Abstract:
A magnet arrangement which is usable as both a retrofit magnetic arrangement in a rotatable cylindrical magnetron sputtering electrode as well as a drive assembly in communication with the electrode for delivering high current into a target surface without adding highly incremental cost to the overall design of the electrode. The electrode includes a cathode body defining a magnet receiving chamber, a rotatable cylindrical target surrounding the cathode body, wherein the target is rotatable about the cathode body. The cathode body further defines a magnet arrangement received within the magnet receiving chamber, wherein the magnet arrangement comprised of a plurality of magnets wherein at least one of the magnets is a profiled magnet having a contoured top portion.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of U.S. Provisional Application Nos. 60/783,689 entitled “Magnetron For Cylindrical Targets” filed on Mar. 17, 2006, and 60/859,393 entitled “Magnetron For Cylindrical Targets And Cathode Design Enhancements” filed on Nov. 16, 2006, which are hereby incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a rotatable cylindrical magnetron sputtering apparatus and, more particularly, to a various hardware used with rotatable cylindrical magnetron electrodes which reduce the cost and complexity of delivering high power AC current into a target surface, and increase the target utilization and the deposition rate while reducing the amount of target material on the chamber walls and shielding.  
         [0004]     2. Description of Related Art  
         [0005]     A typical magnetron sputtering device includes a vacuum chamber having an electrode contained therein, wherein the electrode includes a cathode portion, an anode portion and a target. The term electrode is oftentimes referred to in the industry as a cathode. In operation, a vacuum is drawn in the vacuum chamber followed by the introduction of a process gas into the chamber. Electrical power supplied to the electrode produces an electronic discharge which ionizes the process gas and produces charged gaseous ions from the atoms of the process gas. The ions are accelerated and retained within a magnetic field formed over the target, and are propelled toward the surface of the target which is composed of the material sought to be deposited on a substrate. Upon striking the target, the ions dislodge target atoms from the target which are then deposited upon the substrate. By varying the composition of the target and/or the process gas, a wide variety of substances can be deposited on various substrates. The result is the formation of an ultra-pure thin film deposition of target material on the substrate.  
         [0006]     Over the last decade, the cylindrical magnetron has emerged as the leading technology for sputtering coating on glass substrates. The rotating cylindrical target surface provides for a constant sputtering surface, thus eliminating the traditional erosion groove and large non-sputtered areas associated with planar targets. Further, the cylindrical target eliminates large areas of dielectric buildup that can lead to arcing, material flaking, debris and other process instabilities. Although the rotatable cylindrical magnetron has its advantages over planar magnetrons, the shape of the magnetic field which determines everything from field uniformity and deposition rate to target utilization may still be optimized further to improve the performance of the sputtering application. The use of stationary profiled magnets can be used to control the shape of the magnetic field which optimizes the performance of the sputtering application. U.S. Pat. Nos. 5,736,019 and 6,171,461, which are incorporated herein by reference, disclose and attempt to overcome under utilization of target material via the use of stationary profile magnets. The above-identified patents are directed to magnetron sputtering electrodes that include a plurality of profile magnets, each magnet including a top portion with an apex, wherein each apex is positioned adjacent a target supporting surface in the cathode body. The magnet cooperates to generate magnetic flux lines which form enclosed-looped magnetic tunnels adjacent to the front sputtering surfaces of the target. As described in the above-identified patents, these profile magnets result in optimum utilization of target materials at a reasonable rate of utilization. A problem with the conventional planar magnet arrangement is that the magnets have flat upper surfaces and, therefore, the target which the material is to be sputtered from is not completely utilized.  
         [0007]     The development of mid-frequency AC power supplies has enabled continuous long-term sputtering of targets which are utilized in a reactive gas to form dielectric or poorly conductive thin films. Albeit a dramatic improvement above planar targets used in planar cathodes, rotatable cylindrical targets still have a region just beyond the magnetron ends (i.e., turnarounds) which are not sputtered, but rather collect a portion of the sputtered thin film. When the sputtered material builds up in these turnarounds or unetched regions to a substantial thickness thus forming an insulating layer, this layer can become a source of arcing. Although enabling power supply technology has increased process stability of the deposition process, it has simultaneously introduced increased complexity and cost into the design and arrangement of the hardware associated with the cathode drive assembly which delivers this power to the target surface. The two most common problems associated with the delivery of high power, mid-frequency (20 kHz-120 kHz) current to the cathode are (1) the ability of the brush assemblies to carry sufficient current without overheating and eroding due to the “skin-effect” of these frequencies and (2) the inherent eddy current effects induced by these frequencies which can cause extreme localized heating of various components, particularly the support bearing. To circumvent the high current requirements, many manufacturers are using custom brush assemblies with high silver content in order to overcome the above-mentioned problems. The design and manufacture of custom brushes used in these assemblies are not only costly, but the material is very brittle which can lead to a short operating life. For example, one such solution for addressing the eddy current problem is to use a custom designed ceramic bearing, which is costly and difficult to replace quickly.  
