Abstract:
A magnet unit for a magnetron sputtering system includes a base plate and a plurality of magnet parts each including a first magnet and a first supporting member. The first supporting member supports the first magnet and fixes the first magnet to the base plate. The magnet parts confine a plasma.

Description:
CROSS-REFERENCE TO APPLICATION 
       [0001]    This application is based upon and claims the benefit of priority to Japanese Patent Application No. 2008-50954, filed on Feb. 29, 2008, the entire contents of which are incorporated herein by reference. 
       BACKGROUND 
       [0002]    1. Field 
         [0003]    An aspect of the invention relates to a magnet unit for a magnetron sputtering system. 
         [0004]    2. Description of the Related Art 
         [0005]    A magnetron sputtering system has generally been used to form various thin films on a substrate, such as a semiconductor substrate. The magnetron sputtering system performs sputtering using plasma while generating a magnetic field in the vicinity of the surface of a target, which is a sputtering material. A rotary magnet cathode is used to effectively utilize a target and form a uniform thin film by sputtering the target. The rotary magnet cathode is a device that rotates a plurality of permanent magnets on the rear surface of the target to rotate a magnetic field having a predetermined pattern in the vicinity of the front surface of the target. In order to generate the magnetic field having a predetermined pattern, a magnet unit formed by arranging a plurality of permanent magnets in a predetermined pattern is used. 
         [0006]    The plurality of permanent magnets are arranged in a predetermined pattern such that the target is effectively sputtered. In the same arrangement of the magnets, the sputtering speed of the target or the deposition rate of the target on the substrate depends on the process conditions or the kind of target used during sputtering. Therefore, in this case, the arrangement of the magnets according to the process conditions or the kind of target can be changed. In order to change the arrangement of the magnets, some or all of the permanent magnets provided in the magnet unit can be removed, and the positions where the permanent magnets are attached changed. Hereinafter, the magnet unit to which the permanent magnet is detachably attached is referred to as a detachable magnet unit. 
         [0007]    In many cases, a magnet unit according to the related art includes a base plate to which the permanent magnets are fixed. The base plate is formed of a magnetic material, and serves as a yoke through which magnetic flux generated from the permanent magnet passes. 
         [0008]    Therefore, a detachable magnet unit has been proposed in which a groove is formed in a base plate, serving as a yoke, and the yoke having the permanent magnet attached thereto is fitted into the groove of the base plate and then screwed to the base plate such that it can be detached from the base plate (for example, see Patent Document 1). 
         [0009]    Further, a detachable magnet unit has been proposed in which a pair of permanent magnets are fixed to a yoke member to form a detachable magnet part, and a plurality of detachable magnet parts are screwed to a base plate (for example, see Patent Document 2). 
       [Patent Document 1] 
       [0010]    Japanese Laid-open Patent Publication No. 6-93442 
       [Patent Document 2] 
       [0011]    Japanese Laid-open Patent Publication No. 9-118980 
         [0012]    In the above-mentioned detachable magnet units, a yoke is additionally provided on the base plate, serving as the yoke, to form a double yoke structure, or the yoke is attached to the base plate. Therefore, the thickness of portions other than the permanent magnet, that is, the thickness of the yoke and the base plate is increased, and the thickness of the detachable magnet unit is also increased. When the thickness of the detachable magnet unit is increased, the overall size and weight of the magnetron sputtering system are increased. 
         [0013]    In addition, the permanent magnet provided in the magnet unit is formed of a relatively soft material. Therefore, when the permanent magnet is attached to or detached from the base plate, strong force is applied to the permanent magnet and the permanent magnet may be damaged. 
         [0014]    Therefore, a detachable magnet unit including a yoke member with a minimum thickness is needed. 
       SUMMARY 
       [0015]    According to an aspect of an embodiment, a magnet unit for a magnetron sputtering system includes a base plate and a plurality of magnet parts each including a first magnet and a first supporting member, the first supporting member supporting the first magnet and fixing the first magnet to the base plate, the magnet parts confining a plasma. 
