Abstract:
The present invention is to provide a magnetron sputtering technique for forming a film having an even film thickness distribution for a long period of time. A magnetron sputtering apparatus of the present invention includes a vacuum chamber, a cathode part provided in the vacuum chamber, the cathode part holding a target on the front side thereof and having a backing plate to hold a plurality of magnets on the backside thereof, and a direct-current power source that supplies direct-current power to the cathode part. A plurality of control electrodes, which independently controls potentials, is provided in a discharge space on the side of the target with respect to the backing plate.

Description:
[0001]    This application is a continuation of International Application No. PCT/JP2009/054536 filed Mar. 10, 2009, which claims priority to Japanese Patent Document No. 2008-068534, filed on Mar. 17, 2008. The entire disclosures of the prior applications are herein incorporated by reference in their entireties. 
     
    
     BACKGROUND OF INVENTION 
       [0002]    The present invention generally relates to a technique to form a film by sputtering in a vacuum, and, more particularly, to a film formation technique by magnetron sputtering. 
       BACKGROUND ART 
       [0003]    Conventionally, in a magnetron sputtering apparatus  101  of this kind, a plurality of rod-shaped magnets  112  is arranged on the backside (on the side of a backing plate  108 ) of a target  107  facing a substrate  104  in a vacuum chamber  102 , for example, as shown in  FIG. 6(   a ). 
         [0004]    In such a conventional art, when the target  107  is used for a long period of time, the surface of the target  107  is dug; and therefore, differences in impedance are generated among a plurality of magnets  112 ; and as a result, a problem arises whereby the distribution of plasma in a discharge space becomes uneven. 
         [0005]    For example, in the example shown in  FIG. 6(   a ), a lateral region of the target is dug compared to a target region  107   a  corresponding to the magnet  112  in the center as shown in  FIGS. 6(   b ) and  6 ( c ); and as a result, a problem arises whereby the film thickness on the substrate  104  becomes thinner in the center region than in the edge part region of the substrate  104 . 
         [0006]    Conventionally, such a problem is addressed by changing the distance between the target  107  and the magnet  112  and correcting the magnetic circuit. However sufficient film-thickness uniformity cannot be obtained. See Japanese Unexamined Patent Publication No. 11-200037 and Japanese Unexamined Patent Publication No. 11-302843. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention has been developed in order to solve the problems of the conventional art as described above; and an object thereof is to provide a magnetron sputtering technique capable of forming a film having an even film thickness distribution for a long period of time. 
         [0008]    The present invention developed in order to achieve the above-described object is directed to a magnetron sputtering apparatus comprising a vacuum chamber; a cathode part provided in the vacuum chamber, the cathode part holding a target on the front side of the cathode part and having a holding mechanism that holds a plurality of magnets on the backside thereof; and a power source that supplies power to the cathode part, wherein a plurality of control electrodes capable of independently controlling potentials is provided in a discharge space on the side of the target with respect to the holding mechanism. 
         [0009]    In the present invention, the control electrode is provided corresponding to each of a plurality of magnets in the above-described invention. 
         [0010]    In the present invention, the magnet is formed into a rod-shape and the control electrode is arranged so as to sandwich the holding mechanism and overlap the end part of the magnet in the above-described invention. 
         [0011]    In the present invention, the control electrode is arranged so as to project inward with respect to the end edge part of the target in the invention. 
         [0012]    On the other hand, the present invention is directed to a magnetron sputtering method for generating a magnetron discharge in a vacuum and performing sputtering, comprising the steps of arranging a plurality of control electrodes in a discharge space of a target and making potentials of a plurality of control electrodes different from one another when supplying power to the target in a vacuum and generating plasma. 
