Measurement system for measuring a thickness of a layer on a substrate, deposition apparatus, method of measuring a thickness of a layer on a substrate, and method of controlling a thickness of a layer on a substrate

Abstract

A measurement system (100) for measuring a thickness of a layer on a substrate (10) is described. The measurement system (100) includes a holder for holding the substrate (10) or mask. The holder has a measurement opening (111) for providing optical access to a measurement area of the substrate from a backside (110B) of the holder (110). The measurement area comprises a metal film (11). Additionally, the measurement system (100) includes a light source (120) to provide light through the measurement opening to the measurement area (10M). Further, the measurement system (100) includes a detector (130) for detecting reflected light from the measurement area through the measurement opening (111).

Description

MEASUREMENT SYSTEM FOR MEASURING A THICKNESS OF A LAYER ON A SUBSTRATE, DEPOSITION APPARATUS, METHOD OF MEASURING A THICKNESS OF A LAYER ON A SUBSTRATE, AND METHOD OF CONTROLLING A THICKNESS OF A LAYER ON A SUBSTRATETECHNICAL FIELD

[0001] Embodiments of the present disclosure relate to measurement systems for measuring a layer thickness on a substrate. Further embodiments of the present disclosure relate to deposition apparatuses having a layer thickness measurement system. Yet further embodiments relate to methods of measuring layer thickness and methods of controlling layer thickness.BACKGROUND

[0002] For devices comprising thin film layers, such as OLED devices, meticulous control of film thickness is imperative to meet stringent performance specifications and uphold overall quality standards. Particularly in the realm of OLED devices, a thickness repeatability of ±2% between substrates is the established norm, with an escalating demand for even tighter tolerances to achieve superior device performance and elevate overall quality.

[0003] In pursuit of highly accurate thickness control, the ongoing development involves the implementation of in-situ thickness measurement techniques. However, it is essential to acknowledge that existing solutions, such as spectroscopic reflectometry and spectroscopic ellipsometry, exhibit certain limitations.

[0004] Spectroscopic reflectometry encounters limitations in providing the required sensitivity when dealing with ultra-thin layers, specifically those withthicknesses of 20nm or less. This method faces difficulties in accurately discerning the thickness of each individual layer within a multi-layered structure, demanding dedicated measurement spots for precise characterization.

[0005] Spectroscopic ellipsometry offers the capability to measure extremely thin layers, even as thin as 10nm or less, with the necessary sensitivity. However, it comes with the trade-off of requiring a larger system footprint and a more extended measurement duration. While it provides the potential to measure the thickness of individual layers in a multi-layered structure, the process necessitates a larger system size and incurs a time overhead.

[0006] Accordingly, there is a demand for improved measurement systems, improved deposition apparatuses, and improved methods which at least partially overcome one or more of the disadvantages of the state of the art.SUMMARY

[0007] In light of the above, a measurement system for measuring a thickness of a layer on a substrate, a deposition apparatus for depositing material on a substrate, a method of measuring a thickness of a layer on a substrate, and a method of controlling a thickness of a layer on a substrate according to the independent claims are provided. Further aspects, benefits, and features of the present disclosure are apparent from the claims, the description, and the accompanying drawings.

[0008] According to an aspect of the present disclosure, a measurement system for measuring a thickness of a layer on a substrate is provided. The measurement system includes a holder for holding the substrate or a mask. The holder has a measurement opening for providing optical access to a measurement area of the substrate from a backside of the holder. Themeasurement area includes a metal film. Additionally, the measurement system includes a light source to provide light through the measurement opening to the measurement area. Further, the measurement system includes a detector for detecting reflected light from the measurement area through the measurement opening.

[0009] According to another aspect of the present disclosure, a deposition apparatus for depositing material on a substrate is provided. The deposition apparatus, includes a vacuum deposition chamber, a deposition source provided inside the vacuum deposition chamber, and a measurement system according to any embodiments described herein.

[0010] According to a further aspect of the present disclosure, a method of measuring a thickness of a layer on a substrate is provided. The method includes providing a holder holding the substrate or a mask. The substrate has a measurement area comprising a metal film. Additionally, the method includes providing light to the measurement area from a backside of the holder through a measurement opening of the holder. Further, method includes exciting surface plasmon polaritons on the surface of the metal film and detecting light reflected from the measurement area through the measurement opening.

[0011] According to yet another aspect of the present disclosure, a method of controlling a thickness of a layer on a substrate is provided. The method includes depositing a first layer on the substrate. Further, the method includes measuring a first thickness of the first layer by employing the method of measuring a thickness of a layer on a substrate according to any embodiments described herein. Additionally, the method includes conducting a first analysis of the measured first thickness of the first layer, with respect to a deviation from a target layer thickness of the first layer, based on an optical model for the first layer. Further, the method includes feeding the analysis result back to a deposition rate controller for adjusting the deposition rate for a subsequent first layer deposition on a further substrate. Moreover, the method includes updating the optical model based on the analysis result. The updated opticalmodel is used for conducting a second analysis of a measured second thickness of a second layer, with respect to a deviation from a second target layer thickness of the second layer.

