural feature before the measurement.The desired information obtained from the model, for example in the form of a pattern image or individual pattern parameters are stored in the memory Target information may in one way or another include information about the shape, size, relative position of the typical reflections and their surroundings After taking a dark-field image of the feature, the reflections and / or scatters actually occurring in the image are compared to the expected appearance, being at least the shape and location of the individual reflexes be taken into account. The defect detection is then carried out by comparing the deviations with a predetermined value, which is preferably also stored in the memory device.

The analysis of the recorded reflections and / or light scattering (events) is preferably done by first associated contiguous pixels whose contents (intensity, gray or color values) within a predetermined range of values (intensity, gray or Farbwertintervalls) assigned to the same event become. The events thus determined can then be checked by means of an algorithm for membership in an expected reflex or to a defect fragment or defect. If necessary, this is followed by the classification of the defect according to a specific defect classification.

According to another aspect of the invention, the inspection device has at least one digital camera facing the object surface and a second illumination device, which is arranged relative to the digital camera and to the object surface so that an image of a main surface in the edge environment can be generated under bright field illumination (Bright field image), while the object edge lies in the dark field, a backlight arranged on the side of the object remote from the digital camera so that its light is emitted in the direction of the digital camera, whereby the light emitted in the direction of the digital camera is partially shaded by the object, and an image processing device having a structure recognition means which is set up from the bi-point information of the bright field image on the basis of a contrast difference between the main surface and the object edge and / or on the basis of a contrast subculture hiedes between the Object edge and the background illumination at least to identify a typical shape of the structural feature.

Preferably, in this aspect of the invention, a memory device is further provided, on which a desired information is stored for at least one typical form of the structural features, the Strukturerkennungεmittel is arranged by comparing the desired information to the at least one typical shape with the pixel information of the bright field image, the presence of a Identify structural feature and / or the presence of a defect.

It is assumed that the structural feature will map as a continuous curve of the object edge and / or steady Bevelline. From the sharp image of the object edge in the region of the structural feature, which is like the rest of the edge of the object (at least predominantly) in the dark field of the second illumination device, the bevel of the structural feature can be easily compared with the light background of the edge and against the bright image of the main surface and compare with the nominal form.

The desired information can be stored in different ways. On the one hand, entire reference curves can be deposited. A defect detection then takes place, for example, in that a deviation of the recorded curve from the reference curve is determined and, if this value exceeds a predetermined value, which is preferably also stored in the memory device, a defect is concluded. In this way, all defects which influence the edge geometry or the shape of the structural feature can be detected. Examples of such defects are polishing defects but also breakouts of wafer material on the edge or near the Bevelline. A simpler defect detection can be realized by searching in the measured course of the population and / or shadow edge for abrupt changes in the course, which can be detected, for example, by means of strong changes in the slope. This method has the advantage that fewer specifications are required about the expected course of the edge and the beech in the area of the notch, so that a larger variety of structural feature forms can be inspected independently of stored reference curves. However, the scope of detectable defect types is reduced.

While the methods and devices described last identify defects in the structural feature that affect the progression of the bevel and / or shadow edge, the first described allow an analysis of defects that are in the area between the two transition lines "in the" edge region Therefore, in order to improve the inspection result, the invention can be advantageously combined in all the aforementioned embodiments.

In any case, the information about the shape of the contour of the wafer offers, in addition to the mere notch recognition, the additional possibility of detecting defects. In this case, the separate backlighting allows a contrast adjustment, which differs from the contrast center of gravity or from the intensity, gray or color center of gravity of a defect lying in the dark field. Outbreaks are thus easily distinguishable from a surface defect of another kind.

In contrast to the aforementioned known methods, the invention relates to an inspection device for precise localization of Strukturmerkmais and at the same time for the detection of surface defects in the region of the structural feature.

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.

The separate backlight device also has the advantage that it can be adjusted independently of the first illumination device with respect to its spectrum, the brightness and the emission direction. In this way, an optimal image contrast adjustment can be made in a simple manner, so that the method according to the invention evenly achieves consistently good results, independently of the reflectivity of the wafer surface, for example due to different coatings and / or structures.