         [0008]     Therefore, it is an object of the present invention to improve the performance of the cylindrical magnetron sputtering application by using profiled magnet arrangements to increase the target utilization and the deposition rate while reducing the amount of target material on the chamber walls and shielding of a cylindrical magnetron electrode. It is a further object of the present invention to provide an improved drive assembly for a cylindrical magnetron electrode that is designed to reduce the cost and complexity of delivering high power AC current into a rotating shaft by using common and readily available components.  
       SUMMARY OF THE INVENTION  
       [0009]     The present invention provides for a magnet arrangement which is usable as a retrofit magnetic arrangement in a rotatable cylindrical magnetron sputtering electrode. The electrode includes a cathode body defining a magnet receiving chamber, a rotatable cylindrical target surrounding the cathode body, wherein the target is rotatable about the cathode body. The cathode body further defines a magnet arrangement received within the magnet receiving chamber, wherein the magnet arrangement includes a plurality of magnets and, wherein at least one of the magnets is a profiled magnet having a contoured top portion.  
         [0010]     The present invention also provides for rotatable cylindrical magnetron sputtering device that includes the electrode of the present invention and a drive assembly in communication with the cathode body and the cylindrical target, wherein the drive assembly. comprises a drive shaft and a motor and, wherein the drive shaft is rotatably connected to the cylindrical target. The drive assembly is adapted to rotate the cylindrical target and to introduce high current AC power into the target surface via the rotating drive shaft without adding highly incremental costs to the overall design of the electrode. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is a cross sectional view of a rotatable cylindrical magnetron sputtering device made in accordance with the present invention;  
         [0012]      FIG. 1A  is a top plan view of the magnetron sputtering device shown in  FIG. 1 ;  
         [0013]      FIG. 2  is a sectional front view of an electrode of the magnetron sputtering device shown in  FIG. 1 , wherein magnetic flux lines are shown in relation to a substrate;  
         [0014]      FIG. 3  is a sectional view of a cathode body of the electrode shown in  FIG. 2 ;  
         [0015]      FIG. 4  is a top plan view, partially in section, of a profiled magnet arrangement of the electrode shown in  FIG. 2 ;  
         [0016]      FIG. 5  is a perspective view of a high current brush assembly of the rotatable cylindrical magnetron sputtering device shown in  FIG. 1 ;  
         [0017]      FIG. 6  is a perspective view of a housing of the high current brush assembly shown in  FIG. 5 ; and  
         [0018]      FIG. 7  is a sectional view of a cathode vacuum seal chamber of the rotatable cylindrical magnetron sputtering device shown in  FIG. 1 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0019]     The present invention provides for a rotatable cylindrical magnetron sputtering device  8  that includes an electrode  10  and a drive assembly  11  attached to the electrode  10  as shown in  FIGS. 1 and 1 A. Referring to  FIGS. 1 and 2 , the electrode  10  includes a hollow cylindrical target  12  having an inner surface  13 A and an outer surface  13 B, a cathode body  14  having a first surface  16  and a second surface  18  received within the cylindrical target  12 , a base plate  20  attached to the second surface  18  of the cathode body  14  and a central member  21  such as a shaft or sleeve received within the cylindrical target  12  and attached to the base plate  20  for supporting the cathode body  14 , wherein the cylindrical target  12  is rotatable about the cathode body  14  as shown as arrow Z in  FIG. 2  about the longitudinal axis X. Referring back to  FIG. 1 , the cylindrical target  12  is held in place by an annular target retaining member  23 , which is in communication with the drive assembly  11 . Attachment of the cathode body  14  to the base plate  20  may be accomplished via one or more fasteners such as screws or bolts B or any other suitable fastening arrangement known in the art. Attachment of the base plate  20  to the central member  21  may be accomplished using a clamp or any other suitable clamping arrangement known in the art.  
