Abstract:
Magnetic flux shunting pads for optimizing target erosion in sputtering processes are provided. In one embodiment, the invention relates to a sputtering system for countering uneven wear of a sputter target, the system including a sputter target having an emitting surface and a rear surface opposite to the emitting surface, a moving magnet assembly positioned proximate the rear surface and including a planar base and a magnet fixed to the planar base at a preselected point, the moving magnet assembly configured to be moved such that a position of the magnet relative to the rear surface is varied, and a magnetic shunting pad having a planar shape and positioned between the moving magnet assembly and the target, wherein the shunting pad includes uneven magnetic shunting characteristics.

Description:
FIELD 
     The present invention relates to sputtering processes, and more specifically to magnetic flux shunting pads for optimizing target erosion in sputtering processes. 
     BACKGROUND 
     Sputtering processes can be used to deposit a thin film layer on a substrate or disk. Such sputtering processes can bombard a sputter target with ions and the target becomes the source of the deposition material. Due to the ion bombardment, the atoms of the target deposition material are ejected from the target and deposited on the substrate or disk. As the atoms of the target deposition material are ejected, an erosion pattern is created on the target. 
     The target erosion pattern is largely dictated by a magnetic field of a magnet that is positioned at the back of the target. More specifically, the magnetic field from the magnet confines the electrons which are removed from the target to a certain area of the surface target at the active sputtering area (see, for example,  FIG. 2   c  of U.S. Pat. No. 5,876,576). As the ions bombard and erode the target, annular grooves (also called a race track or an erosion track) are created in the target. The race track or erosion depth limits the effective life of the sputter target. More specifically, when the deepest point of the erosion track reaches the bottom of the target surface, the useful life of the target is over. Typically, 20% to 35% of the sputter target material, as measured by weight, has been consumed (utilization) and the remaining material is refined into powder to form new targets. As such, the wasted target material can be as high as 65% to 80%. Accordingly, an improved sputtering system that decreases the amount of target material wasted in the sputtering process is needed. 
     SUMMARY 
     Aspects of the invention relate to magnetic flux shunting pads for optimizing target erosion in sputtering processes. In one embodiment, the invention relates to a sputtering system for countering uneven wear of a sputter target, the system including a sputter target having an emitting surface and a rear surface opposite to the emitting surface, a moving magnet assembly positioned proximate the rear surface and including a planar base and a magnet fixed to the planar base at a preselected point, the moving magnet assembly configured to be moved such that a position of the magnet relative to the rear surface is varied, and a magnetic shunting pad having a planar shape and positioned between the moving magnet assembly and the target, where the shunting pad includes uneven magnetic shunting characteristics. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a side view of a sputtering system that includes a substrate, two sputter targets, and two magnetic shunting pads for optimizing an erosion pattern of the sputter targets in accordance with one embodiment of the invention. 
         FIG. 2  illustrates a cross sectional view of a portion of the sputtering system of  FIG. 1  including a sputter target, a baking plate, a magnetic shunting pad, and a rotating magnet assembly, where the magnetic shunting pad is positioned between the rotating magnet assembly and the sputter target in accordance with one embodiment of the invention. 
         FIG. 3  illustrates a perspective view of the magnetic shunting pad for the sputtering system of  FIG. 2  in accordance with one embodiment of the invention. 
         FIG. 4  illustrates a cross sectional profile view of a sputter target erosion pattern for a sputtering system using a magnetic shunting pad in accordance with one embodiment of the invention and a sputter target erosion pattern for a conventional sputtering system. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawings, sputtering systems including a sputter target, a moving magnet assembly, and a magnetic shunting pad positioned between the sputter target and the moving magnetic are illustrated. The magnetic shunting pads have uneven magnetic shunting characteristics configured to counter uneven erosion of the sputter target. In several embodiments, the magnetic shunting pads include areas or zones having different shunting characteristics. In one embodiment, for example, the magnetic shunting pads include at least two segmented areas or zones, where the first zone has different shunting characteristics from the second zone. In some embodiments, a third zone is added to the magnetic shunting pads, where the third zone has different magnetic shunting characteristics than either of the other two areas. In many embodiments, the shunting characteristic is a pass through flux characteristic of the respective zone. In several embodiments, the magnetic shunting pads are planar disk shaped pads, and the zones take the form of one or more annular rings. 
       FIG. 1  illustrates a side view of a sputtering system  100  that includes a substrate  102 , two sputter targets  104 , and two magnetic shunting pads  106  for optimizing an erosion pattern of the sputter targets  104  in accordance with one embodiment of the invention. The sputtering system  100  further includes two backing plates  108  and two graphite sheets  110 . The planar shaped substrate  102  is positioned in a central region of the sputtering system  100  and each planar surface thereof faces one of the sputter targets  104 . For each planar shaped sputter target  104 , a stacked structure is positioned on an outer surface thereof (e.g., target surface that is furthest from the substrate  102 ). The stacked structure includes the backing plate  108  that abuts the sputter target  104 , a magnetic shunting pad  106  adjacent to the backing plate  108 , the graphite sheet  110  adjacent to the magnetic shunting pad  106 , and a rotating magnet assembly  114  (not visible in  FIG. 1  but see  FIG. 2 ) spaced apart from the graphite sheet  110 . The sputtering system  100  further includes a vacuum chamber  112  where each of the sputter system components is positioned within in vacuum chamber  112 . 
