WO2012165944A1

WO2012165944A1 - Hot wire chemical vapour deposition process for producing an inorganic-polymer multi-layer stack

Info

Publication number: WO2012165944A1
Application number: PCT/NL2011/050601
Authority: WO
Inventors: Ruud Emmanuel Isidore SCHROPP; Diederick Adrianus SPEE; Jatindra Kumar RATH; Catharina Henriette Maria Van Der Werf
Original assignee: Universiteit Utrecht Holding B.V.; Stichting Voor De Technische Wetenschappen
Priority date: 2011-05-27
Filing date: 2011-09-02
Publication date: 2012-12-06

Abstract

The invention provides a process for the production of a multi-layer stack comprising alternating layers of a polymeric material and an inorganic material, the process comprising a first formation process for the formation of a polymeric material layer or an inorganic material layer followed by a second formation process for the formation of the inorganic material layer or the polymeric material layer; wherein the first formation process and the second formation process comprise a hot wire chemical vapour deposition process using a wire at a predetermined wire temperature and a target substrate at a predetermined substrate temperature; wherein when the formation process comprises the formation of the polymeric material layer, the predetermined wire temperature is at maximum 230 °C; and wherein when the formation process comprises formation of the inorganic material layer, the predetermined substrate temperature is at maximum 110 °C. The invention also provides a device with such multi-layer stack.

Description

Hot wire chemical vapour deposition process for producing an inorganic-polymer multi-layer stack

Field of the invention

The invention relates to a process for the production of a multi-layer stack, a device with a device surface comprising such multi-layer stack, and a hot wire chemical vapour deposition apparatus.

Background of the invention

Sensitive electronic devices can easily be damaged by permeation of oxygen and water vapour into their active layers. This is an issue especially for devices which are made on flexible plastic substrates, such as flexible solar cells, organic light emitting diodes (OLEDs) and reliable displays, since these substrates, contrary to glass or metals, have a very high permeability to water vapour and oxygen. Thus, permeation barrier films deposited on (flexible) substrates are needed for many applications.

WO2005119808 describes structures and components for protecting organic light emitting diodes from environmental elements such as moisture and oxygen. Top- emitting, high-resolution, OLED structures are provided which include a metal foil substrate, a planarization layer, disposed over the metal foil substrate, an OLED stack (which includes lower and upper electrodes as well as an organic region disposed between the electrodes) disposed over the planarization layer, and a multilayer barrier region disposed over the OLED stack. WO2005119808 further describes flexible, top- emitting OLED structures which include a thin substrate region (i.e., a substrate having a thickness that is less than 200 microns), an OLED stack disposed over the flexible substrate region, a transparent upper barrier region that cooperates with the flexible substrate region to encapsulate the OLED stack, thereby protecting it from outside species such as water or oxygen; and a polymeric reinforcement layer which has a Young's Modulus ranging from about 0.3 to 7 GPa, which is disposed (i) below the substrate region, (ii) above the upper barrier region (in which case it is transparent), or (iii) both below the substrate region and above the upper barrier region.

WO2008132671 for instance describes an OLED-arrangement provided with an encapsulating structure for protecting an OLED-device. The OLED-arrangement comprises an internally operative substance binding member and the encapsulating structure comprises a barrier and a covering layer formed by a polymeric material arranged outside the barrier. The barrier is arranged outside the substance binding member. WO2008132671 aims at providing a robust and reliable encapsulation of OLED-arrangements. This document further indicates that the barrier may be formed by a multi-layer barrier. For instance, the multi-layer barrier is formed by inorganic films or the multi-layer barrier is formed by inorganic and organic films.

Summary of the invention

Hybrid barrier layers consisting of alternating inorganic/organic layers have proved to show sufficiently low permeation rates. Especially a combination of silicon nitride (Si _x) and polymer is very suitable to create such a multilayer.

A disadvantage of prior art multi-layer systems is their complexity or the complex and disadvantageous way in which they are produced. For instance, known methods to produce such multi-layers involve two or more different deposition techniques, for instance sputtering and vapour spray deposition, or plasma-deposition and evaporation. In all cases, substrates (or devices) must be transferred repeatedly from vacuum to atmosphere and vice versa. This is cumbersome, expensive, and time consuming. Moreover, the necessity to move the substrates (or devices) from vacuum to atmosphere and back prevents the use of roll-to-roll methods, as production can only be done batch wise. Further, in prior art solutions, it is not easy to provide polymer layers that maintain robustness and/or integrity when applying an inorganic material layer on such polymer layer.

Hence, it is an aspect of the invention to provide an alternative process for the production of a multi-layer stack, and/or a device with a device surface comprising such an alternative multi-layer stack, and/or an alternative hot wire chemical vapour deposition apparatus, which preferably further at least partly obviate one or more of above-described drawbacks.

Surprisingly, it has been found that a process as described in the accompanying claims can provide a multi-layer stack that is robust, and substantially non-permeable to water and/or oxygen. Further, it may be transparent. It also may be flexible. Further, it may be produced in an efficient and relative simple way. It further surprisingly appears that an inorganic material layer, such as a SiN_x, may be provided on a (robust) polymeric material layer, without substantially (disadvantageously) affecting the properties of said polymeric layer, whereas according to prior art methods, the polymeric material layer may deteriorate or even be demolished when providing an inorganic material layer.

Hence, in a first aspect, the invention provides a process for the production of a multi-layer stack (herein also indicated as "stack" or "multi-layer barrier" or "barrier") comprising alternating layers of a polymeric material and an inorganic material (on a target substrate ("substrate")), the process comprising a first formation process for the formation of a polymeric material layer or an inorganic material layer followed by a second formation process for the formation of the inorganic material layer or the polymeric material layer; wherein the first formation process and the second formation process comprise a hot wire chemical vapour deposition (HWCVD) process using a wire at a predetermined wire temperature ("wire temperature") and a target substrate at a predetermined substrate temperature ("substrate temperature") (and at a predetermined wire substrate distance ("wire substrate distance")); wherein when the formation process comprises the formation of the polymeric material layer, the predetermined wire temperature is preferably at maximum 230 °C (and preferably not lower than 200 °C); and wherein when the formation process comprises formation of the inorganic material layer (especially on said polymeric material layer), the predetermined substrate temperature is preferably at maximum 110 °C, such as in the range of 80-100 °C. Therefore, in this embodiment, the thus formed multi- layer stack includes at least one polymeric material layer, formed at the predetermined wire temperature of preferably at maximum 230 °C and at least one inorganic material layer (especially on said polymeric material layer), formed at the predetermined substrate temperature of preferably at maximum 110 °C.

Yet in a further aspect, the invention provides a process for the production of a multi-layer stack comprising alternating layers of a polymeric material and an inorganic material (on a target substrate), the process comprising a first formation process for the formation of a polymeric material layer or an inorganic material layer followed by a second formation process for the formation of the inorganic material layer or the polymeric material layer; wherein the first formation process and the second formation process comprise a hot wire chemical vapour deposition (HWCVD) process using a wire at a predetermined wire temperature and a target substrate at a predetermined wire-substrate distance (and at a predetermined substrate temperature); wherein when the formation process comprises the formation of the polymeric material layer, the predetermined wire temperature is preferably at maximum 230 °C (and preferably not lower than 200 °C); and wherein when the formation process comprises formation of the inorganic material layer (especially on said polymeric material layer), the predetermined wire-substrate distance is preferably at least 10 cm, such as at least 15 cm, like at least 20 cm (and preferably not larger than 35 cm). At the indicated distance (when performing the inorganic material layer formation), it may be able to maintain the substrate at a temperature at maximum 110 °C. Therefore, in this embodiment, the thus formed multi-layer stack includes at least one polymeric material layer, formed at the predetermined wire temperature of preferably at maximum 230 °C and at least one inorganic material layer (especially on the polymeric material layer), formed at the wire-substrate distance of preferably at least 10 cm.

It appears that with these conditions multi-layer stacks can be obtained, with a relative high density, with a strong-barrier function against water vapour and oxygen, with transparent properties (for visible light; i.e. light in the range of 380-780 nm). Further, this is a relatively easy method, allowing direct deposition on electronic devices and which allows roll-to-roll production. Hence, the invention may provide a single low stress, plasma- free, deposition technique, allowing continuous roll-to-roll, or inline, deposition of the complete multi-layer stack. The HWCVD technique is free of ion bombardment and therefore does not cause ion impact induced damage to sensitive electronic layers, such as organic semiconductors. The stack can be highly transparent for visible light, and can therefore be used as barrier layer for displays, solar cells, organic light emitting diodes (OLEDs), etc.

