Abstract:
An in-line sputtering apparatus includes a deposition chamber, a target installed inside the deposition chamber, a substrate holder to hold a substrate, a substrate holder transferring mechanism which transfers the substrate holder relative to the target such that a thin film made of a material of the target that is formed on the substrate held by the substrate holder, first and second thickness distribution correcting members and a plate driving mechanism. The first and second thickness distribution correcting members are provided above the target, and each of the first and second thickness distribution correcting members has a plurality of movable plates. The plate driving mechanism is linked to the first and second thickness distribution correcting members and moves the corresponding movable plates of the first and second distribution correcting plates, symmetrically.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to sputtering apparatuses used for forming metal thin films, piezoelectric thin films, dielectric thin films, and other thin films, and more specifically, the present invention relates to an in-line sputtering apparatus in which a thin film is formed while a substrate is being transferred in front of a plurality of targets. 
     2. Description of the Related Art 
     Conventionally, various kinds of sputtering apparatuses for forming various kinds of thin films such as metal thin films and piezoelectric thin films, have been proposed. Generally, the thicknesses of thin films formed by sputtering apparatuses must be uniform. 
     In Japanese Unexamined Patent Application Publication No. 9-125240, an example of a sputtering apparatus that controls the thickness of a thin film is disclosed. FIG. 11 is a schematic diagram of a sputtering apparatus disclosed in the JP 9-125240, and FIG. 12 is a schematic plan view for explaining a thickness distribution correcting member. 
     As shown in FIG. 11, a sputtering apparatus  101  includes a deposition chamber  102 , in which a substrate holder  103  is disposed. A substrate  104  is fixed on a surface of the substrate holder  103 . 
     A target  105  is arranged such that the target  105  opposes the substrate  104 , and a thickness distribution correcting member  106  is disposed above the target  105 . 
     As shown in FIG. 12 by a plan view, the thickness distribution correcting member  106  includes a pair of supporting plates  106   a  and  106   b  which are fixedly disposed. The supporting plates  106   a  and  106   b  are arranged such that the supporting plates  106   a  and  106   b  oppose each other with the target  105  disposed therebetween and extend parallel to each other. In addition, the supporting plates  106   a  and  106   b  are linked with a plurality of correcting plates  106   c  and  106   d , respectively. The correcting plates  106   c  and  106   d  are constructed to be movable in the direction shown by the arrow in the figure. 
     As shown in FIG. 11, in the sputtering apparatus  101 , target particles  105   a  are sputtered away from the target by ions A, move toward the substrate  104 , and are deposited on the exposed surface of the substrate  104 . Accordingly, a thin film is formed. In this case, thickness uniformity of the thin film formed on the substrate  104  depends on the flatness, attachment angles, and other characteristics of the substrate  104  and the target  105 . As a result, the thickness of the thin film may not be uniform. Thus, in order to ensure thickness uniformity of the thin film, the thickness distribution correcting member  106  is used in the sputtering apparatus  101 . In the thickness distribution correcting member  106 , the size of the opening B surrounded by the inner ends of the correcting plates  106   c  attached to the supporting plate  106   a  and the inner ends of the correcting plates  106   d  attached to the supporting plate  106   b  is adjusted so that the thickness distribution of the thin film can be corrected. More specifically, when some of the correcting plates  106   c  and  106   d  are moved to reduce the gaps therebetween, the movement of the target particles  105   a  toward the substrate  104  is impeded, and the thickness of the corresponding portion of the thin film is reduced. 
     In the sputtering apparatus  101 , when positions of the correcting plates  106   c  and  106   d  of the thickness distribution correcting member  106  are to be adjusted, the deposition chamber  102  is first vented to the atmosphere. Then, correcting plates  106   c  and  106   d  are moved and are fixed at desired positions, such that the gaps therebetween are adjusted, and the pressure in the deposition chamber  102  is reduced again. 
