Method and device for monitoring coating processes

Abstract

The present invention relates to a method for monitoring coating processes, in which, while a substrate with a substrate plane is subjected to a coating process in which a first side parallel to the substrate plane and / or a second side of the substrate opposite the first side and parallel to the substrate plane is / are each provided with at least one coating, a light beam is emitted onto the substrate and is at least partially transmitted through the substrate, a partial light beam is coupled out from the transmitted light beam, the coupled out partial light beam strikes a sensor, and the transmitted light beam, after the coupling out of the partial light beam, is directed back onto the substrate and is again at least partially transmitted through the substrate, and the transmitted light beam strikes a final sensor.A spectrum is determined from the light beam striking the last sensor and from each partial light beam striking a sensor prior to it, and at least one of the determined spectra is used to determine at least one property of the at least one coating of the substrate currently being applied and / or at least one property of the at least one coating of at least another substrate currently being applied, which is subjected to the same coating process as the substrate and / or at least one property of the coating process currently being carried out. Furthermore, the present invention also relates to a device for monitoring coating processes using the method according to the invention.

Description

[0001] The present invention relates to a method for monitoring coating processes, in which, while a substrate with a substrate plane is subjected to a coating process in which a first side running parallel to the substrate plane and / or a second side of the substrate opposite the first side running parallel to the substrate plane is / are each provided with at least one coating, a light beam is emitted onto the substrate and at least partially transmitted through the substrate, a partial light beam is decoupled from the transmitted light beam, the decoupled partial light beam strikes a sensor and the transmitted light beam, after the decoupled partial light beam, is directed back onto the substrate and again at least partially transmitted through the substrate, the transmitted light beam strikes a last sensor,A spectrum is determined from the light beam striking the last sensor and from each partial light beam striking a sensor before it, and using at least one of the determined spectra, at least one property of the at least one coating of the substrate currently being applied and / or at least one property of at least one coating of at least one further substrate currently being applied, which is subjected to the same coating process as the substrate, and / or at least one property of the coating process currently being carried out is determined. Furthermore, the present invention also relates to a device for monitoring coating processes using the method according to the invention.

[0002] Optical coatings are layers of materials applied to the surface of optics to modify their optical properties. An interference filter is a type of optical coating consisting of multiple layers of materials applied to transmit a specific wavelength of light while reflecting other wavelengths or absorbing them if the materials themselves are absorbent. Interference filters are often used in applications where a very narrow spectrum of light wavelengths is required, such as in spectroscopic instruments or color photography.

[0003] Interference filters are manufactured by applying multiple layers of materials with different refractive indices to an optical plate. The thickness of each layer can be calculated to correspond to a whole number of wavelengths at a given wavelength. When light passes through these layers, the waves passing through the layers are delayed in such a way that they amplify or attenuate each other, depending on whether they are in phase or not. This results in interference effects that transmit light at certain wavelengths and absorb others. Alternatively, it is also possible to choose the layer thicknesses so that they do not correspond to a whole number of wavelengths. Here, too, interference effects accumulate to achieve a specific filter function. In the latter case, one speaks of non-periodic designs.

[0004] Interference filters have several advantages over other types of optical coatings. They are very precise and can transmit very narrow spectra of light wavelengths. They are also very robust and can be used many times without degradation in performance. They are often used in applications where high precision and reliability are required, such as medical diagnostics or industrial process control.

[0005] Optical components are usually coated. This coating is often a broadband anti-reflective coating. The substrate material is usually glass or plastic, with a variety of materials being used in each case. For glass, these include quartz, borosilicate glass, SF6, etc. For plastics, CR39, polycarbonate, PMMA, or other materials can be used. Depending on the material, i.e. the refractive index of the optical components, the substrate material reflects a few percent of the light. The reflection R against air is calculated using the formula R=(n−1)2 / (n+1)2 where n is the refractive index of the optical component. The light is reflected or transmitted with different intensities at the transition between two layers. At a transition from layer 1 with refractive index n1 to layer 2 with refractive index n2, the reflection is: R1⇒2=(n1−n2)2 / (n1+n2)2

[0006] By stacking multiple thin layers, almost any desired coating function can be achieved. This is possible as long as the coherence condition is maintained. In the case of visible light, the coherence length can be very large (> 100 μm).

[0007] Anti-reflective coatings are often used. Anti-reflective coatings typically require both sides of the optical components to be coated. Typically, a broad spectral range is used. A simple broadband anti-reflective coating often covers the 420-680 nm range, requiring a reflection of less than 0.5% across this range. For a flat substrate, a single coating, such as the following, is sufficient. Glass−TiO2(10 nm)−SiO2(40 nm)−TiO2(110 nm)−SiO2(85 nm) SiO2 is a low-refractive material with a refractive index of approximately 1.45, while TiO2 is a high-refractive material with a refractive index of 2.4 to 2.7.

[0008] In addition to reflection-reducing layers, various filters can also be created. The function of a periodic dielectric mirror, for example, is described by the layer formula S−(HL)N−air reached.

[0009] S is the substrate. H and L correspond to a high- and low-refractive-index layer, respectively, with a lambda / 4 layer thickness. N is the number of periods of a double-layer sequence (HL = "high-low"). The geometric layer thickness is defined as: Thickness=lambda / 4n.

[0010] With a refractive index of n = 2.0 (for the H-layer) and a wavelength of 550 nm, a lambda / 4 layer would be 62.5 nm thick. Periodic layer stacks are a relatively simple form of optical filter. Layer functions can also be achieved through non-periodic layer structures or through combinations of periodic and non-periodic layers. The more layers used in a layer stack, the more complex requirements the coating can meet. This allows one or more defined spectral ranges to be blocked or transmitted.

[0011] The PVD (Physical Vapor Deposition) process is often used to deposit optical coatings. This is a technique for depositing layers using physical processes that involve the evaporation of materials. One of the most common PVD processes for depositing optical interference coatings is sputtering (magnetron sputtering or ion beam sputtering). ALD (Atomic Layer Deposition), particularly dynamic ALD, is also used. Evaporation of the source material using an electron beam is also state-of-the-art. Corresponding state-of-the-art processes are described, for example, in Milton Ohring, Chapters 3 and 5, Editor: Milton Ohring, Materials Science of Thin Films (Second Edition), Academic Press, 2002, pages 95-144 and 203-275.

