WO2020025102A1

WO2020025102A1 - Method of coating a flexible substrate with a stack of layers, layer stack, and deposition apparatus for coating a flexible substrate with a stack of layers

Info

Publication number: WO2020025102A1
Application number: PCT/EP2018/070603
Authority: WO
Inventors: Christian NICK; Torsten Bruno Dieter; Thomas Deppisch
Original assignee: Applied Materials, Inc.
Priority date: 2018-07-30
Filing date: 2018-07-30
Publication date: 2020-02-06
Also published as: WO2020025153A1; CN112513318A

Abstract

A method of coating a flexible substrate (10) with a stack of layers is described. The method includes providing an initial deposition on the flexible substrate by depositing a first portion (B1) of a second material (B) while guiding the flexible substrate in a forward direction (FD). Additionally, the method includes providing one or more subsequent depositions including depositing a second portion (B2) of the second material (B) and depositing a first portion (A1) of a first material (A) while guiding the flexible substrate in a backward direction (BD). Further, the method includes depositing a second portion (A2) of the first material (A) and depositing a first portion (B1) of the second material (B) while guiding the flexible substrate in the forward direction (FD). Moreover, a layer stack and a deposition apparatus for coating a flexible substrate with a stack of layers are described.

Description

METHOD OF COATING A FLEXIBLE SUBSTRATE WITH A STACK OF LAYERS, LAYER STACK, AND DEPOSITION APPARATUS FOR COATING A FLEXIBLE SUBSTRATE WITH A STACK OF LAYERS

TECHNICAL FIELD [0001] Embodiments of the disclosure relate to thin- film deposition apparatuses and methods, particularly to apparatuses and methods for coating flexible substrates with a stack of thin layers, particularly in roll-to-roll (R2R) deposition systems. In particular, of the disclosure relate to apparatuses and methods for coating a flexible substrate with a stack of layers for thin-film solar cell production, thin-film battery production, and flexible display production.

BACKGROUND

[0002] Processing of flexible substrates, such as plastic films or foils, is in high demand in the packaging industry, semiconductor industries and other industries. Processing may consist of coating a flexible substrate with a material, such as a metal, a semiconductor and a dielectric material, etching and other processing actions conducted on a substrate for the respective applications. Systems performing this task generally include a coating drum, e.g. a cylindrical roller, coupled to a processing system with a roller assembly for transporting the substrate, and on which at least a portion of the substrate is coated. Roll-to-roll (R2R) coating systems can provide a high throughput.

[0003] Therein, a coating process such as a CVD process or a PVD process, particularly a sputter process, can be utilized for depositing thin layers onto flexible substrates. Roll-to-roll deposition systems are understood in that a flexible substrate of a considerable length, such as one kilometre or more, is uncoiled from a storage spool, coated with a stack of thin layers, and recoiled again on a wind-up spool. In the manufacture of thin film batteries as well as in the display industry and the photovoltaic (PV) industry, roll-to-roll deposition systems are in high demand. In particular, the increasing demand for flexible touch panel elements, flexible displays, and flexible PV modules results in an increasing demand for depositing suitable layers, particularly layer stacks, in R2R-coaters. [0004] The functionality of devices produced in roll-to-roll deposition systems typically depends on the quality, e.g. the homogeneity of thickness, of the layers deposited on the flexible substrate. For obtaining high-quality flexible devices, technical challenges with respect to the deposition of coating materials need to be mastered. In particular, depositing layer stacks with layers of different materials is challenging due to different material properties of the different materials for which deposition conditions, e.g. temperature and pressure, have to be adapted in order to achieve optimal coating results.

[0005] Further, it is to be noted that there are some coating materials for which the deposition process is more sensitive as compared to other coating materials. For instance, typically for depositing sensitive coating materials, extra time for process stabilization is needed, e.g. for achieving constant deposition conditions of the employed sputter deposition sources. In this regard, it is to be noted that switching deposition sources off and on, e.g. cathodes of sputter sources, increases the risk of particle generation which can have a negative effect on the deposition result, i.e. the quality of the deposited layer. Further, depositing subsequent layers of different materials in a roll-to-roll process may involve heating and cooling for adjusting the deposition conditions for the different materials to be deposited. Typically, heating and cooling generates thermal stress which increases the risk of layer peel off and particle generation which may result in arcing and thus an unstable deposition process.

[0006] Accordingly, there is a continuing demand for improved apparatuses and methods for coating flexible substrates with layer stacks that overcome at least some of the problems of the state of the art. SUMMARY

[0007] In light of the above, a method of coating a flexible substrate with a stack of layers, a deposition apparatus for coating a flexible substrate with a stack of layers, and a layer stack according to the independent claims are provided. Further aspects, advantages, and features are apparent from the dependent claims, the description, and the accompanying drawings.

[0008] According to one aspect of the present disclosure, a method of coating a flexible substrate with a stack of layers is provided. The method includes guiding the flexible substrate by a coating drum provided in a deposition chamber past one or more first deposition units and past one or more second deposition units. Guiding includes alternately transporting the flexible substrate in a forward direction and in a backward direction. Additionally, the method includes providing an initial deposition on the flexible substrate by depositing a first portion of a second material by the one or more second deposition units while guiding the flexible substrate in the forward direction. Further, the method includes providing one or more subsequent depositions. The one or more subsequent depositions include, while guiding the flexible substrate in the backward direction, depositing a second portion of the second material by the one or more second deposition units on top of the first portion of the second material and depositing a first portion of a first material by the one or more first deposition units on top of the second portion of the second material. Additionally, the one or more subsequent depositions include, while guiding the flexible substrate in the forward direction, depositing a second portion of the first material on top of the first portion of the first material by the one or more first deposition units and depositing a first portion of the second material by the one or more second deposition units on top of the second portion of the first material.