     On the other hand, an in-line sputtering apparatus including a thickness controlling plate is disclosed in Japanese Unexamined Utility Model Application Publication No. 62-162255. As shown in FIG. 13, according to JP 62-162255, a sputtering apparatus  111  includes a deposition chamber  112 , in which a substrate holder  113  is disposed. A substrate  114  is fixed on the substrate holder  113 . Targets  116  are disposed on an inwardly facing surface of a covering member  115 , which is provided for covering the deposition chamber  112 . The substrate  114  is moved along with the substrate holder  113  in the direction shown by the arrow C in the figure, so that, while the substrate  114  is being transferred in front of the targets  116 , target particles continuously accumulate on the substrate  114  to form a thin film. 
     The sputtering apparatus  111  is provided with a thickness controlling member  117 , which is schematically shown in FIG.  13 . The actual shape of the thickness controlling member  117  as seen from the front is shown in FIG.  14 . The thickness controlling member  117  includes a supporting plate  118  having a rectangular shape which is provided with a rectangular opening. Correcting plates  119  and  120  constructed of metal are fixed to the supporting plate  118  at two sides thereof so as to oppose each other in the lateral direction. Inner edges  119   a  and  120   a  of the correcting plates  119  and  120  oppose each other, and the shapes thereof are determined in accordance with the correction of the thickness distribution of the thin film. The shapes of the inner edges  119   a  and  120   a  of the correcting plates  119  and  120 , respectively, are adjusted by cutting metal plates, and vary along the vertical direction as shown in the figure. When the substrate  114  is transferred in the direction shown by the arrow C (FIG.  13 ), the movement of the target particles knocked away from the target  116  is impeded by the correcting plates  119  and  120 . Accordingly, the thickness distribution is corrected such that the thickness of the thin film is reduced at portions where the gap between the inward edges  119   a  and  120   a  is narrow, and is increased at portions where the gap therebetween is wide. 
     As described above, according to the sputtering apparatus shown in FIGS. 11 and 12, which is disclosed in Japanese Unexamined Patent Application Publication No. 9-125240, the thickness distribution is corrected by adjusting the widths of the gaps between the correcting plates  106   c  and  106   d . However, there is a problem in that the relationship between the change of the sizes of the gaps and the change of the thickness distribution of the thin film formed is not reliable, and it is difficult to control the thickness distribution of the thin film with high accuracy. 
     In a sputtering process, an erosion region of the target is sputtered, and target particles are knocked away from the target and accumulated on a substrate so that a thin film is formed. The thickness of the thin film formed on the substrate varies depending on the coverage of the erosion region of the target by the correcting plates  106   c  and  106   d . In the above-described conventional technique, although the gaps between the correcting plates  106   c  and  106   d  are adjusted, the coverage of the erosion region of the target is not determined. 
     Thus, as schematically shown in FIGS. 15A and 15B, the correcting plates  106   c  and  106   d  cover the erosion region of the target  105  asymmetrically. Accordingly, although the thickness of the thin film may be reduced by reducing the gaps between the correcting plates  106   c  and  106   d , a reliable relationship between the displacements of the correcting plates  106   c  and  106   d  and the thickness variation of the thin film cannot be obtained. Thus, in order to make the thickness uniform, processes of adjusting the positions of the correcting plates  106   c  and  106   d  and measuring the thickness distribution of the formed thin film must be performed several times. 
     Thus, in the method according to the above-described conventional technique, only the gaps between the correcting plates  106   c  and  106   d  are adjusted, and the correcting plates  106   c  and  106   d  are not moved symmetrically about the center of the target  105  and the substrate  104 . 
     In addition, in the method according to the above-described conventional technique, the deposition chamber  102  must be vented to the atmosphere when the positions of the correcting plates  106   c  and  106   d  are to be adjusted after having been already set. Thus, a significant amount of time is required to adjust the thickness of the thin film in the deposition process. 