     In operation, the vacuum chamber  112  includes a plasma including a number of ions. The ions bombard the sputter targets  104  at particular concentrated areas of the sputter targets  104 . The atoms of the target material are ejected from the concentrated areas of the target  104  during the ion bombardment and are deposited on the substrate  102 . The concentrated areas of the sputter targets  104  are established by lines of magnetic flux emanating from the rotating magnet assembly positioned  114  behind the target  104 . The lines of magnetic flux are re-directed or shunted by the two magnetic shunting pads  106  positioned between each rotating magnet assembly  114  and the respective target  104 . The two magnetic shunting pads  106  can each have uneven pass through flux characteristics across the respective cross section of the pads. In such case, particular pass through flux zones in the magnetic shunting pads  106  are arranged to facilitate an even erosion pattern. In several embodiments, the arrangement of the pass through flux zones is configured to correspond to positions of magnets in magnetic assemblies (not visible in  FIG. 1  but see  FIG. 2 ) positioned behind the magnetic shunting pads  106 . 
       FIG. 2  illustrates a cross sectional view of a portion of the sputtering system  100  of  FIG. 1  including a sputter target  104 , a baking plate  108 , a magnetic shunting pad  106 , and a rotating magnet assembly  114 , where the magnetic shunting pad  106  is positioned between the rotating magnet assembly  114  and the sputter target  104  in accordance with one embodiment of the invention. The rotating magnet assembly  114  includes a planar base  116  and first and second magnets ( 118   a ,  118   b ) attached along a top surface of the planar base  116  at locations near outer edges of the planar base  116 . In operation, the planar base  116  is configured to rotate about a central shaft  120  that can be driven in either a clockwise or a counter-clockwise direction by a rotation assembly (not visible). 
     A graphite sheet  110  is positioned above, and spaced apart from, the rotating magnet assembly  114 . The magnetic shunting pad  106  is positioned on the graphite sheet  110 . The baking plate  108  is positioned on the magnetic shunting pad  106 . The sputter target  104  is positioned on the baking plate  108 . Each of the baking plate  108 , the magnetic shunting pad  106 , and the graphite sheet  110  can have a planar shaped body with a thickness that is about equal. The sputter target  104  can have a planar shaped body with a thickness that is about two to three times the roughly equal thickness of the baking plate  108 , the magnetic shunting pad  106 , and the graphite sheet  110 . 
     The magnetic shunting pad  106  includes a first zone  106   a  having a first magnetic pass through flux characteristic, a second zone  106   b  having a second magnetic pass through flux characteristic, and a third zone  106   c  having a third magnetic pass through flux characteristic. The first zone  106   a  is positioned such that it is about aligned with one of the corresponding magnets ( 118   a ,  118   b ) of the rotating magnet assembly  114  positioned below the magnetic shunting pad  106 . The third zone  106   c  is positioned closer a central point of the magnetic shunting pad  106  than the first zone  106   a  and is also encircled by the first zone  106   a  (see  FIG. 3 ). The remaining area of the magnetic shunting pad  106  forms the second zone  106   b , which is composed of a central region, an inner ring, and an outer ring (see  FIG. 3 ). 
     As can be seen in  FIG. 2 , magnetic flux lines  122  from the magnets ( 118   a ,  118   b ) are guided and dispersed by the first zone  106   a  to have a relatively wide angle passing through the sputter target  104  as compared to prior art systems. As a result, an erosion line  104   a  of the sputter target  104  illustrates that the target  104  experiences significantly less erosion at the race track areas (e.g., those areas directly above the magnets and first zone  106   a ). As such, the usage of the sputter target material is greatly increased. 
     In several embodiments, the sputter target is formed of one or more materials selected from the group including Co, Cr, Ti, Ru, Fe, B, and Pt. In other embodiments, other suitable sputter target materials can be used. In the embodiment illustrated in  FIG. 2 , the magnetic shunting pad  106  includes a thin top layer of graphite  124   a  and a thin bottom layer of graphite  124   b . In other embodiments, the magnetic shunting pad  106  does not include top and bottom layers of graphite. 
       FIG. 3  illustrates a perspective view of the magnetic shunting pad  106  for the sputtering system of  FIG. 2  in accordance with one embodiment of the invention. As discussed above, the magnetic shunting pad  106  has a planar disk shaped body with the three zones ( 106   a ,  106   b ,  106   c ) having different magnetic pass through flux characteristics. The first zone  106   a  forms a first annular ring around the disk shaped pad  106 . The second zone  106   b  includes a centrally located circular section and two annular ring sections positioned on either side of the first annular ring (e.g., the first zone  106   a ). The third zone  106   c  forms a third annular ring around the disk shaped pad  106  which is positioned within the first annular ring (e.g., the first zone  106   a ) and around the centrally located circular section of the second zone  106   b.    