[0009] According to a further aspect of the present disclosure, a layer stack is provided. The layer stack has an alternating structure of one or more first layers of a first material and one or more second layers of a second material. The one or more first layers of the first material include a first layer portion of the first material and a second layer portion of the first material. The one or more second layers of the second material include a further first layer portion of the second material and a further second layer portion of the second material.

[0010] According to another aspect of the present disclosure, a deposition apparatus for coating a flexible substrate with a stack of layers is provided. The deposition apparatus includes a first spool chamber housing a first spool for unwinding and winding the flexible substrate. Additionally, the deposition apparatus includes a deposition chamber arranged downstream from the first spool chamber and including a coating drum for guiding the flexible substrate past a plurality of deposition units. The plurality of deposition units include a first group of first deposition units for depositing a first material on the flexible substrate and a second group of second deposition units for depositing a second material on the flexible substrate. Further, the deposition apparatus includes a second spool chamber arranged downstream from the deposition chamber and housing a second spool for winding and unwinding the flexible substrate. At least one of the first spool, the coating drum and the second spool include a drive for rotating at least one of the first spool, the coating drum and the second spool in a clockwise direction and an anti-clockwise direction for alternately transporting the flexible substrate in a forward direction and in a backward direction.

[0011] Embodiments are also directed at apparatuses for carrying out the disclosed methods and include apparatus parts for performing the described method aspects. 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

[0012] 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:

FIG. 1 shows a schematic view of a deposition apparatus according to embodiments described herein;

FIG. 2 shows a schematic view of a deposition apparatus according to further embodiments described herein;

FIG. 3 shows a flowchart with pictograms for illustrating a method of coating a flexible substrate with a stack of layers according to embodiments described herein; and

FIG. 4 shows a schematic view of a layer stack according to embodiments described herein.

DETAILED DESCRIPTION OF EMBODIMENTS

[0013] Reference will now be made in detail to the various embodiments of the disclosure, one or more examples of which are illustrated in the figures. Within the following description of the drawings, the same reference numbers refer to same components. Only the differences with respect to individual embodiments are described. Each example is provided by way of explanation of the disclosure and is not meant as a limitation of the disclosure. Further, features illustrated or described as part of one embodiment can be used on or in conjunction with other embodiments to yield yet a further embodiment. It is intended that the description includes such modifications and variations.

[0014] With exemplary reference to FIG. 1, a deposition apparatus 100 for coating a flexible substrate 10 with a stack of layers according to the present disclosure is described. In particular, embodiments of the deposition apparatus 100 as described herein can be used for conducting embodiments of the method of coating a flexible substrate with a stack of layers as described herein. [0015] According to embodiments which can be combined with any other embodiments described herein, the deposition apparatus 100 includes a first spool chamber 110 housing a first spool 112 for unwinding and winding the flexible substrate 10. As indicated by the double sided arrow on the first spool 112 in FIG. 1, the first spool 112 can be configured to rotate clockwise and anti clockwise. In particular, when the first spool 112 rotates clockwise, the flexible substrate is unwound from the first spool 112. Accordingly, when the first spool 112 rotates anti-clockwise, the flexible substrate is wound on the first spool 112.

[0016] Additionally, the deposition apparatus 100 includes a deposition chamber 120 arranged downstream from the first spool chamber 110. The deposition chamber 120 includes a coating drum 122 and a plurality of deposition units 121. In particular, the coating drum 122 is arranged and configured for guiding the flexible substrate 10 past the plurality of deposition units 121. The plurality of deposition units includes a first group of first deposition units 121 A and a second group of second deposition units 121B. The first deposition units 121A are configured for depositing a first material (A) on the flexible substrate. The second deposition units 121B are configured for depositing a second material on the flexible substrate.

[0017] Further, the deposition apparatus 100 includes a second spool chamber 150 arranged downstream from the deposition chamber 120. The second spool chamber 150 houses a second spool 152 for winding and unwinding the flexible substrate 10. As indicated by the double sided arrow on the second spool 152 in FIG. 1, the second spool 152 can be configured to rotate clockwise and anti clockwise. In particular, when the second spool 152 rotates clockwise, the flexible substrate is wound on the second spool 152. Accordingly, when the second spool 152 rotates anti-clockwise, the flexible substrate is unwound from the second spool 152.

[0018] According to embodiments which can be combined with any other embodiments described herein, the first spool 112 and/or the coating drum 122 and/or the second spool 152 include a drive for providing a clockwise and anti clockwise rotation. Accordingly, as exemplarily indicated in FIG. 1, the flexible substrate 10 can be transported in a forward direction (FD) and in a backward direction (BD). In other words, at least one of the first spool 112, the coating drum 122 and the second spool 152 include a drive for rotating at least one of the first spool 112, the coating drum 122 and the second spool 152 in a clockwise direction and an anti-clockwise direction for alternately transporting the flexible substrate 10 in a forward direction (FD) and in a backward direction (BD).

