Patent Publication Number: US-4731116-A

Title: Sputter target and process for producing sputter target

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to sputter targets made of carbides and/or nitrides and/or borides of refractory metals and a process for producing sputter targets. 
     Sputtering, the technique of coating diverse metallic and non-metallic shaped parts by evaporating targets (sputter targets) in cathodic evaporating units has gained rapidly in importance in recent years and is continuing to grow. In the past, sputter targets of carbides and/or nitrides and/or borides of the refractory metals have been produced by pressing and sintering, or by hot pressing powdered carbides, nitrides, borides or mixtures thereof. The required sintering temperatures, or hot pressing temperatures, of such processes are very high, generally in the order of about 2000° C. The shaped parts of these earlier processes generally have poor mechanical strength, are generally difficult to machine and have a tendency of forming cracks. As a result, they have low thermal shock resistance. Materials with these properties are of very limited use as sputter targets. Thus, targets of this type have found little commercial application. 
     SUMMARY OF THE INVENTION 
     According to the present invention, a process is provided for producing sputter targets made of carbides and/or nitrides and/or borides of refractory metals which avoid, or substantially avoid, the disadvantages mentioned above. 
     A product and process are provided as follows: First, a dense composite body is produced from (1) one or more carbides and/or nitrides and/or borides of the refractory metals of Group IV A-VI A of the periodic tables of the elements, and (2) a metallic binding agent of one or more metals of the iron group of the periodic table. The dense composite body is produced by powder metallurgy methods such as by pressing and/or sintering. The shaped target body can then be machined, either before and/or after sintering, and finally the binding agent is removed from the target by chemical or electrochemical treatment. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The shaped sputter targets of the invention are produced by processes, such as pressing and/or sintering a powder blend of carbides and/or nitrides and/or borides of refractory metals having a powdered metal binding agent incorporated therewith. The binding agents can be cobalt, iron, nickel or blends of such metals and the like, or mixtures thereof. 
     Advantageously, the process of the invention provides for use of much lower sintering temperatures of about 1500° C., as compared to the earlier production processes. In cases where machining of the sputter targets is necessary, the sintered shaped parts can be produced in final form, or nearly final form, prior to removing the binding agent. In this manner, the sputter targets can be more easily machined. After machining, the metallic binding agent can be removed completely, or almost completely, by chemical or electrochemical treatment such as by etching. 
     Surprisingly, even after removing the binding agent, the sputter targets of the invention have excellent mechanical strength and high thermal shock resistance. These properties are very important for sputter targets and are considerably higher than the values for sputer targets produced by earlier processes. The binding agents can be removed from the target completely or almost completely by chemical and/or electrochemical treatment. The level of contaminating elements, such as oxygen, nitrogen and the like and the residual binding agent, in the sputter targets of the invention are extremely low and meet the general requirements for sputter targets. 
     Table 1 below shows of contaminant levels and the bending strength values of various tungsten carbide sputter targets produced by the process of the invention, starting with different base materials. 
     
                                           TABLE 1                                 
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Contaminant Levels and Bending Strength of                                
Sputter Targets Produced According to the Invention                       
Base Material              Residual Co                                    
                                   Bending Strength                       
(% by weight)      O.sub.2 ppm                                            
                       N.sub.2 ppm                                        
                           (% by weight)                                  
                                   (N/mm.sup.2)                           
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6% Co 0.3% TaC                                                            
           Remainder WC                                                   
                   250 53  .04     not measured                           
9% Co 0.6% TaC                                                            
           0.2% TiC                                                       
                   780 12  .04     not measured                           
           Remainder WC                                                   
9% Co 10% TaNbC                                                           
           4% TiC  1200                                                   
                       1100                                               
                           .05     475                                    
           Remainder WC                                                   
6% Co 5.5% TaNbC                                                          
           5% TiC  1020                                                   
                       500 .08     614                                    
           Remainder WC                                                   
6% Co      Remainder WC                                                   
                   175 --  .03     395                                    
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     The invention is described in more detail in the following example. 
     EXAMPLE 1 
     Disk-shaped sputter targets of tungsten carbide having a final diameter of 75 mm and a thickness of 6 mm are produced in the following manner. 
     0.3 kg of a cobalt powder with an average grain size of 1.3 um was blended with 4.7 kg tungsten carbide powder having an average grain size of 5.5 um. The total carbon content is adjusted to 5.83% by adding powdered carbon black. This powder mixture is ground for 120 hours in a ball mill in the presence of tungsten carbide balls and acetone as a grinding fluid. After the grinding process is completed, the acetone is removed by distillation. The powder blend obtained in this manner is pressed into a cylindrical blank by an isostatic pressing method at a pressure of 1000 bar. Disks are cut from the cylindrical blank and reduced to a dimension such that a shrinkage of 45% in volume that occurs in sintering is taken into account. The disk-shaped pieces are obtained after sintering which are slightly over-dimensioned with respect to the required final dimensions of the sputter target. Following machining, the disk-shaped pieces are sintered in a vacuum at 1480° C. for one hour. The sintered disk-shaped piece is then reduced to the desired final dimensions by grinding using a diamond grinding wheel. Subsequently, the disk-shaped hard-metal piece is treated for approximately 168 hours in boiling, semi-concentrated hydrochloric acid to dissolve the cobalt binding agent. To remove the residual hydrochloric acid, the disk-shaped sputter target is first treated with distilled water at 100° C. and then dried for 24 hours at 120° C. As a check on whether the cobalt binding agent is removed from the sputter targets, the difference in weight of the sputter targets prior to the hyrochloric acid treatment and after the treatment is measured. Another means of checking for whether the cobalt is removed from the sputter target is magnetic saturation, which is zero if there is no cobalt present. In case any residual cobalt is found, the sputter targets are again subjected to treatment with fresh, boiling, semi-concentrated hydrochloric acid until complete or nearly complete dissolution of the cobalt binder phase is achieved.