[0012] To ensure high-quality coatings, precise control of both the coating thickness and the refractive index is necessary. Therefore, optical monitoring is often used today to control the coating (see, for example, Baumeister, PW, Optical Coating Technology, SPIE Press, Bellingham, WA, 2004, Chapter 9, pages 9-46ff, Section 9.6.2). Transmission or reflection measurements can be used. Optical monitoring during coating processes serves to monitor the progress of the coating process and to evaluate the quality of the resulting coating. This is particularly important in the production of optical coatings, as these layers must be very thin and homogeneous to achieve good performance.

[0013] One of the most common methods for optical monitoring of coating processes is in-situ reflectometry. It allows the measurement of the layer's reflection behavior during the deposition process. A light beam is directed onto the surface of the substrate, and the proportion of reflected light is measured. Based on the wavelength of the light and the layer properties, the layer thickness and homogeneity can be determined. The method is also often used in transmission, where the transmitted light beam is measured. The layer thickness is determined by adjusting the theoretical transmission or reflection to the measured values, with the layer thicknesses being used as fitting parameters. The advantage of in-situ measurement is that the measurement can be repeated frequently, meaning that only the currently growing layer needs to be measured.

[0014] A distinction is made between direct measurements and indirect measurements. Direct measurements are taken directly on the coating material, while indirect measurements are taken on a reference substrate that is moving along, ideally with the same coating as the coating material.

[0015] A transmission or reflection measurement can be performed at individual wavelengths or broadband in a selected spectral range (see, for example, Bruno Badoil, Fabien Lemarchand, Michel Cathelinaud, and Michel Lequime, "Interest of broadband optical monitoring for thin-film filter manufacturing," Appl. Opt. 46, pages 4294-4303 (2007)). Many other methods for optical monitoring of coating processes exist, which can be selected depending on the requirements and available resources.

[0016] Previously known monitoring methods are used to control one-sided coating. The growing coating is measured on one side. However, there are coating systems that coat both sides simultaneously. In this case, not just one side of the substrate is coated, but both sides of the substrate are coated simultaneously. Advantages of this type of coating system include, for example, higher productivity, since coatings often have to be applied to both sides. Another advantage of simultaneous double-sided coating is that with thin layers, the substrates often bend because compressive stress is often required in the layers to achieve good coating properties. This bending can, for example, lead to a change in the coating rate on the various parts of the substrate. This can be avoided by simultaneous double-sided coating.

[0017] However, this poses the problem that it is unclear how coating control can be performed when coating is applied simultaneously to both the front and back surfaces. In principle, in a reflection measurement, the two sides can be separated by optically preventing light from the back from entering the receiver. This can be achieved using an absorbing reference substrate. However, this is not readily possible for a transmission measurement.

[0018] Based on this, the object of the present invention was to provide a method for monitoring coating processes that allows for better monitoring of substrate coatings. Furthermore, the object of the present invention was to provide a device for carrying out such a method.

[0019] This object is achieved with respect to a method for monitoring coating processes having the features of patent claim 1 and with respect to a device for monitoring coating processes having the features of patent claim 11. The respective dependent patent claims represent advantageous developments.

[0020] According to the invention, a method for monitoring coating processes is thus specified, in which, while a substrate with a substrate plane is subjected to a coating process in which a first side running parallel to the substrate plane and / or a second side of the substrate opposite the first side running parallel to the substrate plane is / are each provided with at least one coating, a) a light beam is emitted onto the substrate and at least partially transmitted through the substrate, b) a partial light beam is decoupled from the transmitted light beam, the decoupled partial light beam hits (preferably is directed) (at least) one sensor and the transmitted light beam is directed back onto the substrate after the decoupled partial light beam and is again at least partially transmitted through the substrate, (whereby step b) can optionally be repeated once or several times,) c) the light beam transmitted in step b) hits a final sensor (preferably is directed), d) a spectrum is determined from the light beam striking (or directed) the last sensor in step c) and from each partial light beam striking (or directed) a sensor in step b), and e) using at least one of the determined spectra (preferably using several of the determined spectra, particularly preferably using the determined spectra) - at least one property of the at least one coating of the substrate currently being applied, and / or - at least one property of at least one coating currently being applied to at least one further substrate which is subjected to the same coating process as the substrate, and / or - at least one property of the coating process currently being carried out (or currently being carried out) is determined.

[0021] The method according to the invention is thus a method for monitoring coating processes, which is carried out while a substrate is subjected to a coating process. During this coating process, a first side of the substrate running parallel to the substrate plane (of the substrate) and / or a second side of the substrate opposite the first side running parallel to the substrate plane are each provided with at least one coating. During the coating process, a single-sided or double-sided coating can thus be carried out. Accordingly, both single-sided and double-sided coating of substrates can be monitored using the method according to the invention.

[0022] During the coating process, multiple substrates (or additional substrates) can be coated, each having a substrate plane, wherein a first side running parallel to the substrate plane and / or a second side of each of the substrates opposite the first side running parallel to the substrate plane is / are each provided with at least one coating. The steps of the method for monitoring coating processes can then preferably be performed on one of the other substrates or alternatively on several or all of the substrates.

[0023] The method according to the invention for monitoring coating processes comprises steps a) to e).

[0024] In step a), a light beam is first emitted onto the substrate, with the emitted light beam transmitting at least partially through the substrate. The light beam can be emitted onto the first side or the second side of the substrate. Preferably, the light beam is emitted onto the substrate such that it strikes the substrate (or the first side or the second side of the substrate) substantially perpendicularly.

