Abstract:
A support assembly for the magnetic array in a cylindrical magnetron that greatly reduces the stress placed on the assembly and on the end blocks of the magnetron. The support assembly and method also reduce the time necessary for properly positioning the magnetic array in relation to the target tube, and result in uniform positioning of the magnetic array along the length of the target tube. A cylindrical magnetron incorporating such an assembly produces uniform coatings and requires less adjustment and maintenance.

Description:
BACKGROUND  
         [0001]    1. Field of the Invention  
           [0002]    The present invention generally relates to sputtering systems, and more particularly to positioning of a magnetic array within a cylindrical magnetron.  
           [0003]    2. Related Art  
           [0004]    A cylindrical magnetron utilizes a magnetic array within a target tube. Proper sputtering is dependent upon proper alignment and positioning of the magnetic array within the target tube. Not only must the magnetic array must be properly aligned when installed, in order to ensure proper sputter, the alignment should be maintained until it is necessary to install a new target tube. Prior designs, required a labor intensive, time consuming process that only very skilled technicians could quickly carry out. Furthermore, the magnetic array would frequently become misaligned after only a short time of usage because highly stressed portions of the assembly lead to rapid degradation of the rollers and other various parts.  
           [0005]    Several U.S. patent applications describe cylindrical magnetrons and the various configurations of magnetic arrays, target tubes, and other components, all of which are hereby incorporated by reference in their entireties: U.S. Pat. No. 5,108,574 to Kirs et al; U.S. Pat. No. 5,213,672 to Hartig, et al; U.S. Pat. No. 5,364,518 to No. Hartig, et al; U.S. Pat. No. 5,527,439 to Sieck, et al; U.S. Pat. No. 5,725,746 to Dickey et al; and U.S. Pat. No. 5,853,816 to Vanderstraeten.  
           [0006]    FIGS.  1 A- 1 C illustrate an example of a prior magnetic assembly  102 . Assembly  102  is stationary within a rotating target tube  104  of a cylindrical magnetron. The assembly includes a magnetic array  106  that is mounted to a support pipe  112  that runs the length of the target tube  104 . The magnetic array  106  has a backing plate  108  between the support pipe  112  and the array  106 . For practical purposes the backing plate  108  will be considered part of magnetic array  106 . The support pipe  112  is coupled to the magnetic array  106  via clamps  116  positioned at various points along the pipe and array. The rollers  124  are in tangential contact with the inner diameter of the target tube  104 . The rollers are also fixed directly to the magnetic array  106 , as seen in FIG. 1B. Thus, the magnetic array  106  is not adjustable in relation to the inner diameter of target tube  104 , and has very little freedom of movement. However, fine tuning is possible by deflecting the assembly  102  in along the length of the assembly.  
           [0007]    The position of the magnetic array is fine tuned by manipulating shims  120  located between the clamps  116  and the magnetic array  106 . Different amounts of shimming may be placed at the different clamps  116 . The magnetic array is not free to move, and as a result is not displaced by the full thickness of the shim. This may result in a different amounts of deflection, at times approaching a quasi sinusoidal like pattern. The shimming increases the loading on the rollers and on the end circumference support areas of the support tube. This results in increased compression stresses and premature wear of the rollers and the circumferential end supports. The wear of the rollers, in turn, leads to movement and misalignment of the magnetic array. This misalignment results in less than optimal sputtering with variations in the coatings produced by the magnetrons. Therefore, a more durable and simpler device and method for positioning the magnetic array is needed.  
         SUMMARY  
         [0008]    A magnetic support assembly is located within the target tube of a cylindrical magnetron, and supports a magnetic array within the target tube. The position of the magnetic array is critical to the sputtering of the target tube material. The support assembly uniformly supports the magnetic array such that the distance between the magnetic array and the target tube is constant along the length of the magnetic array. This results in even and uniform sputtering, and therefore even and uniform coatings on the substrate.  
           [0009]    The magnetic support assembly comprises a support member. Rollers attached to the support member are in contact with an inner diameter of the target tube and support the stationary support member as the target tube continually rotates. An support structure is attached to a magnetic array, and the support structure and magnetic array are positioned between the rollers of the support member. The support structure has a length approximately equal to that of the target tube, and the magnetic support assembly is positioned at approximately the middle of the target tube and supports the weight of the magnetic array and support structure from the approximate middle of the target tube.  
           [0010]    Another aspect of the invention is a method for positioning a magnetic array having a span within the target tube of a cylindrical magnetron. The method comprises affixing the magnetic array to a supporting member along the span of the magnetic array, attaching a roller structure to the supporting member at about the middle of the span adjusting a distance between the roller structure and the support member in order to position the magnetic array relative to an inner surface of the target tube. The roller structure, support member, and magnetic array are inserted into the target tube such that the roller structure is at about the middle of the target tube. 
