WO2008147184A2

WO2008147184A2 - Atmospheric pressure glow discharge plasma method and system using heated substrate

Info

Publication number: WO2008147184A2
Application number: PCT/NL2008/050303
Authority: WO
Inventors: Hindrik Willem De Vries
Original assignee: Fujifilm Manufacturing Europe B.V.
Priority date: 2007-05-25
Filing date: 2008-05-22
Publication date: 2008-12-04
Also published as: WO2008147184A3

Abstract

Method and plasma treatment apparatus for treatment of a substrate, using a pulsed atmospheric pressure glow discharge plasma in a treatment space (5) filled with a gas composition. At least two electrodes (2, 3) are connected to a power supply (4) for providing electrical power to the at least two electrodes (2, 3), a gas supply device (8) for providing a gas composition to the treatment space (5), and a temperature control unit (16) for controlling the temperature of the substrate within a range from above 70 up to 130°C.

Description

Atmospheric Pressure Glow discharge plasma method and system using heated substrate

Field of the invention The present invention relates to a method for treatment of a substrate, using an atmospheric pressure glow discharge plasma in a treatment space, in which the atmospheric pressure glow discharge plasma is generated by applying electrical power from a power supply to at least two electrodes in the treatment space, the treatment space being filled with a gas composition. In a further aspect, the present invention relates to a plasma treatment apparatus for treatment of a substrate, using a pulsed atmospheric pressure glow discharge plasma in a treatment space filled with a gas composition, comprising at least two electrodes connected to a power supply for providing electrical power to the at least two electrodes, and a gas supply device for providing a gas composition to the treatment space.

Prior art

Atmospheric pressure glow discharge plasma's are being used for surface treatment of substrates. In order to obtain a stable plasma a pulsed power supply can be used, with a certain on- time. The advantage of using an atmospheric glow discharge plasma is the high density of the plasma while no complicated vacuum equipment is required as is for the conventional plasma's generated under below atmospheric pressure conditions. By the high density of the atmospheric glow discharge plasma's, very efficient treatment processes are possible. In general the atmospheric pressure glow plasma is generated in a treatment space which is filed with a gas or a gas composition. In case reactive gases are used in the treatment space it is important that no dust is formed as dust formation using these high density plasmas is a phenomenon which can occur easily. Plasma surface treatments which might be envisaged are chemical or physical surface modifications, surface cleaning, surface reactions in general and for example depositions on a surface. A method and apparatus for deposition of layers of material on a substrate in order to obtain a barrier layer using atmospheric pressure glow discharge plasma is e.g. described in the not yet published pending international patent application PCT/NL2007/050052. The barrier properties of these deposited layers can be improved by the so called densification of these layers. The densification of barrier layers in low pressure discharge plasma's (PECVD plasma enhanced chemical vapor deposition processing) is usually achieved in the art by ion bombardment or by substrate heating (200-300 ⁰C). For most polymers, however, substrate heating to temperature of 200-300 ⁰C is not acceptable since the glass transition temperature is usually much less. Furthermore according to general knowledge the mechanism of ion bombardment cannot play a role at atmospheric pressure because of the low ion energy (typically les than a few eV), i.e. the ions cannot gain sufficient energy because of high collision rate at atmospheric pressure.

American patent US5,275,665 discloses an atmospheric pressure plasma generation device. The description is a quite general description on obtaining a stable glow discharge plasma at atmospheric pressure, using electrodes provided with a dielectric barrier. Furthermore, this document discloses that a temperature sensor and a heater are provided in the bottom electrode. No specific details, embodiments or advantages of substrate heating are disclosed.

European patent application EP-A-I 340 838 discloses a method and device for atmospheric plasma processing. The atmosphere near a substrate to be treated is controlled using a gas atmosphere conditioning mechanism. Heating of the substrate seems to be discussed but only in relation to a support acting as conveyer belt in the embodiments shown in Fig. 10 and 11. No further specific details or advantages are discussed in relation to heating.

International patent application WO02/098962 discloses a surface treatment method, in which a substrate is provided with a grafted coating layer, and subsequently post -treated by oxidation or reduction using, inter alia an atmospheric pressure glow discharge plasma. Paragraph [0028] specifically mentions substrate heating, but in a very wide temperature range (as broad as any temperature up to and below the melting point of the substrate).