[0025] In step b), a partial light beam is coupled out from the transmitted light beam, wherein the coupled-out partial light beam strikes a sensor, preferably is directed, and the transmitted light beam is directed back onto the substrate after the partial light beam has been coupled out, wherein the light beam directed onto the substrate in this way is again at least partially transmitted through the substrate. The light beam can be directed onto the first side or the second side of the substrate. It is preferred that the light beam is directed onto the side of the substrate to which the light beam was not emitted in step a). This means that if the light beam was emitted onto the first side of the substrate in step a), the light beam is preferably directed onto the second side of the substrate in step b).If the light beam was emitted onto the second side of the substrate in step a), the light beam is preferably directed onto the first side of the substrate in step b). The light beam is preferably directed onto the substrate in such a way that it strikes the substrate (or the first side or the second side of the substrate) essentially perpendicularly. Step b) can be repeated once or several times, so that the light beam transmitted in step a) is transmitted through the substrate several times after the partial light beam has been coupled out, and after each transmission, a partial light beam is coupled out and strikes, preferably directed, a separate further sensor. Alternatively, step b) can also be carried out only once.

[0026] In step c), the light beam transmitted in step b) (once or several times) strikes a final sensor. Preferably, the light beam transmitted in step b) (once or several times) is directed to a final sensor.

[0027] In step d), a spectrum is determined both for the light beam striking (or directed) the last sensor in step c) and for each partial light beam striking (or directed) a sensor in step b).

[0028] In step e), the determined spectra are used - at least one property of the at least one coating of the substrate currently being applied (or manufactured) (through the coating process), and / or - at least one property of at least one coating currently being applied (or manufactured) (through the coating process) to at least one further substrate which is subjected to the same coating process as the substrate, and / or - at least one property of the coating process currently being carried out (or currently being carried out) (of the substrate and optionally of at least one other substrate) is determined.

[0029] In the method according to the invention, a portion of the light beam transmitted through the substrate for the first time, i.e., in step a), is extracted, and the remaining light beam is transmitted through the substrate again. Using various sensors, both the light transmitted through the substrate once and the light transmitted through the substrate twice or more times can be measured. Step b) can be repeated multiple times, so that ultimately two, three, four, or more light transmissions can be measured using different sensors. Thus, multiple measurements, i.e., determined spectra, are available for evaluation.

[0030] A method in which the measuring beam passes through the medium to be measured several times before the measurement can be used, for example, to measure low absorption values. The measurement method is based on the fact that the absorption (if the absorption is not too strong) of substances follows the Lambert-Beer formula: T=T0⋅exp(−K⋅d), with K=(4π⋅k) / λ where T = transmission, T0 = output transmission, K = absorption coefficient, k = absorption index, λ = wavelength, d = path or thickness of the absorbing layer.

[0031] By extending the path d, a decrease in transmission can be measured more effectively.

[0032] In the case of absorption-free materials, changes in transmission can also occur. These are then caused by constructive or destructive interference of partial beams reflected at interfaces within the layer stack. Interfaces arise from the alternation between two layers of different refractive indices. The resulting structures are wavelength-dependent, so that regions of low or high transmission arise depending on the wavelength. The values ​​can also be extremely low, for example, less than 1% transmission or greater than 99% transmission.

[0033] In contrast to previously known methods, the method according to the invention now uses either one or more measurements or even simultaneously one and / or more measurements of a light beam that is transmitted through the substrate with different numbers of times. The present invention therefore aims to enable the use of different measuring beams (or beams measured with different sensors). With the help of the spectra resulting from the different measurements, properties of the coating currently being produced or applied (e.g. the layer thickness) and / or properties of the coating process currently being carried out (e.g. the coating rate) can then be determined (during the coating process). Differences or changes between the different spectra can also be used here, for example.For example, a spectral range can be used that provides the greatest sensitivity for determining the desired property (e.g., layer thickness, or the current coating rate derived from it over time). For example, unlike absorption, the coating rate is a differential parameter and corresponds to the temporal derivative of thickness over time. Thus, with the measurement method according to the invention, edge steepness is more important than the large absorption values ​​themselves.

[0034] A particularly good spectral resolution or slit width of the sensors is helpful for this, for example, a spectral resolution of at most 2 nm, preferably at most 1 nm, more preferably at most 0.5 nm, most preferably at most 0.2 nm. In contrast, in previously known methods the spectral sensors used there only have a spectral resolution or slit width of more than 1 nm to 5 nm. In addition, a high dynamic range is also helpful in the method according to the invention. For example, depending on the current layer, the spectrum of a beam transmitted twice or a beam transmitted three times can be used to determine a certain property. If the transmission is 10% for one pass, it reduces to 1% for two passes and to 0.1% for three passes. A high dynamic range is therefore helpful in order to obtain a precise measurement.It is also possible to evaluate multiple beams simultaneously. Different spectral ranges of one or more of the detected beams can also be used for different beams.

[0035] Optionally, one of the partial beams can also be polarized. The idea here is to incorporate a polarizer into the beam path to create, for example, p- or s-polarization. In this case, the partial beam would be guided through the layer at a specific angle of incidence, allowing measurements to be taken with polarized light. This has the particular advantage that, in some cases, the filter specifications can be monitored directly. These are sometimes specified for oblique incidence and a specific polarization state.

[0036] The method according to the invention can thus be used to monitor coating processes, allowing certain parameters of the coating being formed and / or the coating process to be determined and monitored during the coating process. For example, during the coating process, determining the layer thickness can be used to determine whether or when the coating process is complete, and / or determining the coating rate can be used to monitor whether the coating is being applied at the desired rate.

[0037] Alternatively, reaching the endpoint of a sublayer can be achieved by determining the minimum or maximum transmission with greater accuracy than is possible with a single measurement. Monitoring minimum or maximum transmission at specific wavelengths is particularly suitable for so-called periodic lambda / 4 layer designs, in which lambda / 4 layers are always stacked on top of each other. A lambda / 4 layer is a layer with the following thickness: Thickness = lambda / 4n, where lambda = wavelength and n = refractive index of the layer.

[0038] A particular advantage of the method according to the invention is that, with the aid of the different spectra, which are based on measurements of a light beam transmitted through the substrate with varying frequencies, properties of the coatings currently being applied or produced and / or of the coating process can be determined, preferably even in the case of double-sided coating. This can be achieved, for example, by using different wavelength ranges of the spectra in step e), whereby, for example, one of the different wavelength ranges is used to determine a property of the coating on the first side of the substrate and another of the different wavelength ranges is used to determine a property of the coating on the second side of the substrate.Also, for example, the differences between the different spectra and / or specific regions in the different spectra can be used to determine a property specifically of the coating on the first side of the substrate or a property specifically of the coating on the second side of the substrate.