       
    
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0011]    [0011]FIG. 1A is a perspective view of a prior art magnetic assembly  102 .  
         [0012]    [0012]FIG. 1B is a perspective view of a prior art magnetic assembly  102  seen in FIG. 1A.  
         [0013]    [0013]FIG. 1C is a cross section of a prior art magnetic assembly  102 .  
         [0014]    [0014]FIG. 2A is a cross section of magnetic support assembly  202 .  
         [0015]    [0015]FIG. 2B is a cross section of magnetic support assembly  250 .  
         [0016]    [0016]FIG. 2C is a cross section of magnetic support assembly  250 .  
         [0017]    [0017]FIG. 2D is a cross section of magnetic support assembly  275 .  
         [0018]    [0018]FIG. 3A is a perspective view of magnetic support assembly  300  partially in a target tube.  
         [0019]    [0019]FIG. 3B is a perspective view of a support pipe and the fixation with the end block.  
         [0020]    [0020]FIG. 4 is a perspective view of magnetic support assembly  400 .  
         [0021]    [0021]FIG. 5 is a graph of a deposition profile created by an embodiment of the invention. 
     
    
       [0022]    Like numbers are used to describe the same components in the various figures.  
       DETAILED DESCRIPTION  
       [0023]    All of the embodiments of the present invention simplify the installation of a magnetic support assembly within the target tube of a cylindrical magnetron. Additionally, the embodiments result in more uniform coatings, both initially, and after many hours of operation. The embodiments improve the load and stress distribution within the target tube and upon the end blocks of the magnetron, minimize friction between the rotating parts, and provide for true adjustability of the distance between the magnetic array and the target tube. The magnetic array, once installed will remain precisely aligned during the period of time that elapses while the target erodes for the life of the target tube. This results in a magnetron that produces uniform coatings for extended durations without the need for re-adjustment due to wear or other stress induced variations in the component parts. Should any adjustment be necessary, it can be performed at a convenient time, such as when the target tube is changed.  
         [0024]    [0024]FIG. 2A. is a cross section illustrating magnetic support assembly  202 , an embodiment of the present invention, within target tube  204 . Magnetic support assembly  202 , and all the magnetic support assemblies that will be described, are stationary within the rotating target tube  204 .  
         [0025]    Magnetic support assembly  202  is a fixed design, i.e. the distance between the magnetic array and target tube  204  is not adjustable at the support assembly. Support pipe  212  is secured to the u-shaped support frame  214  by cross pins  222 . Magnetic array  206  is secured to support pipe  218  in any number of ways. It may be secured with screws or bolts that attach directly to support pipe  218 , or may alternatively be secured to a backing plate, which is intern secured to support pipe  218 . It may also be, for example clamped to the support pipe at various points along the pipe, in a manner similar to that shown in FIG. 1A, or otherwise adhered in any well-known way.  
         [0026]    Although support frame  214  is depicted as a simple u-shape, any number of different geometries are within the scope of the present invention. For example, frame  214  may include a hemispherical or stepped inner portion that more closely follows the shape of the cylindrical support pipe  218 . Furthermore, the support pipe  218  may be of any geometry. Preferably, support pipe  218  acts a conduit for cooling water provided by one of the magnetron end blocks (not shown). However, support pipe  212  may also be a solid member. The magnetron and the end blocks are described in co-pending application Ser. No. 10/052732 to Richard Barrett, filed on Jan. 18, 2002, and entitled Cylindrical AC/DC Magnetron With Compliant Drive System And Improved Electrical And Thermal Isolation, which is hereby incorporated by this reference in its entirety.  
         [0027]    [0027]FIGS. 2B and 2C illustrate magnetic support assembly  250 , another embodiment of the present invention. Assembly  250  allows adjustment of the distance between the magnetic array  206  and target tube  204 . There are two portions of the frame, upper frame  216 A, and lower frame  216 B. The support pipe  218  is connected to upper frame  216 A with connecting pins  222 . The support pipe may be connected to the upper frame  216 A in any number of ways such as with rivets, screws, adhesive material, clamps, or by welding. Furthermore, the support pipe  218  may be integrally formed with the upper frame  216 A, and/or lower frame  216 B, in which case the support pipe and (a portion of) the frame would be considered one piece.  