With the process of the invention, one may be able to provide an inorganic material layer at a formerly deposited polymeric material layer, without substantial removal of the polymeric material layer and/or demolition of the polymeric material layer. Hence, in an embodiment the process may further include the formation of the polymeric material layer, followed by the formation of the inorganic material layer on top of said polymeric material layer. Herein, after formation of the polymeric material layer (formed according to the process of the invention), no further layers are applied (see also below), but the next layer, on top of the polymeric material layer, is an inorganic material layer formed according to the process of the invention). Hence, a multi-layer stack can be obtained with at least one sequence of polymeric material layer and inorganic material layer (with the latter having been deposited on the former). Of course, this bi-layer may be part of a larger multi-layer stack.

The technique of hot wire chemical vapour deposition (HWCVD) is known in the art, and is being increasingly used for the deposition of materials such as hydrogenated amorphous or microcrystalline silicon and its alloys and as diamond films. The main part of a deposition system consists in a vacuum chamber evacuated by a pumping unit to some appropriate vacuum level. After achieving the desired (ultimate) vacuum, the process gas mixture may be introduced, for instance via mass flow controllers and the pressure may be kept constant, for instance by a variable conductance valve. Process gas is then decomposed into radicals by the heat generated by a hot filament and the decomposition may be aided by the catalytic activity of the filament material, which is, for instance, tungsten, tantalum or other material. The radicals lead to chemical reactions resulting in the deposition of thin films. Multi-layer stack formation

The stack comprises alternating layers of polymeric material and inorganic material. In principle, this may be any polymeric material and/or any inorganic material, as long as at least one (of the one or more) inorganic material layer(s) is produced according to the formation process for the inorganic material layer according to the invention, and as long as at least one (of the one or more) polymeric material layer(s) is produced according to the formation process for the polymeric material layer according to the invention.

The term "stack comprises alternating layers of polymeric material and inorganic material" indicates in an embodiment a bi layer of a layer of polymeric material and a layer of inorganic material. In another embodiment, it includes a layer of inorganic material, sandwiched between two layers of polymeric material; in yet another embodiment, this term includes a layer of polymeric material, sandwiched between two layers of inorganic material; etc.

Additional layers which are not made according to the process of the invention are herein indicated as "further layers". Hence, the process of the invention may further comprise applying one or more further layers (i) before the first formation process, and/or (ii) between the first formation process and the second formation process, and/or (iii) after the second formation process. The further layers however preferably follow the sequence of the stack, for instance: polymeric material layer (according to the invention) - inorganic material layer (according to the invention) - further layer (polymeric layer)(not according to the invention).

Hence, the process of the invention may also be defined as: (i) optionally providing one or more further layers, (ii) providing in a first formation process the inorganic material layer or the polymeric material layer according to the invention, (iii) optionally providing one or more further layers, (iv) providing in a second formation process the inorganic material layer or the polymeric material layer according to the invention, (v) optionally providing one or more further layers, and (vi) optionally repeating one or more of the process elements (i)-(v). Here, the process elements (ii) and (iv) are according to the invention, the other process elements are optional.

Therefore, the phrase "a first formation process for the formation of a polymeric material layer or an inorganic material layer followed by a second formation process for the formation of the inorganic material layer or the polymeric material layer" does not exclude the intermediate formation of further layers between the first formation process and the second formation process. Further, the phrase "a first formation process for the formation of a polymeric material layer or an inorganic material layer followed by a second formation process for the formation of the inorganic material layer or the polymeric material layer" thus indicates the following combinations: (optionally one or more further layers and then) first an inorganic material layer and then (optionally preceded by the formation of further layers) the polymeric material layer or (optionally one or more further layers and then) first an polymeric material layer and then (optionally preceded by the formation of further layers) the inorganic material layer.

The term "a first formation process" may in an embodiment also include a plurality of first formation processes. Likewise, the term "a second formation process" may in an embodiment also include a plurality of second formation processes. Hence, the multi-layer stack may comprise a plurality of alternating layers of a polymeric material and an inorganic material, comprising a plurality of inorganic material layers (formed according to the process of the invention), one or more polymeric material layers (formed according to the process of the invention), and optionally one or more further layers. In another embodiment, the multi-layer stack may comprise a plurality of alternating layers of a polymeric material and an inorganic material, comprising a plurality of polymeric material layers (formed according to the process of the invention), one or more inorganic material layers (formed according to the process of the invention), and optionally one or more further layers. Yet, in another embodiment, the multi-layer stack may comprise a plurality of alternating layers of a polymeric material and an inorganic material, comprising a plurality of polymeric material layers (formed according to the process of the invention), a plurality of inorganic material layers (formed according to the process of the invention), and optionally one or more further layers. Preferably, all layers of the multi-layer stack are produced according to the process of the invention.

Hence, the term "a plurality of inorganic material layers" does not indicate a plurality of layers on top of each other (although this might be applied), but herein such layers will always be alternated with layers of polymeric material (such as the polymeric material layer formed according to the invention). Likewise, the term "a plurality of polymeric material layers" does not indicate a plurality of layers on top of each other (although this might be applied), but herein such layers will always be alternated with layers of inorganic material (such as the inorganic material layer formed according to the invention).

Whatever specific process embodiments are chosen, the multi-layer stack will comprise alternating layers of a polymeric material and an inorganic material, with in its most straightforward embodiments is a bi-layer of the polymeric material layer and the inorganic material layer, and in any embodiment comprises at least one polymeric material layer as produced according to the invention and at least one inorganic material layer as produced according to the invention.

The term "substrate" may herein indicate a substrate to which the first formation process is going to be applied (a bare or virgin substrate), but the term substrate may also refer to the product of an earlier first formation process or second formation process.

Inorganic material layer formation

In an embodiment, the inorganic material layer comprises a non-oxide compound, such as SiC_y, A1N_Z or Si _x, especially a non-oxide silicon compound, such as SiN_x, where y and z are between 0.8 and 1.2 and x is between 1.0 and 1.6. Especially, the inorganic material layer consists of a non-oxide silicon compound. Preferably, the inorganic material layer comprises SiN_x, and even more preferably, the inorganic material layer consists of SiN_x. Preferably, at least 90 wt.%, especially at least 95 wt.%, yet even more especially at least 99.5 wt.% of (each of) the (individual) inorganic material layer(s) consist of the non-oxide silicon compound, especially SiN_x. The factor x is preferably in the range of 1-1.6, especially 1-1.55, like 1-1.4. Further, hydrogen may be present in the inorganic material layer, such as in an amount up to 30 wt.%, such as 0-5-30 wt.%, like 1-15 wt.%, like for instance 8-12 wt.%.

When more than one inorganic material layer is present, the inorganic material layers may have different chemical compositions.

An advantage of the process of the invention is that the conditions are such, that the inorganic material layer may, if desired, directly be applied on the surface of a device (device surface, see further below), without substantial damage. A further advantage of the process of the invention is that the inorganic material as formed may have a very low surface roughness. The roughness, indicated as rms (root mean square) roughness of the layer as obtained or as formed, is herein indicated as intrinsic (rms) surface roughness. Hence, the process of the invention may further include forming one or more inorganic material layers having an intrinsic rms roughness of equal to or less than 2 nm, such as 0.1-2 nm, like 0.2-1.5 nm. For instance, for spatial periods of 1 μιη or larger, the surface roughness may be equal to or less than 2 nm. For instance, an rms roughness of 1.1 nm was detected for an area of 10x10 μιη². Hence, over an area 10x10 μιη² of the rms roughness may be equal to or less than 2 nm.

The hot wire temperature or hot filament temperature is preferably in the range of 1800-2400 °C, especially in the range of 1900-2200 °C. The temperature of the substrate is preferably below 110 °C, such as in the range of 80-100 °C, like about 90 °C. The pressure in the reaction chamber is preferably in the range of 10-200 μbar, such as 20-60 μbar, like 40 μbar. Assuming the formation of a SiN_x layer, the reaction gas preferably comprises SiH₄ with preferably 2-4 vol.%, such as 3-3.5 vol.% NH₃. The gas flow is especially in the range of 100-200 seem, such as 140-165 seem, per 100 cm² substrate surface. The wire-substrate distance is preferably at least 10 cm, such as at least 15 cm, like at least 20 cm (and preferably not larger than 35 cm).

