Patent Application
20140242365
The invention relates to a method for manufacturing a barrier layer on a flexible substrate. The present invention further relates to a device for manufacturing such a barrier layer. Further the invention relates to a substrate comprising a very thin barrier layer.
Atomic layer deposition (ALD) is used in the art to provide layers of a material on the surface of a substrate. Different from chemical vapor deposition (CVD) and physical vapor deposition (PVD), atomic layer deposition (ALD) is based on saturated surface reactions. The intrinsic surface control mechanism of ALD process is based on the saturation of an individual, sequentially-performed surface reaction between the substrate reactive sites and precursor molecules. The saturation mechanism makes the film growth rate directly proportional to the number of reaction cycles instead of the reactant concentration or time of growth as in CVD and PVD.
ALD is a self-limiting reaction process, i.e. the amount of deposited precursor molecules is determined only by the number of reactive surface sites on the substrate surface and is independent of the precursor exposure after saturation.
The ALD cycle is composed of several steps. In general it is performed in one single treatment space. It starts with providing the surface of a substrate with reactive sites. As a next step a precursor is allowed to react with the reactive sites and the excess material and reaction products are purged out of the treatment space and, ideally, a mono layer of precursor remains attached to the substrate surface via the reactive surface sites. A reactive agent is introduced into the treatment space as next step and reacts with the attached precursor molecules to form a monolayer of the desired material having reactive sites again, after which unreacted material and by-product is purged out. Optionally the cycle is repeated to deposit additional monolayers. With each cycle basically one atomic layer can be deposited which allows a very accurate control of film thickness and film quality.
In the prior art, several methods have been developed to enhance the reaction step in this ALD process, e.g. thermal ALD and plasma assisted ALD. The plasma as used in known ALD methods may be for example a low pressure RF driven plasma or an inductively-coupled plasma (ICP) or capacitively-coupled plasma (CCP), and may be used to deposit Al2O3, HfO2, Ta2O5 and many other materials.
International patent publication WO 01/15220 describes a process for deposition of barrier layers in integrated circuits, in which ALD is used. In the ALD steps, low pressure is used (of about 10 Torr (1330 Pa)) in combination with a thermal reaction step at a high temperature (up to 500° C.). Alternatively it is suggested to use a plasma to produce a reactive environment. All disclosed embodiments describe a very low pressure environment, requiring special measures in the apparatus used.
U.S. patent application U.S. 2004/0219784 describes methods for forming atomic layers and thin films, using either thermal reaction steps, or plasma assisted reaction steps, in which radicals are formed remotely form the substrate and transported thereto. Again, these processes are performed at relatively high temperature (100-350° C.) and low pressure (almost vacuum, typically 0.3 to 30 Torr (40 to 4000 Pa)).
U.S. patent application U.S. 2003/0049375 discloses a CVD process to deposit a thin film on a substrate using a plasma assisted CVD process at low pressure. The formation of a plurality of atomic layers is claimed. The known ALD methods as described above are mainly performed under low pressure conditions, and thus require vacuum equipment. Furthermore, the ALD methods described using thermal reaction steps (at temperatures well above room temperature, e.g. even 300-900° C.), are not suitable for deposition of material on temperature sensitive substrates, such as polymer substrates.
WO 2007145513 from applicant and hereby incorporated by reference discloses by using plasma assisted atomic layer deposition (ALD) water vapor barrier properties can be found in the range of 4*10−3 g/m2*day with a film thickness as low as 10-20 nm thick due to well controlled film growth and high conformality covering irregularities on the surface. However typically more than 100 ALD cycles are needed to achieve this property as for example the maximum growth rate of Al2O3 grown by ALD is typically 0.07˜0.11 nm/ cycle. Due to low film thickness growth per cycle in ALD this sets a limit to the productivity of the ALD process particularly for high volume applications like barrier films.
It is an object of the invention to provide a faster and more efficient method for creating an improved barrier on a substrate, in particular on a flexible substrate.