Summary of the invention

According to the present invention, a method is provided as defined above, wherein the temperature of the substrate is controlled within a range from above 70 up to 130 ⁰C. This range of temperatures is a temperature higher than ambient in the treatment space at the start of the treatment. It has been found, that the efficiency of the atmospheric glow discharge plasma for various applications is significantly improved, in case the substrate is heated. Especially in the mentioned temperature range surprisingly better barrier properties have been observed. The heating of the substrate can be done in various ways. Controlling the temperature of the substrate may be achieved by controlling the temperature of the treatment space, controlling the electrode temperature, or controlling the substrate temperature through heating by IR radiation (e.g. near infra-red, NIR). In one embodiment the substrate is heated, by supplying a heated gas composition to the treatment space. In another embodiment the substrate is heated by near infrared radiation just before APG exposure. In a further embodiment the substrate is heated, by heating the electrode which is nearest to the substrate. In this last embodiment the heating can be intensified by contacting the substrate to the heated electrode. The electrode and substrate are in thermal contact, i.e. the electrode is able to raise the temperature of the substrate directly or indirectly. By using the heated substrate the treatment processes become more efficient. The processes becoming more efficient can be for example: surface cleaning, chemical or physical surface modifications, or depositions on the surface. One of the treatment processes which especially benefits from a heated substrate is the process in which a chemical compound or element is deposited on the substrate. In a specific embodiment, during deposition, at least one of the electrodes is in contact with the substrate and is heated to a predefined temperature. The electrode is for example actively heated to a temperature above normal operating conditions in a plasma treatment space. It has been found that heating the electrode has a beneficial effect on properties of the deposited layer, such as the barrier performance. Especially when depositing an inorganic thin film or layer, such as SiO₂, on a polymer substrate, the barrier performance of the inorganic thin film is improved over films formed without heating of the electrode. Furthermore, it has been found that the process window (the application of plasma power) can be broadened without increasing the dust formation, even up to 2 or 10 ms pulse times. Also processes with continuous pulsations can be obtained.

In an embodiment, the substrate comprises a heat stabilized polymer, and the controlled temperature is below a temperature of heat stabilization of the substrate. Heat stabilized polymers are commercially available, and allow heating of the polymer above the glass transition temperature of the polymer, while the dimensional stability remains very high (i.e. a dimensional variation of a film in the plane of the film remains less than 0.1%, even when cycling the temperature several times). E.g. heat stabilized PET (PolyEthylene Teraphtalate) is available which is dimensionally stable up to 15O⁰C, while the glass transition temperature is 8O⁰C. Also, heat stabilized PEN

(PolyEthylene Naphtalate (Dupont Tejin Q65FA)) is available which is dimensionally stable up to more than 180°C, while its glass transition temperature is 12O⁰C. The temperature to which a substrate may be heated using the present method, may also be indicated relative to the annealing temperature, i.e. the predefined temperature may be in the range where (re-)crystallization of the polymer occurs.

In a further embodiment, the controlled temperature is below a glass transition temperature of the substrate. This boundary is providing good results (i.e. decreased susceptibility to dust formation, better interface adhesion, improving barrier performance), while any possible deformation of the substrate is prevented. The present method may be applied with noticeable effect when the substrate comprises a polymer material on which an inorganic thin film is deposited. Examples of such polymer materials include, but are not limited to PEN (PolyEthylene Naphtalate), PET (PolyEthylene Teraphtalate), PC (PolyCarbonate), COP (Cyclic Olefin Polymer), COC (Cyclic Olefin CoPolymer), etc. The thin film to be deposited may e.g. be a film comprising SiO₂, Si₃N₄, TiO₂, ZnO, SnO, ITO (indium tin oxide),amorphous Si/SiH, Al₂O₃ or combinations . These materials and depositions allow producing flexible substrates having improved characteristics as described earlier.

In a further embodiment, the applied electrical power is pulsed. It has been found during experimentation that even with pulse times up to 2 ms, or even up to 10 ms, there is no dust formation during the deposition process. These longer on-times of the pulsed power result in a quicker and more efficient growth of the deposited layer. In an even further embodiment, the applied electrical power (AC) is continuous. In some experiments even in this case, no noticeable dust formation was observed. Also for the other indicated applications the heating of the web by the various possible means takes care for a stable atmospheric glow discharge plasma process, where the pulse on time can be increased until the level where the applied electrical power is continuous. In a further embodiment, the atmospheric glow discharge plasma is stabilized by a stabilization circuit counteracting local instabilities in the plasma. This provides for a stable and uniform glow discharge plasma in the treatment space, allowing efficient processes occurring in the treatment space. E.g., local instabilities in the plasma are counteracted by applying an AC plasma energizing voltage to the electrodes causing a plasma current and a displacement current, wherein the glow discharge plasma is controlled by applying a displacement current change (dl/Idt) for controlling local current density variations associated with a plasma variety having a low ratio of dynamic to static resistance. In a further embodiment, the displacement current change is provided (just before and/or just after the plasma peak) by applying a change in the applied voltage (dV/Vdt) to the at least two electrodes, the change in applied voltage being about equal to an operating frequency of the AC plasma energizing voltage, and the displacement current change (dl/Idt) having a value of two, three, four or more than five times higher than the change in applied voltage (dV/Vdt). In a further aspect, the present invention relates to a plasma treatment apparatus as described above, further comprising a temperature control unit for controlling the temperature of the substrate to a predefined temperature (e.g. above normal operating conditions). In another embodiment, the temperature control unit is arranged to control the substrate temperature by controlling the treatment space temperature (e.g. using a temperature controlled gas stream), or by controlling the substrate temperature using IR radiation (e.g. near infrared, NIR). In case of heating of the electrode the heating of the substrate can be done indirect, or direct. In the latter case the substrate is in (thermal) contact with the heated electrode. In a specific embodiment the apparatus further comprises a heated electrode connected to the temperature control unit, the heated electrode being in contact with the substrate during operation.. This apparatus is well suited to implement one of the method embodiments of the present invention as described above, with similar effects and advantages.