Likewise, when further layers are present, and these layers are inorganic layers, the same preferred embodiments may apply. Polymeric material layer formation

In an embodiment, the polymeric material layer comprises, especially consists of, a polymeric material with one or more epoxide functional groups. In yet another embodiment, the polymeric material layer comprises, especially consists of, a polyglycidyl methacrylate. Preferably, at least 90 wt.%, especially at least 95 wt.%, yet even more especially at least 99.5 wt.% of (each of) the (individual) polymeric material layer(s) consist of the of polymeric material, especially one or more of the polymeric material with one or more epoxide functional groups and polyglycidyl methacrylate (PGMA).

Especially, the one or more polymeric material layers comprise (each individually) at least 70 wt.%, such as at least 80 wt.%, even more at least 90 wt.%, especially at least 95 wt.% of polymers having a weight average molecular weight of at least 10,000 Dalton, especially at least 12,500 Dalton, for instance at least 20,000 Dalton. It appears that such polymers form stable layers. Hence, the process of the invention may further include forming one or more polymeric material layers (each individually) comprising at least 70 wt.%, such as at least 80 wt.%, even more at least 90 wt.%), especially at least 95 wt.% of polymers having a weight average molecular weight of at least 10,000 Dalton, especially at least 12,500 Dalton.

When more than one polymeric material layer is present, the polymeric material layers may have different chemical compositions.

When the formation process comprises the formation of the polymeric material layer, the formation process comprises an initiated chemical vapour deposition (iCVD) process. In such process a monomer, like glycidyl methacrylate, and an initiator, such as tert-butyl peroxide (TBPO), may be used as gasses to introduce in the reaction chamber (see below) for the formation of the polymer material layer.

The filament or hot wire temperature is especially in the range of 200-230 °C, such as in the range of 210-230 °C, especially 215-225 °C, like about 220 °C. The substrate temperature is preferably not larger than 50 °C, such as 0-40 °C, especially 30-40 °C, such as about 35 °C. The pressure in the reaction chamber is preferably in the range of 170 - 240 μbar, such as 190-220 μbar, like 210 μbar. The gas flow of the monomer, such as GMA, is preferably in the range of 1-10 seem, such as 1-5 seem, like about 3 seem, per 100 cm² substrate surface. The wire substrate distance (for the polymeric material layer formation) may be in the range of 1-7 cm, especially 2-5 cm. Likewise, when further layers are present, and these layers are polymeric layers, the same preferred embodiments may apply.

Specific embodiments

In a specific embodiment, the process includes the formation of said multi-layer stack comprising 2-10 layers, especially 3-10 layers. Especially, all layers of the stack are produced according to the process of the invention, although further layers may also be present. As indicated above, one of the advantages of the present invention is that the layers may be relatively thin.

In another specific embodiment, the process of the invention includes forming one or more inorganic material layers having layer thicknesses in the range of 20-120 nm, such as 30-100 nm, 30-60 nm, especially 35-45 nm, and one or more polymeric material layers having layer thicknesses in the range of 200-500 nm, especially 250-400 nm.

In yet a further specific embodiment, the process of the invention includes forming one or more inorganic material layers comprising Si _x and having layer thicknesses in the range of 20-120 nm, such as 30-100 nm, 30-60 nm, and one or more polymeric material layers comprising polyglycidyl methacrylate, comprising at least 80 wt.% of polymers having a weight average molecular weight of at least 10,000 Dalton, especially at least 12,500 Dalton, and having layer thicknesses in the range of 200-500 nm, wherein the multi- layer stack comprises 3-10 layers, and wherein the multi-layer stack has at 60 °C and at 90% relative humidity a water vapour permeability of equal to or less than 1.10^"5 g/(m².day). Especially such multi-layer stack may be advantageous as barrier layer for (optical) devices.

Hence, in a further aspect, the invention also provides a multi-layer stack (per se) comprising alternating layers of a polymeric material and an inorganic material, preferably 3-10 layers, wherein one or more polymeric material layers preferably comprise polyglycidyl methacrylate and wherein one or more inorganic material layers preferably comprise SiN_x, wherein the one or more inorganic materials layer(s) have layer thicknesses in the range of 20-120 nm, such as 30-100 nm, 30-60 nm, and wherein the one or more polymeric material layer(s) have layer thicknesses in the range of 200-500 nm. Other preferred embodiments of the multi-layer stack are described elsewhere in relation to the process (see above) or device (see below). Apparatus

In a specific embodiment, the process of the invention is applied while using a hot wire chemical vapour deposition apparatus "apparatus" comprising a plurality of hot wire chemical vapour deposition reaction chambers, comprising a first hot wire chemical vapour deposition reaction chamber ("first reaction chamber") wherein the first formation process is performed and a second hot wire chemical vapour deposition reaction chamber ("second reaction chamber") wherein the second formation process is performed, and wherein a substrate is guided through the first hot wire chemical vapour deposition reaction chamber and the second hot wire chemical vapour deposition reaction chamber.

Of course, the apparatus may comprise in an embodiment a plurality of first hot wire chemical vapour deposition reaction chamber and/or a plurality of second hot wire chemical vapour deposition reaction chamber.

In an embodiment, a roll-to-roll process may be applied, wherein the roll is guided through the first reaction chamber and the second reaction chamber. In another embodiment, an in-line process may be applied, wherein the substrate is transported from one chamber to another chamber.

An advantage of the process of the invention is that substantially similar production processes are applied for the formation of the polymeric material layer and the inorganic material layer. This has process advantages, such as that the pressure differences between adjacent reaction chambers may be small. In a specific embodiment, in at least one combination of a first hot wire chemical vapour deposition reaction chamber and a second hot wire chemical vapour deposition reaction chamber, the ratio of the pressures ("pressure ratio"), defined as the quotient of the first pressure in the first hot wire chemical vapour deposition reaction chamber and the second pressure in the second hot wire chemical vapour deposition reaction chamber is in the range of 0.1-10, especially 0.2-5, like 0.25-4, especially 0.5-2, like 0.7-1.5. For instance, the pressure ratio between a reaction chamber wherein the inorganic material layer is applied and an (adjacent) reaction chamber wherein polymeric material layer is applied may be in the range of 0.1-2, especially 0.1-0.5, like 0.2.

In a specific embodiment, the hot wire chemical vapour deposition apparatus comprises 2-10, especially 3-10, alternatingly arranged first hot wire chemical vapour deposition reaction chambers and second hot wire chemical vapour deposition reaction chambers.

Hence, the invention also provides in a further aspect a hot wire chemical vapour deposition apparatus comprising a plurality of hot wire chemical vapour deposition reaction chambers, wherein the chemical vapour deposition chambers comprise a substrate region for positioning a target substrate and a plurality of heatable wires (herein also indicated as "hot wires" or filaments), wherein one or more chemical vapour deposition reaction chambers have a substrate region distance to the substrate region configurable at at least 10 cm, such as at least 15 cm, like at least 20 cm (and preferably not more than 35 cm). The term "configurable" indicates here that the distance between the target substrate and the heatable wires can be controlled. In this embodiment of the apparatus, the apparatus is configured such that during processing, the substrate wire distance can be configured at at least 10 cm.

In another aspect, the invention also provides a hot wire chemical vapour deposition apparatus comprising a plurality of hot wire chemical vapour deposition reaction chambers, wherein the chemical vapour deposition chambers comprise a substrate region for positioning a target substrate and a plurality of heatable wires, wherein one or more chemical vapour deposition reaction chambers have a substrate region distance to the substrate region configured at at least 10 cm, such as at least 15 cm, like at least 20 cm (and preferably not more than 35 cm). Here, the substrate wire distance is fixed. In this embodiment of the apparatus, the apparatus is configured such that during processing, the substrate wire distance is configured at at least 10 cm.

In another aspect, the invention also provides a hot wire chemical vapour deposition apparatus comprising a plurality of hot wire chemical vapour deposition reaction chambers, wherein the chemical vapour deposition chambers comprise a substrate region for positioning a target substrate and a plurality of heatable wires, wherein one or more chemical vapour deposition reaction chambers have a substrate region distance to the substrate region configured or configurable in a range within the range of 1-35 cm (such as configured at 7 cm or configurable in a range of 5-35 cm). In this embodiment of the apparatus, the apparatus is configured or configurable such that during processing, the substrate wire distance is configured or configurable in a range within the range of 1-35 cm (such as configured at 7 cm or configurable in a range of 5- 35 cm). The apparatus may further comprise a substrate temperature control device, especially a substrate cooling device. Especially when a hot wire chemical vapour deposition reaction chamber is configured for the formation of the inorganic material layer, the substrate region distance is configured or configureable at a distance at at least 10 cm and/or the hot wire chemical vapour deposition reaction chamber further comprises such substrate temperature control device, especially a cooling device, configured to maintain the substrate temperature preferably at a temperature of at maximum 110 °C.

