Patent Publication Number: US-6221217-B1

Title: Physical vapor deposition system having reduced thickness backing plate

Description:
RELATED APPLICATION 
     This Application is a Continuation-In-Part of Ser. No. 08/677,951 filed Sep. 10, 1996 now U.S. Pat. No. 5,876,573, which claims priority under 35 U.S.C. § 119(e) (1) to provisional application No. 60/000,852 filed Jul. 10, 1995. 
    
    
     TECHNICAL FIELD OF THE INVENTION 
     This invention relates in general to the field of magnetron sputtering systems, and more particularly to a high magnetic flux cathode apparatus and method for high productivity physical vapor deposition. 
     BACKGROUND OF THE INVENTION 
     The deposition of films using a magnetron sputtering system provides enhanced deposition rates through the creation of a magnetic field at the target surface. It is advantageous in magnetron sputtering systems to increase the magnetic field strength at the target surface. This can be especially true when the target is a magnetic material. 
     One barrier to the strength of the magnetic field is the backing plate upon which the target is bonded. The backing plate serves the purpose of cooling the target and providing part of the chamber wall for forming the vacuum chamber for deposition of the target onto a substrate. In conventional systems, the backing plate experiences a pressure differential from the vacuum chamber to atmospheric pressure. This pressure places limits on the material properties of the backing plate. 
     Conventional systems have attempted to increase the magnetic field at the target using a number of methods. Some conventional systems have attempted to strengthen the magnetic field at the target by decreasing the thickness of the backing plate. However, bowing, deflection and buckling of the backing plate can be caused by the pressure differential between the vacuum inside the chamber and atmospheric pressure outside the chamber. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, a high magnetic flux cathode apparatus and method for high productivity physical vapor deposition is provided that substantially eliminates or reduces disadvantages and problems associated with previously developed magnetron sputtering systems. 
     According to one embodiment of the present invention, a magnetron sputtering system is provided that includes a backing plate with cooling channels. The magnetron sputtering system also generates low pressure region in the magnetron assembly such that the backing plate sees a pressure differential much lower than atmospheric pressure. The backing plate is reduced in thickness and provides less of a barrier to the generated magnetic field on the target. In another embodiment, the present invention includes a backing plate supported with a center post. 
     A technical advantage of the present invention is the thinning of the backing plate to provide less of a barrier to the magnetic field generated by the magnet array, thus increasing the magnetic field seen by the target. 
     A further technical advantage of the present invention is the use of a cooling fluid to cool the backing plate and the target by circulating the cooling liquid through cooling channels in the magnetron assembly. 
     An additional technical advantage of the present invention is the use of low-vapor-pressure liquid in the magnetron assembly so that the liquid does not evaporate at the lower pressures therein. 
     Still another technical advantage of the present invention is the use of low pressure region in conjunction with a thin backing plate to reduce buckling, bowing and deflection of the backing plate. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete understanding of the present invention and advantages thereof may be acquired by reference to the following description taken in conjunction with the accompanying drawings in which like reference numbers indicate like features and wherein: 
     FIG. 1 is a cross-sectional view of one embodiment of a magnetron sputtering system, constructed according to the teachings of the present invention; 
     FIG. 2 is a top view of the magnetron sputtering system of FIG. 1; 
     FIGS. 3A and 3B are a top and cross-sectional view of the backing plate of the magnetron sputtering system; 
     FIGS. 4A,  4 B,  4 C and  4 D are top, cross-sectional, bottom, and partial views of the coolant inlet/out manifold of the magnetron sputtering system; 
     FIGS. 5A and 5B are top and cross-sectional views of the retainer ring of the magnetron sputtering system; 
     FIGS. 6A,  6 B,  6 C and  6 D are top, partial, cross-sectional and perspective views of the bearing support of the magnetron sputtering system; 
     FIGS. 7A and 7B are top and cross-sectional views of a first insulator ring of the magnetron sputtering system; 
     FIGS. 8A and 8B are top and cross-sectional views of a second insulator ring of the magnetron sputtering system; 
     FIGS. 9A,  9 B and  9 C are top, cross-sectional and partial views of the anode ring of the magnetron sputtering system; 