[0012] Embodiments are also directed at apparatuses for carrying out the disclosed methods and include apparatus parts for performing each described method aspect. These method aspects may be performed by way of hardware components, a computer programmed by appropriate software, by any combination of the two or in any other manner. Furthermore, embodiments according to the disclosure are also directed at methods for operating the described apparatus. The methods for operating the described apparatus include method aspects for carrying out every function of the apparatus.BRIEF DESCRIPTION OF THE DRAWINGS

[0013] So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments. The accompanying drawings relate to embodiments of the disclosure and are described in the following:

[0014] FIG. 1 shows a schematic sectional view of a measurement system according to embodiments of the present disclosure;

[0015] FIG. 2 shows a top view of FIG.1 ;

[0016] FIG. 3 shows a schematic sectional view of a measurement system according to further embodiments of the present disclosure;

[0017] FIG. 4A-4C show schematic sectional top views of a deposition apparatus for depositing material on a substrate according to embodiments of the present disclosure;

[0018] FIGS. 5A-5C show schematic top views of various configurations and arrangements of the light source and the detectors of the measurement system according to embodiments of the present disclosure;

[0019] FIG. 6 shows a block diagram for illustrating a method of measuring a thickness of a layer on a substrate according to embodiments of the present disclosure; and

[0020] FIG. 7 shows a block diagram for illustrating a method of controlling a thickness of a layer on a substrate according to embodiments of the present disclosure.DETAILED DESCRIPTION OF EMBODIMENTS

[0021] Reference will now be made in detail to the various embodiments, one or more examples of which are illustrated in each figure. Each example is provided by way of explanation and is not meant as a limitation. For example, features illustrated or described as part of one embodiment can be used on or in conjunction with any other embodiment to yield yet a further embodiment. It is intended that the present disclosure includes such modifications and variations.

[0022] Within the following description of the drawings, the same reference numbers refer to the same or to similar components. Generally, only the differences with respect to the individual embodiments are described. Unless specified otherwise, the description of a part or aspect in one embodiment can apply to a corresponding part or aspect in another embodiment as well.

[0023] With exemplary reference to FIG. 1 , a measurement system 100 for measuring a thickness of a layer on a substrate 10 according to embodiments of the present disclosure is described. According to embodiments, which can be combined with other embodiments described herein, the measurement system 100 includes a holder 110 for holding the substrate 10. Typically, thesubstrate 10 is provided on a front side 110F of the holder 110. In particular, a backside 10B of the substrate 10 is at least partially in contact with the front side 110F of the holder 110. As exemplarily shown in FIGS. 1 and 2, the holder 110 has a measurement opening 111 for providing optical access to a measurement area 10M of the substrate from a backside 110B of the holder 110. The measurement area 10M of the substrate includes a metal film 11. Typically, the metal film 11 is provided on the front side 10F of the substrate 10. Accordingly, as shown in FIGS. 1 and 2, typically the substrate 10 at least partially covers the measurement opening 111. Additionally, the measurement system 100 includes a light source 120 to provide light through the measurement opening 111 to the measurement area 10M. Further, the measurement system 100 includes a detector 130 for detecting reflected light from the measurement area through the measurement opening 111. An exemplary light path 122 from the light source 120 to the detector 130 is indicated in FIG.1 .

[0024] Accordingly, compared to the state of the art, an improved measurement system is provided. In particular, the measurement system according to embodiments described herein is beneficially configured for measuring and monitoring layer thickness on a substrate by surface plasmon resonance. Further, the measurement system has the advantage that the thickness of a layer can be measured and monitored in real-time during material deposition on the substrate.

[0025] Surface plasmon resonance (SPR) is a phenomenon that occurs when surface plasmons oscillate in response to the interaction with electromagnetic waves at the interface between a dielectric (e.g. glass) and a metal film, particularly a thin metal film. When light strikes a metal-dielectric interface at a specific angle (known as the resonance angle), it can excite surface plasmon polaritons on the metal surface. When electromagnetic waves internally reflect at any interface, they create an evanescent wave that extends into the adjacent medium. An evanescent wave does not propagateas electromagnetic wave and decays exponentially with distance from the interface. FIG. 1 schematically indicates the surface plasmon 12 and the evanescent wave 13. The evanescent wave penetrates a short distance into the medium adjacent to the metal surface and propagates to the interface plane for a short distance. Therefore the evanescent wave can be coupled with surface plasmons resulting in excitation of surface plasmon polaritons under specific conditions. The coupling condition is highly sensitive to changes in the refractive indices and the thickness in the medium where the evanescent wave exists. When molecules attach to the metal surface, the refractive indices and the thickness change, leading to alterations in the characteristics of the surface plasmon resonance. By monitoring the changes in the characteristics of surface plasmon resonance, such as changes in intensity at certain angle(s) and wavelength(s), it is possible to detect and quantify interactions at the metal-dielectric interface. The changes in the characteristics of the surface plasmon resonance can be detected by analyzing the light reflected from the metal film.

