HOLLOW CATHODE SYSTEM FOR GENERATING A PLASMA AND METHOD FOR OPERATING SUCH A HOLLOW CATHODE SYSTEM

Abstract

A hollow cathode system generates a plasma. The system includes an anode device, a power supply for applying an electric current between a cathode tube and the anode device, and at least one gas reservoir for supplying the gas flowing through the cathode tube are used, in which at least two cathode tubes are used that are electrically connected to one another, and in which each cathode tube has a separate actuator with which the amount of gas flowing through the respective cathode tube is set.

Claims

1. A hollow cathode system for generating a plasma, the system comprising: at least two cathode tubes; an anode device; a power supply for supplying a voltage between at least one of the cathode tubes and the anode device; and at least one gas reservoir for supplying a gas that flows through at least one of the cathode tubes, wherein at least two of the cathode tubes are electrically connected to one another and each have a separate actuator with which an amount of gas flowing through can be set.

2. The hollow cathode system according to claim 1, wherein tubular axes of the at least two cathode tubes are parallel to one another, or form an angle no greater than 5.

3. The hollow cathode system according to claim 2, wherein the gas flows through the at least two cathode tubes in a same direction.

4. The hollow cathode system according to claim 1, wherein adjacent cathode tubes are no more than 20 mm apart from one another.

5. The hollow cathode system according to claim 1, wherein at least one element in the anode device is annular, wherein this at least one element in the anode device encompasses the at least two cathode tubes.

6. A method comprising: operating a hollow cathode system with an anode device; applying, with a power supply, a voltage between a cathode tube and the anode device; supplying, through at least one gas reservoir, a gas that flows through the cathode tube; utilizing a separate actuator for each of at least two cathode tubes, wherein the at least two cathode tubes are electrically connected to one another; setting, with each of the actuators, an amount of gas flowing through each respective cathode tube; and determining a type of gas.

7. The method according to claim 6, wherein a first amount of gas flowing through a first cathode tube with which an arc discharge can be ignited between the first cathode tube and the anode device is set by a first actuator.

8. The method according to claim 7, wherein in at least a second cathode tube, an amount of gas flowing through the second cathode tube with which an arc discharge can be ignited between the second cathode tube and the anode device is set by a second actuator.

9. The method according to claim 7, wherein the arc discharge is extinguished in at least a first cathode tube in which there currently is an arc discharge between the first cathode tube and the anode device, and an arc discharge is ignited in at least a second cathode tube in which there currently is no arc discharge between the second cathode tube and the anode device.

10. The method according to claim 6, wherein an arc discharge from at least two cathode tubes to the anode device is maintained, with amperages that can be adjusted separately for each cathode tube.

11. The method according to claim 6, wherein the determining the type of gas flowing through the cathode tubes is determined by the separate actuators.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIG. 1 shows a schematic illustration of a hollow cathode system according to an embodiment;

[0020] FIGS. 2a, 2b show a schematic sectional view of a first alternative cathode tube configuration;

[0021] FIG. 3 shows a schematic sectional view of a second alternative cathode tube configuration;

[0022] FIG. 4 shows a schematic sectional view of a third alternative cathode tube configuration; and

[0023] FIG. 5 shows a schematic sectional view of a fourth alternative cathode tube configuration.

DETAILED DESCRIPTION

[0024] FIG. 1 shows a schematic illustration of a hollow cathode system 10 according to the embodiments. This hollow cathode system 10 comprises a first cathode tube 11a and second cathode tube 11b, which are no more than 20 mm from one another. The tubular axes 12a and 12b of the two cathode tubes 11a and 11b are parallel to one another. The hollow cathode system 10 also contains an anode device 13 and a power supply 14, which supplies a voltage necessary for obtaining an arc discharge between the first cathode tube 11a and/or second cathode tube 11b on one side and the anode device 13 on the other side. The two cathode tubes 11a and 11b, as well as the anode device 13, are inside a vacuum chamber, which is not shown in FIG. 1 for purposes of clarity.

[0025] While the hollow cathode system 10 is in operation, a process gas flows through the first cathode tube 11a and/or the second cathode tube 11b, which is supplied by a first gas reservoir 15 and conveyed through gas lines 16 to the cathode tubes 11a and 11b. The first cathode tube 11a has a first actuator 17a and the second cathode tube 11b has a second actuator 17b. The amount of gas flowing through each cathode tube can be set separately by the actuators 17a and 17b. The two cathode tubes 11a and 11b are connected to one another by an electrically conductive contact element 18 and therefore always have the same electrical potential. The contact element 18 can form a threaded socket made of an electrically conductive material, for example, into which the cathode tubes 11a and 11b can be screwed. There is no need for the contact element 18 if the two cathode tubes 11a and 11b are close enough together that they constantly abut one another. A separate arc discharge can therefore be obtained from each of the cathode tubes 11a and 11b to the anode device 13 in the hollow cathode system 10 by means of the two actuators 17a and 17b.

