Abstract:
A cylindrical sputtering target including a cylinder of a first material wherein the inner wall of the cylinder has embedded within it a pattern of small pieces of one or more different materials, whereby such target produces a spatially and compositionally uniform coating on a substrate in a cylindrical sputtering process. The molar ratio of the multiple materials in the coating composition is influenced by the size, shape, and geometrical pattern of the material pieces embedded in the inner cylinder wall.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of U.S. Provisional Application No. 60/657,055 filed on Feb. 28, 2005. 
     
    
     FIELD OF THE INVENTION  
       [0002]     Apparatus for sputter coating of substrates; more particularly to such apparatus wherein the sputtering target is cylindrical; and most particularly to such apparatus wherein the inner wall of the cylindrical targets comprise multiple materials.  
       BACKGROUND  
       [0003]     Sputtering is a well-known process for applying a thin film of material to a substrate. In the sputtering process a target comprised of the material to be deposited onto the substrate is placed within a gas discharge environment and electrically connected as a cathode electrode. Ions from the gas discharge bombard the target with high enough energy to eject, that is to sputter, atoms from the target that will deposit on the substrate. The substrate is suitably located with respect to the target so that it is in the path of the sputtered atoms, whereby a coating of the target material forms on the substrate surface exposed to the impinging sputtered atoms.  
         [0004]     Cylindrical magnetron sputtering, wherein the substrate is located within a cylindrical target, is particularly suited for coating three-dimensional complex objects, such as those used for cutting tools, biomedical de-ices, optical fibers, and so on. Cylindrical magnetron sputtering devices are well known to those of ordinary skill in the art.  
         [0005]     By way of illustration, U.S. Pat. No. 5,069,770 discloses a sputtering process employing an enclosed sputtering target.  
         [0006]     U.S. Pat. No. 5,529,674 discloses a modular, valveless, continuously-open, straight-through magnetron sputtering system comprising: a plurality of elongated hollow cylindrical cathode modules which define a valveless, continuously-open substrate passage.  
         [0007]     U.S. Pat. Nos. 6,066,242 and 6,235,170 disclose a hollow cathode magnetron for sputtering target material from the inner surface of a target onto an off-spaced substrate.  
         [0008]     U.S. Pat. No. 6,432,286 also discloses a hollow cathode magnetron.  
         [0009]     U.S. Pat. No. 6,497,803 discloses an unbalanced plasma generating apparatus having cylindrical symmetry.  
         [0010]     U.S. Pat. No. 6,551,477 discloses interlocking cylindrical magnetron cathodes and targets.  
         [0011]     Published United States patent application 2001/0050225 discloses an unbalanced plasma-generating apparatus.  
         [0012]     Published United States patent application 2002/0195336 discloses a like-polarity unbalanced planar magnetron array.  
         [0013]     Published United States patent application 2003/0183518 discloses a sputtering cathode comprising a concave surface for receiving and supporting a sputtering target having a substantially conformal concave shape.  
         [0014]     A cylindrical magnetron sputtering device is also described by Glocker et al in an article entitled “Nanocomposite Mo—Ti—N Coatings for Wear Resistant Applications,” Society of Vacuum Coaters, 48 th  Annual Technical Conference Proceedings (April 2005).  
         [0015]     Sputtered coatings have a variety of purposes such as increased hardness and wear resistance, corrosion resistance, anti-oxidation properties, and so on. Coatings of binary or ternary compounds often maximize such properties. Such compound coatings usually require an alloy target or multiple targets to acquire the required atoms in the desired molar ratios. Producing various compositions of targets by conventional metallurgical techniques is difficult. Huang and Duh describe a planar magnetron sputtering device for producing binary and ternary sputtered coatings in a paper entitled “Deposition of (Ti,Al)N Films onto Tool Steel by Reactive R.F. Magnetron Sputtering,” Society of Vacuum Coaters, 37 th  Annual Technical Conference Proceedings (1994). Most applications mentioned above, i.e., coating three-dimensional complex objects, such as those used for cutting tools, biomedical devices, optical fibers, and so on, also require high uniformity of the coating over the whole surface of the object. Achieving such high uniformity with planer targets or with multiple cylindrical targets is difficult, especially with large and complex shaped substrates.  
