Method and device for reading identification information encoded in wafers

Abstract

In a method for reading identification information inscribed in a wafer (14) in the form of an identification mark (16), at least one measuring beam (24; ML) of an optical measuring device (20; 110), comprising either an optical coherence tomograph (22) or a chromatic confocal distance sensor (110), scans an area (18) of the wafer (14) in which the identification mark (16) is inscribed. The identification mark (16) is recognized from measurement data generated from the scanning of the wafer (14). Based on the recognized identification mark (16), the identification information associated with it is determined.

Description

BACKGROUND OF THE INVENTION 1. Field of the invention

[0001] The invention relates to a method and a device for reading identification information inscribed in a wafer in the form of identification marks. 2. Description of the state of the art

[0002] Wafers are circular or square discs, approximately one millimeter thick, that serve as substrates for integrated circuits, micromechanical components, or photoelectric coatings. Wafers are manufactured from monocrystalline or polycrystalline ingots, which are sawn perpendicular to their longitudinal axis to create individual wafers. In most cases, wafers are made of silicon, but other materials are also used, such as glass for the production of microlens arrays. Increasingly, two or more very thin wafers made of the same or different materials are bonded together in a bonding process to form a composite structure.

[0003] Wafers are typically assigned identification information that uniquely identifies them and distinguishes them from other wafers. This identification information allows the wafer to be tracked through the numerous process steps of semiconductor manufacturing until it is sliced. This wafer traceability plays a crucial role in maintaining the high quality standards required in semiconductor manufacturing.

[0004] The identification information is represented by an identification mark, which is inscribed into a small area of ​​the wafer using a laser. This identification mark can be, for example, a sequence of alphanumeric symbols or a binary pattern such as a barcode or a QR code. To read the identification information, a camera captures an image of the wafer area where the identification mark is inscribed. Image processing algorithms recognize the identification mark in the image, associate the recognized identification mark with the identification information, and transfer this information to a higher-level display or processing unit.

[0005] However, the identification mark is often difficult to discern in the images. One reason for this is that the very small inscribed symbols or patterns are frequently damaged during various processing steps such as masking, exposure, and etching. Another reason for the difficulty in recognizing the identification mark can be low contrast, as is particularly common with glass wafers that are bonded to other wafers. Even if the identification mark is undamaged and has high contrast, structures above or below it can partially obscure it in the captured image, making it difficult for image processing algorithms to clearly identify.

[0006] If identification information cannot be reliably read, it may be impossible to determine the next processing steps assigned to the wafer and to assign detected defects on the wafers to specific process steps. This makes it more difficult to comply with the required quality standards.

[0007] To make wafer identification more reliable, US patent 2023 / 0046712 A1 proposes creating specially shaped holes in glass wafers when inscribing the markings with a laser beam. However, inscribing such identification marks is very time-consuming.

[0008] Cameras with special lighting systems that can generate different light and dark field illumination modes improve detectability. However, the equipment required for this is complex.

[0009] Alternatively or additionally, attempts are made to improve the recognizability of the identification mark by optimizing image processing algorithms or error detection. For example, US patent 2014 / 0093157 A1 discloses the ability to automatically detect and correct errors in image processing. When an error is detected, a wafer identification system generates interactive graphics and overlays them onto the wafer images.

[0010] However, these well-known software-based methods still require operator intervention. Furthermore, even the best image processing algorithms reach their limits when faced with very poor-quality images of the identification marks. SUMMARY OF THE INVENTION

[0011] The object of the invention is to provide a method and a device with which identification information inscribed in a wafer in the form of an identification mark can be read more reliably.

[0012] Regarding the method, the problem is solved by a procedure for reading identification information inscribed on a wafer in the form of an identification mark. In this procedure, at least one measuring beam from an optical measuring device, comprising either an optical coherence tomograph or a chromatic confocal distance sensor, scans an area of ​​the wafer in which the identification mark is inscribed. The identification mark is recognized from measurement data generated from the wafer scan. Finally, the associated identification information is determined based on the recognized identification mark.

