WO2017188947A1

WO2017188947A1 - System for atomic layer deposition on flexible substrates and method for the same

Info

Publication number: WO2017188947A1
Application number: PCT/US2016/029621
Authority: WO
Inventors: Brian Einstein Lassiter
Original assignee: Applied Materials Inc
Current assignee: Applied Materials Inc
Priority date: 2016-04-27
Filing date: 2016-04-27
Publication date: 2017-11-02
Anticipated expiration: 2018-10-27

Abstract

A processing apparatus for atomic layer deposition of a thin film on a flexible substrate is described. The processing apparatus comprises a substrate support configured to continuously transport the flexible substrate. The processing apparatus further comprises a plurality of first gas distribution enclosures arranged opposite to a substrate front side for deposition of a first precursor material and a plurality of second gas distribution enclosures arranged opposite to the substrate front side for deposition of a second precursor material, wherein the plurality of first gas distribution enclosures and the plurality of second gas distribution enclosures are arranged alternatingly.

Description

SYSTEM FOR ATOMIC LAYER DEPOSITION ON FLEXIBLE SUBSTRATES AND

METHOD FOR THE SAME

TECHNICAL FIELD

[0001] Embodiments of the present disclosure relate to an apparatus for depositing a layer stack including deposition by atomic layer deposition (ALD) on flexible substrates, a barrier layer stack, and methods of depositing layer stacks including deposition by atomic layer deposition (ALD) onto a flexible substrate and generating a barrier layer stack. Embodiments of the present disclosure furtiier relate to a roil-to-roil processing apparatus configured to continuously transport the flexible substrate and to contact the flexible substrate on the back side thereof. Embodiments of the present disclosure particularly relate to a method for encapsulating a quantum dot layer stack.

BACKGROUND

[0002] Barrier films are utilized in applications where materials require very low ingress of moisture and/or oxygen. Barrier films are utilized for television screens, computer monitors, mobile phones, other hand-held devices, etc. for displaying information. For example, such devices can be organic light emitting diodes (OLED). A typical OLED may include layers of organic material situated between two electrodes that are all deposited on a substrate in a manner to form a matrix display panel having pixels that can be individually energized.

[0003] A new type of display technology is the quantum dot (QD) display type. Quantum, dots can provide an alternative for commercial display technology. Quantum, dots can support large, flexible displays but would not degrade as readily as OLEDs, making them appropriate candidates for screens such as flat-panel TVs, digital cameras, or mobile phones. Quantum Dot Enhancement Films (QDEF), are optical film components for LED driven LCD displays. [0004] Besides the 30% to 50% less power consumption than LCDs, 50-100 times brighter illumination than cathode ray tube (CRT) displays, better saturated red and green colors, and the use of the same material to generate different colors, QD LEDs provide the advantage of manufacturahility on polymer substrates.

[0005] Typical applications for barrier films are OLED films on flexible substrates, quantum dot enhancement films (QDEF) on flexible substrates for LCD displays, transparent food packaging, medical packaging, or organic photovoltaics. The display industry, particularly the OLED and/or the QD industry, as well as other industries that utilize substrate processing techniques, encapsulate moisture- or oxygen- sensitive devices to protect them from ambient moisture exposure.

[0006] ALD is a modified CVD process for the deposition of thin films by two or more self-limiting surface reactions. ALD employs chemisorption techniques to deliver precursor molecules on a substrate surface in sequential cycles. The cycle exposes the substrate surface to a first precursor and then to a second precursor. Optionally, a purge gas may be introduced between introductions of the precursor materials. The first and second precursors react to form a product compound as a film on the substrate surface. The cycle is repeated to form the layer to a predetermined thickness.

[0007] One method of performing ALD is by Time-Separated (TS) pulses of precursor gases in one deposition chamber. TS-ALD has several advantages over other methods; however one drawback of TS-ALD is that each surface exposed to the precursors, for example the interior of the chamber, will be coated with deposition. If these deposits are not removed periodically, the deposits will tend to flake and peel off eventually, leading to particulates ending up on the substrate and hence degraded moisture barrier performance of the deposited layer. If there is no effective way to clean the undesired deposits from the chamber surfaces in situ, then those chamber surfaces can be removed for cleaning "offline".

[0008] Another method of performing ALD is providing separated deposition chambers for each precursor, known as Spatially Separated ALD (SS-ALD). To form a layer of predetermined thickness, the substrate gets alternatingly processed in the first and second deposition chamber. The cycle is repeated until the layer of a predetermined thickness has been formed. [0009] Further improvements for performing ALD layers, e.g. on continuously transported large-scaled substrates are desired.

SUMMARY

100101 In light of the above, a processing apparatus for atomic layer deposition of a thin film on a flexible substrate, a barrier layer stack deposited onto a flexible substrate, a method for depositing a barrier film on a flexible substrate, and a method for encapsulating a quantum dot structure are provided. Further aspects, advantages, and features of the present disclosure are apparent from the description, and the accompanying drawings.

10011] According to one embodiment, the processing apparatus for atomic layer deposition of a thin film on a flexible substrate is provided. The apparatus includes a substrate support configured to continuously transport the flexible substrate, a plurality of first gas distribution enclosures arranged opposite to a substrate front side for providing a first precursor material on the front side of the flexible substrate, and a plurality of second gas distribution enclosures arranged opposite to the substrate front side for providing a second precursor material on the front side of the flexible substrate, wherein the plurality of first gas distribution enclosures and the plurality of second gas distribution enclosures are arranged alternatingly.