In an embodiment, the electrode heater comprises one of an electrical heater, a conduction heater, or a radiation heater. The electrical heater may e.g. be using induction or resistance to generate the necessary heat. The conduction heater may use an external heat source, or e.g. water to provide for the heating effect. The radiation heater may also use an external heat source, but may also use light (e.g. from a laser) or other electromagnetic waves. In a further embodiment the temperature control unit is connected to a heating device in order to control the substrate temperature. The temperature control unit for the substrate as well as the unit controlling the temperature of the electrode may use a feedback loop using a temperature sensor to control the temperature. The temperature control unit may be arranged to perform the method embodiments relating to temperature control as described above.

The power supply of the plasma deposition apparatus may be further arranged to execute the method embodiment relating to the power supply to the electrodes, as described above. E.g. the power supply may comprise a stabilization circuit. The present invention also relates to the use of a plasma treatment apparatus according to any one of the embodiments of the present invention for depositing a layer of material on a substrate in the treatment space. The substrate may e.g. be a polyethylene naphthalate (PEN) film, PET (Polyethylene Terephthalate), PC (Polycarbonate), COP (Cyclic Olefin Polymer), COC (Cyclic Olefin CoPolymer), etc and the material deposited may be SiO₂, Si₃N₄, TiO₂, ZnO, SnO, ITO, amorphous Si/SiH, Al₂O₃ or combinations.

Also, the present invention relates to a treated substrate in general and more specific to the substrate provided with a deposition layer, which deposition layer is deposited using the method or the apparatus according to one of the embodiments of the present invention.

Short description of drawings

The present invention will be discussed in more detail below, using a number of exemplary embodiments, with reference to the attached drawings, in which Fig. 1 shows a schematic diagram of an atmospheric glow discharge plasma apparatus according to an embodiment of the present invention;

Fig. 2 shows a schematic diagram of an atmospheric glow discharge plasma apparatus according to a further embodiment of the present invention;

Fig. 3 shows a schematic diagram of an atmospheric glow discharge plasma apparatus according to a third embodiment of the present invention;

Fig. 4 shows a plot of the water vapor transmission ratio (WVTR) of some typical substrates provided with an inorganic layer according to the present invention, as function of the temperature of the electrode during operation; and Fig. 5 shows a schematic diagram of an atmospheric glow discharge plasma apparatus according to an even further embodiment of the present invention.

Detailed description of exemplary embodiments Fig. 1, 2, and 3 show schematic views of embodiments of a plasma apparatus 10 in which the present invention may be applied. A treatment space 5, which may be a treatment space within an enclosure 1 , or a treatment space 5 with an open structure, comprises two electrodes 2, 3. In general the electrodes 2, 3 are provided with a dielectric barrier (here indicated by layer 7 and substrate 6) in order to be able to generate and sustain a glow discharge plasma at atmospheric pressure in the treatment space. Alternatively, a plurality of electrodes 2, 3 is provided. The electrodes 2, 3 are connected to a power supply 4, which is arranged to provide electrical power to the electrodes 2, 3 for generating the glow discharge plasma under an atmospheric pressure in the treatment space 5. As indicated in the embodiments of Fig. 1, 2, 3 the power supply 4 comprises an AC power source 20 connected to a stabilisation circuit 21.

In the treatment space 5, a combination of gasses is introduced from a gas supply device 8, optionally comprising a precursor in case a deposition application is considered. The gas supply device 8 may be provided with storage, supply and mixing components as known to the skilled person. The gases used may vary depending on the intended application. The gasses can be selected for example from noble gases like argon and the like, an inert gas like nitrogen, reactive gases like oxygen, hydrogen, carbon(di)oxide, nitrogen-oxide combinations of these reactive gases and inert or noble gases and a precursor in case of deposition applications. In case of the use of a precursor it is the purpose to have the precursor decomposed in the treatment space 5 to a chemical compound or chemical element which is deposited on the substrate 6. When using embodiments including a precursor in general dust formation is observed after very short deposition times and a smooth dust-free deposition cannot be obtained. In plasmas used for high quality applications (microelectronics, permeation barrier, optical applications) dust formation is a serious concern. For such applications the dust formation can compromise the quality of the coating. At atmospheric pressure dust formation is a common fact, due to the typical large power density of the plasma and large concentrations of reactive molecules. For this reason the industrial use of atmospheric glow discharge plasmas for coating applications is presently limited to low-end applications such as increasing adhesion. With respect to the mechanism of dust formation in plasma's at atmospheric pressure, it is assumed that the clustering seeds for dust formation are negative and positive ions formed by the dissociation of reactive molecules. In order to prevent dust formation it is necessary to limit the dissociation of molecules by plasma in order to avoid excessive degradation of the molecules or the formation of macro polymers in the plasma. The use of low pressure plasma's is one method to achieve this. At low pressure the ions can not survive more than few milliseconds after the plasma is extinguished and at low pressure the dust particles grow relatively slow (about 10 s) to become of significant size. Pulsing the power is one of the methods to control the energy transferred to the plasma per unit of time.