[0026] In a first variation of the method, the amount of gas flowing through the first cathode tube 11a with which it is possible to obtain an arc discharge between the first cathode tube 11a and the anode device 13 is first set with the first actuator 17a. An arc discharge between the first cathode tube 11a and the anode device 13 is therefore ignited and maintained. Any cathode tube participating in an arc discharge shall be referred to as an activated cathode tube below. If there is an arc discharge from the first cathode tube 11a to the anode device 13, then at this point, only the first cathode tube 11a is an activated cathode tube, while the second cathode tube 11b remains inactive. At this point, any substrates in the vacuum chamber can be processed with the plasma generated by the first cathode tube 11a. When the first cathode tube 11a wears out, the arc discharge between the first cathode tube 11a and the anode device 13 is extinguished. The amount of gas flowing through the second cathode tube 11b is then set by the second actuator 17b to obtain an arc discharge between the second cathode tube 11b and the anode device 13 that is ignited and maintained such that the processing of one or more substrates inside the vacuum chamber can continue with the plasma generated by the second cathode tube 11b. By this means, the operating time of the hollow cathode system can be extended in comparison with that of the prior art without having to open the vacuum chamber. Alternatively, the two cathode tubes 11a and 11b can be activated in alternating cycles, so that the cathode tubes 11a and 11b wear out at more or less the same times. The second cathode tube is preferably activated only when the first cathode tube has been deactivated. It is also possible to active the second cathode tube just before or at the same time the first cathode tube is deactivated.

[0027] In a second variation of the method, as with the first variation, the amount of gas flowing through the first cathode tube 11a with which it is possible to obtain an arc discharge between the first cathode tube 11a and the anode device 13 is set by the first actuator 17a. Therefore, only the first cathode tube 11a is activated initially to generate a plasma with which one or more substrates inside the vacuum chamber can be processed. When a stronger plasma is later needed for processing substrates inside the vacuum chamber, the amount of gas flowing through the second cathode tube 11b with which it is possible to obtain an arc discharge between the second cathode tube 11b and the anode device 13 is then set by the second actuator 17b, by means of which a supplementary plasma cloud is generated. The amperages necessary for maintaining the respective arc discharges from each cathode tube can be set individually. Because the two cathode tubes 11a and 11b are right next to one another, their plasma clouds merge, at least in part, such that a more powerful overall plasma can be generated. If a less powerful plasma is needed later, the arc discharge from one of the activated cathode tubes 11a and 11b can then be extinguished.

[0028] In the exemplary embodiment of a hollow cathode system according to the embodiments shown in FIG. 1, the cathode tube configuration comprises a total of two cathode tubes. The hollow cathode system according to the embodiments can also have a cathode tube configuration comprising more than just two cathode tubes. There is no upper limit to the number of possible cathode tubes. It is only necessary for the cathode tubes to be electrically connected to one another, and that the adjacent cathode tubes be no more than 20 mm from one another.

[0029] A cross section of an exemplary cathode tube configuration 20 according to the embodiments is schematically illustrated in FIG. 2a, which comprises three cathode tubes 21a-21c. The cathode tubes 21a-21c are electrically connected to one another by contact elements 28a-28c. As explained above in reference to the device 10 in FIG. 1, each of the cathode tubes 21a-21c has a separate actuator with which the amount of gas flowing through each cathode tube can be set separately. Consequently, a separate arc discharge to the anode device can also be obtained from each cathode tube 21a-21c, such that a hollow cathode system according to the embodiments that has this cathode tube configuration 20 can also be operated with both variations of the method described above in reference to FIG. 1. The same also applies to hollow cathode systems according to the embodiments that have the cathode tube configurations 20 described below. FIG. 2b also shows a cross section of the cathode tube configuration shown in FIG. 2a in a schematic illustration. In the embodiment shown in FIG. 2b, the cathode tube configuration 20 is encompassed by an annular element 23 of the anode device for the cathode tubes, at least at the end of the cathode tubes where the discharge orifice is located. Cathode tubes in a hollow cathode system according to the embodiments can also be operated with an annular anode of this type using the method described in DE 10 2006 027 853 A1, for example. An annular element 23 in an anode device can also be used with all of the cathode tube configurations according to the embodiments describe herein, in which the annular element encompasses all of the cathode tubes in a cathode tube configuration, at least at the ends where the gas discharge orifices are located.

[0030] The cathode tubes in the hollow cathode system according to the embodiments in all of the exemplary embodiments described above are formed by separate tubes connected to one another by electrically conductive contact elements. FIG. 3 shows a cross section of a schematic illustration of a cathode tube configuration 30 in which a total of four cylindrical holes 31a-31d pass through a block 38 made of an electrically conductive material. The outer cylindrical surfaces of the four holes 31a-31d in the block 38 function as the cathode tubes in this case, through which a process gas for obtaining an arc discharge flows. Each hole 31a-31d has a separate actuator with which the gas flowing through it can be controlled separately.