[0012] According to another embodiment a roll-to-roll processing apparatus for atomic layer deposition of a thin film on a flexible substrate is provided. The roll-to-roll processing apparatus includes a winding system for transporting said flexible substrate from an unwinding roller to a re-winding roller, a substrate support configured to continuously transport the flexible substrate and to contact the flexible substrate on a back side thereof, a plurality of first gas distribution enclosures arranged opposite to a substrate front side for deposition of a first precursor material, a plurality of second gas distribution enclosures arranged opposite to the substrate front side for deposition of a second precursor material, wherein the pluralit - of first gas distribution enclosures and the plurality of second gas distribution enclosures are arranged alternatingly, at least one gas separation stage arranged between at least one first gas distribution enclosure of the plurality of first gas distribution enclosures and at least one second gas distribution enclosure of the plurality of second gas distribution enclosures, and an excitation unit coupled to the at least one first or second gas distribution enclosure configured to induce a chemical reaction, wherein the excitation unit is a plasma source.

[0013] According to another embodiment, a bamer layer stack deposited onto a flexible substrate is provided. The barrier layer stack includes at least one barrier layer deposited by atomic layer deposition followed by at least one barrier layer deposited by plasma-enhanced chemical vapor deposition having an overall thickness of at least 50 nm, for example 120 nm. or more.

[0014] According to a yet further embodiment, a method for depositing a barrier film on a flexible substrate is provided. The method includes continuously transporting a flexible substrate from an unwinding roller to a re-winding roller, contacting the flexible substrate on the back side thereof, depositing a first precursor material on the flexible substrate in a first gas distribution enclosure arranged opposite to the substrate front side, depositing a second precursor material on the flexible substrate in a second gas distribution enclosure arranged opposite to the substrate front side, forming a product compound by a chemical reaction of the first precursor material and the second precursor material, generating a barrier layer stack by repeating the deposition of the first precursor material and the second precursor material on the flexible substrate, and depositing a layer by plasma-enhanced chemical vapor deposition over the barrier layer stack.

[0015 J According to a yet another embodiment, a method for encapsulating a quantum dot structure is provided. The method includes continuously transporting a flexible substrate, depositing a first precursor material on the flexible substrate in a first gas distribution enclosure arranged opposite to the substrate front side, depositing a second precursor material on the flexible substrate in a second gas distribution enclosure arranged opposite to the substrate front side, forming a product compound by a chemical reaction of the first precursor material and the second precursor material, generating a barrier layer stack by repeating the deposition of the first precursor material and the second precursor material on the flexible substrate, depositing a layer by plasma-enhanced chemical vapor deposition over the barrier layer stack to form a quantum dot encapsulation layer stack, and encapsulating one or more quantum dot structures with the quantum dot encapsulation layer stack. BRIEF DESCRIPTION OF THE DRAWINGS

100161 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 cross-sectional view of a layer stack according to embodiments described herein;

FIG. 2 shows a schematic depiction of an ALD reaction cycle according to embodiments described herein;

FIGS. 3a, 3b show a schematic view of first and second gas distribution enclosures according to embodiments described herein;

FIG. 4 shows images of test samples according to embodiments described herein;

FIGS. 5a, 5b show analysis results of test samples according to embodiments described herein;

FIG. 6 shows a schematic view of a roll-to-roll processing apparatus according to embodiments described herein;

FIG. 7 shows a schematic view of a roll-to-roll processing apparatus according to embodiments described herein;

FIG. 8 shows a cross-sectional view of a quantum dot encapsulation according to embodiments described herein;

FIG. 9 shows a cross-sectional view of a quantum dot encapsulation according to embodiments described herein;

FIG. 10 shows a flow chart illustrating a method for depositing a barrier layer on a flexible substrate according to embodiments described herein; and FIG. I I shows a flow chart illustrating a method for encapsulating a quantum dot structure according to embodiments described herein.

DETAILED DESCRIPTION

[0017] 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. Generally, 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.

[0018] A thm conformal layer of material is beneficial as a means of reducing Water Vapor Transmission Rate (WVTR) through encapsulation layer(s). High performance barrier films can be defined as having WVTR < 1x10^"J g/m²/day, with some applications requiring as low as IxlO^"6 g/m²/day.

[0019] There are a number of commercial ways to encapsulate devices. According to some embodiments described herein, an ALD process to cover a moisture-sensitive device is provided. Plasmaless atomic layer deposition can denote an ALD process for which no plasma is produced for forming a solid layer. Depending on the precursor gases, it may be beneficial to induce the chemical reaction by excitation of a precursor gas. Plasma-enhanced atomic layer deposition can denote an ALD method in which the second precursor (starting compound) is fed with a plasma being simultaneously produced. Alternatively, temperature- enhanced atomic layer deposition can denote an ALD method in which the precursor gases are fed during being simultaneously heated.

[0020] Substrates such as PET (polyethylene terephthalate), PEN (polyethylene naphthalate), or PI (poiyimide) are used, followed by a sequence of thin films which act as a barrier, for example a water vapor barrier or a gas barrier. Plasma-enhanced chemical vapor deposited (PECVD) layers such as SiN_x or Si0₂ are often used as barrier layers due to their high deposition rates (>100nm/min) and low ideal WVTR (< lxlO^"7 g/m²/day). However, defects in the films lead to much higher WVTR in practice due to particles on the substrate surface, defects in the substrate, and/or grain boundaries in the film. PECVD layer thicknesses are typically in the lOOnm - Ι μιη range. Rather than covering any defects on the substrate surface with the layer, the defects typically propagate through the film, leading to increased local WVTR.

[00211 Atomic layer deposition (ALD) is also used for barrier layers such as AI₂O₃, TiQ₂, ZrQ₂, SiO_?., ΗίΌχ, and others, and combinations thereof. An advantage of ALD is a high-quality, conformal film., leading to very low WVT^'R. As compared to PECVD, ALD deposition rates are typically very low (< 2 nm/'min). For example, film thicknesses can be several tens of nanometers such as 20 mil, 30 mil, or 40 nm, wherein a limitation may exist e.g. due to a reasonable production time. With these thicknesses, ALD layers can for example be disrupted by larger particles, especially those that may detach from the surface, leaving a void with high WVTR.