     FIGS. 10A,  10 B,  10 C,  10 D and  10 E are top, partial, cross-sectional, side and zoomed views of the magnet assembly housing of the magnetron sputtering system; 
     FIGS. 11A and 11B are top and cross-sectional views of a third insulator ring of the magnetron sputtering system; 
     FIGS. 12A and 12B are top and cross-sectional views of the bearing retainer of the magnetron sputtering system; 
     FIGS. 13A and 13B are top and cross-sectional views of the magnet holder of the magnetron sputtering system; 
     FIGS. 14A and 14B are top and cross-sectional views of the spacer ring of the magnetron sputtering system; 
     FIGS. 15A,  15 B, and  15 C are cross-sectional and partial views of the conduit tube of the magnetron sputtering system; 
     FIGS. 16A and 16B are top and side views of the jacket insulator of the magnetron sputtering system; 
     FIGS. 17A,  17 B and  17 C are top and cross-sectional views of the inlet/outlet manifold of the magnetron sputtering system; 
     FIG. 18 is a schematic view of another embodiment of a magnetron sputtering system constructed according to the teachings of the present invention; and 
     FIG. 19 is a view of another embodiment of the backing plate of the present invention having a center post support. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 is a cross-sectional view of a magnetron sputtering system, indicated generally at  10 , constructed according to the teachings of the present invention. System  10  is used to perform sputtering of target material from a target onto a substrate. 
     Chamber walls  12  define a vacuum deposition chamber  14 . Chamber walls  12  are constructed from a metal material capable of supporting the evacuated state. A target  16  is positioned within vacuum chamber  14  and is mounted to a target backing plate  18 . Target backing plate  18  should preferably be constructed from copper. Backing plate  18  includes conduits  19 , as are described in more detail below. 
     The backing plate  18  can be coupled to target  16  by means of a bonding process. The bonding process should preferably be a low-temperature, for example, less than 200 degrees Celsius, bonding process to allow de-bonding of the backing plate  18  from a used target  16 . This allows the backing plate  18  to be re-used. An indium bonding process can accomplish this aim of allowing de-bonding of the target  16  from the backing plate  18  to allow re-use of backing plate  18 . 
     A magnet array assembly  20  is positioned above backing plate  18  and target  16 , as shown. Magnet array assembly  20  provides the magnetron enhancement of physical vapor deposition in chamber  14 . One embodiment of a magnet array assembly is disclosed and described in U.S. Pat. No. 5,248,402, the disclosure of which is incorporated herein by reference. 
     Backing plate  18  includes conduits  19  that provide cooling channels to cool target  16  during the sputtering process. In one embodiment of the present invention, backing plate  18  serves as a cathode for creating plasma within chamber  14 . To create a plasma cathode, electrically-conductive backing plate  18  can be coupled to either a D.C. source or a radio frequency (RF) source. Backing plate  18  can couple to the DC or RF energy source via conduit tubes  44 . For example, FIG. 1 shows backing plate  18  connected to an RF source by means of an RF strap  68 . Because the chamber walls  12  provide system ground, backing plate  18  must be electrically isolated from chamber walls  12  when backing plate  18  serves as a cathode. 
     A coolant manifold  22  is positioned proximate backing plate  18  such that coolant manifold  22  connects to conduits  19 . Coolant manifold  22  provides a coupling means for providing fluid communication to conduits  19 . The structure of one embodiment of coolant manifold  22  is described in more detail below. 
     Backing plate  18  is held in place by retainer ring  24  which is coupled to a bearing support  26 , as shown. Bearing support  26  also provides support for a bearing  27 . In one embodiment of the present invention, bearing  27  is a KAYDON bearing, part number KD100XPO. A first insulator ring  28 , and a second insulator ring  30 , couple between bearing support  26  and chamber walls  12 , while isolating the metal bearing support  26  from metal chamber walls  12 . A third insulator ring  36  couples between bearing support  36  and magnetron assembly housing  34 . For embodiments of the present invention that include energizing backing plate  18  to form a cathode, backing plate  18  and all associated structures (an example being the bearing support  26 ) must be electrically isolated from chamber walls  12 . Insulator rings  28  and  30 , made from a non-conductive, elastomer material, effectively isolate bearing support  26  (and therefore cathode backing plate  18 ) from ground (the chamber walls and the magnetron assembly housing). 