[0013] The invention is based on the finding that certain optical distance sensors, namely optical coherence tomographs and chromatic confocal distance sensors, can detect the identification mark inscribed in a wafer much more reliably than is possible with conventionally used cameras. The laser inscription process locally modifies the surface profile, which can be detected by measuring the distance or thickness. This also applies in cases where the inscribed structures are not visible, or not reliably visible, in a camera image due to insufficient contrast. Furthermore, the optical properties of the inscribed structures, and in particular the reflectivity, change at the relevant optical interface. This can be detected by the highly sensitive, point-by-point scanning optical measuring device and used for structure recognition.

[0014] The measurement data generated by the optical measuring device during scanning can therefore represent, in particular, parameters such as the distance between the measuring device and the wafer, the thickness of the wafer, the reflectivity of an optical interface of the wafer, and / or the interference contrast. Reflectivity, for example, can be measured directly with a chromatic confocal distance sensor using a spectrograph. With an optical coherence tomograph, interference generally occurs even when the reference arm is blocked, due to reflections at different interfaces. In this case, indirect conclusions about the reflectivity of the optical interface can be drawn from the interference contrast, which is defined as the amplitude of the oscillation and is greater the more light is reflected at the interface.

[0015] Additional aids such as external lighting are not required in the method according to the invention, since the optical measuring device itself has a light source that provides the measuring beam.

[0016] Since the optical measuring device measures distances and / or thicknesses, it can be used not only to read identification information but also to measure the wafers. Recognizing the identification mark can then be an inherent part of wafer measurement, eliminating the need for additional equipment and processing time for reading the identification information. This reduces the processing time of a semiconductor device and increases process throughput.

[0017] Instead of, or in addition to, the previously mentioned parameters such as the distance between the measuring device and the wafer, the wafer thickness, the reflectivity of an optical interface of the wafer, and / or interference contrast, further parameters can be considered for the recognition of the identification mark. These include the signal-to-noise ratio, the height of the signal peaks, and wavelength-dependent information. In the case of optical coherence tomography, for example, the height of the signal peaks can be processed into a quality parameter according to the following calculation procedure: First, the largest coefficients in the discrete Fourier spectrum are identified. The corresponding value, along with the values ​​of the two adjacent coefficients, is summed and divided by the sum of the values ​​of all other coefficients.A quality parameter defined in this way also allows indirect conclusions to be drawn about the reflectivity of an optical interface and can therefore be used to recognize the inscribed identification mark.

[0018] Preferably, the measuring beam is generated by electromagnetic radiation with wavelengths outside the visible spectrum. It has been shown that identifying marks, which are barely recognizable in camera images using visible light, can be detected significantly better with measuring beams whose wavelengths lie in the infrared spectral range.

[0019] Silicon, for example, is transparent to infrared light. This allows an infrared measuring beam to penetrate a silicon wafer and scan an identification mark inscribed in an underlying wafer. When using a camera for character recognition, such a composite structure must first be flipped so that the camera can detect the identification mark.

[0020] As mentioned previously, the measuring beam can also scan a further area of ​​the wafer where no identification mark is inscribed, in order to obtain a surface and / or thickness profile of the wafer in this further area. In this way, the optical measuring device can be used for both profile measurement and for reading the identification information.

[0021] At least one geometric quantity can be derived from the measured surface and / or thickness profile. This can be, in particular, the TTV (Total Thickness Variation), which is the maximum difference between the thickest and thinnest points of a wafer. Other geometric quantities include bow, defined as the maximum deviation of the wafer's median surface from a reference plane, and warp, which is the deviation of the wafer's median surface from the reference plane after correcting for bowing across the entire wafer surface.

[0022] An optical coherence tomograph suitable as an optical measuring instrument comprises a light source and is designed to direct light generated by a light source onto the wafer and to detect (a) either the interference of multiple reflections at the wafer or (b) the interference of a reflection at the wafer and a reflection in a reference arm of the coherence tomograph.

[0023] A chromatically confocal distance sensor suitable as an optical measuring instrument comprises a light source that generates broadband light, a chromatically uncorrected lens that focuses the light into wavelength-dependent focal planes, and a spectrometer that spectrally analyzes the light reflected from a wafer.