         [0013]    In the present invention, the potential of the control electrode in a specific region of the target among a plurality of control electrodes is made higher than the potential of the control electrodes in regions other than the specific region of the target when supplying power to the target in a vacuum and generating plasma in the above-described invention. 
         [0014]    In the present invention, the specific region of the target is the center region of the target in the above-described invention. 
         [0015]    In the present invention, the potential of the control electrode in the specific region of the target is set at a floating potential; on the other hand, the potential of the control electrodes in regions other than the specific region of the target are set at a ground potential in the above-described invention. 
         [0016]    According to the present invention, a plurality of control electrodes is arranged in a discharge space of a target. When supplying power to the target in a vacuum and generating plasma, the potentials of a plurality of control electrodes are made different from one another, whereby the impedance of each magnet can be adjusted. Consequently, it is possible to achieve the evenness of film thickness by correcting the unevenness of the distribution of plasma in a discharge space. 
         [0017]    In the present invention, if the (absolute value of the) potential of the control electrode in a specific region (for example, the center region) of a target among a plurality of control electrodes is set higher than the (absolute value of the) potential of the control electrodes in regions (for example, lateral regions) other than the specific region of the target, it is possible to relatively increase the plasma density in the discharge space in the specific region. As a result, according to the present invention, it is possible to achieve the evenness of film thickness in a case whereby the center region on the target surface is dug in a long-term use of the target, for example. 
         [0018]    In this case, if the potential of the control electrode in the specific region of the target among a plurality of control electrodes is set at a floating potential and on the other hand, if the potential of the control electrodes in regions other than the specific region of the target is set at a ground potential, it is possible to easily aim at the evenness of film thickness by increasing the film formation rate higher in the specific region of the target. 
         [0019]    According to the apparatus of the present invention, the above-described invention can be embodied easily with a simplified structural arrangement. 
         [0020]    In particular, for example, when the control electrode is provided corresponding to each of a plurality of magnets, or when the magnet is formed into a rod-shape and the control electrode is arranged so as to sandwich the holding mechanism and overlap the end part of the magnet, and when the control electrode is arranged so as to project inward with respect to the end edge part of the target, it is possible to set the potential of the control electrode in the specific region of the target higher than the potential of the control electrodes in regions other than the specific region of the target. 
       EFFECTS OF THE INVENTION 
       [0021]    According to the present invention, it is possible to provide a magnetron sputtering technique capable of forming a film having an even film thickness distribution for a long period of time. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  is a sectional view illustrating an internal structural arrangement of an embodiment of a magnetron sputtering apparatus according to the present invention. 
           [0023]      FIG. 2  is a plan view illustrating an external constitution of a cathode part of the magnetron sputtering apparatus. 
           [0024]      FIG. 3  is a graph for showing a relationship between the magnitude of a current, which flows to a control electrode, and the film formation rate. 
           [0025]      FIG. 4  is a diagram for illustrating a method of measuring a relationship between the projection length of a control electrode and the film thickness. 
           [0026]      FIG. 5  is a graph for showing a relationship between the distance between the tip end part of the control electrode and the measurement point (B⊥0) and the film thickness. 
           [0027]      FIG. 6(   a ) is a sectional view for showing an internal structural arrangement of a conventional magnetron sputtering apparatus. 
           [0028]      FIG. 6(   b ) is a diagram for illustrating a problem of the conventional art. 