[0026] In the present disclosure, a "measurement system for measuring a thickness of a layer on a substrate" can be understood as a system configured to measure and determine a thickness of a layer deposited on a substrate surface. In particular, the measurement system as described herein is configured to measure and monitor a thickness of a layer in real-time during layer deposition, particularly by using SPR. In other words, the measurement system is configured to exploit the SPR phenomenon for the determination of a film thickness on a substrate.

[0027] In the present disclosure, a "substrate" can be understood as a material or object onto which some form of processing, treatment, or material deposition is applied. In particular, the substrate can be a large area substrate as described herein. Typically, the substrate is of transparent material, e.g. transparent glass or transparent plastic.

[0028] According to embodiments, which can be combined with other embodiments described herein, the substrate thickness can be from 0.1 to 1 .8 mm. For example, the substrate thickness can be about 0.9 mm or below, such as 0.5 mm. The term “substrate” as used herein may particularly embrace substantially inflexible substrates, e.g., a glass plate, a plastic plate or other suitable substrates. However, the present disclosure is not limited thereto and the term “substrate” may also embrace flexible substrates such as a web or a foil. The term “substantially inflexible” is understood to distinguish over “flexible”. Specifically, a substantially inflexible substrate can have a certain degree of flexibility, e.g. a glass plate having a thickness of 0.9 mm or below, such as 0.5 mm or below, wherein the flexibility of the substantially inflexible substrate is small in comparison to the flexible substrates.

[0029] In the present disclosure, a "holder for holding a substrate or a mask" can be understood as a tool, fixture, or platform configured to securely support a substrate during substrate processing. Typically, the holder ensures stability, protection, and proper positioning of the substrate during processing, e.g. layer deposition. It is to be understood that the holder can be configured for holding a large area substrate as described herein. The holder may also be referred to as substrate holder. The substrate holder can include an electrostatic chuck (E-chuck) providing an electrostatic force for holding the substrate, particularly at a substrate support surface of the holder, e.g. the front side 110F of the holder 110 shown in FIG. 1 . For example, the substrate holder may include an electrode arrangement configured to provide an attracting force acting on the substrate. Typically, the holder 110 is configured for holding the substrate 10 or a mask during material deposition in a substantially vertical orientation. A “substantially vertical orientation” of the substrate or the mask can be understood in that the orientation of the substrate or the mask is vertical within a tolerance T of T < ±15°, particularly T < ±10°, from the perfect vertical orientation. Alternatively, the holder can be configured holding a substrate or a mask during material deposition in a substantially horizontal orientation. A “substantially horizontal orientation” of the substrate or the mask can beunderstood in that the orientation of the substrate or the mask is horizontal within a tolerance T of T < ±15°, particularly T < ±10°, from the perfect horizontal orientation. According to an example, the holder can be a carrier. A carrier is typically configured for transporting an object, e.g. a substrate or a mask. A holder does typically not travel within a processing system. Accordingly, a substrate holder or mask holder stays in the process chamber (at least for a certain period), whereas a carrier travels with the substrate / mask within the processing system. According to an example, the mask holder can include magnets for attracting a metal mask which is provided in front of the substrate, whereas the mask holder with the magnets is arranged behind the substrate. Accordingly, the mask holder may be configured for contactless holding a metal mask by magnetic forces. Embodiments described herein particularly relate to deposition of materials, e.g. for display manufacturing on large area substrates. According to some embodiments, large area substrates or holders supporting one or more substrates may have a size of 0.5 m2or larger, particularly of 1 m2or larger. For instance, the deposition system may be adapted for processing large area substrates, such as substrates of GEN 4.5, which corresponds to about 0.67 m2of substrate (0.73x0.92m), GEN 5, which corresponds to about 1.4 m2substrates (1.1 m x 1.3 m), GEN 6, which corresponds to about 2.7 m2(1.5 m x about 1.8 m), GEN 7.5, which corresponds to about 4.29 m2substrates (1.95 m x 2.2 m), GEN 8.5, which corresponds to about 5.7 m2substrates (2.2 m x 2.5 m), or even GEN 10, which corresponds to about 8.7 m2substrates (2.85 m x 3.05 m). Even larger generations such as GEN 11 and GEN 12 and corresponding substrate areas can similarly be implemented. According to yet further implementations, half sizes of the above-mentioned substrate generations can be processed.