As indicated above, the apparatus may in an embodiment be a roll-to-roll apparatus, and may in another embodiment be an in-line apparatus.

In a further embodiment, at least one hot wire chemical vapour deposition chamber comprise a substrate temperature control device, especially a substrate cooling device. For instance, when forming the inorganic material layer on a polymeric material layer, the substrate may be cooled.

Device

As indicated above, the multi-layer stack may be applied to a device, especially an electronic device. For instance, the device is selected from the group consisting of a display device, an optical device, and a solar cell. One may think of a thin film PV (photovoltaic cell), a thin film (O)LED, a thin film TFT-FPD (thin film transistor flat panel display), especially OPV, OLED, OTFT driven FPDs etc (with O indicating the organic version). Such devices may for instance be flexible and/or rollable and/or foldable. In such embodiments, the device may be the substrate (or in other words: the substrate may be a device).

Hence, in a further aspect, the invention provides a device with a device surface comprising a multi-layer stack comprising alternating layers of a polymeric material and an inorganic material, wherein one or more inorganic materials layer(s) have layer thicknesses in the range of 20-120 nm, such as 30-100 nm, 30-60 nm, and wherein one or more polymeric material layer(s) have layer thicknesses in the range of 200-500 nm.

Specific embodiments are also described above, but some will also further be elucidated below. In a specific embodiment, the one or more polymeric material layers comprise polyglycidyl methacrylate and(/or) the one or more inorganic material layers comprises SiN_x. In another specific embodiment, the one or more inorganic materials layer(s) have an intrinsic rms roughness equal to or less than 2 nm. Especially, x is in the range of 1-1.4. In a further specific embodiment, the one or more polymeric material layers comprise at least 80 wt.% of polymers having a weight average molecular weight of at least 10,000 Dalton, especially at least 12,500 Dalton. Especially, the multi-layer stack comprises 3-10 layers and has at 60 °C and at 90% relative humidity a water vapour permeability of equal to or less than 1.10^"5 g/(m².day). Even more especially, the one or more inorganic materials layer(s) comprise Si _x and have layer thicknesses in the range of 20-120 nm, such as 30-100 nm, 30-60 nm, wherein the one or more polymeric material layer(s) comprise polyglycidyl methacrylate, comprise at least 80 wt.% of polymers having a weight average molecular weight of at least 10,000 Dalton, especially at least 12,500 Dalton, and having layer thicknesses in the range of 200-500 nm, wherein the multi-layer stack comprises 3-10 layers, and wherein the multi-layer stack has at 60 °C and at 90% relative humidity a water vapour permeability of equal to or less than 1.10^~5 g/(m².day).

As indicated above, the multi-layer stack further may comprise one or more further layers.

Several configurations in related to the device surface may be chosen. In an embodiment, a first layer attached to the device surface may comprise an inorganic layer and, in a specific embodiment, a final stack layer, most remote from the first layer, comprises a polymeric layer. Alternatively, a first layer attached to the device surface may comprise a polymeric layer and, in a specific embodiment, a final stack layer, most remote from the first layer, comprises a polymeric layer. However, the device may in an embodiment also be sandwiched between two multi-layer stacks.

In yet a further embodiment, after formation of the polymeric material layer (formed according to the process of the invention), no further layers are applied (see also below), but the next layer, on top of the polymeric material layer, is an inorganic material layer formed according to the process of the invention). Hence, a stack can be obtained with at least one sequence of polymeric material layer and inorganic material layer (with the latter having been deposited on the former).

Further specific embodiments

Sensitive electronic devices can easily be damaged by permeation of oxygen and water vapor into their active layers and by contact degradation. This is an issue especially for devices which are made on flexible plastic substrates, such as flexible solar cells, organic light emitting diodes (OLED) and rollable displays, since these substrates, contrary to glass or metals, have a very high permeability to water vapor and oxygen. The mentioned thin film (opto-)electronic active devices need to be protected against atmospheric gases as well as from volatile substances from plastic carrier materials. Also when these devices are deposited on glass or metal sheets, they need to be protected against water vapor and oxygen at the top side. Thus, permeation barrier films deposited on flexible substrates are needed for many applications.

Only hybrid barrier layers consisting of alternating inorganic/organic layers have proved to show permeation rates that are low enough for use with organic semiconductors.

The invention may be a method for producing a multilayer structure of alternating polymer and non-oxide inorganic, especially silicon, compound (e.g. Si _x or SiC_y (with y especially in the range of 0.8-1.2) layers using HWCVD for depositing the polymer and non-oxide silicon compound layers. Further, the invention is a multilayer structure produced by this method, consisting of alternating polymer and non-oxide silicon compound layers. The invention may be an apparatus for producing multilayer structures, consisting of more than one segment with HWCVD technology, where the segments are provided with individual process gas and substrate control (e.g. pressure, temperature, gas composition). Amongst other, the polymer for which this has been tested is poly(glycidyl methacrylate) (PGM A). As a non-oxide silicon compound a Si _x layer has been tested as an amorphous a-Si _x:H layer where preferably 1.0 < x < 1.55. The advantage of the invention is that both layers are deposited by a single technique, namely HWCVD. This allows for continuous deposition of the layers in one single apparatus comprising a multitude of contiguous deposition zones. Deposition can be done batch wise, in line, or roll-to-roll.

Five advantageous aspects: (1) The development of polymer layers and a-Si _x:H layers with a single deposition technique (HWCVD); (2) The purity and long chain length of polymers obtained; (3) The fact that HWCVD type deposition does not deteriorate already existing polymer layers; (4) The achievement of high mass density (low void fraction) a-Si _x:H at reduced temperature < 150°C; allowing application also directly on organic active materials, on plastic substrates, and devices on plastic substrates; (5) The low mechanical stress of HWCVD deposited coatings. Application of the described technology is exemplified, but not limited to displays, OLED lighting, solar cells and on conformable (flexible) foils:

Examples of displays: "electronic paper" (e-paper), mobile terminal displays or displays wearable as clothing.

- Examples of lighting devices: room lighting, car or airplane interior lighting, medical skin treatment, jaundice treatment, etc.

Examples of solar cell devices: a-Si:H, μΰ-8ί:Η, tandem (micromorph), multi- junction devices, CIS based, CdTe based, organic, dye-sensitized solar cells, etc. Flexible electronic devices with thin high quality semiconducting active layers will serve both as small hand- held and large area applications.

Thus far, all existing and known methods for depositing alternating inorganic and organic layers involve two or more different deposition techniques, for instance sputtering and vapor spray deposition, or plasma-deposition and evaporation. In all cases, devices must be transferred repeatedly from vacuum to atmosphere and vice versa. This is cumbersome, expensive, and time consuming. Moreover, the necessity to move the devices from vacuum to atmosphere and back prevents the use of roll-to-roll methods, as production can only be done batch wise. To the best of our knowledge we are the first to show an organic/inorganic stack with a single low stress deposition technique, allowing for continuous roll-to-roll or in line deposition of the complete multilayer barrier. With the HWCVD technique, we have now succeeded in demonstrating a method that allows this type of production technology.

Moreover, the HWCVD is free of ion bombardment and therefore does not cause ion impact induced damage to sensitive electronic layers (such as organic semiconductors). For this reason, if needed, the thin film gas barrier encapsulation can be deposited directly onto the devices.

Moreover, the layer stack is highly transparent for visible light and can thus be used for displays, solar cells, and lighting, even on the side that should be transparent to light.

The thin film devices are moved from a cooled susceptor at a T of 15 - 25 °C for polymer deposition, to a susceptor at moderately elevated temperature 25 - 150 °C for Si _x deposition, and thus undergo a modest temperature cycle. The depth of the temperature cycle is small; this may not be an issue for the operation of the devices and needs to be further investigated. Further, should in line or roll-to-roll deposition be used, the processing pressure is different for polymer deposition and for Si _x deposition. The pressure for nitride deposition is in the range of 0.5 - 20 Pa, preferably 4 Pa, and the pressure for the polymer deposition is in the range of 5 - 100 Pa, preferably 20 Pa. While the ranges overlap, the optimal individual process pressure difference can be overcome by differential pumping and narrow slit valves.