           [0029]      FIG. 6(   c ) is a diagram for illustrating a problem of the conventional art. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0030]    A preferred embodiment of the present invention will be described below in detail with reference to the drawings. 
         [0031]      FIG. 1  is a sectional view illustrating an internal structural arrangement of an embodiment of a magnetron sputtering apparatus according to the present invention; and 
         [0032]      FIG. 2  is a plan view illustrating an external structural arrangement of a cathode part of the magnetron sputtering apparatus. 
         [0033]    As shown in  FIG. 1 , a sputtering apparatus  1  of the present embodiment has a vacuum chamber  2  connected to a vacuum evacuating system (not shown schematically). The vacuum chamber  2  is at ground potential. 
         [0034]    Inside the vacuum chamber  2 , a flat plate-shaped substrate (object to be film-formed)  3  is held by a substrate holder  4  in such a manner that the substrate  3  faces a cathode part  6  via a mask  5 . 
         [0035]    The cathode part  6  has a backing plate (holding mechanism)  8  for holding a target  7 , whereby the target  7  faces the substrate in parallel. The backing plate  8  is connected to a direct-current power source  30 . 
         [0036]    In the region around the target  7 , for example, an inner shield member  9  made of a ring-shaped metal is arranged. 
         [0037]    In the region around the backing plate  8 , for example, an outer shield member  10  made of a ring-shaped metal is provided. 
         [0038]    The inner shield member  9  is in a floating potential state. On the other hand, the outer shield member  10  is insulated from the inner shield member  9  and is at ground potential. 
         [0039]    As shown in  FIG. 2 , on the backside of the backing plate  8 , a plurality of magnets  12  (five in the present embodiment) made of permanent magnets held by a holding part  11  is provided. 
         [0040]    In the present embodiment, a rod-shaped magnet is used for each of magnets  12   a  to  12   e ; and magnets are arranged in parallel with one another at a predetermined interval. The size and position of each of the magnets  12   a  to  12   e  are determined so as not to bulge out from the region of the target  7 . 
         [0041]    Further, in the present embodiment, at a pair of edge parts  91 ,  92 , which face the inner shield member  9 , control electrodes  21 ,  22  are arranged, respectively. 
         [0042]    The control electrodes  21 ,  22 , for example, made of a rectangular plate-shaped member, are configured by, for example, a metal material (such as, stainless). The control electrodes  21 ,  22  and the inner shield member  9  are electrically insulated from each other. 
         [0043]    The size and the position of the respective control electrodes  21 ,  22  are determined so as to stick out from the respective edge portions  91 ,  92  of the inner shield member  9  toward the side of the target  7 , which is located inside the edge portions  91 ,  92 . 
         [0044]    In the present embodiment, the control electrodes  21 ,  22  are configured by five control electrodes  21   a  to  21   e  and five control electrodes  22   a  to  22   e , respectively, so as to correspond to each of the magnets  12   a  to  12   e.    
         [0045]    The control electrodes  21   a  to  21   e  and the control electrodes  22   a  to  22   e  are respectively formed so as to be somewhat wider than the magnets  12   a  to  12   e , and arranged in a manner such that the respective tip end parts on the side of the target  7  overlap the respective end parts of the magnets  12   a  to  12   e  while sandwiching the backing plate  8  and the target  7 . 
         [0046]    Further, the control electrodes  21   a  to  21   e  and the control electrodes  22   a  to  22   e  are respectively connected electrically in such a manner that an opposed pair of the control electrodes  21   a  and  22   a , an opposed pair of the control electrodes  21   b  and  22   b , an opposed pair of the control electrodes  21   c  and  22   c , an opposed pair of the control electrodes  21   d  and  22   d , and an opposed pair of the control electrodes  21   e  and  22   e  are at the same potential, respectively, the respective opposed pairs of the control electrodes  21   a  to  21   e  and  22   a  to  22   e  sandwiching each of the magnets  12   a  to  12   e.    
         [0047]    Further, the control electrodes  21   a  to  21   e  and the control electrodes  22   a  to  22   e  are connected to ground outside the vacuum chamber  2  via a variable resistor  23 , respectively. 