[0024] With regard to the device, the aforementioned problem is solved by a device for reading identification information inscribed in a wafer in the form of an identification mark. According to the invention, the device comprises an optical measuring instrument, which includes either an optical coherence tomograph or a chromatic confocal distance sensor. The measuring instrument is configured to scan an area of ​​the wafer in which the identification marks are inscribed using at least one measuring beam. The device further comprises an evaluation unit, which is configured to recognize the identification mark from measurement data generated from the scanning of the wafer and to determine the identification information associated with it based on the recognized identification mark.

[0025] The measurement data can represent at least one measurement parameter selected from the group consisting of: distance between measuring device and wafer, thickness of the wafer and reflectivity of an optical interface of the wafer.

[0026] The optical measuring device may have a light source for generating the measuring beam, which is designed to produce electromagnetic radiation with wavelengths outside the visible spectrum.

[0027] In one embodiment, the device is configured to scan a further area of ​​the wafer with the measuring beam, an area in which no identification mark is inscribed, in order to obtain a surface and / or thickness profile of the wafer in this further area. The device can further be configured to derive at least one geometric measurement from the surface and / or thickness profile, selected from the group consisting of: TTV, deflection, and warping.

[0028] The invention also relates to the use of an optical measuring device comprising either an optical coherence tomograph or a chromatic confocal distance sensor for reading identification information inscribed in a wafer in the form of an identification mark. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Exemplary embodiments of the invention are explained in more detail below with reference to the drawings. These show: Fig. 1a a composite structure made of two directly bonded wafers in a perspective and not-to-scale representation; Fig. 1b the two in the Fig. 1a shown before bonding, wherein an identification mark is inscribed in one of the wafers; Fig. 2 those in the Fig. 1a Composite structure shown in an axial section; Fig. 3 an optical measuring device used according to the invention for reading the identification mark according to a first embodiment in a schematic meridional section, wherein the optical measuring device comprises an optical coherence tomograph; Fig. 4 important parts of a scanning device that are part of the system in the Fig. The measuring device shown in Figure 3 is in a simplified perspective representation; Fig. 5. An image of an area of ​​one of the objects calculated by the optical measuring device. Fig. 1a identifiable wafer in which an identification mark is located near the edge; Fig. 6 an optical measuring device used according to the invention for reading the identification mark according to a second embodiment in a schematic meridional section, wherein the optical measuring device has a chromatically confocal distance sensor; Fig. 7 A top view of a pinhole aperture with a two-dimensional arrangement of aperture openings for the [missing information] in the Fig. 6 measuring devices shown; Fig. 8 a top view of a pinhole aperture with a one-dimensional arrangement of aperture openings; Fig. 9 a wafer deviating from its intended geometry in a perspective view; and Fig. 10 A top view of an area of ​​a wafer near its edge in which a barcode is inscribed as an identification mark. DESCRIPTION OF PREFERRED EXAMPLES 1. Identification marks on wafers

[0030] The Fig. Figure 1a shows a perspective view, not to scale, of a composite structure 10 consisting of a first wafer 12 and a second wafer 14. The two wafers 12 and 14 are bonded directly, i.e., without a bonding layer. Bonding can be achieved, for example, by pressing the two wafers 12 and 14 against each other, by heat treatment, or by a combination of both. The thicknesses of the wafers 12 and 14 are shown in the Fig. Figure 1a is greatly exaggerated. The diameters of wafers 12 and 14 can be up to 30 cm, while the thickness is usually less than 1 mm. Therefore, wafers 12 and 14 should be thought of less as plates and more as flexible films. In the illustrated embodiment, the first wafer 12 consists of crystalline silicon and the second wafer 14 of glass.

[0031] In the Fig. Figure 1b shows the two wafers 12 and 14 before bonding. In this illustration, it can be seen that the second wafer 14 is marked near its circumferential edge with an identification mark 16, which is shown in the Fig. 1a is covered by the first wafer 12. The area 18, in which the identification mark 16 is located, is in the upper right corner. Fig. 1b is shown enlarged in section C.