[0039] The method according to the invention can be carried out as a direct measuring method or as an indirect measuring method. In the direct measuring method, measurements are taken directly on one or more of the substrates to be coated, i.e. directly on the coating material. In the indirect measurement, on the other hand, measurements are taken on a concurrent reference substrate (or a monitoring substrate) which (ideally) receives the identical coating as the coating material. The reference substrate (or monitoring substrate) can be a test glass, for example. Based on the measurements carried out on the reference substrate, not only the properties of the coating on the reference substrate can be determined, but also indirectly the properties of the coating on the other substrates, i.e. the coating material.

[0040] The substrate can thus preferably be a reference substrate (or a monitoring substrate), wherein in addition at least one further substrate is subjected to the same coating process as the reference substrate and in step e) at least one property of the at least one coating of the at least one further substrate currently being applied and / or at least one property of the coating process currently being carried out is determined.

[0041] A preferred variant of the method according to the invention is characterized in that step b) is repeated at least once before step c), preferably from one to five times, particularly preferably once, twice, or three times. During each of the repetitions, a partial light beam is extracted from the light beam transmitted in the previous pass of step b), the extracted partial light beam strikes (preferably is directed) a sensor that does not correspond to any of the other sensors used in step b), and the transmitted light beam, after the extraction of the partial light beam, is redirected onto the substrate and again at least partially transmitted through the substrate. The light beam can be directed (in each case) onto the first side or the second side of the substrate.In this case, it is preferred that the light beam is (in each case) directed onto the side of the substrate to which the light beam was not emitted in the previous pass of step b). This means that the light beam is preferably always directed alternately onto the first side and the second side of the substrate. If the light beam was emitted, for example, onto the first side of the substrate in one pass of step b), the light beam is preferably directed onto the second side of the substrate in the pass of step b) following the one pass of step b), or if the light beam was emitted, for example, onto the second side of the substrate in one pass of step b), the light beam is preferably directed onto the first side of the substrate in the pass of step b) following the one pass of step b). The light beam is preferably directed (in each case) onto the substrate in such a way that it is essentially perpendicular to the substrate (orThe number of repetitions of step b) can preferably be adapted to the transmission of the light beam through the substrate. This means that the higher the transmission of the light beam through the substrate, the higher the number of repetitions of step b) can preferably be.

[0042] A further preferred variant of the method according to the invention is characterized in that - between step a) and step b), and / or - between step b) and step c), and / or - between two passes (or two repetitions) of step b), the light beam is directed back onto the substrate without coupling out a partial light beam therefrom and is again at least partially transmitted through the substrate. This can preferably be repeated once or several times. The light beam is directed (in each case) onto the first side or the second side of the substrate. It is preferred that the light beam is directed (in each case) onto the side of the substrate to which the light beam was not directed or emitted for the previous transmission of the light through the substrate. I.e. the light beam is preferably always directed alternately onto the first side and the second side of the substrate. if the light beam in one pass of step b), e.g.was emitted onto the first side of the substrate, the light beam is preferably directed onto the second side of the substrate in the pass of step b) following the one pass of step b), or if the light beam was emitted onto the second side of the substrate in the pass of step b), for example, the light beam is preferably directed onto the first side of the substrate in the pass of step b) following the one pass of step b). Preferably, the light beam is (in each case) directed onto the substrate in such a way that it strikes the substrate (or the first side or the second side of the substrate) essentially perpendicularly.

[0043] A further preferred variant of the method according to the invention is characterized in that - the at least one property of the at least one coating of the substrate and / or the at least one property of the at least one coating of the at least one further substrate is selected from the group consisting of the layer thickness, the layer thickness gradient, the homogeneity, the refractive index(es) and its spectral dispersion, the wavefront, the phase and its dispersion, the polarization, the surface roughness, the color values, and combinations thereof, and / or - the at least one property of the coating process is selected from the group consisting of coating rate, temperature, particles, particle flux, and combinations thereof.

[0044] According to a further preferred variant of the process according to the invention, in step e) - the at least one determined property of the at least one coating of the substrate, and / or - the at least one determined property of the at least one further substrate, and / or - at least one determined property of the coating process indicates when the coating process is completed.

[0045] A further preferred variant of the method according to the invention is characterized in that the light beam emitted onto the substrate in step a) strikes the first or second side of the substrate substantially perpendicular to the substrate plane and is transmitted through the substrate.

[0046] A further preferred variant of the method according to the invention is characterized in that the light beam striking (or directed) the last sensor in step c) and each partial light beam striking (or directed) a sensor in step b) each have essentially the same intensity. This allows for better comparability of the determined spectra. To achieve essentially the same intensity of the beams, a correspondingly large portion of the light beam can be coupled out, depending on the number of sensors used.

[0047] According to a further preferred variant of the method according to the invention, in step b), when the partial light beam is extracted from the transmitted light beam, only at least one specific intensity range and / or at least one specific wavelength range of the transmitted light beam is extracted. For example, a specific intensity range and / or a specific wavelength range of the transmitted light beam can be extracted that is required for determining a specific property or is particularly suitable for this purpose. Accordingly, for example, only those ranges can be extracted that are required (at the respective time) to determine a corresponding required property. For example, only those ranges can be extracted that are expected to produce sufficient signal or signal change.

[0048] A further preferred variant of the process according to the invention is characterized in that in step e) - the at least one property of the at least one coating of the substrate currently being applied and / or (of the at least one further substrate currently being applied), and / or - the at least one property of the coating process currently being carried out is determined using at least one specific wavelength range of the determined spectra, wherein the at least one specific wavelength range is preferably determined by a simulation of the determined spectra carried out before and / or during the coating process. For example, a specific wavelength range of the transmitted light beam can be evaluated that is required for determining a specific property or is particularly suitable for this purpose. Accordingly, for example, only those ranges can be evaluated that are required (at the respective time) to determine a corresponding required property. For example, only those ranges can be evaluated that are expected to produce sufficient signal or signal change.By simulating the spectra, a suitable wavelength range can be determined quickly and easily.