[0022] According to embodiments of this disclosure, an ALD starting layer is deposited prior to PECVD deposition to decrease the number of defects in the barrier film. A mechanism for this improvement can be that the ALD starting layer provides a defect-free surface for the PECVD deposition. This defect-free surface provides fewer defects to propagate through the subsequent deposited PECVD layer. Defects in the SiN layer can be subject to hydrolysis at high temperature and/or humidity conditions. According to some embodiments, the ALD layer can acts as a buffer layer or a seed layer to prevent contact between water vapor diffusing through the plastic substrate and the SiN_x layer deposited thereon.

[0023] According to an embodiment of the present disclosure as illustrated in FIG. 1, a barrier structure can include a barrier layer 120 deposited by ALD onto a flexible substrate 110. The barrier layer 120 deposited by ALD can be a layer stack comprising several monolayers formed of a product compound by a chemical reaction of a first precursor material and a second precursor material. The barrier layer stack deposited by ALD can have a thickness of 3 nm or above. According to another embodiment, the barrier layer stack deposited by ALD can have a thickness of 20 nm or below. According to yet a further embodiment, the barrier layer stack deposited by ALD can have a thickness of 3 nm or above and of 20 nm. or below. Over this ALD barrier layer stack, a layer by plasma-enhanced chemical vapor deposition (PECVD layer 130) is deposited. The barrier layer stack includes at least one barrier layer deposited by atomic layer deposition followed by a PECVD layer e.g. having an overall thickness of at least 50 nm or above, particularly of 100 nm. or above, more particularly of 500 nm or above.

[0024] According to embodiments described herein, FIG. 2 illustrates a process of forming a product compound by a chemical reaction of the first precursor material and the second precursor material. The product compound can be formed on the flexible substrate 1 10 during transportation of the flexible substrate. In a first gas distribution enclosure 150 arranged opposite to the substrate front side as illustrated in FIGS. 3a and 3b, the first precursor material A can be provided on the substrate surface by chemisorption. As illustrated in FIG. 2, during passage, the flexible substrate 1 10 is covered by an increasing number of particles of the first precursor A. In the first gas distribution enclosure 150, the flexible substrate 1 10 is provided with a layer, e.g. a closed layer, of particles of precursor A.

[0025] The flexible substrate 110 leaving the first gas distribution enclosure 150 can be transported into the second gas distribution enclosure 160 as shown in FIGS. 3a and 3b. As illustrated in FIG. 2, during transportation of the flexible substrate through the second gas distribution enclosure, the second precursor material B can be provided by chemisorption on the substrate having a surface coated with a film of precursor A. In the second gas distribution enclosure 160, the flexible substrate 1 10 is provided with a layer, e.g. a closed layer, of particles of the precursors A and B.

[0026] By a chemical reaction, the deposited particles of precursors A and B can form a product compound AB. Depending on the nature and/or the combination of the first and second precursors A and B, the chemical reaction can autonomously start self-induced. It can be beneficial to promote or induce the chemical reaction by an excitation unit 140. The excitation unit 140 can be optionally installed in the first and/or second gas distribution enclosures. For example, the excitation unit can be a plasma source or a heater. For instance, the plasma can be generated from a precursor gas by a micro-wave antenna or by a RF antenna. [0027] The substrate section passing the first and second gas distribution enclosures can be provided with a mono layer of the product compound AB. For forming a barrier layer by atomic layer deposition having a sufficient thickness, the substrate can be provided with several mono layers of the ALD product compound AB one above the other. An ALD layer stack of several mono layers can be generated by aiternatingly passing a first gas distribution enclosure and second gas distribution enclosure. For each mono layer of product compound AB, a pair of first and second gas distribution enclosures can be passed. Beneficially, a plurality of first and second gas distribution enclosures can be arranged aiternatingly.

[0028] The flows of the first and second precursor gases can be adapted to the transportation velocity of the flexible substrate. It is beneficial to saturate the surface quickly. With increasing saturation rate, the dimensions of the first and second gas distribution enclosures can be reduced. Reducing the dimensions of the gas distribution enclosures leads to smaller dimensions of the processing apparatus for atomic layer deposition. Reducing the dimensions of the processing apparatus leads to lower cost of ownership.

[0029] According to embodiments of the present disclosure, the precursors A can be selected from the group consisting of: Trimethylaluminum (TMA), Tetrakis(dimethylamido)Hafhium(IV) (TDMAHf), Tetrakis[EthyiMethylAmino |Hafnium (TEMAHf), Tetrakis(dimethylamido)Zirconium(IV) (TDMAZr), tris(dimethylamino)silane (TDMAS), Titanium, tetrachloride (T^'iCU), or Tetrakis(dim.ethylamino)Titanium (TDMAT). The first precursor materials such as metal precursors are typically very volatile, so thermal activation is sufficient. The second precursors B can be selected from the group consisting of: S 1,0. S ί,Ο,. () ·, {) :. \ .{).

[0030] The second precursor material can be an oxidizer. For plasma-less ALD the oxidizer can be, e.g. water or Q₃, which are thermally activated. In case of plasma-enhanced ALD, for example oxygen is injected into the second gas distribution enclosure as an oxidizer. An oxygen plasma can be ignited by a plasma source. The plasma source can be installed in the second gas distribution enclosure. The oxygen particles excited by the plasma can react with the first precursor material chemisorbed to the substrate surface.

[0031] According to embodiments described herein, FIGS. 3a and 3b illustrate a pair of first and second gas distribution enclosures. For generating an ALD barrier layer of sufficient layer thickness, a plurality of first gas distribution enclosures 150 and a plurality of second gas distribution enclosures 160 can be arranged opposite to the substrate front side for deposition of a first and second precursor material, wherein the plurality of first gas distribution enclosures 150 and the plurality of second gas distribution enclosures 160 are arranged aiternatingiy.