         [0016]    Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part will be obvious from the description, or may be learned by practice of the present invention. The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0017]      FIG. 1  is a diagram schematically illustrating the overall structure of a magnetron sputtering system; 
           [0018]      FIG. 2  is an enlarged cross-sectional view illustrating a magnetron cathode; 
           [0019]      FIG. 3  is a plan view illustrating a magnet unit according to a first embodiment; 
           [0020]      FIG. 4  is a perspective view illustrating a magnet part; 
           [0021]      FIG. 5  is a cross-sectional view illustrating the magnet part screwed to a base plate; 
           [0022]      FIG. 6  is a cross-sectional view illustrating another magnet part screwed on the magnet part; 
           [0023]      FIG. 7  is a cross-sectional view illustrating a magnet part having supporting members with different thicknesses on both side screwed to the base plate; 
           [0024]      FIG. 8  is a cross-sectional view illustrating a part of a magnet unit according to a second embodiment; 
           [0025]      FIG. 9  is a cross-sectional view illustrating a height adjusting member additionally provided in the structure shown in  FIG. 8 ; 
           [0026]      FIG. 10  is a cross-sectional view illustrating an example in which a coil spring is used instead of the height adjusting member; 
           [0027]      FIG. 11  is a cross-sectional view illustrating an example in which a rubber member is used instead of the height adjusting member; 
           [0028]      FIG. 12  is a perspective view illustrating a magnet part using an arc-shaped permanent magnet; and 
           [0029]      FIG. 13  is a diagram for explaining a magnet attaching/detaching method using guide pins. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0030]    Hereinafter, an example of a magnetron sputtering system according to an embodiment of the invention will be described with reference to  FIG. 1 . 
         [0031]    A magnetron sputtering system shown in  FIG. 1  sputters a target T, which is a deposition target, in a vacuum chamber  12  to form a film on a substrate W. A substrate holder  14  is provided at an upper part in the vacuum chamber  12 , and the substrate W is mounted to the substrate holder  14 . A target holder  16  is provided below the substrate holder  14 , and the target T is mounted to the target holder  16 . 
         [0032]    A magnetron cathode  18  is provided on the rear side of the target T mounted to the target holder  16 . The magnetron cathode  18  includes a magnet unit  20  that generates a magnetic field and a rotating mechanism  22  that rotates the magnet unit  20 . Almost all parts of the target holder  16  and the magnetron cathode  18  except for a portion facing the substrate W are covered by a shield  24 . 
         [0033]    In the above-mentioned structure, the vacuum chamber  12 , substrate holder  14  (substrate W), and the shield  24  are connected to the ground. A power source applies a voltage of several hundred volts to the magnetron cathode  18 . In general, in a sputtering method, an inert gas, such as argon (Ar), is used to generate plasma. The inert gas is supplied into the vacuum chamber  12  through a gas inlet  12   a,  and discharged from an exhaust port  12   b.    
         [0034]    A magnet unit (see  FIG. 2 ), which is also called a magnetic circuit, is incorporated into the magnetron cathode  18 . When a high voltage is applied to the magnetron cathode  18 , Ar in the vacuum chamber  12  is changed into plasma, and the plasma is confined in the vicinity of the front surface of the target T by the magnetic field generated by the magnet unit  20 . Electrons in the plasma collide with Ar atoms by the voltage applied to the magnetron cathode  18  to generate Ar ions (Ar+). The Ar ions (Ar+) are accelerated by a sheath electric field generated between the plasma and the target T and collide with the target T. In this way, the target T is sputtered, and the sputtered target material is deposited on the substrate W held by the substrate holder  14 . 