A simple version of the barrier layer has been tested for water vapor permeability and has been found to have excellent barrier properties (10^~5 g/m².day; this was done under very severe test conditions: 60 °C, and 90% relative humidity). The layer structure was a simple triple layer structure (SiN_x/polymer/SiN_x). The water vapor impermeability will increase by repeating the deposition of polymer/SiN_x double layers on top of each other. In an embodiment, the proposed multilayer structure is a polymer/SiN_x structure by HWCVD that is repeated multiple times and can be preceded by a Si _x layer (as in the test structure).

Hence, in a further aspect, the invention provides a process for the production of a multi-layer stack comprising alternating layers of a polymeric material and an inorganic material, the process comprising a first formation process for the formation of a polymeric material layer or an inorganic material layer followed by a second formation process for the formation of the inorganic material layer or the polymeric material layer; wherein the first formation process and the second formation process comprise a hot wire chemical vapour deposition process using a wire at a predetermined wire temperature and a target substrate at a predetermined wire-substrate distance; wherein when the formation process comprises the formation of the polymeric material layer, the predetermined wire temperature is preferably at maximum 230 °C (and preferably not lower than 200 °C); and wherein when the formation process comprises formation of the inorganic material layer, the wire-substrate distance is in the range of 1-35 cm, especially in the range of 1-7 cm, like 1-5 cm, such as 2-5 cm. Especially, in this embodiment, the substrate may, during formation of the inorganic material layer be cooled (for instance a cooled carrier or susceptor may be applied). In a further related specific embodiment, in at least one combination of a first hot wire chemical vapour deposition reaction chamber and a second hot wire chemical vapour deposition reaction chamber, the ratio of the pressures ("pressure ratio"), defined as the quotient of the first pressure in the first hot wire chemical vapour deposition reaction chamber and the second pressure in the second hot wire chemical vapour deposition reaction chamber is in the range of 0.1-10, especially 0.2-5, like 0.25-4, especially 0.5- 2, like 0.7-1.5. For instance, the pressure ratio between a reaction chamber wherein the inorganic material layer is applied and an (adjacent) reaction chamber wherein polymeric material layer is applied may be in the range of 0.1-10, especially 0.5-2, like 0.7-1.5. Further, especially the pressure in the reaction chamber wherein the inorganic material is applied may preferably be in the range of 170 - 240 μbar, such as 190-220 μbar, like 210 μbar.

The term "substantially" herein, such as in "substantially consists", will be understood by the person skilled in the art. The term "substantially" may also include embodiments with "entirely", "completely", "all", etc. Hence, in embodiments the adjective substantially may also be removed. Where applicable, the term "substantially" may also relate to 90% or higher, such as 95% or higher, especially 99% or higher, even more especially 99.5% or higher, including 100%. The term "comprise" includes also embodiments wherein the term "comprises" means "consists of.

Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

The devices or apparatus herein may amongst others be described during operation. As will be clear to the person skilled in the art, the invention is not limited to methods of operation or devices in operation.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "to comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the device or apparatus claims enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

The invention further applies to an apparatus or device comprising one or more of the characterising features described in the description and/or shown in the attached drawings. The invention further pertains to a method or process comprising one or more of the characterising features described in the description and/or shown in the attached drawings.

The various aspects discussed in this patent can be combined in order to provide additional advantages. Furthermore, some of the features can form the basis for one or more divisional applications.

Brief description of the drawings

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:

Fig. 1 schematically depicts an embodiment of a hot wire chemical vapour deposition apparatus (having one reaction chamber);

Figs. 2a-2e schematically depict some aspects of the multi-layer stack;

Figs. 3a-3c schematically depict some aspects of the device;

Figs. 4a-4d schematically depicts some embodiments and aspects of the apparatus;

Fig. 5 shows (a) Refractive index at a wavelength of 632 nm and (b) deposition rate dependence on SiH₄/NH₃ flow ratio;

Fig. 6 shows (a) Integrated absorption of the N-H and Si-H peaks and (b) Si-H FTIR peak position as a function of SiH₄/NH₃ flow ratio;

Fig. 7 shows (a) Extinction coefficients k for different layers and (b) k at 400 nm for different SiH₄/NH₃ flow ratios;

Fig. 8 shows the transmission and reflection spectra, which shows that a highly transparent double layer was made. Although the reflection is higher than that of bare glass, due to the higher refractive index of SiN_x, the absorption is very low; Fig. 9 shows in the top FTIR graph PGMA, the middle FTIR graph of SiN_x and the lowest FTIR graph from Si _x on PGMA, produced according to the invention;

Fig. 10 shows an FTIR graph of PGMA before and after deposition of Si _x on it at a too high temperature;

Fig. 11 shows experiments with varying wire temperature and polymer molecular weights.

Description of preferred embodiments

Fig. 1 schematically depicts a hot wire chemical vapour deposition apparatus ("apparatus") 1 having one reaction chamber 100. Figure 1 shows apparatus 1 comprising a deposition chamber or reaction chamber 100 with hot wires or filament wires ("filaments") 110, and gas dosage system 120 (also indicated as shower head).

The film apparatus 1 comprises gas dosage system 120 for introducing a gas or a mixture of gases, with gas inlets 121. It further includes a gas outlet 113, which is in general connected to a pumping system 31 for decreasing the pressure in the apparatus, as indicated with a gas exit flow 30.

The filament wires 110 may be heated by passing a current through them from power supply (not shown). The power supply can for instance be an alternating current

(ac) or direct current (dc) supply.

Further, the apparatus 1 is shown with a substrate 10 in the reaction chamber 100.

The substrate 10 has a substrate surface 11. The substrate may be hold by a substrate carrier 18. The substrate carrier 18 may in an embodiment be a (substrate) susceptor.

The substrate 10 may be heated during the film formation process by the filament wires 110. The film formation process can be conducted such that no additional heating of the substrates 10 is needed, thus reducing the cost of manufacturing of the films. If desired the substrates 10 can be heated by an additional heater or cooled by a cooler, which may be arranged in contact or in proximity with substrate carrier 18. The apparatus may also contain a shutter 17 to shield the substrate from the filament wires.

The shutter may be moveable parallel to the substrate between a first open position, wherein the shutter is removed from between the substrates 10 and the filaments 110, and a second closed position wherein the shutter is placed between the substrates and the filaments as shown in fig. 1. The distance between the filaments 110 and the substrate 10 (more precisely the substrate surface 11) is indicated with d_ws. When the reaction chamber is applied for formation of the polymeric material layer, the substrate wire distance d_ws may be small, such as 3 cm, but when applying the inorganic material layer, the substrate wire distance d_ws may be larger, such as at least 10 cm. Note that when further layers are applied (see also below), i.e. inorganic layers or organic layers which are not formed according to the invention, the parameters may of course be different.

Figs. 2a-2e schematically depict some aspects of the multi-layer stack. Fig. 2a schematically depicts the substrate 10 (which may be a device, see also below), having a substrate face 11 and second substrate face 12, which is in general arranged opposite of the substrate surface 11, and which may be substantially parallel to the substrate surface 11. Fig. 2a thus schematically depicts a target substrate or shortly substrate 10, which is used as substrate for the formation of the multi-layer stack 200.

On the substrate surface 11, a multi-layer stack 200 may be formed, see figs. 2b- 2d. The multi- layer stack comprises layers 201. These layers 201 may in principle be any inorganic layers and or polymeric layers, as long as there is at least one inorganic material layer, indicated with reference "i" and at least one polymeric material layer, indicated with reference "p", which are formed according to the process of the invention. As shown in figs. 2b-2c, first an inorganic material layer i may be provided, indicated with first i_{l s} i.e. the first layer on the substrate surface 11 is the inorganic material layer i; or first a polymeric material layer p may be provided, indicated with first pi, i.e. the first layer on the substrate surface 11 is the polymeric material layer p. applying first a polymeric material layer p may advantageously have a smoothening effect on the substrate 10, i.e. a flat layer may be provided.

The height of the polymeric material layer is indicated with h_p; the height of the inorganic material layer is indicated with hi. Note that when more of such layers may be present, the heights of the individual (polymeric material layers and/or inorganic material layers) may be independent of each other.