     An anode ring  32  is positioned inside chamber  14  along the upper inner edge of chamber wall  12  as shown. Anode ring  32  serves as an anode for system  10  and is grounded through contact with chamber wall  12 . In one embodiment of the present invention, anode ring  32  is constructed from aluminum. Anode ring  32  is electrically isolated from backing plate  18 . This isolation can be accomplished either through use of an insulator or an open air space as shown in FIG.  1 . 
     A magnetron assembly housing  34 , in contact with chamber walls  12 , is coupled to first and second insulator rings  28  and  30 , opposite bearing support  26 . Magnetron assembly housing  34  provides a housing for the entire magnetron assembly  35  which sits on top of chamber  14 . A third insulator ring  36  is positioned between magnetron assembly housing  34  and bearing support  26  to electrically isolate bearing support  26  and backing plate  18  from magnetron assembly housing  34 . 
     A bearing retainer  38  is coupled to bearing support  26  and provides, along with bearing support  26 , the outer race for bearing  27 . A magnet holder  40  couples to magnet array assembly  20  and provides part of an inner race for bearing  27  as well as supporting magnet array assembly  20 . A spacer ring  42  is positioned proximate magnet holder  40  and provides the remaining portion of the inner race for bearing  27 , as shown. 
     A conduit tube  44  extends through magnetron assembly housing  34 , third insulator ring  36 , bearing support  26 , and into coolant manifold  22 , as shown. Conduit tube  44  provides fluid communication to conduits  19  of backing plate  18 . Conduit tube  44  couples to coolant manifold  22  to provide the ability to pump fluid into and out of cooling channels provided by conduits  19  of backing plate  18 . In one embodiment of the present invention, there are eight conduit tubes  44  coupled to coolant manifold  22 , as described in more detail below. An insulating jacket  46  electrically insulates conduit tube  44  from magnetron assembly housing  34 , as shown. 
     In one embodiment of the present invention, the conduit tubes  44  couple to an electrical source such as an RF or DC source, to provide an energy path to backing plate  18 . The energized backing plate then provides a cathode for the magnetron sputtering system  10 . In the illustrated embodiment, an RF strap  68  is coupled to conduit tube  44  to provide an RF source to backing plate  18 . In other embodiments, a DC source can couple to one or more conduit tubes  44  to provide a DC source for creation of plasma within chamber  14 . Generally, a DC source is used where target  16  is a conductive material, and an RF source is used where target  16  is a semiconductor or insulating material. 
     An inlet/outlet manifold  48  is coupled to magnetron assembly housing  34 . Inlet/outlet manifold  48  comprises inlets and outlets which are in fluid communication. Inlet/outlet manifold  48  is connectable in fluid communication with each conduit tube  44  and conduit  19  such that coolant can be pumped into and out of the cooling channels. 
     A plate  50  is coupled to magnet array assembly  20 , and a plate  52  is coupled to magnetron assembly housing  34 , as shown. A sealed rotating shaft  54  extends through plate  52  and is coupled to plate  50  to provide rotation of magnet array assembly  20 . As shown, a ferrofluidic feedthrough  56  allows the shaft of sealed rotating shaft  54  to extend through magnet assembly housing  34  without compromising the seal. A coupling  58  connects rotating shaft  54  with shaft  60  of motor  62 . In one embodiment of the present invention, coupling  58  comprises an OLDHAM coupling. 
     A number of fastening devices  70  are used to couple pieces of system  10  together, as shown. In the illustrated embodiment, fastening devices  70  comprise screws of various sizes, although other fastening devices could be used. In addition, various sealing devices  72  provide sealing of chamber  14  and of the inside of the magnetron assembly  35  from outside atmospheric pressure. In the illustrated embodiment, sealing devices  72  comprise elastomer seals, although other sealing devices could be used. 
     In operation, magnetron sputtering system  10  operates to sputter material from target  16  into chamber  14 . A plasma is generated in chamber  14  such that physical vapor deposition of the material sputtered from target  16  occurs. Magnetron sputtering system  10  provides magnetron enhancement of the sputtering process. 