According to the present invention, it has been found that excellent water vapor barrier layers can be made on flexible substrates having an inorganic oxide layer on top in a rather efficient and fast mode using atmospheric pressure discharge plasma. According to a present invention embodiment, a method is provided for manufacturing a barrier layer on a flexible substrate, the method comprising a first step comprising depositing an inorganic oxide layer on the flexible substrate using an atmospheric pressure plasma and a second step comprising consecutive deposition of between 1 and 70 atomic layers on the inorganic oxide layer.
Surprisingly we have found that after an ultra-fast deposition step of an inorganic layer in the first step (resulting in no to little barrier improvement) by using an atmospheric pressure plasma on a flexible substrate an excellent water vapor property can be reached by far less ALD cycles than on samples prepared on substrates treated only by ALD and not having undergone the first step of the present embodiment.
In an embodiment of the present invention, the first step is executed using an atmospheric pressure glow discharge (APGD) plasma apparatus. This provides for a very efficient and uniform deposition of the inorganic oxide layer.
In one embodiment the first step comprises deposition of the inorganic oxide layer with a thickness between 10 and 100 nm. In exemplary embodiments the inorganic oxide layer is a silicon oxide layer from which the thickness may vary between 10 and 100 nm. In case of speed of the process being relevant, the thickness is as low as possible i.e. 20, 25, 30, 35, 40, 50, 60, 65, 70, 75, 80 or 90 nm.
In a further embodiment, the ALD layer deposited in the second step is Al2O3 having a thickness of between 0.5 to 10 nm, preferably between 1 to 10 nm. Also here in case the speed of the process being relevant, the thickness is as low as possible i.e. 1, 2, 3, 4, 5, 6, 7, 8 or 9 nm.
E.g. when using a 70 nm thin SiO2 layer deposited using an atmospheric pressure glow discharge plasma, a water vapor transmission rate of 4.8*10−3 g/m2*day (40° C./100% RH) barrier was observed after 7 cycles of ALD. The substrate made by the invention method in this particular case comprises an ALD layer of only 1 nm thick.
By use of the APGD system in the first step of the present invention an inorganic oxide layer may be deposited at high deposition rates between 20 and 200 nm/s and results in a layer having no or little moisture barrier improvement compared to the bare flexible substrate whereon it has been deposited. The inorganic layer resulting after the first step of the present invention embodiments is preferably a layer having a free pore volume of between 0.3 and 10%, more preferably between 0.3 and 3%.
Typically the treated substrates do not possess a good water vapor barrier property after the first step deposition and are in general not better than the barrier properties of the bare polymer substrate.
Preferred precursors which may be used for forming an inorganic oxide layer as first step in the present invention on a flexible substrate by using an atmospheric pressure glow discharge plasma are for example TEOS, HMDSO, TPOT, TEOT, TMA, TEA, etc. as disclosed in WO 2009 104 957 by applicant and is hereby incorporated by reference.
The flexible substrate may be any kind of polymeric film. In an exemplary embodiment PET or PEN film is used having a thickness of 50 to 200 μm.
Other examples of substrate which may be used are transparent sheets of ethylene vinyl acetate (EVA), of polyvinyl butyral (PVB), of polytetrafluoroethylene (PTFE), perfluoroalcoxy resins (PFA), i.e., copolymers of tetrafluoroethylene and perfluoroalkyl vinyl ether, tetafluoroethylene-hexafluoropropylene copolymers (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether-hexafluoro-propylene copolymers (EPE), tetrafluoroethylene-ethylene or propylenecopolymers (ETFE), polychlorotrifluoroethylene resins (PCTFE), ethylene-chlorotrifluoroethylene copolymers (ECTFE), vinylidene fluoride resins (PVDF), and polyvinyl fluorides (PVF) or coextruded sheets from polyester with EVA, polycarbonate, polyolefin, polyurethane, liquid crystal polymer, aclar, aluminum, of sputtered aluminum oxide polyester, sputtered silicon oxide or silicon nitride polyester, sputtered aluminum oxide polycarbonate, and sputtered silicon oxide or silicon nitride polycarbonate.