[0019] Accordingly, embodiments of the apparatus as described herein are beneficially configured for conducting a roll-to-roll coating method for manufacturing a multi-layer stack which is produced by alternately coating a flexible substrate with different materials. In particular, compared to the state of the art, embodiments of the method of coating a flexible substrate with a stack of layers as described herein which can be carried out by the apparatus described herein, beneficially provide for a significant reduction of process time for manufacturing layer stacks, as explained in more detail with reference to FIG. 3 in the following.

[0020] Before various further embodiments of the present disclosure are described in more detail, some aspects with respect to some terms used herein are explained.

[0021] In the present disclosure, a“deposition apparatus” can be understood as an apparatus configured for depositing material on a substrate, particularly on a flexible substrate as described herein. In particular, the deposition apparatus can be a“vacuum deposition apparatus” and can be understood as an apparatus configured for processing a substrate, particularly a flexible substrate as described herein. More specifically, the deposition apparatus may be a roll-to-roll (R2R) vacuum deposition apparatus configured for coating a flexible substrate with a stack of layers. Typically, the vacuum deposition apparatus has at least one vacuum chamber, particularly a vacuum deposition chamber. In the present disclosure, a“deposition chamber” can be understood as a chamber having at least one deposition unit for depositing material on a substrate. 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 ⁵ mbar and about 10 ⁸ mbar, more typically between 10 ⁵ mbar and 10 ⁷ mbar, and even more typically between about 1 O ⁶ mbar and about 1 O ⁷ mbar.

[0022] Further, the deposition apparatus may be configured for a substrate length of 500 m or more, 1000 m or more, or several kilometres. The substrate width can be 300 mm or more, particularly 500 mm or more, more particularly 1 m or more. Further, the substrate width can be 8 m or less, particularly 6 m or less.

[0023] In the present disclosure, a“flexible substrate” can be understood as a bendable substrate. For instance, the“flexible substrate” can be a“foil” or a “web”. In the present disclosure, the term“flexible substrate” and the term “substrate” may be synonymously used. For example, the flexible substrate as described herein may include materials like PET, HC-PET, PE, PI, PU, TaC, OPP, BOOP, CPP, one or more metals, paper, combinations thereof, and already coated substrates like Hard Coated PET (e.g. HC-PET, HC-TaC) and the like. In some embodiments, the flexible substrate is a COP substrate provided with an index matched (IM) layer on both sides thereof. For example, the substrate thickness can be 1 pm or more and 200 pm or less. More specifically, the substrate thickness can be selected from the range of having a lower limit of 8 pm and an upper limit of 25 pm, for instance for food packaging applications. According to an example, the flexible substrate may be a PET substrate having a substrate thickness of approximately 125 pm.

[0024] In the present disclosure, the terms“upstream from” and“downstream from” may refer to the position of the respective chamber or of the respective component with respect to another chamber or component along the substrate transportation path. For example, during operation, the substrate is guided from the first spool chamber 110 through the deposition chamber 120 and subsequently guided to the second spool chamber 150 in a forward direction (FD) along the substrate transportation path via a roller assembly. Accordingly, in the forward direction, the deposition chamber 120 is arranged downstream from the first spool chamber 110, and the first spool chamber 110 is arranged upstream from the deposition chamber 120. When, during operation, the substrate is first guided by or transported past a first roller or a first component in the forward direction and subsequently guided by or transported past a second roller or a second component in the forward direction, the second roller or second component is arranged downstream from the first roller or first component.

[0025] In the present disclosure, a“coating drum” can be understood as a drum or a roller having a substrate support surface for contacting the flexible substrate. In particular, the coating drum can be rotatable about a rotation axis 123, as exemp lardy shown in FIG. 1, and may include a substrate guiding region. Typically, the substrate guiding region is a curved substrate support surface, e.g. a cylindrically symmetric surface, of the roller device. The curved substrate support surface of the roller device may be adapted to be (at least partly) in contact with the flexible substrate during the guiding of the flexible substrate. The substrate guiding region may be defined as an angular range of the roller device in which the substrate is in contact with the curved substrate surface during the guiding of the substrate, and may correspond to the enlacement angle of the roller device. In some embodiments, the enlacement angle of the roller device may be 120° or more, particularly 180° or more, or even 270° or more.

[0026] In the present disclosure, a“deposition unit” can be understood as a unit or device configured for depositing material on a flexible substrate as described herein. In particular, the deposition unit may be a sputter deposition unit, e.g. an AC sputter source or a DC sputter source. However, the processing apparatus described herein is not limited to sputter deposition, and other deposition units may additionally or alternatively be used. For example, in some implementations, CVD deposition units, evaporation deposition units, PECVD deposition units or other deposition units may be utilized. Accordingly, it is to be understood that the deposition units, e.g. a plasma deposition source, can be adapted for depositing a multi-layer stack including two more layers of different material on a flexible substrate, e.g., to form a flexible display device, a touch screen device component, or other electronic or optical devices. [0027] According to some embodiments which can be combined with other embodiments described herein, the first deposition units 121 A can be sputter deposition units having a target of the first material. For example, the first material may include silicon. In particular, the first material can be silicon oxide Si0₂. The second deposition units 121B can be sputter deposition units having a target of the second material. For instance, the second material may include Niobium. In particular, the second material can be Niobium pentoxide Nb₂Os.

