Method and device for synthesis of highly insulating coatings

Abstract

The invention relates to a coating chamber with a hollow discharge anode (HDA) forming body connected electrically insulating and vacuum tight to an opening of the coating chamber, wherein the inner surface of the body comprises a hollow space with an opening to the hollow space, wherein the interior surfaces of the body are at least partially constructed to be electrically conducting and the opening to the hollow space is attached to the opening of the coating chamber so that a gas exchange between the hollow space and the coating chamber is enabled, whereby distanced from the opening of the hollow space at least one gas supply is foreseen through the body into the hollow space, the opening between the coating chamber and the body is limited in size by an orifice. The invention also covers a coating process using the mentioned coating chamber.

Description

[0001] Method and device for synthesis of highly insulating coatings

[0002] The invention is related to a device for coating technology and coating processes for synthesis of coatings with physical and / or chemical deposition from the gas phase, i.e. Physical Vapor Deposition (PVD) and / or Chemical Vapor Deposition (CVD). The invention is in particular related to cathodic arc deposition and / or Plasma Enhanced Chemical Vapor Deposition (PECVD).

[0003] The invention describes particularly also a solution, to produce highly insulation coatings through PECVD, alone or in combination with cathodic arc deposition, and to guarantee high process stability and process reproducibility for the deposition of thin coatings.

[0004] The invention allows higher deposition rates from cathodic arc deposition and improves uniformity of the coating in industrial size coating equipment.

[0005] The coating of surfaces of substrates is a standard procedure to reduce corrosion. Protective coatings are necessary in particular at high temperatures (above ca 800 °C) for substrate materials like Ni-, Co-, or NiCo-based super alloys, but also for Ti-Aluminides or ceramic matrix composite materials (CMC) that contain C, Si-C, or Si-N materials. Further examples of substrate materials, whose surfaces under these conditions must be protected, are Borides, Carbides, Carbonitrides or materials carbon fiber reinforced materials (CFRP, C / C).

[0006] Insulating coatings are in this context of particular interest, for application at high temperatures as well as low temperatures, since corrosion mechanisms that relate to charge transport are reduced. Low temperatures are in the context of this description to be understood as temperatures below 800 °C. High temperatures in the context of this description is to be understood as temperatures from 800 °C up to and including 10 000 °C. Super high temperatures, i.e. temperatures above 10 000 °C are not in scope.

[0007] In addition to the large potential application as protective coatings at low temperatures, insulating coatings can furthermore help to extend the application potential for low-cost base materials, such as low alloyed steels, glasses, plastic materials, and composite materials, towards higher temperature. Thereby expensive base materials can be replaced.

[0008] In addition to surface finish of base materials, insulating coatings can furthermore play an important role in the control of diffusion processes, in particular in cases where diffusion processes must be reduced in coating comprising several layers or at the interface between base material and coating. Control of diffusion towards the base material is important for adhesion of the protective layer and may not compromise the long term functionality.

[0009] The following text will foremost focus on insulation coatings, but the inventive device may also be used for conductive coatings without restrictions.

[0010] The production process, on which the invention is based, is a combination of PVD technology and CVD technology and take place in a highly reactive plasma environment under vacuum conditions. For the PVD technology, in particular cathodic arc deposition is in focus. The reason that arc deposition is particularly advantageous is because it allows operation in pure oxygen atmosphere, which is useful for the synthesis of oxidic and insulating coatings. The process should therewith be applicable for an as broad spectrum of coatings as possible.

[0011] The invention relates to high current discharges, which are used for deposition of coatings. A high current discharge in the context of the present invention is understood to include cathodic arc discharges and discharges created via a heated filament, also called hot filament discharges.

[0012] A reactive arc deposition in oxygen, for the synthesis of oxides, is enabled through the simultaneous prevention of thick insulating coatings on the targets and on the anode. A persistent oxidation on the cathodic target can be preventive through specific configurations of the magnetic field. Further embodiments are known for the anode, which guarantees the electrical conductivity during the deposition of insulating coatings.

[0013] The disclosed methods are sufficient to synthesize oxide coatings through arc deposition in a reproducible and safe way. The arc deposition from a flat target surface is due to its inherent characteristics a non-directional evaporation, therefore for example covered areas are not exposed to oxide, which guarantee accessible anode areas. Furthermore, oxides produced in this manner display reduced adhesion on certain components of the coating chamber (e.g. heater) as a result of that no bias is applied to these components. The reduced adhesion leads to coating spallation on said components during cyclical operation, which contributes to generate free anode spots.

[0014] The conditions do however change in the case of the herein described inventive method for synthesis of insulating coatings. The combination of PVD (arc deposition sources) and CVD enables the coating of cavities and the coating of covered areas of the coating chamber. The results are coatings on components in the coating chamber with good adhesion that can also be exposed to cyclic thermal loads.