         [0035]      FIG. 2  is an enlarged cross-sectional view illustrating the target holder  16  and the magnetron cathode  18 . The magnet unit  20  according to a first embodiment is incorporated into the magnetron cathode  18  shown in  FIG. 2 . The target holder  16  is provided so as to cover the magnet unit  20 , and the target T is mounted to the target holder  16  so as to be arranged around an upper part of the magnet unit  20 . 
         [0036]    The magnetron cathode  18  includes the magnet unit  20  and the rotating mechanism  22  that rotates the magnet unit  20 . The magnet unit  20  includes a plurality of magnet parts  30  and a base plate  32 . The magnet parts  30  are fixed to the base plate  32  while being arranged in a predetermined pattern. 
         [0037]      FIG. 3  is a plan view illustrating the magnet unit  20 . Among the magnet parts  30  arranged in a predetermined pattern, for example, the outer magnet parts  30 A are fixed to the base plate  32  such that their upper surfaces are magnetized to the N-pole, and the inner magnet parts  30 B are fixed to the base plate  32  such that their upper surfaces are magnetized to the S-pole. The outer magnet parts  30 A (N-pole) and the inner magnet parts  30 B (S-pole) are arranged adjacent to each other such that leakage flux is emitted upward from the upper surface of the outer magnet part  30 A (N-pole) and then bent  180  degrees to enter the inner magnet part  30 B (S-pole). The lower surfaces of the magnet parts  30 A and  30 B come into contact with the base plate  32 , serving as a yoke, and the magnetic flux from the magnet part  30 B passes through the base plate  32  to enter the magnet part  30 A. Therefore, closed magnetic flux lines passing through the magnet parts  30 A and  30 B are generated. 
         [0038]    A portion of the leakage flux generated from the upper surfaces of the magnet parts  30 A and  30 B passes through the target T provided above the magnet unit  20  and is then emitted from target T upward. The magnetic flux causes plasma to be confined in the vicinity of the surface of the target T. As a result, sputtering is performed. 
         [0039]    The polarity of the upper surface of the magnet part  30  and the arrangement pattern of the magnet parts  30  depend on the sputtering conditions or the kind of target T. In addition, the arrangement pattern of the magnet parts  30  depends on the thickness of the target T or the shape of the surface of the target T. That is, the arrangement pattern of the magnet parts  30  such that the leakage flux generated around the surface of the target T is most suitable for the process conditions is changed. 
         [0040]    In this embodiment, the magnet part  30  is fixed to the base plate  32  by screws. A plurality of screw holes  34  are formed in the base plate  32 , and the screw holes  34  are used to fix the magnet parts  30  to the base plate  32 . Each of the magnet parts  30  has through holes  30   a  ( FIG. 4 ) formed at predetermined positions, and the screw holes  34  are formed at positions corresponding to the through holes  30   a.  That is, among a plurality of screw holes  34 , some screw holes  34  (four screw holes  34  in example shown in  FIG. 3 ) provided in a region for fixing one magnet part  30  are selected, and the selected screw holes  34  are used to fix the magnet part  30  to the base plate  32 . 
         [0041]    A plurality of screw holes  34  are provided in the entire surface of the base plate  32 , and it is possible to select four screw holes  34  corresponding to four through holes  30   a  of the magnet part  30  at any position. Therefore, it is possible to fix the magnet part  30  at a desired position or in the vicinity of the desired position by selecting one of a plurality of positions capable of fixing the magnet parts  30  to the base plate  32 . In this way, it is possible to select positions for fixing a plurality of magnet parts  30  to the base plate. As a result, it is possible to arrange the magnet parts  30  in a desired pattern. 
         [0042]    The magnet unit  20  is rotated about the center of the base plate  32 . Therefore, in order to smoothly rotate the magnet unit  20 , it is preferable to align the center of gravity of the magnet unit  20  with the center of the base plate  32  to obtain a good rotation balance. In the example shown in  FIG. 3 , balance weights  31  are attached to the base plate  32  to align the position of the center of gravity of the magnet unit  20  with the center of rotation thereof. In this case, the screw holes  34  can be used to screw the balance weights  31  to the base plate. 
