Abstract:
A low temperature target and backing plate bonding process and assemblies made thereby. A plurality of male projections ( 8 ) are formed in one member ( 2 ) of the assembly with a plurality of corresponding female recesses ( 9 ) formed in the other member ( 4 ). The assembly is bonded by conventional techniques around the peripheral boundary ( 25 ) that surrounds the male and female portions ( 8,9 ). The assembly is then pressure consolidated at low temperature so that the projections ( 8 ), circumscribed by the bonded zone, are force fit into the female recesses ( 9 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Priority filing benefit of (1) International PCT application PCT/US00/18968 filed Jul. 12, 2000, and published under PCT 21(2) in the English language and (2) U.S. provisional application Ser. No. 60/143,314 filed Jul. 12, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     The present application pertains to a low temperature sputter target/backing plate joining technique and to assemblies made thereby. 
     In my U.S. provisional patent applications No. 60/099,981, filed Sep. 11, 1998 and No. 60/129,559, filed Apr. 16, 1999, a target and backing plate are provided wherein the harder material of the two is machined or otherwise formed so as to have a plurality of ridges or other salient surface portions thereof. These ridges or salient portions are formed along the interior surface of the target or backing plate. The ridged surface is then placed alongside the mating surface of the other member of the assembly along the target/backing plate interface wherein joining will occur. 
     The peripheral portion of the interfacial surface assembly, surrounding the ridges or salient portions, is joined by conventional means such as electron beam welding, TIG welding, friction welding, soldering, brazing, etc., preferably under vacuum. The assembly is then pressed at a low temperature, preferably at room temperature. 
     The projections or ridges formed along either the target or backing plate bend upon penetration into the mating metal surface along the target/backing plate interface and form an interlocking grip over the softer metal on the opposing mating surface. 
     SUMMARY OF THE INVENTION 
     In this invention, a target and backing plate are provided wherein both materials are similar in mechanical properties and both are machined or otherwise formed so as to have a plurality of ridges and grooves or other salient surface portions thereof. These ridges or salient portion are formed along the interior surface of the target or backing plate. The ridged surface is then placed alongside the mating surface (having appropriately positioned mating members) of the other member of the assembly along the target/backing plate interface wherein joining will occur. 
     The peripheral portion of the interfacial surface assembly is joined by conventional means such as electron beam welding, TIG welding, friction welding, soldering, brazing, etc., preferably under vacuum. The assembly is then pressed at a low temperature, preferably at room temperature. 
     The projections or ridges formed along either the target or backing plate penetrate into the mating members along the target/backing plate interface. The projections penetrate into the grooves on the opposing mating surface. 
     The projections and grooves have different sizes so that after penetration, a force or friction fit joint will be formed. 
    
    
     Other objects and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic cross sectional view of a target and backing plate assembly showing the friction fit joining mechanisms in the form of cylindrical male projections ready for insertion into cylindrical bores; 
     FIG. 2 is a schematic cross section showing another embodiment of the joining members having square male projections in one member and correspondingly square shaped recesses formed in the other member, 
     FIG. 3 is a schematic cross sectional view of the assembly shown in FIG. 1 in the mating or joined position; 
     FIG. 4 is a schematic cross sectional view of the assembly shown in FIG. 2 in the mating or joined position; 
     FIG. 5 is a partially exploded perspective view of the assembly of FIG. 1 before bonding, and 
     FIG. 6 is a partially exploded perspective view of the assembly of FIG. 2 before bonding. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Turning first to FIG. 1 there is shown a target/backing plate assembly. The assembly comprises a target  2  having a top side  23  carrying metal or metal alloy that, in accordance with conventional sputtering methods, will be ejected from the target via ionic bombardment and will travel to and coat the desired substrate. 
     A backing plate  4  is provided under the target, with the bottom side  11  of the target adapted to mate with the top side  13  of the backing plate to define an interfacial surface area  28 . Commonly, a heat exchange fluid such as water is circulated adjacent the bottom side  21  of the backing plate so as to cool the assembly during its sputtering operation. 