[0030] In the present disclosure, a "measurement opening of the holder " can be understood as a specific aperture (intentionally) provided and positioned within the holder to allow optical access to a measurement area of the substrate. The term "optical access" indicates that the measurement opening allows light to reach the measurement area of the substrate. Typically,a size of the measurement opening is less than 10%, particularly less than 5%, more particularly less than 2.5%, of a total size of the holder. FIG. 2 shows a non-limiting example in which the measurement opening 111 is provided at an edge portion of the holder 110. An edge portion of the holder can be understood as the outer 20%, particularly outer 15%, more particularly the outer 10%, of the holder 110. As exemplarily shown in FIG. 2, the measurement opening 111 may have an open lateral side towards the edge of the holder 110. However, also not explicitly shown, it is to be understood that the measurement opening 111 can have a closed opening edge.

[0031] In the present disclosure, a "measurement area of the substrate" can be understood as a specific region or portion of the substrate that is the focus of optical measurements. In particular, the measurement area is the part of the substrate for which optical access is provided through the measurement opening in the holder. The measurement area includes a metal film, particularly configured for SPR. Typically, the metal film is a thin metal film with a film thickness T of T < 80 nm, particularly 5 nm < T < 50 nm. For instance, the metal film can be of gold, silver, aluminum, or other metals suitable for SPR.

[0032] In the present disclosure, a "detector for detecting reflected light" can be understood as a device configured for detecting light. In particular, typically the detector is configured for capturing and analyzing changes of specific wavelength(s) and / or incident angle(s) and / or intensity of light, particularly light reflected from the metal film 11 as described herein. It is to be understood that after interacting with the metal film, the reflected light carries information about the SPR phenomenon. The detector captures reflected light, transforming the captured light into an electrical signal. Typically, the parameters monitored are the intensity of the reflected light at specific wavelength(s) and / or incident angle(s). Changes in these parameters correspond to variations in the refractive indices and the thickness of the layers coated on the metal surface of the metal film.

[0033] With exemplary reference to FIG. 3, according to embodiments, which can be combined with other embodiments described herein, the measurement system 100 includes an optical coupling element 140, particularly a prism, provided in a light path 122 between the light source 120 and the detector 130. In the present disclosure, an “optical coupling element” can be understood as an optical component that is used to facilitate the coupling of light into the metal film on the substrate, leading to the excitation of surface plasmon polaritons. Instead of a prism alternative optical coupling elements or configurations involving gratings, fibers, or waveguides, may be used to achieve the coupling effect.

[0034] According to embodiments, which can be combined with other embodiments described herein, the optical coupling element 140 is at least partially arranged within the measurement opening 111 , as exemplarily shown in FIGS. 1 and 3. Typically, the optical coupling element 140 is attached and / or connected to the holder 110.

[0035] According to embodiments, which can be combined with other embodiments described herein, the measurement system 100 includes a polarizer 121 , provided in the light path 122 between the light source 120 and the measurement area l OM. In particular, the polarizer 121 is a linear polarizer. A “polarizer” can be understood as an optical device that selectively transmits light waves oscillating in a specific direction while absorbing or blocking light waves oscillating in other directions. A “linear polarizer” is a type of polarizer that selectively transmits light waves oscillating in a specific linear direction. In the context of SPR, a polarizer, particularly a linear polarizer, may be used to control the polarization state of incident light. In particular, the polarizer is used to gain p-polarized light (parallel to the incident plane). The p component fulfills the condition to excite surface plasmon polaritons.

[0036] With exemplary reference to FIG. 3, according to embodiments, which can be combined with other embodiments described herein, the light source 120 and the detector 130 can be arranged within an atmospheric box150. In the present disclosure, an “atmospheric box” can be understood as an enclosed volume or space in which atmospheric conditions, particularly atmospheric pressure conditions, are provided and / or can be controlled. Typically, the atmospheric box 150 has a first transparent portion 151 for allowing light emitted from the light source 120 to exit the atmospheric box 150. Further, the atmospheric box 150 typically has a second transparent portion 152 for allowing light reflected from the measurement area 10M to enter the atmospheric box 150 towards the detector 130. Alternatively, the atmospheric box 150 may have a first fiber optic vacuum feedthrough in which a first optical fiber is provided for allowing light emitted from the light source 120 to exit the atmospheric box 150. Further, the atmospheric box 150 can have a second fiber optic vacuum feedthrough in which a second optical fiber is provided for allowing light reflected from the measurement area 10M to enter the atmospheric box 150 towards the detector 130.

[0037] According to embodiments, which can be combined with other embodiments described herein, the atmospheric box 150 is attached or connected to the holder 110, particularly to the backside 110B of the holder 110, as exemplarily shown in FIGS. 3 and 4A. Alternatively, the atmospheric box 150 can be attached or connected to a wall of a vacuum deposition chamber 210 as exemplarily shown in FIGS 4B and 4C. According to another alternative configuration, the atmospheric box 150 can be attached a structure inside the vacuum deposition chamber 210, which may have some advantages with respect to adjustment and positioning. FIG. 4B shows an example in which the atmospheric box 150 is attached or connected to an interior side of a wall of a vacuum deposition chamber 210. FIG. 4B shows an example in which the atmospheric box 150 is attached or connected to an exterior side of a wall of a vacuum deposition chamber 210.