         [0048]    In the present embodiment as discussed above, a plurality of the control electrodes  21 ,  22  is arranged in a discharge space of the target  7 ; and when supplying direct-current power to the target  7  in a vacuum and generating plasma, for example, the potential of the control electrodes  21   c ,  22   c  in the center region of the target  7  among a plurality of the control electrodes  21 ,  22  is set at, for example, a floating potential, whereby, the potential is set higher than the potential of the control electrodes  21   a ,  21   b ,  21   d  and  21   e  and the control electrodes  22   a ,  22   b ,  22   d  and  22   e  in the lateral region of the target  7 . 
         [0049]    As a result, it is, for example, possible to relatively increase the plasma density in the discharge space in the center region of the target  7 , whereby it is possible to achieve the evenness of the film thickness even when, for example, the center region of the surface of the target  7  is dug in the long-term use of the target  7 . 
         [0050]    According to the magnetron sputtering apparatus  1  in the present embodiment, it is possible to easily embody the above-discussed invention with a simple structural arrangement. 
         [0051]    The present invention is not limited to the above-discussed embodiment but can be modified in a variety of ways. 
         [0052]    For example, in the above-discussed embodiment, the potential of the control electrodes  21   c ,  22   c , for example, in the center region of the target  7  among a plurality of the control electrodes  21 ,  22  is set higher than the potential of the other control electrodes  21   a ,  21   b ,  21   d  and  21   e  and the other control electrodes  22   a ,  22   b ,  22   d  and  22   e . However, the present invention is not limited to the above and it is also possible to independently adjust the potential of any of the other control electrodes  21   a ,  21   b ,  21   d  and  21   e  and the other control electrodes  22   a ,  22   b ,  22   d  and  22   e.    
         [0053]    In the above-discussed embodiment, the five control electrodes  21   a  to  21   e  and the five control electrodes  22   a  to  22   e  are provided, respectively, so as to correspond to each of the magnets  12   a  to  12   e . However, the present invention is not limited to the above, and it is also possible to provide a control electrode so as to correspond only to a specific magnet. 
         [0054]    Further, the shape and the position of the control electrode are not limited to those in the above-discussed embodiment; and they can be changed appropriately as long as they remain within the scope of the present invention. 
       EXAMPLE 
       [0055]    An example of the present invention will be described below in detail along with a comparative example. 
         [0056]    Sputtering was performed under the condition such that the target-to-magnet distance is 45 mm and the target-to-substrate distance is 125 mm by using the magnetron sputtering apparatus shown in  FIG. 1  and  FIG. 2  and using aluminum (Al) as a target. 
         [0057]    In this case, the input power is 42.8 kW and the pressure is kept at 0.35 Pa by feeding argon (Ar) into the vacuum chamber at 100 sccm. 
         [0058]    Further, as a control electrode, a flat plate-shaped electrode made of stainless (140 mm wide) is used; and the control electrode is set in such a manner that it projects 20 mm from each of the end edge parts of the target toward the inside of the target and that the gap between the target and the control electrode is 5 mm. 
         [0059]    Sputtering is then performed for 56 seconds, while oscillating each magnet by 100 mm; and thus, a film is formed on the substrate. The result is shown in Table 1 to Table 3. 
         [0060]    Table 1 shows film thicknesses when all of the control electrodes are set at the ground potential (condition 1); Table 2 shows film thicknesses when only the control electrodes ( 21   c ,  22   c ) in the center are set at the floating potential (condition 2); and Table 3 shows the result of calculation of differences between film thicknesses under condition 2 and those under condition 1. 
         [0061]    Figures in Tables 1 to 3 denote film thicknesses at the measurement positions on the substrate corresponding to the center part of each magnet (the distance from the end part of the substrate is attached for reference) in units of Å. 
         [0062]    Figures in the row and column outside Table 1 and Table 2 denote averages of film thicknesses in the rows and columns in each of the Tables. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 All control electrodes are at ground potential (condition 1: Å) 
               