[0049] A further preferred variant of the method according to the invention is characterized in that during the coating process both the first side and the second side of the substrate are provided at least partially simultaneously with at least one coating, wherein in step e) - at least one property of the at least one coating of the first side of the substrate currently being applied and / or (of the at least one coating of the first side currently being applied) of the at least one further substrate, and / or - at least one property of the coating process just performed on the first side of the substrate and / or (of the coating process just performed on the first side) of the at least one further substrate is determined using at least one specific first wavelength range of the determined spectra and using at least one specific second wavelength range of the determined spectra that differs from the first wavelength range - at least one property of the at least one coating of the second side of the substrate currently being applied and / or (of the at least one coating of the second side currently being applied) of the at least one further substrate, and / or - at least one property of the coating process just carried out on the second side of the substrate and / or (of the coating process just carried out on the second side) of the at least one further substrate is determined, wherein preferably the at least one specific first wavelength range and / or the at least one specific second wavelength range is determined by a simulation of the determined spectra carried out before and / or during the coating process.

[0050] In this way, in the case of double-sided coating, properties of the two coatings currently being applied or produced and / or of the coating process can be determined. In step e), different wavelength ranges of the spectra are used, for example one of the different wavelength ranges being used to determine a property of the coating on the first side of the substrate and another of the different wavelength ranges is used to determine a property of the coating on the second side of the substrate. In this case, the differences between the different spectra or the specific ranges in the different spectra can preferably be used to determine a property specifically of the coating on the first side of the substrate and / or a property specifically of the coating on the second side of the substrate.By simulating the spectra, suitable wavelength ranges can be determined quickly and easily.

[0051] The present invention also relates to a device for monitoring coating processes using the method according to the invention, comprising a light source for emitting a light beam onto a substrate having a substrate plane, a first side running parallel to the substrate plane and a second side opposite the first side running parallel to the substrate plane, a beam splitter for coupling out a partial light beam from a light beam emitted by the light source and at least partially transmitted through the substrate, a sensor for receiving light, which is arranged so that the partial light beam coming from the beam splitter hits it, a last sensor for receiving light, which is arranged so that a light beam transmitted multiple times through the substrate impinges on it, and a device for determining spectra of light beams received by the sensors, wherein - the device comprises a light-guiding device for directing the transmitted light beam coming from the beam splitter, from which the partial light beam has been coupled out, onto the substrate, or - the beam splitter is configured so that the transmitted light beam, from which the partial light beam was coupled out, is directed (with the aid of the beam splitter) onto the substrate and transmitted through the substrate.

[0052] A preferred embodiment of the device according to the invention is characterized in that the device comprises the light-guiding device for directing a transmitted light beam coming from the beam splitter onto the substrate, wherein the device additionally comprises at least one further beam splitter for coupling out a partial light beam, wherein the at least one further beam splitter is arranged such that a light beam transmitted multiple times through the substrate strikes it, at least one further light-guiding device for directing a multiply transmitted light beam coming from the at least one further beam splitter onto the substrate, wherein the at least one further light-guiding device is preferably arranged such that the directed light beam strikes the first or second side of the substrate substantially perpendicular to the substrate plane and is at least partially transmitted through the substrate, and comprises at least one further sensor for receiving light, which is arranged in such a way that the partial light beam coming from the at least one further beam splitter strikes it, wherein preferably the beam splitter for coupling out a partial light beam, the at least one further beam splitter for coupling out a partial light beam, the light directing device for directing the transmitted light beam coming from the beam splitter onto the substrate and the at least one further light directing device for directing a light beam coming from the at least one further beam splitter coming multiple transmitted light beam onto the substrate are arranged outside a coating chamber for coating the first and / or second side of the substrate.

[0053] A further preferred embodiment of the device according to the invention is characterized in that the beam splitter is arranged in such a way that the transmitted light beam, from which the partial light beam was decoupled, is directed (with the aid of the beam splitter) onto the substrate and transmitted through the substrate, wherein the device additionally at least one, preferably one or two, further beam splitters for coupling out a partial light beam, wherein the at least one further beam splitter is arranged such that a light beam transmitted multiple times through the substrate impinges on it, and is designed such that the light beam from which the partial light beam was coupled out is directed onto the substrate and at least partially transmitted through the substrate, and comprises at least one further sensor for receiving light, which is arranged such that the partial light beam coming from the at least one further beam splitter impinges on it, wherein preferably the beam splitter for coupling out a partial light beam and the at least one further beam splitter for coupling out a partial light beam are arranged within a coating chamber for coating the first and / or second side of the substrate.

[0054] A further preferred embodiment of the device according to the invention is characterized in that the device comprises exactly two of the further beam splitters for coupling out a partial light beam, wherein these two further beam splitters are arranged and configured such that a light beam transmitted through the substrate is reflected back and forth several times between the two further beam splitters, wherein the light beam is transmitted through the substrate after each reflection at one of the further beam splitters before it strikes the other of the further beam splitters, and wherein the further beam splitters are configured such that they only couple out a partial light beam of the light beam which strikes the at least one further sensor (preferably is directed) in some of the cases in which the light beam strikes one of them.

[0055] A further preferred embodiment of the device according to the invention is characterized in that - the sensors have a spectral slit width of at most 5 nm, preferably at most 1 nm, particularly preferably at most 0.5 nm, most preferably at most 0.2 nm, and / or - the sensors are broadband sensors, preferably with a measuring range of 190 to 2500 nm, and / or - the sensors are arranged outside a coating chamber for coating the first and / or second side of the substrate, and / or - the light source is broadband, whereby ◯ the light source is preferably a broadband laser, a halogen lamp, or a laser-driven arc lamp, and / or ◯ has a wavelength range of 190 nm to 2500 nm, and / or - the light source is arranged such that the light beam strikes the first or second side of the substrate substantially perpendicular to the substrate plane and is at least partially transmitted through the substrate, and / or - the light source is arranged outside a coating chamber for coating the first and / or second side of the substrate, and / or - the light-guiding device and / or the further light-guiding device(s) is / are each a mirror, and / or - the light-guiding device and / or the further light-guiding device(s) are each arranged such that the light beam directed onto the substrate strikes the first or second side of the substrate substantially perpendicular to the substrate plane and is at least partially transmitted through the substrate, and / or - the beam splitter and / or the further beam splitter(s) for coupling out a partial light beam from the transmitted light beam are arranged outside or inside a coating chamber for coating the first and / or second side of the substrate.

