NUNES PADIAL, Alexandre (Rua José Fernandes Teixeira, 199Vila Rosa, -270 Carapicuíba - SP, 06317, BR)
DA ROCHA MORDENTE, Paulo José (Rua Capitão Curado, n° 823Vila Progresso, -271 Jundiaí - SP, 13202, BR)
NUNES PADIAL, Alexandre (Rua José Fernandes Teixeira, 199Vila Rosa, -270 Carapicuíba - SP, 06317, BR)
| CLAIMS 1. Plasma processing device (100) comprising means for generating a plasma discharge and means capable of confining the plasma discharge in a magnetic field (9), particularly by means of a hollow cathode voltaic arc, the plasma processing device (100) having: -at least two magnetic field generating sets (11), each one comprised by at least a first rotary magnetic component (1) and at least a second rotary magnetic component (2); -at least two plasma sources (10), each plasma source (10) having a first planar cathode (3) in parallel and opposite to a second planar cathode (4) defining a space between them, wherein a magnetic field generating set (11) is associated with each plasma source (10); the plasma processing device (100) being characterized in that: -the plasma source (10) is connected to a power source (5) which operates in radiofrequency; -the at least two plasma sources (10) are arranged surrounding the piece (8) to be coated to generate a magnetic field (6) of closed plasma (9); and -the magnetic intensity applied to the planar cathodes (3,4) varies from a first intensity substantially located in a central portion to a second intensity substantially located in their extremities, where the second intensity is lower than the first one. 2. Plasma processing device (100) according to claim 1 characterized in that the feeding of cathodes (3,4) is continuous. 3. Plasma processing device (100) according to claims 1 and 2 characterized in that the magnetic intensity of the first (1) and second (2) magnetic components varies from a first intensity substantially located in the center to a second intensity located in their extremities, where the second intensity is lower than the first one. 4. Plasma processing device according to claims 1 , 2 and 3 characterized in that the plasma sources are arranged in a substantially opposite manner. 5. Plasma processing device according to claims 1 , 2, 3 and 4 characterized in that the coating is for metal pieces. 6. Plasma processing device according to claims 1 , 2, 3, 4 and 5 characterized in that the coating is hard coating. 7. Plasma processing device according to claims 1 , 2, 3, 4, 5 and 6 characterized in that the coating has hardness higher than 900 Vickers. 8. Plasma processing device according to claims 1 , 2, 3, 4, 5, 6 and 8 characterized in that each magnetic component (1 ,2) is comprised by a plurality of segments, each one with its own charge and intensity. |
The present invention refers to a device for processing plasma of planar hollow cathodes which operates associated with a magnetic field capable of magnetically confining the generated plasma with the goal of evaporating the cathodes and transferring this material as a hard protective layer for a substrate.
Background of the Invention
In the sector of superficial treatments, film deposition can be performed by several techniques according to the goal to be achieved. Among the several possibilities, the focus of the present invention is on the superficial treatments that make use of deposition by means of plasma.
The most known processes that make use of plasma for film deposition include the techniques of sputtering and electric arc (also referred to as cathodic arc). The sputtering technique, when compared with the electric arc technique, works with lower density of ions and, consequently, very lower deposition rates. The technique of plasma deposition that operates via electric arc has, on the other hand, quite higher deposition rates due to the high ionic density produced, presenting itself as a powerful technology for plasma processing for film coating, for instance, hard films (known by those skilled in the art as hard coating).
Discharge via electric arc is generated between two electrodes assembled and separated by a certain distance, being kept by a pre- established power source. A continuous flow of gas is provided and obliged to pass through a region where the stabilized arc is found, leaving the region as a plasma flow. In most of the cases, the electric arc is generated by power sources of direct current (DC).
At least since 1983, there has been the development of power sources that operate, alternatively, in alternating current in radiofrequency - RF. Since then, several configurations of cathodes have been used in the search for better efficiency. One of these techniques is presented by document WO 9511322, which describes a method/device capable of generating a plasma discharge through a linear arrangement of circular hollow cathodes. The technique described by document WO 9511322 presents satisfactory results for certain power regimes (such as one capable of promoting sputtering^. It shall be also mentioned that this document foresees the use of power sources both in DC regime (direct current) and in AC regime (alternating current).