[0032] In the illustrated embodiment, the identification mark 16 is a sequence of Latin letters and Arabic numerals. In this case, the identification mark 16 directly represents identification information that uniquely identifies the second wafer 14 and the composite structure 10 based on it, making them distinguishable from other wafers or composite structures. Instead of alphanumeric symbols, an identification mark 16 can also be used that is designed as a binary pattern and encodes the identification information. A barcode, such as the one used in the Fig. The symbol shown in 10 and labeled 16' indicates a QR code or a Data Matrix code. In principle, the identification mark 16 can contain any structure to which information can be assigned.

[0033] The identification mark 16 is generated using a laser that inscribes the alphanumeric symbols or the pattern structures into the surface of the second wafer 14. The writing process creates small dot- or line-like indentations on the surface. Fig. Figure 2, which shows the composite structure 10 in cross-section, shows a depression of this type on the right edge of the second wafer 14, not shown to scale, and labelled 19. Depending on the angle of incidence of the light, the depression 19 causes light scattering, which can be detected with the naked eye or with a camera.

[0034] However, capturing the indentation 19 with a camera can be unreliable. Since the first wafer 12 is made of silicon, no visible light can penetrate it. The indentation 19 can therefore only be captured by a camera from below using reflected light. However, the contrast may be so weak that the identification mark 16, composed of several indentations 19, cannot be reliably recognized by an image processing algorithm.

[0035] To more reliably detect the recesses 19 and the identification marks 16 composed therefrom, an optical measuring device 20 is used, with which distances and / or thicknesses and / or reflectivities can be measured. Two exemplary embodiments of such an optical measuring device are explained in more detail in the following sections. 2. Optical measuring device with coherence tomography

[0036] The Fig. Figure 3 shows a schematic representation of an optical measuring device according to the invention and designated overall by 20, according to a first embodiment. In addition to detecting identification marks 16, the optical measuring device 20 serves to measure the composite structure 10 made of bonded wafers 12, 14, which is supported by a holder 21. The holder 21 can, for example, be designed as a simple three-point support, as is the case in the Fig. 3 is indicated by supports 23. In the illustrated embodiment, the bracket 21 is itself supported on a base 25. Typically, the bracket 21 and the base 25 are not part of the measuring device 20. During measurement within the production process, the composite structure 10 can be fed to the measuring device 20, for example, from a conveyor belt or other conveying device.

[0037] The optical measuring device 20 comprises an optical coherence tomograph 22, which generates a measuring light beam 24 and whose structure is explained in more detail below.

[0038] A scanning device, indicated by 26, deflects the measuring light beam 24 variably in two orthogonal scanning directions x, y. For this purpose, the scanning device 26 has a first scanning mirror 28, which is rotatably mounted about a first axis of rotation 30. A second scanning mirror 32 is rotatably mounted about a second axis of rotation 34, which is oriented perpendicular to the first axis of rotation 30. The scanning mirrors 28, 32 are driven by galvanometer drives (not shown), which are controlled by a control unit 36. Fig. Figure 4 shows the scanning device 26 with scan mirrors 28, 32 shown here in a rectangular format, enlarged in a perspective and highly schematic representation.

[0039] The measuring device 20 also includes an image-side telecentric optical system 38, which is located in the Fig. 3 is indicated by three lenses L1, L2 and L3. In the illustrated embodiment, the optical system 38 focuses the measuring light beam 24 deflected by the scanning device 26 such that it always strikes the surface 40 of the composite structure 10 facing the optical system 38 at approximately a perpendicular angle. The respective point of impact of the measuring light beam 24, which depends on the position of the scanning mirrors 28, 32, defines a measuring point 39, 39'.

[0040] The optical coherence tomograph 22 includes a light source 42, a first beam splitter 44 which splits the light generated by the light source into the measuring light beam 24 and a reference light beam 46, a reference arm 48 for guiding the reference light beam 46, and an object arm 50 which uses the optical system 38 and the scanning device 26 and in which the measuring light beam 24 is guided.