         [0043]      FIG. 4  is a perspective view illustrating the magnet part  30 . The magnet part  30  according to this embodiment includes a permanent magnet  36  and supporting members  38  that are formed of a non-magnetic material, such as stainless steel. The supporting member  38  is a plate member that is formed of a non-magnetic material. The shape of the surface of the supporting member  38  is substantially the same as that of the side surface of the permanent magnet  36 , and the supporting members  38  are attached to the side surfaces (surfaces orthogonal to the surfaces serving as the N-pole and the S-pole) of the permanent magnet  36 . It is preferable to fix the supporting members  38  to the permanent magnet  36  by an adhesive. However, other fixing methods may be used. Since the permanent magnet  36  is formed of a relatively soft material, it is preferable to use a method of fixing the supporting members  38  to the permanent magnet  36  without punching the permanent magnet  36 . The supporting members  38  are fixed to the permanent magnet  36  by an adhesive to form the magnet part  30 . 
         [0044]    The screw through holes  30   a  are formed in the supporting members  38 . Since the permanent magnet  36  is formed of a relatively soft material, it is difficult to process the permanent magnet  36 . Therefore, the through holes  30   a  are formed in the supporting members  38 , and the supporting members  38  having the through holes  30   a  formed therein are fixed to the permanent magnet  36  by an adhesive. 
         [0045]    In the example shown in  FIG. 4 , the supporting members  38  are fixed to both sides of the permanent magnet  36 . However, the supporting member  36  may be fixed to only one side surface of the permanent magnet  36  as long as it can be reliably fixed to the permanent magnet  36 . 
         [0046]      FIG. 5  is a cross-sectional view illustrating the magnet part  30  screwed to the base plate  32 . The screws  40  are inserted into the through holes  30   a  to be engaged with the screw holes  34  of the base plate  32 , thereby fixing the magnet part  30  to the base plate  32 . The screw  40  is formed of a non-magnetic material, such as stainless steel, similar to the supporting member. 
         [0047]    The target T is provided above the magnet part  30  so as to be adjacent to the magnet part  30 . Therefore, it is preferable that a hexagon socket head bolt be used as the screw  40  so that the socket head of the screw  40  does not protrude from the magnet part  30  and strong tightening force is obtained. 
         [0048]    In the example shown in  FIG. 5 , the screw hole  34  engaged with the screw  40  does not pass through the base plate  32 . However, the screw hole  34  may be formed so as to pass through the base plate. On the contrary to the example shown in  FIG. 5 , instead of the through holes  30   a , the screw holes may be formed in the supporting member  38 , and, instead of the screw holes  34 , the through holes may be formed in the base plate  32 . That is, the screws may be inserted into the through holes formed in the base plate  32  from the rear side to be engaged with the screw holes formed in the supporting member  38 , thereby fixing the magnet part  30  to the base plate  32 . However, as in the example shown in  FIG. 5 , it is preferable to insert the screws  40  from the upper side of the magnet part  30 . In this case, it is possible to easily position the magnet part  30  and easily tighten the screw  40  while viewing the magnet part  30 . When the screw is inserted from the rear side of the base plate  32 , the operator tightens the screw from the rear side while viewing the front side of the magnet part  30 . As a result, it is difficult to tighten the screw. 
         [0049]    As in the example shown in  FIG. 5 , when the screw  40  is inserted from the upper side of the magnet part  30 , as shown in  FIG. 6 , it is possible to fix another magnet part  44  onto the magnet part  30  by the screws  40 . Similar to the magnet part  30 , the magnet part  44  is formed by fixing supporting members  48  to the side surfaces of the permanent magnet  46  by an adhesive. The magnet part  44  provided on the magnet part  30  makes it possible to increase the density of leakage flux generated from the magnet and to adjust a magnetic field for confining plasma. 
