Device and method for determining flat dielectric overlays on substrates in real time

Abstract

The invention relates to a device (10) and a method for determining, in real time, flat overlays (20) of dielectric materials, in particular organic materials, on strip-shaped or plate-like substrates (11), such as material webs made of metal or plastic, having an optical, ellipsometry-based detection device (1) for detecting and quantifying coatings or overlays (20) on the substrate (11) on the basis of changes in a polarisation state of light reflected at the substrate (11) or the overlay (20); having at least one light source (2), which is directed onto a surface of the substrate (11) at a predetermined angle of incidence α; having at least one image detection device (3) arranged opposite the light source (2) according to an angle of incidence α' for detecting light reflections on the substrate (11); and having an evaluation unit (4) configured and designed for ascertaining and evaluating overlays (20) on the substrate (11), wherein the device (10) is characterised in that the light source (2) comprises an infrared light source (21, 22) and the image detection device (3) comprises an infrared camera (31); in that optical means (5) are provided for limiting the incident light beams from the light source (2), which define a linear or substantially rectangular detection area E of light reflected from the substrate (11) for detecting overlays (20) by means of the infrared camera (31); and in that a polarisation splitting device (7) is provided for at least 2-fold polarisation splitting of the infrared light detected by the infrared camera (31) between the substrate (11) and the infrared camera (31) in such a way that an at least 2-fold image with at least two different polarisations can be generated from the detection area E.

Description

[0001] Device and method for determining planar dielectric deposits on substrates in real time

[0002] The present invention relates to a device and a method for the real-time determination of planar deposits made of dielectric materials, such as oil deposits, on strip-shaped or plate-like substrates using a detection device based on ellipsometry. Determining and ascertaining or quantifying such oil deposits or other planar deposits on material webs, such as metal webs, is an important factor in the manufacture and processing of, for example, metal sheets or metal strips during further processing, for example, in forming processes or similar. Therefore, it is important, for example in the automotive industry, to enable complete and precise determination of such planar deposits on substrates in real time, as if by means of an online measurement during the ongoing process.

[0003] To date, infrared spectroscopy technology has been used for this purpose, for example. This involves penetrating the layer or coating on a substrate surface with infrared radiation, allowing a spectroscopic evaluation of the shape and composition of the coatings based on specific wavelengths. This allows the composition and thickness of the coatings to be determined locally with considerable precision. However, there are disadvantages with regard to the speed of the measurement and the influence of substrate surface roughness, which can lead to falsified measurement results. Furthermore, this type of spectroscopy technology generally only allows for point-by-point measurements of the metal strips, so that a large-area determination of the coatings in real time on a passing metal strip is only possible with considerable equipment complexity, e.g., using traversing detection devices.

[0004] Furthermore, systems for determining oil deposits or other dielectric layers on substrates based on the ellipsometry method have been provided in the prior art. Lasers, e.g., a HeNe laser with a wavelength of 632.8 nm, were used as light sources, and the layer thickness or deposit on the substrates was determined using specially adapted detection elements and evaluation devices. However, even in this case, only a local or point-by-point detection of the respective deposits on the substrates can be performed. Furthermore, these methods are generally not suitable for the rapid, full-surface detection of the surfaces of metal tracks, which would enable real-time evaluation, quasi as an online measurement of deposits or layers.Furthermore, the usability of such laser-based measuring devices for typical technical roughnesses in the pm range is severely limited due to the short wavelength.

[0005] An ellipsometry-based method for determining deposits on substrates or layers is known, for example, from US Pat. No. 4,516,855. Here, a laser serves as the light source, directed at a substrate at a predetermined angle. On the output side, measurements are taken using a modified TV camera with a polarization filter connected upstream and a rotating device for acquisition at 0°, 60°, or 120°, respectively. The layers are thus acquired sequentially, with the surfaces being scanned one after the other using the modified TV camera. While fast, large-area image acquisition in real time is theoretically possible with the method proposed there, this system lacks practical suitability. Due to the use of three different cameras, this method is relatively expensive, requires large-scale equipment, and requires complex mutual alignment of the cameras.Furthermore, measurements can only be performed in the visible light range, which again limits their usefulness for technical surfaces with roughness, particularly in the pm range. Furthermore, the use of a laser as a light source for images is problematic due to the occurrence of speckles. Large amounts of data must also be processed, as three full images are generated by each of the three different cameras and must be mathematically evaluated to determine the layer thickness. Document US 4,516,855 also mentions an alternative design involving a conversion of a color camera, which originally only had one picture tube and could be segmented into groups of three using upstream color filters.However, this has the disadvantage that the polarization measurements in a group are not performed on the same light beam, but on three different neighboring beams, which leads to problems with strong contrast changes. Furthermore, implementing such a pixel-by-pixel polarization measurement is relatively complex with the high-resolution sensors used today.

[0006] US Pat. No. 5,963,326 also describes a laser-powered device for detecting deposits or layers on substrates. A CCD camera system is used in conjunction with a double afocal lens system to perform a planar measurement of the layer thickness on the substrates using imaging ellipsometry. This system is only of limited use for real-time measurements because the polarization measurement is based on a rotatable polarizer (analyzer), and multiple measurements must be taken at different analyzer positions to determine a polarization state.

[0007] EP 1 835257 B1, in turn, describes a method for determining contact surfaces on a continuously moving metal strip, which method uses a laser light source and a first and a second single-wave ellipsometer. The first ellipsometer is arranged above a moving metal strip, while the second ellipsometer is located below the metal strip. When determining contact surfaces on the metal strip, the measured values ​​are further processed in an evaluation unit based on conversion functions stored in a database and a specific selection factor. The selection factor can be a parameter such as the temperature of the strip or information from pre-treatment or a preliminary system. This system also uses a simple laser light source without imaging optics, so that large-area measurement of contact surfaces in real time is not possible.It is also necessary to determine an additional parameter for the selection factor, including the integration of other required sensors.

[0008] It is found that a real-time, planar polarization measurement using infrared light, which is advantageous for technical surfaces, has not yet been realized in the state of the art as described, in contrast to realizations in the visible range of light rays with the associated technical disadvantages.

[0009] Against this background, it is the object of the present invention to provide a device and a method for determining planar deposits of dielectric materials on substrates, such as metal tracks or the like, with a detection device based on ellipsometry, in particular in real time, with which an efficient and yet fast online measurement over the entire surface area or width range of a substrate is enabled and the accuracy and the realizable measuring range of layers of different thicknesses, with a typical thickness of a few pm, are further improved and increased.

[0010] This object is achieved by a device having the features of claim 1 and by the method having the steps according to claim 11. Advantageous embodiments and further developments of the invention are the subject of the dependent claims.

[0011] According to the invention, as stated in claim 1, a device for determining in real time planar deposits of dielectric materials, in particular organic materials, on strip-shaped or plate-like substrates such as material webs made of metal or plastic, with an optical detection device based on ellipsometry for detecting and quantifying coatings or deposits on the substrate on the basis of changes in a polarization state of light reflected from the substrate or the deposit, with at least one light source which is directed onto the surface of the substrate at a predetermined angle of incidence α, with at least one image detection device arranged opposite to the light source according to an angle of reflection α' for detecting light reflections on the substrate, and with an evaluation unit,which is set up and designed to detect and assess overlays on the substrate, wherein the device according to the invention is characterized in that the light source comprises an infrared light source, that the image capture device comprises an infrared camera, that optical means for limiting the light rays incident from the light source are provided in front of or behind the substrate, which define a linear or substantially rectangular detection area E of light reflected from the substrate for detecting overlays by the IR camera, and that a polarization splitting device for at least two-fold (2-fold) polarization splitting - optionally also three-fold or four-fold,

[0012] Polarization splitting - of the IR light detected by the IR camera between the substrate and the IR camera is provided in such a way that at least a double image with at least two different polarizations of one and the same light beam can be generated from the detection area E.

[0013] For the real-time determination of planar deposits on substrates, the device thus has an infrared light source on the light source side, while at least one infrared camera is provided on the image capture device side, with which the reflected infrared light rays from the substrate in the limited capture area E can be specifically captured and further processed.Furthermore, the device according to the invention comprises an evaluation unit which, together with a polarization splitting device in front of or within the infrared camera, enables the determination and quantification of the deposits on the substrate in a linear detection area E and in real time, thus providing a type of online measurement (real-time measurement) and, for example, continuous, large-area determination of the thickness of the deposits using a novel imaging ellipsometer, for example, achieved by the movement of the substrate during the measurement. In the polarization splitting device, the IR light beams recorded by the detection device in the detection area E are split at least twice in the sense of beam splitting for further processing according to the invention in the evaluation unit.This means that the light rays in the infrared range are split into a first and second differently polarized line or image, with e.g. horizontal and vertical polarization or with 45° and 135° polarization, by the polarization splitting device, so that the IR camera continuously and in real time records a double line of reflection from the current state of supports in the detection area E, on the basis of which the parameters of a layer thickness and a position of the layers can be determined and calculated in a relatively large thickness range using ellipsometry, ie by forming a ratio of the intensities of the IR light radiation along the line.

[0014] The inventive combination of using an infrared source as the light source and an infrared camera with an integrated or upstream polarization splitting device with at least two-fold splitting of the light beams provides an effective device for precise online measurement of such deposits, such as oil deposits, particularly on continuously moving metal strips of relatively large widths, for example, up to 2500 mm. This device requires less computational effort than previously because no spectroscopic measurement is performed, but rather only an intensity measurement of the spectrum in the IR range of light beams, optionally restricted by a bandpass filter. Furthermore, the deposits can be determined and thickness measurements can be performed not only pointwise or locally.The device allows, even without, for example, traversing movement of the detection means, a relatively large-area simultaneous determination of the supports in the detection area E, which is generated specifically in a linear or substantially rectangular manner over, for example, the entire width of the substrate by optics and / or a slit aperture.

[0015] By means of limiting the IR light rays to a substantially linear or rectangular narrow detection area E, the invention achieves that the most accurate and precise analysis and imaging of the actual conditions (position, thickness, thickness profile, etc.) of the overlays on the substrate can be realized in the polarization splitting device of the image capture device and subsequently in the evaluation unit of the device according to the invention. The means for limiting to a linear or relatively narrow rectangular area thus allow a significantly improved use of the ellipsometry method in the capture device compared to the prior art: In the polarization splitting device, the respectively detected linear line or line of IR light rays reflected in the rectangular detection area E can be split into two, three, or four images by polarization.The resulting doubled or quadrupled images of the actual intensity ratios of the reflected IR light rays on the substrate (e.g., metal strip) are sufficiently precise and accurate for further processing to calculate the actual thickness ratios or position information for such deposits or similar. With the device according to the invention designed in this way, more precise results can be achieved in terms of quality assurance than was previously the case with spectroscopy or other optical monitoring methods. The simplified form of calculating the thickness and position of oil deposits on such substrates can thus be implemented more quickly than before, with significantly reduced computational effort. This enables 100% real-time monitoring of metal strips or metal sheets, or non-metallic substrates, passing by during the production process.