[0041] During a measurement, the measuring light beam 24, propagating in the object arm 50, is focused onto the surface 40 of the first wafer 12 of the composite structure 10, where it is reflected predominantly specularly and to a lesser extent diffusely, and travels along the same light path back through the object arm 50 to the first beam splitter 44. There, the reflected portion of the measuring light beam 24 is superimposed with the reference light beam 46, which is guided in the reference arm 48 and reflected there by a mirror 52. Both light components are directed by a second beam splitter 54 onto a detector 56, which converts the optical interference signal into electrical signals.

[0042] In the illustrated embodiment, the optical coherence tomograph 22 is designed as an FD-OCT (FD stands for Fourier Domain). The detector 56 therefore contains a spectrometer that records the spectral intensity distribution of the interference signal. From this, an evaluation unit 57 connected to the detector 56 can calculate, in a manner known per se, the distance of an optical interface, e.g., the surface 40 of the first wafer 12, to the measuring device 20 (e.g., the lens L3) at the point of incidence of the measuring light beam 24. For further details on the optical coherence tomograph, reference is made to DE 10 2017 128 158 A1 (corresponding to US 2018 / 0164089 A1).

[0043] The wavelength range of the light generated by the light source 42 can be selected such that the measurement beam 24 can penetrate at least partially into the first wafer 12. In particular, the wavelength range lies in the infrared or near-infrared range. This corresponds to wavelengths between 950 nm and 2000 nm, with the wavelength range from 1000 nm to 1300 nm being preferred. Reflections then occur at all interfaces of the two wafers 12, 14, which are detected by the optical coherence tomograph 22. A spectral peak is obtained for each interface, from which the distance to the respective interface can be determined.

[0044] In addition, the optical coherence tomograph 22 can be used in a thickness mode. In this case, the evaluation unit only analyzes interference signals generated by interference between measurement light components reflected at different interfaces. In thickness mode, it is important to prevent light from propagating into the reference arm 48, as this would also interfere and thus generate unwanted noise signals. For this purpose, the reference arm 48 contains a switchable diaphragm, indicated at 59, which can be designed, for example, as a central or focal-plane shutter. When switching from distance mode to thickness mode, the switchable diaphragm 59 is automatically closed, preventing any light from the reference arm 48 from contributing to the interference on the detector 56.When switching back to distance mode, the switchable dimming device 59 clears the way for the reference light beam 46 again.

[0045] In the Fig. In the embodiment shown in Figure 3, the measuring light 24 propagates completely in free space. In other embodiments, the light is guided partially within optical fibers. 3. Reading the identification information

[0046] To read the identification information inscribed in the second wafer 14, the area 18 of the composite structure 10, containing the identification mark 16, is measured using the measuring device 20. For this purpose, the depressions 19 in the second wafer 14, which together form the identification mark 16, must be detected. The measurement is performed by guiding the measuring light beam 24 over the area 18 of the composite structure 10 using the scanning device 26. In this way, the composite structure 10 is scanned in a grid pattern. The lateral distance between adjacent measuring points depends on the required resolution and can be on the order of approximately 20 µm.

[0047] The depressions 19 represent irregularities in the otherwise flat upper interface of the second wafer 14. If the measuring device 20 measures the distance to this interface, the depressions 19 can be identified as locations with increased spacing. The distances to the other interfaces are not relevant for this measurement.

[0048] A false-color image can be created from the distances measured for the individual measuring points, as shown in the Fig. 5 is shown. The gray values ​​in the Fig. Figure 5 represents different distances, with the plane of the aforementioned upper interface of the second wafer 14 shown in white. This image should not be confused with an image taken by a camera, which would only contain information about the reflection behavior at the upper surface of the composite structure 10 facing the measuring device 20. Rather, the image in the Fig. Figure 5 shows a two-dimensional surface profile of the upper interface of the second wafer 14 located inside the composite structure 10, in which the identification mark 16 is inscribed.

[0049] On the in the Fig. In the surface profile shown in Figure 5, the identification mark 16 is clearly visible. A simple image recognition algorithm, contained in the evaluation unit 57, can easily recognize the sequence of alphanumeric symbols from this image. The evaluation unit 57 then determines the identification information associated with the recognized identification mark 16. If, as in the present case, the identification mark 16 is a sequence of alphanumeric symbols, these can directly form the identification information, so that no further assignment is necessary. If, however, the identification mark 16 is a binary code, such as the one shown in the Fig. For the barcode shown in 10, the identification information must first be determined by decoding from the identification mark 16.