         [0020]     Referring to  FIGS. 2 and 3 , the electrode  10  further includes a guide member such as a pair of rollers R or other guide assemblies positioned adjacent the cathode body  14  and contacting the inner surface  13 A of the cylindrical target  12 , thereby allowing the target  12  to rotate about the cathode body  14  at a fixed distance. The cylindrical target  12  may be, for example, standard titanium hollow tubing having a 5″ inside diameter and a 6″ outside diameter, which is held at a fixed distance, such as 0.60″, away from the first surface  16  of the cathode body  14  to account for uniformity adjustments. Referring to  FIG. 2 , a substrate S is positioned directly above the cathode body  14 , wherein target material is sought to be deposited onto the substrate S. Chamber walls  22  surrounding the electrode  10  and the substrate S provide a shielding for the sputtering application.  
         [0021]     Referring to  FIGS. 2-4 , the cathode body  14  forms a magnet receiving chamber which contains a profiled magnet arrangement  24 . The profiled magnet arrangement  24  uses profiled magnets as shown and described in U.S. Pat. Nos. 5,736,019 and 6,171,461 which are hereby incorporated by reference in their entirety. The magnet arrangement  24  includes a profiled central magnet  26  and profiled end magnets  28 A,  28 B. Each of the profiled magnets  26 ,  28 A and  28 B has a base  30  and a contoured top portion  32 . The shape of the contoured top portion  32  is shown angled, but may include sloped, conical, parabolic, convex, and concave shapes. If the contoured top portion  32  is angled, it is preferable for an apex of the contoured top portion  32  to be flat, desirably between 0.01 inch to 0.060 inch or up to half the thickness of the magnets  26 ,  28 A and  28 B. Having a flat apex minimizes the possibility of chipping the magnets  26 ,  28 A and  28 B during routine use of the completed assembly. Alternatively, the apex may come to a point. The use of such contoured shapes is conducive to directing magnetic flux lines from the contoured top portion  32  of each of the magnets  26 ,  28 A and  28 B.  
         [0022]     With continued reference to  FIGS. 2 and 3 , the top portion  32  of the profiled end magnets  28 A,  28 B is preferably angled on one side away from the central magnet  26  wherein the apex of the top portion  32  is adjacent to the central magnet  26 . The top portion  32  of the central magnet  26  is preferably angled on both sides, wherein the apex of the top portion  32  is at the center of the central magnet  26 . The magnet arrangement  24  is also shown using a planar magnet having flat surfaces as shown in phantom in  FIGS. 2 and 3 . The primary magnetic field lines L generated from the profiled magnets  26 ,  28 A and  28 B are more centered than the magnetic field lines L′ (shown in phantom) generated from planar magnets, such that an overall width W of field lines L is less than an overall width W′ of the field lines L′ as shown in  FIG. 2 . The field lines L using the profiled magnets  26 ,  28 A and  28 B reduce the off angle sputtering that is inherent to the sputtering process, thus resulting in more of the target sputtering material on the substrate S and less on the chamber walls  22 . For example, a computer simulation demonstrated that the magnetic flux lines F generated using the profiled magnet arrangement  24  resulted in an angle reduction of about 15 degrees compared to the magnetic flux lines F′ (shown in phantom in  FIG. 2 ) generated using the planar magnet arrangement (i.e., an angle A approximately 15 degrees and angle A′ approximately 30 degrees), thus reducing the amount of sputtered material on the chamber walls  22  from about 16.7% to 9.2%. When the sputtered material builds up on the chamber walls  22 , it can fall off onto the target  12  or the substrate S thus causing the device to short out or create debris which would reduce the yield or quality of substrate S.  
         [0023]     Further, the use of the profile magnets  26 ,  28 A and  28 B in electrode  10  provides for a greater increase in magnetic field intensity using the same size magnets in contrast to conventional planar magnets. This increase in the magnetic field intensity and the reduction of flux material on the chamber walls  22  results in an overall rate increase and target utilization in the electrode  10  of the present invention.  
         [0024]     Initial processing uniformity may be established by adjusting the dynamic field stroke along the length of the electrode  10  to compensate for known facts such as the tendency for the magnetron ends (i.e. turnaround) to sputter at faster rates than at the center of the target  12 . Therefore, it is contemplated that the ends of the central magnet  26  of the profiled magnet arrangement  24  have a diverter magnet D of a different profile such as is shown in  FIG. 4 . This magnet having a different profile can slow down the sputtering effect at the ends, thus reducing erosion of the target  12  at these ends.  
