Abstract:
A magnetron sputtering electrode for use within a magnetron sputtering device that includes a cathode body, a target receiving area defined adjacent the cathode body, a plurality of magnets received within a magnet receiving chamber and an anode shield surrounding the cathode body. At least a portion of a coolant passageway is defined by the anode shield, whereby the coolant passageway is adapted to receive coolant to circulate therethrough thereby cooling the anode shield.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application No. 60/676,231 entitled “High Power Cathode,” filed on Apr. 29, 2005, which is hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a magnetron sputtering apparatus and, more particularly, to a high power cathode, which provides better uniformity in the material deposited, particularly in the area of semi-conductor manufacturing. 
     2. Description of Related Art 
     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, 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. 
       FIG. 1  is a sectional side view of a prior art magnetron sputtering electrode  1  that includes a target  2  held in place by a clamping ring  4 , which in turn, is affixed to a top of the cathode body  10  via a plurality of screws  6  and  8 , respectively. The electrode  1  also includes a sealing plate  12 , which forms a seal between the cathode body  10  and the sealing plate  12  via an O-ring  14 . The water chamber  16  is defined between the cathode body  10  and the sealing plate  12  and includes a magnetic assembly comprising a magnetic field shaping ring  18 , a plurality of magnets  20  and  22 , a base ring  24  and a central magnet  26  centered within the magnetic field shaping ring  18 . The magnets  20 ,  22  and  26  are generally standard magnets that can produce a residual flux density of about 38 MGO (Mega Gause Orstead). The electrode  1  further includes a water inlet supply  28  and a water outlet  30  for allowing cooling water to flow through the water chamber  16 . The electrode  1  also includes a ring-shaped anode shield  32  that is affixed to an anode shield support  34  via a plurality of screws  36  and  38 , respectively. The anode shield support  34  is affixed to a base plate  40  via a plurality of screws  42  and  44 . An insulating plate  46  is interposed between base plate  40  and sealing plate  12 , wherein the insulating plate  46  electrically insulates the cathode body  10  and the sealing plate  12  from the base plate  40 . A water-tight seal is maintained between the insulating plate  46  and the sealing plate  12  by an O-ring  48  interposed therebetween. A power cable  50 , which is affixed to the sealing plate  12  via a screw  52 , supplies electric current to the cathode body  10  over the interface of the cathode body  10  with sealing plate  12  in the vicinity of O-ring  14 . 
     There are several problems that exist with respect to prior art sputtering devices. Because the sputtering process produces intense heat, the power rating of the sputtering device is limited primarily by the ability to cool the device by means of flowing water. Overheating of the device due to inefficient cooling will cause stress cracks to form in highly stressed target materials, such as ceramic and brittle metals, which can cause arcing and short outs. This heat buildup causes higher electrical resistance, which impedes the flow of electrons thereby yielding lower deposition rates than would otherwise have been possible if such heat were not present. Further, because the prior art anode shield  32  is above the target surface level, buildup of target material occurs on a surface of the anode shield  32 , which has a tendency to flake off and fall back onto the target  2  thus causing a short out. 
     In semi-conductor manufacturing, electrical components, for example, resistors, transistors, and capacitors, are commonly mounted on circuit panel structures, such as printed circuit boards. Circuit panels ordinarily include a generally flat sheet of dielectric material with electrical conductors disposed on a major, flat surface of the sheet, or on both major surfaces. The conductors are commonly formed from metallic materials, such as copper and serve to interconnect the electrical components mounted to the board. Where the conductors are disposed on both major surfaces of the panel, the panel may have via conductors extending through holes (or through vias) and the dielectric layer so as to interconnect the conductor on opposite surfaces. These vias can be on the order of sub-atomic sizes. Presently, prior art electrodes, such as electrode  1  shown in  FIG. 1 , can typically provide continuous discharge at power levels of 250 watts/in 2  thus resulting in non-uniform coating C of a via V of a substrate S such as shown in  FIG. 2 . 