According to embodiments of the present invention, a different approach is used, which provides surprisingly good results especially for diminishing dust formation and improving barrier performance of the treated substrate 6. By heating the substrate 6 slightly, e.g. by heating electrode 3 slightly, it was surprisingly found that the dust formation was reduced, or even eliminated, while still obtaining good deposition results on the substrate 6.

When treating a polymer substrate 6, the temperature of, e.g., the electrode 3 can be raised to a temperature which is higher than normal in inorganic layer deposition on substrate 6 using uniform glow plasma discharges. The temperature may be raised up to the glass transition temperature of the material (e.g. a polymer) of the substrate 6, and in some cases even higher, up to the annealing temperature of the polymer substrate 6. Some commercially available polymer substrates are dimensionally stable above the glass transition temperature, i.e. after heating to a temperature above the glass transition temperature and then cooling down, no change in dimension is observed. In some instances this is even possible almost up to the temperature at which the polymer substrate starts to decompose. E.g. heat stabilized PET (Polyethylene Terephthalate) is available which is dimensionally stable up to 15O⁰C, while the glass transition temperature is 80°C. Also, heat stabilized PEN (PolyEthylene Naphtalate) is available which is dimensionally stable up to more than 200°C, while its glass transition temperature is 12O⁰C. In a temperature range of the polymer substrate 6 from above 70°C up to 130°C, a positive effect on WVTR characteristics after treatment has been observed. In order to raise the temperature in treatment zone 5 various embodiments can be used.

In one embodiment (see Fig. 2) the heating is provided by heating the incoming gas, e.g. using a heater 30 connected to a heating element 31 in the gas supply 8. This heating can be done in various ways dependent on the gas used. One can use an electrical heating element 31 , or a heating element 31 based on heated oil or a steam heater. In case of the use of a precursor it is preferred not to heat the precursor prior to introduction into the treatment space 5. In another embodiment, the treatment space 5 is heated in its entirety by heating elements as for example IR heating elements (not shown), in which case the gases need not be heated. The temperature may be controlled using the temperature control unit 16, which is connected to the heater 30 and a temperature sensor 32.

In another embodiment (see Fig. 3) the substrate 6 itself is heated. In this embodiment it is also shown that the substrate 6 is introduced in the plasma treatment apparatus 10 from roll to roll. A very useful method for heating the substrate 6 before entering the treatment space 5 is by (near) infrared heating. As shown in the exemplary embodiment of Fig. 3, the temperature may be controlled using the temperature control unit 16, which is connected to a Near-Infrared heater element 41 and a temperature sensor 42. In this case the heating should be done just before the treatment space 5 ('just before' to be understood as that the distance between the NIR heater element 41 and the treatment space 5 is not more than 5 cm preferably less than 3 cm).

In still another embodiment the heating of the substrate is done by heating of the electrode 3 (see Fig. 1). For this, the lower electrode 3, which is positioned near to the substrate 6 during operation, is provided with an electrode heater 15, e.g. in the form of an electric heater (e.g. a resistance wire applied throughout the electrode 3). The electrode heater 15 may be a resistive type of heater element integrated in or in thermal contact with the electrode 3. However, also other types of electrical heater elements may be used, such as inductive heaters, eddy current heaters, etc. Also, the electrode 3 may be heated using a radiation type of electrode heater element 15, e.g. using electromagnetic waves and a suitable type of radiator or source (e.g. light, such as a laser light source). As a further alternative, a conduction type of electrode heater element 15 may be used, e.g. closed circuit water based heater, heat pump, etc. In order to accurately control the temperature of the substrate in mentioned embodiments, temperature control units 16 are provided for each embodiment. In general the temperature control unit 16 measures the temperature of the substrate 6 (indirectly using a temperature sensor 17, 32 in the embodiments of Fig. 1 and 2, or directly using a temperature sensor 42 in the embodiment of Fig. 3), which gives feed back to the temperature control units 16, controlling the heating element 15, 31, 41. The temperature sensors 17, 32, 42 used may be of a type of any choice, as long as operation thereof is compatible with the operation of the plasma deposition apparatus 10. Sensors may include, but are not limited to thermocouples, infrared sensors, etc. Furthermore, one sensor 17, 32, 42 may be used, or a plurality of sensors 17, 32, 42 arranged in a suitable pattern over the electrode 3 (see Fig. 1) or over the substrate 6 (see Fig. 2, 3).