[0015] Furthermore, oxides, nitrides, oxynitrides, silicates, and further ternary and quaternary oxides display good insulating properties. The good insulating properties also hold for e.g. all insulating coatings produced with the described method when a gaseous Si precursor is used. The good insulating properties is mainly due to the low number of droplets generated.

[0016] While process stability can be achieved with known methods with respect to the surface of the cathode (target), the known and commonly utilized methods are not enough with respect to anode configurations. As a result, an uncontrollable increase in the voltage is obtained for the arc discharge, which tends to instable processes. Therefore, the process stability for insulating coatings can no longer be guaranteed.

[0017] The document W02009056173A1 describes a device, in which areas of the anode of an arc source is designed in the form of cavities. These cavities are described as «hollow anodes» as under certain process conditions a protective plasma is created, which shields areas of the anode from insulating coatings. The efficiency is, however, strongly depending on the process parameters, as described in the document, in particular from the geometry of the cavity (diameter) and the process pressure (pressure in the vacuum coating system). The process window of this device is thus narrow and limits the freedom for process design in a restrictive manner.

[0018] The disadvantages are particularly severe, in case, as with the herein described inventive process, a combination of cathodic arc deposition and plasma enhanced CVD is in focus. For such a process, the process pressure can usually not be kept constant. The dimensioning of the hollow-anode cavity therefore would have to be selected differently in each case, to generate the protective plasma.

[0019] This requirement limits the flexibility in the process control in several aspects. Firstly, several hollow anodes with different dimensions would be required, which is usually not compatible with the limited space in the process chamber or would come at the expense of reduced loading capacity. Secondly, and more severely for the process stability, is that the hollow anodes, which are not providing a protective plasma in a certain process step, i.e. a specific process pressure, would be coated with an insulating coating and thereby loose the capability to operate properly under the pressure range for which they are dimensioned. Also the alternative option in W02009056173A1 , in which the anode cavity has a pressure stage, did not lead to stable operation, but only to an increased layer deposition in the area of the pressure stage opening and again to instable process conditions. The combination of cathodic arc deposition and plasma enhanced CVD amplifies the deposition conditions in such a way that the in W02009056173A1 suggested solution is not sufficient.

[0020] As a conclusion from the described experimental experience, there is a need to look for a process pressure independent solution in order to realize a combination of PVD and CVD processes that enables stable deposition processes, in particular with respect to the deposition of insulating coatings.

[0021] The objective of the invention is to provide a stable deposition process, where a combination of cathodic arc deposition and plasma enhanced CVD (the combination is herein designated as PVD+) is used in the same deposition system, simultaneously or sequentially, to deposit conducting and in particular insulating coatings.

[0022] A further objective of the invention is to increase the deposition rate in such a coating system, since components of both PVD and CVD processes are incorporated into the coating.

[0023] A further objective of the invention is to ensure an improved coating uniformity.

[0024] A further objective of the invention is to enable the use of PVD+ in a coating chamber consisting of insulating materials.

[0025] A further objective of the invention is to provide an anode configuration that enables a stable arc evaporation from metallic targets (cathodes) for the synthesis of conducting and insulting coatings (PVD) and the simultaneous or time-shifted operation of cathodic arc deposition with a PECVD coating (i.e. PVD+).

[0026] A further objective of the invention is to design the anode configuration so that it can be used for one as well as for several arc discharges.

[0027] A further objective of the invention is to use several spatially displaced anode configurations for an arc discharge, to achieve an improved coating distribution.

[0028] A further objective of the invention is to enable the simultaneous operation of several anode configurations with a number of cathodic arc sources and gases, with or without simultaneous gas discharges. A further objective of the invention is to provide an anode configuration in a coating chamber that can be operated for the synthesis of fully insulating coatings.

[0029] A further objective of the invention is that the anode configuration can be operated separated from ground.

[0030] A further objective of the invention is to design the anode configuration so that the interior surface of hollow-body shaped substrates can be deposited.

[0031] A further objective of the invention is to use several spatially distributed anodes at different times for a coating deposition.

[0032] Description of the most important elements of a coting process for improved understanding of the inventive device

[0033] In the following the procedure for coating processes will be described, in which exemplary an insulating coating is synthesized, to show the necessity and function of the inventive device, a hollow discharge anode (HDA). Reference is made to Figure 1.

[0034] Process before the main deposition step

[0035] The coating process is carried out in a vacuum deposition chamber 1 , which trough a vacuum pump 2 (only indicated by an arrow) can be pumped to a starting pressure below 10’5mbar, where, however, the substrate preparation steps can be started already at a starting pressure below 10-4mbar. The substrates 3 are mounted on substrate holders 4 before the pumping of the deposition chamber, wherein several substrate movements and / or rotations (not shown in the picture) are possible during the coating process. The substrate holder is typically electrically insulated from ground, so that an electrical potential can be applied to the substrate holder in order to influence the coating properties.