[0028] With exemplary reference to FIG. 1, it is to be understood that typically the deposition apparatus 100 is configured such that the flexible substrate 10 can be guided from the first spool chamber 110 to the second spool chamber 150 along a substrate transportation path in the forward direction FD as well, such that the flexible substrate 10 can be guided from the second spool chamber 150 to the first spool chamber 110 along a substrate transportation path in the backward direction BD. The substrate transportation path leads through the deposition chamber 120. Further, as exemplarily shown in FIG. 1, a roller assembly including a plurality of rolls or rollers can be provided for transporting the substrate along the substrate transportation path. In FIG. 1, a roller assembly comprising four rollers is shown. It is to be understood that, according to different configurations, as exemplarily shown in FIG. 2, the roller assembly may include five or more rollers, particularly ten or more rollers, arranged between the first spool 112 and the second spool 152.

[0029] With exemplary reference to FIGS. 1 and 2, according to some embodiments herein, which can be combined with any other embodiments described herein, the roller assembly may be configured to transport the flexible substrate along a partially convex and partially concave substrate transportation path from the first spool chamber to the second spool chamber and vice versa. In other words, the substrate transportation path may be partially curved to the right and partially curved to the left, such that some guiding rollers contact a first main surface of the flexible substrate and some guiding rollers contact a second main surface of the flexible substrate opposite the first main surface. [0030] For example, the first guiding roller 107 in FIG. 1 contacts a second main surface of the flexible substrate, and the flexible substrate is bent to the left while being guided by the first guiding roller 107 (“convex” section of the substrate transportation path). The second guiding roller 108 in FIG. 1 contacts a first main surface of the flexible substrate, and the flexible substrate is bent to the right while being guided by the second guiding roller 108 (“concave” section of the substrate transportation path).

[0031] In some embodiments, one or more rollers, e.g. guiding rollers, of the roller assembly may be arranged between the first spool 112 and the coating drum 122 and/or downstream from the coating drum. For example, in the embodiment shown in FIG. 1, two guiding rollers are provided between the first spool 112 and the coating drum 122, wherein at least one guiding roller may be arranged in the first spool chamber 110 and at least one guiding roller may be arranged in the deposition chamber 120 in the forward direction FD upstream from the coating drum 122. In some embodiments, as exemplarily shown in FIG. 2, three, four, five or more, particularly eight or more guiding rollers are provided between the first spool and the coating drum. The guiding rollers may be active or passive rollers.

[0032] An“active” roller or roll as used herein may be understood as a roller that is provided with a drive or a motor for actively moving or rotating the respective roller. For example, an active roller may be adjusted to provide a predetermined torque or a predetermined rotational speed. Typically, the first spool 112 and/or the second spool 152 and/or the coating drum 122 may be provided as active rollers. Further, active rollers can be configured as substrate tensioning rollers configured for tensioning the substrate with a predetermined tensioning force during operation. A“passive” roller may be understood as a roller or roll that is not provided with a drive for actively moving or rotating the passive roller, particularly in a clockwise direction and an anti-clockwise direction. The passive roller may be rotated by the frictional force of the flexible substrate that may be in direct contact with an outer roller surface during operation. [0033] As exemplarily shown in FIG. 1, one or more guiding rollers 113 may be arranged downstream (in the forward direction FD) from the coating drum 122, and upstream (in the forward direction FD) from the second spool chamber 150. For example, at least one guiding roller may be arranged in the deposition chamber 120 downstream from the coating drum 122 for guiding the flexible substrate 10 towards the second spool chamber 150, arranged downstream (in the forward direction FD) from the deposition chamber 120. Additionally or alternatively, at least one guiding roller may be arranged in the second spool chamber 150 upstream (in the forward direction FD) from the coating drum 122 for guiding the flexible substrate in a direction essentially tangential to the substrate support surface of the second spool 152, in order to smoothly guide the flexible substrate onto the second spool 152.

[0034] According to some embodiments, some chambers or all chambers of the deposition apparatus may be configured as vacuum chambers that can be evacuated. For instance, the deposition apparatus 100 may include components and equipment allowing for the generation of or maintenance of a vacuum in the first spool chamber 110 and/or the deposition chamber 120 and/or the second spool chamber 150. In particular, the deposition apparatus may include vacuum pumps, evacuation ducts, vacuum seals and the like for generating or maintaining a vacuum in the first spool chamber 110 and/or the deposition chamber 120 and/or the second spool chamber 150. Accordingly, the first spool chamber 110 and/or the deposition chamber 120 and/or the second spool chamber 150 can be vacuum chambers.

[0035] With exemplary reference to FIG. 1, according to embodiments which can be combined with other embodiments described herein, sealing devices 105 may be provided between adjacent chambers, e.g. between the first spool chamber 110 and the deposition chamber 120 and/or between the deposition chamber 120 and the second spool chamber 150. Accordingly, beneficially the winding chambers (i.e. the first spool chamber 110 and the second spool chamber 150) may be vented or evacuated independently, in particular independently from the deposition chamber. The sealing device 105 may include an inflatable seal configured to press the substrate against a flat sealing surface.

[0036] With exemplary reference to FIG. 1, according to embodiments which can be combined with other embodiments described herein, the individual deposition units of the plurality of deposition units 121 may be provided in separate compartments which allows for a modular combination of several different subsequent deposition processes (e.g. CVD, PECVD and/or PVD) and ensures very good gas separation between the different subsequent deposition processes. Accordingly, dependent from the selected sequence of deposition units, various different stack layers can be deposited on the flexible substrate.