[0050] The identification mark 16 can also be detected by the measuring device 20 in another way. For example, instead of measuring the distance to the upper interface of the second wafer 14, the device could switch to the thickness mode mentioned above and measure the thickness of the second wafer 14. In the area of ​​the depressions 19, the second wafer 14 has a reduced thickness. A thickness profile measured in this way results in a similar image to the surface profile shown in the Fig. 5 is shown.

[0051] In the distance or thickness measurements described above, structures already lithographically produced on the first wafer 12 do not interfere. Variations in the distance to the upper surface of the first wafer 12 result in peaks in the spectrum that are far removed from the peaks associated with the upper interface of the second wafer 14. Similarly, in thickness measurements, peaks attributable to such structures on the first wafer 12 can be easily identified if wafers 12 and 14 have different thicknesses.

[0052] When the measuring light beam 24 strikes a depression, less measuring light is specularly reflected there. As a result, the detector 56 detects less measuring light at these measuring points. Consequently, the location of the depressions can also be deduced from the intensity of the received measuring light. If this intensity is represented as a false color for each measuring point, an image similar to the one shown is obtained. Fig. 5. This utilizes the fact that the first wafer 12 is transparent to the infrared wavelengths of the measuring light beam 24. This allows the measuring light beam 24 to reach the recesses 19 inside the composite structure 10 largely unimpeded. 4. Optical measuring device with chromatic confocal distance sensor

[0053] The Fig. Figure 6 shows a schematic meridional section of an optical measuring device, designated 110, for distance measurement according to a second embodiment. The optical measuring device 110 is designed as a chromatically confocal distance sensor and is described in more detail below.

[0054] The measuring device 110 includes a light source 112 that generates broadband measuring light ML. The measuring light ML preferably has a continuous spectrum. However, the use of comb spectra or other discrete spectra is also generally possible, provided the wavelength peaks are sufficiently close together. In the illustrated embodiment, the light source 112 comprises a broadband light-emitting diode (LED) 114 and a converging lens 116 arranged behind it in the direction of light propagation.

[0055] The measuring light ML generated by the light-emitting diode 114 is first collimated by the converging lens 116. A further converging lens 116' focuses the measuring light ML so that it just completely illuminates a pinhole aperture 118, which is arranged in a plane E1. In the top view of the pinhole aperture 118 according to the Fig. Figure 7 shows that the pinhole aperture contains a two-dimensional pattern of aperture openings 122. If a pinhole aperture with a one-dimensional, i.e., linear, pattern of aperture openings 122 is used, as in the Fig. As shown in Figure 8 in top view, the converging lens 116' can be configured as a cylindrical lens or as another anamophotic optical element with varying refractive power along orthogonal directions. This minimizes light loss. Alternatively, a light source with an elongated exit surface can be used, which is imaged onto the pinhole 118 and illuminates it accordingly.

[0056] When illuminated with the measuring light ML, the aperture openings 122 of the pinhole aperture 118 represent the first apertures from which the measuring light ML emerges divergently.

[0057] A collimator lens 132 is arranged in the light path behind the aperture 118, its front focal plane coinciding with plane E1. The beams of light exiting from aperture openings 122 are therefore collimated as they pass through the collimator lens 132.

[0058] The collimated beams strike a non-polarizing beam splitter cube 133, which has a beam splitter surface 134 inclined at 45° to the optical axis. A predetermined fraction of the incident light, e.g., 50%, is reflected at the beam splitter surface 134 and is lost for the measurement. The remaining measuring light ML passes through the beam splitter cube 133 without deflection due to the collimated beam path and strikes a chromatically uncorrected objective 136, which has an object plane at infinity. Together with the imaging optics 124 and the collimating lens 132, the objective 136, due to its longitudinal chromatic aberration, images the aperture openings 22 arranged in the plane E1 into image planes, three of which are located in the Fig. 6 indicated and labeled B1 to B3, whose axial positions are wavelength-dependent. In the Fig. Figure 6 indicates this through different dashed lines. Each wavelength is assigned exactly one image plane B1 to B3. If – as in the present embodiment – ​​the spectrum generated by the light source 112 is continuous, a continuous sequence of image planes is consequently created.