[0016] The evaluation unit contains appropriate means for calculating an image of the respective supports in the detection area E based on ellipsometry and the polarization splitting from the polarization splitting device. The light beams are split at least twice using polarizing optics, for example, a combination of Brewster plates or wire grid polarizers and mirrors in front of or integrated into the detection device. The Brewster plates are generally coated in such a way that the polarization separation is enhanced, and for a specific wavelength determined by the coating, an almost complete splitting into p- and s-polarized light is achieved. In the context of the present application, Brewster plates primarily refer to coated Brewster plates (enhanced Brewster plates). So-called nanowire polarizers can be used as wire grid polarizers.A wire grid polarizer has the advantage over a coated Brewster plate in that it provides clean polarization separation over a relatively wide wavelength range. However, the disadvantage is higher absorption of the wire grid polarizer and possible interference with the beam path due to grating diffraction.

[0017] However, the splitting of the light beams in the polarization splitting device can also be implemented in a further development as a triple or quadruple split, e.g., with the polarization states 0° linear & 90° linear & right-hand circular & left-hand circular, or 45° linear & 135° linear & right-hand circular & left-hand circular, or 0° linear & 90° linear & 45° linear & 135° linear, thus enabling further advantages, such as even more precise thickness measurement and a doubling of the measuring range. The invention also allows for direct real-time measurement of relatively wide substrates with widths of up to 2500 mm.

[0018] With the device according to the invention, deposits of, for example, oil films in the range 0-3 pm with 2-fold splitting and 0-6 pm with 4-fold splitting on metallic substrates can be detected accurately in real time, particularly when using a bandpass filter with maximum transmission at a wavelength of approximately 14 pm of the infrared light beam. By using infrared light as the basis for the detection device via the infrared camera according to the invention, measured values ​​can now also be recorded over large areas in the mid-infrared range of, for example, 8 to 14 pm wavelengths, which leads to a significant expansion of the detection ranges in this regard compared to the prior art. According to the invention, previous problems regarding any roughness of the surfaces of metal strips or other substrates are also significantly reduced by the new device according to the invention based on IR ellipsometry.

[0019] The present invention provides a simple and robust measuring device that obtains real-time, areal information on layer thickness distributions. These typically concern layers of dielectric substances such as oils, varnishes, adhesives, adhesion promoters, passivations, primers, etc. in the pm range on generally metallic substrates. Conversely, the device according to the invention can also be used to precisely and quickly measure very thin metallizations on non-metallic substrates. However, due to the shallow penetration depth of IR radiation into metals, the measurable layer thickness range is smaller and more precise, in particular significantly less than one pm. This application also requires an angle of incidence α in the range 54-60°, since the Brewster angle of a non-metallic substrate typically lies in this range.

[0020] The invention addresses the above-mentioned problems in the prior art by using only one IR camera / image capture device and a corresponding beam splitting system, which, together with the described imaging optics, generates two, three, or four separate, but otherwise identical images on the IR camera sensor, measuring different polarization components. This enables a relatively compact and inexpensive measurement system that is easily implemented for all types of surface-capturing electromagnetic radiation measuring devices. It also handles high-contrast images and can thus be adapted much better to the data to be captured or typical measurement tasks as needed.

[0021] Splitting the polarization into two different images in the polarization splitting device is easy to implement and allows for processing information on the incident polarization and, consequently, the thickness of the coating on the substrate. For example, for an oil layer on a metallic substrate at a wavelength of λ=10.6 pm and an angle of incidence α=85°, the ratio R45 = (145-1135) / (145+1135) shows a unique relationship with the oil layer thickness in the thickness range 0-1 pm, whereas the ratio Rps = Ip / Is (or equivalently: Rps2 = (lp-ls) / (lp+ls)) shows a unique relationship with the oil layer thickness in the thickness range 1-2.5 pm. If the polarization angle is chosen between 0 and 45°, e.g., 20° and 110° as the second angle, thus determining a ratio of R20 = (120-111O) / (I2O+111), this compromise can be used to clearly measure the oil layer thickness of a coating on the substrate in the thickness range of 0-2.5 pm. Thicknesses greater than the second5pm requires either a longer wavelength or the measurement of a second ratio for unambiguous determination.

[0022] In general, the embodiments described below measure specific mutually orthogonal polarization components in the beam reflected from the substrate. The measured polarization components are advantageously limited to relatively easy-to-process polarization states, such as linear or circular polarization. However, the described methods can also be extended to measure orthogonal, i.e., complex, elliptically polarized polarization components by varying the position and effect of individual components, which can be advantageous in special cases.

[0023] The invention advantageously uses, among other things, the measurement of a circular ratio Rz = (IR-IL) / (IR+IL) in the evaluation unit by means of a quarter-wave retarder prior to the splitting in the polarization splitting device. The main axis of the retarder must enclose an angle of 45° with the mutually normal polarization directions of the polarizing beam splitters, such as a Brewster plate or wire grid—also called a polarizer here. The absolute position, i.e., the angle to the main plane, plays no role here; for example, a p- and s-alignment of the polarizers is recommended for simple implementation and advantageous arrangement of the two individual images on the image sensor. Depending on the specific material parameters, the measurement of the circular ratio Rz allows, for example, a highly sensitive oil thickness measurement in the range 0–0.5 pm or, alternatively, a measurement of 0.5-4pm, whereby it is not possible to distinguish between these ranges without measuring a further ratio such as Rps, Rps2, R45. It should also be mentioned that an oblique viewing of the substrate as an object results in increased effort to produce a consistently sharp image, but in return the object size can be significantly larger, up to a factor of 10, than the entrance aperture of the viewing lens, which would otherwise not be possible due to the collimated beam with a fixed angle of incidence. This means that very long detection ranges E or wide bandwidths, e.g. of metal strips, can be detected. With parallel beam guidance, a bandwidth of around 1000 mm of the substrate can be detected relatively easily with the device according to the invention, whereas with convergent beam guidance, substrates with a bandwidth of up to 2500 mm can be viewed and assessed in a single step.

[0024] With the device according to the invention, the position and thickness of various layers or coatings on, for example, metal strips can be reliably detected and determined. Thus, by using an infrared light beam with the described polarization splitting device and evaluation unit, different types of oil or oil mixtures can also be reliably detected and imaged in the pm range. Unknown mixtures of dielectric materials that may be present on the substrates or the metal strip can also be reliably determined and imaged in real time with relatively low computational effort.

[0025] According to an advantageous embodiment of the invention, a slit aperture, mask, or optical limitation between the light source and the IR camera, or alternatively a special shape or positioning of the IR light source, is provided as a means for limiting the detection area E to a linear or substantially rectangular shape of the detection area E. As an example of a special shape of the IR light source, a rod-shaped IR light source can be used for this purpose. Several different means for generating the limited detection area are therefore possible. The slit aperture can, for example, be provided both on the side of the infrared light source in front of the substrate in the beam path of the IR light rays, and on the imaging side, i.e., after the reflection of the IR light rays on the substrate and between the substrate and the detection device with the IR camera.Alternatively and additionally, other means for limiting the detection area E to a linear or substantially narrow rectangular shape can also be provided, either optically or as electrical elements such as a glowing wire. By limiting the detection area E to a linear shape or a narrow rectangular area, preferably with the length aligned across the entire width of the substrate or metal strip, the measurement accuracy is further increased when determining even very thin oil deposits in the pm range in the device.

[0026] The position of the slit aperture is selected to create a line image of the detection area. As long as the detection area is limited to a narrow, approximately linear area within a section of the substrate that reflects IR light rays, the invention allows for accurate and rapid measurement of the surfaces of such substrates.

[0027] According to a further advantageous embodiment of the invention, imaging optics are provided upstream of the polarization splitting device or integrated therein. Such optics or "imaging optics" can be formed from multiple lenses, for example, in the form of a bi-telecentric lens consisting of two confocal lenses. Optics for convergent beam guidance are also possible. Furthermore, the imaging optics can optionally also have an additional pinhole or aperture. Combinations of mirrors, in particular concave mirrors, can be used as another possible form of imaging optics.The polarization splitting device itself comprises, for example, a combination of Brewster plates, mirrors, (nano-)wire grid polarizers, λ / 4 mirrors, and λ / 4 plates so that the reflected IR light radiation from the substrate in the image capture device can be displayed by the IR camera in the form of at least a twofold polarization split, i.e., a kind of double line, or a fourfold split, i.e., a quadruple line. A threefold split is also possible within the scope of the invention with quarter-wave retardation.

[0028] According to an exemplary embodiment of the invention for polarization splitting, a λ / 4 plate can be realized by a simple glass plate in the beam path, which is subjected to mechanical tension by a tensioning device perpendicular to the beam propagation. This possible implementation of the invention is based on so-called stress-induced birefringence, which is otherwise exploited in tension optics. The force direction indicated by the tensioning device also defines the main axis of this implementation of a retarder. By varying the force, the retardation is adjusted, e.g., to an λ / 4 retardation. The advantage of this possible form or implementation of the invention is that λ / 4 plates are otherwise difficult to realize in the mid-infrared light range.A particularly advantageous embodiment dispenses with a separate glass plate and provides the optical lenses of the imaging objective with a corresponding clamping device that tensions them to a certain extent. Since, due to the relatively long wavelengths, typically in the range 8-15 pm, quite high mechanical stresses must be induced to achieve quarter-wave retardation, a smaller retardation, e.g., approximately λ / 8, can under certain circumstances be generated with smaller forces in order to nevertheless measure sufficiently circular portions of the IR light reflected from the substrate with the device according to the invention. Such a clamping device can use piezo actuators to specifically place the optics under mechanical stress. This results in the advantage of very fast and simple control of the retardation of this polarization splitting device.

[0029] According to a further advantageous embodiment of the invention, the polarization splitting device comprises at least one Brewster plate and at least one mirror in the region of the reflected IR light beam at the angle of reflection a'. By arranging a Brewster plate and mirrors, the polarization splittings according to the invention can be reproduced in at least two linear images using relatively simple optical measures. From the intensity ratios of the detected two (or four) linear IR beams in the detection area E, the evaluation unit can then calculate and display the position and thickness of the respective layers or coatings on the substrate.