In the present invention embodiments the exact type of ALD process in the second step is not very relevant. In one embodiment, the second step is executed using a plasma assisted atomic layer deposition (ALD), and in a further embodiment, the second step is executed using a thermal atomic layer deposition (ALD) step. Variants of ALD equipment using such techniques may also be used, such as low pressure inductively-coupled plasma (ICP) or capacitively-coupled plasma (CCP) or RF driven plasma or thermal ALD.
In a further aspect, the present invention relates to an apparatus for manufacturing a barrier layer on a substrate, the apparatus comprising:
wherein the apparatus is arranged to provide an inorganic layer on the substrate using the atmospheric pressure glow discharge (APGD) plasma apparatus, and to provide a consecutive deposition of between 1 and 70 atomic layers on the inorganic oxide layer using the ALD device.
In a further embodiment, the ALD device comprises a treatment space and gas supply devices for providing various gas mixtures to said treatment space, the gas supply device being arranged to provide a gas mixture comprising a precursor material to the treatment space for allowing reactive surface sites to react with precursor material molecules to give a surface covered by a monolayer of precursor molecules attached via the reactive sites to the surface of the substrate in the first treatment space and to provide a gas mixture comprising a reactive agent capable to convert the attached precursor molecules to active precursor sites. The various steps and interposed purging steps may be executed in a single treatment space.
In an even further embodiment, the atmospheric pressure glow discharge (APGD) plasma apparatus comprises at least two opposing electrodes and a treatment space between the at least two opposing electrodes, a dielectric barrier being provided in the treatment space between the at least two opposing electrodes and comprising in operation the substrate, the at least two opposing electrodes being connected to a plasma control unit for generating an APGD plasma in the treatment space.
The ALD device comprises at least two separate treatment spaces having a first and second gas supply devices for providing various gas mixtures to the at least two treatment spaces in a further embodiment. The first gas supply device is operated to provide a gas mixture comprising a precursor material to the treatment space for allowing reactive surface sites on the substrate surface to react with precursor material molecules to provide a surface of the substrate covered by a monolayer of precursor molecules attached via the reactive sites to the surface of the substrate in the first treatment space, and the second gas supply is operated to provide a gas mixture comprising a reactive agent capable to convert the attached precursor molecules to active precursor sites, the method further comprising moving the substrate between the first and second treatment spaces, and generating an atmospheric pressure plasma in the gas mixture comprising the reactive agent.
In an even further embodiment, the atomic layer deposition (ALD) device comprises a plurality of first and second treatment spaces placed sequentially one behind the other in a circular or linear arrangement.
When different treatment spaces exist, they may be connected via a transport device which is capable to transport the substrate from treatment space to treatment space.
The at least two electrodes are roll electrodes in a further embodiment, and the flexible substrate is moved through the treatment spaces continuously.
An even further aspect of the present invention is related to a substrate with a very thin barrier layer having improved barrier properties and robustness property after exposure in water-saturated vapor conditions. In one embodiment, the flexible barrier substrate comprises a 10 to 100 nm thick inorganic oxide layer having a free pore volume of 0.3 to 10% and a 0.5 to 10 nm ALD layer (e.g. a free pore volume of 0.3 to 3% and a 1 to 10 nm ALD layer). In a further embodiment, the flexible substrate comprises a 10 to 100 nm thick inorganic oxide layer having a free pore volume of 0.3 to 10% and 0.5 to 5 nm ALD layer (e.g. a free pore volume of 0.3 to 3% and a 1 to 5 nm ALD layer). In an even further embodiment, the flexible substrate comprises a 10 to 100 nm thick SiO2 layer having a free pore volume of 0.3 to 10% and a 0.5 to 5 nm Al2O3 ALD layer (e.g. a free pore volume of 0.3 to 3% and a 1 to 5 nm Al2O3 ALD layer). All embodiments are made using the present invention method and/or apparatus embodiments. The flexible substrates thus obtained are produced in a fast and efficient manner and have excellent water vapor barrier properties which could not be reached by both steps separate and deposited alone (i.e. the first step without the second step deposition or the second step without the first step deposition).