[0059] If the image of an aperture 122 lies in an image plane at whose level the at least partially reflective surface 138 of the wafer 12 is located, the incident light beam is partially reflected back on itself and travels along the same path via the lens 136 back to the beam splitter surface 134 of the beam splitter cube 133. For the configuration shown here, this condition is met, for example, for the aperture 22 located on the optical axis OA of the measuring device 110 at a wavelength for which the image of the aperture 22 lies in the image plane B2. Of course, not only light of a single wavelength is reflected at the surface 138. However, there is only one wavelength at which the measuring light beam is reflected back on itself in such a way that a larger proportion of the reflected light can contribute to imaging the measurement spot onto the plane E1 or a conjugate plane E2.

[0060] At the beam splitter surface 134, a predetermined fraction of the reflected measurement light ML is reflected by 90° and focused by a converging lens 142 onto a spatial filter 144, which is arranged in a second plane E2. The spatial filter 144 is transparent to measurement light ML at certain locations 145 (or reflective in the case of a reflective spatial filter), while it blocks the measurement light ML at the remaining locations. The transparent locations 145 form second apertures through which the measurement light ML must pass in order to be detected.

[0061] In the simplest case, the room filter 144 is the same pinhole aperture that is used in the Fig. Figure 7 is shown in top view, possibly reduced or enlarged by the magnification of the intermediate optics. The entire optics in the light path between the pinhole 118 and the spatial filter 144, i.e., the collimator lens 132, the objective 136, and the focusing lens 142, cause the pinhole 118 to be imaged onto the spatial filter 144. The planes E1 and E2 are therefore optically conjugated. Measuring light ML, which has passed through a specific first aperture (one of the aperture openings 122 of the pinhole 118), thus passes through a second aperture (transmissive location 145 in the spatial filter 144), which is associated with the first aperture by optical conjugation. Intermediate images are formed in the image planes B1 to B3 on the surface 138 of the wafer 12.

[0062] The spatial filter 144 thus ensures that only measurement light beams with a very specific wavelength reflected from the surface 138 can be further evaluated. Measurement light ML that does not meet this condition is blocked by the static spatial filter 144 according to the chromatic confocal measurement principle.

[0063] A spectrometer 146 with multiple input channels is arranged in the light path behind the static spatial filter 144. In each input channel, reflected measurement light ML, which has passed through a light-transmitting location of the static spatial filter 144 associated with the respective input channel, is spectrally analyzed. The spectrometer 146 typically contains a dispersive optical element, e.g., an optical grating or a prism 147, as well as a row-like arrangement 148 of light-sensitive cells 149 for each input channel, as shown in the Fig. 6 is schematically indicated for some input channels.

[0064] A control and evaluation unit 130 calculates, during a measurement, distances between measuring points on the surface 138 and the measuring device 110 from wavelengths measured by the spectrometer 146, as is known for chromatic confocal measuring devices. The measuring points are images of the apertures 122. Each aperture 122 is assigned its own input channel, so that the distance measurement for all apertures can be carried out simultaneously, provided that the apertures are spaced sufficiently apart to prevent optical channel crosstalk. If higher lateral resolution is required, switchable spatial filters can be used, as described in detail in DE 10 202 211 7536 A1.

[0065] In an alternative embodiment, the measuring device 110 is designed such that the light passes through completely separate optical systems on its way from the aperture openings 122 to the wafer 12 and from the wafer 12 to the light-transmitting locations 145 of the space filter 44, as is disclosed, for example, in DE 10 2019 118 600 A1.