     On the other hand, in the sputtering apparatus disclosed in Japanese Unexamined Patent Application Publication No. 62-162255, the shapes of the inner edges  119   a  and  120   a  of the correcting plates  119  and  120  are determined in accordance with targets and substrates. Thus, if the deposition process is performed and the target is changed after the correcting plates  119  and  120  are cut and the shapes of the inner edges  119   a  and  120   a  are determined, the inner edges  119   a  and  120   a  of the correcting plates  119  and  120  must be reprocessed in accordance with the new target. Since the correcting plates  119  and  120  must be reprocessed, a significant amount of time is required for correcting the thickness distribution, and high costs are incurred. 
     In addition, in the sputtering apparatus  111 , the substrate  114  is transferred in front of the target  116 . However, the substrate holder  113  may be inclined in the transfer direction (horizontal direction) or in the vertical direction. Thus, even when the thickness distribution is corrected by using the thickness controlling member  117 , the distance between the substrate  114  and the target  116  is not always constant in the vertical or in the above-described transfer direction. Accordingly, even when the thickness is controlled by the thickness controlling member  117 , it is difficult to form thin films having a uniform thickness with high reproducibility. 
     SUMMARY OF THE INVENTION 
     In order to overcome the problems described above, preferred embodiments of the present invention provide an inline sputtering apparatus which makes the adjusting operation for the thickness control simpler and reduces the time required therefor, and forms a thin film having a uniform thickness reliably and easily. 
     According to a preferred embodiment of the present invention, an in-line sputtering apparatus includes a deposition chamber, a target installed inside the deposition chamber, a substrate holder to hold a substrate, a substrate holder transferring mechanism which transfer the substrate holder relative to the target such that a thin film including a material of the target is formed on the substrate held by the substrate holder, first and second thickness distribution correcting members and the plate driving mechanism. The first and second thickness distribution correcting members are provided above the target, and each of the first and second thickness distribution correcting members has a plurality of moveable plates. The plate driving mechanism is linked to the first and second thickness distribution correcting members and symmetrically moves the corresponding moveable plates of the first and second distribution correcting plates. 
     The plate driving mechanism may include a control unit which is disposed outside of the deposition chamber, and a link mechanism of which one end is linked to the control unit and the other end is linked to the first and the second thickness distribution correcting members. 
     The substrate holder transferring mechanism may include a guide rail that is disposed in the deposition chamber and extends along the transfer direction of the substrate and along which the substrate holder is constructed to be moveable, and a driving mechanism for driving the substrate holder. 
     The in-line sputtering apparatus may further include an ambient gas injection pipe for injecting an ambient gas into the deposition chamber. The ambient gas injection pipe preferably includes nozzles to eject the ambient gas toward the centers of the target. 
     In the in-line sputtering apparatus according to various preferred embodiments of the present invention, each of the first and the second thickness distribution correcting members preferably includes a plurality of moveable plates. The moveable plates of the first and the second thickness distribution correcting members are moved in pairs symmetrically by the plate driving mechanism. Since the moveable plates are moved in pairs symmetrically, the relationship between the displacements of the moveable plates of the thickness distribution correcting members and the change of the thickness distribution is reliably obtained, and the thickness distribution is controlled with high accuracy. 
     Accordingly, in the in-line sputtering apparatus in which a thin film is formed on a substrate while the substrate is being transferred in front of a plurality of targets, a thin film having a uniform thickness is reliably formed, even when regional differences in thickness thereof are caused at each of the targets, by correcting the thickness distribution with the use of the first and the second thickness distribution correcting members and the plate driving mechanism. 
     The plate driving mechanism may include a control unit which is disposed outside of the deposition chamber and a link mechanism of which one end is linked to the control unit and the other end is linked to the first and the second thickness distribution correcting members. In such a case, the thickness distribution control using the first and the second thickness distribution correcting members is easily performed by operating the control unit which is disposed outside of the deposition chamber. Accordingly, it is not necessary to vent the deposition chamber to the atmosphere, and the operation of adjusting the thickness distribution is performed more easily. 
     When a guide rail is provided in the deposition chamber and a substrate holder is constructed to be moveable along the guide rail, the substrate held by the substrate holder is more reliably transferred in the transfer direction. Accordingly, differences in thicknesses between thin films formed on substrates held by different substrate holders are eliminated. 