[0038] FIGS. 5A-5C show schematic top views of various configurations and arrangements of the light source and the detector of the measurement system according to embodiments.

[0039] FIG. 5A shows an exemplary configuration with a single light source 120, particularly with a linear polarizer 121 , and a single detector 130.

[0040] According to embodiments, which can be combined with other embodiments described herein, the light source 120 is a VIS-NIR light source. In particular, the VIS-NIR light source is configured for providing light in the visible wavelength spectrum and the near infrared wavelength spectrum. For instance, the VIS-NIR light source can be configured for providing light with a wavelength A of 380 nm < A < 3000 nm. Accordingly, the detector 130 may be a VIS-NIR spectrometer configured for detecting light in the visible wavelength spectrum and the near infrared wavelength spectrum. For instance, the VIS- NIR spectrometer can be configured for detecting light with a wavelength A of 380 nm < A < 3000 nm.

[0041] With exemplary reference to FIG. 5B, according to embodiments, which can be combined with other embodiments described herein, the light source 120 may include a first light source 120A and a second light source 120B. Typically, the first light source 120A is configured for providing light with a first wavelength range. The second light source 120B can be configured for providing light with a second wavelength range which is at least partially different from the first wavelength range. At the exit of the first light source 120A a first linear polarizer 121 A can be provided. At the exit of the second light source 120B a second linear polarizer 121 B can be provided. Typically, the optical properties of the first linear polarizer 121 A are different from the optical properties of the second linear polarizer 121 B.

[0042] According to embodiments, which can be combined with other embodiments described herein, the detector 130 may include a first detector 130A and a second detector 130B, as exemplarily shown in FIG. 5B. Typically, the first detector 130A is configured for detecting light from the first light source 120A. The second detector 130B is typically configured for detecting light from the second light source 120B. It is to be understood, that the light source(s) and the detector(s) are supposed to be placed to have appropriate incidentangle(s) to observe SPR depending on the wavelength(s) or the wavelength range(s) and the refractive indices of the layers.

[0043] It is to be understood, that typically the first light source 120A and the first detector 130A provide a first optical measurement arrangement and the second light source 120B and the second detector 130B provide a second optical measurement arrangement.

[0044] With exemplary reference to FIG. 5C, according to embodiments, which can be combined with other embodiments described herein, the light source 120 may include an array 125 of three or more light sources. In particular, the three or more light sources of the array 125 can be lasers. Typically, the one or more of the lasers are configured for providing light with a different wavelength compared to the other lasers. Typically, each laser of the array 135 of lasers is configured for providing light with a different wavelength compared to the other lasers.

[0045] According to embodiments, which can be combined with other embodiments described herein, the detector 130 may include an array 135 of three or more detectors, as exemplarily shown in FIG. 5C, for detecting the light of the array 125 of the three or more light sources. Typically, the three or more detectors are photodiodes configured for detecting the light of the three or more lasers.

[0046] With exemplary reference to FIGS. 4A to 4C, a deposition apparatus 200 for depositing material on a substrate 10 according to embodiments of the present disclosure is described. According to embodiments, which can be combined with other embodiments described herein, the deposition apparatus 200 includes a vacuum deposition chamber 210, a deposition source 220 provided inside the vacuum deposition chamber 210, and a measurement system 100 according to any embodiments described herein.

[0047] The deposition apparatus 200 may also be referred to as a vacuum deposition apparatus. The vacuum deposition apparatus can be understood as an apparatus or configured for vacuum deposition of organic or inorganic materials including metallic materials, particularly for display manufacturing, e.g. for OLED display manufacturing.

[0048] In the present disclosure, a "vacuum deposition chamber" can be understood as a chamber configured for vacuum deposition. The term "vacuum", as used herein, can be understood in the sense of a technical vacuum having a vacuum pressure of less than, for example, 10 mbar. Typically, the pressure in a vacuum chamber as described herein may be between 10’5mbar and about 10’8mbar, particularly between 10’5mbar and 10-7mbar.

[0049] In the present disclosure, a “deposition source” can be understood as an arrangement or an assembly configured for material deposition on a substrate as described herein. In other words, the deposition source is configured for providing a source of material to be deposited on the substrate. For instance, the deposition source may have one or more crucibles configured to evaporate the source material to be deposited. A "crucible" can be understood as a device having a reservoir for the material to be evaporated by heating the crucible. Accordingly, a "crucible" can be understood as a source material reservoir, which can be heated to evaporate the source material into a gas by at least one of evaporation and sublimation of the source material. The crucible can include a heater to evaporate the source material in the crucible into a gaseous source material. For instance, initially the material to be evaporated can be in the form of a powder or a grain. The reservoir can have an inner volume for receiving the source material to be evaporated, e.g. organic or inorganic materials, e.g. metallic materials.