[0032] Between at least one first gas distribution enclosure 150 of the plurality of first gas distribution enclosures and at least one second gas distribution enclosure 160 of the plurality of second gas distribution enclosures, a gas separation stage 170 can be arranged. The gas separation stage 170 can include a gas feeding unit 200 such as a gas lance for providing a purge gas or a separation gas between a first and a second gas distribution enclosure. The gas lance can have several gas outlet openings over the length of the lance, e.g. along a width of a flexible substrate or in a direction perpendicular to a substrate transport direction, for uniformly providing the purge gas or a separation gas over the width of the flexible substrate. The precursor gases A and B exiting the first and/or second gas distribution enclosures, respectively, can be evacuated by vacuum pumps arranged in the rear of the gas separation stages 170 as indicated by arrows 210.

[0033] The precursor gases A and B exiting the first and the second gas distribution enclosures, respectively, can be evacuated by vacuum pumps together with the purge gas or the separation gas. The purge gas or separation gas can reduce the concentration of precursor gases or dilute the precursor gases A and B such that a reaction can be avoided. Without a reaction of the precursor gases A and B, the components outside the first and second gas distribution enclosures can be kept free of depositions from product compound AB. Without such depositions, a pollution of installed components can be avoided.

[0034] According to the embodiment illustrated in FIG. 3a, the first and/or second precursor gases A and B can be fed into the first and/or second gas distribution enclosures as indicated by arrows 180. The precursor gases can pass a gas distribution plate 190, for example a shower head, for a uniform distribution of the precursor gas over the substrate surface. The gas distribution plate, e.g. the shower head, can be provided with a plurality of openings. The pressure of the precursor gases at the input side of the gas distribution plate, e.g. of the shower head, is according to some embodiments higher than at the deposition side of the gas distribution plate, e.g. of the shower head, resulting in a pressure difference. For example, the pressure difference can be one order of magnitude.

[0035 J According to an alternative embodiment as illustrated in FIG. 3b, the first and second gas distribution enclosures can each include a precursor gas feeding unit 220 arranged inside the housing of the gas distribution enclosures. One precursor gas feeding unit 220 can provide the first precursor gas into the first gas distribution enclosure. A second precursor gas feeding unit 220 can provide the second precursor gas into the second gas distribution enclosure. The precursor gas feeding units 220 can be gas lances, for example, having several gas outlet openings over the length. Further, the first and/or the second the gas distribution enclosures can be provided with an excitation unit 140. In FIG. 3b, the excitation unit 140 is shown in the second gas distribution enclosure 160. Alternatively or additionally, an excitation unit 140 can be provided in the first gas distribution enclosure 150.

[0036] According to an embodiment, the barrier layer stack can include at least one barrier layer deposited by atomic layer deposition followed by a PECVD layer. A PECVD layer such as SiN_x or S1O₂ can be used as a barrier layer. According to embodiments of this disclosure, the ALD harrier layer is deposited as a starting layer followed by the deposition of a PECVD layer. The ALD barrier layer can decrease the number of defects in the growing PECVD layer. A mechanism for this improvement can be that the ALD starting layer provides a defect-reduced or a defect-free surface for the PECVD deposition. This defect- reduced or defect-free surface provides fewer defects to propagate through the subsequent deposited PECVD layer.

[0037] Defects in the PECVD layer can be subject to hydrolysis at high temperature and/or humidity conditions. As a result of the hydrolysis, the WVTR increases, i.e. the effect of the barrier film decreases. According to embodiments described herein, the ALD barrier layer can act as a buffer layer to prevent contact between the water vapor diffusing through the plastic substrate and the PECVD layer deposited thereon. The buffer effectiveness of the ALD barrier layer can be demonstrated by an aging test in a chamber at environmental conditions of 85°C and 85% H (relative humidity). In this aging test, the WVTR is detected.

[0038] A common method to quantify WVTR is the calcium test. For example, the calcium test is known from publication "Evaluating High Performance Diffusion Barriers: the Calcium Test" by G. Nisato, PCP Bouten, PJ Slikkerveer, WD Bennett, GL Graff, N Rutherford, and L Wiese (Proc, Int. Display workshop/ Asia Display, 2001/10/16, p. 1435- 1438). The barrier layer stack is coated by a thin film of calcium (Ca) and then sealed to a glass lid with a getter-containing adhesive. The Ca layer starts as an opaque film having an optical transmission of, for example, about 10% for a 60nm Ca layer. As the Ca layer is exposed to water, there is a chemical reaction from Ca to Ca(OH)₂, which is transparent.

[0039] The Ca test provides the following data: from the optical transmission of the Ca layer at areas with no defects before starting the test, the thickness of the Ca layer can be calculated. Using the change in optical transmission, i.e. the change of thickness over time, the WVTR rate can be calculated. This is referred to as the "bulk permeation". If there are defects in the barrier layer stack, pinholes will appear in the Ca layer over time. Both the number densit ' and area of these pinholes can be calculated over time. The Ca test data disclosed herein were generated according to test method A as described in the above mentioned publication.

0040] The sample structures as shown in Table 1 were subjected to the Ca test:

[00411 FIG. 4 illustrates the images of the Ca test data for the four samples of Table I at different aging times. The samples were aged in an environmental chamber at a temperature of 85°C and a humidity of 85%RH. As can be seen from FIG. 4, the single layer samples present the highest WVTR. The TiQ₂ lay er (sample 1) presents defects in the bamer layer visualized by pinholes in the Ca layer. The decreasing areal optical density of the SiN_x single layer (sample 2) indicates a high bulk permeation of water vapor. The lowest defect density presents sample 4 with the layer stack of a seed layer of TiQ₂ deposited by ALD and a barrier layer of SiN_x deposited by PECVD.

[0042] The plot of FIG. 5a illustrates the analysis of the Ca area remaining for samples in FIG. 4. Tire Ca area begins at 100%, and decreases as the Ca area is exposed to water vapor. The sample with only SiN_x fails after approximately 150 h.