The applicant has made some tests according to the technique described by the document WO 9511322 and found out that for higher power regimes, capable of generating discharges via electric arc, the results show a localized behavior in the cathodes, particularly, in only one of the circular hollow cathodes, contributing with an heterogeneous deposition on the material to be coated and with the undesirable irregular wearing of the cathodes.
In order to overcome the difficulties concerning the deposition by plasma, document DE 4235953 describes a device comprised by planar hollow cathodes capable of operating sputtering, this document only foresees that the power source operates in DC (direct current) regime.
In order to enable better conditions for the plasma operation, devices that use planar hollow cathodes that operate via electric arc and together with a magnetic field have been created.
The most relevant prior art document is North-American US
6,351 ,075 patent family which describes a device having planar hollow cathodes which operates in electric arc regime to generate plasma. The document further describes that the generated plasma will suffer interaction with a variable magnetic field, wherein said magnetic field is created by a set of permanent and rotary magnets. This document focuses on achieving a flow of plasma where its formation in the cathode is guided by the variable magnetic lines. The document shows cross-sections of the cathodes which enable to attest that an angular variation of the magnetic set allows the magnetic lines to have variable interaction with the cathode discharge. Alterations in the discharge of the hollow cathodes allow alterations in the hot regions of the cathodes, that is, a variation of the region of erosion of the cathodes. Anyway, the teachings of North-American patent US 6,351 ,075 cannot overcome one of the biggest difficulties concerning the homogenous consumption of the cathode plates. Just as referred to in figure 5, as well as in specific tests, it is possible to realize that the extreme regions of the cathode undergo higher erosion than the central portions thereof.
Thus, although more favorable conditions for the plasma deposition are achieved, it was not possible to reach yet a plasma generating device capable of promoting a homogenous and continuous consumption of the planar hollow cathodes.
So far, the durability in production of the planar hollow cathodes does not allow keeping a productive process without the constant (and inconvenient) premature replacement of the cathodes. This situation is caused by said irregular erosion of the cathodes which occurs mainly on their . extreme portions. This way, it is necessary to constantly exchange the cathodic material, a fact which is translated into low productive efficiency.
Additionally, it is important to highlight that, even under regular work conditions, the hot region of the cathodes is located on their extreme portions and this way, some irregularity occurs in the generation of plasma, once its generation intensifies in these peripheral regions of the plates, causing differences in the intensity and distribution of the particles to be deposited. This situation makes the particles reach the surface of the material to be treated either with very high energy or with very low energy, directly contributing with the existence of an undesirable variation of the internal stress of the layer deposited by the technique of the state of the art, i.e., raising the internal stress of the film deposited over the piece.
Considering the explanation above and taking into account the deposition of hard films (hard coating) on metal pieces, it is very important that the internal stresses remain low so as to allow a good adhesion of the film and the consequent durability of the coating treatment.
It was not possible to obtain yet a plasma processing device which is capable of effectively controlling the deposition process by plasma and which operates with a power source in radiofrequency, in electric arc regime, with planar hollow cathodes where the generated plasma is closed inside a magnetic field so as to allow for coating with better adhesion and cohesion and with low internal stress.
Purposes of the Invention
Therefore, one purpose of the invention is to provide a plasma processing device which enables coating with better adhesion and cohesion and with low internal stress.
Another purpose of this invention is to provide a plasma processing device that operates in electric arc regime with planar hollow cathodes associated with a magnetic field that allows homogeneous plasma distribution for continuously feeding the cathodes.
Summary of the Invention
The purposes of this invention are met through the supply of a plasma processing device comprising means for generating a plasma discharge and means capable of confining the plasma discharge in a magnetic field, particularly by means of a hollow cathode voltaic arc, the plasma processing device having at least two magnetic field generating sets, each one comprised by at least a first rotary magnetic component and at least a second rotary magnetic component; at least two plasma sources, each plasma source having a first planar cathode in parallel and opposite to a second planar cathode defining a space between them, wherein a magnetic field generating set is associated with each plasma source; wherein the plasma source is connected to a power source which operates in radiofrequency; the at least two plasma sources are arranged surrounding the piece to be coated to generate a magnetic field of closed plasma ; and the magnetic intensity applied to the planar cathodes varies from a first intensity substantially located in a central portion to a second intensity substantially located in their extremities, where the second intensity is lower than the first one.