For example for the heating of the substrate 6 by heating of the electrode 3, the apparatus 10 in this embodiment is provided with a temperature control unit 16, connected to the electrode heater 15, and a number of temperature sensors 17 located in various positions in the electrode 3 (e.g. in holes provided on the backside of electrode 3), also connected to the temperature control unit 16. The temperature control unit 16 is arranged to control the temperature of the electrode 3 in a manner known as such to the skilled person, e.g. in the form of a feedback loop. The temperature of the substrate 6 can be controlled by controlling the electrode temperature. The heat transfer of the electrode 3 to the substrate 6 is dependent on the distance between electrode 3 and substrate 6 and is most efficient in case substrate 6 and electrode 3 contact each other. In a further embodiment, the plasma treatment apparatus 10 is arranged to treat two substrates 6 simultaneously, by also using the upper electrode 2. In case the substrate is heated by heating the treatment space in its entirety (see Fig. 2) by the use of heated gas or infra-red heaters optionally an additional heat sensor can be used measuring the temperature of the second substrate. In case the substrate 6 (or web) is heated by NIR the second substrate may be heated by a separate NIR heating device where the proper heating is controlled by a separate temperature control unit. In case of direct electrode heating, electrode 2 may be arranged in a similar manner as bottom electrode 3 as shown in Fig. 1. The temperature control unit 15 may then also be provided twofold, or the temperature control unit may be arranged as a single unit controlling the temperature of both electrodes 2, 3. The electrodes 2, 3 can be shaped rectangular, but also electrode configurations can be used in which the electrodes have a cylindrical appearance. A further embodiment is shown schematically in Fig. 5, which is similar to the embodiment of Fig.l, but with cylinder type electrodes 2, 3 instead of planar type electrodes 2, 3. The cylinder type electrode 3 is, e.g. rotated with the same surface speed as the substrate or web 6 by which scratching of the back-side is prevented and which is very useful in roll to roll applications. Also, static applications of the cylinder type electrodes 2, 3 are possible, i.e. wherein the electrodes 2, 3 and/or the substrate 6 do not move.

The atmospheric pressure glow plasma was generated and stabilized by displacement current control in some experiments using the set-up of the plasma deposition apparatus 10 as described in the embodiments above. It was observed that the susceptibility to dust formation is much less and a significant improvement of barrier performance of an inorganic barrier film substrate 6 is observed when the substrate 6 is heated up (only slightly) to 40 ⁰C or more. When it is desired to perform a deposition on polymer substrates 6 care has to be taken to limit the temperature of the heating method to below the annealing temperature of the polymer (which in general is still well above the glass transition temperature of the polymer). Barrier improvement was observed in a temperature range from above 7O⁰C up to 130°C.

Application of a heated substrate according to the present invention gives an enormous broadening of the process window for all kind of applications relating to the pulse train parameters of the power supplied by the power supply 4. For deposition applications especially susceptibility to dust formation is decreased and moisture barrier performance is increased of substrates 6 provided with a layer of for example SiO2 deposited by APG plasma. Without heating a barrier improvement factor (BIF) for oxygen of typically 40 was observed, however, for moisture permeation almost no improvement is observed. By heating the substrate 6 the BIF for oxygen was further improved to a factor 300, and a BIF for moisture of at least 10 has been achieved. Another important observation is that for all kind of applications the process window for the pulse duration can be extended into the millisecond range: 2 ms up to 10 ms pulse times and even continuous pulsing can be used. In deposition application even with these extended pulse times no significant powder formation was observed.

In general the atmospheric pressure plasma is generated between the two electrodes 2, 3. In case the electrodes 2, 3 have a surface area which is at least as big as the substrate 6, the substrate 6 can be fixed in the treatment space between the two electrodes. In case the substrate 6 is larger than the electrode area, the substrate 6 may be moved through the treatment space 5, e.g. at a linear speed using a roll-to-roll configuration known as such, and e.g. shown in the embodiment of Fig. 3. The power supply 4 can be a power supply providing a wide range of frequencies. For example, it can provide a low frequency (f= 10-450 kHz) electrical signal during the on-time. It can also provide a high frequency electrical signal for example f = 450 kHz - 30 MHz. Also other frequencies can be provided like from 450 kHz- 1 MHz or from 1 to 20 MHz and the like. The on-time may vary from very short, e.g. 20 μs, to short, e.g. 500 μs or as long as 2 minutes or continuous. The on- time effectively results in a pulse train having a series of sine wave periods at the operating frequency, with a total duration of the on-time. In deposition applications we surprisingly found, that by heating the substrate no visible indication of dust formation was observed not for the very short, e.g. 20 μs, or short, e.g. 500 μs and also not for periods as long as 2 minutes. In further deposition experiments, even 'continuous wave' applications of AC power by power supply 4 have been used without resulting in any significant dust formation.