[0036] After pumping of the deposition chamber to the required pressure a pre-treatment of the substrate follows typically with methods which are well known for the skilled person in this area, essentially consisting of heating and plasma pre-treatment steps. For the plasma pretreatment, for example, a gas discharge can be used, typically with argon as the noble gas, which is generated with a plasma source 5 between a heated filament 6 of this plasma source as a cathode and an anode 7 in switch position a and which is fed with an electrical supply 12. The electrical switch with switch positions a and b as depicted in Figure 1 enables to switch between two different operation modes of the plasma source. In switch position a, the plasma source 5 with the heated filament 6 is operated with the anode 7. In switch position b, the plasma source 5 with heated filament 6 is operated with the hollow discharge anode (HDA) 11 , as will be further described below.

[0037] The dashed arrow designates the supply of Argon for the plasma source 5. The plasma source 5 with filament 6 and anode 7 are therefore insulating or connected with high resistance relative to ground. As a guideline and example, a voltage of 50 V and a discharge current of 200 A are given here for such a gas discharge. These characteristic parameters can vary considerably, as is known to those skilled in the art.

[0038] The charge carriers of this gas discharge can be used for substrate pretreatment by applying a voltage to the substrate to be coated using a bias supply. A negative voltage results in sputter cleaning of the substrates by bombardment with argon ions, a positive voltage initiates bombardment with electrons and contributes to heating the substrates.

[0039] Process step for PECVD and reactive PECVD

[0040] Of particular importance is the gas discharge for PECVD processes, which are a component of the PVD+ coating technology. The high discharge currents (electron currents) enable efficient decomposition of the gaseous precursors, that can be mixed into the gas discharge, with the result that the non-volatile elements can be deposited as coating on the substrates. For example, a silicon coating will result if silane is added to the gas discharge, or, as a second example, the deposition of a carbon coating, in case acetylene is added. This leads to chemical reactions with other deposited coating components on the surface of the substrate, for example, reaction with nitrogen to form a nitride, or the reaction with oxygen to form an oxide.

[0041] Process steps for PVD

[0042] In order to coat the substrates with PVD, targets 9 are mounted in the solid-state sources 8 in the vacuum chambers. Metallic vapor is generated from the targets which condense on the substrate surface. Thermal evaporators, sputter sources and / or arc evaporators can be used as PVD sources. The invention is described based on the example of a cathodic arc source, which represents the most important solid-state source which also guarantees the largest economic benefit. In case the solid-state source 8 is an arc source, then a critical component is the electrically conducting target 9, which during cathodic arc evaporation is connected as cathode. On the target, an anodic arc is ignited, typically in that a short circuit is crated with an ignition finger (not shown) to an anode in the vicinity of the target and / or conducting and insulating wall of the coating chamber at ground potential. An electrical discharge is created in the vapor of the target material, which through evaporation of further material is stabilized, possibly through the addition of a noble gas. Corresponding modes of operation are not shown in Picture 1 , since they form state of the and are particularly known to the skilled person. The evaporated target material condenses as coating on the surface of the substrate 3. Also in this case, a voltage between 20V and 30V and arc current of 200A can be mentioned as guideline and example.

[0043] Process for reactive PVD

[0044] In order to synthesize coatings that do not only correspond to the target material, the cathodic arc discharge can be additionally supplied with gaseous precursors, for example over one or several flow meters 10. The gaseous precursors can for example be nitrogen, to synthesize a nitride coating, or oxygen to synthesize an oxide coating.

[0045] Many nitrides which are synthesized through arc evaporation of a metallic target are electrically conducting. This means that*the anode as well as the vacuum chamber wall remain conducting throughout the deposition of the nitride coating and can be used as anode for the arc discharge.

[0046] The situation is different when an oxide is synthesized through the arc discharge. The arc evaporation possesses a predominantly line-of-sight directed evaporation, which results in that the chamber wall as well as components in the interior of the coating chamber which are “seeing” the target surface will be covered with an oxide coating, in addition to the substrate surfaces which are the intentional objects to be coated. This fact leads to that the anode surfaces according to state of the art will become increasingly insulating in character. The insulation coatings is not a problem for process stability under normal conditions since sufficient non-insulation spots are present in the coating chamber, for example on the chamber walls behind installed components, which are not covered with oxide, or for example also on heaters, where the coatings are spalling of when the heaters are turned on and off.

[0047] Problem of state of the art: PECVD

[0048] The situation will be fundamentally different as soon as insulating coatings, such as Si-O or Si- N in a first preferred process embodiment (= process embodiment A), are synthesized with PECVD. Since the aforementioned coatings are synthesized solely from the gas phase (e.g. employing gaseous precursors like silane, oxygen, nitrogen), the precursors can be dissociated through the plasma source 5 alone, which is operated to form a gas discharge between the filament 6 and the anode 7.