     Plasma density refers to the number of gaseous ions retained within the magnetic field. With an increase in plasma density, higher power such as in the range of 500-1000 watts/in 2  can be supplied allowing for higher deposition rates. However, the typical prior art sputtering electrode  1  operating in a range of 500-1,000 watts/in 2  can only be achieved through pulsing the electrode instead of a continuous discharge, or otherwise the electrode will quickly burn out. This pulsing of the electrode at power levels ranging from 500-1,000 watts/in 2  also results in a non-uniform coating C of the via V of the substrate S as shown in  FIG. 2 . 
     It has been shown that a continuous pulse discharge at power levels in the range of 500-1,000 watts/in 2  provide sputtering that is more orderly and straight resulting in a coating C of uniform thickness of a via V′ of a substrate S′ as shown in  FIG. 7 . Therefore, there is a need for a robust high power cathode (i.e., electrode) that has a more efficient cooling arrangement than that of the prior art electrode such that the cathode can provide continuous discharge at high power as opposed to a pulsing arrangement. 
     SUMMARY OF THE INVENTION 
     The present invention provides for a magnetron sputtering electrode for use within a magnetron sputtering device that includes a cathode body having an upper surface and a lower surface, a back plate secured to the upper surface of the cathode body, a target retainer engaged with the back plate, an insulator plate secured to the lower surface of the cathode body, a base plate secured to the insulator plate, wherein the back plate, the insulator plate and the cathode body define a magnet receiving chamber therein. A plurality of magnets are received within the magnet receiving chamber, wherein the magnets cooperate to generate magnetic flux lines which form a closed loop magnetic tunnel adjacent to a top surface of the target. The electrode further includes an anode shield secured to the base plate, wherein the anode shield surrounds and contains the cathode body, the back plate and the insulator plate. The anode shield also defines a plurality of recesses, and a side wall secured to the anode shield and covering the recesses, wherein the recesses define a passageway for allowing coolant to circulate therethrough. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional side view of a prior art magnetron sputtering electrode; 
         FIG. 2  is an elevational view of a substrate having a via with a coating of non-uniform thickness deposited thereon using a prior art magnetron sputtering electrode; 
         FIG. 3  is a perspective view of a magnetron sputtering electrode made in accordance with the present invention; 
         FIG. 4  is a top plan view of the sputtering electrode shown in  FIG. 3 ; 
         FIG. 5  is a sectional view of the sputtering electrode shown in  FIG. 4  taken along lines V-V; 
         FIG. 6  is a sectional view of the sputtering electrode shown in  FIG. 4  taken along lines VI-VI; and 
         FIG. 7  is an elevational view of a substrate having a via with a coating of uniform thickness deposited thereon using the magnetron sputtering electrode of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIGS. 3-6 , the present invention provides for a magnetron sputtering electrode  70  for use within a magnetron sputtering device that includes a target  2 , a cathode body  72  having an upper surface  74  and a lower surface  76  and a ring-shaped anode shield  100  surrounding the cathode body  72 . Target  2  is held in place by an annular or ring-shaped target clamping ring  78 , which also functions as a cathode seal. The electrode  70  is preferably annular shaped, but may also be rectangular shaped in which the target  2 , clamping ring  78  and anode shield  100  would be shaped to fit the shape and size of the electrode  70 . The clamping ring  78  is affixed to the upper surface  74  of the cathode body  72  via a plurality of fasteners F about the circumference of the clamping ring  78 . Interposed between the clamping ring  78  and the upper surface  74  of the cathode body  72  is a metallic back plate  80 , wherein the target  2  is affixed to the back plate  80 , and the back plate  80  is sealed to the cathode body  72  via a seal O such as an O-ring. The electrode  70  also includes an insulating plate  82  and a base plate  98 , wherein the insulator plate  82  is sandwiched between the lower surface  76  of the cathode body  72  and the base plate  98  thus forming a water tight seal via a seal O interposed therebetween. The insulator plate  82  is preferably made of ceramic, such as alumina or MACOR®. These ceramic insulators are capable of withstanding the intense heat caused by the sputtering process without warping or cracking. 
