Patent Document

CROSS-REFERENCE TO RELATED APPLICATIONS 
   Not applicable 
   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   Not applicable 
   INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC 
   Not applicable 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates generally to systems for coating objects by sputtering deposition, and more particularly to an improved sputtering cathode assembly having features which greatly improve the duration of useful or working time afforded before the target material must be replaced. 
   2. Description of Related Art 
   The sputtering deposition of materials onto objects to be coated with the sputtered material is well known and includes the process of material removal from a target material by its bombardment with highly energized ions formed after high energy electrons are emitted from the target material by placing a high RF or d.c. voltage between the target and the objects to be coated. These emitted electrons ionize processed gas such as argon placed within a vacuum chamber after it has been substantially evacuated of air up to 100 m Torr vacuum pressure. 
   The processed gas ions then form a plasma, an electrically neutral association of electrons and positive ions. The plasma is caused by the emitting of electrons from the target material. The plasma ions accelerate and strike the target causing atoms to be ejected from the target material which is then deposited onto the objects having previously been placed within the vacuum chamber. 
   Ideally, the duty cycle of each fresh target of each cathode assembly should last until a significant portion, i.e. 40% to 45% of the target has been deposited onto objects within the vacuum chamber. However, the duty cycle of the target attached to the cathode assembly is so severe that physical deformities in the target and the supporting structure associated with the cathode assembly rapidly deteriorate, requiring premature replacement of the target material. The expense of reconditioning each cathode assembly, including the target material, is substantial both with respect to maintenance, replacement components and system downtime. 
   Commercially available sputtering cathode assemblies have a threaded hole or use a HELICOIL E-Z LOK as a threaded insert to attach target clamps against the edge of the target positioned directly atop a copper body or top plate of the cathode assembly. Typically within only hours of operation, the target bolts begin to loosen, the HELICOILS become damaged or the bolt is simply sheered off. When the target must be changed, most of the HELICOILS require replacement or the threaded inserts seize and require replacement, usually causing damage to the copper top plate itself. Special tools are required to disassemble and remove damaged HELICOILS and, if damage to the top plate is sufficiently severe, it must be totally replaced. 
   Sputtering cathode assemblies require that the target and the cathode body be cooled by water to prevent meltdown or damage to the sputtering magnets contained within the magnet module positioned adjacent the top copper plate. To seal off the water cavity, commercially available cathode assemblies must have the target clamped tightly to the cathode body, leaving little or no room for the target to expand. At low duty cycles of low power density, this issue is not sufficiently severe to represent a reduction in duty cycle. However, at higher power densities, the duty cycle is substantially reduced. 
   There are two ways that a target may be cooled: (a) by direct cooling wherein the back of the target is used to seal the water jacket or (b) indirect cooling utilizing a thin copper top plate or backing plate against which the target is directly clamped. Even with the indirect technique or method, the target is still required to be tightly clamped to the thin backing plate to prevent leakage of water from the water passageway. Thicker backing plates which are sufficiently strong to withstand warpage during high power input levels interfere with heat transfer and reduces target thickness through the thicker top plate causing excess thermal expansion of the target due to overheating. At low power densities of less than 200 watts/in 2  are viable under these cooling techniques. However, in applications that require cathodes to work under a duty cycle of densities of 300 watts/in 2  or higher, thermal expansion of the target during the duty cycle causes the target clamps to loosen, leading to water leakage. The tightening of target clamps after this occurs is usually not sufficiently remedial to stop water leakage as the target itself is typically warped as well from the thermal duty cycle. 
   Under these adverse conditions, commercially available targets will only last about 24 hours at higher power levels whereas, the target contains sufficient material for vacuum deposit which could last at least ten working days otherwise. 
   Commercially available cathode assemblies use either a silver braised water tube or a female pipe tube threaded into the back or base plate of the cathode body. The silver braised water tube over time and misuse in handling can break and require a costly replacement. The threaded female pipe thread over time will also weaken, causing permanent damage and requiring costly replacement of the entire cathode body base plate. 
   The present invention addresses and substantially improves upon all of the above-described shortcomings currently being experienced by the operator of sputtering deposition systems to greatly increase the longevity of the duty cycle afforded by each fresh sputtering cathode assembly containing a fresh target. Not only is the operative duty cycle extended, but the reconditioning or refurbishing of each cathode assembly when replacing the mostly expended target is greatly facilitated and requiring substantially less time and replacement costs associated therewith. 