[0049] A noble gas (typically argon) is added to the chamber of the filament (indicated through the dashed arrow, which indicates argon supply) and a voltage is applied between the filament 6 and the anode 7 to ignite and maintain the gas discharge with the electrical power supply 12. After supplying for example 50 seem Silan and 100 seem O2, a SiC>2 coating are formed on the substrates which are located on the substrate holders. A substrate bias 13 can support and influence the film formation, in particular when the bias for the insulating coating is formed in a pulsed or bipolar pattern. In any case, coating deposition will result on the substrate, as well as simultaneously deposition of an insulating coating on the anode side of the plasma discharge. The increasingly insulated anode 7 increases the burning voltage of the plasma discharge and will eventually result in termination of the plasma discharge. The use of a graphite part, as is recommended according to state of the art, can only partially solve this problem, as certain reactive gases also react with graphite, resulting in an increase in the resistance with possible disruption of the discharge.

[0050] To solve the above-mentioned problems, according to a first inventive process, the anode 7 is replaced with an inventive HDA 11 , i.e. a hollow anode (in the following also described as Hollow Discharge Anode) with switch position b (described in figure 1 ), which enables a stable coating process.

[0051] Problems with state of the art: combination PECVD and PVD

[0052] Similar instable conditions are encountered in a second preferred process embodiment (= process embodiment B), wherein not only gaseous precursors are used, but in combination with arc evaporation of metallic target. As an example, the synthesis of an Al-Si-O coating is described, which should not be interpreted as limiting the scope to only this material. The substrates to be coated 3, are, as described above, placed on the substrate holder 4 and the vacuum chamber is pumped to vacuum. The substrates are thereafter heated and exposed to a plasma pre-treatment.

[0053] To adjust a functional coating (in this example, the functional coating is the Al-Si-O coating) to the substrate material it is in many cases advantageous or even required to deposit a further coating as a layer in between, a so-called interface-coating. The interface-coating can have different purposes according to the application, however, in general the interface between substrate and coating is stabilized. For example, one purpose of the interface-coating can be to reduce the diffusion between functional coating and substrate during use at high temperatures, and / or the purpose can be to achieve a better conformity of the CTE (coefficient of thermal expansion = CTE) and / or the purpose can be to simply enhance the technical surfaces regarding roughness and reproducibility.

[0054] For the herein described example, a Si-C substrate serves as substrate. A such material belongs to the class of so-called High Specific Strength Materials (HSSM), i.e. display a high mechanical stability also at low specific weight. These materials are in the form of reinforced composite materials (SiC CMC) particularly suited for uses in the aero industry, since the weight of airplanes can be reduced and thereby fuel savings achieved. However, these materials are vulnerable to water vapor and oxygen at temperatures above 1000°C. Therefore a protective barrier coating is required. Such barrier coatings are for example compounds like Al-Si-O or compounds of rare earth elements with silicon or oxygen (= rare earth silicates, for example Yb-Si-0 or Y-Si-O to name a few examples.

[0055] A Si-coating is deposited as an interface coating on the SiC substrate after the pre-treatment steps (see above) to achieve a good adhesion to the functional coating. For the step of depositing the Si-coating, the PECVD process embodiment as described above is used, i.e. a gas discharge is ignited and silane is dissociated in order to deposit a silicon coating. As elemental Si is not an insulator, the anode 7 can be used without problems for the gas discharge between the filament 6 and anode 7 (switch position a in Figure 1 ). Of course, the for the chamber intended HDA in switch position b in Figure 1 can alternatively be used. For example, in this process step a DC substrate bias of -40V can be used.

[0056] The deposition of the Si interface coating is followed - as one of several possible process transitions - by turning off the gas discharge. Thereafter oxygen is introduced into the chamber and the cathodic arc discharge of the Al target is ignited and Silane is again introduced. Since the discharge current during the cathodic arc discharge are of about the same magnitude as during the gas discharge, the discharge currents will serve to dissociate and activate the gaseous precursors (in this case silane and oxygen) and a deposition of an Al-Si coating and simultaneously the oxidation to AI-Si-0 on the substrate surface.

[0057] A skilled person in the area of coatings knows that such coating processes can be operated with one as well as with several targets, and that the oxygen and silane flow can be adjusted accordingly in order to obtain the desired coating composition. Furthermore, as mentioned above, the deposition with metallic vapor from the target (here Al as example) is distributed in approximately a line-of-site geometry, but through the use of the gaseous precursors, i.e. through the combination with PECVD, surfaces behind covers will also be coated. Therefore the active anode surface (i.e. anode surrounding the target and the wall of the coating chamber according to state of the art) will become increasingly insulated and it comes to a process interruption. Besides process interruption, there is also a considerable risk of damage to the equipment due to high current densities on the remaining free anode spots.