[0066] To obtain a thickness profile for a larger area on the wafer 12, relative movement must be generated between the measuring instrument 110 and the wafer 12, since the image of the aperture 118 only covers a small area on the wafer 12. For this purpose, the wafer 12 can, for example, be moved in a meandering motion under the measuring light beams ML using a traversing table. In this way, the measuring instrument 110 acquires a two-dimensional profile of the surface 38 of the first wafer 12. If there are depressions 19 on this surface that together form an identification mark 16, a surface profile is obtained that is similar to the one in the Fig. 5 false color image shown looks like.

[0067] Advantageously, the optical measuring devices 22, 110 described above scan not only the area containing the identification mark 16, but the entire wafer or the composite structure 10 composed of wafers. Important geometric parameters of wafers, including TTV, deflection, and warping, can be determined from the surface or thickness profile thus obtained. These parameters describe manufacturing-related deviations of the wafer 12' geometry from the ideal circular cylindrical shape 12' as specified in the Fig. 9 are exaggeratedly suggested.

[0068] In this case, the same optical measuring device 22, 110 is used both for measuring the wafers 12, 14 (or composite structures 10 made up of them) as part of quality control and for reading out the identification information. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] US 2023 / 0046712 A1

[0007] US 2014 / 0093157 A1

[0009] DE 10 2017 128 158 A1

[0042] US 2018 / 0164089 A1

[0042] DE 10 202 211 7536 A1

[0064] DE 10 2019 118 600 A1

[0065]

Claims

[1] Method for reading identification information inscribed in a wafer (14) in the form of an identification mark (16), characterized by , that at least one measuring beam (24; ML) of an optical measuring device (20; 110), comprising either an optical coherence tomograph (22) or a chromatic confocal distance sensor (110), scans an area (18) of the wafer (14) in which the identification mark (16) is inscribed, that from measurement data generated from the scanning of the wafer (14), the identification mark (16) is recognized, and that The identification information associated with the identified identification mark (16) will be determined on the basis of that mark. [2] Method according to claim 1, characterized by, that the measurement data represent at least one measurement quantity selected from the group consisting of: distance between measuring instrument (20) and wafer (14), thickness of wafer (14), reflectivity of an optical interface of wafer (14) and interference contrast. [3] Method according to claim 1 or 2, characterized by , that the measuring beam (24; ML) is formed by electromagnetic radiation with wavelengths outside the visible spectrum. [4] Method according to any one of the preceding claims, characterized by , that the measuring beam (24) also scans a further area of ​​the wafer (14) in which no identification mark (16) is inscribed, in order to obtain a surface and / or thickness profile of the wafer in the further area. [5] Method according to claim 4, characterized by, that at least one geometric measurement is derived from the surface and / or thickness profile, which is selected from the group consisting of: TTV, bending and warping. [6] Device for reading identification information inscribed in a wafer (14) in the form of an identification mark (16), characterized by an optical measuring device (20) comprising either an optical coherence tomograph (22) or a chromatic confocal distance sensor (110) and configured to scan an area (18) of the wafer (14) in which the identification marks (16) are inscribed with at least one measuring beam (24), and by an evaluation device (57) which is designed to recognize the identification mark (16) from measurement data generated from the scanning of the wafer (14) and to determine the identification information associated with the recognized identification mark (16) on the basis of the identified identification mark (16). [7] Device according to claim 6, characterized by , that the measurement data represent at least one measurement quantity selected from the group consisting of: distance between measuring instrument (20) and wafer (14), thickness of wafer (14) and reflectivity of an optical interface of wafer (14). [8] Device according to claim 6 or 7, characterized by a light source (42; 114) for generating the measuring beam (24; ML) which is designed to generate electromagnetic radiation with wavelengths outside the visible spectrum. [9] Device according to any one of claims 6 to 8, characterized by, that the device is configured to scan with the measuring beam (24; ML) also a further area of ​​the wafer in which no identification mark (16) is inscribed, in order to obtain a surface and / or thickness profile of the wafer (14) in the further area. [10] Device according to claim 9, characterized by that the device is set up to derive at least one geometric measurement parameter from the surface and / or thickness profile, selected from the group consisting of: TTV, bending and warping. [11] Use of an optical measuring device (20) comprising either an optical coherence tomograph or a chromatic confocal distance sensor for reading out identification information inscribed in a wafer (14) in the form of an identification mark (16).

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