Ultra-high purity NiPt alloys and sputtering targets comprising same

Abstract

A method of making a NiPt alloy having an ultra-high purity of at least about 4N5 and suitable for use as a sputtering target, comprises steps of: heating predetermined amounts of lesser purity Ni and Pt at an elevated temperature in a crucible to form a NiPt alloy melt, the crucible being composed of a material which is inert to the melt at the elevated temperature; and transferring the melt to a mold having a cavity with a surface coated with a release agent which does not contaminate the melt with impurity elements. The resultant NiPt alloy has a very low concentration of impurity elements and is subjected to cross-directional hot rolling for reducing thickness and grain size.

1 . A method of making an ultra-high purity NiPt alloy of at least 4N5 purity, comprising steps of:
 (a) heating predetermined amounts of lesser purity Ni and Pt at an elevated temperature in a crucible to form a NiPt alloy melt, said crucible being composed of a material which is inert to said melt at said elevated temperature; and   (b) transferring said melt to a mold having a cavity with a surface coated with a release agent which does not contaminate said melt with impurity elements.   
   
   
       2 . The method according to  claim 1 , wherein:
 step (a) comprises heating at a temperature from about 1455 to about 1650° C. to form said NiPt alloy melt.   
   
   
       3 . The method according to  claim 1 , wherein:
 step (a) comprises heating predetermined amounts of lesser purity Ni and Pt in Ni:Pt atomic ratios ranging from about 99:1 to about 20:80.   
   
   
       4 . The method according to  claim 1 , wherein:
 step (a) comprises vacuum induction melting (VIM).   
   
   
       5 . The method according to  claim 1 , wherein:
 step (a) comprises forming said NiPt alloy melt in a crucible composed of yttria stabilized zirconia (YSZ).   
   
   
       6 . The method according to  claim 1 , wherein:
 step (a) comprises purifying said NiPt alloy melt by removing impurity-containing slag which forms at an upper surface of said melt.   
   
   
       7 . The method according to  claim 1 , wherein:
 step (a) comprises purifying said NiPt alloy melt by evaporation of impurities from said melt.   
   
   
       8 . The method according to  claim 1 , wherein:
 step (b) comprises directly transferring said melt to said mold without use of a tundish.   
   
   
       9 . The method according to  claim 1 , wherein:
 step (b) comprises directly transferring said NiPt alloy melt to a mold composed of graphite and having a cavity coated with Al 2 O 3  release agent.   
   
   
       10 . The method according to  claim 1 , further comprising steps of:
 (c) removing an ingot of solidified NiPt alloy from said mold; and   (d) subjecting said ingot to thermo-mechanical rolling for reducing thickness and grain size of said NiPt alloy.   
   
   
       11 . The method according to  claim 10 , wherein:
 step (d) comprises alternate rolling in straight and cross directions.   
   
   
       12 . The method according to  claim 11 , wherein:
 step (d) comprises re-heating said NiPt alloy during said straight direction rolling.   
   
   
       13 . A 4N5 ultra-high purity NiPt alloy fabricated by the process according to  claim 12 . 
   
   
       14 . A 4N5 ultra-high purity NiPt alloy having a Si concentration of <1 ppm, a B concentration of <0.2 ppm, a Ca concentration of <0.05 ppm, an Al concentration of <0.1 ppm, and a total impurity concentration of <50 ppm. 
   
   
       15 . The NiPt alloy as in  claim 14 , having a Ni:Pt atomic ratio in the range from about 99:1 to about 20:80. 
   
   
       16 . The NiPt alloy as in  claim 14 , having with a grain size from about 200 to about 300 μm. 
   
   
       17 . A sputtering target comprising the 4N5 ultra-high purity NiPt alloy of  claim 16 .