         [0025]     Referring to  FIG. 1 , the drive assembly  11  of the magnetron sputtering device  8  includes a drive unit  34 , wherein the drive unit  34  includes a drive shaft  36  and a motor  38 . The drive shaft  36  is rotatably coupled to the retaining member  23 . The motor  38  is coupled to the drive shaft  36 , so that activation of the motor  38  causes the drive shaft  36  to rotate about an axis “X”, which in turn causes the retaining member  23  having the attached cylindrical target  12  to rotate about the cathode body  14 . The drive assembly  11  further includes a brush assembly  40  surrounding the drive shaft  36 , wherein the brush assembly  40  coacts with the rotating drive shaft  36  to supply AC and DC electrical current to the cathode body  14 , and a cathode vacuum seals and support chamber assembly  60  for introducing high current AC power from atmosphere into the rotating vacuum drive shaft  36  with negligible eddy current heating effects. The remaining components of the drive assembly  11  will not be described because these components are known in the art and are common for typical rotating cylindrical magnetron sputtering devices.  
         [0026]     Referring to  FIG. 1 , the drive shaft  36  is electrically connected to the central member  21 , which is affixed to the base plate  20  of the cathode body  14 . Rotation of the drive shaft  36  causes the brush assembly  40  to generate high electrical current to the drive shaft  36 , which transfers the current through the central member  21  and to the base plate  20  and then to the cathode body  14 . The central member  21  may be, for example, a shaft made of a conductive material in order to carry electrical current to the cathode body  14 .  
         [0027]      FIGS. 5 and 6  show the high current brush assembly  40  that includes a disc-shaped housing  42  defining a central opening  44  therein, a plurality of circumferentially spaced spacers  46  arranged on a front surface  48  of the housing  42 , a plurality of brushes  50  positioned between each spacer  46  and a cap  52  attached to the front surface  48  of the housing  42 . The housing  42  is preferably made of copper. The brushes  50  may be standard motor brushes made of, for example, a metal graphite material such as a low grade graphite or a graphite having a slightly higher conductivity. These brushes are readily available by most major suppliers of motors. In operation, specifically when operating at high currents in the AC power mode, cooling of the brushes  50  is required to increase further the current capacity of the brushes  50 .  FIG. 6  shows the housing  42  without the cap  52  being supplied with cooling water as represented by arrows A, which circulates within the housing  42  thereby cooling the brushes  50 . Compression of the brushes  50  onto the rotating shaft  36  extending through the opening  44  is achieved by the use of a garter spring  54  shown in  FIG. 5 . By using small individual segments of brushes  50  and a copper housing  42 , the surface area of the entire brush assembly  40  is increased as well as the ability to cool the brushes  50 , thereby achieving a higher current capacity.  
         [0028]      FIG. 7  shows a sectional view of the cathode vacuum seals and support chamber assembly  60  that includes a housing  62  and a wear sleeve  64  centrally positioned within the housing  62 . An insulating member  66  is positioned between a wall W of the housing  62  and the sleeve  64  for electrically insulating the housing  62  from high voltage and electrical current. Atmosphere to vacuum seals are achieved through static O-rings  68  positioned between the housing wall W and the insulating member  66  as well as spaced rotary vacuum seals  70  positioned between the sleeve  64  and the insulating member  66 . Spacer blocks  72  and  74  keep the rotary seals  70  spaced apart and aligned. The drive shaft  36  carrying the current (shown in  FIG. 1 ) extends through the sleeve  64  and rotates about axis “X”, wherein the sleeve  64  functions as front support bushing as well as a vacuum seal surface. A graphite or plastic bearing  76  is located between the sleeve  64  and the vacuum seals  70 . Preferably, the bearing  76  may be manufactured from highly durable plastics such as polyimides or from highly durable graphite. The size of the bearing  76  may vary depending on the cathode size and the spacers  72 ,  74  as well as the sleeve  64 . It is important to preferably use materials for the components that cannot only support a load induced by the cathode, but also prevent eddy currents from setting up, thereby causing extreme heating. For example, conductive materials such as highly durable plastics may be used for the bearing  76  and the other components within the vacuum assembly  60  because the high voltage is kept off of the vacuum housing  62  by the insulating member  66 , thereby making these components non-susceptible to eddy current heating.  
         [0029]     The present invention also provides for a method of improving target utilization and deposition rate in cylindrical magnetron sputtering application that includes providing a substrate S and a rotatable cylindrical magnetron device  8  of the present invention. The cylindrical target  12  is rotated around a magnet arrangement  24  and target material for the cylindrical target  12  is obtained and deposited on the substrate S.  
         [0030]     While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. The presently preferred embodiments described herein are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the intended claims and any and all equivalents thereof.