[0050] Further, the deposition source can have one or more distribution assemblies or distribution pipes configured for providing the evaporated material towards the substrate. For instance, a distribution tube or distributionpipe as described herein may provide a line source with a plurality of openings and / or nozzles which are arranged in lines along the length of the distribution tube. Accordingly, the distribution assembly can include a linear distribution showerhead, for example, having a plurality of openings, particularly nozzles (or an elongated slit) disposed therein. A showerhead as understood herein can have an enclosure, hollow space, or tube, in which the evaporated material can be provided or guided, for example from the evaporation crucible to the substrate. According to embodiments which can be combined with any other embodiments described herein, the length of the distribution pipe may correspond at least to the height of the substrate to be deposited. In particular, the length of the distribution pipe may be longer than the height of the substrate to be deposited, at least by 10% or even 20%. Accordingly, a uniform deposition at the upper end of the substrate and / or the lower end of the substrate can be provided. For instance, the source material to be deposited may be an organic or inorganic material, e.g. a metallic material, for use as electrode materials or electron transport layer materials in organic light emitting diode (OLED) production.

[0051] According to embodiments which can be combined with any other embodiments described herein, the deposition apparatus is configured for material deposition in a substantially vertical orientation of the substrate. Accordingly, typically the vacuum deposition chamber 210 and the deposition source 220 are configured for material deposition on a substantially vertically arranged substrate 10. Accordingly, it is to be understood that the holder 110 holding the substrate 10 or a mask during material deposition is typically also configured for holding the substrate or the mask in a substantially vertical orientation.

[0052] With exemplary reference to FIG. 4C, according to embodiments, which can be combined with other embodiments described herein, the vacuum deposition chamber 210 may include a window 211 . The light source 120 and the detector 130 can be arranged outside of the vacuum deposition chamber210. In particular, the light source 120 is arranged to provide light through the window 211 to the measurement area 10M of the substrate 10. The detector 130 is arranged to detect reflected light from the measurement area 10M through the window 211. Alternatively, instead of a window, the vacuum deposition chamber 210 may be provided with fiber optic vacuum feedthroughs in which optical fibers are provided for sending light from the light source 120 to the measurement area 10M and receiving reflected light from the measurement area 10M by the detector 130, respectively. When the light source 120 and the detector 130 are arranged outside of the vacuum deposition chamber 210, it is to be understood that the atmospheric box 150 may be omitted (indicated by the dotted line in FIG. 4C), particularly when there are atmospheric conditions outside of the vacuum deposition chamber 210.

[0053] With exemplary reference to the block diagram shown in FIG. 6, a method 300 of measuring a thickness of a layer on a substrate 10 according to embodiments of the present disclosure is described. According to embodiments, which can be combined with other embodiments described herein, the method 300 includes providing a holder 110 (represented by block 310 in FIG. 6), wherein the holder 110 holds the substrate 10. The substrate 10 has a measurement area 10M including a metal film 11. Additionally, the method 300 includes providing light (represented by block 320 in FIG. 6) to the measurement area 10M from a backside 110B of the holder 110 through a measurement opening 111 of the holder 110. Further, the method 300 includes exciting (represented by block 330 in FIG. 6) surface plasmon polaritons on the surface of the metal film 11 . Moreover, the method 300 includes detecting light (represented by block 340 in FIG. 6) reflected from the measurement area 10M through the measurement opening 111.

[0054] Typically, the method 300 includes analyzing the detected light (represented by block 350 in FIG. 6) by using an optical model to determine the thickness of the layer. The analysis of the detected light based on theoptical model is typically conducted by a computer 160, as schematically indicated in FIG. 3.

[0055] With exemplary reference to the block diagram shown in FIG. 7, a method 400 of controlling a thickness of a layer on a substrate 10 according to embodiments of the present disclosure is described. According to embodiments, which can be combined with other embodiments described herein, the method 400 includes depositing (represented by block 410 in FIG. 7) a first layer on the substrate 10. Further, the method 400 includes measuring (represented by block 420 in FIG. 7) a first thickness of the first layer by employing the method 300 of measuring a thickness of a layer on a substrate 10 according to any embodiments described herein. Additionally, the method 400 includes conducting a first analysis (represented by block 430 in FIG. 7) of the measured first thickness of the first layer with respect to a deviation from a target layer thickness of the first layer, based on an optical model 415 for the first layer. Further, the method 400 includes feeding (represented by block 440 in FIG. 7) the analysis result back to a deposition rate controller for adjusting the deposition rate for a subsequent first layer deposition (represented by block 460 in FIG.7) on a further substrate. Moreover, the method 400 includes updating (represented by block 450 in FIG. 7) the optical model based on the analysis result. The updated optical model 415’ can be used for conducting a second analysis (represented by block 431 in FIG. 7) of a measured second thickness of a second layer with respect to a deviation from a second target layer thickness of the second layer.