     According to the present invention, the magnetron assembly housing is formed to enclose the magnet array assembly  20  and form a space, or the magnet array chamber  37 , within the magnetron assembly housing. Magnet array chamber  37  comprises the space within magnetron assembly  35  that lies above backing plate  18 . In operation, the pressure within the magnet array chamber can be reduced to a pressure much lower than atmospheric pressure. This reduction in pressure can be accomplished by operating a pump through pump port  88  that connects to magnet array chamber  37 . In one embodiment of the present invention, the lower pressure ranges from 10 to 100 Torr in the magnet array chamber  37 . During operation, chamber  14  is a vacuum, the magnet array chamber  37  is at subatmospheric pressure, and the remainder of system  10  is at atmospheric pressure. 
     The backing plate  18  will, therefore, experience pressure in the vacuum chamber on the target side of the backing plate  18 , while at the same time the backing plate  18  will experience pressure force from within the magnet array chamber  37  on the magnet array assembly side of the backing plate. According to the teachings of the present invention, backing plate  18  sees a lower pressure differential due to the decrease in pressure within the magnet array chamber  37 . This decrease in pressure differential will decrease the deflection force on the backing plate  18 . This allows backing plate  18  to be decreased in thickness without experiencing the level of buckling, bowing, and deflection that would occur if the backing plate saw a more severe pressure differential. A thinner backing plate provides less of a barrier to the magnetic field generated by magnet array assembly  20 . 
     The present invention can include a center post  150  that connects at one end to the magnetron assembly housing  34  and at its opposite end to the backing plate  18 . The center post  150  can be a stationary rod or post that does not move during the operation of the PVD chamber (as opposed to the magnet array  20  which can be rotating during chamber operation). The center post  150  can aid in supporting the backing plate  18  to reduce any potential deflection the backing plate  18  would encounter due to a pressure differential between the vacuum chamber  14  and the magnet array chamber  37 . This allows for the use of an even thinner backing plate  18  according to the teaching of the present invention. An embodiment of the present invention incorporating a center post  150  is described more fully in FIG.  19 . 
     The reduction of the thickness of backing plate  18  provides enhanced penetration of the magnetic field generated by magnetic array assembly  20 . This enhanced strength of the magnetic field increases the effectiveness of magnetron sputtering system  10 , and provides increased deposition rates and better utilization of target  16 . In addition, the provision of cooling channels and the pumping of cooling liquid into and out of magnetron assembly  35  provides enhanced target cooling during operation. In the illustrated embodiment, cooling channels are provided by conduits  19 . 
     FIG. 2 is a top view of the magnetron sputtering system  10  of FIG.  1 . FIG. 2 illustrates an arrangement of conduits  19  in backing plate  18  and the connection of conduits  19  to coolant manifold  22 . In the illustrated embodiment, twelve v-shaped conduits  19 , each having an input end and an output end, are divided into eight groups which can include four input and four output groups. For example, collector region  74  and collector region  76  collect opposite ends of three pairs of connected conduits  19 . Collector region  74  and collector region  76  can serve respectively as an inlet and as an outlet for coolant. Thus, for each set of three conduits  19 , a coolant can flow into the conduits through inlet collector region  74 , through the three v-shaped conduits  19 , and exit through outlet collector region  76 . 
     As shown in FIG. 2, two manifolds  48  are positioned on either side of motor  62 . One inlet/out manifold  48  can be connected in fluid communication with each inlet collector region  74 , and the other inlet/out manifold  48  can be connected in fluid communication with each outlet collector region  76 . In this manner, one inlet line is used to pump coolant fluid into and one outlet line is used to pump coolant fluid out of conduits  19  in backing plate  18 . 
     The thickness of backing plate  18  can be substantially reduced due to the decrease in the pressure differential seen by backing plate  18  and the cooling of backing plate  18  using cooling channels such as conduits  19 . This provides enhancement of the operation of magnetron sputtering system  10 . 