     In several embodiments, the magnetic shunting pad  106  has a diameter of about 180 millimeters (mm) and a thickness of about 4 to 5 mm. In some embodiments, the first annular ring of the first zone  106   a  has a width of about 20 to 30 mm, and the third annular ring of the third zone  106   c  has a width of about 20 to 50 mm. In one embodiment, the width of the third zone is increased such that the circular portion of the second zone  106   b  in the center of the shunting pad  106  is effectively eliminated. In other embodiments, the zones can have other suitable dimensions. In several embodiments, the widths of the zones are determined based on the strength and shape of the corresponding magnet of the rotating magnet assembly proximate the respective zone and the original erosion pattern for the sputtering system prior to use of the novel magnetic shunting pad  106 . 
     In several embodiments, the first zone  106   a  is formed of a first alloy providing a relatively low pass through flux characteristic. For example, in some embodiments, the first zone  106   a  and first alloy provide for less than about 10 percent flux passage. In one such embodiment, the first zone  106   a  provides for about 1 percent flux passage. In several embodiments, the second zone  106   b  is formed of a second alloy providing a relatively high pass through flux characteristic. In some embodiments, for example, the second zone  106   b  and second alloy provide for about 95 to about 100 percent flux passage. In one such embodiment, the second zone  106   b  provides for about 100 percent flux passage. In several embodiments, the third zone  106   c  is formed of a third alloy providing a relatively average or medium pass through flux characteristic. In some embodiments, for example, the third zone  106   c  and third alloy provide for about 45 to about 65 percent flux passage. In one such embodiment, the second zone  106   b  provides for about 55 percent flux passage. In other embodiments, each of the zones ( 106   a ,  106   b ,  106   c ) can provide for other suitable flux passage percentages. 
     In several embodiments, the first alloy of the first zone  106   a  includes one or more materials selected from the group including Ni, W, Al, Fe, Co, Zr, B, and Cu. In one embodiment, the first alloy of the first zone  106   a  includes NiWAlFe. In several embodiments, the second alloy of the second zone  106   b  includes one or more materials selected from the group including Ni and W. In one embodiment, the first alloy of the first zone  106   a  includes NiW. In several embodiments, the third alloy of the third zone  106   c  includes one or more materials selected from the group including Ni, W, Al, Fe, Co, and Ta. In one embodiment, the third alloy of the third zone  106   a  includes NiWAlFe. In other embodiments, any of the three alloys can be formed of other suitable materials. 
     In the embodiment illustrated in  FIG. 3 , the magnetic shunting pad  106  includes three zones having preselected shapes (e.g., annular rings). In other embodiments, magnetic shunting pad  106  includes only two zones, or alternatively, more than three zones. In other embodiments, the preselected shapes for the zones of different magnetic shunting can have other suitable shapes. For example, in other embodiments, the annular rings can be arranged in other ways and have different thicknesses than the illustrated thicknesses. In the embodiment illustrated in  FIG. 3 , the magnetic shunting pad  106  has a planar disk shape. In other embodiments, the magnetic shunting pad can have another suitable shape (e.g., thin block shape). In several embodiments, the zones are arranged such that the magnetic shunting pad effectively provides a gradient of pass through flux characteristics across the planar surface of the shunting pad. In other embodiments, other suitable arrangements of zones for providing uneven pass through flux characteristics to offset conventional or undesirable erosion patterns can be used. 
     In several embodiments, the magnetic shunting pad can be installed in a model  3010 ,  3040 , or  3050  sputter system made by Canon ANELVA Corporation of Tokyo, Japan. In other embodiments, the magnetic shunting pad can be used in other suitable sputter systems. 
       FIG. 4  illustrates a cross sectional profile view of a sputter target erosion pattern  204  for a sputtering system using a magnetic shunting pad in accordance with one embodiment of the invention and a sputter target erosion pattern  205  for a conventional sputtering system. The view further includes a vertical axis legend  207  with horizontal depth lines for quantifying the amount of erosion found along each of the sputter targets ( 204 ,  205 ). As can be seen in  FIG. 4 , the conventional sputter target  205  used in a sputter system without a magnetic shunting pad provides for material usage of about 20 to 35 percent. However, the sputter target  204  used in the improved sputter system with the novel magnetic shunting pad improves material usage by more than about 50 percent. In several embodiments, the magnetic shunting pad can also improve the sputtering rate, which can improve the outer diameter and inner diameter thicknesses by about 15 to about 20 percent. 
     While the above description contains many specific embodiments of the invention, these should not be construed as limitations on the scope of the invention, but rather as examples of specific embodiments thereof. Accordingly, the scope of the invention should be determined not by the embodiments illustrated, but by the appended claims and their equivalents.