[0043] The plot of FIG. 5b illustrates the analysis of the number of defects for samples in FIG. 4, as evidenced by the appearance of pinholes in the Ca layer. Pinholes become detectible when the diameter exceeds lOum, as the pixel size of the images is approximately Sum. It is notable that for the TiCVSiN_x sample, there are very few defects when the sample is aged at >450 h.

[00441 Table 2 shows the performance metrics of FIGS. 5a and 5b for different barrier layer configurations, assuming an acceleration factor of lOOx. The acceleration factor of lOOx is based on the assumption that aging 100 hours at 85°C/85%RH is comparable to aging 10,000 hours at 20°C/50%RH. A WVTR of 2x10^"5 g m7day is the detection limit for this apparatus. Error ranges are calculated from the standard deviation of at least three samples fabricated simultaneously.

[0045] The Ca test demonstrated that the performance of the PECVD barrier films was significantly improved by the incorporation of an ALD seed layer. Specifically, the number of defects in the barrier film was decreased significantly. The overall performance of the ALD/PECVD layer was significantly better than either material alone, or the common structure consisting of PECVD/ALD. In effect, the ALD barrier layer is improving the quality of the subsequent PECVD barrier layer,

[0046] According to embodiments described herein which can be combined with other embodiments, synthetic substrate materials such as PET (polyethylene terephthalate), PEN (polyethylene naphthalate), or PI (polyimide) can be coated, for example, in roll-to-roll processing apparatuses. A roll-to-roll processing apparatus can include an unwinding chamber, a processing chamber, and/or a re-winding chamber. In some roll-to-roll processing apparatuses, unwinding and re-winding of the flexible substrate can be performed in a common winding chamber.

[0047] The processing chamber can include a plurality of transport rollers. Tl e transport rollers can act as supports for a flexible substrate. A transport roller can be a processing drum such as a coating drum or a coating roller. The processing drum can provide a surface for contacting the backside of the flexible substrate. The surface of the processing drum can be kept at a predetermined temperature level. The processing region can be arranged adjacent to the front side of the traveling flexible substrate. A transport roller can further be a guide roller for deflecting tlie transport direction of the flexible substrate from a straight direction. The flexible substrate can be moved through a processing region by one or more guide rollers.

[0048] According to another embodiment, the flexible substrate may further be transported on several guide rollers providing a free-span path. Processing of the substrate, such as coating of the substrate can be provided at a free-span path. The free-span path maybe a portion of the transportation path of the flexible substrate. Temperature adjustment devices such as heaters or radiation heaters can be provided in the free-span path facing the backside of the flexible substrate.

10049] It is noted here that a flexible substrate or web as used within the embodiments described herein can typically be characterized in that the flexible substrate is bendable. The term "web" may be synonymously used with the term "strip^", the term "tape", or the tenn "flexible substrate". For example, the web, as described in embodiments herein, may be a foil or another flexible substrate. However, as described in more detail herein, the benefits of embodiments described herein may also be provided for non-flexible substrates or carriers of other inline deposition systems. Yet, it is understood that particular benefit can be utilized for flexible substrates and applications for manufacturing devices on flexible substrates.

[0050] In certain roll-to-roll processing apparatuses, the flexible substrate can be transported along a serpentine path around guiding rollers or deflection rollers spaced apart. This serpentine path configuration results in altematingly contacting the front side and the back side of the flexible substrate by rollers when the flexible substrate moves through the system. Such a mechanical contact can interfere with the ALD process, as the mechanical contact can disturb the chemisorbed precursor or result in mechanical damage to the coating and/or underlying substrate surface. Typically, this damage can be caused by imperfections or particles on the surface of rollers, or by surface imperfections generated in the deposited ALD layer. The rollers contacting an already deposited ALD layer can press particles into the coated surface or can lift off sections of the deposited ALD layer. Such damages of the coated side of the substrate can reduce or compromise the barrier properties.

[0051] According to some embodiments of the present disclosure, in order to avoid the above described damages, the flexible substrate is transported by the transport rollers such that only the backside of the flexible substrate is contacted. All rollers are contacting only the backside of the flexible substrate. No roller contacts the front side of the flexible substrate.

[0052] FIG. 6 shows a schematic view of a roll-to-roll processing apparatus 225 according to embodiments described herein. The roii-to-roll processing apparatus 225 can be a vacuum deposition apparatus which can be evacuated by vacuum pumps (not depicted in FIG.6), The flexible substrate 110 can be transported from unwinding roller 230 via processing drum 240 to re-winding roller 250. A plurality of first gas distribution enclosures 150 and a plurality of second gas distribution enclosures 160 can be arranged opposite to the substrate front side for the deposition of a first and second precursor material A and B, respectively, wherein the plurality of first gas distribution enclosures 150 and the plurality of second gas distribution enclosures 160 are arranged altematingly. The front side of the flexible substrate 110 is the coated side where the layer or layer stacks can be deposited. A contact of the front side of the flexible substrate 110 with any roller can be avoided to keep the deposited layers free of defects. [0053] According to embodiments described herein, the plurality of first gas distribution enclosures 150 and the plurality of second gas distribution enclosures 160 can be arranged altematingly in series or in a row. Accordingly, the plurality of first gas distribution enclosures 150 and the plurality of second gas distribution enclosures 160 are arranged altematingly one after the other and between a rewinding roller, e.g. a first position, and a winding roller, e.g. a second position, for example along the path of a flexible substrate in a roll-to-roll processing apparatus. As illustrated in FIG. 6 and FIG. 7, the sequence of first and second gas distribution enclosures can be arranged altematingly. The sequence of the altematingly arranged plurality of first and second gas distribution enclosures provides the possibility to perform a plurality of ALD monolayers generated one above the other. The plurality of ALD monolayers provide an ALD layer of preselected layer thickness.