[0058] Therefore, in a second inventive process B, the anode on the cathodic arc source and the as anode working chamber wall is replaced by one or several HDA 11 (description in figure 2), to enable a stable coating process.

[0059] So far, the two process embodiments were described, which cannot be realized through current state of the art, i.e. not realizable without the utilization of one or several HDA, at least not for longer process times, which are required to grow coatings with higher coating thicknesses.

[0060] The solution which stabilizes or at all makes the realization of such processes possible is based on the use of the HDA. Furthermore, the solution can as well be used with PVD processes, which without PECVD is used to synthesize insulating coatings, i.e. for such processes which are possible to realize according to current state of the art, even though not for all materials. In comparison with state of the art, where covered spots and / or heating elements are used, the solution has the advantage of a stable discharge voltage for the arc evaporation, which is advantageous in particular for longer coating times for larger coating thicknesses.

[0061] The hollow discharge anode HDA according to the present invention can be used as an anode for one or several cathodic arc discharges and / or one or several filaments. The hollow discharge anode HDA may thus be operated as anode for several high current discharges on the cathode side. Furthermore, several hollow discharge anodes HDAs can be used as anode for one cathodic arc discharge and / or one filament. Two or a multitude of hollow discharge anodes HDAs may thus be operated as anode for one high current discharge on the cathode side. The invention thus allows operation of one or a multitude of high current discharges as cathode with one or a multitude of hollow discharge anodes HDAs as anode.

[0062] For the efficiency of the process, productivity and coating distribution, the possibility to freely position the HDA in the chamber is essential. This includes the utilization of more than one HDA for one cathodic arc source and the utilization of one HDA for more than one cathodic arc source. The inventive hollow discharge anode HDA thus allows to produce coatings with improved coating uniformity.

[0063] The inventive hollow discharge anode HDA provides an anode configuration that enables a stable arc evaporation from metallic targets (cathodes) for the synthesis of conducting and insulting coatings (PVD) and the simultaneous or time-shifted operation of cathodic arc deposition with a PECVD coating (i.e. PVD+).

[0064] Description of the HDA and its embodiments

[0065] In WO 2009 / 056173 A1 devices for hollow anode configurations are disclosed, which serves to prevent coating deposition on certain areas of the anode during operation of a catohodic arc discharge. In order to create such a hollow anode discharge, the geometric dimensions of the hollow anode desing must be adjusted to the pressure conditions in the coating chamber, In case that different pressure conditions occur during the coating depsosition, it is required to use different geometrical adjustments for the hollow andode geometry. This has proven to be a disadvantage as non-active hollow anode geometries occur during previous process steps, which prevents the ignition of the hollow anode discharge in a following process step.

[0066] This effect also occurred in several cases for the in WO 2009 / 056173 A1 described version with gas supply and pressure stage (Figure 13 in WO 2009 / 056173 A1). An insulating coating was formed on either the inner surface of the hollow anode or the pressure stage (in cases where it was used), which resulted in that electrically conducting anode surfaces could not be provided in a stable manner for all coatings.

[0067] In conclusion, one can say that the in WO 2009 / 056173 A1 disclosed solution could not be used to the full extent necessary for insulating coatings, in particular if the requirements on reproducibility regarding coating thickness and insulating properties were high. The desired flexibility for synthesis for coating systems, consisting of several of insulating coatings of different materials was not possible, as the changing conditions on the anode surface limited the reproducibility of the process.

[0068] The inventive solution has therefore defined as goal to provide a process, with which the coating of the anode surfaces can be efficiently avoided. To reach this goal, a cathodic arc discharge, as already indicated in figure 1 , is separated from ground on the side of the anode 7. (The cathode is separated from ground as standard.) It was presented schematically that the dotted spots (which should indicate insulators) are in areas between the plasma source, the arc source as well as the HDA on the one side and the grounded chamber on the other side.

[0069] Figure 2 shows the schematic construction of the HDA. For smooth functioning of the HDA it was advantageous to separate the plasma in the coating chamber 20 (chamber in which the substrate are coated) from the electrically active anode surface in the HDA. An opening in the coating chamber wall of the coating system enables charge carrier transport from either the plasma source or the arc source to the inner anode surface 25 of the HDA.