             
          
           
               
                   
                 10 mm 
                 137.5 mm 
                 275 mm 
                 412.5 mm 
                 540 mm 
               
               
                   
                   
               
             
          
           
               
                  10 mm 
                 3118 
                 3631 
                 3515 
                 3796 
                 3281 
                 3468 
               
               
                 162.5 mm   
                 3315 
                 4032 
                 3700 
                 3990 
                 3373 
                 3682 
               
               
                 325 mm 
                 3390 
                 3780 
                 3520 
                 3570 
                 3290 
                 3510 
               
               
                 487.5 mm   
                 3555 
                 4065 
                 3635 
                 3795 
                 3286 
                 3667 
               
               
                 640 mm 
                 3242 
                 3829 
                 3492 
                 3667 
                 3126 
                 3471 
               
               
                   
                 3324 
                 3867.4 
                 3572.4 
                 3763.6 
                 3271.2 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Control electrodes in the center are 
               
               
                 at floating potential (condition 2: Å) 
               
             
          
           
               
                   
                 10 mm 
                 137.5 mm 
                 275 mm 
                 412.5 mm 
                 540 mm 
               
               
                   
                   
               
             
          
           
               
                  10 mm 
                 2950 
                 3725 
                 4025 
                 3930 
                 2980 
                 3522 
               
               
                 162.5 mm   
                 3120 
                 4080 
                 4400 
                 4305 
                 3230 
                 3827 
               
               
                 325 mm 
                 3305 
                 4150 
                 4235 
                 3940 
                 3100 
                 3746 
               
               
                 487.5 mm   
                 3440 
                 4285 
                 4330 
                 3920 
                 3170 
                 3829 
               
               
                 640 mm 
                 3170 
                 3850 
                 3970 
                 3580 
                 3000 
                 3514 
               
               
                   
                 3197 
                 4018 
                 4192 
                 3935 
                 3096 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 Differences between condition 2 and condition 1 (Å) 
               
             
          
           
               
                   
                 10 mm 
                 137.5 mm 
                 275 mm 
                 412.5 mm 
                 540 mm 
               
               
                   
                   
               
             
          
           
               
                  10 mm 
                 −168 
                 94 
                 510 
                 134 
                 −301 
               
               
                 162.5 mm   
                 −195 
                 48 
                 700 
                 315 
                 −143 
               
               
                 325 mm 
                 −85 
                 370 
                 715 
                 370 
                 −190 
               
               
                 487.5 mm   
                 −115 
                 220 
                 695 
                 125 
                 −116 
               
               
                 640 mm 
                 −72 
                 21 
                 478 
                 −87 
                 −126 
               
               
                   
               
             
          
         
       
     
         [0063]    As will be understood from Table 1 to Table 3, when the control electrodes ( 21   c ,  22   c ) in the center are set at the floating potential, the film thicknesses in the center and the regions on both sides of the control electrodes ( 21   c ,  22   c ) in the center are large (700 Å at maximum), as compared to the case where all of the control electrodes are set at the ground potential. 
         [0064]    It is thought that the plasma density increases and the film formation rate increases in the vicinity of the control electrodes ( 21   c ,  22   c ), which are set at the floating potential. 
         [0065]    Table 4 shows film thicknesses when a resistor of 100Ω is connected only to the control electrodes ( 21   c ,  22   c ) in the center (condition 3); and Table 5 shows the result of the calculation in the differences between film thicknesses under condition 3 and film thicknesses under condition 1 (when all of the control electrodes are set at the ground potential). 
         [0066]    Under condition 3, a current that flows through the control electrodes ( 21   c ,  22   c ) in the center was −0.7. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 4 
               
             
             
               
                   
               
               
                 Resistor of 100 Ω is connected to control electrodes in the center (condition 3: Å) 
               
             
          
           
               
                   
                 10 mm 
                 137.5 mm 
                 275 mm 
                 412.5 mm 
                 540 mm 
               
               
                   
                   
               
             
          
           
               
                  10 mm 
                 2928 
                 3509 
                 3598 
                 3790 
                 3260 
                 3417 
               
               
                 162.5 mm   
                 3311 
                 3847 
                 4003 
                 4313 
                 3483 
                 3791 
               
