Patent Publication Number: US-2007116592-A1

Title: Fabrication of Ruthenium and Ruthenium Alloy Sputtering Targets with Low Oxygen Content

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application claims priority from provisional application Ser. No. 60/738,945 filed Nov. 22, 2005 for “Fabrication of Ruthenium and Ruthenium Alloy Sputtering Targets with Low Oxygen Content.” 
    
    
     FIELD OF THE INVENTION  
      This invention relates to methods for fabricating ruthenium and ruthenium alloy sputtering targets.  
     BACKGROUND OF THE INVENTION  
      Sputtering targets for sputtering processes can be prepared from ruthenium and alloys of ruthenium with one or more other components, typically one or more elemental metals or ceramic materials. These other components can be added to ruthenium and ruthenium alloy compositions for sputtering targets to provide specific characteristics to the sputtering target or to the film that is deposited on a substrate in a sputtering process. In some instances, it may desirable to reduce the oxygen content of the composition.  
     SUMMARY OF THE INVENTION  
      The invention is a method for fabricating ruthenium and ruthenium alloy sputtering targets having an oxygen content of 200 ppm or less by subjecting ruthenium or ruthenium alloy preforms to hydrogen reduction. The hydrogen reduction step is performed after the billet is pressed and before obtaining final density. The preform can be machined to form a sputter target after final density has been obtained. Thus, the invention provides a hydrogen reduction step prior to encapsulation and hot isostatic pressing (HIPing) the perform. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Ruthenium and ruthenium alloy powders are blended to create a homogenous mixture and then consolidated into a preform or billet that is used for fabricating the sputtering targets. The blended powders from which the preform is pressed can include any additional elemental metals, alloys, nonmetallic materials, and ceramic materials, including oxides. Typically, other components may be added to the ruthenium or ruthenium alloy in amounts that can vary from less than about 1% to more than about 30% by weight of the powder mixture. The specific amount of other components added, if any, depends on the properties desired in the target or film formed from the target. More or less may be used depending on the specific properties being sought. Other elemental metals include any of the metals from the periodic table, including, but not limited to, chromium, cobalt, nickel, and iron. Various alloys of these metals can be used. Nonmetallic and ceramic materials include boron, carbon, silicon, various oxides, and others.  
      The homogeneous powder should be consolidated into a preform by cold isostatic pressing (CIPing) or, alternatively, mechanical pressing, followed by hydrogen reduction, encapsulating, hot isostatic pressing (HIPing), and machining. Pressures for initial consolidation of the powders normally are in the range of from about 10 to 100 ksi. A CIP unit is typically a cylindrical pressure vessel that is large enough to house one or more flexible containers, normally latex or plastic, in which the powders are placed to form the preform. The pressure within the pressure vessel can be increased by introduction of a liquid, typically either an oil or water with a rust inhibitor added.  
      Once the preforms have been pressed, they should be subjected to hydrogen reduction prior to encapsulation and hot isostatic pressing (HIP) cycles. The preform is heated in a hydrogen furnace to reduce oxygen. The reduction furnace should be operated at a temperature of from about 500 to 3,800° F. Typically, pressure will be about 1,000 psi or less, including less than atmospheric pressure. The broad temperature and pressure ranges are directed to achieving low oxygen content. Specific conditions within these ranges may be selected depending on particular desired properties in the target or film formed from the target.  
      After the preforms have been heated in the hydrogen reduction atmosphere and the oxygen removed, they should be encapsulated in a deformable metal container. The deformable metal container is evacuated and sealed after heating to ensure the removal of any moisture or trapped gases that may be present. Typically, the deformable metal container will have a geometry that is close to the final material configuration that is desired for the sputtering target.  
      Once encapsulated, the preforms can be subjected to a HIP cycle to obtain the final density for the preform. The HIP unit is similar to a CIP unit, except the HIP unit includes resistance-heating elements lining the inner walls of the vessel. The pressure is controlled by the introduction of an inert gas. The HIP conditions should include a temperature from about 500 to 3,800° F. at a pressure from about 5 to 50 ksi. Typically the HIP cycle will be run from about 1 to 24 hours. Thereafter, the dense billet can be machined to form a sputter target.