[0070] The HDA in itself is connected in a vacuum tight manner to the wall of the coating chamber and electrically insulated from the grounded coating chamber wall 21. The latter feature is realized through insulators 22 between the coating chamber wall and the HDA. In addition, in a preferred embodiment of the HDA, an electrically floating orifice 23 is foreseen. Noble gases (mostly Ar) which are introduced into the HDA through a gas supply 24 is flowing through the orifice towards the coating chamber. The orifice can also be a part of the insulators 22 (not shown) The gas supply with a noble gas (preferred Ar) in the anode configuration prevents the coating of the interior surface of the anode chamber with insulating coatings. The anode inner surface 25 is depicted as a cylindrical form, which however is not absolutely necessary. Due to the impact of high electron currents originating from the plasma source or from the arc discharge on the anode, it is advantageous to provide cooling for the anode surface. This can be realized through supply of a cooling media 27. As example, the anode can be made of cupper or comprise cupper, whereby the walls of the anode posses an integrated channel system through which the cooling media water is flowing. This channel system can for example be constructed through that the bodies forming the anode walls 25 are build up using 3D printing.

[0071] For temperature stable materials, the anode body can be constructed without such a described cooling system. An electrical connection 28 ensures the connection to the electrical power supply.

[0072] The orifice may be constructed with different size and shape. In one embodiment, the orifice is circular with a diameter in the range between 10 mm and 100 mm, preferably in the range between 20 mm and 50 mm, most preferred in the range between 25 mm and 35 mm. To optimize the hollow anode configurations of the HDA with respect to hardware and stabilization of the anode conductivity, different configurations of orifice sizes and Ar flow was investigated. Figure 7 displays an example of measurements where a cathodic arc source was operated with a hollow discharge anode HDA. Plotted are the values of the arc source voltage obtained for different combinations of circular orifices with different diameters and Ar-flow thorough the HDA. It is noted that the arc source voltage can be tuned by selection of Ar-flow and / or orifice size (diameter). As can be seen in the figure, smaller orifice diameter lowers the arc source voltage at a constant Ar flow, and increased Ar-flow lowers the arc source voltage at a constant orifice diameter. To reduce the efforts for insulation, it is beneficial to run the arc discharge at low voltages. This can be achieved by adjusting argon flow and orifice diameter. One further approach is to use an anode material with high melting point for which cooling is not necessary, like for example graphite.

[0073] On the other hand, an increased arc discharge voltage is necessary to achieve the cleaning effect of the hollow anode. This means that the anode drop should be increased compared to the typical discharge voltage that is obtained if the whole chamber wall is utilized as anode. It has been shown that if the magnitude of the anode drop is larger than the magnitude of the cathode drop (comparing absolute values), cleaning of the cooled anode electrode can be achieved. To achieve the anode drop, a current density at the orifice of the hollow anode should be in a range between 10 A / cm2and 200 A / cm2. The current density at the orifice is calculated as the current the hollow discharge anode HDA carries divided by the cross-sectional area of the orifice, i.e. the opening of the orifice to the coating chamber. Typical cathode drop is 20 V and typical anode drop is 40 V. The range of anode drop is preferentially between 30 V and 100 V.

[0074] The anode drop is defined as the potential difference between ground, e.g. the grounded coating chamber wall, and the electrical connection to the hollow discharge anode HDA. The cathode drop is defined as the potential difference between ground, e.g. the grounded coating chamber wall, and of the anode which may be a filament plasma source or a cathodic arc source.

[0075] Figure 5 exemplifies the measurements of cathode drop (Vc) and anode drop (VA) when the hollow discharge anode HDA is operated with a filament plasma source. The cathode drop (Vc) may be measured between the grounded coating chamber wall and the connection from the power supply 12 to the cathode 6. The anode drop (VA) may be measured between the grounded coating chamber wall and the connection from the power supply 12 to the hollow discharge anode HDA 11 . Figure 6 exemplifies the measurements of cathode drop (Vc) and anode drop (VA) when the hollow discharge anode HDA is operated with a cathodic arc discharge. The cathode drop (Vc) may be measured between the grounded coating chamber wall and the connection from the power supply 12 to the cathode 9, i.e. the evaporation target. The anode drop (VA) may be measured between the grounded coating chamber wall and the connection from the power supply 12 to the hollow discharge anode HDA 11.

[0076] In figure 3, two further embodiments of the HDA are described. One magnetic device 30 can be provided, preferably on the atmospheric side. The magnetic device serves to provide a magnetic field, which in turn influences the discharge voltage. Furthermore, a body 29, preferably in the form of a rod or another geometry in the interior of the HDA can be provided, for the same purpose to influence the discharge voltage. This body 29 can be manufactured of cooled cupper, but also from another material as for example a graphite containing material. Combinations of materials are also possible.

[0077] The electrical interconnection of the plasma source 5 and the arc source 8 with the HDA is depicted in figure 4. The ignition of the arc discharge between the cathode (target) 9 and the HDA is conducted as usual with an electrical supply 12, through that a short temporary contact between the HDA, which is separated from ground, and the cathode, which is separated from ground, is created, which leads to an arc on the cathode 9 and generates an arc discharge. A such ignition for the plasma source 5 is not necessary as it operates based on an internal discharge between the hot filament 6 in connection with the argon, which already generates a discharge.

