Abstract:
A method of producing a sputter target assembly including a metal target attached to a metal-matrix-composite backing plate and sputter target assemblies made thereby. The method includes hot isostatically pressing a silicon carbide-aluminum powder composition to form a backing plate while simultaneously bonding the powder composition to a metal target to form a diffusion-type bond between the target and the backing plate such that the target assembly possesses extremely high resistance to warpage at high operating temperatures. A second embodiment of the sputter target assembly includes an annular sealing member of machined aluminum disposed in the backing plate around the target.

Description:
PRIOR PROVISIONAL APPLICATION 
     Applicant claims the benefit of the filing date of Provisional Application Ser. No. 60/095,250, filed Aug. 4, 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention pertains to a design and a method of manufacturing sputter target assemblies for magnetron sputter thin film coating processes. 
     Sputtering targets attached to aluminum or copper based backing plates are used to deposit thin films on substrates for semiconductor device manufacturing. These target assemblies provide mechanical and electrical attachment of the target material to the sputter apparatus, provide vacuum sealing surfaces to maintain proper chamber environment, and typically provide a path of heat removal for effective cooling of the target material during sputter deposition. 
     Until now, copper or aluminum backing members fulfilled these functions adequately. Recently, however, target assembly designs have increased in size, typically by 30%. During operation, traditional copper and aluminum materials do not provide enough mechanical strength to prevent excessive deformation of the target assembly which results in poor deposited film quality and may stress the target-to-backing member joint to the breaking point. Accordingly, there is a need for sputter target assemblies having increased deflection resistance with strong target-to-backing member joint strength, vacuum-capable sealing surfaces, and high heat conductivity. 
     SUMMARY OF THE INVENTION 
     The sputter target assembly of the invention comprises a target selected from the group consisting of aluminum, copper, titanium, and alloys thereof; and a backing plate comprising a metal-matrix-composite (MMC) material. In one embodiment of the sputter target assembly, the metal-matrix-composite backing plate is made of silicon carbide impregnated aluminum. The silicon carbide may be in the form of particles, fibers, or mesh. 
     A method of making the sputter target assembly of the invention includes the steps of providing a target material, placing the target material in a hot isostatic press (HIP) can, blending aluminum or aluminum alloy powders with silicon carbide powders to a specific ratio, placing the blended powders in the HIP can in contact with the target material, sealing the HIP can, evacuating the can, and subjecting the can to hot isostatic pressing. This process results in a fully joined assembly wherein the target material is bonded in-situ to the silicon carbide impregnated aluminum backing material. 
     It is an object of the invention to provide a sputter target assembly capable of withstanding high temperature stress with minimal warpage or deformation of the sputter target assembly. 
     It is another object of the invention to provide a sputter target assembly having a backing plate comprised of metal-matrix-composite material. 
     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 shows a first embodiment of a sputter target assembly made in accordance with the present invention; 
     FIGS. 2-5 diagrammatically illustrate a series of steps performed in accordance with the invention for making the sputter target assembly of FIG. 1; 
     FIG. 6 shows a second embodiment of the sputter target assembly of the invention; and 
     FIGS. 7-10 diagrammatically illustrate a series of steps performed in accordance with the invention for making the sputter target assembly of FIG.  6 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, a sputter target assembly  10  includes a target  12  which is bonded to a backing plate  14 . The target plate  12  may be made of aluminum, aluminum alloy, copper, copper alloy, titanium, or titanium alloy. The backing plate  14  may be made of aluminum or aluminum alloy impregnated with silicon carbide particles, silicon carbide fibers, or silicon carbide mesh. The bond between the target  12  and the backing plate  14  is of the diffusion type wherein the target plate  12  is joined to the backing plate  14 . 
     With reference to FIGS. 2-5, a method of producing the sputter target assembly  10  of the present invention comprises placing a target plate  12  within a HIP can  20 . The target plate  12  preferably includes a freshly machined flat lower surface facing upwardly within the can  20 . 
     The target plate  12  is overlaid with a leveled out blended powder composition  22  as is illustrated in FIG.  2 . The powder is preferably a composition of aluminum or aluminum alloy impregnated with silicon carbide particles. Silicon carbide fibers or mesh may also be used. Preferably, the blended powder composition  22  comprises about 99-24 vol. % aluminum or aluminum alloy with the remainder being silicon carbide particles having a size of from about 1 micron to about 50 microns preferably 2 to 25 microns. 
     A pressing punch  24  is then inserted into the can  20  above the powder  22  and the powder  22  is compacted in a ram-type press at room temperature until the powder  22  is compressed to at least 50% of its final density as shown in FIG.  3 . It should be noted that the initial thickness of the aluminum-silicon carbide powder layer is selected such that it is adequate to obtain the desired fmal full density thickness at the conclusion of the target assembly forming process. 
     After the initial compaction of the powder  22 , a top closure plate  26  is welded onto the can  20  to form a can assembly  28  defining a vacuum tight closure, as shown in FIG.  4 . Further, residual air is removed from the interior of the can assembly  28  through a tube attached thereto (not shown). 