     FIGS. 3A and 3B are top and cross-sectional views of backing plate  18 . As shown in FIG. 3A, backing plate  18  comprises a number of conduits  19 . In the illustrated embodiment, v-shaped conduits  19  are divided into four quadrants, with each quadrant having six holes  78  connecting to three conduits  19 , respectively. In one embodiment of the present invention, conduits  19  are formed by drilling into backing plate  18  from the side. The conduits are then plugged and welded on the periphery, after which holes  78  are drilled from the top to connect to conduits  19 . FIG. 3B shows the interconnection of holes  78  with conduits  19 . In another embodiment of the present invention, conduits  19  are formed by cutting grooves in the top of backing plate  18  and mounting a plate over the grooves. Other suitable methods of forming conduits  19  are possible. 
     FIGS. 4A,  4 B,  4 C and  4 D show top, cross-sectional, bottom and partial views of coolant manifold  22 . In the embodiment illustrated in FIG. 4A, coolant manifold  22  comprises eight openings  80  on the top of coolant manifold  22 . Each opening  80  is in fluid communication with a collector  82 . Each opening  80  is also operable to connect to a conduit tube  44  to receive fluid from or to deliver fluid to the conduit tube  44 . FIG. 4B shows eight collectors  82  on the bottom of coolant manifold  22 . Each collector  82  includes an O-ring  84  for sealing coolant manifold  22  to backing plate  18  when assembled. Each collector  82  is operable to cover three of holes  78  on the top of backing plate  18 . In this manner, fluid can be communicated to and from conduits  19  through the eight openings  80  on the top of coolant manifold  22 . FIG. 4C shows an exploded partial view of the positioning of O-ring  84 . 
     FIGS. 5A and 5B are top and cross-sectional views of retainer ring  24 . In the illustrated embodiment, retainer ring  24  is constructed from stainless steel and has an L-shaped cross-section. Retainer ring  24  hold backing plate  18  in place. 
     FIGS. 6A,  6 B,  6 C and  6 D are top, partial, cross-sectional and perspective views of bearing support  26 . Bearing support  26  provides an outer race  86  for bearing  27  as shown in FIG.  6 C. FIG. 6B shows a view of the O-ring groove and venting for bearing support  26 . In the illustrated embodiment of the present invention, bearing support  26  is constructed from an aluminum alloy. 
     FIGS. 7A and 7B are top and cross-sectional views of a first insulator ring  28 . First insulator ring  28  should be constructed from a non-conductive material, such as an elastomer material. In one embodiment of the present invention, insulator ring  28  is constructed from a nylon material. 
     FIGS. 8A and 8B are a top and cross-sectional view of a second insulator ring  30 . As shown in FIG. 8B, second insulator ring  30  has an L-shaped cross-section. Second insulator ring  30  is constructed from a suitable insulating material, such as nylon. 
     FIGS. 9A,  9 B and  9 C are a top, cross-section and partial view of anode ring  32 . As shown in FIG. 9B, anode ring  32  has a somewhat reverse C shape. Anode ring  32  is constructed from an electrically-conductive metal material. 
     FIGS. 10A,  10 B,  10 C,  10 D and  10 E are top, partial, cross-sectional, side and zoomed views of magnetron assembly housing  34 . In the illustrated embodiment of the present invention, magnetron assembly housing  34  is constructed from stainless steel and sealed to contain a subatmospheric state. As shown in FIG. 10A, magnetron assembly housing  34  comprises eight feedthroughs  86 , through which conduit tubes  44  can extend. In addition, pump outlet  88  provides a port for lowering the pressure inside magnetron assembly  35  after magnetron sputtering system  10  is assembled. FIG. 10B shows a partial view of the O-ring groove and venting for magnetron assembly housing  34 . 
     FIGS. 11A and 11B show top and cross-sectional views of the third insulator ring  36 . In the illustrated embodiment of the present invention, third insulator ring  36  is constructed from nylon material. As shown in FIG. 11A, third insulator ring  36  comprises eight feedthrough openings  90  through which conduit tubes  44  can extend. Feedthrough openings  90  are wider at the top to receive insulating jacket  46 . Insulator ring  36  serves, in part, to provide a seal for magnet array chamber  37 . 