     The cathode body  72  cooperates with the insulator plate  82  to form a coolant chamber or magnet receiving chamber  84 , which is made water tight via a seal O interposed therebetween. Contained within the chamber  84  is a magnet assembly, which may include annular magnet  88  and a center magnet  90 . This magnet assembly is similar to the magnet assembly described in U.S. Pat. Nos. 5,736,019 and 6,171,461, which are hereby incorporated by reference in their entirety. Coolant such as cooling water enters chamber  84  via an inlet supply  92  and exits the chamber  84  via an outlet  94 . The magnets  88 ,  90  are preferably high energy magnets, such as, for example, rare earth magnets (Samarium Cobalt or Neodymium Iron Boride) that have an MGO for a low mass of magnetic material as compared to a standard grade magnet such as an Aluminum Nickel Cobalt magnet for the same mass. Preferably, the high energy magnets  88 ,  90  can produce a high residual flux density greater than 40 MGO, preferably in the range of 40 to 50 MGO. 
     Electric current is supplied to the cathode body  72  via a power cable  96 , which is affixed directly to the cathode body  72  via a fastener F. The direct connection of the power cable  96  to the cathode body  72  provides for low resistivity and impedance, and eliminates the oxidation problem associated with the prior art electrode  1  in which the power connection is made to the sealing plate  12  and then to the cathode body  10 . 
     The anode shield  100  having an upper end  102  and a lower end  104  surrounds the cathode body  72  and is affixed about its circumference to the base plate  98  via a plurality of fasteners F. The upper end  102  of the anode shield  100  is chamfered to form a contoured top portion  106 . The contoured top portion  106  is shown angled on one side away from the target  2 , wherein the apex of the top portion  106  is spaced from the target  2 . The shape of the contoured top portion  106  may include, but not limited to sloped, conical, parabolic, convex, and concave shapes. Further, the apex of the top portion  106  of the anode shield  100  is shown slightly below a top surface TS of the target  2 , but may also be positioned at the same level as the target surface TS. The position of the upper end  102  of the anode shield  100  at or below the target surface TS minimizes the buildup of target material on the anode shield  100 , and the use of such contoured shapes allows for any buildup of the target material on the anode shield  100  to flake off in a direction away from the target surface TS thus preventing short outs. 
     Adjacent the anode shield  100  is a sidewall  108  secured to a portion of the anode shield  100  between the upper end  102  and the lower end  104 . The anode shield  100  also defines a plurality of recesses  110 , wherein the sidewall  108  covers the recesses  110  thereby defining a plurality of axially spaced, radially extending coolant passageways W as defined by a plurality of planar sections taken across the anode shield  100 , the passageways W positioned between the anode shield  100  and the sidewall  108 . See  FIGS. 5 and 6 . The passageways W, which are positioned about the cathode body  72 , are spaced between the upper end  102  and the lower end  104  of the anode shield  100 . Coolant enters the passageways W of the anode shield  100  via an anode inlet  112  and exits the passageways W via an anode outlet  114 . A coolant coupling  116  (shown in  FIGS. 3 and 6 ) allows coolant to flow in a direction from the upper end  102  to the lower end  104  of the anode shield  100 , thereby cooling the anode shield  100  between the upper end  102  and the lower end  104  thereof. The passageways W generally have one or more diverters or baffles B (shown in  FIGS. 5 and 6 ) in order to create greater turbulent flow characteristics when coolant circulates through the passageways W. These baffles can be ridges and bumps or any other arrangement positioned in the passageways W to mix the water, as it flows through the passageways W to improve cooling via conduction and convection. The turbulent flow of the coolant allows for more efficient cooling of the anode shield  100  in contrast to laminar flow. The coolant may be, for example, water, air or refrigerant. 
     The electrode  70 , which can have a field strength on the order of one telsa, can provide continuous discharge at high power in the range of 500-1,000 watts/in 2  without burning out. This is due to the fact that electrode  70  has cooling both at the anode shield  100  and at the center of the cathode body  72 . Because of the additional cooling, continuous discharge at higher powers can be achieved with the electrode  70  thus permitting higher deposition rates resulting in a more uniform coating C′ of a via V′ of a substrate S′ as shown in  FIG. 7 . 
     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 appended claims and any and all equivalents thereof.