[0030] According to a further advantageous embodiment of the invention, at least one imaging object-side telecentric optic is provided between the substrate and the IR camera. Typically, but not necessarily, a bi-telecentric lens is used, so that image-side telecentricity is also present on the side of the detection device. With this telecentric optic, the light components of the IR light beam detected by the IR camera are converted into a largely parallel light beam shape, which increases the accuracy of the results when detecting and evaluating the images of the polarized lines. With such collimated beam guidance through the telecentric optics of the device, comparatively simple data evaluation is achieved. The identical angle of incidence at every point in the illuminated detection area E eliminates the need to adapt the evaluation to different angles of incidence.Alternatively, such an imaging optics can also be implemented with a combination of concave mirrors. This system is particularly suitable for smaller substrate widths or metal strips up to a strip width of approximately 1000 mm. For wider metal strips or substrates, for example, 2500 mm, several measuring systems or devices according to the invention must be mounted parallel to one another, distributed across the strip width.

[0031] According to a further advantageous embodiment of the invention, an imaging object-side optics system is provided for capturing or imaging convergent infrared rays between the substrate and the IR camera of the detection device. This allows convergent portions of the infrared light rays emanating from the light source to be transmitted in a convergent manner upon reflection from the substrate or a coating or oil coating on the substrate. This allows larger width ranges of substrates or metal strips up to 2500 mm to be captured directly and with a measuring system, even with relatively small standard optics. This reduces the cost of the device, and meaningful values ​​for coatings with oil coatings or similar can still be obtained precisely.With the convergent generation and detection of IR rays, the evaluation unit must perform even more extensive calculations and adjustments, particularly with regard to the angular distribution during data evaluation. The respective changing angles of incidence a are not constant across the width of the substrate or metal strip. The corresponding adjustment of the changed angular relationships is then carried out using the known values ​​stored, for example, in a database.

[0032] According to a further advantageous embodiment of the invention, the infrared light source and detection device are adapted for a mid-infrared light range, in particular a range from 5 pm to 15 pm, preferably 8 pm to 14 pm. According to the invention, the infrared light rays in the measuring device are therefore in a mid-infrared range and are thus outside the near-IR range and significantly removed from the wavelengths in the visible light range used in previous systems of this type. The mid-infrared range has proven particularly effective for the purposes of detecting such thin layers or deposits on substrates such as metal strips, in the sense that detection and calculation could be achieved with greater accuracy than usual.

[0033] According to a further advantageous embodiment of the invention, a bandpass filter or an edge filter is provided between the infrared light source and the IR camera in the beam path of the IR rays. The optional bandpass filter or edge filter serves to limit the reflected IR light rays entering the detection device to the narrowest possible bandwidth of the wavelength of the IR light. Thus, approximately monochromatic IR light is generated. The IR camera of the detection device can thus be precisely tuned to a specific wavelength, increasing the accuracy of the ellipsometric evaluation and expanding the detectable layer thickness range by limiting it to the longest possible wavelength, preferably in the range of 13-15 pm. Other wavelength ranges are also conceivable within the scope of the invention.This enables even more precise measurement and detection of such oil deposits or similar on substrates over a wider thickness range than before.

[0034] According to a further advantageous embodiment of the invention, the light source and the detection device are each arranged laterally from the substrate and are preferably configured to determine deposits on a continuously moving substrate, such as a metal strip. The components of the device are thus positioned laterally outside the area of ​​the substrate, at its side edges. This prevents disruption to the processing sequence. The device can also be easily adapted to substrates or metal strips of different widths by positioning the laterally arranged components, namely the light source in the form of the infrared light source and the IR camera, accordingly outside the area of ​​the substrates. This is particularly advantageous for larger widths of the detection area E, for example 2500 mm.Alternatively, the IR light source and IR camera can be arranged above the substrate in order to carry out the measurement in the conveying direction of the belt.

[0035] According to a further advantageous embodiment of the invention, the angle of incidence (AOI) a and thus the corresponding angle of reflection a' of the light beam from the infrared light source, relative to the vertical perpendicular to the substrate or the plane of the substrate, lies in a range of a = 75° to 85° or 87°. A relatively flat arrangement of the IR light source and the IR camera recording the reflected polarized images from the detection area has the advantage of enabling the use of ellipsometry for metallic substrates. The flatter the incidence of the IR light rays on the substrate, the closer the beam path of the IR light is to the Brewster angle of the metallic substrate. Thus, a clearly emerging polarization or a clear change in polarization due to supports can be recorded in the evaluation unit.The Brewster angles for metallic substrates are also typically relatively flat, ranging from a = 75° to 85° or 87°. For non-metallic substrates such as paper or plastic, the Brewster angle and thus the selected angle of incidence a will be between 54° and 60°, and the invention can also be used for these.

[0036] According to a further advantageous embodiment of the invention, the polarization splitting device is designed for triple or quadruple polarization splitting of the IR light beam and has at least one beam splitter such that a triple or quadruple image or replica with three or four different polarizations can be generated from the light in the detection area E. As a component for such a further, i.e. additional or second beam splitting (triple or quadruple) of the IR rays in relation to the double polarization, a quarter-wave plate or a quarter-wave mirror can be used for one polarization, e.g. a 45° linear polarization. The additional polarization and splitting then leads to a triple or quadruple image of the linear detection area. The quarter-wave plate orA quarter-wave plate can be used for this purpose, as can a 50 / 50 beam splitter with additional mirrors and Brewster plates. With such quadruple polarization in the polarization splitting device, the double polarization described above is then performed in a first stage. In a second stage, further polarizing splitting is performed using the additionally described means, using polarizers, mirrors, Brewster plates, etc. The additional polarizing splitting performed in the second stage serves to further image line patterns with different forms of polarization. This enables even further improvements in the final image of the layer thickness and position of the deposits on substrates.

[0037] The measurement of three different polarization contents in the polarization splitting device and evaluation unit of a fully polarized beam allows a fairly complete determination of its polarization (triple splitting). Similarly, the polarization ellipse can be determined using an intensity sensor and a polarizer connected upstream in three different positions. However, to determine whether the polarization is clockwise or counterclockwise, which corresponds to the sign of A (= phase difference of the complex reflection amplitudes for p- and s-polarization), a retarder must be placed in front of the polarizer for at least one measurement. The ratio calculation or i / A calculation (i / A, etc., standard ellipsometry parameters) is not intuitive or easy to perform. Partial polarization leads to incorrect results. For example, it is practical to measure three linear polarization contents at 45° or 60° angular separation.Another advantageous approach is to measure two linearly polarized intensity components at a 90° angular separation and a third circularly polarized intensity component. Another variant is to measure the left- and right-circularly polarized intensity components and a linearly polarized intensity component.

[0038] The measurement of four different polarization contents (4-way splitting) of a polarized beam allows the complete determination of its polarization and a statement as to whether complete polarization or only partial polarization is present.

[0039] Compared to a triple measurement, this has the further advantage that the measurement is even more robust against disturbances and that the meaningful relationships can be determined directly, without additional, complex conversions in the evaluation unit. In particular, two non-trivial components of the normalized Stokes vector (1 , Rps2, R45, Rz) can be directly determined.T measured, whereby for a fully polarized beam all three combinations: Rps2 & R45, Rps2 & Rz or R45 & Rz are mathematically equivalent. In practice, the advantages of choosing specific combinations depend on the application and the practical implementation. For example, for dielectric layers on metals the combination Rps2 & Rz or R45 & Rz is advantageous. As a rule, the Rz measurement is particularly advantageous within the scope of the invention. The 4-way beam splitting can be achieved in a variety of ways by combining non-polarizing beam splitters (dielectric and possibly coated windows, perforated metal mirrors, etc.), polarizing beam splitters (Brewster windows, wire grids, birefringent crystals, etc.), mirrors, polarizers, retarders (quarter-wave plate, quarter-wave mirror, Fresnel rhombus, etc.).

[0040] Compared to the 2-fold splitting, the 4-fold splitting offers a potential doubling of the clearly detectable layer thickness range, e.g. from 0-3pm with 2-fold splitting to 0-6pm with 4-fold splitting, whereby these values ​​apply to oil coating on metal when using a bandpass filter with a central wavelength in the wavelength range 13-15pm.

[0041] According to the invention, a method for determining in real time planar deposits or coatings of dielectric materials on substrates such as metal strips or the like is also provided according to claim 13.

[0042] The invention thus relates to a method for determining in real time coatings made of dielectric materials, in particular organic materials, on strip-shaped or plate-like substrates, such as material webs made of metal or plastic, with an optical detection device based on ellipsometry for detecting and quantifying coatings or coatings on the substrate on the basis of changes in a polarization state of light reflected from the substrate or the coating, with at least one light source directed onto a surface of the substrate at a predetermined angle of incidence α, with at least one image detection device arranged opposite to the light source according to an angle of reflection α' for detecting light reflections on the substrate and with an evaluation unit which is set up and designed to detect and assess coatings on the substrate,The method is characterized by the following steps: a) illuminating a delimited, predefined linear or substantially rectangular detection area E on the substrate by means of a light source designed as an infrared light source, using optical or optically acting means to delimit light reflected from the substrate for detecting supports; b) splitting the reflected linear IR light beam from the detection area E into at least two differently polarized images by a polarization splitting device; c) detecting the IR light beams reflected from the substrate by an infrared camera of the image detection device in the detection area E on the substrate; d) calculating, determining, and quantifying an image of the support in real time in the evaluation unit based on reflections of the light with at least 2-fold polarization detected by the IR camera.

[0043] According to the method according to the invention, as defined in claim 13, in a first step a linear or substantially rectangular detection area E is illuminated with an infrared light source as the light source, wherein optical or optically acting means are provided for delimiting the linear or rectangular detection area E.

[0044] Subsequently, a polarization splitting device is used to split reflected IR light from the linear reflected light of the detection area E at least twice - possibly also three or four times. Such splitting or polarization with various forms of polarization according to the invention can be carried out, for example, by means of polarization in the form of preferably with the polarization states 0°-linear & 90°-linear & right-circular & left-circular or 45°-linear & 135°-linear & right-circular & left-circular or 0°-linear & 90°-linear & 45°-linear & 135°-linear.