[0078] In one embodiment, ignition of the arc discharge is possible utilizing a HDA, whereby during a short moment, electrons are created at the cathode side during a short contact with the HDA.

[0079] The plasma which is generated in this way in the coating chamber 20 can now be supplied arbitrarily with further gases, which are needed for synthesis of the desired coating materials. Table 1 presents some examples for synthesis of coatings. Furthermore, Table 1 includes some values for process parameters of the coating process. Table 1 does only include insulating coating materials. Analogously, the inventive process can be used for synthesis of conducting or semiconducting coatings, for example Ti-N or Ti-AI-N coatings. The selection of the examples in Table 1 should therefore not be interpreted as a limitation. The adjustment of the stoichiometry of the synthesized coating materials is performed in an iterative process, wherein the evaporation rate of the used target and the flow of reactive gases are adjusted so that a specific coating composition are achieved.

[0080] As is exemplified in Table 1 , coating processes may be operated using one or several reactive gases, for example comprising at least one of the gases SiFU, O2, N2, and C2H2. The reactive gases are preferably supplied to the coating chamber for distribution to the substrates. The gas supplies for the coating chamber and the hollow discharge anode HDA are preferably separated such that the coating chamber can be supplied with one gas or gas mixture and the hollow discharge anode can be independently supplied with one gas or gas mixture. The gas supply for the coating chamber and the hollow discharge anode HDA may occur simultaneously, sequentially, or in interchangeable sequences.

[0081] During some coating process, the coating chamber to which the hollow discharge anode HDA is connected is or may become fully insulating.

[0082] Features of the described embodiments with respect to equipment and processes may be combined to form new embodiments in as far as not contradictory, as evident to a person skilled in the art.

[0083] Table! : Brief description of the figures

[0084] Figure 1 depicts a coating chamber for coating of substrates.

[0085] Figure 2 shows a detailed view of the hollow discharge anode HDA.

[0086] Figure 3 shows a hollow discharge anode HDA in an embodiment including a body as protrusion and / or magnetic devices.

[0087] Figure 4 shows a coating chamber with a filament plasma source, an arc source, and a hollow discharge anode HDA. In switch position a, the arc source is operated with HDA. In switch position b, the filament plasma source is operated with HDA

[0088] Figure 5 illustrates measurement points for cathode drop (Vc) and anode drop (VA) when the hollow discharge anode HDA is operated with a filament plasma source.

[0089] Figure 6 illustrates measurement points for cathode drop (Vc) and anode drop (VA) when the hollow discharge anode HDA is operated with a cathodic arc source.

[0090] Figure 7 shows measurements of arc source voltage as function of Ar-flow through the hollow discharge anode HDA. Three measurement series were performed with different orifice types. Two measurements with constant diameters of the orifice: 035 mm and 025 mm respectively. The third orifice, designated 0 35 / 25 mm featured a combination of one segment with 35 mm diameter and one segment with 25 mm diameter.

[0091] A coating chamber is disclosed with a HDA forming body connected electrically insulating and vacuum tight to an opening of the coating chamber, wherein the inner surface of the body comprises a hollow space with an opening to the hollow space, wherein the interior surfaces of the body are at least partially constructed to be electrically conducting and the opening to the hollow space is attached to the opening of the coating chamber so that a gas exchange between the hollow space and the coating chamber is enabled, whereby distanced from the opening of the hollow space at least one gas supply is foreseen through the body into the hollow space,

[0092] The interior of the hollow space may be equipped with an electrical connection to the exterior side, wherein the electrical connection is distanced from the opening of the hollow space. The gas supply may be a gas supply for a noble gas, preferably Argon.

[0093] The current carrying capacity of the electrical connection may be dimensioned for currents larger than 5A, preferably larger than 100A, most preferably larger than 1000A.

[0094] The interior surface of the body can at least partially be constructed of cupper containing and / or carbon containing material and in the component formed by the material can preferably contain channels which enable cooling with at least one fluid and preferably enabling water cooling.

[0095] The hollow space may include protrusions and / or can be equipped with at least one orifice, which is preferably electrically insulated from the conductive parts of the inner surfaces.

[0096] The hollow space may contain at least one pin, wherein the pin preferably comprises carbon containing material.

[0097] A vacuum coating process is disclosed, based on a high current discharge in a noble gas, preferably argon, between a heated filament and an anode or based on a cathodic arc discharge in a noble gas, preferably argon, between an electrically conducting target as cathode and an anode, wherein the coating is conducted in a coating chamber according to one or several of the previous claims.