The present invention will be discussed in more detail below, using a number of exemplary embodiments, with reference to the attached drawings, in which
a/b shows schematic views of an embodiment of the invention of the first step of the present method.
The present invention will now be described in reference to exemplary embodiments of the invention.
According to the present invention, a faster and more efficient procedure is provided for manufacturing a water vapor barrier on a flexible polymer substrate. A method is provided for manufacturing a barrier layer 1b on a flexible substrate 1, the method comprising a first step comprising depositing an inorganic oxide layer 1a on the flexible substrate 1 using an atmospheric pressure plasma and a second step comprising consecutive deposition of between 1 and 70 atomic layers on the inorganic oxide layer 1a. Furthermore, according to the present invention, an apparatus for manufacturing a barrier layer 1b on a substrate 1, the apparatus comprising an atmospheric pressure glow discharge (APGD) plasma apparatus comprising at least two electrodes 2, 3 arranged to generate an atmospheric pressure glow discharge plasma in a treatment space 5 formed between said two electrodes 2, 3 and an atomic layer deposition (ALD) device, wherein the apparatus is arranged to provide an inorganic oxide layer 1a on the substrate 1 using the atmospheric pressure glow discharge (APGD) plasma apparatus, and to provide a consecutive deposition of between 1 and 70 atomic layers (1b) on the inorganic oxide layer 1a using the ALD device.
a and b show schematic views of exemplary embodiments of an atmospheric pressure glow discharge (APGD) plasma apparatus in which a first step of the present method embodiments according to the present invention may be practiced. A treatment space 5, which may be a treatment chamber within an enclosure (not shown in
Other forms of the electrodes 2, 3 and of the gap or treatment space 5 are possible, e.g. as part of a cylindrical arrangement of the plasma treatment apparatus. E.g., the treatment space may be cylindrical, or elliptic, or have another form adapted to treat a specific type of substrate 1. Both electrodes 2, 3 may have the same configuration being flat orientated (as shown in
In general the atmospheric pressure glow discharge plasma is generated between the two electrodes 2, 3 in the treatment space 5. Alternatively a plurality of electrodes 2, 3 is provided. In case the electrodes 2, 3 have a surface area which is at least as big as the substrate 1, the substrate 1 can be fixed in the treatment space 5 between the two electrodes 2, 3.
b shows a further embodiment of a plasma treatment apparatus wherein two substrates 1, 1′ are treated simultaneously. In this alternative embodiment, not one substrate 1 but two substrates (1, 1′) are positioned in the treatment space 5 (and two side tabs 6a, 6b) in a fixed way or moving at a certain speed in the treatment space 5 to utilize the gas supply 8 even more efficiently.
In case the substrate 1 is larger than the electrode area, the substrate 1, 1′ may be moved through the treatment space 5, e.g. at a linear speed using a roll-to-roll configuration, an example of which is shown in the embodiment of
The electrodes 2, 3 are connected to a power supply 4 (see embodiment of
The power supply 4 can be a power supply providing a wide range of frequencies for example f=10 kHz-30 MHz .
Very good results can be obtained by using an atmospheric pressure glow discharge (APGD) plasma as this step can be done ultra-fast. As a result of the first deposition step an inorganic oxide layer 1a is provided on the substrate 1 (see cross sectional view in
Until recently APGD plasmas suffered from a bad stability, but using the stabilization circuits as for example described in U.S. Pat. No. 6,774,569, EP 1383359, EP 1547123 and EP 1626613 (which are incorporated herein by reference), very stable APG plasmas can be obtained in a treatment space 5. In general these plasmas are stabilized by a stabilization circuit 21 (as shown
In one embodiment the apparatus of the present invention including the stabilization circuit 21 is used to generate an atmospheric glow discharge plasma in a gas composition including a precursor for a compound or element to be deposited by which a single layer may be deposited. In another embodiment multiple layers of compound or element may be deposited by having multiple passes of the substrate 1 through the treatment space 5, or by having several treatment spaces 5 placed in series with each other. In this last embodiment layers of different composition can be applied over each other in a very efficient way, having a thickness of each layer of 1 nm or more.