[0037] With exemplary reference to FIG. 2, some further optional features of the deposition apparatus are described. For instance, gas separation units 510 may be provided between two adjacent deposition units in order to reduce a flow of process gases from one deposition unit to other deposition units, e.g. to an adjacent deposition unit during operation, respectively. The gas separation units may be configured as gas separation walls which divide the inner volume of the deposition chamber in a plurality of separate compartments, wherein each compartment may include one deposition unit. One deposition unit may be arranged between two neighboring gas separation units, respectively. In other words, the deposition units may be separated by the gas separation units, respectively. Accordingly, beneficially a high gas separation between neighboring compartments/ deposition units can be provided.

[0038] Further, as exemplarily shown in FIG. 2, the deposition apparatus 100 may include an annealing unit 114 provided upstream (in the forward direction) from the plurality of deposition units 121. The annealing unit 114 may be configured for heating or annealing the flexible substrate 10. Heating of the flexible substrate may be beneficial, in order to allow for a degassing of the flexible substrate particularly before a first deposition. For instance, the annealing unit 114 may include a heatable roller 115 arranged in the first spool chamber 110 directly downstream (in the forward direction) from the first spool 112, as is exemplarily shown in FIG. 2. Additionally or alternatively, the annealing unit 114 may include a radiation heater 116 arranged in the first spool chamber 110. The radiation heater 116 can be configured as a heating lamp, e.g. an infrared lamp.

[0039] According to some embodiments, which may be combined with other embodiments described herein, a pretreatment device 201 may be provided, particularly upstream (in the forward direction) from the plurality of deposition units 121, as exemplarily shown in FIG. 2. For example, the pretreatment device 201 may be located in the deposition chamber 120 upstream (in the forward direction) from the plurality of deposition units 121. In some embodiments, the pretreatment device 201 is arranged such that the flexible substrate can be pretreated when the flexible substrate is in contact with the substrate support surface of the coating drum 122. The pretreatment device 201 may be configured to activate the first main surface of the flexible substrate, in order to promote the adhesion of the stack of layers to be deposited. For instance, the pretreatment device may include a DC glow discharge.

[0040] According to one example, the pretreatment device 201 may include a plasma source, e.g. an RF plasma source, configured for pretreating the flexible substrate with plasma. For example, the pretreatment with a plasma can provide for a surface modification of the substrate surface to enhance the adhesion of a film deposited thereon, or can improve the substrate morphology in another manner to improve processing thereof.

[0041] According to another example, the pretreatment device 201 may be an ion source, particularly a linear ion source (LIS). The pretreatment device 201 may be configured for pre-cleaning the first main surface of the flexible substrates directly prior to the coating of the first main surface. The pretreatment device 201 may be configured to direct a plasma jet towards the first main surface of the flexible substrate in order to bum off hydrocarbons and in order to activate the surface to promote the adhesion of the layer to be deposited.

[0042] According to some embodiments, which may be combined with other embodiments described herein, one or more tension measurement rollers may be provided for measuring the substrate tension at a specific position along the substrate transportation path. As an example, in the embodiment shown in FIG. 2, a first tension measurement roller 184 is provided being associated to the first spool 112, a second tension measurement roller 185 is provided being associated to a tensioning roller 181, and a third tension measurement roller 188 is provided being associated to the second spool 152. For instance, the second tension measurement roller 185 may be located directly downstream (in the forward direction) from the coating drum 122 and directly upstream (in the forward direction) from the tensioning roller 181. If a tension value above a preset target value is measured by the second tension measurement roller 185, the torque value provided by a drive of the tensioning roller 181 may be decreased. If a tension value below the target value is measured by the second tension measurement roller 185, the torque value provided by the drive of the tensioning roller 181 may be increased. Accordingly, an appropriate tension of the flexible substrate around the coating drum can be ensured.

[0043] With exemplary reference to the flowchart shown in FIG. 3, embodiments of a method 190 of coating a flexible substrate with a stack of layers are described.

[0044] According to embodiments which can be combined with any other embodiments described herein, the method 190 includes guiding (represented by block 191 in FIG. 3) the flexible substrate 10 by a coating drum 122 provided in a deposition chamber 120 past one or more first deposition units 121 A and past one or more second deposition units 121B. Guiding the flexible substrate includes alternately transporting the flexible substrate 10 in a forward direction FD and in a backward direction BD. Additionally, the method 190 includes providing an initial deposition (represented by block 192 in FIG. 3) on the flexible substrate by depositing a first portion Bl of a second material B by the one or more second deposition units 121B while guiding the flexible substrate in the forward direction FD. Further, the method 190 includes providing one or more subsequent depositions (represented by block 193 in FIG. 3). The one or more subsequent depositions include depositing a second portion B2 of the second material B by the one or more second deposition units 121B on top of the first portion Bl of the second material B and depositing a first portion Al of a first material A by the one or more first deposition units 121 A on top of the second portion B2 of the second material B, while guiding the flexible substrate in the backward direction BD (represented by block 194 in FIG. 3). Further, the one or more subsequent depositions include depositing a second portion A2 of the first material A on top of the first portion Al of the first material A by the one or more first deposition units 121 A and depositing a first portion Bl of the second material B by the one or more second deposition units 121B on top of the second portion A2 of the first material A, while guiding the flexible substrate in the forward direction FD (represented by block 195 in FIS. 3).

[0045] Accordingly, it is to be understood that a layer stack having an alternating structure of one or more first layers of a first material and one or more second layers of a second material can be deposited on the flexible substrate.