Very good results can now be obtained by using an atmospheric pressure glow discharge (APG) plasma. Until recently these plasma's suffered from a bad stability, but using the stabilization circuits as for example described in US-6774569, EP-A- 1383359, EP-A-1547123 and EP-A-1626613 (which are incorporated herein by reference), very stable APG plasma's can be obtained. In general these plasma's are stabilized by a stabilization circuit 21 (see description of Fig. 1, 2, and 3 above) counteracting local instabilities in the plasma. Using the stabilization circuit 21 in combination with the AC power source 20 in the power supply 4 for the plasma generating apparatus 10 results in a controlled and stable plasma, without streamers, filamentary discharges or other imperfections.

The various embodiments shown in Fig. 1, 2, and 3 can be applied in various uses, like surface treatment, chemical or physical, cleaning, deposition and the like. Although oxygen as a reactive gas has a many advantages in for example surface modification uses or in uses where oxidative processes occur, also other reactive gases might be used like for example hydrogen, carbon dioxide, ammonia, oxides of nitrogen, and the like. In this invention, one or more carrier gasses are used chosen from the group comprising argon, nitrogen, or a combination of both. However, also other inert gasses (e.g. helium) or combinations of inert gasses may be used.

In one embodiment the apparatus of this 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 6 through the treatment space 5, or by having several treatment spaces 5 placed in line 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.

The precursors can be can be selected from (but are not limited to): W(CO)₆, Ni(CO)₄, Mo(CO)₆, Co₂(CO)₈, Rh₄(CO)I₂, Re₂(CO)i₀, Cr(CO)₆, or Ru₃(CO)i₂ , Tantalum Ethoxide (Ta(OC₂Hs)s), Tetra Dimethyl amino Titanium (or TDMAT) SiH₄ CH₄ , B₂H₆ or BCl₃ , WF₆ , TiCl₄, GeH₄, Ge₂H₆Si₂H₆ (GeH₃)₃SiH ,(GeH₃)₂SiH₂. hexamethyldisiloxane (HMDSO), tetramethyldisiloxane (TMDSO), 1,1,3,3,5,5- hexamethyltrisiloxane, hexamethylcyclotetrasiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentanesiloxane, tetraethoxysilane (TEOS), methyltrimethoxysilane, methyltriethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, trimethylethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, n- propyltrimethoxysilane, n-propyltriethoxysilane, n-butyltrimethoxysilane, i- butyltrimethoxysilane, n-hexyltrimethoxysilane, phenyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, aminomethyltrimethylsilane, dimethyldimethylaminosilane, dimethylaminotrimethylsilane, allylaminotrimethylsilane, diethylaminodimethylsilane, 1-trimethylsilylpyrrole, 1- trimethylsilylpyrrolidine, isopropylaminomethyltrimethylsilane, diethylaminotrimethylsilane, anilinotrimethylsilane, 2-piperidinoethyltrimethylsilane, 3 -butylaminopropyltrimethylsilane, 3 -piperidinopropyltrimethylsilane, bis(dimethylamino)methylsilane, 1 -trimethylsilylimidazole, bis(ethylamino)dimethylsilane, bis(butylamino)dimethylsilane, 2- aminoethylaminomethyldimethylphenylsilane, 3 -(4- methylpiperazinopropyl)trimethylsilane, dimethylphenylpiperazinomethylsilane, butyldimethyl-3-piperazinopropylsilane, dianilinodimethylsilane, bis(dimethylamino)diphenylsilane, 1 , 1 ,3,3-tetramethyldisilazane, 1 ,3- bis(chloromethyl)- 1,1,3,3 -tetramethyldisilazane, hexamethyldisilazane, 1 ,3-divinyl- 1,1,3,3-tetramethyldisilazane, dibutyltin diacetate, aluminum isopropoxide, trimethylaluminium, triethyl aluminium, dimethoxymethyl aluminium, tris(2,4- pentadionato)aluminum, dibutyldiethoxytin, butyltin tris(2,4-pentanedionato), tetraethoxytin, methyltriethoxytin, diethyldiethoxytin, triisopropylethoxytin, ethylethoxytin, methylmethoxytin, isopropylisopropoxytin, tetrabutoxytin, diethoxytin, dimethoxytin, diisopropoxytin, dibutoxytin, dibutyryloxytin, diethyltin, tetrabutyltin, tin bis(2,4-pentanedionato), ethyltin acetoacetonato, ethoxytin (2,4-pentanedionato), dimethyltin (2,4-pentanedionato), diacetomethylacetatotin, diacetoxytin, dibutoxydiacetoxytin, diacetoxytin diacetoacetonato, tin hydride, tin dichloride, tin tetrachloride, triethoxytitanium, trimethoxytitanium, triisopropoxytitanium, tributoxytitanium, tetraethoxytitanium, tetraisopropoxytitanium, methyldimethoxytitanium, ethyltriethoxytitanium, methyltripropoxytitanium, triethyltitanium, triisopropyltitanium, tributyltitanium, tetraethyltitanium, tetraisopropyltitanium, tetrabutyltitanium, tetradimethylaminotitanium, dimethyltitanium di(2,4-pentanedionato), ethyltitanium tri(2,4-pentanedionato), titanium tris(2,4-pentanedionato), titanium tris(acetomethylacetato), triacetoxytitanium, dipropoxypropionyloxytitanium, dibutyryloxytitanium,monotitanium hydride, dititanium hydride, trichlorotitanium, tetrachlorotitanium, tetraethylsilane, tetramethylsilane, tetraisopropylsilane, tetrabutylsilane, tetraisopropoxysilane, diethylsilane di(2,4-pentanedionato), methyltriethoxysilane, ethyltriethoxysilane, silane tetrahydride, disilane hexahydride, tetrachlorosilane, methyltrichlorosilane, diethyldichlorosilane, isopropoxyaluminum, tris(2,4-pentanedionato)nickel, bis(2,4- pentanedionato)manganese, isopropoxyboron, tri-n-butoxyantimony, tri-n- butylantimony, di-n-butylbis(2,4-pentanedionato)tin, di-n-butyldiacetoxytin, di-t- butyldiacetoxytin, tetraisopropoxytin, zinc di(2,4-pentanedionate), diethylzinc, dimethylzinc and combinations thereof. Furthermore precursors can be used as for example described in EP-A- 1351321 or EP-A- 1371752. Generally the precursors are used in a concentration of 2-500 ppm e.g. around 50ppm of the total gas composition, but also concentrations over 500ppm can be used, for example lOOOppm, 2000ppm or 5000ppm and higher. The substrate 6, which should be treated or on which an (in)organic layer is deposited using the present method and apparatus may, as already indicated above, be a PEN or PET film. Also other types of substrates 6 may be used, e.g. PC (PolyCarbonate), COP (Cyclic Olefin Polymer), COC (Cyclic Olefin CoPolymer), etc.