In the plasma treatment apparatus a gas supply device 8 is arranged in order to direct gas comprising at least one precursor towards an inner region of the substrate 1 to be processed, as shown in
A gas supply inlet may be used to direct the gas into the treatment space 5 as shown in EP 2 226 832 by applicant and hereby incorporated by reference. The gas supply device 8 may be provided with storage, supply and mixing components as known to the skilled person. Preferred precursors are TEOS and HMDSO resulting in a deposited layer 1a of 10 to 100 nm silicon oxide on substrate 1.
According to the present invention embodiments, a time-wise faster and thus more efficient process for forming a barrier layer on a (flexible) substrate 1 is provided. A second step of atomic layer deposition (ALD) is provided in addition to forming an inorganic layer using an atmospheric pressure glow discharge plasma in a first step.
As second step of the method embodiments according to the present invention the type of ALD process itself is not relevant. The second step of ALD is not limited to vacuum (batch) processing but can be done at atmospheric pressure in any of the thermal, ozone or plasma assisted ALD methods which are known as such, using a spatial scheme to enable roll-to-roll processing.
The second step may be done by (spatial) plasma assisted ALD as for example an atmospheric pressure glow discharge (APGD) plasma as disclosed by applicant in WO 2007145513 and WO 2009031886 and hereby incorporated by reference.
In the second step of the present invention embodiments, using ALD in several consecutive cycles a very thin second layer 1b is grown of about 1 to 10 nm on top of the inorganic oxide layer 1a (formed in the first step), as shown in the cross sectional view of
The second (ALD) step of the present invention embodiments is sub-divided in four steps (so-called A/I/B/I steps), as shown schematically in
The second step of the present invention embodiments can be done in one treatment space. The gas supply devices 8 for the A/I/B/I-step are arranged to control the ALD process properly.
Advantageously in the process is further that the ALD step may be done using at least two separate treatments spaces (one for the precursor step) and the second (for the plasma assisted reaction step) as is shown schematically for an exemplary embodiment (a spatial assisted ALD equipment) in
In the embodiment of
Use of an atmospheric plasma obviates the need to work at very low pressure. So the use of an atmospheric pressure plasma assisted ALD process step may be used advantageously too. Hence no complex constructions are necessary to obtain a vacuum or near vacuum at the substrate surface during processing, thus enabling roll to roll atmospheric barrier film manufacture.
Further the use of a spatial atmospheric plasma makes it possible to make the process even more efficient as the ALD of the second step of the invention method may be done consecutively and continuously using a moving web-substrate as shown in
The precursor material is e.g. tri-methyl-aluminum (TMA) as shown in
According to a further embodiment, the precursor material is provided in a concentration of between 0.1 and 5000 ppm. This concentration is sufficient to obtain a uniform layer of precursor molecules on the substrate surface in the second step of the present method embodiments.
The reactive agent mixture may in a further embodiment comprise an inert gas selected from a noble gas such as helium, nitrogen or a mixture of these gases.
In a further embodiment, the reactive agent is a reactive gas, such as oxygen, an oxygen comprising agent such as ozone or water, a nitrogen comprising agent, etc.
In an even further embodiment, the gas mixture of the reactive agent and inert gas of the second step of the present invention comprises between 1 and 50% reactive agent. This is sufficient to have a good reaction result in the second step of the present method embodiments.