[0046] Further, with exemplary reference to the layer stack 200 shown in FIG. 4, it is to be understood that the one or more first layers Ll of the first material A are produced by subsequently depositing a first portion Al of the first material A and a second portion A2 of the first material A. In particular, depositing the first portion Al of the first material A may be conducted while guiding the flexible substrate in the backward direction BD. Depositing the second portion A2 of the first material A may be conducted while guiding the flexible substrate in the forward direction FD. Further, it is to be understood that the first portion Al of the first material A and the second portion A2 of the first material A add up to 100%. For example, the first portion Al of the first material A may be 50% of the total material of the layer of material A and the second portion A2 of the first material A may be 50% of the total material of the layer of material A. According to other embodiments, the ratio of the amount of the first portion Al of the first material A to the second portion A2 of the first material A may be different, e.g. 40 % of Al and 60% of A2 or vice versa. However, it is to be understood that other any suitable ratios of A1/A2 may be realized.

[0047] Further, with exemplary reference to the layer stack 200 shown in FIG. 4, it is to be understood that the one or more second layers L2 of the second material B are produced by subsequently depositing a first portion Bl of the second material B and a second portion B2 of the second material B. In particular, depositing the first portion Bl of the second material B may be conducted while guiding the flexible substrate in the forward direction FD. Depositing the second portion B2 of the second material B may be conducted while guiding the flexible substrate in the backward direction BD. Further, it is to be understood that the first portion Bl of the second material B and the second portion B2 of the second material B add up to 100%. For example, the first portion Bl of the second material B may be 50% of the total material of the layer of material B and the second portion B2 of the second material B may be 50% of the total material of the layer of material B. According to other embodiments, the ratio of the amount of the first portion Bl of the second material B to the second portion B2 of the second material B may be different, e.g. 40 % of Bl and 60% of B2 or vice versa. However, it is to be understood that any other suitable ratios of B1/B2 may be realized.

[0048] Accordingly, it is to be understood that the term“first portion” of a material, e.g. material A or B, as used herein can be understood as a first amount of the material deposited, e.g. material A or B, being a first fraction, e.g. 50%, of the total amount of the material used for providing the respective layer on the flexible substrate. The term“second portion” of a material, e.g. material A or B, as used herein can be understood as a second amount of the material deposited, e.g. material A or B, being a second fraction, e.g. 50%, of the total amount of the material used for providing the respective layer on the flexible substrate. The sum of the first fraction and the second fraction adds up to 100%.

[0049] As exemplarily described with reference to FIG. 1, according to some embodiments of the method which can be combined with other embodiments described herein, in the forward direction FD the one or more second deposition units 121B are arranged downstream of the one or more first deposition units 121 A. Accordingly, when the flexible substrate is guided in the forward direction FD, the flexible substrate first passes the one or more first deposition units 121A and then the one or more second deposition units 121B. When the flexible substrate is guided in the backward direction BD, the flexible substrate first passes the one or more second deposition units 121B and then the one or more first deposition units 121 A.

[0050] According to some embodiments of the method which can be combined with other embodiments described herein, the one or more first deposition units 121 A are sputter deposition units for depositing the first material A. Similarly, the one or more second deposition units 121B can be sputter deposition units for depositing the second material B. Typically, the first material is a material having a low refractive index. For example, the first material can have a first refractive index nl of 1.0 < nl < 1.8, particularly 1.2 < nl < 1.6. In particular, the first material A may include silicon. In particular, the first material can be silicon oxide Si02, e.g. having a first refractive index nl ~ 1.4 ± 0.1.

[0051] According to some embodiments of the method which can be combined with other embodiments described herein, the second material is a material having a high refractive index. For example, the second material can have a second refractive index n2 of 1.8 < n2 < 2.8, particularly 2.0 < n2 < 2.5. In particular, the second material B may include Niobium. In particular, the second material can be Niobium pentoxide Nb₂0₅, e.g. having a second refractive index n2 ~ 2.3 ± 0.1. [0052] According to some embodiments of the method which can be combined with other embodiments described herein, the method further includes unwinding the flexible substrate from a first spool 112 provided in a first spool chamber 110 and winding the flexible substrate on a second spool 152 provided in a second spool chamber 150 while guiding the flexible substrate in the forward direction FD. Accordingly, in the forward direction, the flexible substrate is transported from the first spool chamber 110, through the deposition chamber 120 first past the one or more first deposition units 121 A and secondly past the one or more second deposition units 121B, to the second spool chamber 150.

[0053] According to some embodiments of the method which can be combined with other embodiments described herein, the method further includes unwinding the flexible substrate from a second spool 152 provided in a second spool chamber 150 and winding the flexible substrate on a first spool 112 provided in a first spool chamber 110 while guiding the flexible substrate in the backward direction BD. Accordingly, in the backward direction, the flexible substrate is transported from the second spool chamber 150, through the deposition chamber 120 first past the one or more second deposition units 121B and secondly past the one or more first deposition units 121 A, to the first spool chamber 110.

[0054] According to some embodiments of the method which can be combined with other embodiments described herein, the one or more subsequent depositions comprise a number N of subsequent depositions, the number N being 5 < N < 40, particularly 10 < N < 35. Accordingly, with the method as described herein, multi-layer stacks with an alternating structure layer of different materials, e.g. material A and material B, can be produced.