         [0050]    As a modification of the magnet part  30  shown in  FIG. 5 , supporting members  38 A and  38 B having different thicknesses may be fixed to both side surfaces of the permanent magnet  36 , as shown in  FIG. 7 . In this case, it is possible to change the position of the permanent magnet  36  only by rotating the magnet part  30  180 degrees horizontally and fixing the magnet part  30 . 
         [0051]    The magnet part  30  shown in  FIG. 4  includes through holes  30   b  in addition to the through holes  30   a.  The through hole  30   b  extends in a direction that is vertical to the extension direction of the through hole  30   a.  The arrangement of the through holes  30   b  is the same as that of the through holes  30   a.  Therefore, it is possible to rotate the magnet part  30  90 degrees and fix the magnet part  30  to the base plate  32  by the screws  40 , as shown in  FIG. 5 . In this way, it is possible to change the direction of the permanent magnet  36  and change the magnetic field generated by the magnet part  30 . 
         [0052]    Next, a magnet unit according to a second embodiment is described with reference to  FIGS. 8 to 11 . Similar to the magnet unit according to the first embodiment, in the magnet unit according to the second embodiment, a plurality of screw holes are formed in a base plate. Therefore, it is possible to change the fixing position of the magnet part. 
         [0053]    As shown in  FIG. 8 , the magnet unit according to the second embodiment includes a magnet part  50  formed by fixing supporting members  38 , each having a size that is smaller than that of a permanent magnet  36 , to the permanent magnet  36 , and a base plate  52  having a magnet accommodating groove  52   a  provided therein. That is, the upper and lower parts of the permanent magnet  36  protrude from the upper and lower surfaces of the supporting members  38 , respectively. Therefore, the lower part of the permanent magnet  36  protruding from the supporting members  38  is accommodated or fitted into the magnet accommodating groove  52   a  formed in the base plate  52 . In this state, the magnet part  50  is screwed to the base plate  52 . 
         [0054]    In the structure shown in  FIG. 9 , it is possible to easily adjust the height of the magnet part  50  (the height of the upper surface of the permanent magnet  36  from the base plate  52 ) using a height adjusting member  54 , as shown in  FIG. 9 . The height adjusting member  54  is formed of a non-magnetic material, similar to the supporting member  38 . It is possible to increase the height of the upper surface (the surface serving as the N-pole or the S-pole) of the permanent magnet  36  by a value corresponding to the thickness of the height adjusting member  54  by inserting the height adjusting member  54  having a thickness corresponding to a desired height between the supporting member  38  and the base plate  52  and fixing it by screws. 
         [0055]    The depth of the magnet accommodating groove  52   a  provided in the base plate  52  is set to be sufficiently larger than the thickness of the height adjusting member  54 . Therefore, even when the height adjusting member  54  is additionally provided, a portion of the permanent magnet  36  is fitted into the magnet accommodating groove  52   a,  and the permanent magnet  36  is connected to the base plate  52  without any gap therebetween. That is, the contact between the side surface of the permanent magnet  36  and the side wall of the magnet accommodating groove  52   a  is maintained. The magnetic flux of the permanent magnet  36  can enter the base plate  52  through the contact portion. Therefore, it is possible to reduce magnetic resistance, as compared to the case when the magnetic flux passes through a gap. As a result, even when the height adjusting member  54  is additionally provided, the magnetic flux density of the permanent magnet  36  is not greatly reduced. 
         [0056]    Instead of additionally providing the height adjusting member  54 , the supporting members  38  may be fixed to the base plate  52  by the screws  40  with elastic members interposed therebetween. In the example shown in  FIG. 10 , as the elastic member, a coil spring  56  is interposed between the supporting member  38  and the base plate  52 . In the example shown in  FIG. 11 , as the elastic member, a rubber member  58  is interposed between the supporting member  38  and the base plate  52 . 