The schematically depicted substrate 10 with multi-layer stacks 200 in figs 2b-2c can on their turn again be target substrate for further layer formation, for instance, to obtain substrates 10 with multi-layer stacks 200 as schematically depicted in figures 2d-2e. Fig. 2d schematically depicts an embodiment with a plurality of inorganic material layers and polymeric material layers (all produced according to the invention). In addition to the inorganic material layer (i) and the polymeric material layer (p) produced according to the process of the invention, also further layers, indicated with reference f, may be present. This is shown in fig. 2e. As can be perceived from this schematic drawing, at least one inorganic material layer and at least one polymeric material layer according to the invention are present; however, further layers f may also be part of the multi-layer stack 200.

Figs. 3a-3c schematically depict some aspects of the device, which is indicated with reference 300. Note that the substrate 10 is now device 300. By way of example, a three-layer multi-layer stack 200 is provided on the substrate surface 11, here the device surface indicated with reference 31 1. As first layer, a polymeric material layer p (i.e. pi) is applied on this device surface 311, which layer sandwiches together with another polymeric material layer the inorganic material layer. Such multi-layer stack 200 may already provide excellent barrier properties and optical properties (transparency).

For some devices, it may be desirable to have it contained between barrier layers.

Fig. 3b schematically depicts wherein the device 300 is sandwiched between two multilayer stacks. The multi-layer stack in contact with the second substrate face 12, i.e. second device face 312, is indicated with reference 200(2) (second multi-layer stack).

Fig. 3c schematically depicts a further embodiment of the device, for instance a PV (photo voltaic) device as device 300, being sandwiched between two multi-layer stacks 200. The device 300 in this case further comprises a carrier or carrier foil, indicated with reference 500, as a result of the product process of the PV. Hence, the second multi-layer stack 200 is provided on the carrier 500, which can be considered part of the (PV) device in this embodiment. In another embodiment, not depicted, a device is provided comprising the following structure: multi-layer stack - carrier - multi-layer stack - device - multi-layer stack. With reference to figure 3c, this would imply a further multi-layer stack between carrier foil 500 and device 300.

Figs. 4a-4d schematically depicts some embodiments and aspects of the apparatus, indicated with reference 1. Fig. 4a schematically depicts an in-line embodiment of the apparatus 1. By way of example, the apparatus comprises four reaction chambers 100, but two would suffice, and less or more than four may also be possible. The reaction chamber in this apparatus are indicated with references 100a- lOOd. By way of example, the reaction chambers are depicted with wires 130 for power input to the filaments 110. Further, pumps 140 are shown, which may individually control the pressure in the reaction chambers 100. Between the adjacent reaction chambers 100, ports 150, preferably with valves, are depicted. In this way, the conditions in each reaction chamber 100 may be controlled individually, without influence of other reaction chambers 100. Further, by way of example, substrate temperature control devices 160 are depicted. In an embodiment, these may be used to heat, and in another embodiment, these may be used to cool. In a further embodiment, these substrate control devices may have the ability to heat or to cool, dependent upon the desired conditions. Further, the apparatus 1 may comprise a control unit 170, configured to control one or more of the temperature of the filaments in the reaction chambers (individually), the temperature in the reaction chambers (individually), the temperature of the control devices 160 (individually), transport from one reaction chamber to another reaction chamber (individually), the reaction time in the chambers (individually), the gas mixture and/or flow speed into the reaction chambers (individually), etc.

By way of example, the first reaction chamber 100a and the third reaction chamber 100c may be applied for the inorganic material layer formation, and the second reaction chamber 100b and the fourth reaction chamber lOOd may be applied for the polymeric material layer formation, as can be seen from the wire substrate distances. Note that optionally the wire substrate distance may be controllable for (each of) the reaction chamber(s).

Guiding the substrate 10 from one reaction chamber to another reaction chamber may be in this embodiment batch wise, and may for instance be performed manual, with robots, with assembly line units (with assembly line elements within each reactor chamber; for instance rolling transport elements).

Fig. 4b schematically depicts an embodiment of the apparatus 1 wherein the apparatus is a roll-to-roll apparatus. By way of example, five reaction chambers, indicated with reference lOOa-lOOe are depicted, but two would suffice, and less or more than five may also be possible. References 401 and 402 indicated the pay-off roller and take-up roller, respectively. The roll is indicated with reference 410, which may be in an embodiment considered a carrier (see also below) to carry a device (not shown in detail), but may also function as substrate itself. This embodiment may comprise ports 150, without valves, as the (pressure) conditions in the within adjacent reaction chambers may substantially be the same, such as within a ratio of 0.1-10

Here, guiding the substrate is performed by the transport of the roll 410 through the reaction chambers 100. This may be a (semi-)batch wise process, wherein the reaction is performed, transport is started to the next reaction chamber, the (next) reaction is performed, and transport is continued, etc. etc.

Note that in both embodiments, the filaments have an axis substantially perpendicular to the direction of transport direction, indicated with 19, and substantially parallel to the substrate surface (or carrier surface). Herein, the filaments or hot wires 110 are preferably longitudinal rods that are heated. Deviations from perpendicularity and parallelity are preferably within 5°, especially within 1°, even more especially within 0.5°.

Shutters 17 may be present, but are not drawn for the sake of clarity.

Fig. 4a thus schematically depicts and embodiment of the hot wire chemical vapour deposition apparatus comprising 4 alternatingly arranged first hot wire chemical vapour deposition reaction chambers and second hot wire chemical vapour deposition reaction chambers, which may be used for the formation of a multi-layer stack comprising 2-4 layers; Fig. 4b schematically depicts and embodiment of the hot wire chemical vapour deposition apparatus comprising 5 alternatingly arranged first hot wire chemical vapour deposition reaction chambers and second hot wire chemical vapour deposition reaction chambers, which may be used for the formation of a multi-layer stack comprising 2-5 layers.

Figs. 4c and 4d schematically depict some embodiments (amongst others in relation to figs 4a-4b), wherein in Fig. 4c the roll carries the device 10, and can thus be considered carrier 18 (see for instance also Fig.l). However, the roll 410 may not only carry the device (Fig. 4c), but may also comprise the device (Fig. 4d). For instance, a PV foil may be used as roll 410.

Experimental

High quality non porous silicon nitride layers were deposited by hot wire chemical vapour deposition at substrate temperatures lower than 110°C. The layer properties were investigated using FTIR, reflection/transmission measurements and 1 :6 buffered HF etching rate. A Si-H peak position of 2180 cm^"1 in the Fourier transform infrared absorption spectrum indicates a N/Si ratio around 1.2. Together with a refractive index of 1.97 at a wavelength of 632 nm and an extinction coefficient of 0.002 at 400 nm, this suggests that a transparent high density silicon nitride material has been made below 110 °C, which is compatible with polymer films and is expected to have a high impermeability. To confirm the compatibility with polymer films a silicon nitride layer was deposited on polyglycidyl methacrylate made by initiated chemical vapour deposition, resulting in a highly transparent double layer.

A combination of silicon nitride (Si _x) and polymer is very suitable to create such a multilayer. In our case the polymer is polyglycidyl methacrylate (PGM A). Both layers can be deposited using a continuous process: SiN_x using hot wire chemical vapor deposition (HWCVD) and PGMA using initiated chemical vapor deposition (iCVD), a variant of HWCVD where an initiator is dissociated into two radicals at a hot filament and starts the polymerization process.

Both techniques use radical formation at heated wires, allowing for a continuous roll to roll process. The wires provide a linear source of radicals, resulting in a homogenous deposition along the wire direction. When the substrate is moved perpendicular to the wires, the deposition will be homogeneous in both dimensions.

To enable SiN_x deposition on PGMA layers, two main requirements need to be fulfilled: (i) the PGMA should be very stable against the flux of chemical species during SiN_x deposition, and (ii) the SiN_x must be deposited at low substrate temperatures, compatible with common plastic substrates and also PGMA. Experiments discussed below concentrate on the latter.