[0056] The present invention is explained in more detail with reference to the following figures and examples, without limiting the invention to the specifically illustrated parameters. Example 1

[0057] Fig. 1 shows an exemplary embodiment of the invention. Light from a light source 7, e.g., a lamp, is passed through a window 3 of the coating system or coating chamber. Window 3 can also be referred to as a vacuum window or coupling-out window. The coating system has chamber walls 2. Substrates 4 are substrates to be coated. Substrate 5 is a monitoring substrate, e.g., a test glass. Coating is carried out dynamically, i.e., substrates 4 and 5 move linearly or in a circular motion between the measuring station and one or more coating areas, and optionally also one or more plasma areas.

[0058] A beam splitter 8, e.g., a partially transparent mirror, is used to extract a partial light beam from the transmitted light beam, which is then directed onto a sensor 1. This sensor can be a broadband sensor that measures, for example, an entire light spectrum in the UV-VIS-NIR range or parts thereof. A typical measuring range is 200 to 1700 nm. Using a light-directing device 6, e.g., a mirror, the transmitted light beam is directed back onto the substrate 5 after the partial light beam has been extracted, and then retransmitted through the substrate 5. Polarization compensation can be achieved here. The beam splitter 8 is arranged between the window 3 and the sensor 1.

[0059] The light beam redirected onto the substrate transmits again through the substrate 5. From the light thus retransmitted, a further partial light beam is decoupled using a further beam splitter 8a, e.g. a semi-transparent mirror, which strikes a sensor 1a. With the help of a light directing device 6a, e.g. a mirror, the light beam is redirected onto the substrate 5 after the further partial light beam has been decoupled, transmitted again through the substrate 5 and then strikes a final sensor 1b. The sensors 1a and 1b can also be broadband sensors that measure, for example, an entire light spectrum in the UV-VIS-NIR range or parts thereof, with a typical measuring range being 200 to 1700 nm.

[0060] To ensure equal light intensities for the three sensors 1, 1a, and 1b, it is advisable to coat the beam splitter 8 so that 1 / 3 of the light is extracted and incident on the sensor 1, so that 2 / 3 of the light is reflected back to the substrate by the light-guiding device 6. 50% of the light should then be extracted by the beam splitter 8a, so that ultimately all three sensors 1, 1a, and 1b receive the same intensity.

[0061] Using a spectral detection device 9, spectra of light beams received by sensors 1, 1a, 1b can be detected. Using one or more of these spectra, at least one property of the coating currently being applied to substrates 4 and / or 5 can be detected and / or at least one property of the coating process currently being performed or currently being performed can be detected. Example 2

[0062] Fig. Figure 2 shows a further exemplary embodiment of the invention. The meaning of the reference numerals corresponds to the meaning of the reference numerals in embodiment 1. For reasons of clarity, Fig. 2 Some elements, such as the light source and the device for determining spectra, are not shown.

[0063] In contrast to the Fig. 1, where the optical elements used to split and direct the light beams, ie the beam splitters 8, 8a and light directing devices 6, 6a, are arranged outside the coating chamber, are in the Fig. In the arrangement shown in Figure 2, the optical elements used to split and direct the light beams, namely the beam splitters 8b and 8c, are arranged within the coating chamber. The beam splitter 8b is a beam splitter designed so that the transmitted light beam, from which the partial light beam was coupled out, is directed onto the substrate and transmitted through the substrate. The beam splitters 8c are two mirrored walls that together form a type of waveguide structure. The light beam directed by the beam splitter 8b onto the substrate and transmitted again through the substrate is threaded into the waveguide structure consisting of the two beam splitters 8c in the form of two mirrored walls, so that it is transmitted through the substrate multiple times and a higher measurement resolution can be achieved.Due to the more compact structure, it is preferable to use a light beam that can be well focused and also easily parallelized over a longer path. This is possible, for example, with a broadband laser. Example 3 - Example of a measurement on a single layer

[0064] In this example, the measurement of a single layer of a Ta2O5 coating on glass is investigated, which was carried out within the framework of an exemplary variant of the method according to the invention. Fig. The diagram shown in Figure 3 shows the transmission as a function of wavelength for a 65 nm thick layer when the light passes through the substrate once, twice, and three times. When the layer thickness is changed to 66 nm, the signal change is very small, so it would not be visible in the diagram. Therefore, in the Fig. The diagram shown in Figure 4 shows the difference in the measurement signals (transmission at 66 nm - transmission at 65 nm thickness). Line 1 shows a measurement of the difference in the transmission spectra for a single pass, line 2 for two passes, and line 3 for three passes. Typical noise was added to each measurement. This is typically in the range of a few 0.1% of the actual measurement signal. Example 4 - Filter

[0065] In this embodiment, the process for manufacturing a so-called ultra-narrowband filter was simulated. This filter typically has a transmission range of a few to less than one nm. The transmission spectrum of the filter is Fig. 5. Typically, such a filter is made of periodic lambda / 4 layers.

[0066] The filter shown here has the following formula and consists of 53 layers: Glass−(HL)4 12H(LH)8L 12H(LH)8L 12H_(LH)4−air

[0067] The underlined layer 12H (layer no. 45) will be examined in more detail below. Here, H is a high-index lambda / 4 layer and N is a low-index lambda / 4 layer, each at a wavelength of 550 nm. 12H represents a layer twelve times the thickness of the lambda / 4 layer. "^4" represents a fourfold repetition of the layer pair.