   BRIEF SUMMARY OF THE INVENTION 
   This invention is directed to a sputtering cathode assembly attachable to a cathode mounting plate for a thin-film vapor deposition chamber. The cathode assembly includes a magnet module and a cathode body generally coextensive with and sealingly housing the magnet module and defining a water channel between a top plate of the cathode body and a cooling channel plate of the magnet module. An elongated target is releasably connected atop and coextensive with the top plate and secured in place by threaded fastener engagement between a target clamp and an edge portion of the cathode body whereby the target is replaceable without disassembly of the cathode body. Unique replaceable elongated fastener receiving inserts releasably secure said target against the target plate to effect target replacement without disassembly of the cathode body. 
   It is therefore an object of this invention to provide a sputtering cathode assembly for use in a sputter coating vacuum deposition system which affords a greatly enhanced duty cycle before reconditioning and/or replacement is required. 
   Still another object of this invention is to provide a sputtering cathode assembly which will facilitate the vacuum vapor deposition of substantially all of the target material before replacement is required. 
   Yet another object of this invention is to provide a sputtering cathode assembly in which the target material may be easily removed and replaced without upsetting the sealed condition of the cooling water jacket. 
   The present invention further provides a new drop-in insert for securing the target which is easily replaceable and prevents damage to the cathode body base plate. 
   Still another object of this invention is to provide a split cathode body which does not require that the clamped target form a water seal with the water cavity itself so that the water is completely isolated from the vacuum chamber and the target is not required to be tightly clamped to seal the water cavity itself. 
   Yet another object of this invention is to provide a target and mating target clamp structure which controls the direction of thermal expansion of the target during the duty cycle to eliminate damage to the target clamps positioned at the ends of the target. 
   Still another object of this invention is to provide an O-ring sealed water inlet/outlet tube which is easily replaceable and which avoids damage caused to the cathode body itself when fatigue or failure of the water inlet/outlet tube might occur. 
   In accordance with these and other objects which will become apparent hereinafter, the instant invention will now be described with reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
       FIG. 1  is a top plan simplified schematic view of a sputter coating deposition system including the present invention. 
       FIG. 2  is a broken perspective view of the interior of the vacuum deposition chamber showing the present invention. 
       FIG. 3  is a simplified top plan schematic view of the vapor deposition chamber also showing the present invention. 
       FIG. 4  is a perspective view of the present invention. 
       FIG. 5  is an exploded end elevation view of the cathode assembly of  FIG. 4 . 
       FIG. 6  is a side elevation view of a portion of the cathode assembly in partially exploded view. 
       FIG. 7  is an enlarged longitudinal section view of one end of  FIG. 6 . 
       FIG. 8  is an enlarged cross section view of the invention shown in  FIG. 6 . 
       FIG. 9  is an enlarged longitudinal section view of the center portion of the invention as shown in  FIG. 6 . 
       FIG. 10  is a top plan view of the new target clamp. 
       FIG. 11  is an enlarged view of area C in  FIG. 10 . 
       FIG. 12  is a top plan view of the new target of  FIG. 6 . 
       FIG. 13  is an end elevation view of  FIG. 12 . 
       FIG. 14  is an enlarged view of area E of  FIG. 12 . 
       FIG. 15  is an elevation view of the new water inlet/outlet fitting of  FIG. 6 . 
       FIG. 16  is an end view of  FIG. 15 . 
       FIG. 17  is a longitudinal section view of the new drop-in insert for target clamping. 
       FIG. 18  is an end plan view of  FIG. 17 . 
       FIG. 19  is a top plan view of the magnet module. 
       FIG. 20  is a section view in the direction of arrows  20 — 20  in  FIG. 19 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to the drawings, and initially to  FIGS. 1 to 3 , a typical sputtering deposition system is shown generally at numeral  10  in  FIG. 1  and includes a sputter coating apparatus  12  which generally includes a vacuum chamber  14  and two spaced oppositely facing longitudinally extending polymerization apparatus  16 . The polymerization apparatus  16  are described in detail in U.S. Pat. No. 5,895,531 which is incorporated herein by reference. 
   The sputter coating apparatus  12  also includes two spaced oppositely facing sputtering cathode assemblies  20  which are positioned as best seen in  FIGS. 1 and 3  adjacent to the opening  26  for door  22  or  24  of the vacuum chamber  14 . Each of these sputtering cathode assemblies  20  is generally coextensive with the longitudinal axis of the elongated vacuum chamber  14  itself. The apparatus  12  further includes swingable or pivotably closable doors  22  and  24  which are hingedly connected about upright axes  36  and  38 , respectively and, when individually closed, seal the interior  18  of the vacuum chamber  14 . 