         [0057]    The magnet part  50  is fixed to the base plate  52  with the elastic member, such as the coil spring  56  or the rubber member  58  elastically deformed. Therefore, when the screw  40  is loosened, the magnet part  50  is moved up. When the screw  40  is tightened, the magnet part  50  is moved down. In this way, it is possible to arbitrarily adjust the height of the magnet part  50 , that is, the height of the upper surface (the surface serving as the N-pole or the S-pole) of the permanent magnet  36 . 
         [0058]    In the first and second embodiments, the permanent magnet  36  has a rectangular parallelepiped shape. However, the shape of the permanent magnet  36  is not limited to the rectangular parallelepiped. For example, as shown in  FIG. 12 , the permanent magnet  36  may have an arc shape. In this case, the supporting member  38  also has an arc shape corresponding to the shape of the permanent magnet. In addition, in the magnet part shown in  FIG. 12 , the supporting member  38  is fixed to only one side of the arc-shaped permanent magnet  36 . 
         [0059]    As described above, when the magnet units according to the first and second embodiments are used, it is possible to easily adjust the position of the magnet part in both the horizontal and vertical directions and easily generate a magnetic field having a desired shape and intensity. In addition, it is possible to firmly fix the permanent magnet to the base plate without processing the permanent magnet. 
         [0060]    Next, a method of attaching or detaching the magnet unit is described with reference to  FIG. 13 . 
         [0061]    The permanent magnet  36  of the magnet part  30  generates a very strong magnetic force. Since the base plate  32  serves as a yoke through which the magnetic flux passes, the magnet part  30  is strongly attracted to the base plate  32 . Therefore, when the magnet part  30  is manually detached from the base plate  32 , the magnet part  30  is attracted to the base plate  32  and is likely to diagonally collide with the base plate  32 . When the magnet part  30  is attached to the base plate  32 , the magnet part  30  is likely to fall on the base plate  32  with a thud. In this case, the permanent magnet  36  made of a relatively soft material is likely to be damaged due to an impact caused by collision or falling. Once the magnet part  30  is loaded on the base plate  32 , it is difficult to change the position of the magnet part  30  and align the through hole  30   a  with the screw hole  34 . 
         [0062]    Therefore, as shown in  FIG. 13 , guide pins  60  are inserted into the screw holes  34  of the base plate  32  in advance, and the magnet part  30  is loaded on the base plate  32  while inserting the guide pins  60  into the through holes of the magnet part  30 . According to this magnet attaching method, the movement of the magnet part  30  is guided by the guide pins  60 . Therefore, the operator does not need to give attention to attaching the magnet part  30  so as not to be inclined and can pay attention to other things. Therefore, it is possible to prevent the magnet part  30  from falling from the hand of the operator and strongly colliding with the base plate  32  immediately before the magnet part  30  is loaded on the base plate  32 . 
         [0063]    Further, since the through holes  30   a  of the loaded magnet part  30  are guided by the guide pins  60 , they are accurately aligned with the screw holes  34 . Therefore, positioning is automatically performed, and it is possible to easily position the magnet part  30  in a short time. 
         [0064]    When the magnet part  30  is detached from the base plate  32 , the screws  40  are loosened, and the magnet part is lifted up along the guide pins  60  inserted into the through holes  30   a  and the screw holes  34 . 
         [0065]    As described above, according to the magnet parts of the first and second embodiments, it is possible to achieve a method of easily attaching or detaching the magnet part in a short time. 
         [0066]    Further, it is possible to fix the magnet part at a different position by selecting some of a plurality of screw holes formed in the entire surface of the base plate and fixing the magnet part to the base plate by screws. Therefore, it is possible to change the arrangement pattern of the magnet parts without replacing the base plate. 
         [0067]    The order of the embodiments is not meant to show the superiority of any embodiments over any other embodiments. Although the embodiments of the present inventions have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.