[0045] In the next step, the reflected IR light rays in the linear or rectangular narrow form are captured by an infrared camera of the image capture device. The IR camera thus captures at least a double image of the differently polarized IR light rays in the capture area E. With double polarization, there are two images of the linear IR light rays that are reflected. With triple or quadruple polarization, there are three or four images or linear representations of the intensities of the reflected IR light rays. In a subsequent fourth step, the image of the overlay or coating on the substrate, such as an oil layer on a continuously moving metal strip, is calculated, determined, and quantified in the evaluation unit based on the differently polarized images of the capture area E captured by the IR camera.

[0046] By calculating the ratios of the different intensities of the reflected IR rays in double, triple, or quadruple imaging, the invention allows for precise determinations of coatings or oil coatings, particularly on metal strips. The invention eliminates the need for complex and time-consuming spectroscopic measurements. Expensive and complex laser devices are also no longer required as illumination sources. With relatively simple components, namely an IR light source and an evaluation unit with an image capture device including an IR camera, thin layers and coatings can be effectively determined and calculated even in the range from 0 to 3 pm—or 0-6 pm with quadruple splitting.Overall, this provides an efficient, real-time measurement method that allows for reliable and highly accurate analysis of oil deposits and similar materials, even when metal strips are continuously moving through the production process. The quality of the end products from such manufacturing processes for metal strips or metal plates is thus significantly increased. The method according to the invention enables better and faster real-time results to be achieved when determining such layers of dielectric materials.

[0047] According to an advantageous aspect of the method according to the invention, the infrared camera of the image capture device detects infrared light in the mid-infrared range from 5 pm to 15 pm, preferably in a range from 8 pm to 14 pm. Such a mid-IR range of the IR rays generated by the IR light source and reflected by the substrate, which are then detected in the IR camera after polarization, has proven particularly advantageous for determining the position and layer thicknesses of such overlays. In contrast to the visible range of light rays or the near-IR range, significantly better results in terms of measurement efficiency and accuracy could be achieved here. In particular, the robustness towards substrate roughness and the possibility of easily and directly obtaining clear measurement results even with pm-thick layers are worth emphasizing.

[0048] According to a further advantageous embodiment of the method according to the invention, the determination and quantification of the deposits on the substrate is carried out based on an at least doubly polarized image of the IR light rays, representing an intensity ratio from the various polarized line-shaped images from the IR camera. Using the previously described possible forms of different polarizations in a polarization splitting device in the simplest form of dual polarization, the intensities of the reflected IR light are processed differently for further use in the determination of the deposits. Due to the polarized light rays and the splitting in various forms, the intensity ratios of the light intensities allow the actual conditions of the deposits to be precisely determined, both in terms of their position and the layer thickness.With the method according to the invention, the requirements can be determined quickly in real time with relatively little computational effort and with exact results.

[0049] According to a further advantageous embodiment of the method according to the invention, the evaluation unit calculates position-dependent layer thicknesses of overlays and the recorded intensity ratios of the images of IR light rays in the detection range E, as well as composing an overall image of a layer thickness distribution on the substrate, preferably a continuously moving substrate. A profile of the layer thickness distribution and the position of the respective layer thicknesses shown in the final result can thus be easily calculated based on the intensity ratios in the evaluation unit. The differently polarized and reflected light rays in the linear or narrow rectangular form allow for a precise determination and calculation of the actual ratios of such layer overlays made of dielectric materials on, for example, metal strips.

[0050] According to a further advantageous embodiment of the method according to the invention, at least a second beam splitting is performed in the sense of a triple or quadruple polarization determination of infrared light beams detected in the detection area E, preferably by a quarter-wave plate or a quarter-wave mirror, with the additional splitting of the IR rays into a triple or quadruple image. The quarter-wave plates and mirrors enable the circular polarization content of the reflected radiation to be determined with a quadruple splitting, each with different polarizations. The detectable layer thickness range in the measurement is thus further increased compared to the double splitting.Quadruple polarization can also be achieved by means other than quarter-wave plates or quarter-wave mirrors, as long as different polarizations are detected in addition to the double polarization of the line-reflected IR rays, which is the basic principle of the invention.

[0051] According to a further advantageous embodiment of the method according to the invention, a layer thickness of the coating on the substrate is calculated in an evaluation unit from a ratio of a p- / s intensity Rps or Rps2, a 45° / 135° ratio R45 and / or a circular ratio Rz.

[0052] According to a further advantageous embodiment of the invention, as defined in claim 19, the imaging optics in front of the IR camera are designed such that, instead of parallel rays, they now preferably capture slightly convergent rays and image them onto the camera sensor. Additionally, the illumination side can be modified by inserting or moving appropriate optics and / or by enlarging the area emitting IR radiation so that the proportion of appropriately convergent radiation is increased. This convergent beam guidance allows for a larger possible substrate width range of up to 2500 mm. The measurement of the substrate coating can thus be carried out in real time on even wider substrates, such as metal strips with widths of up to 2500 mm, directly without additional measuring systems. The costs for implementing the device using the method according to the invention are reduced.Due to the convergent beam guidance, the dimensions and size of such devices are also reduced while maintaining consistently good results in the ellipsometry measurement of the coatings of such deposits on substrates. Further features, aspects, and advantages of this device are described below.

[0053] The invention will be described in more detail using several embodiments of the device and method according to the invention with reference to the accompanying drawings. In the drawings:

[0054] Fig. 1 is a cross-sectional view of a first embodiment of an apparatus according to the invention for imaging infrared ellipsometry measurement;

[0055] Fig. 2 is a top plan view of an embodiment of an apparatus according to the invention for imaging infrared ellipsometry measurement;

[0056] Fig. 3 is a schematic longitudinal view of a second embodiment of a device according to the invention:

[0057] Fig. 4 is a schematic longitudinal view of a third embodiment of a device according to the invention:

[0058] Fig. 5a, Fig. 5b and Fig. 5c show several schematic views of variants of a detail of an embodiment of the device according to the invention with regard to the design of the polarization splitting device for the double or quadruple splitting of infrared rays in front of the IR camera;

[0059] Fig. 6a and Fig. 6b two schematic views of variants with regard to the polarization splitting device;

[0060] Fig. 7 is a perspective schematic view of another

[0061] Embodiment of an inventive device for imaging infrared ellipsometry measurement with convergent beam guidance of the IR rays;

[0062] Fig. 7a and Fig. 7b are two schematic side views to explain the embodiment of Fig. 7 with the convergent beam guidance and the imaging optics provided therefor, wherein Fig. 7b is a scaled representation based on a substrate with a width of 2000 mm and corresponding angle of incidence a and angle of reflection a' of an example; and Fig. 8 is a schematic longitudinal view of another embodiment of a device according to the invention with two concave mirrors as imaging optics

[0063] The device 10 according to the invention for determining flat deposits 20 made of dielectric materials, such as oil deposits on substrates 11, essentially comprises, as shown in a cross-sectional view in Fig. 1 and a top view in Fig. 2, a detection device 1 designed to enable precise and rapid determination of deposits 20 and determination of the deposit thickness on the substrate 11, for example a continuous metal strip or the like, based on the ellipsometry method. Opposite the detection device 1 is a light source 2 with which an infrared light beam is directed onto the surface of the substrate 11 at a predetermined angle of incidence α. After being reflected by the substrate 11 or the deposit 20, the light beam is recorded and further processed by an image capture device 3 of the detection device 1 via an IR camera 31.The detection device 1 is coupled to an evaluation unit 4, which is equipped with stored data and processing algorithms for the use of the ellipsometry method.

[0064] According to the invention, an infrared light source 21, 22 is used as the light source 2, and an infrared camera 31 or another means for detecting infrared light rays serves as the image capture device 3. For example, a heat radiator that is as point-shaped as possible - e.g. a ceramic radiator or a small incandescent filament - can be used as the IR light source 21, which, after collimation by the lens 61, emits an IR light beam that is as collimated as possible onto a detection area E of the substrate 11. Alternatively, a rod-shaped IR light source 22 can also be used as the light source 2, which light source already illuminates a linear or rectangular area on the substrate 11 for the one detection area E defined according to the invention. In the exemplary embodiment shown in Fig. 1, the IR camera 31 is arranged at a corresponding angle of reflection a' opposite the heat radiator 21 of the light source 2, wherein the angle a ora' can be set within a range of approximately 85°, for example, when using device 10 to determine oil deposits on metal strips as substrate 11. In this example, the light incidence from infrared light source 21 is chosen to be shallow enough to be close to the Brewster angle of substrate 11, since in this range a support 20 has a relatively significant effect on the polarization of the reflected light, thus enabling ellipsometry. Metals generally have quite high Brewster angles, typically in the range of a = 75-87°.

[0065] On the light source 2 side, a means 5 for limiting incoming light rays in front of the substrate 11 in the beam path is provided according to the invention in order to limit a predetermined, defined illumination area by the IR light source 21, which ultimately serves as the detection area E for the image capture device 3 (cf. Fig. 2). In this case, the limiting means 5 is implemented by optics 6 with a slit aperture 51 and optionally a polarization filter 62. A bandpass filter 12 can be used as a limiting means for the wavelength of the infrared radiation from the IR light source 21. By limiting the image capture to a narrow wavelength spectrum in the linear detection area E, the measurement accuracy is potentially increased. The bandpass filter 12 can be arranged at any position in the beam path of the IR light.Through the slit aperture 51, a substantially rectangular or linear detection area E is specifically illuminated by the, for example, point-shaped infrared light source 21 on the surface of the substrate 11, which is continuously recorded in real time by the IR camera 31 of the detection device 1 and processed in the evaluation unit 4 to determine the measured value. Alternatively, the slit aperture 51 can also be located on the imaging side of the detection device 1, so that although a larger area on the substrate 11 is illuminated, only a narrow rectangular or linear area is imaged by the slit aperture 51. The slit aperture 51 must be mounted in front of the polarization splitting device 7 according to the invention, explained further below, in order to obtain clean, i.e. distinguishably separated images of different polarizations.

[0066] According to the invention, the IR rays recorded in this process are advantageously in a mid-infrared range of, for example, wavelengths from 5 pm to 15 pm, preferably in a range from 8 pm to 14 pm, in which common IR cameras are particularly sufficiently sensitive for the purposes of the invention. Good measurement results for overlays are achieved in this spectrum by the device according to the invention. Tests and developments by the inventors have shown that in this special infrared wavelength range, a significantly larger thickness range of overlays 20 can be detected and greater accuracy can be achieved in the measurement of such overlays 20 on substrates 11, even with surfaces of varying roughness of the substrates 11.