   The sputtering system  10  further includes a plenum  28  which facilitates the evacuation of air through grill  40  from the interior  18  of chamber  14  to draw the vacuum atmosphere within the chamber  18  down to in the range of 100 m Torr pressure level during each vacuum deposition cycle. A polypod  32  is operably connected to a refrigeration unit  34   a . A rotary vein pump  30 , interconnected with plenum  28 , effects the depressurization the interior volume  18 . Polymer reservoir  34 , interconnected to the polymerization apparatus  16  adjacent thereto, transfers the polymerization material to each of the polymerization apparatus  16 . A driving gear  50  at the bottom of the chamber  14  as seen in  FIG. 2  causes an upright reel assembly with objects loaded thereon (not shown) to rotate within the interior  18  at a desired rate of rotation during system operation and material deposition. 
   Referring now to  FIGS. 4 to 8 , the improved sputtering cathode assembly of the present invention is there shown generally at numeral  20  and includes a replaceable target  52  having a thickness of ½″ and formed of elongated flat deposition material such as pure aluminum or other sputter materials. A notched upper perimeter  54  is provided to receive target clamps  48  to hold the target  52  atop a top plate  56  of a two-part cathode body which also includes a cathode body base plate  76 . 
   The top plate  56  is formed of solid copper material and has a thinner central portion  58  ⅛″ thick and enlarged perimeter edges  60  which are substantially thicker (½″) than the central portion  58 . The top plate  56  and the cathode body base plate  76  are held together in sealed fashion by the O-ring therebetween shown in  FIG. 8  by spaced threaded fasteners  147  engaged into aligned female threads  78 . 
   The target  52  is held securely against the outer surface of the top plate  56  by target clamps  48  which engage over the notched margin  54  of the target  52  and are held in place by threaded fasteners  146  slidably fit through champhered holes  106 . This aspect of the invention presents a substantial improvement in reducing the cost of refurbishing of cathode assemblies  20  generally. These threaded fasteners  146  threadably engage into female threads  122  the drop-in inserts  120  as best also seen in  FIGS. 17 and 18 . One end  124  of these inserts  120  is enlarged forming a thin head having anti-rotation flats  126  machined on opposite sides so as to engage against the machined slot formed into one edge margin of the cathode body base plate  76  at  80 . As seen in  FIGS. 5 ,  6 ,  7  and  8 , an elongated retention strip  142  is held against the enlarged ends  124  by threaded fasteners  144  for assembly convenience. Because there is no water sealing requirement of the target  52  against the top plate  56 , the tightening or clamping requirement of this arrangement is reduced and as noted in the Background, previously threaded structure formed into the edge of the cathode body base plate or HELICOILS inserted therein have been eliminated altogether so that the threaded engagement is only established between the easily replaceable drop in insert  120  and the threaded fastener  146 . 
   Housed within the cavity defined between the top plate  56  and the cathode body base plate  76  is the magnet module  61  seen best in  FIG. 5  which includes a cooling channel plate  62  preferably machined of brass and magnet module base  64  preferably formed of stainless steel. This cooling plate channel  62  and magnet module base  64  are held together by threaded fasteners  168  seen in  FIG. 19 . The magnet module  61  also includes elongated lengths of rare earth permanent magnet material  160 ,  162  and  164  which are available commercially. These magnets  160 ,  162  and  164  are positioned to be held as shown between the cooling channel plate  62  and magnet module base  64  as best seen in  FIG. 8 . 
   The exposed surface of the cooling channel plate  62  as best also seen in  FIGS. 19 and 20 , again formed of preferably brass material, includes two parallel generally coextensive water channels  152  and  154  which receive water flowing in the direction of the arrows from the water inlet  94  toward and out through the water outlet  94   a . Turbulence steps  156 ,  158  typical on each side of the raised central portion of each water channel  152  and  154  serve to disrupt laminar flow of water so as to enhance the cooling effect of water passing therethrough. The other side of the water passageway  152  and  154  is defined by the facing surface of the central portion  58  of the top plate  56 . The cooling channel plate  62  and the magnet module base  64  are held together by fasteners  168  seen in  FIG. 19  while the entire magnet module  61  is held in place against the cathode body plate  76  by threaded fasteners  166 . By this arrangement, the target  52  may be removed and serviced or replaced without disrupting the sealed relationship between the top plate  56  and the cathode body plate  76  and the intact magnet module  61 . 