     In addition, when nozzles of ambient gas injection pipes are disposed such that ambient gas is ejected toward the centers of the targets, the gas uniformly flows over the targets. Accordingly, the thickness distribution is accurately adjusted by the thickness distribution correcting members with high reproducibility. 
     For the purpose of illustrating the invention, there is shown in the drawings several forms which are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1A is a schematic plan view of a sputtering apparatus according to a preferred embodiment of the present invention; 
     FIG. 1B is a schematic representation of a carrier which shows a manner in which substrates are fixed on a substrate holder. 
     FIG. 2 is a schematic cross-sectional view of the sputtering apparatus shown in FIG. 1, which is cut along line A—A. 
     FIGS. 3A and 3B are schematic diagrams showing the relationship of a target and first and second thickness distribution correcting members according to a preferred embodiment of the present invention, wherein FIG. 3A is a schematic diagram of a portion of the sputtering apparatus shown in FIG. 1 as seen from a direction shown by the arrow X and FIG. 3B is a sectional view of FIG. 3A which is cut along line Y—Y. 
     FIG. 4 is a schematic diagram for explaining a linking mechanism used in the sputtering apparatus according to a preferred embodiment of the present invention. 
     FIG. 5 is a schematic front view of the sputtering apparatus according to a preferred embodiment of the present invention, in which a control unit constructed with switches is provided on the exterior thereof. 
     FIG. 6 is a schematic side view of first and second thickness distribution correcting members according to a modification of preferred embodiments of the present invention. 
     FIG. 7A is a schematic diagram showing a state in which one of five pairs of movable plates is moved, and FIG. 7B is a graph showing the relationship between the thickness distribution of a thin film above a target when the moveable plates are in the state shown in FIG.  7 A. 
     FIG. 8A is a schematic diagram showing a state in which one of five pairs of moveable plates is moved, and FIG. 8B is a graph showing the relationship between the thickness distribution of the thin film above the target when the moveable plates are in the state shown in FIG.  8 A. 
     FIG. 9A is a schematic diagram showing a state in which one of five pairs of moveable plates is moved, and FIG. 9B is a graph showing the relationship between the thickness distribution of the thin film above the target when the moveable plates are in the state shown in FIG.  9 A. 
     FIG. 10 is a schematic diagram for explaining the relationship between the targets and gas injection pipes. 
     FIG. 11 is a schematic diagram for explaining an example of a conventional sputtering apparatus. 
     FIG. 12 is a schematic plan view for explaining correcting plates used in the conventional sputtering apparatus for controlling the thickness distribution of a thin film. 
     FIG. 13 is a perspective view for explaining another example of a conventional sputtering apparatus. 
     FIG. 14 is a schematic front view for explaining correcting plates used in the sputtering apparatus shown in FIG. 13 for controlling the thickness distribution of a thin film. 
     FIGS. 15A and 15B are a schematic plan view and a schematic sectional view, respectively, for explaining an operation of adjusting gaps between the correction plates in the conventional sputtering apparatus shown in FIG.  11 . 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Hereinafter, preferred embodiments of the present invention are explained in detail with reference to the drawings. 
     The present invention will be further illustrated by describing an in-line sputtering apparatus according to preferred embodiments of the present invention with reference to the attached drawings. Although the in-line sputtering apparatus of preferred embodiments described below is provided with a plurality of targets, the present invention may also be applied to in-line sputtering apparatuses having only one target. 
     FIG. 1A is a schematic plan view for explaining a construction of an in-line sputtering apparatus according to a preferred embodiment of the present invention. A sputtering apparatus  1  preferably includes a preparation chamber  2 , a load lock chamber  3 , and a deposition chamber  4 . A plurality of carriers  5  are preferably disposed in the preparation chamber  2 . 