[0055] According to some embodiments of the method which can be combined with other embodiments described herein, the method further includes adjusting at least one deposition process parameter for the one or more subsequent depositions. The at least one deposition process parameter can be selected from the group consisting of guiding speed of the flexible substrate, deposition rate, deposition temperature and deposition pressure. For instance, the deposition rate of a deposition unit as described herein can be adjusted by adjusting the power, e.g. the power supplied to the cathode of the deposition unit. Further, by adjusting the guiding speed of the flexible substrate, the layer thickness may be adjusted. By adjusting deposition temperature and deposition pressure, physical properties of the deposited layers can be adjusted.

[0056] In particular, adjusting a deposition rate of the one or more first deposition units may include selecting a power Pl of the first deposition units to be 10 kW < Pl < 40 kW, particularly 15 kW < Pl < 35 kW, more particularly 20 kW < Pl < 30 kW. According to an example, the power Pl of the first deposition units may be selected to be Pl ~ 26kW. [0057] Adjusting a deposition rate of the one or more second deposition units may include selecting a power P2 of the second deposition units to be 1 kW < P2 < 20 kW, particularly 3 kW < P2 < 15 kW, more particularly 5 kW < P2 < 10 kW. According to an example, the power P2 of the second deposition units may be selected to be Pl < 5 kW.

[0058] With exemplary reference to FIG. 5, a layer stack 200 according to the present disclosure is described. As exemp lardy shown in FIG. 5, the layer stack 200 includes an alternating structure of one or more first layers Ll of a first material A and one or more second layers L2 of a second material B. The one or more first layers of the first material A include a first layer portion LA1 of the first material A and a second layer portion LA2 of the first material A. The one or more second layers L2 of the second material B include a further first layer portion LB1 of the second material B and a further second layer portion LB2 of the second material B. For instance, the one or more first layers Ll may be layers of a low refractive index material and the one or more second layers L2 may be layers of a high refractive index material.

[0059] For example, the one or more first layers Ll can have a first refractive index nl of 1.0 < nl < 1.8, particularly 1.2 < nl < 1.6. In particular, the first material A of the one or more first layers Ll may include silicon. In particular, the first material A can be silicon oxide Si02, e.g. having a first refractive index nl ~ 1.4 ± 0.1. The one or more second layers L2 can have a second refractive index n2 of 1.8 < n2 < 2.8, particularly 2.0 < n2 < 2.5. In particular, the second material B may include Niobium. In particular, the second material can be Niobium pentoxide Nb₂0₅, e.g. having a second refractive index n2 ~ 2.3 ± 0.1. [0060] According to some embodiments, which can be combined with other embodiments described herein, the one or more first layers Ll of the first material A may have a first thickness Tl of 10 nm < Tl < 180 nm. The one or more second layers L2 of the second material B may have a second thickness T2 of 10 nm < T2 < 180 nm. [0061] FIG. 4 shows a layer stack having an alternating layer structure of two second layers L2 and two first layers Ll, i.e. an alternating layer structure with a total number N_T of layers of N_T = 4 is provided. However, it is to be understood that the layer stack may include more second layers and more first layers. For instance, an alternating layer structure of second layers L2 and first layers Ll can be provided, wherein the total number N_T of layers is 4 < N_T < 40. Further, it is to be understood that the last layer of the layer stack can be a last layer of the first material A (exemplarily shown in FIG. 4) or a last layer of the second material B (not explicitly shown).

[0062] In the case that the last layer to be deposited is a layer of the first material A, in the last deposition, e.g. here while guiding the flexible substrate in the forward direction, the first deposition units 121 A are activated and the second deposition units 121B are deactivated, such that the last deposition is a deposition of the second portion A2 of material A.

[0063] In the case that the last layer to be deposited is a layer of the second material B, in the last deposition, e.g. here while guiding the flexible substrate in the backward direction, the second deposition units 121B are activated and the first deposition units 121 A are deactivated, such that the last deposition is a deposition of the second portion B2 of material B.

[0064] It is to be understood that the exemplary layer stack as shown in FIG. 4 as well as other multi-layer stacks with alternating layers of different materials can be produced by the method of coating a flexible substrate with a stack of layers according to any embodiments described herein. Further, the method of coating a flexible substrate with a stack of layers can be conducted by the deposition apparatus as described herein.

[0065] In view of the embodiments described herein, it is to be understood that compared to the state of the art, an improved deposition apparatus and an improved method of coating a flexible substrate with a stack of layers is provided. In particular, embodiments of the present disclosure beneficially provide for a significant reduction of process time for manufacturing a layer stack. More specifically, with the embodiments of the apparatus and the method as described herein, the process time for manufacturing a layer stack can be substantially reduced by a factor of two. In other words, with the embodiments of the present disclosure, a process time for manufacturing a layer stack can be achieved which is approximately half of the process time achievable by conventional apparatuses and methods. Further, compared to the state of the art, with the embodiments of the apparatus and the method of the present disclosure during the deposition process the different deposition units, particularly the first deposition units and the second deposition units as described herein, beneficially can remain in an activated state, i.e. the deposition units do not have to be switched on and off for depositing the different materials, e.g. the first material A and the second material B as described herein. Accordingly, the embodiments of the apparatus and the method of the present disclosure have the advantage that a stable deposition process can be achieved and that the risk of particle generation can substantially be reduced or even eliminated.

[0066] While the foregoing is directed to embodiments, other and further embodiments may be devised without departing from the basic scope, and the scope is determined by the claims that follow.