   An improved water inlet and outlet fitting is also provided at  66  as best seen in  FIGS. 15 and 16 , and includes an elongated inner tubular passageway  70  defined by a main threaded section  72  and a smaller in diameter distal tubular section  74 . An enlarged flange  68  having alignment flats  75  is provided for mounting the fitting  66 . The flange  68  as best seen in  FIG. 7  is positioned in alignment and registry with the water inlet  94  (and with the water outlet  94   a  at the opposite end of the magnet module  61 ). The flange  68  is entrapped within a mating cavity formed into the cathode body base plate  76  and sealingly engaged against the O-ring as shown in  FIG. 7 . Thus, no fasteners are required to retain the fitting  66  in the operative position there shown. Note that the water aperture  140  formed into the magnet module base  64  is enlarged over the size of the inlet  94  so as to create additional water turbulence for enhanced heat transfer between the turbulent water flow and the heated cooling channel plate  62  and top plate  56 . 
   Referring now to  FIGS. 10 to 14 , another important improvement of the present invention is there shown. In commercially available prior art systems, the target, despite being clamped in place by closely spaced highly tightened fasteners connected through the target clamps, will expand in length due to extreme temperatures experienced during the vapor deposition cycle. As Murphy&#39;s Law would have it, one end or the other is slightly more tightly clamped so that the thermal expansion will typically occur in only one direction or from one end of the target toward the opposite end. This means that the prior art targets will expand in only one direction and will push sufficiently against the fasteners and target clamps at the opposite end so as to potentially distort or even snap the fasteners completely off due to the power of the expansion forces generated within the target. 
   To avoid this potential damaging effect of the linear thermal expansion of the improved target  52 , notches  112  are formed at the center point of each side margin  54  of the target  52  as seen in  FIGS. 12 and 14 . These notches  112  closely matably engage with tabs  108  formed into the locking flange of the target clamps  48  while side margin  54  matably engages with edge groove  110 . By this arrangement, when fully clamped in place, the notches  112  are held stationary by tabs  108  so that thermal expansion occurs in either direction D about the transverse center of the target  52  which has been shown to eliminate any fastener distortion or fracture at the ends of the target  52 . 
   The entire cathode assembly  20  in one aspect also may be described as including a cathode mounting plate  84  which is generally coextensive therewith. However, this cathode mounting plate  84  must remain electrically isolated from the cathode body and its cathode body base plate  76 . This is accomplished by a NYLON, TEFLON or DELRON annular or ring-shaped seal  82  associated with each fitting  66  and which is of sufficient thickness, when positioned within aperture  85 , so as to electrically space and create a gap  92  between the cathode body base plate  76  and the cathode mounting plate  84 . To retain this arrangement, jamb nut  90  is threadably engaged onto threads  72  of fitting  66 . A backing plate  87 , also formed of nonmetallic material such as TEFLON or DELRON is positioned against a power connector  96  attachable to a source of electrical power. The jamb nuts  90  threadably engaged onto external threads  72  of water fittings  66  at each end of the cathode assembly  20  provide the only means for securement between the cathode mounting plate  84  and the cathode body base plate  76 . 
   To attach the cathode assembly  20  into operative position within the vacuum chamber  12  as previously described in  FIGS. 1 to 3 , a cathode-mounting flange or frame  150  as best seen in  FIGS. 7 and 8  is also provided. The threaded fastener engagement between apertures  86  and threaded fastener  93  is provided for this purpose and the interface between the cathode mounting plate  84  and the cathode mounting flange  150  is sealed by o-ring  170 . 
   Referring now to  FIGS. 6 and 9 , because of the great potential for distorting the target  52  during the extreme temperature duty cycle it must endure, a central strengthening fitting  100  is also provided. This strengthening fitting  100  includes an enlarged flange  101  which is trapingly engaged and held in sealed fashion by the O-ring shown between the magnet module base  64  and the cathode body base plate  76 . An annular nonmetallic non-conductive isolator disk  136  sealingly engaged by O-rings as shown in  FIG. 9  is also provided to maintain the electrical gap  92  between the cathode mounting plate  84  and the cathode body base plate  76 . A mounting bracket  102  is held in position by threaded fasteners into a mating cavity and threaded apertures formed into the central portion of the cathode mounting plate  84  as seen in  FIG. 9  while a jamb nut  104  is threadably engaged onto the distal end of the fitting  100  with nonconductive spacer washer  138  therebetween as shown. 
   Because of the extreme weight of the cathode assembly  20 , handles  88  are also provided attached to the cathode mounting plate  84  in spaced relation by spacers  89  and fasteners  91  as best seen in  FIGS. 5 and 6 . 
   While the instant invention has been shown and described herein in what are conceived to be the most practical and preferred embodiments, it is recognized that departures may be made therefrom within the scope of the invention, which is therefore not to be limited to the details disclosed herein, but is to be afforded the full scope of the claims so as to embrace any and all equivalent apparatus and articles.

Technology Category: 5