     As shown in FIG. 1B, each of the carriers  5  preferably includes a base  5   a  and substrate holders  5   b , which extend upwardly from the base  5   a . As shown in FIG. 2, which will be described below, substrate holders  5   b  are arranged as pairs, and substrates  6  are individually fixed on the substrate holders  5   b  at the outwardly facing surfaces thereof. In the present preferred embodiment, thin films are formed on the exposed surfaces of the substrates  6 , which are individually fixed to the substrate holders  5   b , preferably by sputtering. 
     The carriers  5  are transferred from the preparation chamber  2  to the load lock chamber  3 , and are then transferred from the load lock chamber  3  to the deposition chamber  4 . The carriers  5  including the substrate holders  5   b  are transferred by a driving unit such as a motor or other suitable driving mechanism which is not shown in the figure. 
     FIG. 2 is a cross-sectional view of the deposition chamber  4 . Each of the carriers  5  preferably includes a pair of substrate holders  5   b  as described above, and rotatable pulleys  7  are individually linked with the substrate holders  5   b  at the inwardly facing sides thereof. In addition, the deposition chamber  4  is provided with guide rails  8  which extend in a transfer direction. Although a detailed construction is not shown in FIG. 1, a pair of guide rails  8  extend downwardly from the ceiling of the deposition chamber  4  as shown in FIG. 2, and a partition plate  8   x  is provided between the guide rails  8 . The end portions of the guide rails  8  are bent toward the substrate holders  5   b  such that upright wall portions  8   a  are formed at the outward ends of the bent portions. The wall portions  8   a  are arranged such that the inwardly facing surfaces thereof extend in a direction that is substantially parallel to the extending direction of the guide rails  8 . 
     The pulleys  7  are constructed such that the peripheries thereof come into contact with the inwardly facing surfaces of the wall portions  8   a  while they are rotated. Thus, when the carriers  5  are transferred, the pulleys  7  are rotated while the peripheries thereof are in contact with the inwardly facing surfaces of the wall portions  8   a . Accordingly, the carriers  5  are reliably transferred inside the deposition chamber  4  along the guide rails  8  in the above-described transfer direction. In the carriers  5 , the substrate holders  5   b  are fixed to the base  5   a  at the lower ends thereof, and are linked with the guide rails  8  via the pulleys  7  at positions near the upper ends thereof. Accordingly, by adjusting the diameters of the pulleys  7 , the outwardly facing surfaces of the substrate holders  5   b  can reliably be positioned in the transfer direction and the vertical direction with high accuracy while the carriers  5  are being transferred. More specifically, the film depositing surfaces of the substrates  6 , which are fixed to the substrate holders  5   b , are also reliably positioned in the vertical direction and the transfer direction with high accuracy. 
     In addition, a plurality of targets  9  and  10  are disposed on sidewalls  4   a  and  4   b  of the deposition chamber  4 , and are arranged in the transfer direction. When the substrates  6  are transferred in front of the targets  9  and  10 , target particles emitted from erosion regions of the targets  9  and  10  accumulate on the surfaces of the substrates  6 , so that thin films are formed. 
     In addition, first and second thickness distribution correcting members  11  and  12  are disposed in front of the targets  9  and  10 , that is, at the sides closer to the substrates  5 . In addition, ambient gas injection nozzles  13  for injecting an ambient gas at the centers of the targets  9  and  10  are preferably provided. 
     The relationship of the first and second thickness distribution correcting members  11  and  12  and the target  9  will be described below with reference to FIGS. 3A and 3B. 
     FIG. 3A is a schematic side view of the target  9  and the first and second thickness distribution correcting members  11  and  12  as seen from the direction shown by the arrow X in FIG.  1 A. FIG. 3B is a sectional view of FIG. 3A cut along line Y—Y. The substrate  5  is schematically shown in FIG.  3 B. 