Examples

An atmospheric pressure glow discharge plasma was generated using displacement current stabilisation, using a set-up similar to the embodiment shown in Fig. 1. The metal electrode 3 of the plasma apparatus 10 was heated up. Surprisingly, it was observed that the process of depositing a layer on substrate 6 becomes much less sensitive to dust formation if the electrode 3 is heated. The dust formation was evaluated by making static deposits.

Furthermore, the electrode heating allows for a broadening of the process window. This was observed by increasing the pulse train duration by a factor of ten, so from 0.2 ms to a pulse time of 2 ms, no visual dust formation was observed in the static deposition. In a next experiment continuous wave deposition was carried out. A static deposit was formed to study the dust formation. Even in the case of continuous wave deposition using a deposition time of 2 minutes (which may be considered as continuous) no visible indication of dust was observed. Three different heat stabilized base substrates 6 were used: i.e. an optical grade PET ST505, a PEN Q65FA and a PEN Q65FA-P. Typical roughness of the optical PET is Ra=I.7 nm, Q65FA Ra=I.5 nm and Q65FA-P with planarizing layer Ra <1 nm.

Example 1

High voltage generator having a frequency of 150 kHz is connected through a dedicated matching network (together forming the power supply 4) with the DBD reactor (i.e. electrodes 2, 3). Plasma was pulsed using pulse trains with a typical duration of 200-500 us in this case 200 us, and a duty cycle of 10 to 20%.

Mixtures of argon (lOslm (= standard liter per minute)) /nitrogen (2 slm) /oxygen (0.2slm) adding HMDSO at 1200 mg/hr were used (e.g. using the gas supply device 8 of Fig. 1) to deposit a uniform barrier coating of 100 nm on the above mentioned three different substrates 6.

Barrier layers were deposited as a function of different substrate temperatures. For all tests, the resulting water vapor transmission ratio (WVTR) was measured using a Mocon permatron equipment as known to those skilled in the art and the results are shown in the graph of Fig. 4. Surprisingly, it was observed that an electrode temperature of 5⁰C showed hardly any barrier effect of the treated substrates 6, while an increase in electrode temperature shows a clear decrease in the WVTR showing the best results at a substrate temperature range from above 7O⁰C up to 13O⁰C as visible in Fig. 4. A limitation of this trend may occur near the glass transition and/or annealing temperature of the substrates 6. Possible reason for sudden increase of WVTR above 13O⁰C may be due to the fact that a temperature gradient exists between the point of measurement of temperature and the actual surface temperature of the electrode (facing the plasma).

Example 2

Using mixtures of nitrogen (10slm)/oxygen (0.2slm) and HMDSO 1200 mg/hr again big improvement of moisture barrier performance is observed in the case of using a heated electrode, 3 in operation, with an apparatus 10 as described above. Similar results as in example 1 were obtained as shown in Fig. 4.

Example 3

Using a mixture of argon (1 OsIm) /nitrogen (2slm)/oxygen (0.2 slm) and TEOS 300mg/hr using the embodiment of Fig 1 similar results were achieved as shown in fig 4 with respect to the barrier characteristics using an apparatus 10.