         [0016]     Provided are cylindrical sputtering targets that produce highly uniform coatings of compound materials on large and complex substrates. Also provided is a method of controlling the ratios of the materials in a compound coating produced from such cylindrical sputtering targets.  
         [0017]     A distributed multiple material cylindrical sputtering target comprised of a cylinder of a first material wherein the inner wall of the cylinder has embedded within it a pattern of small chips or pieces of one or more additional materials is provided. In a cylindrical sputtering process, such target produces a substantially spatially uniform and substantially compositionally uniform coating on a substrate. The molar ratio of the multiple materials in the coating composition is controlled by the size, shape, and geometrical pattern of the material chips or pieces embedded in the inner cylinder wall. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]      FIG. 1  is a cross-sectional view of a prior art cylindrical magnetron sputtering device having a single cylindrical target;  
         [0019]      FIG. 2  is a cross-sectional view of a prior art cylindrical magnetron sputtering device having two cylindrical targets;  
         [0020]      FIG. 3A  is a cross-sectional view of one embodiment of a cylindrical magnetron sputtering device having a distributed multiple material target;  
         [0021]      FIG. 3B  is a cross-sectional view of a wall section of one embodiment of the cylindrical magnetron sputtering device in  FIG. 3A ;  
         [0022]      FIG. 3C  is a cross sectional view of a wall section of another embodiment of the cylindrical magnetron sputtering device in  FIG. 3A ; and  
         [0023]      FIG. 4  is a cross-sectional view of a another embodiment of a cylindrical magnetron sputtering device having a distributed multiple material target. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]     Referring now to the drawings, wherein like reference numerals designate the same or similar elements throughout the several figures,  FIG. 1  shows a cross-sectional view of a cylindrical magnetron  5  as disclosed in the prior art. A cylindrical sputtering target  20  is disposed within a cylindrical cathode  10 . Cylindrical sputtering apparatus are known to those skilled in the art, and therefore details of prior art cylindrical magnetron are not shown in order to simplify the drawings. For example, not shown are cooling means for cathode  10 , axial magnetic fields within cylindrical magnetron  5  produced by conventional means, the plasma formed within cylindrical magnetron  5 , and means for containing such plasma. Also not shown are the vacuum pumps, vacuum chamber, gas flow equipment and other means of producing a vacuum coating environment within cylindrical sputtering target  20 . A substrate  30  to be coated, for example, cutting tool, biomedical device, optical fiber, and so on, is placed within the interior  22  of cylindrical sputtering device  5 . Application of an appropriate voltage to cathode  10  and target  20  in the presence of a sputtering gas at the proper gas pressure produces a plasma that bombards the inner wall  24  of target  20  and thereby produces a sputtered coating of target material on substrate  30 . Oxygen and/or nitrogen may also be incorporated into the sputtered coating on substrate  30  by feeding quantities of these gases into the plasma chamber in addition to the plasma gas. The amount of oxygen and/or nitrogen in the coating is determined by the flow rates of these cases relative to the flow rate of the plasma gas.  
         [0025]     Referring now to  FIG. 2 , there is shown a cross-sectional view of a prior art cylindrical sputtering device  15  for co-sputtering two materials to produce a binary coating on a substrate  30 . Device  15  is comprised of two cathodes  10  and  10 ′ within each of which are placed cylindrical targets  20  and  20 ′ respectively. Target  20  is comprised of a first material and target  20 ′ is comprise of a second material. Application of appropriate voltages to cathodes  10  and  10 ′ and targets  20  and  20 ′ in the presence of a sputtering gas at the proper gas pressure produces a plasma that bombards the inner Walls  24  and  24 ′ of targets  20  and  20 ′ respectively, and thereby produces, on substrate  30 , a compound sputtered coating comprised of a compound of the first material of target  20  and the second material of target  20 ′.  
         [0026]     A shortcoming of device  15  in  FIG. 2  for sputtering compound coatings is that, depending on the size and shape of the substrate  30  to be coated, the coating may not be uniform, over the surface of substrate  30 , in the desired molar ratio of the two different materials from targets  20  and  20 ′. For example, the molar ratio of the coating may be too high in the first material from target  20  at position  32  on substrate  30  and too high in the second material from target  20 ′ at position  34  on substrate  30 .  