     As shown in the FIG. 1 embodiment a plurality of cylindrical male projections  8  are machined into the surface  11 . The surface  13  is provided with cylindrical female bore members  9  of smaller diameter than the diameter of the male projections  8 . 
     In some cases, it is desired to provide a filler material  6 , such as an Al 4%Si alloy or other suitable alloy, in the form of a ring or the like, adjacent the peripheral border  25  of the assembly between the target and backing plate. The filler material  6  enhances bonding of the target to the backing plate as shall be explained hereinafter. 
     The assembly is first bonded around the peripheral border  25 . This initial bonding along the peripheral border of the assembly may be achieved by conventional means such as by E-beam welding under vacuum conditions, TIG welding, and friction welding and the like. Preferably, the bonding of the peripheral boundaries of the target and backing plate is performed via E-beam welding under vacuum conditions. 
     After the peripheral bonding, the assembly is consolidated, via pressure application thereto, at pressure of about 50 tons-5,000 tons; preferably less than about 1,000 tons, under low temperature conditions. The male members  8  are friction fit into the corresponding female bores  9 . 
     After the low temperature pressure consolidation, the assembly may be subjected to a low temperature annealing step conducted at temperatures of about room to 400° C. for a period of 0.5 to 4 hours. This will help ensure adequate adhesion of the pressure consolidated surfaces. 
     The phrase “low temperature pressure consolidation” refers to pressure consolidation that may occur at temperatures of less than about 50% of the melting temperature of the lower melting member of the target and backing plate. Preferably, this temperature is less than about 200° C.; most preferably at about room temperature up to about 38° C. 
     Turning now to FIG. 2, there is shown another embodiment of the invention wherein the target and backing plate may be joined by low temperature pressure consolidation. Here, the male projections  8  are in the form of elongated square cross sectioned members that are force fit into square recesses  9  formed in the backing plate  4 . 
     FIGS. 3 and 4 show the assemblies of FIGS. 1 and 2 respectively in their mated positions in which, by reason of the low temperature pressure consolidation, the projecting male members are frictionally free fit in their mating, female recesses and in which the target and backing plate are bondingly joined. 
     FIG. 5 shows, in perspective, the male and female coupling members of the FIG. 1 embodiment. Male members  8  are in the form of a cylindrical dowel-like projection adapted for mating with the cylindrical bores  9 . The bores  9  have a smaller id than the od of the projecting male members  8 . As shown, the male members  8  and the bores  9  are arranged in a pattern of concentrically arranged annular rows. 
     FIG. 6 depicts the male/female mating members shown in the FIG. 2 embodiment. Here, the male members  8  are in the form of elongated square cross-sectioned studs adapted for reception into the smaller openings  9 . 
     In one target/backing plate assembly bonding in accordance with the invention, rectangular cross-sectioned male projections were used and frictionally fit into corresponding rectangular female openings. The target and backing plate were both copper and the female openings were about 0.010″ smaller than the male members. The male and female members were machined into the respective surfaces. The target/backing plate assembly was pressed so that the male and female coupling members were friction fit. After pressing, the peripheral portion of the assembly was welded via electron beam. After the welding step, a final machining operation was performed so that the welded area was not removed. 
     The locking joint of the invention can therefore be described as a friction fit joint formed between a projecting male member disposed on one member and a corresponding female opening formed in the other member. 
     While the methods described herein, and the target/backing plate assemblies produced in accordance with the methods, have been described with certain specific forms and certain modifications thereof, it will be appreciated that a wide variety of other modifications can be made without departing from the scope and spirit of this invention as defined in the appended claims. It is also to be kept in mind that reference to a metal or metal component herein also includes reference to alloyed forms of the stated metal. 
     Although copper to copper bonding is specifically mentioned, other metals can benefit from the invention. For example, Al target to Al backing plates may be joined using the methods herein disclosed. Other target to backing plate combinations are possible provide the mechanical characteristics of the metals such as hardness and thermal expansion, are similar. 
     The present invention provides advantage over diffusion bonding and other joining techniques that require higher temperatures in the consolidation. Higher temperature conditions sometimes result in undesirable grain growth in the target metal.