Claims

1. A method of coating a flexible substrate (10) with a stack of layers, the method comprising:

- guiding the flexible substrate by a coating drum (122) provided in a deposition chamber (120) past one or more first deposition units (121 A) and past one or more second deposition units (121B), wherein guiding comprises alternately transporting the flexible substrate in a forward direction (FD) and in a backward direction (BD);

- providing an initial deposition on the flexible substrate by depositing a first portion (Bl) of a second material (B) by the one or more second deposition units

(121B) while guiding the flexible substrate in the forward direction (FD); and

- providing one or more subsequent depositions, comprising:

while guiding the flexible substrate in the backward direction (BD), depositing a second portion (B2) of the second material (B) by the one or more second deposition units (121B) on top of the first portion (Bl) of the second material (B) and depositing a first portion (Al) of a first material (A) by the one or more first deposition units (121 A) on top of the second portion (B2) of the second material (B), and

while guiding the flexible substrate in the forward direction (FD), depositing a second portion (A2) of the first material (A) on top of the first portion (Al) of the first material (A) by the one or more first deposition units (121 A) and depositing a first portion (Bl) of the second material (B) by the one or more second deposition units (121B) on top of the second portion (A2) of the first material (A).

2. The method of claim 1, wherein in the forward direction the one or more second deposition units (121B) are arranged downstream of the one or more first deposition units (121A).

3. The method of claim 1 or 2, wherein the one or more first deposition units (121 A) are sputter deposition units for depositing the first material (A).

4. The method of any of claims 1 to 3, wherein the one or more second deposition units (121B) are sputter deposition units for depositing the second material (B).

5. The method of any of claims 1 to 4, wherein the first material (A) is a material having a first refractive index nl of 1.0 < nl < 1.8, particularly comprising silicon, particularly silicon oxide Si0₂.

6. The method of any of claims 1 to 5, wherein the second material (B) is a material having a second refractive index n2 of 1.8 < n2 < 1.8, particularly comprising Niobium, particularly Niobium pentoxide Nb₂0_5.

7. The method of any of claims 1 to 6, further comprising unwinding the flexible substrate from a first spool (112) provided in a first spool chamber (110) and winding the flexible substrate on a second spool (152) provided in a second spool chamber (150) while guiding the flexible substrate in the forward direction.

8. The method of any of claims 1 to 7, further comprising unwinding the flexible substrate from a second spool (152) provided in a second spool chamber (150) and winding the flexible substrate on a first spool (112) provided in a first spool chamber (110) while guiding the flexible substrate in the backward direction.

9. The method of any of claims 1 to 8, wherein the one or more subsequent depositions comprise a number N of subsequent depositions, the number N being 5 < N < 40, particularly 10 < N < 35.

10. The method of any of claims 1 to 9, further comprising adjusting at least one process parameter for the one or more subsequent depositions, the at least one process parameter being selected from the group consisting of guiding speed of the flexible substrate, deposition rate, deposition temperature and deposition pressure.

11. A layer stack (200) having an alternating structure of one or more first layers (Ll) of a first material (A) and one or more second layers (L2) of a second material (B), the one or more first layers (Ll) of the first material (A) comprise first layer portion (LA1) of the first material (A) and a second layer portion (LA2) of the first material (A), and the one or more second layers (L2) of the second material (B) comprise a further first layer portion (LB1) of the second material (B) and a further second layer portion (LB2) of the second material (B).

12. The layer stack of claim 11, wherein the one or more first layers (Ll) of the first material (A) have a first thickness Tl of 10 nm < Tl < 180 nm, and wherein the one or more second layers (L2) of the second material (B) have a second thickness T2 of 10 nm < T2 < 180 nm.

13. The layer stack of claim 11 or 12, wherein the first material (A) is a material having a first refractive index nl of 1.0 < nl < 1.8, particularly comprising silicon, particularly silicon oxide Si0₂, and wherein the second material (B) is a material having a second refractive index n2 of 1.8 < n2 < 1.8, particularly comprising Niobium, particularly Niobium pentoxide Nb₂0₅.

14. The layer stack of any of claims 11 to 13, the layer stack being produced by a method of any of claims 1 to 10.

15. A deposition apparatus (100) for coating a flexible substrate (10) with a stack of layers, comprising:

a first spool chamber (110) housing a first spool (112) for unwinding and winding the flexible substrate (10), a deposition chamber (120) arranged downstream from the first spool chamber (110) and comprising a coating drum (122) for guiding the flexible substrate past a plurality of deposition units (121), the plurality of deposition units comprising a first group of first deposition units (121 A) for depositing a first material on the flexible substrate and a second group of second deposition units (121B) for depositing a second material on the flexible substrate,

a second spool chamber (150) arranged downstream from the deposition chamber (120) and housing a second spool (152) for winding and unwinding the flexible substrate (10),

wherein at least one of the first spool (112), the coating drum (122) and the second spool (152) include a drive for rotating at least one of the first spool (112), the coating drum (122) and the second spool (152) in a clockwise direction and an anti-clockwise direction for alternately transporting the flexible substrate in a forward direction and in a backward direction.

16. The deposition apparatus (100) of claim 15, wherein the first deposition units (121 A) are sputter deposition units having a target of the first material, and wherein the second deposition units (121B) are sputter deposition units having a target of the second material.

17. The deposition apparatus (100) of claim 15 or 16, wherein the first material (A) is a material having a first refractive index nl of l.0 < nl < l.8, particularly comprising silicon, particularly silicon oxide Si0₂, and wherein the second material (B) is a material having a second refractive index n2 of 1.8 < n2 < 1.8, particularly comprising Niobium, particularly Niobium pentoxide Nb₂0_5.