         [0027]     Referring now to  FIG. 3A , there is shown a cross-sectional view of a cylindrical sputtering device  25  that overcomes the shortcoming of device  15  shown in  FIG. 2  and described above. In cylindrical sputtering device  25  a cylindrical target  40 , comprised of a first material  42 , is disposed within cylindrical cathode  10 . Embedded on the inside wall  48  of cylindrical target  40  is a predetermined pattern of chips or pieces  44  of at least a second material  46 . This embodiment will produce a compound sputtered coating on substrate  30 , comprising first material  42  atoms and second material  46  atoms. The predetermined pattern of chips or pieces  44  is such that the molar ratio of first material  42  to second material  46  in the coating sputtered onto substrate  30  is substantially uniform over the entire surface of substrate  30 .  
         [0028]     The shape of chips or pieces  44  in  FIG. 3A  is shown as circular, but alternatively may be any other shape such as square, oval, etc. In certain embodiments, chips or pieces  44  in  FIG. 3A  may have a maximum dimension in the range from about 1 millimeter to about 1 centimeter. Chips or pieces  44  may be embedded on inside wall  48  of cylindrical target  40  in a substantially uniform pattern at a predetermined density so that energy contacting such inside wall  48  will cause the generation of first material  42  atoms and second material  46  atoms in the desired molar ratio. The predetermined pattern of chips or pieces  44  may be a regular periodic pattern on wall  48  or it may be a random pattern substantially uniformly distributed on the surface of wall  48 . The percentage of inside wall  48  covered by the pattern of chips or pieces  44  should be sufficient to produce the desired molar ratio of first material  42  to second material  46  in the sputtered coating. In one embodiment the percentage coverage of inner (inside) wall  48  (of  FIG. 3A ) by the amount of first material  42  is in the range from about 2% to about 90%. In an alternative embodiment, the percentage coverage of inner (inside) wall  48  (of  FIG. 3A ) by the amount of second material  46  is in the range from about 2% to about 90%.  
         [0029]     Chips or pieces  44  may be embedded into inside wall  48  by conventional means. Referring now to  FIG. 3B  there is shown an enlarged cross-sectional view of one embodiment of a section of the wall of cylindrical target  40  in  FIG. 3A , the section passing through a row of chips or pieces  44 . In this embodiment, chips or pieces  44  were inserted into blind holes that were bored into the inner (inside) wall  48  of cylindrical target  40  and the inside wall was machined so that or pieces  44  were flush with wall  48 . In another embodiment, and referring to  FIG. 3C , chips or pieces  44  were inserted into blind holes that were bored into wall  4 S, but were left protruding from the blind holes. As discussed herein, a blind hole is a hole that does not pass completely through the object into which it is bored.  
         [0030]     Referring now to  FIG. 4 , there is shown a cross-sectional view of another embodiment, cylindrical sputtering device  35 , in which chips or pieces of at least a second material  52  and a third material  54  are embedded into inside wall  48  of cylindrical target  40  composed of first material  42 . This embodiment will produce a compound sputtered coating on substrate  30 , comprising first material  42  atoms, second material  52  atoms, and third material  54  atoms. As with cylindrical sputtering device  25  in  FIG. 3A , the molar ratios of materials  42 ,  52 , and  54  in the sputtered coating from cylindrical sputtering device  35  in  FIG. 4  may be controlled by the size and pattern of the chips or pieces of the second and third materials imbedded in wall  48  of cylindrical target  40 .  
         [0031]     Similarly an additional number of materials can be present as chips or pieces in the cylindrical target, whose number, size, and pattern control the ratio of the materials present in a sputtered coating prepared in a cylindrical device sputtering process.  
         [0032]     The patents, patent applications, and patent application publications referenced herein, are hereby incorporated into this specification as a fully written out below.  
         [0033]     Although the invention has been described in detail through the above detailed description and the proceeding examples, these examples are for the purpose of illustration only and it is understood that variations in modifications can be made by one skilled in the art without the departing from the spirit and scope of the invention. It should be understood that the embodiments described above are not only in the alternative, but can be combined.