[0068] In Fig. Figure 6 shows the signal change when the light passes through layer 45 once, twice, and three times. Layer 45 is the cavity layer with a thickness of 12 times lambda / 4. It can be seen that the signal change is significantly steeper when passing through the layer three times than when the light passes through the layer once or twice. Since the production of the cavity layer depends on the precise setting of the correct layer thickness at the end of the layer, a greater steepness means that the signal change is greater when the light passes through the layer two or three times. This allows the layer thickness to be adjusted more precisely, which is also evident from the illustration in Fig. 7 is shown. Example 5 - Double-sided coating

[0069] The method and the device according to the invention can also be used particularly well for double-sided coating, as described in this example.

[0070] Shown is the transmission measurement of a double-sided coating, which was performed as part of an exemplary variant of the inventive method. A layer stack of the form (HL)^5 is located on both sides, with the lambda / 4 wavelength being 550 nm on the front side and 700 nm on the back side.

[0071] Layer 1: (HL)^550nm on the front or (HL)^700nm on the back.

[0072] In Fig. Two spectra are shown in the diagram shown in Figure 8. One has the exact thickness according to the formula (layer 1), while the second spectrum is calculated by increasing the thickness of the upper and lower layers by 1 nm each, thus: Layer 2: (HL)^550nm + 1nm L on the front or (HL)^700nm + 1nm L on the back.

[0073] The two spectra differ only minimally, so they can hardly be distinguished by measurement.

[0074] In the Fig. The differential signal was evaluated as shown in Figure 9. The difference in transmission values ​​at each wavelength between the two layers was calculated: Differential signal = Transmission (layer 1) - Transmission (layer 2).

[0075] In addition, the multiple passes were also calculated: Difference signal#2=Transmission2(Layer1)−Transmission2(Layer 2). Difference signal#3=Transmission6(Layer1)−Transmission6(Layer 2).

[0076] It now becomes apparent that the most favorable signal change depends on the wavelength. While the difference signal is highest in the wavelength range between 450 and 700 nm with a single pass, it is highest at a wavelength of 1000 nm and above with a double or, even better, a six-fold pass. The difference signal at 450 to 700 nm is too small to be measured with a six-fold pass. Therefore, preselecting the correct spectral range is advisable to obtain the best possible result.