[0054] Referring back to FIG. 6, the processing dram can be provided with a tempering unit configured for tempering the flexible substrate (not shown in FIG. 6). Tempering the flexible substrate can be heating or cooling. The tempering unit can be provided with a control unit. The control unit provides the possibility to adjust the process temperature to a preselected temperature level. By tempering the flexible substrate, the deposition process can be adapted to the type of ALD process to be performed. For example, encapsulation of OLEDs or QD structures typically is usually performed at lower temperatures between 80°C and I 10°C, so as not to damage either the underlying flexible substrate or OLED layer stack or QD structure.

[0055] Between at least one first gas distribution enclosure 150 of the plurality of first gas distribution enclosures and at least one second gas distribution enclosure 160 of the plurality of second gas distribution enclosures, a gas separation stage 170 can be arranged. The gas separation stage 170 can include a gas feeding unit 200 such as a gas lance for providing a purge gas or a separation gas between a first and a second gas distribution enclosure. The gas lance can have several gas outlet openings over the length for uniformly providing the purge gas or a separation gas over the width of the flexible substrate. The precursor gases A and B exiting the first and/or second gas distribution enclosures, respectively, can be evacuated by vacuum pumps arranged in the rear of the gas separation stages 170 as indicated by arrows 210. [0056] According to embodiments described herein, the roll-to-roll processing apparatus 225 can be provided with at least one further deposition chamber. For example, the at least one further deposition chamber can be configured for plasma-enhanced chemical vapor deposition (PECVD). The PECVD deposition chamber 260 can include a plasma source 270. The PECVD deposition chamber 260 can be configured to deposit a PECVD layer onto the barrie r layer or barrier layer stack deposited by ALD. For example, the PECVD layer can be a Si0₂ layer, a Si x layer, or a SiN layer. The at least one deposition chamber configured for plasma-enhanced chemical vapor deposition (PECVD) can be the first deposition chamber in the direction of transport of the flexible substrate downstream of the plurality of first gas distribution enclosures and the plurality of second gas distribution enclosures. The depicted number and/or type of gas distribution enclosures or further deposition chambers is arbitrary and is not to be regarded as delimiting the scope of disclosure. According to an alternative embodiment, a PECVD layer can be deposited in a separate roll-to-roll deposition apparatus.

[0057] FIG. 7 shows a schematic view of another roll-to-roll processing apparatus according to embodiments described herein . The roll-to-roll processing apparatus 225 can be a vacuum deposition apparatus which can be evacuated by vacuum pumps (not depicted in FIG.7). The roll-to-roll processing apparatus 225 includes two separate chambers for unwinding and re-winding the flexible substrate 110. The unwinding chamber can be provided with unwinding roller 230. The re-winding chamber can be provided with rewinding roller 250.

100581 The unwinding chamber and the re-winding chamber can be provided with a separate winding system for unwinding and re-winding an interleaf web or foil. The interleaf winding system is depicted with dotted lines in FIG. 7. The interleaf web or foil can protect the front side of the flexible substrate. Particularly, the barrier layers deposited onto the processed flexible substrate can be protected against damages.

100591 The unwinding chamber and the re-winding chamber can be separated with a maintenance zone 280. The maintenance zone 280 provides space for an operator to access the unwinding and/or re-winding chambers for maintenance. For example during maintenance, a bale of processed flexible substrate can be exchanged by an empty re- winding shaft. Further, an empty re-winding shaft can be exchanged by an uncoated bale of flexible substrate 1 10.

[0060] The roll-to-roll processing apparatus 225 of FIG. 7 can further provide two processing drums 240 and 240', respectively. The processing chamber comprising the two processing drums can be separated from the unwinding chamber and/or the re-winding chamber by load-lock valves 290. The flexible substrate 110 can be transported from unwinding roller 230 via processing drum 240 and processing drum 240^" to re-winding roller 250. A plurality of first gas distribution enclosures 150 and a plurality of second gas distribution enclosures 160 can be arranged opposite to the substrate front side for the deposition of a first and second precursor material A and B, respectively, wherein the plurality of first gas distribution enclosures 150 and the plurality of second gas distribution enclosures 160 are arranged alternatingly.

[0061] In the section of the transportation path which transfers the flexible substrate 110 from processing drum 240 to processing drum 240% a further plurality of first gas distribution enclosures and a further plurality of second gas distribution enclosures can be arranged opposite to the substrate front side for the deposition of a first and second precursor materia] A and B, respectively, wherein the further plurality of first gas distribution enclosures and the further plurality of second gas distribution enclosures are arranged alternatingly. In tins section of the transportation path, the flexible substrate can be transported in free-span manner supported by several guiding rollers 300.

[0062] The processing dram can be provided with a tempering unit configured for tempering the flexible substrate. Further, for tempering the substrate in the free-span section of tlie transportation path, the flexible substrate can be heated by heating units provided in the rear side of the flexible substrate. For sake of clarity , the tempering units are not shown in FIG. 7.

[0063] The embodiment according to FIG. 7 which can be combined with other embodiments described herein provides the possibility to increase the number of the plurality of first and second gas distribution enclosures. By increasing the number of the first and second gas distribution enclosures, an increased number of atomic layers of the barrier lay er deposited by ALD can be deposited in a single processing cycle. This results in an increased thickness of the ALD barrier layer and/or an increased throughput, e.g. an increased substrate transportation speed. An increased layer thickness of the ALD barrier layer stack can provide a decreased WVTR.

[0064] Between at least one first gas distribution enclosure 150 of the plurality of first gas distribution enclosures and at least one second gas distribution enclosure 160 of the plurality of second gas distribution enclosures, a gas separation stage can be arranged. In FIG.7, ihe gas separation stages are omitted for sake of clarity. A contact of the front side of the flexible substrate 110 with any roller can be avoided to keep the deposited layers free of defects.