     Insulator rings  28 ,  30 , and  36  work in tandem to insulate the backing plate  18  from chamber walls  12  and magnet assembly housing  34 . These insulator rings operate to electrically isolate an RF or DC charged backing plate  18  from ground (chamber walls  12  and magnet assembly housing  34 ). 
     FIGS. 12A and 12B are top and cross-sectional views of bearing retainer  38  that provides an outer race for bearing  27 . In the illustrated embodiment of the present invention, bearing retainer  38  is constructed from aluminum material. 
     FIGS. 13A and 13B are top and cross-sectional views of magnet holder  40 . In the illustrated embodiment of the present invention, magnet holder  40  is constructed from aluminum material. Magnet holder  40  provides a portion  92  of an inner race for bearing  27 . 
     FIGS. 14A and 14B are top and cross-sectional views of spacer ring  42 . Spacer ring  42  provides a remaining portion  94  of the inner race for bearing  27 . 
     FIGS. 15A,  15 B, and  15 C are cross-sectional and exploded views of conduit tube  44 . In one embodiment of the present invention, conduit tube  44  is constructed from copper. Conduit tube  44  comprises a first end  96  and a second end  98 . First end  96  is operable to connect to coolant manifold  22 . Second end  98  is operable to provide fluid communication to inlet/out manifold  48  for either pumping of cooling fluid into or out of backing plate  18 . In the embodiment of FIG. 1, four conduit tubes  44  (inlet conduit tubes) supply coolant, through coolant manifold  22 , to conduits  19  in backing plate  18 , while four conduit tubes  44  (outlet conduit tubes) receive coolant exiting from conduits  19  in backing plate  18 . 
     FIGS. 16A and 16B provide top and side views of insulating jacket  46 . Insulating jacket  46  is constructed from insulating material to electrically isolate conduit tube  44  from magnet assembly housing  34 . 
     FIGS. 17A,  17 B and  17 C are cross-sectional and top views of inlet/out manifold  48 . In the illustrated embodiment of the present invention, inlet/out manifold  48  is constructed from aluminum and aluminum alloy as indicated. Inlet/out manifold  48  includes four conduit tube openings  100 , and one inlet/outlet opening  102 . Conduit tube openings  100  and inlet/outlet opening  102  are in fluid communication via conduit  104 . Inlet openings  100  are operable to connect with four of conduit tubes  44 . Outlet opening  102  is operable to connect in fluid communication with a pump for either pumping cooling fluid into or out of inlet/out manifold  48 . As shown in the embodiment of FIG. 2, the system  10  includes two manifolds  48 . One inlet/out manifold  48  (the inlet manifold) couples (by means of a tubing) to the four inlet conduit tubes  44 , while the other inlet/out manifold  48  (the outlet manifold) couples to the four outlet conduit tubes  44  via conduit tube openings  100 . 
     In operation, coolant flows into inlet/outlet manifold  48  through inlet/outlet opening  102  from a coolant source (not shown), flows via conduit  104  to conduit tube openings  100 , and into inlet conduit tubes  44 . The coolant then flows from inlet conduit tubes  44 , through coolant manifold  22 , into conduits  19  (serving as cooling channels) through inlet collection region  74 . Coolant flows through conduits  19 , exits backing plate  18  through outlet collector region  76 , flows through coolant manifold  22 , into the four outlet conduit tubes  44 . Coolant flows through the four outlet conduit tubes  44  into the four conduit tube openings  100  of inlet/outlet manifold  48 . The coolant then mixes in conduit  104  and exits inlet/outlet manifold  48  through inlet/outlet opening  102 . 
     FIG. 18 illustrates another embodiment of a magnetron sputtering system, indicated generally at  110 . Magnetron sputtering system  110  comprises a bonded target  112  that can be a high utilization target. An insulator disk  114  is positioned between target  112  and magnet assembly housing  116 . Insulator disk  114  can comprise an AlN insulator disk for an ultra-high vacuum design. An electrical feedthrough  118  is positioned at the center of insulator disk  114  to provide electrical connection to target  112 . 