[0098] During the coating process, reactive gas may be introduced into the coating chamber, wherein the reactive gas preferably comprises silane and / or oxygen and / or nitrogen and / or hydrocarbons and / or hydrogen, most preferably a mixture of oxygen and hydrogen.

[0099] The process may be operated potential-free, i.e. cathode and anode forming bodies and if present also filament are not grounded, i.e. not earthed.

[0100] The discharge current of the high current discharge can be adjusted to be at least temporarily larger than 10 A, preferably larger than 50 A, most preferably larger than 100 A and / or the discharge voltage of the high current discharge can be adjusted to be at least temporarily higher than 30 V, preferably higher than 50 V, most preferably higher than 80 V.

[0101] One or several HDA can be connected to the coating chamber and / or the coating chamber may comprise several devices for high current discharges and / or the coating chamber may comprise several devices for cathodic arc discharges.

Claims

Claims1. Coating chamber with at least one hollow discharge anode (HDA) forming body connected electrically insulating and vacuum tight to an opening of the coating chamber, wherein the inner surface of the body forms a hollow space with an opening, wherein the interior surfaces of the body are at least partially constructed to be electrically conducting and the opening to the hollow space is attached to the opening of the coating chamber so that a gas exchange between the hollow space and the coating chamber is enabled, whereby distanced from the opening of the hollow space at least one gas supply is foreseen through the body into the hollow space, characterized in that, the opening between the coating chamber and the body is limited in size by an orifice.

2. Coating chamber according to claim 1 , characterized in that the orifice is circular, preferably with a diameter in the range from 10 mm to 100 mm, further preferred with a diameter in the range from 25 mm to 35 mm.

3. Coating chamber according to claim 1 , characterized in that the orifice is designed for current density in the range between 10 A / cm2and 200 A / cm2calculated based on the area of the orifice.

4. Coating chamber according to any of the preceding claims, characterized in that the gas supply may be a gas supply for a noble gas, preferably Argon.

5. Coating chamber according to claim 1 , characterized in that the coating chamber further comprises at least one source for high current discharges, preferably at least one hot filament plasma source and / or at least one cathodic arc evaporation source.

6. Coating chamber according to claim 5, characterized in that during operation of the at least one source for high current discharges, an anode drop (VA) on the hollow discharge anode (HDA) in the range from 30 V to 100 V is obtained.

7. Coating chamber according to claim 6, wherein the cathode drop (Vc) is lower in magnitude than the magnitude of the anode drop (VA).

8. Coating chamber according to claim 6 or 7, characterized in that the at least one source for high current discharges is a cathodic arc evaporation source.

9. Coating chamber according to claim 5, where more than one source for high current discharges is designed to operate together with one hollow discharge anode HDA.

10. Coating chamber according to claim 9, characterized in that all the sources for high current discharges are cathodic arc evaporation sources.

11. Coating chamber according to claim 5, where more than one hollow discharge anode HDA is designed to operate together with one source for high current discharges.

12. Coating chamber according to claim 11 , characterized in that the source for high current discharges is a cathodic arc evaporation source.

13. Coating chamber according to claim 1 characterized in that the hollow space comprises at least one protrusion, preferably a pin, made of carbon containing material.

14. Coating chamber according to claim 1 , characterized in that the interior surface of the coating chamber is fully insulating.

15. Process for performing at least one step of coating of substrates utilizing a coating chamber according to claim 1 , characterized in that the current density at the orifice is in the range between 10 A / cm2and 200 A / cm2during the at least one step of coating.

16. Process according to claim 15, wherein the current density at the orifice is tuned by adjusting the Ar-flow or the size of the orifice.

17. Process according to claim 15, wherein the anode drop (VA) on the hollow discharge anode (HDA) is in the range from 30 V to 100 V during the at least one step of coating.

18. Process according to claim 17, characterized in that the cathode drop (Vc) is lower in magnitude than the magnitude of the anode drop (VA) during the at least one step of coating.

19. Process according to claim 15, characterized in that at least one gas selected from the list of SiH4, O2, N2, and C2H2 is introduced into the coating chamber during the at least one step of coating.

20. Process according to claim 19, characterized in that at least one hot filament plasma source is operated simultaneously with the introduction of gas during the at least one step of coating.

21. Process according to claim 19, characterized in that at least one cathodic arc source is operated simultaneously with the introduction of gas during the at least one step of coating.

22. Process according to claim 15, characterized in that more than one source for high current discharges is operated together with one hollow discharge anode HDA during the at least one step of coating.

23. Process according to claim 22, characterized in that all the operated sources for high current discharges are cathodic arc evaporation sources.

24. Process according to claim 15, where more than one hollow discharge anode HDA is operated together with one source for high current discharges.

25. Process according to claim 24, characterized in that the source for high current discharges is a cathodic arc evaporation source.

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