A dedicated hot wire reactor was built for low temperature deposition, in which the wire-substrate distance can be increased up to 20 cm, thereby greatly reducing the radiative heating of the substrate compared to a conventional hot-wire reactor assembly. In this way Si _x layers could be grown, keeping the substrate temperature below 110°C at all times, even without actively cooling the substrate. This prevents the need of installing a cooling stage in our laboratory system. A disadvantage of the large wire-substrate distance is that low gas pressures are needed to avoid dust formation, thus resulting in low deposition rates. However, keeping in mind that in an actual roll- to-roll process the thermal budget is relatively low and active cooling of the moving substrate is relatively easy, this is not an essential drawback of the HWCVD technology. Below, it is shown that by HWCVD it is possible to deposit SiN_x layers that are compatible with PGMA layers and are close to stochiometry, resulting in high density, high transparency (low extinction coefficient k) and low refractive index n. To confirm the compatibility with PGMA layers a dense SiN_x layer was deposited on a film of PGMA. This resulted in a highly transparent double layer.

EXPERIMENTAL DETAILS

All depositions were performed in a two-filament hot wire (HW) reactor, dedicated to low temperature deposition that is part of an ultra high vacuum multi chamber deposition system (PASTA). Pure silane (SiH₄) and ammonia (Ν¾) were used as source gasses. No hydrogen dilution was used. In all depositions the ammonia flow was kept constant at 150 seem and the silane flow was altered to obtain different flow ratios. The deposition pressure was set at a value of 40 μbar. The source gasses were catalytically decomposed at two tantalum filaments with a diameter of 0.125 mm, held at 2100°C. The wires are placed 20 cm above the substrate. To control the duration of the deposition, a shutter was situated between the sample and the filaments. No active cooling was applied on the substrate. Thermindex TC8020 temperature indication stickers were attached on the front side of the substrate to be able to accurately determine the maximum temperature reached during deposition.

The thicknesses of the films as well as the n and k values of the deposited layers were determined by reflection/transmission measurements of the samples deposited on Corning Eagle XG glass. The Kramer-Kronig dispersion relations were used together with an O'Leary Johnson Lim band model to model the optical properties of the material for fitting in the SCOUT 2.1 program. The infrared active bonds in the films were investigated using Fourier transform infrared (FTIR) spectroscopy in transmission mode on a Bruker Vertex70 spectrometer, in the wavenumber range of 500-4000 cm^{" 1}.

The etch rate of the film deposited with a SiH₄/NH₃ flow ratio of 5/150 was determined using a 16BHF solution (5 parts 40% NH₄F with 1 part 50% HF). To determine the surface morphology a Nanoscope® Ilia atomic force microscope (AFM) was used in the tapping mode.

The layer of PGMA, on which the SiN_x layer was deposited, was made by iCVD in a home built reactor (PANDA),⁹'¹⁵ after a design originating from MIT labs.¹⁶ The monomer, GMA (97%, Aldrich) and initiator, tert-butyl peroxide (TBPO) (98%, Aldrich), were fed into the reactor through a gas mixing stage. The TBPO was thermally decomposed at a parallel array of nichrome wires, 3 cm above the substrate and heated to 220°C. The substrate holder was water cooled to keep the substrate at 17°C.

RESULTS AND DISCUSSION

In vacuum, where the substrate was only heated by filament radiation in the HWCVD reactor, the substrate temperature was found to never exceed 90°C when the filaments were kept at 2100°C. During an actual deposition of 1.5 hours at 40 μbar the substrate temperature was found to increase slightly, however it saturated below a temperature of 110°C. This makes the deposited layers compatible with PGMA layers and allows for a continuous deposition. Since there is no need to stop the deposition due to overheating of the substrate, the process remains simple.

In Figure 5 (b) the deposition rates as a function of flow ratio are shown. The deposition rate decreases with the SiH₄ flow, as expected. The refractive index at 632 nm, also shown in Figure 5 (a), decreases with decreasing SiH₄/NH₃ flow ratio. A low refractive index is important for avoiding interference effects in a multilayer, since it will ease the adjustment of the individual layer thicknesses significantly when alternating layers have a refractive index close to each other (that of most polymers is around 1.5). The decrease in refractive index can be explained by the increasing band gap due to an increasing N/Si ratio. However, the refractive index cannot be used as an absolute measure for the N/Si ratio, since it is also dependent on the density of the layer.

An accurate figure for the N/Si ratio of the layers can be derived from the FTIR spectra. The integrated absorptions of the N-H and the Si-H peaks are shown in Figure 6(a). The ratio is around 1 for a flow ratio of 5/150. The position of the Si-H peak in the FTIR spectrum is also related to the N/Si ratio in the layer. It shifts for different ratios because the electron affinity of Si and N atoms is different. The peak shifts to a higher wavenumber for higher N/Si ratios. The different positions as a function of flow ratio are shown in Figure 6(b). The peak position for a flow ratio of 5/150 is 2180 cm^"1, which indicates a N/Si ratio around 1.2. The N/Si ratio being close to stochiometry suggests a dense layer. To confirm this, the layer made at a flow ratio of 5/150 was etched in 16BHF. The etch rate was found to be around 25 nm/min. Although this is not as low as for state of the art high density nitride made at 450 °C (7 nm/min), it indicates a high density of the film, close to 2.5 g/cm³. Furthermore this layer was found to be extremely smooth, with an rms roughness of 1.1 nm (in an area of 10x10 μιη²). A smooth layer is considered to be beneficial for the construction of an impermeable coating.

The extinction coefficient k of the material decreases when approaching stochiometry. This can again be explained by an increasing band gap with increasing N/Si ratio. In Figure 7(a) the dependence of k on the wavelength for different layers is shown and indeed it can be seen that k decreases for layers made at lower SiH₄/NH₃ flow ratios. In Figure 7(b) the values of k at a wavelength of 400 nm are shown for different layers. The values for the layers made at flow ratios of 5/150 and 3/150 are respectively 0.002 and 0.0001. This shows that the layers are highly transparent.

To confirm that the deposited Si _x layers are compatible with PGMA and can thus be used in multilayers, on top of a PGMA layer deposited by iCVD a Si _x layer was deposited, using a SiH₄/NH₃ flow ratio of 5/150. A smooth double layer was made. The results are shown in Figures 8-9. The transmission and reflection spectra in Figure 8 show that a highly transparent double layer was made. Although the reflection is higher than that of bare glass, due to the higher refractive index of SiN_x, the absorption is very low. Comparing the FTIR spectra of the individual layers with that of the double layer in Figure 9, it is confirmed that the PGMA layer is not damaged and the Si _x grows the same as on a silicon wafer. In fig. 9, the top graph is of PGMA, the middle graph of SiN_x and the lowest graph is from SiN_x on PGMA.

CONCLUSION

Si _x layers for the use in impermeable thin film multilayers were deposited in a dedicated low temperature HWCVD reactor at substrate temperatures lower than 110°C, making them compatible with polymer layers. FTIR spectra suggest that layers were deposited with a N/Si ratio of 1.2, close to stochiometry. This results in a low refractive index of 1.97 and high transparency (k₄oo of 0.002). A high impermeability can be expected since the 16BHF etch rate of 25 nm/min indicates a high density.

Depositing such a layer on PGMA resulted in a highly transparent double layer, showing that indeed the SiN_x is compatible with polymer layers and smooth multilayers can be made. Comparative Examples

Fig. 10 shows FTIR spectra, with in the top graph again PGMA, and in the lower graph Si _x on PGMA, but now with the substrate at 250 °C. It shows the deterioration from PGMA at this high temperature.

Further, polymers were deposited having a weight average molecular weight substantially lower than 10,000 Dalton. This resulted in black samples (thus not transparent), which is not desired in most of the conceived applications.

The weight averaged molecular weight of the polymers was formed as well as the wire temperature when forming those polymers was varied, see fig. 11. The upper data (with the dotted trend line) relate to wire temperatures of 250 °C, whereas the lower data (within the ellipse) relate to wire temperatures of 220 °C. The samples at the latter temperature are clearly more stable. Hence, with the process of the invention, one may be able to provide an inorganic material layer at a formerly deposited polymeric material layer, without substantial demolition of the polymeric material layer and/or demolition of the polymeric material layer properties.

Barrier measurement

The water vapour transmission rate (WVTR) was measured for a sample prepared according to the process of the invention with a tri-layer structure with 2 Si _x layers of each about 60 nm thickness (height) sandwiching a PGMA layer of 200 nm. The WVTR measured was 9.12* 10^"6 g/m²/day.

Claims

1. A process for the production of a multi-layer stack comprising alternating layers of a polymeric material and an inorganic material on a target substrate, the process comprising a first formation process for the formation of a polymeric material layer or an inorganic material layer, followed by a second formation process for the formation of the inorganic material layer or the polymeric material layer; wherein the first formation process and the second formation process comprise a hot wire chemical vapour deposition process using a wire at a predetermined wire temperature and a target substrate at a predetermined substrate temperature; wherein when the formation process comprises the formation of the polymeric material layer, the predetermined wire temperature is at maximum 230 °C; and wherein when the formation process comprises formation of the inorganic material layer, the predetermined substrate temperature is at maximum 110 °C.