[0056] According to embodiments, which can be combined with other embodiments described herein, the method 400 may include depositing (represented by block 411 in FIG. 7) a second layer on the substrate 10. Further, the method 400 may include measuring (represented by block 421 in FIG. 7) a second thickness of the second layer by employing the method 300 of measuring a thickness of a layer on a substrate 10 according to any embodiments described herein. Additionally, the method 400 can includeconducting a second analysis (represented by block 431 in FIG. 7) of the measured second thickness of the second layer with respect to a deviation from a target layer thickness of the second layer based on the updated optical model 415’ for the second layer. Further, the method 400 includes feeding (represented by block 441 in FIG. 7) the analysis result of the second layer back to the deposition rate controller for adjusting the deposition rate for a subsequent second layer deposition (represented by block 461 in FIG.7) on the further substrate. Moreover, the method 400 includes updating (represented by block 451 in FIG. 7) the optical model used for the second layer based on the analysis result of the second layer. The updated optical model 415” can be used for conducting a third analysis (represented by block 432 in FIG. 7) of a measured third thickness of a third layer with respect to a deviation from a third target layer thickness of the third layer.

[0057] It is to be understood depending on the number of layers to be provided on the substrate, that the method steps as outlined above for the first layer and the second layer, can be repeated for each further layer. For instance, in the case of three layers, the method 400 may include depositing (represented by block 412 in FIG. 7) a third layer on the substrate 10. Further, the method 400 may include measuring (represented by block 422 in FIG. 7) a third thickness of the third layer by employing the method 300 of measuring a thickness of a layer on a substrate 10 according to any embodiments described herein. Additionally, the method 400 can include conducting a third analysis (represented by block 432 in FIG. 7) of the measured third thickness of the third layer with respect to a deviation from a target layer thickness of the third layer based on the updated optical model 415” for the third layer. Further, the method 400 includes feeding (represented by block 442 in FIG. 7) the analysis result of the third layer back to the deposition rate controller for adjusting the deposition rate for a subsequent third layer deposition (represented by block 462 in FIG.7) on the further substrate. In the case of a fourth layer, the method may further include updating the optical model used for the third layer based on the analysis result of the third layer. Said updatedoptical model can be used for conducting a fourth analysis of a measured fourth thickness of a fourth layer with respect to a deviation from a fourth target layer thickness of the third layer.

[0058] Accordingly, in view of the embodiments describe herein, it is to be understood that compared to the state of the art, an improved measurement system, an improved deposition apparatus, an improved method of measuring a thickness of a layer on a substrate, and an improved method of controlling a thickness of a layer are provided. In particular, embodiments disclosed herein offer distinct advantages, specifically by measuring the surface plasmon resonance (SPR) effect on one or more dedicated spot(s) on the substrate, to assess the thickness of the deposited layer through optical modeling. Further, the measurement can be conducted from the backside of the substrate. It is to be understood that through the use of an appropriate combination and / or range of wavelengths and incident angles in the measurement system, it becomes feasible to detect deviations with a control precision of ±1 %, even for layers as thin as 10nm. Further embodiments described herein provide for the capability to measure layer deposition on the molecular level, such that extremely thin layers can be measured, and the measurement is not limited to layers with sufficient thickness. A further advantage is that it is possible to use one measurement area, particularly one measurement point or location, for layers of a layer stack subsequently deposited. As described herein, the measurement components can be coupled to the holder, such that no additional space within the deposition chamber is needed. Further, the measurement requires no additional time, since the measurement can be carried out during deposition and / or during deposition source rotation / change and / or substrate transportation. Further, as described herein, optical modules (excluding the optical coupling element, e.g. the prism) can be positioned inside or outside the deposition chamber.

[0059] While the foregoing is directed to embodiments of the disclosure, other and further embodiments of the disclosure may be devised withoutdeparting from the basic scope thereof, and the scope thereof is determined by the claims that follow.

[0060] In particular, this written description uses examples to disclose the disclosure, including the best mode, and also to enable any person skilled in the art to practice the described subject-matter, including making and using any devices or systems and performing any incorporated methods. While various specific embodiments have been disclosed in the foregoing, mutually non-exclusive features of the embodiments described above may be combined with each other. The patentable scope is defined by the claims, and other examples are intended to be within the scope of the claims if the claims have structural elements that do not differ from the literal language of the claims, or if the claims include equivalent structural elements with insubstantial differences from the literal language of the claims.

Claims

WHAT IS CLAIMED:1 . A measurement system (100) for measuring a thickness of a layer on a substrate (10), comprising:- a holder (110) for holding the substrate (10) or a mask, wherein the holder has a measurement opening (111 ) for providing optical access to a measurement area (10M) of the substrate from a backside (110B) of the holder (110), wherein the measurement area (10M) comprises a metal film (11 );- - a light source (120) to provide light through the measurement opening (111 ) to the measurement area (10M); and- a detector (130) for detecting reflected light from the measurement area (10M) through the measurement opening (111 ).