The digital camera is preferably a line scan camera which is arranged such that the single image line recorded with the line scan camera lies in a plane that is perpendicular to the plane of the object or object edge. The optical axis of the camera may, according to a first embodiment, be oriented such that it defines, together with the image line, an optical plane which coincides with a radial plane of the wafer. The advantage of this embodiment is that fewer image distortions occur.

In another embodiment, the optical axis of the camera is oriented so that the defined together with the image line 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 has the advantage that the same camera arrangement can be used in a simple manner for a bright field image of the wafer edge by an additional bright field illumination device is used in mirror image arrangement relative to the camera arrangement with respect to the radial plane through the focal point on the Waferoberf. 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.

If the inspection device according to a preferred embodiment 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 in synchronism with the rotation of the turntable, a plurality of image lines of the object edge can be taken sequentially with such a line camera The object rotates together with the turntable. For this purpose, the triggering of the camera, for example, by means of a synchronization pulse by the drive motor (eg., Stepper motor) or a positiongebeπden sensor system done. The sequentially recorded image lines of the object edge in different angular position of the object are then combined to form a (panoramic) image of the object edge. The image processing device preferably has an edge detection means, which is set up to identify an edge of the object on the basis of a contrast difference between the object edge and the background illumination.

Assuming that the rest of the object edge will map as a continuous edge curve, the object edge lying in the dark field of the first illumination device can be determined in the same way on the one hand against the light background and on the other hand against the bright main surface and examined for defects.

Further, the edge detection means may identify uneven running of the wafer (horizontal vibration in the wafer plane) due to centering inaccuracy or wafer flutter (vertical vibration perpendicular to the wafer plane) due to unevenness or resonant excitation. So far, efforts have been made to minimize the sources of error by active and sometimes mechanically very complex centering and damping measures, compared to any defects horizontal or vertical vibrations but provide a periodic, low-frequency waveform 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.

The inventors have also recognized that, depending on the lighting situation, different sections of the defects are illuminated, that is to say different fragments are displayed under different directions of light incidence. To a more complete Therefore, in order to obtain the entire defect, a second illumination device is advantageously provided, which is arranged relative to the digital camera and to the object surface in such a way that an image of the object surface can be generated under Helffeld illumination. An exemplary arrangement has already been explained above. Thus, two images of the object surface can be recorded one after the other and the detected defect fragments can be identified separately from one another. The identification of defect fragments in the bright field image proceeds in the same way as in the dark field image. Thereafter, the two (or more) images of the object surface are combined in a virtual surface image, so that the sum of the information from the healing field image and the dark field image can produce a more comprehensive picture of the entire defect.

Preferably, the image processing device is further configured to define a coordinate system on the basis of the identified edge and 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 the apex center at a constant distance from the apex center in the case of a known shape of the edge profile and the observation angle at which the camera looks at the object edge identified 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 calculating the position of the true object edge. As 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.

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 Lagebestimmuπg can include, for example, both the extent of the defect or defect fragment so its center of gravity and orientation. Overall, the accuracy and reproducibility of the information about each defect are increased by the inventive identification of the object edge and the structural feature.

Preferably, the image processing device has an edge detection means which is set up to identify a Bevelline based on a contrast difference between the main surface and the object edge.

The wafer edge usually gets a polished surface. If the polishing process of the edge is done properly, the Bevelline and the wafer edge must always be parallel.

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

Thus, in combination with the second illumination device, the invention offers the additional possibility of detecting polishing defects in the entire circumference of the wafer.