[0067] On the side of the detection device 1 of the device 10, which in the example of Fig. 1 and Fig. 2 is also arranged laterally next to the metal strip as substrate 11, a special polarization splitting device 7 according to the invention is provided in front of the image detection device 3, which is designed as an IR camera. This polarization splitting device enables at least a double beam splitting or polarization splitting of the detected IR light. In order to obtain the incidence / emission angles defined over the entire substrate area required for ellipsometry, the IR light beams from the detection area E are shaped via imaging optics 8, for example, by two confocal lenses 81, 82 as a bitelecentric lens, and a pinhole 13, so that a sharp image is created.

[0068] Due to the inclined position of the substrate 11, an inclined position of the lenses 81, 82 and the camera 31 is required. On the one hand, the pinhole 13 increases the depth of field, so that a sufficiently sharp image can be achieved even if the camera sensor of the IR camera 31 does not exactly match the image position. On the other hand, the pinhole 13 limits the acceptance angle of the lens, so that IR rays reflected by the substrate 11 are only detected in a relatively small angular range, thus ensuring a defined viewing angle across the entire image area for excellent further processing in the evaluation unit 4.

[0069] In the polarization splitting device 7 of the device 10 according to the invention, the linear, reflected IR rays are polarized, for example, using a Brewster plate 71 and a mirror 72 in the simplest variant of a double split (see Fig. 5a). From the measured values, which are determined in real time as a quasi-online measurement even with a continuously moving metal strip as substrate 11, the evaluation unit 4 calculates a ratio of the s-reflection Is and the p-reflection Ip from the corresponding images of the current, actual surface and the supports 20 using the ellipsometry method. The designations s- and p- in Fig. 5a refer to the local light plane defined by the Brewster window or by the wire polarizer, respectively, defined by the transmitted and reflected beam.The installation position of the device 7 determines whether the local p and s designation matches the p and s designation defined by the substrate, is possibly swapped, or if the installation position is rotated, for example, corresponds to a diagonal polarization measurement. Thus, for example, a psi ratio Rps or Rps2 can be measured, so that the precise determination of coatings as well as real-time online thickness measurement of the respective coating in a thickness range of, for example, up to approximately 0 to 3 pm is enabled with the device according to the invention. If the installation position of the device 7 is rotated by 45° around the incident central light beam, a ratio R45 can alternatively be measured, which has increased sensitivity for layer thicknesses below 1 m. If the angle of rotation is only 20°, a ratio R20 can be determined.

[0070] If, according to an alternative embodiment, the optics 81, 82 are provided with a type of tensioning device that induces mechanical stress and thus stress-induced birefringence, a λ / 4 retardation can also be induced very easily, so that a circular ratio Rz can also be detected. Even smaller retardation values ​​can suffice to increase the sensitivity of the detected intensity ratio, for example, to particularly thin deposits on the substrates 11. Such a solution can also be used in a similar way in the further embodiments explained below.

[0071] On the illumination side, for example with a point-shaped heat radiator or infrared light source 21 or another IR light source, a polarization filter 62 in the sense of a 45° polarizer is also present in the embodiments shown in Fig. 1 and Fig. 2. With this polarization filter 62, the IR light is polarized at 45°. A defined and known input polarization is necessary for ellipsometric measurements. The standard here is 45° linear polarization, but other input polarizations, such as circularly polarized light, are also possible. Only in the case of a pure Rps or Rps2 measurement can the (expensive) polarization filter 62 advantageously be omitted, provided that the IR source emits purely unpolarized light or at least light with known proportions of p- and s-polarization. According to the invention, the detection area E is essentially rectangular or linear, as shown in Fig. 2.In combination with the polarization splitting device 7 present on the detection side of the detection device 1 and the infrared camera 31 of the image detection device 3, the IR rays incident in the detection area E and reflected differently due to supports or the surface of the substrate 11 are detected according to the invention in a mid-infrared light range of wavelengths, for example, from 8 pm to 14 pm, or preferably (optionally) in a narrower wavelength range restricted by a bandpass filter 12, for further processing in real time. These light rays thus recorded by the IR camera 31 in the predefined detection area E allow for rapid, real-time calculation of the entire surface and situation of supports 20 on the particularly moving substrate 11, such as oil layers on metal strips, which was previously only possible as quasi-point detection in the prior art.

[0072] In Fig. 2, the deposits 20, for example, an oil film on a metal strip as substrate 11, are depicted as patches for illustrative purposes. In reality, however, such a deposit 20 will be present over the entire surface of the substrate 11, possibly with varying layer thickness. This thickness variation of deposits 20 in the width direction and in the length direction of the substrate can be accurately recorded, displayed, and assessed in real time using the device 10.

[0073] Two further embodiments of a device 10 according to the invention for determining planar supports 20 on substrates 11 according to the invention are shown in two schematic further cross-sectional views in Fig. 3 and Fig. 4.

[0074] The embodiments of Fig. 3 and Fig. 4 are explained below only with regard to the differences from the previous embodiments of Fig. 1 and Fig. 2. The other elements and components as well as the functions of the device 10 correspond to those of the previously described embodiments. In the second embodiment of Fig. 3, a ceramic radiator with as point-shaped radiation as possible is used as the infrared light source 21 instead of a heat radiator. The light source 2 is formed, for example, also by using reflectors or other means such that an IR light beam from a light source that is as point-shaped as possible is emitted towards the surface of the substrate 11 in the essentially linear detection area E at the relatively flat angle of incidence α. In this embodiment of Fig.3, on the side of the light source 2, means 5 are provided for limiting the detection area E to a substantially linear or rectangular, narrow illumination area, in the form of, for example, a slit aperture 51. Further optics 6 in the form of collimating optics 61, for example, as a plano-convex lens or cylindrical lenses, are provided between the substrate 11 and the infrared light source 21. Furthermore, a polarization filter 62 is arranged on the IR light generation side of this device 10 according to the invention. In contrast to the previous two embodiments (Fig. 1, Fig. 2), in this second embodiment of Fig. 3, the image capture device 3 is also present in a modified design.

[0075] The imaging optics 8 here comprise two confocal lenses 81, 82 in the form of a bitelecentric lens, for example, a Kepler telescope / spyglass, and are slightly tilted relative to the axis of the reflected IR light beams and no longer aligned at an angle of 90° to it as in the previous embodiments, as illustrated in Fig. 3 with the drawn axis lines. This serves to ensure a clean image of the tilted object in the form of the substrate 11, which can, for example, be a passing continuous metal strip from a production process. The infrared camera 31 is also slightly tilted or aligned obliquely relative to the orientation of the emerging IR light beam according to angle a' (cf. Fig. 1). However, both the lenses 81, 82 and the infrared camera 31 are located in the beam path of the emerging reflected IR light from the detection area E.With this tilted arrangement of the elements 31, 81, 82, an even improved imaging of the linearly reflected IR light beam is achieved in accordance with the Scheimpflug condition. The imaging of such oblique objects according to the Scheimpflug condition can achieve a sharp image if the object, image, and lens planes intersect in a common line. With the slightly inclined position of the IR camera 31 and the imaging optics 8 (lenses 81, 82), a better and sharper representation and imaging of the at least doubly polarized linear IR light beams from the reflected IR light on the substrate 11 is achieved. Otherwise, the design of Fig. 3 with the evaluation unit 4 and the calculations of the light intensities and the dual polarization or quadruple polarization in the polarization splitting device 7 based on the ellipsometry method corresponds to the previously described embodiments.

[0076] In Fig. 4, the infrared camera 31 and the lenses 81, 82 of the imaging optics 8 are also slightly obliquely positioned or tilted in relation to the beam path of the emerging IR light, as in the example of Fig. 3. Furthermore, a ceramic radiator with point-shaped radiation of IR light is also present here as the infrared light source 21. As a difference to the previous example of Fig. 3, in the embodiment of the device 10 according to Fig. 4, the schematic cross-sectional view shows a division of the polarization splitting device 7 into a first polarization split 7a and a second polarization split 7b in the sense of a quadruple polarization according to the present invention.In the beam path of the IR rays, which are reflected by the substrate 11 and forwarded towards the image capture device 3, a combination of a Brewster plate 71 and a mirror 72 is initially provided as the first polarization splitting device 7a in the region of the pinhole 13. As an alternative to the Brewster plate 71, a (nano) wire grid device—i.e., a wire polarizer—could also be provided here to carry out the first polarization. A second polarization splitting device 7b is then located further along the IR light beam directly in front of the IR camera 31, which can also be formed either from a Brewster plate 71 with corresponding mirrors 72 or from a nano wire grid 76. The division of the first splitting device 7a and the second splitting device 7b shown in this way is thus realized here in separate elements.Alternatively, a combination of the elements in a common polarization splitting device 7 can optionally be used.

[0077] The first polarization splitter 7a can preferably be equipped with a λ / 4 mirror or a λ / 4 wave plate, and it can also be combined, alternatively, with the pinhole diaphragm or with a polarization filter, or with both. See the description of Figs. 5a, 5b, 5c, 6a, 6b. Thus, the third embodiment shown in Fig. 4 also offers the advantages of better utilization of the available space and thus an easier-to-realize, precise and exact imaging of the linearly reflected IR light rays in the sense of a quadruple-polarized image, which can then be further processed in the evaluation unit 4 (not shown in Fig. 4) to provide a composite image of the actual overlay 20 on the substrate 11 for the control and quality assurance of manufacturing and processing processes for such metal strips.

[0078] Fig. 5a, Fig. 5b, and Fig. 5c show schematic views of respective exemplary embodiments of a polarization splitting device 7 for use in a device 10 according to the invention. The variant of Fig. 5a shows a dual polarization splitting in its simplest form with a Brewster plate 71, preferably specially coated to enhance the polarizing splitting, and a mirror 72. The incoming IR rays are split into a component Is and a component Ip, from which, with the appropriate installation position, the psi ratio Rps is calculated in the form of Rps = Ip / Is (alternatively (I p-Is) / (I p+Is)) in the evaluation unit 4 for the ellipsometry evaluation. "I" denotes the intensity of the IR light, and "p / s" denotes an s-reflection or p-reflection, respectively. According to an advantageous embodiment, the dark value is subtracted from the measured values ​​Ip, Is beforehand, iethe measured value curve determined when the light source is switched off.