2. The measurement system (100) of claim 1 , further comprising an optical coupling element (140), particularly a prism, provided in a light path between the light source (120) and the detector (130).

3. The measurement system (100) of claim 2, wherein the optical coupling element (140) is at least partially arranged within the measurement opening (111 ).

4. The measurement system (100) of any of claims 1 to 3, further comprising a polarizer (121 ), particularly a linear polarizer, provided in a light path between the light source (120) and the measurement area (10M).

5. The measurement system (100) of any of claims 1 to 4, wherein the light source (120) is a VIS-NIR light source, particularly configured for providing light with a wavelength A of 380 nm < A < 3000 nm, and wherein the detector (130) is a VIS-NIR spectrometer, particularlyconfigured for detecting light with a wavelength A of 380 nm < A < 3000 nm.

6. The measurement system (100) of any of claims 1 to 4, wherein the light source (120) comprises a first light source (120A) and a second light source(120B), wherein the first light source (120A) is configured for providing light with a first wavelength range, and wherein the second light source (120B) is configured for providing light with a second wavelength range at least partially different from the first wavelength range, and wherein the detector (130) comprises a first detector (130A) for detecting light from the first light source (120A) and a second detector (130B) for detecting light from the second light source (120B).

7. The measurement system (100) of any of claims 1 to 4, wherein the light source (120) comprises an array (125) of three or more light sources, particularly the three or more light sources being lasers with different wavelengths, and wherein the detector (130) comprises an array (135) of three or more detectors, particularly the three or more detectors photodiodes configured for detecting the light of the lasers.

8. The measurement system (100) of any of claims 1 to 7, wherein the light source (120) and the detector (130) are arranged within an atmospheric box (150), particularly wherein the atmospheric box (150) has a first transparent portion (151 ) for allowing light emitted from the light source (120) to exit the atmospheric box (150), and particularly wherein the atmospheric box (150) has a second transparent portion (152) for allowing light reflected from the measurement area (10M) to enter the atmospheric box (150) towards the detector (130).

9. The measurement system (100) of any of claims 1 to 7, wherein the light source (120) and the detector (130) are arranged within an atmospheric box (150), and wherein the atmospheric box (150) has a first fiber opticvacuum feedthrough in which a first optical fiber is provided for allowing light emitted from the light source (120) to exit the atmospheric box (150), and wherein the atmospheric box (150) has a second fiber optic vacuum feedthrough in which a second optical fiber is provided for allowing light reflected from the measurement area (10M) to enter the atmospheric box (150) towards the detector (130).

10. The measurement system (100) of claim 8 or 9, wherein the atmospheric box (150) is attached to the holder (110).11 . The measurement system (100) of any of claims 7 to 10, wherein the atmospheric box (150) is attached to a wall of a vacuum deposition chamber (210) or to a structure inside the vacuum deposition chamber(210).

12. A deposition apparatus (200) for depositing material on a substrate (10), comprising:- a vacuum deposition chamber (210)- a deposition source (220) provided inside the vacuum deposition chamber (210); and- a measurement system (100) according to any of claims 1 to 11 .

13. The deposition apparatus (200) of claim 12, wherein the vacuum deposition chamber (210) comprises a window (211 ), and wherein the light source (120) and the detector (130) are arranged outside of the vacuum deposition chamber (210), wherein the light source (120) is arranged to provide light through the window (211 ) to the measurement area (10M), and wherein the detector (130) is arranged to detect reflected light from the measurement area (10M) through the window(211 ).

14. A method (300) of measuring a thickness of a layer on a substrate, comprising:- providing (310) a holder (110) holding the substrate (10) or a mask, wherein the substrate (10) has a measurement area (10M) comprising a metal film (11 );- providing (320) light to the measurement area (10M) from a backside (110B) of the holder (110) through a measurement opening (111 ) of the holder (110);- exciting (330) surface plasmon polaritons on the surface of the metal film (11 ), and- detecting (340) light reflected from the measurement area (10M) through the measurement opening (111 ).

15. The method (300) of claim 14, further comprising using a measurement system (100) according to any of claims 1 to 11 .

16. A method (400) of controlling a thickness of a layer on a substrate, comprising:- depositing (410) a first layer on the substrate (10);- measuring (420) a first thickness of the first layer by employing the method according to claims 14 or 15;- conducting a first analysis (430) of the measured first thickness of the first layer with respect to a deviation from a target layer thickness of the first layer based on an optical model for the first layer;- feeding (440) the analysis result back to a deposition rate controller for adjusting the deposition rate for a subsequent first layer deposition (460) on a further substrate; and- updating (450) the optical model based on the analysis result, the updated optical model being used for conducting a second analysis (431 ) of a measured second thickness of a second layer with respect to a deviation from a second target layer thickness of the second layer.

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