Brief Description of the Drawings
The present invention will be further described in more details, based on examples of implementation represented in the drawings. The Figures show:
Figure 1 - is a lateral view of a plasma source;
Figure 2a - is a perspective view of a plasma processing device of the present invention comprised with one embodiment of magnets;
Figure 2b - is a cross sectional cut of a plasma processing device presented in figure 2a;
Figure 2c - is a transversal cut of a plasma processing device presented in figure 2b;
Figure 2a - is a perspective view of a plasma processing device of the present invention comprised with one embodiment of magnets different from the one in figure 2a;
Figure 3 - is a top view of a plasma processing device comprised by 4 plasma generating units;
Figure 4 - is a top view of a plasma processing device comprised by 3 plasma generating units;
Figure 5 - is a top view of a plasma processing device comprised by 2 plasma generating units;
Detailed Description of the Figures
The present invention proposes a plasma generating device 100 with innovative characteristics capable of enabling a better control of the deposition process and also capable of allowing an industrial use.
A preferred embodiment of the plasma source 10 of the present invention is schematically represented by figure 1 which illustrates a plasma source 10 of planar hollow cathodes, wherein the cathodes are comprised by a first planar cathode 3 arranged in parallel and opposite to a second planar cathode 4. The plasma source 10 also has a power source 5 of radiofrequency (RF) for activation of an electric arc capable of promoting the plasma discharge.
Additionally to figure 1 , figure 2a, 2b, 2c and 2d schematically presents a plasma source 10 associated with a magnetic field generating set 11 , represented by figures 2b and 3, wherein the magnetic field generating set 11 is formed by at least a first rotary magnetic component 1 and at least a second rotary magnetic component 2, wherein the rotary magnetic components 1 ,2 are arranged opposite to each other (one on each side of the pair of cathodes 3,4) and with the respective opposite polarities so as to allow the magnetic lines to move from a S charge to an N charge to form a magnetic field.
As one can see from figures 2a and 2d, the rotary magnetic components 1 ,2 can have different configurations in which the rotary magnetic components 1 ,2 can be arranged by one single magnet or by several magnets 21 placed adjacent to each other.
On the preferred embodiment, presented by figure 2a, the rotary magnetic components 1 ,2 can have a rotary movement by the rotation of the axis where the magnets 21 are arranged (this means that the magnets 21 are solid with the axis) or, alternatively, the axis can be stationary and the magnets 21 can perform a rotary movement over the axis.
In the embodiment disclosed by figure 2b, the rotary magnetic components 1 ,2 must maintain a kind of V or U configuration. The rotary of the magnetic components 1 ,2 is preferentially performed by the rotation of the magnets 21 over a stationary axis. Alternatively, in a V configuration, if a solid connection between the axis and the magnets 21 is necessary, then the axis must be divided into two independent axis by each side of the cathodes 3,4. In other words, this results in four rotary of the magnetic components 1 ,2 arranged in pairs to provide the V configuration, each pair being placed by each side of the cathodes 3,4.
As exemplified by figure 5, the plasma generating device 100 of the present invention makes use of at least two plasma sources 10, each one of them having a magnetic set 11 , in a way that the plasma sources 10 are substantially arranged opposite to each other and surrounding the piece 8 to be coated to generate a magnetic field 6 capable of confining the closed plasma 9. However, it is evident that this number can vary more freely without leaving the resulting invention outside the protection scope of the claims. Additionally, the, plasma sources 10 of the present invention receive a gas 7 by the extremities of the planar hollow cathodes 3,4 which are farther from the piece 8 to be coated. This gas 7 will travel the space between the planar hollow cathodes 3,4 to allow the formation of plasma in the region of formation of the electric arc, i.e., in the region of the planar cathodes 3,4 which is closest to the piece/substrate 8 to be coated (exit region), wherein the gas 7 flow through the hollow cathodes leverages the transference of the particles ionized by the plasma to the surface of the piece to be coated.
Preferentially, but not mandatorily, the present invention is represented by figure 3, which illustrate a non limiting preferred embodiment of a plasma generating device 100 comprised by four plasma sources 10, each one associated with a magnetic field generating set 11 , wherein the plasma sources 10 are arranged opposite to each other and surrounding the substrate 8 to be coated. Please note that each plasma source 10 has the configuration already described in figure 1 and 2, i.e., each plasma source is fed by a gas 7 and has a power source 5 RF. This way, the representation of figure 3 has four plasma sources 10 and four magnetic field generating sets
11 arranged in the exit region of the planar hollow cathodes 3,4.