[0065] According to embodiments which can be combined with other embodiments described herein, the roll-to-roll processing apparatus 225 as shown in FIG. 7 can be provided with at least one further deposition chamber. For example, the at least one further deposition chamber can be configured for plasma-enhanced chemical vapor deposition (PECVD). The at least one deposition chamber configured for plasma-enhanced chemical vapor deposition (PECVD) can be the first deposition chamber in the direction of transport of the flexible substrate downstream of the plurality of first gas distribution enclosures and the plurality of second gas distribution enclosures. The PECVD deposition chamber 260 can be configured to deposit a PECVD layer onto the barrier layer or barrier layer stack deposited by ALD. For example, the PECVD layer can be a Si0₂ layer, a SiNx layer, or a Si layer.

[0066] Additionally or alternatively, a deposition chamber configured for plasma- enhanced chemical vapor deposition (PECVD) can be the first deposition chamber in the direction of transport of the flexible substrate downstream of the unwinding roller 230. The additional or alternative PECVD deposition chamber 260' configured for plasma-enhanced chemical vapor deposition (PECVD) provides the possibility to deposit a planarization layer deposited directly on the flexible substrate. The planarization layer can eliminate the unevenness or roughness of the surface of the flexible substrate. Surface roughness can lead to growth of nodules. Nodules in the barrier layer can be a reason for defects in the ALD barrier layer. By smoothing the substrate^'s surface, the planarization layer can further reduce the number of defects in the ALD barrier layer. The planarization layer can further reduce the WVTR of the barrier film. [0067] Besides quantum dot enhancement films (QDEF), there are quantum dot LEDs (QD-LED) available. The structure of a QD-LED can include cadmium selenide (CdSe) nanocrystals as light emitting centers. The layer of cadmium-selenium quantum dots is sandwiched between layers of electron-transporting and hole-transporting organic materials. This layer stack can be sandwiched between a cathode layer and an anode layer, respectively. The organic materials of a QD display as well as the organic materials of an OLED display can be encapsulated by a barrier layer stack for reducing a degradation of the organic materials.

[00681 According to embodiments as described herein, an encapsulation of quantum dot structures can have the architecture: substrate barrier layer stack/QDs/bamer layer stack/substrate as illustrated in FIG. 8. The substrate can be PET or a different flexible substrate. The barrier layer stack can include the ALD harrier layer and the PECVD barrier layer. A quantum dot structure can be a quantum dot enhancement film QDEF or a QD-LED structure.

[00691 The uantum dot encapsulation 310 can include a first barrier structure 100 and a second barrier structure 100'. The first barrier structure 100 can include a flexible substrate 1 10, a barrier layer 120 deposited by ALD, and a PECVD layer 130. On this barrier structure 100, a quantum dot structure 320 can be deposited directly. For encapsulation, a second barrier structure 100' can be laminated. The second barrier structure 100' can include a flexible substrate 1 10', a barrier layer 120' deposited by ALD, and a PECVD layer 130'. The PECVD layer 130' of the second barrier structure faces the quantum dot structure 320.

[0070] According to another embodiment as illustrated in FIG . 9, a quantum dot structure 320 can be deposited on a substrate 115. Substrate 115 can be made of a material having a WVTR lower than that of the barrier structure 100 and/or the barrier structure 100'. For example, substrate 115 can be a wafer, or a thin, bendable glass foil or a metal foil. For encapsulation, the quantum dot structure 320 can be covered with a barrier structure 100 which is arranged above the quantum dot structure 320.

[0071 ] FIG. 10 shows a flow chart illustrating a method 700 for depositing a barrier film on a flexible substrate according to embodiments described herein. According to an aspect of the present disclosure, the method 700 includes in block 710 continuously transporting a flexible substrate from an unwinding roller to a re-winding roller. According to embodiments described herein, the method 700 further includes in block 720 contacting the flexible substrate on the back side thereof. According to embodiments described herein, the method 700 further includes in block 730 depositing a first precursor material on the flexible substrate in a first gas distribution enclosure arranged opposite to the substrate front side. According to embodiments described herein, the method 700 further includes in block 740 depositing a second precursor material on the flexible substrate in a second gas distribution enclosure arranged opposite to the substrate front side. According to embodiments described herein, the method 700 further includes in block 750 forming a product compound by a chemical reaction of the first precursor material and the second precursor material. According to embodiments described herein, the method 700 further includes in block 760 generating a barrier layer stack by repeating the deposition of the first precursor material and the second precursor material on the flexible substrate. According to embodiments described herein, the method 700 further includes in block 770 depositing a layer by plasma-enhanced chemical vapor deposition over the barrier layer stack.

[0072] FIG. 11 shows a flow chart illustrating a method 800 for encapsulating a quantum dot structure according to embodiments described herein. According to an aspect of the present disclosure, the method 800 includes in block 810 continuously transporting a flexible substrate. According to some embodiments, the method 800 further includes in block 820 depositing a first precursor material on the flexible substrate in a first gas distribution enclosure arranged opposite to the substrate front side. According to embodiments described herein, the method 800 further includes in block 830 depositing a second precursor material on the flexible substrate in a second gas distribution enclosure arranged opposite to the substrate front side. According to embodiments described herein, the method 800 further includes in block 840 forming a product compound by a chemical reaction of the first precursor material and the second precursor material. According to embodiments described herein, the method 800 further includes in block 850 generating a barrier layer stack by repeating the deposition of the first precursor material and the second precursor material on the flexible substrate. According to embodiments described herein, the method 800 further includes in block 860 depositing a layer by plasma-enhanced chemical vapor deposition over the barrier layer stack to form a quantum dot encapsulation for encapsulating one or more quantum dot structures with at least one first encapsulation layer stack. According to further embodiments described herein, the method 800 includes forming at least one second encapsulation layer stack and encapsulating the one or more quantum dot structures between at least two encapsulation layer stacks.

