Patent Application
20090242397
The invention relates generally to vapor deposition systems and more specifically, to cathodic arc vapor deposition systems
Cathodic vapor deposition typically involves a source material and a substrate to be coated placed in an evacuated deposition chamber. The chamber contains only a relatively small amount of gas. A negative lead of a direct current (DC) power supply is attached to the material to be evaporated (hereinafter referred to as the “cathode”) and a positive lead is attached to an anodic member (hereinafter referred to as the chamber). An arc-initiating trigger, at or near the same electrical potential as the anode, contacts the cathode and subsequently moves away from the cathode. When the trigger is still in close proximity to the cathode, the difference in electrical potential between the trigger and the cathode causes an arc of electricity to extend there between. As the trigger moves further away, the existing potential between the cathode and chamber causes an arc to develop and stay on the cathode. The exact point, or points, where an arc touches the surface of the cathode is referred to as a cathode spot.
Absent a steering mechanism, a cathode spot will move randomly about a surface of the cathode. The energy deposited by the arc at a cathode spot is intense; on the order of 105 to 107 amperes per square centimeter with a duration of a few to several microseconds. The intensity of the energy raises the local temperature of the cathode spot to approximately equal that of the boiling point of the cathode material. As a result, cathode material at the cathode spot vaporizes into a plasma containing atoms, molecules, ions, electrons, and particles. Positively charged ions liberated from the cathode are attracted towards the substrate or a workpiece within the deposition chamber having a negative electrical potential relative to the positively charged ion. Some deposition processes maintain the substrate to be coated at the same electrical potential as the anode. Other processes use a biasing source to lower the potential of the substrate and thereby make the substrate relatively more attractive to the positively charged ions. In either case, the substrate becomes coated with the vaporized material liberated from the cathode. The random movement of the arc leads to a non-uniform erosion of the cathode, thus limiting useful life of the cathode.
Accordingly, there is a need for an improved cathodic arc deposition system and specifically, there is a need for an improved steering mechanism for the electric arc.
In accordance with an embodiment of the invention, a system for controlling cathodic arc discharge is provided. The system includes a vacuum chamber forming the anode. The system also includes a power supply connected to the vacuum chamber, wherein the power supply is configured to generate an electric field within the vacuum chamber. The system further includes a cathode disposed within the vacuum chamber. The system also includes at least one permanent magnet configured to actuate in a translational direction inwards and outwards of the cathode. The magnet is further configured to apply a magnetic field in a direction perpendicular to a face of the cathode and to the electric field to burn the cathode at a predetermined radius on the face of the cathode.
In accordance with another embodiment of the invention, a system for controlling cathodic arc discharge is provided. The system includes a vacuum chamber forming the anode. The system also includes a power supply connected to the vacuum chamber, wherein the power supply is configured to generate an electric field within the vacuum chamber. The system further includes a cathode disposed within the vacuum chamber. The system also includes multiple permanent magnets configured to spin around in a vicinity of the cathode, wherein the magnets are further configured to apply a magnetic field in a direction transverse to the surface of the cathode and to the electric field resulting in a bum at a predetermined radius on the surface of the cathode. The system also includes at least one impeller coupled to the permanent magnets. The system further includes at least one cooling channel adapted to cool the cathode, and further configured to provide a cooling fluid to propel the impeller, wherein the impeller is configured to rotate the permanent magnets about a centerline axis of the cathode.
In accordance with another embodiment of the invention, a system for controlling cathodic arc discharge is provided. The system includes a vacuum chamber forming an anode. The system also includes a power supply connected to the vacuum chamber, wherein the power supply is configured to generate an electric field within the vacuum chamber. The system further includes a cathode disposed within the vacuum chamber. The cathode is configured to rotate about a centerline axis in the presence of a transverse magnetic field and disposed within the vacuum chamber. The system also includes a permanent magnet configured to apply the magnetic field transverse to the surface of the cathode and the electric field, resulting in a burn at a radius on the surface of the cathode, based upon strength of the magnetic field.
In accordance with another embodiment of the invention, a system for controlling cathodic arc discharge is provided. The system includes a vacuum chamber forming an anode. The system also includes a power supply connected to the vacuum chamber, wherein the power supply is configured to generate an electric field within the vacuum chamber. The system further includes a cathode disposed within the vacuum chamber. The system also includes at least one permanent magnet configured to rotate circumferentially around the cathode, wherein the magnet is further configured to apply a magnetic field in a direction parallel to a face of the cathode and to the electric field to burn the cathode at a predetermined radius on the face of the cathode.
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
As discussed in detail below, embodiments of the invention include a system for controlling cathodic arc discharge employing mechanically manipulated permanent magnets. As used herein, the term “cathodic arc discharge” refers to an arc discharge produced under vacuum that vaporizes a material of the cathode that is further coated on a surface of a substrate or a workpiece.
At least one permanent magnet 24 is arranged axially about a current conductor 26 to the vacuum chamber 12 such as to actuate in a translational direction 28 inwards and outwards relative to the cathode 14 via a linear actuator 29. Non-limiting examples of the conductor 26 include aluminum, brass, copper and stainless steel. The magnet 24 actuates such that a magnetic field is applied in a direction perpendicular to a surface of the cathode 14. The magnetic field controls and directs a path of movement of the electric arc along a defined closed track such as, a circle of a predetermined radius, on the face of the cathode 14. In one embodiment, the predetermined radius includes a range between about 0.25 inch to about 1.125 inches. In a particular embodiment, the magnet 24 is actuated via a motor or a similar device. The interaction of field generated by the electric arc and the magnetic field provided by the permanent magnet 24 will cause a cathode spot to be controlled in a more predictable manner.
A holder 30 attaches the cathode 14 to a large evaporator plate 32 and a small evaporator plate 34. Furthermore, the large evaporator plate 32 and the small evaporator plate 34 are separated by electrical insulation 36. Multiple cooling channels 38 pass through the large evaporator plate 32 and the small evaporator plate 34 that enable cooling of the cathode 14, thus maintaining a desirable temperature of the cathode 14. In one embodiment, the cooling channels 38 provide a cooling fluid such as, but not limited to, water to the cathode 14 and the vacuum chamber 12. A sleeve 39 is employed as an insulating layer between the cathode 14 and a ground shield 40.
The various embodiments of a system for controlling cathodic arc discharge described above thus provide an efficient and convenient means for steering an electric arc around a cathode. These techniques and systems also allow for uniform deposition of coating on a substrate or a workpiece. In addition, velocity of the arc around a circumference of the cathode, being a function of strength of magnetic field and amount of current supplied, may be manipulated by changing either the magnetic field or the current or both. Further, the system employs a cost-effective cathode, wherein the cathode can be cut, for example, from a cylindrical casting. Such a cathode requires minimal expensive machining, thereby reducing cost of the cathode and overall coating process. Moreover, a circumferentially uniform erosion of the cathode enables maximizing the life of the cathode prior to a replacement.
Of course, it is to be understood that not necessarily all such objects or advantages described above may be achieved in accordance with any particular embodiment. Thus, for example, those skilled in the art will recognize that the systems and techniques described herein may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.
Furthermore, the skilled artisan will recognize the interchangeability of various features from different embodiments. For example, the use of an example of a disk-shaped cathode described with respect to one embodiment can be adapted for use in a system employing a rack-and-pinion linear motion drive described with respect to another. Similarly, the various features described, as well as other known equivalents for each feature, can be mixed and matched by one of ordinary skill in this art to construct additional systems and techniques in accordance with principles of this disclosure.
While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.