Additionally, figure 3 represents a configuration of the present invention in a situation of work, where it is possible to observe that the planar hollow cathodes 3,4 are arranged between a closed box 12. This closed box
12 is capable of providing a vacuum situation inside it. Note that the vacuum is usually necessary for the correct process of this technology. In this manner, the closed box encloses the plasma 9 inside it, as well as the subtract 8 to be coated.
This closed box 12 belongs to the device and the rotary magnetic field generating sets 11 are arranged outside the closed box 12, wherein, alternatively, the rotary magnetic field generating sets 11 can be arranged internally to said closed box 12.
Just as mentioned, a first magnetic component 1 is arranged opposite to a second magnetic component 2 so as their polarities N,S are opposite and thus successively so that, in association with the other magnetic field generating sets 11, they form a magnetic field 6 capable of homogeneously confining the plasma 9 and without any loss or waste of plasma 9. The magnetic field 6 formed is controlled by an adequate/synchronized rotary movement of the first and second magnetic components 1 ,2 of each plasma source 10, wherein all the rotary magnetic sets 11 synchronically work to promote the desired magnetic fields 6 (exemplified with the dash line) confined inside the vacuum chamber provided by the closed box 12. Additionally, the substrate 8 to be coated is arranged internally to the confined plasma 9 and, depending on the need, may suffer rotation to optimize the quality and quantity of coating.
Alternatively, the invention may present the configuration presented in figures 4 and 5, and an essential point for the correct configuration of the present invention is that, at least, two plasma sources 10, each one having a magnetic set 11 , should be substantially arranged opposite to each other and surrounding the piece 8 to be coated to generate a closed magnetic field 6 capable of confining the plasma 9.
Said conditions on the arrangement of the elements that compose the plasma generating device 100 are very important so that the generated plasma 9 is actually confined without loss inside a magnetic field 6.
Anyway, the present invention presents an innovative characteristic that allows the magnetic field 6 to keep a homogeneous consumption of the planar hollow cathodes 3,4 when working in a RF regime.
Obviously, the quantity of plasma formed will depend on several process variables; however, it is interesting to report that, regardless of these variables, the region of plasma formation occurs in the portion of electric arc formation and, in this region, the hot zones and zones of erosion of the cathodic material are formed.
Contrary to the state of the art, the planar hollow cathodes 3,4 do not present preferential evaporation zones that promote a higher consumption of these regions as regards other ones of the same cathode. Such characteristic is achieved by means of an equalized magnetic field 6 which foresees that the peripheral regions of the cathodes 3,4, usually the region of higher wearing, receive a differentiated magnetic intensity from the central region of the cathode 3,4. This way, the intensity applied to the planar hollow cathodes 3,4 varies from a first intensity substantially located in a central portion to a second intensity substantially located on their extremities, where the second intensity is lower than the first one.
To verify such situation, preferentially but not mandatorily, the extreme portions of the first and second rotary magnetic components 1 ,2, longitudinally taken, have lower magnetic intensity when compared with the central portion of the rotary magnetic components 1 ,2 (figure 2a).
Alternatively, in another configuration (example of figure 2d), the magnetic components 1 ,2 can have constant intensity but the rotary magnetic components 1 ,2 have to be shaped as an arc (U) or V, or in any other shape which allows the central portions of the rotary magnetic components 1 ,2 to be closer to the planar hollow cathodes 3,4 and the extreme regions of the rotary magnetic components 1 ,2 to be farther from the planar hollow cathodes 3,4. This type of geometry and arrangement in relation to the planar hollow cathodes 3,4 promotes the same magnetic intensity received by the planar hollow cathodes 3,4, as in the configuration presented in figure 1.
Therefore, there is no difference, between the configurations of the figures 2a and 2d, in the intensity of the magnetic field 6 applied to the cathodes 3,4. In other words, in the configuration of figure 2a, the distance from the rotary magnetic components 1 ,2 to the hollow cathodes 3,4 is constant and the magnetic intensity of the magnets 21 varies from the extremities to the center. In the configuration presented by figure 2d, the distance of the rotary magnetic components 1 ,2 varies from their extremities to the center, but the magnetic intensity is constant.