The invention is furthermore directed to an apparatus which is capable of executing the method embodiments of this invention, such as the apparatus embodiments shown in
Further the invention is directed to a flexible barrier substrate 1 having a thin inorganic oxide layer 1a having a free pore volume between 0.3 and 10% and a thin ALD layer 1b between 0.5 and 10 nm thick (see
WVTR (water vapor transmission rate) is determined using a Mocon Aquatran Model 1 which uses a coloumetric cell (electrochemical cell) with a minimum detection limit of 5*10−4 g/m2*day. This method provides a more sensitive and accurate permeability evaluation than the permeation measurement by using IR absorption. All measurements were done at 40° C./100% RH.
Film thickness is characterized using a Woollam Spectroscopic Ellipsometer type D2000 and the optical density (refractive index) was measured using a vacuum chamber and heating stage implemented on the Spectroscopic Ellipsometer. The free pore volume of the inorganic oxides was determined using the Lorentz-Lorenz equations by measuring the optical density difference of the material.
Based on the ellipsometric measurement a growth rate of 0.12 nm/cycles was determined for the ALD-process.
Several examples 1 and 6-14 were prepared by depositing on a PEN Q65-FA (100 μm thick) substrate 1 by using a APGD-CVD plasma apparatus as disclosed in WO 2009 104 957 in a treatment space 5 using a plasma power of 600 W, an excitation frequency of 200 kHz and a gas composition (95% N2/5% O2) using TEOS precursor (3 ppm) with a DR of 60 nm/s resulting in a 70 nm SiO2-layer 1a (having active hydroxyl surface sites) in the first step of the present invention embodiments.
Example 1 is a comparative example: a SiOx layer 1a was deposited on a PEN Q65 substrate 1 by above described APGD-CVD but without the ALD treatment of the second step of the present invention. The free pore volume has been measured between 0.3-3% ; WVTR is 2 g/m2*day which is almost same as the WVTR of the bare PEN substrate 1.
Examples 6-10 are samples having the same first APGD-treatment as example 1 and as second step a spatial (vacuum) plasma assisted ALD treatment using OxfordFlexAl apparatus to deposit barrier films 1b of respectively about 0.5, 1, 2, 5 and 20 nm thick by transporting a substrate 1 respectively 5, 10, 20, 50 and 200 cycles through the ALD system as second step of the present invention. Conditions: vacuum 10−6 Torr; A step 20 ms TMA/I purge step 1.5 s/B step 2 s plasma O2/I purge step 1.5 s; The films 1b were grown at a substrate temperature of 80° C. by sequentially injecting the TMA and adding plasma assisted O2 gas to the substrate 1.
Examples 11-14 are made by using a thermal ALD apparatus to deposit barrier films 1b of respectively about 1, 2, 5 and 20 nm thick by respectively 10, 20, 50 and 200 cycles through the thermal ALD system. The films 1b were grown at a substrate temperature of 90° C. by sequentially injecting TMA as step A and H2O as step B.
Examples 2-5 are comparative examples and are prepared on PEN Q65-FA substrates 1 (100 μm thick) by using a (vacuum) plasma assisted OxfordFlexAl ALD apparatus treatment in the same way as described for respectively examples 6-9 however without the first APGD step of the present invention.
Example 15 is a comparative example and is prepared on a PEN Q65-FA substrate 1 (100 μm thick) by using a thermal ALD system like for examples 11-14 however without the first APGD step of the present invention.
Example 16 is an inventive example and prepared under the same conditions as for example 6 however as substrate 1 a ST505 (Melinex) PET (100 μm thick) from DuPont Tejin is used.
Single Al2O3-layers are susceptible to damage by water vapor. The barrier properties of single layers 1a of Al2O3 (for examples 2-5) deteriorated markedly after 5 days when the ALD film was exposed to saturated H2O vapor pressure. Surprisingly examples 6-14 do not show this phenomenon. The SiO2 layer 1a is effective against this phenomenon showing robustness improvement for these samples.
In table 1 the examples and performance on the WVTR and the deterioration after 5 days at saturated water vapor is summarized.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1117242.6 | Oct 2011 | GB | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/GB2012/052378 | 9/26/2012 | WO | 00 | 4/3/2014 |