Claims

[1] Method for monitoring coating processes, in which, while a substrate (4, 5) with a substrate plane is subjected to a coating process in which a first side running parallel to the substrate plane and / or a second side of the substrate (4, 5) opposite the first side running parallel to the substrate plane is / are each provided with at least one coating, a) a light beam is emitted onto the substrate (4, 5) and at least partially transmitted through the substrate (4, 5), b) a partial light beam is decoupled from the transmitted light beam, the decoupled partial light beam strikes a sensor (1, 1a) and the transmitted light beam is directed back onto the substrate (4, 5) after the decoupled partial light beam and is again at least partially transmitted through the substrate (4, 5), c) the light beam transmitted in step b) hits a last sensor (1b), d) a spectrum is determined from the light beam striking the last sensor (1b) in step c) and from each partial light beam striking a sensor (1, 1a) in step b), and e) using at least one of the spectra determined - at least one property of the at least one coating of the substrate (4, 5) currently being applied, and / or - at least one property of at least one coating currently being applied to at least one further substrate (4) which is subjected to the same coating process as the substrate, and / or - at least one property of the coating process just carried out is determined. [2] Method according to the preceding claim, characterized bythat step b) is repeated at least once, preferably once to five times, particularly preferably once, twice or three times, before step c), wherein in each of the repetitions a partial light beam is decoupled from the light beam transmitted in the previous pass of step b), the decoupled partial light beam strikes a sensor (1a) which does not correspond to any of the other sensors used in step b), and the transmitted light beam is directed back onto the substrate (4, 5) after the decoupled partial light beam and is again at least partially transmitted through the substrate (4, 5). [3] Method according to one of the preceding claims, characterized by , that - between step a) and step b), and / or - between step b) and step c), and / or - between two passes of step b) the light beam is directed back onto the substrate (4, 5) without coupling out a partial light beam therefrom and is again at least partially transmitted through the substrate (4, 5). [4] Method according to one of the preceding claims, characterized by , that - the at least one property of the at least one coating of the substrate (4, 5) and / or the at least one property of the at least one coating of the at least one further substrate (4) is selected from the group consisting of the layer thickness, the layer thickness gradient, the homogeneity, the refractive index(es) and its spectral dispersion, the wavefront, the phase and its dispersion, the polarization, the surface roughness, the color values, and combinations thereof, and / or - the at least one property of the coating process is selected from the group consisting of the coating rate, the temperature, the particle type, the particle material, the particle size, the particle shape, the particle flow, and combinations thereof. [5] Method according to one of the preceding claims, characterized by that in step e) it is concluded from the at least one determined property of the at least one coating of the substrate (4, 5) and / or from the at least one determined property of the at least one coating of the at least one further substrate (4) and / or from the at least one determined property of the coating process when the coating process is completed. [6] Method according to one of the preceding claims, characterized bythat the light beam emitted onto the substrate (4, 5) in step a) strikes the first or second side of the substrate (4, 5) substantially perpendicular to the substrate plane and is transmitted through the substrate (4, 5). [7] Method according to one of the preceding claims, characterized by that the light beam striking the last sensor (1b) in step c) and each partial light beam striking a sensor (1, 1a) in step b) each have substantially the same intensity. [8] Method according to one of the preceding claims, characterized by that in step b) when coupling out the partial light beam from the transmitted light beam, only at least one specific intensity range and / or at least one specific wavelength range of the transmitted light beam is coupled out. [9] Method according to one of the preceding claims, characterized byin that in step e) the at least one property of the at least one coating of the substrate (4, 5) and / or of the at least one further substrate (4) currently being applied and / or the at least one property of the coating process currently being carried out is determined with the aid of at least one specific wavelength range of the determined spectra, wherein the at least one specific wavelength range is preferably determined by a simulation of the determined spectra carried out before and / or during the coating process. [10] Method according to one of the preceding claims, characterized bythat during the coating process, both the first side and the second side of the substrate (4, 5) are each provided with at least one coating, at least partially simultaneously, wherein in step e) at least one property of the at least one coating currently being applied to the first side of the substrate (4, 5) and / or the at least one further substrate (4) and / or at least one property of the coating process currently being carried out on the first side of the substrate (4, 5) and / or the at least one further substrate (4) is determined using at least one specific first wavelength range of the determined spectra, and at least one property of the at least one coating currently being applied to the second side of the substrate (4,5) and / or of the at least one further substrate (4) and / or at least one property of the coating process just carried out on the second side of the substrate (4, 5) and / or of the at least one further substrate (4) is determined, wherein preferably the at least one specific first wavelength range and / or the at least one specific second wavelength range is determined by a simulation of the determined spectra carried out before and / or during the coating process. [11] Device for monitoring coating processes with a method according to one of the preceding claims, comprising a light source (7) for emitting a light beam onto a substrate (4, 5) having a substrate plane, a first side running parallel to the substrate plane and a second side opposite the first side running parallel to the substrate plane, a beam splitter (8, 8b) for coupling out a partial light beam from a light beam emitted by the light source (7) and at least partially transmitted through the substrate (4, 5), a sensor (1) for receiving light, which is arranged so that the partial light beam coming from the beam splitter (8, 8b) strikes it, a last sensor (1b) for receiving light, which is arranged so that a light beam transmitted several times through the substrate (4, 5) strikes it, and a device (9) for determining spectra of light beams received by the sensors (1, 1a, 1b), wherein - the device comprises a light-guiding device (6) for directing the transmitted light beam coming from the beam splitter (8), from which the partial light beam has been coupled out, onto the substrate (4, 5), or - the beam splitter (8b) is arranged such that the transmitted light beam, from which the partial light beam was coupled out, is directed onto the substrate (4, 5) and transmitted through the substrate (4, 5). [12] Device according to claim 11, characterized by that the device comprises the light-guiding device (6) for directing a transmitted light beam coming from the beam splitter (8) onto the substrate (4, 5), wherein the device additionally at least one further beam splitter (8a) for coupling out a partial light beam, wherein the at least one further beam splitter (8a) is arranged such that a light beam transmitted several times through the substrate (4, 5) impinges on it, at least one further light-guiding device (6a) for directing a multiply transmitted light beam coming from the at least one further beam splitter (8a) onto the substrate (4, 5), wherein the at least one further light-guiding device (6a) is preferably arranged such that the directed light beam strikes the first or second side of the substrate (4, 5) substantially perpendicular to the substrate plane and is at least partially transmitted through the substrate (4, 5), and at least one further sensor (1a) for receiving light, which is arranged so that the partial light beam coming from the at least one further beam splitter (8a) strikes it, wherein preferably the beam splitter (8) for coupling out a partial light beam, the at least one further beam splitter (8a) for coupling out a partial light beam, the light directing device (6) for directing the transmitted light beam coming from the beam splitter (8) onto the substrate (4, 5) and the at least one further light directing device (6a) for directing a multiply transmitted light beam coming from the at least one further beam splitter (8a) onto the substrate (4, 5) are arranged outside a coating chamber for coating the first and / or second side of the substrate (4, 5). [13] Device according to claim 11, characterized by that the beam splitter (8b) is arranged so that the transmitted light beam, from which the partial light beam was coupled out, is directed onto the substrate (4, 5) and transmitted through the substrate (4, 5), wherein the device additionally at least one, preferably one or two, further beam splitters (8c) for coupling out a partial light beam, wherein the at least one further beam splitter (8c) is arranged such that a light beam transmitted multiple times through the substrate (4, 5) impinges on it, and is designed such that the light beam from which the partial light beam was coupled out is directed onto the substrate (4, 5) and at least partially transmitted through the substrate (4, 5), and at least one further sensor (1a) for receiving light, which is arranged so that the partial light beam coming from the at least one further beam splitter (8c) strikes it, wherein preferably the beam splitter (8b) for coupling out a partial light beam and the at least one further beam splitter (8c) for coupling out a partial light beam are arranged within a coating chamber for coating the first and / or second side of the substrate. [14] Device according to claim 13, characterized byin that the device comprises exactly two of the further beam splitters (8c) for coupling out a partial light beam, wherein these two further beam splitters (8c) are arranged and configured such that a light beam transmitted through the substrate (4, 5) is reflected back and forth several times between the two further beam splitters (8c), wherein the light beam, after each reflection at one of the further beam splitters (8c), transmits through the substrate (4, 5) before striking the other of the further beam splitters (8c), and wherein the further beam splitters (8c) are configured such that they couple out a partial light beam of the light beam which strikes the at least one further sensor (1a) only in some of the cases in which the light beam strikes one of them. [15] Device according to one of claims 11 to 14, characterized by , that - the sensors (1, 1a, 1b) have a spectral slit width of at most 5 nm, preferably at most 1 nm, particularly preferably at most 0.5 nm, most preferably at most 0.2 nm, and / or - the sensors (1, 1a, 1b) are broadband sensors, preferably with a measuring range of 190 to 2500 nm, and / or - the sensors (1, 1a, 1b) are arranged outside a coating chamber for coating the first and / or second side of the substrate (4, 5), and / or - the light source (7) is broadband, preferably a broadband laser, a halogen lamp, or a laser-driven arc lamp, preferably with a wavelength range of 190 nm to 2500 nm, and / or - the light source (7) is arranged such that the light beam strikes the first or second side of the substrate (4, 5) substantially perpendicular to the substrate plane and is at least partially transmitted through the substrate, and / or - the light source is arranged outside a coating chamber for coating the first and / or second side of the substrate, and / or - the light-guiding device (6, 6a) is a mirror, and / or - the light-guiding device (6, 6a) is arranged such that the light beam directed onto the substrate (4, 5) strikes the first or second side of the substrate substantially perpendicular to the substrate plane and is at least partially transmitted through the substrate, and / or - the beam splitter (8, 8a) for coupling out a partial light beam from the transmitted light beam is arranged outside or inside a coating chamber for coating the first and / or second side of the substrate (4, 5).

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