     Magnet assembly housing  116  includes cooling channels  120 . As shown, cooling channels  120  are positioned above a magnet assembly  122 . A space  124  is established between magnet assembly  122  and magnet assembly housing  116 . Space  124  can be filled with liquid having a low-vapor-pressure to communicate cooling and heating by water in cooling channels  120  to target  112 . The low-vapor-pressure liquid can comprise mercury or gallium such that the liquid does not evaporate at reduced pressure inside the assembly. This will provide complete liquid thermal contact between the magnet assembly housing  116  and insulation disk  114  for increased cooling. In this embodiment, the cooling channels  120  are formed in magnet assembly housing  116  instead of the backing plate. 
     With continued reference to FIG. 18, an electrical lead jacket  128  holds an electrical connection lead  130 , as shown. Electrical connection lead  130  is coupled to electrical feedthrough  118  and to target  112 . Space  132  surrounding electrical lead jacket  128  comprises a vacuum sealed space having a rough vacuum. 
     A bearing support  134  provides rotational bearing support for rotating tube  135  and magnet assembly  122 . Wheel  136  is an inner multipolar wheel connected to rotating tube  135  connected to magnet assembly  122 . A rotation drive  138  is coupled to wheel  136  and comprises a magnetically coupled rotation drive having a four-magnet multipolar ring. Gear drive  140  is coupled to rotation drive  138  and to a rotation motor  142 , as shown. Rotation motor  142  can comprise a stepper motor. 
     A seal  144  provides a sealing surface for rotating tube  135 . A valve  146  provides control for flow of air and liquid metal through port  148 . Port  148  serves as both an entry for liquid metal and a vacuum pump inlet. 
     In operation, magnetron assembly  110  sputters material from target  112  into a vacuum chamber to allow deposition of the material on a wafer surface. Cooling channels  120  provide cooling of the assembly such that target  112  does not require contact to a backing plate. 
     The present invention provides a magnetron cathode assembly for increasing the magnetron sputtering rate and enhancing the productivity of physical vapor deposition tools. The magnetron sputtering rate is increased by reducing the thickness of the target backing plate and can be further increased by using an improved magnet array design. The present invention provides a cathode structure having a thin backing plate. In one embodiment of the present invention, the permanent magnet assembly is supported by a bearing inside an enclosed cavity above the target backing plate. The permanent magnet assembly cavity has a pump/vent port and a ferrofluidic feedthrough. The latter is for coupling rotation from an external motor to the magnet assembly. The pump port can be used to establish a low pressure (e.g. 10 to 100 Torr) ambient (e.g. air, nitrogen, etc.) within the magnet array chamber in order to reduce the differential pressure across the target backing plate from atmospheric pressure down to the lower pressure established. This allows the thickness of the backing plate to be reduced without causing excessive bowing of the backing plate. Target cooling can be accomplished using cooling channels embedded within the backing plate such as the conduits described above. In an alternative embodiment, the cooling channels can be built into the top of the magnetron housing. The housing can be filled with a low-vapor-pressure thermally conductive liquid to cool the target, thereby eliminating the requirement of having a backing plate. 
     FIG. 19 shows a portion of a PVD chamber including a vacuum chamber  14  and a magnet array chamber  37 . As described earlier, a pressure differential can, and typically does exist between the vacuum chamber  14  and the magnet array chamber  37  during physical vapor deposition of the target  16  material onto the substrate. The reason for this is that the magnet array chamber  37  has typically been maintained at atmospheric pressure, while the vacuum chamber  14  is evacuated to a near vacuum state. This pressure differential between chambers causes a deflection “d” of the backing plate  18 , which is maximum at the center of backing plate  18  as illustrated in FIG.  19 . As described in FIG. 1, a pump port  88  can be included to reduce the pressure in magnet array chamber  37 , which reduces the bowing of the backing plate  18  (and therefore the target  16 ). In other words, the deflection “d” can be reduced by reducing the pressure in the magnet array chamber  37 . This, in turn, allows the utilization of a reduced thickness backing plate that increases the magnetic field seen by the target to enhance the sputtering process. The embodiment of FIG. 19 illustrates an alternative system and method for reducing the backing plate thickness that includes a center post  150  that supports the backing plate and constrains its vertical motion. The center post  150  can be used as a stand alone solution to reducing the backing plate  18  thickness, or can be used in conjunction with the reduction of the pressure differential between the two chambers. 