[0073] The present disclosure has several advantages including a continuously deposited ALD layer on flexible substrates particularly on elongated flexible substrates such as foils bands or tapes, avoiding a front contact of the flexible substrate by the transport rollers, providing a PECVD barrier layer on the ALD layer without breaking the vacuum of the processing apparatus, and/or producing a barrier layer of improved barrier effect.

[0074] While the foregoing is directed to embodiments of the disclosure, other and further embodiments of the disclosure may be devised without departing from, the basic scope thereof, and the scope thereof is determined by the claims that follow.

Claims

1. A processing apparatus for atomic layer deposition of a thin film on a flexible substrate, comprising:

a substrate support configured to continuously transport the flexible substrate; a plurality of first gas distribution enclosures arranged opposite to a substrate front side for providing a first precursor material on the front side of the flexible substrate; and a plurality of second gas distribution enclosures arranged opposite to the substrate front side for providing a second precursor material on the front side of the fl exible substrate, wherein the plurality of first gas distribution enclosures and the plurality of second gas distribution enclosures are arranged alte natingiy.

2. The processing apparatus according to claim 1, wherein the substrate support configured to continuously transport the flexible substrate from a first position to a second position different than the first position, and wherein the plurality of alternatingiy arranged first and second gas distribution enclosures are arranged in series between the first position and the second position.

3. The processing apparatus according to any of claims 1 or 2, further comprising: at least one gas separation stage arranged between at least one first gas distribution enclosure of the plurality of fi rst gas distribution enclosures and at least one second gas distribution enclosure of the plurality of second gas distribution enclosures.

4. The processing apparatus according to any of claims 1 or 2, further comprising: an excitation unit configured to induce a chemical reaction, particularly wherein the excitation unit is provided in the at least one of a first or second gas distribution enclosure.

5. The processing apparatus according to claim 3, wherein the excitation unit is a plasma source or a heater.

6. The processing apparatus according to any of the preceding claims, further comprising at least one deposition chamber configured for plasma-enhanced chemical vapor deposition (PECVD).

7. The processing apparatus according to claim 5, wherein the at least one deposition chamber configured for plasma-enhanced chemical vapor deposition (PECVD) is a first deposition chamber in a direction of transport of the flexible substrate downstream of the plurality of first gas distribution enclosures and the plurality of second gas distribution enclosures.

8. The processing apparatus according to any of the preceding claims, wherein the plurality of first gas distribution enclosures and/or the plurality of second gas distribution enclosures comprise a gas distribution plate.

9. The processing apparatus according to any of the preceding claims, wherein the plurality of first gas distribution enclosures and/or the plurality of second gas distribution enclosures comprise a gas lance with openings.

10. The processing apparatus according to any of the preceding claims, further comprising:

a winding system for transporting said flexible substrate from an unwinding roller to a re-winding roller, wherein the substrate support is at least one processing drum configured to continuously transport the flexible substrate and to contact the flexible substrate on a back side thereof.

11. A barrier layer stack deposited onto a flexible substrate, the barrier layer stack comprising at least one barrier layer deposited by atomic layer deposition followed by at least one barrier layer deposited by plasma-enhanced chemical vapor deposition having an overall thickness of at least 100 ran.

12. The barrier layer stack according to claim 11, wherein a material of the at least one barrier layer is selected from the group consisting of AI2O₃, Ti0₂, Zr0₂, Si0₂, HfO_x, and combinations thereof ,

13. A roll-to-roll processing apparatus for atomic layer deposition of a thin film on a flexible substrate, comprising:

a winding system for transporting said flexible substrate from an unwinding roller to a re-winding roller;

a substrate support configured to continuously transport the flexible substrate and to contact the flexible substrate on a back side thereof;

a plurality of first gas distnbution enclosures arranged opposite to a substrate front side for deposition of a first precursor material;

a plurality of second gas distribution enclosures arranged opposite to the substrate front side for deposition of a second precursor material, wherein the plurality of first gas distribution enclosures and the plurality of second gas distribution enclosures are arranged altemaiingiy;

at least one gas separation stage arranged between at least one first gas distri bution enclosure of the plurality of first gas distribution enclosures and at least one second gas distribution enclosure of the plurality of second gas distribution enclosures; and

an excitation unit coupled to the at least one first or second gas distribution enclosure configured to induce a chemical reaction, wherein the excitation unit is a plasma source.

14. A method for depositing a barrier film on a flexible substrate comprising:

continuously transporting a flexible substrate from an unwinding roller to a rewinding roller;

contacting the flexible substrate on a back side thereof;

depositing a first precursor material on the flexible substrate in a first gas distribution enclosure arranged opposite to a substrate front side;

depositing a second precursor material on the flexible substrate in a second gas distribution enclosure arranged opposite to the substrate front side; forming a product compound by a chemical reaction of the first precursor material and the second precursor material;

generating a barrier layer stack by repeating the deposition of the first precursor material and the second precursor material on the flexible substrate: and

depositing a layer by plasma-enhanced chemical vapor deposition over the barrier layer stack,

15. A method for encapsulating a quantum dot structure, comprising:

continuously transporting a flexible substrate;

depositing a second precursor material on the flexible substrate in a second gas distribution enclosure arranged opposite to the substrate front side;

forming a product compound by a chemical reaction of the first precursor material and the second precursor material;

generating a barrier layer stack by repeating die deposition of the first precursor material and the second precursor material on the flexible substrate;

depositing a layer by plasma-enhanced chemical vapor deposition over the barrier layer stack to form a quantum dot encapsulation layer stack; and

encapsulating one or more quantum dot structures with the quantum dot encapsulation layer stack.

16. The method according to claim 15, further comprising:

forming at least one second quantum dot encapsulation layer stack and encapsulating the one or more quantum dot structures between the quantum dot encapsulation layer stack and at least one second encapsulation layer stack.