The process steps of the image processing, in particular the identification of the structural features, the comparison of the image information with the typical reflections or shapes and the assignment of the event to defects, can be implemented individually or jointly 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 plan view of an embodiment of the inspection device according to the invention;

Fig. 2 is a side view of the embodiment of FIG. 1;

3 shows a flowchart according to the first aspect of the method according to the invention;

4 shows an operating scheme according to the second aspect of the method according to the invention;

Fig. 5 in section the course of shadow edge 40 and

Bevelline 50 at a regular notch without defects; Fig. 6 in section the course of shadow edge 40 and

Bevelline 50 at a Notch with defect 45 at the Apex and defect 55 at the Bevelkante;

Fig. 7 in section the course of shadow edge 40 and

Bevelline 50 on a regular notch without defects in dark field humidification, which lead to direct reflexes 60 in appearance and

Fig. 8 in section the course of shadow edge 40 and

Bevelline 50 on a Notch with defects in the Bevelbereich, which lead to modified Reflex 65 and additional scattered light 67.

Figures 1 and 2 show in simplified Darsteliung an embodiment of the inspection device according to the invention for inspecting an upper edge environment of a semiconductor wafer 10. The wafer 10 rests on a turntable 12, which motor, preferably mitteis stepper motor, driven and the wafer 10 during the measurement in Rotation offset. A motor control and / or an absolute or relatively positional sensor system (not shown) may be provided to output 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 inspection device further has a digital camera 14, which is aligned and focused by means of an optical system 16 on the edge 18 of the wafer 10. The digital camera 14 is specially designed for edge inspection of the wafer 10 by being aligned with the edge 18 at an oblique angle, preferably at 45 ° to the object plane or upper side 22 of the wafer 10. The Digital camera 14 thereby detects an edge environment which comprises a part of the upper side or main surface 22 of the wafer 10, its upper, slightly oblique edge region or bevel 24, and at least a part of the frontal edge region or apex 26.

The digital camera is preferably a time camera whose image line lies in the radial axis shown as dashed line 20. This case is shown in FIG. However, the line scan camera can also be swiveled out of the radial plane 20 by an angle, which can be used to generate a bright field image of the wafer edge in conjunction with a bright field moistening device (not shown here) tilted out of the radius plane in the other direction as already described above.

Furthermore, a first illumination device 28 is provided which, in this example, is designed in the form of a focused light gun of high intensity in each case in the form of 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 can suffice, or several can be provided, up to a quasi-flat, arcuate light source in whose center or focus the object edge lies. While such a planar light source due to its large angular spectrum evenly illuminates the edge region almost independent of its geometry, the single light source has the advantage to be focused in a simple manner and thus to generate a light spot of high intensity on the object surface.

With the arrangement of the digital camera 14 and the illumination device 28 shown, a dark field image of the Wafer edge 18, since the optical axis of the camera 14, viewed in the projection on the object edge, is perpendicular to the wafer edge and the illumination device 28 are pivoted out of the radial plane 20. Therefore, the light rays reflected at an intact object edge 18 at the angle of reflection α 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 32, here as a nearly point-like, not kαllimiert emitting 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 32 is imaged as a blurred area light spot on the sensor of the camera. In contrast to such a bright 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.

FIG. 2 additionally shows a possible arrangement of a second illumination device 30. The illumination device 30 is arranged such that its light is reflected directly from the upper main surface 22 of the wafer 10 into the camera optics 16. As a result, a helical field image of the main surface 22 is generated, as far as the angle of view of the camera detects it. As a result, the contrast difference between the main surface 22 in the bright field image and the oblique edge 24, which already in Dunkeifeid both Lighting devices 28, 30 is particularly large, so that the Bevelline, so the linear transition from Bevel 24 to the main surface 22, can be particularly easily detected. In principle, the second beeing device and the Bevellineerkennung described here can also be combined with another edge detection. In connection with the exact edge detection according to the invention, the width of the Bevei and thus the polishing accuracy of the object edge over the entire circumference of the wafer can be detected with particularly high precision.

The invention can also be combined with a medical field recording of the entire edge region. In this case, a further extended second illumination device is needed which flatly illuminates the entire profile of the imaged wafer edge. The different lighting devices 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.