As already mentioned, it is worth noting that each magnetic component 1 ,2 can, in fact, be comprised by a plurality of segments 21 , each one with its own charge and intensity, as long as there is, in the opposite magnetic component, a related segment, that is, with a corresponding inverse polarity.
This innovative configuration of a plasma generating device 100 is very important and beneficial for the industry. When observed at work, the planar hollow cathodes 3,4 undergo constant wearing which allows the feeding of the planar hollow cathodes 3,4 through a system which constantly or intermittently displaces the material to be evaporated to the region of cathode exit adjacent to the magnets, therefore, it is not necessary to constantly stop the equipment for replacement of the planar hollow cathodes 3,4.
Industrially, the present invention provides two great advantages. At a first moment, it is ensured a very significant raise in productivity combined with lower costs and, on the other hand, it is ensured an effective raise in the quality of coatings.
The raise in productivity is achieved by the fact that the reactor presents a very high evaporation rate and consequently deposition rate on the substrate 8 to be protected. Productivity is also leveraged by the fact that it is no longer necessary the frequent exchange of the planar hollow cathodes 3,4 before they are practically consumed as a whole. As there are no regions of preferred consumption of the cathodes over the length of the magnets, a situation which occurred in the state of the art disclosed by North-American patent US 6351075, it is now possible to continuously feed the planar hollow cathodes 3,4 until their total consummation.
As one can see in figures 2a and 2d, the hollow cathodes 3,4 are preferably refrigerated by the presence of coolers 15 in their extremities. Usually, in the state of art, the coolers are statically fixed to the hollow cathodes 3,4 in a way that the consumption of the hollow cathodes 3,4 increases the distance between the cathodes output of plasma and the substrate 8. In other words, in the state of art techniques the consumption of the cathodes moves in the same direction in which they are fed, starting from the nearest portion to the farthest portion of the substrate 8. Between other side effects, the deposition of the material in the substrate 8 is not homogeneous.
In the present invention, the coolers 15 are placed very close to the hollow cathodes 3,4, but not in contact with them. They are placed close enough to allow the heat transfer from the hollow cathodes 3,4 to the coolers 15. The present technique is different from the state of art since now the coolers 15 are static but, as the hollow cathodes 3,4 are being consumed, they move in the direction of the subtract 8 to maintain the distance therein.. This innovation allows homogeneous deposition of material in the substrate 8, not to mention that the equipment can be conceived so that the hollow cathodes 3,4 are continuously fed, reducing the chances of inadvertent stops to practically zero.
This characteristic is extremely innovative, still more when referring to coating metal pieces by means of plasma generated via electric arc. If ones takes into account the formation of hard films (hard coating) which require large amounts of deposited particles, the current invention is absolutely essential for its industrial use once it allows deposition rates that are very higher than those of the state of the art. Additionally, it is possible to achieve a quite significant reduction in the production cost, once the premature replacement of the cathodes 3,4 is avoided, due to the formation of localized regions of erosion in the cathodes over the length of the magnets.
Concomitantly to these benefits, once it is possible to confine the plasma 9 in a closed vacuum region through an enhanced magnetic field 6, it is ensured an homogeneous control of the deposition of particles on the surface of the substrate 8, reaching a process stability that allows better adhesion and cohesion of the coating, as well as a reduction in its internal stress. For situations in which the coating to be performed is hard coating, with hardness preferably higher than 900 Vickers, it is very important that the process control allows for achieving a film with low internal stress so as to ensure good coating adherence.
Thus a product was successfully developed, making it possible to achieve a continuous and homogeneous confinement of the plasma 9, in a vacuum environment, during the productive process, being possible to observe a higher densification of the plasma 9 and better capacity of plasma 9 concentration for the deposition of the particles on the surface of the substrate 8 to be coated. Consequently, it is possible to obtain better values concerning the homogeneity of material deposition with low values of internal stress which arise from a uniform consumption of the planar hollow cathodes 3,4, being possible to extend these conditions until the almost total consumption of the cathodes 3,4.
After describing examples of preferred embodiments, it shall be understood that the scope of the present invention encompasses other possible variations, being limited only by the contents of the attached claims, where the possible equivalents are included.
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