         [0028]    The lower frame  216 B has the rollers  210  that contact the inner diameter of the rotating target tube  204 . The lower frame may be as large or small as desired, and in fact, if the lower frame is minimized it may comprise only rollers and an adjustable coupling to the rollers that adjusts to vary the distance between the rollers (in contact with the inner diameter of the target tube) and the magnetic array  206 . Set screws  230  in lower frame  216 B are used to adjust the distance between magnetic array  206  and target tube  204  by varying the distance between upper frame  216 A and lower frame  216 B. The set screws are accessed through passages in upper frame  216 A. Clamp screws  226  hold the upper and lower frame together. The set screws  230  are shown threaded into lower frame  216 B, however the set screws may be configured many different ways, such as for example being threaded in the upper frame  216 A and abutting a solid portion of lower frame  216 B or vice versa.  
         [0029]    [0029]FIG. 2D illustrates magnetic support assembly  275 , another embodiment of the present invention. Magnetic support assembly  275  is similar to magnetic support assembly  250 , but shims  234  are used to vary the distance between the magnetic array  206  and the target tube  204 . The shims  234  are positioned between upper frame  216 A and lower frame  216 B in order to vary the distance between the upper and lower frame and thus between the magnetic array  206  and the inner diameter of target tube  204 .  
         [0030]    [0030]FIG. 3A illustrates magnetic support assembly  300  according to another embodiment of the invention. Assembly  300  has a fixed frame  304  with two rollers  210  per side. The previously described assemblies had one roller per side. It is envisioned that any number of rollers can be included in an assembly, although preferably two are included to minimize cost. The rollers are made of a very durable material such as nylon that does not break down in water, or in very high electrical and magnetic fields, and the very high temperatures common in high power cylindrical magnetrons. Preferably the nylon has other constituents such as finely divided particles of molybdenum disulphide (MoS 2 ) to enhance its load bearing capabilities while maintaining the impact resistance inherent to nylon. Additionally, it is preferred that the nylon (composite) is cast, although it may also be extruded or otherwise formed, and includes oil or other lubricant for improved frictional characteristics. Furthermore, the rollers  210  are continually lubricated from lubricant reservoir  310 . The reservoir is filled with lubricant through nipple  312  prior to installation of the magnetic support assembly  300  into target tube  204 . Although the reservoir can easily be periodically refilled, it is sufficiently large to provide continual lubrication throughout the life of a target tube. Clamp  308  holds the magnetic array  206  to the support pipe  318 , one of the many ways discussed earlier of adhering support pipe  318  to magnetic array  206 .  
         [0031]    In all of the embodiments discussed thus far, the magnetic array  206  and support pipe  218  are supported in three positions. At each end of the target tube  204  there is an end plate  320 , as can be seen in FIG. 3B. Each end plate  320  has a circular groove in which support pipe  218  fits. The end plate and the groove support the pipe  218  at each end of the pipe. The support pipe is approximately the length of the target tube, but may be slightly longer or shorter than the target tube, depending on the particular configuration of the end block utilized. The magnetic support assemblies depicted in all of the various figures are positioned at roughly the middle of the length of the support pies  218  so that when they are inserted into a target tube  204 , they will support and position the magnetic array  206  at roughly the middle of the target tube. While it is preferred to use one support assembly in the middle of the pipe and target tube, more than one support assembly can be utilized to support the pipe and magnetic array at various locations along the pipe. While this is more costly, in coating situations requiring long target tubes where sagging of the support pipe is more likely, or in situations where very high precision is of the utmost importance, utilizing more than one support assembly may be advantageous.  
         [0032]    [0032]FIG. 4 is a perspective view of magnetic support assembly  400 . Magnetic support assembly  400  comprises an upper frame  416 A and a lower frame  416 B. The support pipe and magnetic array  206  are connected to upper frame  416 A with support pins  423 . Upper frame  416 A can be separated from lower frame  416 b by jack screws  430 . This intern varies the distance between the magnetic array  206  and the inner diameter of the target tube (not shown). Support pins  423  may also be used to vary the distance between the magnetic array and the target tube.  
         [0033]    [0033]FIG. 5 is a graph of a TiO 2  coating deposited with a cylindrical magnetron utilizing an embodiment of the present invention, and with a cylindrical magnetron using a prior art magnetic support assembly (shortly after installation and alignment) as seen in FIG. 1. The coating deposited with present invention is much more uniform across the entire length of the coater. The uniformity profiles shown are after the prior support assemblies were freshly tuned, under optimum conditions. As described previously, the prior assembly was prone to quickly lose alignment and thus would typically result in a coating inferior to the one shown in the graph, whereas the present invention solves that problem, and produces uniform coatings for the life of the target tube. Therefore, a coater utilizing any of the embodiments of the present invention will produce a coating far superior to that produced with prior designs.  
         [0034]    While particular embodiments of the present invention and their advantages have been shown and described, it should be understood that various changes, substitutions, and alterations can be made therein without departing from the spirit and scope of the invention as defined by the appended claims.