[0079] In the variant of a polarization splitting device 7 according to the invention shown in Fig. 5b, the IR light beam is split fourfold in front of the IR camera 31. For this purpose, a non-polarizing 50 / 50 beam splitter 73 is additionally used, together with the already described mirrors 72 and Brewster plates 71. Furthermore, a quarter-wave plate or λ / 4 plate 74 is used to determine the proportion of left and right circular polarization. Depending on the specific installation position (see explanations for Fig. 5a), this allows, in addition to the psi ratio Rps = Ip / Is (alternatively (Ip-Is) / (Ip+Is)), a circular ratio or a circular ratio Rz = (IR - IL) / (IR + II) to be calculated in the evaluation unit 4, with IR, L, etc. being the intensity of the right and left circularly polarized reflected light. Alternatively, if the installation position of device 7 is rotated by 45°, R45 and Rz can also be measured together.With a 45° twist of only part of the.

[0080] Alternatively, by using setup 7 and omitting the λ / 4 delay, Rps and R45 can be measured together. The simultaneous measurement of two ratio values ​​allows, above all, a doubling of the measurable layer thickness range.

[0081] The quarter-wave plate 74 can also be mounted in the straight path and there, in addition to its polarizing effect, may reduce the optical path length difference between the split beams.

[0082] Fig. 5c shows an alternative embodiment of a quadruple polarization splitting in the polarization splitting device 7 according to the inventive apparatus 10 compared to Fig. 5b. Instead of a quarter-wave plate 74, a quarter-wave mirror 75 is used together with a 50 / 50 beam splitter 73. The other components, including the mirrors 72 and the Brewster plates 71, correspond to the previously described embodiments. This also allows a circular ratio Rz to be determined for the thickness determination via the psi ratio Rps (=lp / Is, alternatively also (lp-ls) / (lp+ls)).

[0083] Further possible variants of a polarization splitting device 7 for use in a device 10 according to the invention are schematically illustrated in Figs. 6a and 6b. Both variants (Figs. 6a and 6b) also involve quadruple polarization in the polarization splitting device 7, corresponding to the previous examples in connection with Figs. 5b and 5c.

[0084] In the variant shown in Fig. 6a, in addition to the mirror 72 and the beam splitter 73 in the lower beam path, a λ / 4 plate or quarter-wave plate 74 is used before the IR light rays impinge on the Brewster platter 71 and are differently polarized together with the additional mirror 72. The quarter-wave plate 74 causes a 90° delay between p-polarization and s-polarization, i.e., + / - 45° of the circularly polarized light. The advantage of positioning the quarter-wave plate 74 in the straight path is that it reduces the path length difference in the split, polarized light beam components, making it easier to focus the images generated on the camera sensor together.

[0085] In the further variant of quadruple polarization in the polarization splitting device 7 according to the apparatus 10 of the invention, as shown in Fig. 6b, a quarter-wave plate 74 is also used to retard or delay the lower beam path after the beam splitter 73. The variant of Fig. 6b also uses a so-called (nano-)wire grid polarizer 76, i.e., a wire polarizer, instead of a Brewster plate 71 (cf. Fig. 6a). Such a wire polarizer 76 can also be used in the other previously shown embodiments as an alternative to the Brewster plate 71 otherwise described therein for the purposes of ellipsometry and polarization splitting in 2-fold or 4-fold form according to the present invention. The advantage of the embodiment shown in Figs. 6a, 6b is a smaller number of optical components.

[0086] With regard to the local p- and s-directions in Figs. 5b, 5c, 6a, 6b, the relevant explanation for Fig. 5a applies. The specific installation position of the device 7 determines which polarization components and ratios are actually measured, which is provided according to the invention to provide optimal results of polarization splitting for the thickness measurement of the overlays 20 on the substrate 11.

[0087] The 2-fold polarization splitting in the polarization splitting device 7 consists of a polarizing beam splitter for IR rays, typically a Brewster plate 71 or nanowire grating or any type of wire polarizer, and a mirror 72. Additionally, an λ / 4 retardation plate 74 can optionally be used, or, with the same effect, an λ / 4 mirror 75 can be used instead of the mirror 72.

[0088] The polarization splitting of the polarization splitting device 7 according to this example works as follows:

[0089] - It creates two line images from a single line image, each with a different polarization, e.g., horizontally and vertically linearly polarized (e.g., p- and s-polarized, e.g., 0° and 90° polarized). Or 45° and 135° linearly polarized. Or right / left circularly polarized using a λ / 4 delay.

[0090] It can be located directly in front of the camera lens of the IR camera 31, where the intermediate image generated by the lens 8 is essentially doubled according to the invention. Or it can be located directly after the pinhole 13 within the lens 8, or accordingly, have an integrated pinhole 13 as the input aperture. In this case, a camera lens of the IR camera 31 can be omitted, since a multiplied image is generated directly after the lens 8, in the position of which the camera sensor of the IR camera 31 is then advantageously placed.

[0091] Another embodiment of the invention with 4-way polarization splitting, as shown in Figs. 5b, 5c, 6a, and 6b, consists of a first stage with the polarization-preserving 50 / 50 beam splitting device 73 and a mirror 72, and a second stage consisting of a polarizer and a mirror 72. Additionally, a λ / 4 retardation plate 74 can be used, or, with the same effect, an λ / 4 mirror can be used instead of the mirror. The operation is as follows:

[0092] - It generates four line images from one line image, each with a different polarization, or with intensity curves that correspond to the four different polarization contents.

[0093] It can be located directly in front of the camera lens of the IR camera 31, where the intermediate image generated by the telecentric lens 8 is duplicated. Or it can be located after the pinhole 13 within the lens 8. In this case, the camera lens of the IR camera 31 can be omitted. It can also be spatially divided, with the first stage after the pinhole 13 and the second stage at the position of the intermediate image in front of the camera lens of the IR camera 31. The latter version can be advantageously implemented.

[0094] Evaluation of the polarization splitting in the evaluation unit 4: In each image of a line or a narrow rectangle from the detection area E, a specific evaluation area ROI (Region Of Interest) is defined in the evaluation unit 4 (see Fig. 2). This ROI encompasses the sharply imaged part of interest and is generally only slightly shorter than the image and usually smaller in width, but can also encompass the full width. All ROIs defined in this way must correspond to exactly the same area in the detection area E on the substrate 11. In each ROI, the intensity values ​​are averaged in the direction of the ROI width, and the previously determined or calculated dark value, which depends on the substrate temperature of the substrate 11 with the light source 2, 21 switched on or shaded, is subtracted. An intensity value is now defined for each longitudinal position in the ROI.From this intensity curve along each ROI from the detection area E, a ratio curve is now calculated, namely as the ratio of the intensity values ​​of two ROIs or as the ratio of the difference and sum of the intensity values ​​of two ROIs.

[0095] From these ratios—usually one or two ratios of the type Rps, Rps2, R45, Rz—the layer thickness profile of the support 20 (e.g., oil film) is calculated along the illuminated line of the detection area E on the substrate 11. From the movement of the substrate 11 in the direction and from the juxtaposition of the continuously determined layer thickness profiles, an image of the layer thickness distribution on the substrate 11 results.

[0096] With a stationary substrate 11, the evaluation can also be performed per pixel, without averaging in the width direction of the ROI. This yields the layer thickness distribution in the entire, albeit narrow, acquired area. This would be an application of the device 10 of the invention to a stationary plate element instead of a continuously moving metal strip as the examined substrate 11. However, with moving substrates, line imaging and line evaluation are advantageous compared to full-surface pixel-by-pixel analysis, as this facilitates polarizing image splitting and enables a more robust and simpler measurement.

[0097] A further embodiment of a device 10 according to the invention is shown in Figs. 7, 7a and 7b in schematic perspective and side views, respectively. In this embodiment of Fig. 7, an imaging optic 8 is used between the detection area E on the substrate 11 and the image capture device 3 or IR camera 31, which brings about convergent beam guidance or detection of the IR rays reflected in the detection area E. The imaging optic 8 is provided with lenses 81, 82 and a pinhole or aperture 13 such that the detected IR rays from the IR light source 21 impinge on the image capture device 3 in a convergent form. The imaging optic 8 thus does not bring about collimated beam guidance as in the previous embodiments, but rather brings about convergent beam guidance.This allows for smaller device sizes for the device 10, and imaging a relatively long, narrow detection area E in the width direction of the strip with substrate 11 widths of up to 2500 mm is possible with a single measuring system of the device 10. The angle between the optical axis of the device 10 and the motion vector V of the substrate 11 is referred to as the azimuth angle Aw (see Fig. 2). Fig. 7 shows an embodiment with an azimuth angle Aw = 0°, i.e., with a central light propagation parallel to the movement of the substrate 11, such as a metal strip.

[0098] The basic structure of the optics 8 of the device 10 according to Fig. 7 is shown again in Fig. 7a. A first lens 81, an intermediate pinhole 13, and a second lens 82 are provided to achieve convergent beam detection of the infrared light rays from the detection area E. The difference from the previously explained bi-telecentric or confocal arrangement of the lenses 81, 82 is that lens 81 is now shifted in the direction of the pinhole in order to detect, in combination with the pinhole, convergent instead of parallel beams (cf. dashed position and lines vs. solid lines in Fig. 7a). This embodiment of Fig. 7 also includes a polarization splitting device 7 with corresponding optical means for polarization splitting, such as a Brewster plate 71, mirrors 72, or beam splitters 73.Here too, according to the invention, a double polarizing image splitting or, in certain embodiments, a triple or quadruple polarizing image splitting can be carried out.

[0099] Fig. 7b shows a schematic side view of the structure and true-to-scale relationships of such an embodiment according to the device 10 according to Fig. 7, but deviating from Fig. 7 with an azimuth angle Aw = 90°, the angle between the direction of movement of the substrate and the central optical plane spanned by the central incident and central exiting / reflected light beam. The angle of incidence α, or exit angle cf, in this example is in the range 82-87°, depending on the position on the substrate. The convergent beam guidance of the IR light beams, which are directed onto the detection area E of the substrate 11 and recorded in the exit area by the image capture device 3 and the IR camera 31, are illustrated in Figs. 7a and 7b. The polarization splitting device 7 can also be positioned between the imaging unit and the substrate.This is advantageous if only the imaging unit on the camera side is to be used, and this camera lens does not allow any interventions or installations. In this case, however, for a clean image split, the beam path must be limited to the detection of a narrow detection area E essentially before device 7.

[0100] Such a line image with the means 5 for limiting the detection area E can generally be realized, for example, by the following measures:

[0101] - 1a) Restriction of the illuminating light beam in the detection area E by a slit aperture 51 just before / after or on the optics 61 (possibly as a mask on the optics or lens 61: painted, vapor-deposited, glued, etc.)

[0102] - 1b) Restriction of the reflected light beam by a slit aperture 51 just before / after or on the optics 81 (possibly as a mask on lens 81: painted, vapor-deposited, glued, etc.)