[0031] As explained above, hollow cathode systems normally have auxiliary devices such as a heating coil with a power supply with which an arc discharge in a cathode tube can be ignited. The cathode tubes in all of the exemplary embodiments described above can also have such an auxiliary device for igniting an arc discharge. In this manner, with exemplary embodiments in which the cathode tubes are formed by separate tubes, as is the case in the exemplary embodiments shown in FIGS. 1 through 2b, each cathode tube can have a separate heating coil wound around it, or each cathode tube can have a separate heating element. In the exemplary embodiment shown in FIG. 3, a heating coil can be wound around the entire block 38.

[0032] FIG. 4 shows a cross section of a schematic illustration of a cathode tube configuration 40 comprising four cathode tubes 41a-41d, which are electrically connected to one another by contact elements 48a-48d. A plasma can be generated inside a vacuum chamber with the cathode tubes 41a-41d using the approach described above, by means of which at least one substrate can be processed inside the vacuum chamber. There is a fifth cathode tube 49 in the middle of the four cathode tubes 41a-41d, which is electrically insulated from the four cathode tubes 41a-41d, and has a separate power supply for obtaining an arc discharge. When the hollow cathode system according to the embodiments, which comprises the cathode tube configuration 40, is in operation, an arc discharge from the fifth cathode tube 49 is ignited to generate a plasma. This plasma, generated by the fifth cathode tube 49, has a lower intensity than the plasma obtained with the first four cathode tubes 41a-41d. The plasma generated with the fifth cathode tube 49 is also not primarily involved in the processing of a substrate, but instead is mainly used as a charge carrier in the space between the cathode tubes and the anode device, which facilitates ignition of at least one the cathode tubes 41a-41d.

[0033] Because the plasma generated by the fifth cathode tube 49 has a low intensity, this cathode tube 49 is subjected to less wear than the other cathode tubes 41a-41d. Consequently, an arc discharge can be maintained with the fifth cathode tube 49 during the entire operating time of the hollow cathode system according to the embodiments that has this cathode tube configuration 40, while the cathode tubes 41a-41d are activated successively or in alternating cycles.

[0034] It has already been explained that with the hollow cathode system according to the embodiments, at least two cathode tubes take part, wherein at least one first cathode tube can be activated while at least one second cathode tube is inactive during the operation of the hollow cathode system according to the embodiments. When the second cathode tube is inactive, either no gas flows through the cathode tube, or only a small amount of gas flows through the second cathode tube, which is not enough to obtain an arc discharge between the second cathode tube and the anode device. When a smaller amount of gas flows through the second cathode tube than that necessary for obtaining an arc discharge, it can be used to clean the second cathode tube to prevent an accumulation of particles therein from the activated first cathode tube or the material coating a substrate inside the vacuum chamber. The process gas in the first gas reservoir, which is the same gas that is used to obtain an arc discharge in an activated cathode tube, can also be used for the cleansing gas in an inactive cathode tube, for example. It is also possible to use another gas, preferably an inert gas, to clean the cathode tube, which can be contained in a second gas reservoir.

[0035] When a different gas is used to clean a cathode tube than that used for igniting and maintaining an arc discharge, the type of gas that flows through the respective cathode tubes can be determined by the actuator that also sets the amount of gas flowing through the cathode tube. The type of gas flowing through a respective cathode tube can also be determined by a separate actuator.

[0036] While the cathode tubes in the exemplary embodiments shown in FIGS. 1, 2a, 2b, and 4 are formed by separate tubes, and by holes in a block of material in the exemplary embodiment shown in FIG. 3, FIG. 5 shows a cathode tube configuration 50 cut longitudinally in a schematic illustration, which is composed of a combination of separate cathode tubes and holes in a block of material. The cathode tube configuration 50 comprises a base element 58 made of an electrically conductive material, which contains two cylindrical holes 59a and 59b that extend through the entire length of the base element 58. These holes 59a and 59b are not as long, however, as a cathode tube. For this reason, cathode tube subsections 51a and 51b are also attached to the base element 58, preferably releasably, such that the tubular axis 52a of the cathode tube subsection 51a and the cylinder axis of the cylindrical hole 59a are identical, and the tubular axis 52b of the cathode tube subsection 51b and the cylinder axis of the cylindrical hole 59b are also identical. The cylinder axis of a hole and the tubular axis of the associated cathode tube subsection can also be offset, in order to break any beam coming from the interior of the vacuum chamber. To form the releasable connection, the cathode tube subsections 51a and 51b can have external threads that are then screwed into the base element 58. This results in a first cathode tube formed by the hole 59a and the associated cathode tube subsection 51a, while the hole 59b forms a second cathode tube with the associated cathode tube subsection 51b. The cathode tube configuration 50 comprises only two cathode tubes in this example, but can also comprise more than two cathode tubes in other embodiments.

[0037] As explained above, a hollow cathode normally wears out only in the active zone, which is located in the cathode tube subsections 51a and 51b in a hollow cathode system that has the cathode tube configuration 50. This means that it is only necessary to replace the worn out cathode tube subsections in the cathode tube configuration 50, without having to replace the entire cathode tubes, thus reducing material waste. This saves a significant amount of material if the length of the holes 59a and 59b is at least 30% of the overall length of the cathode tube, comprising the length of the hole combined with that of the associated cathode tube subsection.