FIG. 3 shows the flowchart according to the first aspect of the method according to the invention, wherein after taking the digital image with dark-field illumination of the wafer edge (first step), first the position of the notch in the image is roughly determined on the basis of the global profile of the wafer edge (second step). Then in the third step from the real appearance, more precisely from the pixel contents, actual information (position, size, shape, etc.) to the direct reflections and / or light scattering (based on gray or color values and assignment rules of the above type) in the area the notch is extracted. This is then compared in the fourth step with the stored target information, ie the expected appearance. The deviations (in single or multiple parameters) are then also included in the fifth step deposited thresholds. In the case of deviations which exceed these threshold values, the reflex or scattered light is identified as a defect in the sixth step, which can then be visualized, stored or otherwise output in the seventh step, for example, or subjected to a downstream classification.

FIG. 4 shows the flowchart according to the second aspect of the method according to the invention, whereby, after taking the digital image with bright field illumination of the main surface (first step), the position of the notch in the image is also roughly determined based on the global profile of the wafer edge (second step). , In the third step, the course of the wafer edge and / or the bevel is analyzed from the image, more precisely from the pixel contents (actual information). This is then compared in the fourth step with the stored desired information about the shape of the wafer edge and / or the Beveiiine. The deviations (in single or multiple parameters) are compared in the fifth step with likewise stored threshold values. Deviations which exceed these threshold values are identified as a defect in the sixth step, which can then be visualized, stored or otherwise output in the seventh step, for example, or which can be subjected to a downstream classification.

The detail of FIG. 5 shows the course of wafer edge 40 on a regular notch without defects in the recorded image with backlighting as a contrast jump between the background 38 and the Bevel 24 or the wafer edge, and the Bevelline 50 in the recorded image under bright field illumination Main surface as a contrast jump between Bevel 24 and the main surface 22nd The section according to FIG. 6 shows the course of wafer edge 40 and Beveliine 50 on a notch with defect 45 at the apex and defect 55 at the edge of the Bevel.

The detail according to FIG. 7 shows the course of wafer edge 40 and Beveliine 50 on a regular notch without defects in dark field illumination. This leads to direct, regular reflections 60 in the appearance due to the curvature of the wafer edge in the area of the notch in all spatial directions. The wafer edge 40 and the Beveliine 50 can be seen in the image only with simultaneous backlighting and brightfield illumination of the main surface 22.

The section according to FIG. 8 shows the course of wafer edge 40 and Beveliine 50 on a notch with defects in the Bevel region, which lead to altered reflection 65 and additional scattered light 67.

LIST OF REFERENCE NUMBERS

10 wafers

12 turntable

14 digital camera

16 optics

18 wafer edge

20 radial plane 2 main surface, upper side of the wafer 4 upper edge region, Bevei 6 front edge region, Apex 8 first illumination device 0 second illumination device 2 background illumination device 8 background beyond the wafer edge 0 wafer edge 5 defect at the apex 0 Bevelline 5 defect at the transition Bevel / main surface 0 Direct reflexes 5 Modified reflex 7 Additional reflex

Claims

claims

1. Inspection device for the optical examination of object surfaces in the region of a structural feature of an edge of the object, in particular for the optical examination of Notch a wafer, with at least one of the object surface facing and focusable on the object edge digital camera, a first Beieuchtungseinrichtung relative to the digital camera and is arranged to the object edge so that an image of the object edge can be generated under dark field illumination and an image processing device with a structure detection means which is adapted to identify from pixel information of the dark field image at least one typical reflection of the feature under dark field illumination.

2. Inspection apparatus according to claim 1, characterized by a memory device, on which a desired information for at least one typical reflection of the structural feature is deposited, wherein the Strukturerkennuπgsmittel is arranged by comparing the So N information to the at least one typical reflex with the pixel information of the dark field image Presence of a structural feature and / or the presence of a defect and / or stray light to identify.

3. Inspection device for the optical examination of object surfaces in the region of a structural feature of a Edge of the object, in particular for the optical examination of the notch of a wafer, with at least one of the Objektoberfiäche facing and focusable on the object edge digital camera,

a second illumination device, which is arranged relative to the digital camera and to the object surface such that an image of a main surface in the edge environment can be generated under bright field illumination (bright field image) while the object edge is in the dark field, a side of the object facing away from the digital camera arranged so

Backlight device that is emitted by their light towards the digital camera, wherein the light emitted in the direction of the digital camera is partially shaded by the object, and

an image processing device having a structure recognition means which is set up to identify at least one typical shape of the structure feature from pixel information of the bright field image based on a contrast difference between the main surface and the object edge and / or based on a contrast difference between the object edge and the backlight.