               
                 325 mm 
                 3331 
                 3884 
                 3883 
                 3953 
                 3397 
                 3690 
               
               
                 487.5 mm   
                 3447 
                 4096 
                 3950 
                 3910 
                 3332 
                 3747 
               
               
                 640 mm 
                 3239 
                 3757 
                 3657 
                 3702 
                 3174 
                 3506 
               
               
                   
                 3251.2 
                 3818.6 
                 3818.2 
                 3933.6 
                 3329.2 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 5 
               
             
             
               
                   
               
               
                 Differences between condition 3 and condition 1 (Å) 
               
             
          
           
               
                   
                 10 mm 
                 137.5 mm 
                 275 mm 
                 412.5 mm 
                 540 mm 
               
               
                   
                   
               
             
          
           
               
                  10 mm 
                 −190 
                 −122 
                 83 
                 −6 
                 −21 
               
               
                 162.5 mm   
                 −4 
                 −185 
                 303 
                 323 
                 110 
               
               
                 325 mm 
                 −59 
                 104 
                 363 
                 383 
                 107 
               
               
                 487.5 mm   
                 −108 
                 31 
                 315 
                 115 
                 46 
               
               
                 640 mm 
                 −3 
                 −72 
                 165 
                 35 
                 48 
               
               
                   
               
             
          
         
       
     
         [0067]    As will be understood from Table 1, Table 4, and Table 5, when the resistor of 100Ω is connected to the control electrodes in the center, the film thicknesses in the center and the regions on both sides of the control electrodes in the center become large (300 Å at maximum), as compared to the case where all of the control electrodes are set at the ground potential. 
         [0068]    It is thought that the plasma density increases and the film formation rate increases in the vicinity of the control electrodes to which the resistor of 100Ω is connected. 
         [0069]      FIG. 3  is a graph for showing a relationship between the magnitude of a current that flows through the control electrode and the film formation rate in the above-discussed example. 
         [0070]    As will be understood from  FIG. 3 , when the magnitude of the current that flows through the control electrode is zero (that is, when the control electrodes in the center are at the floating potential), the film formation rate reaches a maximum; and there is a tendency that as the magnitude of the current that flows through the control electrode increases, the film formation rate decreases. 
         [0071]    In this case, the film formation rate changes when the current that flows through the control electrode is 0 A to 2 A. Even when the current that flows through the control electrode exceeds 2 A, the film formation rate does not change (decrease). 
         [0072]    The inventors of the present invention have confirmed through experiments that when the magnitude of the current, which flows through the control electrode, is varied, the film formation rate does not change in the longitudinal direction of the magnet, as will also be understood from Table 1 and Table 2. 
         [0073]    Further, the inventors of the present invention have confirmed by experiments that the film formation rate does not change either when the potential of the inner shield member is set at the ground potential or when it is set at the floating potential and the film formation rate can be adjusted by changing the potential of the control electrode, as described above. 
         [0074]      FIG. 4  is a diagram for illustrating a method of measuring a relationship between the projection length of the control electrode and the film thickness in the above-described example; and  FIG. 5  is a graph representing a relationship between the distance (Δx) between the tip end part of the control electrode and the measurement point (B⊥0) and the film thickness. The measurement point (B⊥0) is a point where the orthogonal component of a magnetic field vector, which is formed by the magnet, with respect to the target is zero on the target surface. 
         [0075]    As will be understood from  FIG. 4  and  FIG. 5 , as the distance Δx between the tip end parts of the control electrodes  21 ,  22  and the measurement point decreases (that is, as the projection length toward the inside of the target  7  of the control electrodes  21 ,  22  increases), there is a tendency for the ratio of the film thickness at the floating potential with respect to the film thickness at the ground potential to increase. 
         [0076]    This means that the film formation rate is increased due to the projection length of the control electrodes  21 ,  22  being made longer, as seen from the results shown in  FIG. 3  and as described above.