[0103] - 1c) Restriction of the intermediate image: Position between lens 81 and camera 3, advantageously realized by slit aperture 51 or as input aperture of the polarizing image splitting in device 7, or 7b (Brewster window and mirror together automatically create a slit / slit with the desired effect).

[0104] - 2) Formation of the illuminating light beam as line illumination by cylindrical lenses

[0105] - 3) Imaging a linear IR emitter 21 (glowing wire) onto the substrate 11 or sheet metal, e.g., using a (bi-telecentric) lens system with Scheimpflug-inclined lenses. For a convergent beam path, the second lens must be shifted accordingly toward the sheet metal or substrate 11.

[0106] - 4) purely on the evaluation side in the evaluation unit 4 by using a linear evaluation area ROI (see Fig. 2)

[0107] - 5) By measuring on a roll, e.g., when measuring on (metal) foils. Due to the divergent reflected radiation and the limited acceptance angle of the imaging optics, a sharp line image is automatically obtained.

[0108] - 6) By combinations of the above possibilities, whereby the position of the polarization splitting device 7 determines the applicability of each possibility.

[0109] Fig. 7 schematically shows essential elements of this embodiment of the invention of a device 10 with azimuth angle Aw = 0, i.e. in the direction of the moving substrate 11 (motion vector V) and 2-fold splitting in the polarization splitting device 7. An IR radiation source 2 illuminates a substrate 11, shown here as an example as a continuous band with motion vector V, in the linear or narrow rectangular detection area E at the angle of incidence α = 87° with convergent radiation which is 45° linearly polarized. This IR radiation is reflected and directed into an image plane by an optics 8, here consisting of two lenses 81, 82. In this image plane, an image B1, B2 of the entire detection area E is created. By means of a pinhole 13, the acceptance angle of the image capture is adjusted so that the entire area E of the substrate 11 is captured.The position of the pinhole 13 is where the desired rays to be imaged form a focus. The second lens 82 is advantageously, but not necessarily, positioned so that its focal point coincides with the position of the pinhole 13, since then, after the lens 82, the central image generators run parallel and the image scale remains constant when the camera sensor of the IR camera 31 is moved along the optical axis. The size of the pinhole 13 determines the depth of field, image brightness, and the angle of incidence spectrum and must define a compromise between these conflicting requirements. If the rays incident on the detection area E deviate slightly from the desired rays, the pinhole 13 can be omitted. It can also be omitted if the acceptance angle is already sufficiently restricted by the entrance aperture of the imaging lens.

[0110] The beams are split according to the invention, e.g., by means of a Brewster plate 71 (not shown here), advantageously in the position of the pinhole 13 or shortly thereafter – here the beam splitting can be particularly compact due to the small beam diameter. Using a mirror 72 (not shown here), the deflected partial beams can be redirected into the optics so that a second image B2 of the detection area E is created. Beam splitting with a Brewster window results in polarizing beam splitting, and in the illustrated case, a p-polarization of image B1 and an s-polarization of image B2. Alternatively, the beam splitting can also be non-polarizing, and the desired polarization can be set using separate polarizers for images B1 and B2, for example, a 45° and 135° linear polarization.This diagonal polarization can also be achieved by rotating an arrangement of device 7 originally intended for p-s splitting, e.g., a Brewster window 71 with mirror 72 (not shown here), by 45° around the optical axis. In this case, however, the two images B1 and B2 are offset from each other by 45°, which means poor utilization of the image sensor of the IR camera 31. This 45° shift can be eliminated by readjusting the mirror 72 (not shown here). Alternatively, a birefringent crystal can be used, with which the illustrated beam path of the IR rays can be realized without additional elements. This, of course, requires appropriate transparency for the desired wavelength spectrum. Alternatively, the beam splitting can also be mounted directly in front of the image plane in the image acquisition unit 3.

[0111] If the image plane is an intermediate image plane, i.e., images B1 and B2, and possibly also with triple or quadruple polarization, a third image B3 (not shown) and a fourth image B4 (not shown), are imaged via a second lens onto the actual camera sensor of the IR camera 31, the beam splitting can also occur directly in the image plane, and a two-stage beam splitting can also occur in the polarization splitting device 7, with a first splitting into two beams at the position of the pinhole 13 and a second splitting of two into four beams at the position of the image plane. Both positions are predestined and advantageous for implementing the invention because the cross-section of the beam path is then comparatively small, which facilitates splitting and polarization or even makes it possible in the first place.

[0112] For moving substrates 11, it is advantageous to select the linear or narrow rectangular detection area E such that it encompasses the entire width of interest of the substrate 11 transversely to the direction of movement V, but is significantly smaller in the direction of movement V, since an overall image of the substrate 11 can be accumulated anyway due to the substrate movement. The area E will therefore essentially have a significantly smaller width than length and essentially correspond to a narrow parallelogram, or better, a narrow rectangle or a type of line, or at least enable evaluation within a narrow rectangular area. This shape of the area E significantly simplifies the beam splitting in the polarization splitting device 7 and multiple imaging, enabling a practical implementation of the device 10.

[0113] The main plane can now lie essentially perpendicular to the motion vector V of the substrate 11 in the detection area E or essentially parallel to it. Both variants, i.e. Aw ~ 0° and Aw ~ 90°, have advantages and disadvantages and require different optical solutions in order to image the entire detection area 2-, 3-, or 4-fold onto the camera sensor. With a main plane perpendicular to the movement (Aw ~ 90°) and a small width of the substrate 11, a collimated radiation incidence, i.e. a substantially parallel beam of rays, is advantageous, since the same angle of incidence α is then present at every point in the area E. A parallel beam of rays can be achieved, for example, by placing a point-shaped infrared light source 21 at the focus of a collimating optics (lens or concave mirror or concave mirror).

[0114] Alternatively, a linear, extended or rod-shaped infrared light source 21, 22 or many point-like IR radiation sources arranged in a row can be imaged onto the area E with a telecentric optic 6 essentially parallel, i.e., with the same angle of incidence a. However, this parallel beam guidance reaches its limits with larger substrate widths, since the apertures, i.e., the diameters of the optics 8, grow with the size of the substrate 11 and cause corresponding costs for the device 10.

[0115] Alternatively, when using convergent radiation, the imaging optics 8 or the aperture of the imaging optics can be kept relatively small. On the illumination side of the light source 2, the correspondingly larger output aperture can be achieved by a series of smaller radiators with / without optics 6, 61, extended infrared light sources 21 (incandescent wire / resistor), or by point-shaped radiators with inexpensive large collimation optics 61, in particular metal mirrors. This exploits the fact that good imaging quality and good angular selectivity can be achieved solely by measures on the imaging side, namely the imaging quality by precisely positioned high-quality optics 8 (lenses or mirrors) and the angular selectivity by a pinhole 13 located at the converging point of the first optics.The radiation generation, optionally with optics 6, can therefore be carried out accordingly coarsely and cost-effectively, so that in the limiting case, ultimately just a flat radiating surface without any additional optics can suffice as IR light source 2. However, it must be considered that a 45° linearly polarized input polarization is assumed for all polarization measurements described here, with the exception of the pure Rps measurement, which also works with unpolarized radiation since no phase shift A is measured. The selected IR light source 2 must therefore be appropriately polarized or polarizable. In principle, any other input polarization is possible, as long as it contains significant p- and s- components, is precisely defined, and can thus be taken into account in the evaluation.

[0116] A disadvantage of an embodiment of the device 10 according to the invention with this convergent beam guidance at an azimuth angle Aw ~ 90° is that the angle of incidence α is not constant, but depends on the observed point in the detection area E. However, as long as the angle of incidence α is known for each observed point, this can easily be taken into account in the image evaluation or layer thickness calculation in the evaluation unit 4, or is also automatically taken into account by reference to the uncoated substrate 11. The application of convergent beam guidance with the imaging optics 8 at an azimuth angle of 90° is also simplified for metallic substrates 11 (e.g. rolled or deep-drawn sheets) by the fact that the minimum of the p-reflection at the Brewster angle is often relatively flat, thus deviations of the angle of incidence from the Brewster angle hardly change the sensitivity on coatings or overlays 20.

[0117] An advantage of choosing an azimuth angle Aw ~ 90° is that the lighting and measuring systems of the device 10 can each be mounted laterally on the strip / substrate 11, which accommodates the typical space conditions in the production line / application. With regard to imaging, the problem with an azimuth angle Aw ~ 90° is that a detection area E that is very oblique to the optical axis must be sharply imaged over its entire length. To achieve this, the optics (lens or mirror) of the imaging optics 8 and also the IR camera 31 itself can be slightly tilted within the main plane in order to fulfill the so-called Scheimpflug condition, which makes statements about oblique images. For example, in the case of imaging with a lens, an oblique object plane intersects the lens plane and the resulting oblique image plane in a common straight line. In a similar way, a linear IR emitter, e.g.a heating wire, with appropriately inclined optics 6 in combination with an inclination of the radiator or the infrared light source 21 itself can be imaged onto the detection area E. If a corresponding pinhole diaphragm is not possible on the imaging side, a restriction of the angle of incidence at each point of E can also be provided on the illumination side, with a positioning of a pinhole diaphragm 13 in the beam path focus resulting from the desired directional characteristic.

[0118] With an azimuth angle Aw ~ 0°, the advantages are that the angle of incidence on the substrate 11 is constant over the entire detection area E and that no tilting of the optics 8 and IR camera 31 is required, since the short side of the area E is now inclined to the optical axis and the depth of field of the imaging system is generally sufficient to image the entire area E sharply.

[0119] A further advantage of this embodiment of the device 10 is that, unlike with Aw ~ 90°, the length of the image of E remains constant when the angle of incidence α changes. A disadvantage is that this is more likely to lead to space problems in the production lines, since the entire measuring setup of the device 10 is located over the substrate 11 in its full length along its direction of movement V. By positioning it at an angle, e.g. with Aw = 10°, any space problems can be alleviated, since then the image capture device 3 in particular can be mounted at least partially to the side of the production line. Furthermore, space can be gained by deflecting the beam path of the IR light rays with mirrors, although a potentially undesirable polarizing effect of the mirrors must be taken into account.However, a quarter-wave mirror 75 can also be used to simultaneously achieve an advantageous folding of the beam path and also the necessary retardation for an Rz measurement.

[0120] The imaging optics 6 can be a telecentric optic for smaller widths of substrates 11, so that the beam of rays is incident parallel with a defined angle of incidence a.