     As shown in FIG. 19, center post  150  is a stationary rod or post that is attached or secured at one end to a rigid section of the magnet array housing  34  (such as to a thick top plate as shown) at joint  152  and attached at its opposite end to the backing plate  18  at joint  154  through a welded or screwed joint. Joint  154  can be located at approximately the center of the backing plate  18 , while joint  152  securely connects the center post  150  to a rigid section of the magnet array housing  34 . It should be understood that while it is preferable for mechanical considerations to connect the center post  150  to the backing plate  18  at approximately the center of the backing plate  18 , the center post  150  can also connect to the backing plate at other locations. Each joint  152 ,  154  can be a welded or fastened joint (such as a screw or secure clamp connection). As shown, the center post  150  is preferably contained within hollow rotating motor shaft  54  that connects to motor  62  at one end and magnet array  20  at the opposite end. Motor  62  is coupled to and supported by the magnet array housing  34 . During physical deposition processing, the motor  62  will cause motor shaft  54  to rotate magnet array  20  for rotating magnetron plasma sputtering. The magnetic field generated from the rotating magnet array will pass through backing plate  18  to cause the sputtering of material from target  16  to the substrate within the vacuum chamber  14 . The motor shaft  54  is hollow to allow the rotation of magnet array  20  while providing a place for center post  150  to reside. As shown, the diameter of the hollow motor shaft  54  must exceed the diameter of the center post  150  to allow the motor shaft  54  to rotate without any interference. 
     Minimizing the diameter of the motor shaft  54  by minimizing the diameter or rotating cross section of center post  150  is preferred in order to maximize the effective size of magnet array  20 . For example, as the diameter of center post  150  increases, the diameter of the rotating motor shaft  54  must also increase to allow the motor shaft  54  to rotate during operation. As the diameter of motor shaft  54  increases, the actual amount of magnet array  20  surface area that faces the backing plate  18  is reduced, thus reducing the effective magnetic field seen by the target  16 , especially at the center of the target  16 , if all other factors remain constant. Minimizing the center post  150  diameter requires constructing the center post  150  from a rigid material capable of withstanding the vertical force (tensile force) that will occur during operation. The center post  150  could be a metallic rod made from, for example, stainless steel, titanium, or aluminum. The height of the center post  150  should be the approximately the distance from the inner top side of the magnet array housing  34  to the magnet array housing side of the backing plate  18  when a vacuum is not being pulled in the vacuum chamber  14 . The top of the center rod has negligible displacement as a result of pulling vacuum within the process chamber  14 . 
     As discussed previously, during operation of the PVD chamber, a pressure differential exists between the magnet array chamber  37  and the vacuum chamber  14  which are separated by the backing plate  18  and target  16 . The pressure differential will produce a deflection force on the backing plate  18 . Absent center post  150 , the backing plate  18  is only supported at its periphery so that the deflection force will cause the backing plate/target combination to bow out toward the vacuum chamber by a deflection “d” as indicated by the dotted line in FIG.  19 . Center post  150  will provide additional support to the backing plate  18  at the joint  154  at the center of backing plate  18  and will limit the center displacement. Thus, the deflection of backing plate  18  is now “d 1 ” as shown, and this new “d 1 ” deflection is less than the deflection “d” because the center post  150  provides a support from the magnet array housing  34  that supports the center of backing plate  18 . As shown in FIG. 19, the center post  150  transfers and reduces the maximum deflection from a single location at the center of the backing plate  18  (as shown by “d”) to a ring located between the center of the backing plate  18  and the outer diameter of the backing plate  18  (shown as “d 1 ” at two places). By using the center post  150  to support the backing plate  18  from the magnet array housing  34 , the deflection force results in a substantial reduction in the maximum deflection of the backing plate  18  allowing the use of a thinner backing plate  18 . The thinner backing plate, in turn, allows more of the magnetic field to reach the target and therefore enhances the sputtering operation. 
     Although the present invention has been described in detail, it should be understood that various changes, substitutions and alterations can be made hereto without departing from the spirit and scope of the invention as defined by the appended claims.