4. inspection device according to claim 3, characterized by a memory device on which a target information is stored for at least one typical form of the feature, wherein the structure recognition means is arranged by comparing the desired information to the at least one typical shape with the pixel information of the Heüfeldbildes Presence of a structural feature and / or the presence of a defect and / or stray light to identify.

5. Inspection device with the features of one of claims 1 or 2 and the features of one of claims 3 or 4.

6. Inspection device according to one of the preceding claims, characterized by a motor-driven turntable for rotatably supporting the object, wherein the digital camera is arranged to record a digital image of the rotating object edge in synchronism with the rotation of the turntable.

7. Inspection device according to one of claims 3 to 6, characterized in that the Biidverarbeitungseinrichtung comprises an edge detection means which is adapted to identify a border of the object based on a contrast difference between the object edge and the background lighting.

8. Inspection device according to claim 7, characterized in that the image processing device is set up to determine a coordinate system on the basis of the identified edge and the identified structural feature.

9. Inspection device according to claim 8, characterized in that the image processing device is adapted to determine the location of the identified surface defects with respect to the coordinate system.

10. Inspection device according to one of claims 3 to 9, characterized in that the image processing means comprises an edge detection means which is arranged to identify a Bevelline based on a contrast difference between the main surface and the object edge.

1 1. Inspection device according to claim 10, characterized in that the image processing device is adapted to determine the position of the Bevelline with respect to the coordinate system and / or the identified object edge.

12. An inspection method for the optical examination of object surfaces in the region of a structural feature of an edge of the object, in particular for the optical examination of the notch of a wafer, in which a digital image is taken of an object edge at least in the region of a structural feature by means of a digital camera under dark field illumination and off Cabin point information of the dark field image at least a typical reflection of the structural feature under dark field illumination is identified.

13. Inspection method according to claim 12, characterized in that a desired information is compared to at least one typical reflex with the pixel information of the dark field image and is concluded from the comparison on the presence of a structural feature and / or the presence of a defect and / or stray light.

14. Inspection method for the optical examination of object surfaces in the region of a structural feature of an edge of the object, in particular for the optical examination of the notch of a wafer, in which a digital image is taken of an edge environment of the object at least in the region of a structural feature by means of a digital camera, wherein a main surface is imaged in the edge environment under bright field illumination (bright field image) and the object edge is in the dark field and wherein while recording a backlight on the side facing away from the digital camera of the object is switched on, the light emits in the direction of the digital camera, which in the direction of the digital camera emitted light is partially shaded by the object, and in which from pixel information of the bright field image based on a Koπtrastunterschiedes between the main surface and the object edge and / or based on a contrast difference between the Objektk Ante and the backlight at least one typical form of the structural feature is identified.

15. Inspection method according to claim 14, characterized in that a desired information is compared to at least one typical shape with the pixel information of the bright field image and is concluded from the comparison on the presence of a structural feature and / or the presence of a defect and / or stray light.

16. Inspection method with the features of one of the claims

12 or 13 and the features of one of claims 14 or 15.

17. Inspection method according to one of claims 14 to 16, characterized in that based on a contrast difference between the object edge and the background illumination, an edge of the object is identified.

18. Inspektionsvθrfahren according to claim 17, characterized in that based on the identified edge and the identified structural feature, a coordinate system is set.

19. Inspection method according to claim 18, characterized in that the position of the identified surface defects with respect to the coordinate system is determined.

20. Inspection method according to one of claims 14 to 19, characterized in that a Bevelline is identified on the basis of a contrast difference between the main surface and the object edge.

21. Inspection method according to claim 20, characterized in that the position of the Bevelline is determined with respect to the coordinate system and / or the identified object edge.