[0121] A further exemplary embodiment is shown in a schematic view in Fig. 8, in which the device 10 according to the invention uses an alternative form of the imaging optics 8 of the previous exemplary embodiments: Here, instead of the lenses 81, 82, an imaging optics 9 consisting of a combination of concave mirrors 91, 92 is used. For example, a concave mirror with a focal length f=1200mm can be used as the concave mirror for the concave mirror 91 and a concave mirror with a focal length f=90mm can be used for the oppositely aligned concave mirror 92, which then transmits the IR rays to the IR camera 31. With such an alternative form of the imaging optics 9, advantages are achieved with regard to the width of the measuring area in the detection area E on the substrate 11. Even larger widths of metal strips or other substrates 11 of up to 2300mm can be detected and assessed directly and in real time using a device according to the invention.With the illustrated form of the imaging optics 9 with the concave mirrors 91, 92, a parallel image of the IR illumination area from the substrate 11 toward the IR camera 31 is also generated, so that, according to the inventive solution, no imaging corrections need to be calculated for the individual images of the detection area in the different polarizations in the IR camera 31. Here, too, a quasi-parallel image with the same angle of incidence and reflection a and a' is achieved across the entire metal strip width of the substrate 11, specifically for a larger width range with a comparatively compact design of the device 10.

[0122] In addition or as an alternative, an alternative light source 2 can optionally be used here in this further exemplary embodiment, which is shown in Fig. 8, namely a rod-shaped IR light source 22 instead of the IR light source 21 described in the previous exemplary embodiments. This rod-shaped IR light source 22 can, for example, be used in the form of a so-called glowing rod and has the advantage that a linear or narrow rectangular detection area E on the substrate 11 is directly illuminated without the need for additional slit apertures or the like. The use of such a rod-shaped IR light source 22 can also be applied in alternative embodiments of the exemplary embodiments of the invention to the previously described exemplary embodiments of Figs. 1 to 7.Likewise, the imaging optics 9 with concave mirrors 91, 92 used here in this embodiment can also be used partially or entirely in the previously described embodiments without departing from the scope of the invention as defined in the appended claims. List of reference symbols.

[0123] 1 recording device

[0124] 2 light source

[0125] 21 Infrared light source

[0126] 22 rod-shaped infrared light source

[0127] 3 Image capture device

[0128] 31 Infrared camera (IR camera)

[0129] 4 Evaluation unit

[0130] 5 Means of limiting the detection area E

[0131] 51 slit aperture

[0132] 6 illumination-side optics

[0133] 61 Collimation optics (e.g. plano-convex lens or cylindrical lenses)

[0134] 62 polarizing filters (e.g. a wire grid polarizer or a Brewster window)

[0135] 7 Polarization splitting device

[0136] 71 Brewster Plate

[0137] 72 mirrors

[0138] 73 beam splitters

[0139] 74 quarter-wave plate or A / 4 plate

[0140] 75 quarter-wave mirrors or A / 4 mirrors

[0141] 76 Nanowire or wire grid polarizer

[0142] 8 imaging optics (e.g. bi-telecentric lens consisting of two confocally arranged lenses 81 , 82 or lenses arranged for convergent beam guidance)

[0143] 9 imaging optics made of concave mirrors

[0144] 91 first concave mirror

[0145] 92 second concave mirror 10 device

[0146] 11 Substrat

[0147] 12 bandpass filters, or general wavelength filters, and also an edge filter

[0148] 13 Pinhole or aperture

[0149] 20 Coating or layer of dielectric material

[0150] B1, B2 images with dual polarization

[0151] E linear or narrow rectangular detection area

[0152] V Motion vector of substrate 11 or metal strip a, a' Angle of incidence and reflection of IR rays in the detection area E

[0153] ROI Region of Interest = Evaluation area

[0154] Aw Azimuth angle = angle between motion vector V and the central light plane

Claims

Claims 1. A device (10) for determining in real time planar coatings (20) made of dielectric materials, in particular organic materials, on strip-shaped or plate-like substrates (11), such as material webs made of metal or plastic, with an optical, ellipsometry-based detection device (1) for detecting and quantifying coatings or coatings (20) on the substrate (11) on the basis of changes in a polarization state of light reflected from the substrate (11) or the coating (20), with at least one light source (2) directed onto a surface of the substrate (11) at a predetermined angle of incidence α, with at least one image detection device (3) arranged opposite the light source (2) according to an angle of reflection α' for detecting light reflections on the substrate (11), and with an evaluation unit (4),which is set up and designed to detect and assess supports (20) on the substrate (11), characterized in that the light source (2) comprises an infrared light source (21, 22) and the image capture device (3) comprises an infrared camera (31), that optical means (5) are provided for limiting the light rays incident from the light source (2), which define a linear or substantially rectangular detection area E of light reflected from the substrate (11) for detecting supports (20) by the IR camera (31), and that a polarization splitting device (7) for at least 2-fold polarization splitting of the IR light detected by the IR camera (31) is provided between the substrate (11) and the IR camera (31) in such a way that at least 2-fold images with at least two different polarizations can be generated from the detection area E.

2. Device (10) according to claim 1, characterized in that the means (5) for limiting the detection area E comprise a slit aperture (51), mask or optical limitation between the light source (2) and the IR camera (31) or a special shape or positioning of the light source (2) itself.

3. Device (10) according to claim 1 or 2, characterized in that imaging optics (8, 9) or optical elements (12, 13) are provided upstream of the polarization splitting device (7) or integrated therein.

4. Device (10) according to one of the preceding claims, characterized in that the polarization splitting device (7) has at least one optical means, in particular a Brewster plate (71) and at least one mirror (72) in the region of the IR light rays reflected at the angle of reflection a' for at least twice the imaging of the IR rays on the IR camera (31).

5. Device (10) according to one of the preceding claims, characterized in that at least one imaging object-side telecentric optics (8, 9) for imaging collimated infrared rays is provided between the substrate (11) and the IR camera (31).

6. Device (10) according to one of claims 1 to 4, characterized in that an imaging optics (8) for imaging convergent infrared rays is provided between the substrate (11) and the IR camera (31).

7. Device (10) according to one of the preceding claims, characterized in that the infrared light source (21, 22) and the detection device (1) are set up and adapted for a medium infrared range, in particular a range from 5 pm to 15 pm, preferably 8 pm to 14 pm.

8. Device (10) according to one of the preceding claims, characterized in that a bandpass filter (12) or edge filter is provided between the infrared light source (21, 22) and the IR camera (31) in the beam path of the IR light rays.

9. Device (10) according to one of the preceding claims, characterized in that the light propagation is substantially normal to the substrate movement and the light source (2) and the detection device (1) are each arranged laterally from the substrate (11) and are preferably designed to determine supports (20) on a continuously moving substrate (11).

10. Device (10) according to one of the preceding claims, characterized in that means are provided such that the light propagation is substantially parallel to the substrate movement and the light source (2) and the detection device (1) are each arranged above the substrate (11) and are preferably designed to determine supports (20) on a continuously moving substrate (11). 11 Device (10) according to one of the preceding claims, characterized in that the angle of incidence a of the light beam of the infrared light source (21, 22) in relation to the vertical perpendicular to the substrate (11) is in the range of a = 75° - 87° for metallic substrates (11) and in the range of a = 54° - 60° in the case of non-metallic substrates (11).

12. Device (10) according to one of the preceding claims, characterized in that the polarization splitting device (7) is designed for 3-fold or 4-fold polarization splitting of the IR light beam and has at least one beam splitter (73) such that a 3-fold or 4-fold image with three or four different polarizations can be generated from the detection area E in the area of ​​the IR camera (31).

13. Method for determining in real time coatings (20) made of dielectric materials, in particular organic materials, on strip-shaped or plate-like substrates (11), such as material webs made of metal or plastic, in particular by means of a device (10) according to one of claims 1 to 12, with an optical detection device (1) based on ellipsometry for detecting and quantifying coatings or coatings (20) on the substrate (11) on the basis of changes in a polarization state of light reflected from the substrate (11) or the coating (20), with at least one light source (2) which is directed onto a surface of the substrate (11) at a predetermined angle of incidence α, with at least one light source (2) which is opposite to the light source (2) according to an angle of reflection α' arranged image capture device (3) for capturing light reflections on the substrate (11) and with an evaluation unit (4) which is set up and designed to detect and assess overlays (20) on the substrate (11), the method being characterized by the steps: a) illuminating a delimited, predefined, linear or substantially rectangular detection area E on the substrate (11) by means of a light source (2) designed as an infrared light source (21, 22) by means of optical or optically acting means (5) for limiting light reflected on the substrate (11) for capturing overlays (20); b) splitting the reflected linear IR light beams from the detection area E into at least two differently polarized images by means of a polarization splitting device (7);c) detecting the IR light rays reflected on the substrate (11) by an infrared camera (31) of the image capture device (3) in the detection area E on the substrate (11); d) calculating, determining, and quantifying a real-time image of the support (20) in the evaluation unit (4) based on light reflections captured by the IR camera (31) by means of at least 2-fold polarization of captured light rays by the polarization splitting device (7) in front of the IR camera (31); 14. The method according to claim 13, wherein the infrared camera (31) of the image capture device (3) detects infrared light in the mid-infrared range from 5 pm to 15 pm, preferably in a range from 8 pm to 14 pm.

15. The method according to claim 13 or 14, wherein the determination and quantification of the deposits (20) on the substrate (11) is carried out on the basis of the at least doubly polarized image of the IR light rays of an intensity ratio from the differently polarized line-shaped images from the IR camera (31).

16. Method according to one of claims 13 to 15, characterized by calculating position-dependent layer thicknesses of supports (20) with the evaluation unit (4) and of detected intensity ratios of the images of IR light rays in the detection area E and composing an overall image of a layer thickness distribution on the preferably continuously moving substrate (11).

17. Method according to one of claims 13 to 16, wherein at least a second beam splitting in the sense of a triple or quadruple polarization of infrared light beams detected in the detection area E is carried out by preferably a quarter-wave plate (74) or a quarter-wave mirror (75) for additional splitting of the IR rays into a triple or quadruple image.

18. The method according to any one of claims 13 to 17, wherein a layer thickness of the overlay (20) on the substrate (11) is calculated in the evaluation unit (4) from a ratio of a p- / s intensity, a 45°-135° ratio or a circular ratio of the p- and s-polarization in the polarization splitting device (7).

19. Method according to one of claims 13 to 18, wherein the IR rays emitted by the infrared light source (21, 22) are bundled by imaging optics (8, 9) into convergent rays for detection by the IR camera (31).

Images