     Next, the can assembly  28  is subjected to a HIP process at a predetermined temperature and pressure for a selected time period. The particular conditions used for the HIP process are selected to meet the final backing material requirement as well as to achieve a sound bond between the powder composition forming the backing plate  14  and the target plate  12 . In a preferred HIP process, the can assembly  28  may be subjected to a temperature of about 600° C. and a pressure of 15,000 ksi for a time period of 2 hours. 
     After the HIP process has been completed, the HIP can assembly  28  is placed in a platen press  30  to press the can assembly  28  to a desired flatness as is shown in FIG.  5 . 
     Finally, the flattened assembly may then be machined by conventional means to desired dimensions for the final target assembly  10 . 
     During the consolidation of the powder composition  22 , the target plate  12  undergoes a reduction in diameter as a result of being drawn radially inwardly by the silicon carbide impregnated powder composition  22  as it contracts and increases in density. The surface straining that occurs during this phase of operation aids in producing a sound metallurgical bond between the target  12  and the backing plate  14 . 
     By producing a diffusion bond between the target  12  and the backing plate  14  with the target  12  and the backing plate  14  having closely matched thermal expansion rates, the final target assembly  10  has an enhanced strength and high operating temperature capability, and thus is operable over a wide range of sputtering power levels. 
     Referring to FIG. 6, a second embodiment  40  of the sputter target assembly of the invention is shown. In addition to a target  42  bonded to a backing plate  44 , the sputter target assembly  40  includes a sealing member  46  embedded in a top surface of the backing plate  44 . The backing plate  44  has a greater diameter than the target  42  and the target  42  is centered coaxially on the backing plate  44  so that an annular portion of the backing plate  44  extends radially outwardly from the target  42 . The sealing member  46  forms an annular air-tight seal around the target  42  in cooperation with a sealing edge of a vacuum chamber (not shown). 
     As with the first embodiment, the target  42  may be formed of aluminum, copper, or titanium, or alloys thereof. The backing plate  44  may be made of a metal matrix composite material such as aluminum or aluminum alloy with silicon carbide particles, fibers, or mesh distributed uniformly throughout. 
     Referring now to FIGS. 7-10, a method of producing the second embodiment  40  of the sputter target assembly of the invention may be seen. A target  42  composed of a desired material to be sputtered is placed in a HIP can  50 . The target plate  42  preferably includes a freshly machined flat bottom surface facing upwardly within the can  50 . 
     A sealing member  46  formed as an annular ring of machined aluminum or aluminum alloy is placed in the HIP can  50  concentric with the target  42 . Of course, the sealing member  46  may have other shapes, or be located off-center with respect to the target  42 , if desired. 
     A blended powder composition  52  of metal matrix composite such as aluminum or aluminum alloy powder and silicon carbide particles or fibers is placed in the can  50  covering the target  42  and sealing member  46  and leveled as shown in FIG.  7 . Alternatively, silicon carbide mesh may be used by layering the mesh and aluminum powder over the target  42  and sealing member  46 . Preferably, the powder composition  52  comprises about 99-45 vol % aluminum or aluminum alloy with the remainder being silicon carbide particles having a particle size of from about 1 micron to about 50 microns. 
     A press punch  54  is then inserted into the HIP can  50  above the powder  52  and sealing member  46  and the powder  52  is compacted in a ram-type press at room temperature until the powder  52  is compressed to at least 50% of its final density as shown in FIG.  8 . As before, the quantity of powder composition  52  deposited over the target  42  and sealing member  46  is such that it is adequate to realize the final full density thickness of the backing plate  44  at the conclusion of the target assembly  40  forming process. 
     After initial compaction of the powder  52 , a top closure plate  56  is welded onto the can  50  to form a can assembly  58  defining a vacuum tight closure, as shown in FIG.  9 . Residual air is then removed from the can assembly  58  through an attached tube (not shown). 
     Next, the can assembly  58  is subjected to a HIP process at a predetermined temperature and pressure for a selected time period such as those set forth above. 
     Although the metal matrix composite material herein exemplified is a composite of Al or Al alloy with SiC material dispersed therein, the artisan will appreciate that a wide variety of metals and alloys may be chosen with a similar wide variety of reinforcing materials blended therein. These metal matrix composites are more fully described in U.S. Pat. No. 5,167,920 (Skibo et al.) incorporated by reference herein. 
     As to the Al materials, these may comprise Al or a wide range of alloys such as, 6061, 2024, 7075, 7079, and A356. 
     Additionally although the presently preferred method of manufacture includes a heat consolidation, preferably HIPing of the metal matrix composite (MMC) in powder form to the target material, the MMC can often be purchased in the form of a sheet like material that could in turn be heat and pressure bonded to the target such as by a hot press or the like. 
     While the methods herein described, and the products produced by these methods constitute preferred embodiments of this invention, it is to be understood that the invention is not limited to these precise methods and products, and that changes may be made in either without departing from the scope of the invention, which is defined in the appended claims.