2. The process according to claim 1, wherein the first formation process and the second formation process comprise a hot wire chemical vapour deposition process using the target substrate at a predetermined wire-substrate distance; wherein when the formation process comprises formation of the inorganic material layer, the predetermined wire-substrate distance is at least 10 cm..

3. The process according to any one of the preceding claims, wherein the process includes the formation of the polymeric material layer, followed by the formation of the inorganic material layer on top of said polymeric material layer.

4. The process according to any one of the preceding claims, wherein the inorganic material layer comprises a non-oxide silicon compound.

5. The process according to any one of the preceding claims, wherein the inorganic material layer comprises SiN_x.

6. The process according to any one of the preceding claims, wherein the polymeric material layer comprises a polymeric material with one or more epoxide functional groups.

7. The process according to any one of the preceding claims, wherein the polymeric material layer comprises polyglycidyl methacrylate.

8. The process according to any one of the preceding claims, including forming one or more inorganic material layers having layer thicknesses in the range of 20-120 nm and one or more polymeric material layers having layer thicknesses in the range of 200-500 run.

9. The process according to any one of the preceding claims, including forming one or more inorganic material layers having an intrinsic rms roughness of equal to or less than 2 nm.

10. The process according to any one of the preceding claims, wherein when the formation process comprises the formation of the polymeric material layer, the formation process comprises an initiated chemical vapour deposition (iCVD) process.

11. The process according to any one of the preceding claims, further comprising cooling of the substrate during formation of the inorganic material layer.

12. The process according to any one of the preceding claims, using a hot wire chemical vapour deposition apparatus comprising a plurality of hot wire chemical vapour deposition reaction chambers, comprising a first hot wire chemical vapour deposition reaction chamber wherein the first formation process is performed and a second hot wire chemical vapour deposition reaction chamber wherein the second formation process is performed, and wherein a substrate is guided through the first hot wire chemical vapour deposition reaction chamber and the second hot wire chemical vapour deposition reaction chamber.

13. The process according to claim 12, wherein in at least one combination of a first hot wire chemical vapour deposition reaction chamber and a second hot wire chemical vapour deposition reaction chamber, the ratio of the pressures, defined as the quotient of the first pressure in the first hot wire chemical vapour deposition reaction chamber and the second pressure in the second hot wire chemical vapour deposition reaction chamber is in the range of 0.1 - 10

14. The process according to any one of claims 12-13, wherein the hot wire chemical vapour deposition apparatus comprises 3-10 alternatingly arranged first hot wire chemical vapour deposition reaction chambers and second hot wire chemical vapour deposition reaction chambers.

15. The process according to any one of the preceding claims, including the formation of said multi-layer stack comprising 3-10 layers.

16. The process according to any one of the preceding claims, wherein x is in the range of 1-1.4.

17. The process according to any one of the preceding claims, including forming one or more polymeric material layers comprises at least 80 wt.% of polymers having a weight average molecular weight of at least 10,000 Dalton, especially at least 12,500 Dalton.

18. The process according to any one of the preceding claims, including forming one or more inorganic material layers comprising SiN_x and having layer thicknesses in the range of 20-120 nm, and one or more polymeric material layers comprising polyglycidyl methacrylate, comprising at least 80 wt.% of polymers having a weight average molecular weight of at least 10,000 Dalton, especially at least 12,500 Dalton, and having layer thicknesses in the range of 200-500 nm, wherein the multi- layer stack comprises 3-10 layers, and wherein the multi- layer stack has at 60 °C and at 90% relative humidity a water vapour permeability of equal to or less than 1.10^"5 g/(m².day).

19. The process according to any one of the preceding claims, further comprising applying one or more further layers (i) before the first formation process, and/or (ii) between the first formation process and the second formation process, and/or (iii) after the second formation process.

20. A device with a device surface comprising a multi-layer stack comprising alternating layers of a polymeric material and an inorganic material, wherein one or more inorganic materials layer(s) have layer thicknesses in the range of 20-120 nm, and wherein one or more polymeric material layer(s) have layer thicknesses in the range of 200-500 nm.

21. The device according to claim 20, wherein the one or more polymeric material layers comprise polyglycidyl methacrylate and wherein the one or more inorganic material layers comprise SiN_x.

22. The device according to claim 20-21, wherein the one or more inorganic materials layer(s) have an intrinsic rms roughness equal to or less than 2 nm.

23. The device according to claim 20-22, wherein x is in the range of 1-1.4.

24. The device according to any one of claims 20-23, wherein the one or more polymeric material layers comprise at least 80 wt.% of polymers having a weight average molecular weight of at least 10,000 Dalton, especially at least 12,500 Dalton.

25. The device according to any one of claims 20-24, wherein the device is selected from the group consisting of a display device, an optical device, and a solar cell.

26. The device according to any one of claims 20-25, wherein the multi-layer stack comprises 3-10 layers and has at 60 °C and at 90% relative humidity a water vapour permeability of equal to or less than 1.10^~5 g/(m².day).

27. The device according to any one claims 20-26, wherein the one or more inorganic materials layer(s) comprise SiN_x and have layer thicknesses in the range of 20-120 nm, wherein the one or more polymeric material layer(s) comprise polyglycidyl methacrylate, comprise at least 80 wt.% of polymers having a weight average molecular weight of at least 10,000 Dalton, especially at least 12,500 Dalton, and have layer thicknesses in the range of 200-500 nm, wherein the multi-layer stack comprises 3-10 layers, and wherein the multi-layer stack has at 60 °C and at 90% relative humidity a water vapour permeability of equal to or less than 1.10^"5 g/(m².day).

28. The device according to any one of claims 20-27, wherein the multi-layer stack further comprises one or more further layers.

29. The device according to any one of claims 20-28, wherein a first layer attached to the device surface comprises an inorganic layer and wherein a final stack layer, most remote from the first layer, comprises a polymeric layer.

30. The device according to any one of claims 20-29, wherein a first layer attached to the device surface comprises a polymeric layer and wherein a final stack layer, most remote from the first layer, comprises a polymeric layer.

31. The device according to any one of claims 20-30, sandwiched between two multilayer stacks.

32. A multi-layer stack comprising alternating layers of a polymeric material and an inorganic material, wherein one or more polymeric material layers comprise polyglycidyl methacrylate and wherein one or more inorganic material layers comprise SiN_x, wherein the one or more inorganic materials layer(s) have layer thicknesses in the range of 20-120 nm, and wherein the one or more polymeric material layer(s) have layer thicknesses in the range of 200-500 nm.

33. The multi-layer stack according to claim 32, wherein the one or more polymeric material layer(s) comprise at least 80 wt.% of polymers having a weight average molecular weight of at least 10,000 Dalton, especially at least 12,500 Dalton, and have layer thicknesses in the range of 200-500 nm, wherein the multi-layer stack comprises 3-10 layers, and wherein the multi-layer stack has at 60 °C and at 90% relative humidity a water vapour permeability of equal to or less than 1.10^"5 g/(m².day).

34. A hot wire chemical vapour deposition apparatus comprising a plurality of hot wire chemical vapour deposition reaction chambers, wherein the chemical vapour deposition chambers comprise a substrate region for positioning a target substrate and a plurality of heatable wires, wherein one or more chemical vapour deposition reaction chambers have a substrate region distance to the substrate region configurable at at least 10 cm.

35. A hot wire chemical vapour deposition apparatus comprising a plurality of hot wire chemical vapour deposition reaction chambers, wherein the chemical vapour deposition chambers comprise a substrate region for positioning a target substrate and a plurality of heatable wires, wherein one or more chemical vapour deposition reaction chambers have a substrate region distance to the substrate region configured at at least 10 cm.

36. The apparatus according to any one of claims 34-35, wherein at least one hot wire chemical vapour deposition chamber comprise a substrate temperature control device, especially a substrate cooling device.

37. The apparatus according to any one of claims 34-36, wherein the apparatus is a roll- to-roll apparatus.

38. The apparatus according to any one of claims 33-36, wherein the apparatus is inline apparatus.

39. A device comprising a multi-layer stack obtainable with the process according to any one of claims 1-19.