Example 4

Using a mixture of nitrogen (10slm)/oxygen (0.2slm) and TEOS (1200mg/hr) similar results were achieved, again using a similar set-up.

Claims

1. Method for treatment of a substrate (6), using an atmospheric pressure glow discharge plasma in a treatment space (5), in which the atmospheric pressure glow discharge plasma is generated by applying electrical power from a power supply (4) to at least two electrodes (2, 3) in the treatment space (5), the treatment space (5) being filled with a gas composition, and wherein the temperature of the substrate (6) is controlled within a range from above 70 up to 130 ⁰C.

2. Method according to claim 1 , wherein controlling the temperature of the substrate is achieved by controlling the temperature of the treatment space, controlling the electrode temperature, or controlling the substrate temperature through heating by IR radiation.

3. Method according to claim 1 or 2 , wherein, during treatment, an electrode (2, 3) is in thermal contact with the substrate (6) and is heated.

4. Method according to any one of claims 1-3, in which the substrate comprises a heat stabilized polymer, and the controlled temperature is below a temperature of heat stabilization of the substrate.

5. Method according to claim any one of claims 1-4, in which the controlled temperature is below a glass transition temperature of the substrate.

6. Method according to any one of claims 1-5, in which the substrate comprises a polymer material on which an inorganic thin film is deposited.

7. Method according to any one of claims 1-6, in which the applied electrical power is pulsed.

8. Method according to any one of claims 1-7, in which the applied electrical power is continuous.

9. Method according to any one of claims 1-8, in which the atmospheric glow discharge plasma is stabilized by a stabilization circuit counteracting local instabilities in the plasma.

10. Method according to claim 9, in which local instabilities in the plasma are counteracted by applying an AC plasma energizing voltage to the electrodes causing a plasma current and a displacement current, wherein the discharge plasma is controlled by applying a displacement current change (dl/Idt) for controlling local current density variations associated with a plasma variety having a low ratio of dynamic to static resistance.

11. Method according to claim 10, in which the displacement current change is provided by applying a change in the applied voltage (dV/Vdt) to the two electrodes, the change in applied voltage being about equal to an operating frequency of the AC plasma energizing voltage, and the displacement current change (dl/Idt) having a value at least five times higher than the change in applied voltage (dV/Vdt).

12. Method for deposition of a chemical element or compound on a substrate, using an atmospheric pressure glow discharge plasma in a treatment space (5), in which an atmospheric pressure glow discharge plasma is generated by applying electrical power from a power supply (4) to at least two electrodes (2, 3) in the treatment space (5), the treatment space (5) being filled with a gas composition including a precursor for the chemical element or compound to be deposited, wherein the temperature of the substrate is controlled within a range from above 70 up to 130 ⁰C .

13. Plasma treatment apparatus for treatment of a substrate, using a pulsed atmospheric pressure glow discharge plasma in a treatment space (5) filled with a gas composition, comprising at least two electrodes (2, 3) connected to a power supply (4) for providing electrical power to the at least two electrodes (2, 3), a gas supply device (8) for providing a gas composition to the treatment space (5), and a temperature control unit (16) for controlling the temperature of the substrate within a range from above 70 up to 130 ⁰C.

14. Plasma treatment apparatus according to claim 13, wherein the temperature control unit (16) is arranged to control the substrate (6) temperature by controlling the treatment space (5) temperature, or by controlling the substrate (6) temperature using IR radiation.

15. Plasma treatment apparatus according to claim 13, further comprising a heated electrode (3) connected to the temperature control unit (16), the heated electrode (3) being in thermal contact with the substrate (6) during operation.

16. Plasma treatment apparatus according to claim 15, in which the heated electrode (3) comprises an electrode heating element (15; 41) selected from an electrical heater, a conduction heater, or a radiation heater.

17. Plasma treatment apparatus according to any one of claims 13-16, in which the temperature control unit (16) is arranged to perform the method according to one of the claims 1-6.

18. Plasma treatment apparatus according to any one of claims 13-17, in which the power supply (4) is further arranged to execute the method according to claim 7 or 8.

19. Plasma treatment apparatus according to any one of claims 13-18, in which the power supply (4) comprises a stabilization circuit (21) arranged to perform the method according to any one of claims 9-11.

20. Plasma treatment apparatus according to any one of claims 13-19, in which the treatment comprises a deposition of a layer of a chemical element or a chemical compound on the substrate (6), and the gas composition comprises a precursor of the chemical element or chemical compound to be deposited.

21. Use of a plasma treatment apparatus according to any one of claims 13-20 for depositing a layer of material on a substrate (6) in the treatment space (5).

22. Use according to claim 21, in which the substrate can be selected from Polyethyleneterphthalaat (PET) polyethylene naphthalate (PEN) film, PC (PolyCarbonate), COP (Cyclic Olefin Polymer), COC (Cyclic Olefin CoPolymer).

23. Substrate provided with a deposition layer, which deposition layer is deposited using the method according to claim 12 or the apparatus according to claim 20.