     As shown in FIGS. 3A and 3B, the thickness distribution correcting member  11  includes a base plate  13  and moveable plates  14   a ,  14   b  and  14   c  which are moveably linked with the base plate  13 . Similarly, the thickness distribution correcting member  12  preferably includes a base plate  15  and moveable plates  16   a ,  16   b  and  16   c  which are moveably linked with the base plate  15 . The thickness distribution correcting members  11  and  12  are fixed to shield plates  18   a  and  18   b  via struts  17   a  and  17   b , respectively. The target is disposed between the shield plates  18   a  and  18   b.    
     As shown in FIG. 3A, the thickness distribution correcting members  11  and  12  are provided with three moveable plates  14   a ,  14   b  and  14   c  and three moveable plates  16   a ,  16   b  and  16   c , respectively, which are arranged vertically. The moveable plates  14   a ,  14   b  and  14   c  and  16   a ,  16   b  and  16   c  are individually provided with long holes  19  which extend in the transfer direction. In addition, the base plates  13  and  15  are provided with tapped holes in the upper surface thereof at positions corresponding to the long holes  19 . Bolts  20  are inserted through the long holes  19  formed in the moveable plates  14   a ,  14   b  and  14   c  and  16   a ,  16   b  and  16   c , and are screwed into the above-described tapped holes formed in the base plates  13  and  15 . Accordingly, the moveable plates  14   a ,  14   b , and  14   c  and  16   a ,  16   b  and  16   c  are attached to the base plates  13  and  15 , respectively, in a manner moveable in the extending direction of the long holes  19 , by using the bolts  20  and the tapped holes formed in the base plates  13  and  15 . 
     Due to the above-described long holes  19 , the moveable plates  14   a ,  14   b  and  14   c  and  16   a ,  16   b  and  16   c  are moveable relative to the base plates  13  and  15  in the extending direction of the long holes, that is, in a direction in which the moveable plates  14   a ,  14   b  and  14   c  and  16   a ,  16   b  and  16   c  move toward and away from the target  9 . 
     In FIG. 3A, the moveable plate  14   b  of the thickness distribution correcting member  11  which is disposed in the middle is projected toward the target  9  relative to the moveable plates  14   a  and  14   c  which are disposed at the ends. Similarly, the moveable plate  16   b  of the second thickness distribution correcting member  12  which is disposed in the middle is projected toward the target  9 . 
     The present preferred embodiment is characterized in that the moveable plates  14   a ,  14   b  and  14   c  of the first thickness distribution correcting member  11  disposed at one side of the target  9  and the moveable plates  16   a ,  16   b  and to  16   c  of the second thickness distribution correcting member  12  disposed at the other side of the target  9  are constructed such that they are moved symmetrically with respect to a line which passes through the center of the target  9  and is substantially perpendicular to the substrate transferring direction. This construction will be described below with reference to FIGS. 4 and 5. 
     It should be noted that the moveable plates  14   a ,  14   b  and  14   c  and  16   a ,  16   b  and  16   c  are schematically shown in FIG. 4, and are shown by patterns having shapes different from those shown in FIG.  3 . 
     The moveable plates  14   a ,  14   b  and  14   c  are provided with racks  14   a   1 ,  14   b   1  and  14   c   1  at the outward ends thereof. The racks  14   a   1 ,  14   b   1  and  14   c   1  are arranged such that the moveable plates  14   a ,  14   b  and  14   c  can be moved in the direction shown by the arrow Z in FIG. 4, that is, in the transfer direction and in the direction reverse thereto. Pinions  21 ,  22  and  23  are disposed in such a manner that the pinions  21 ,  22  and  23  are engaged with the racks  14   a   1 ,  14   b   1  and  14   c   1 . In addition, first linking bars  24 ,  25  and  26  which are provided with racks  24   a ,  25   a  and  26   a , respectively, and which extend substantially perpendicularly to the above-described arrow Z are disposed such that the racks  24   a ,  25   a  and  26   a  are engaged with the pinions  21 ,  22  and  23 . The linking bars  24 ,  25  and  26  are also provided with additional racks  24   b ,  25   b  and  26   b  at the other ends relative to the ends at which the racks  24   a ,  25   a  and  26   a  are disposed. In addition, pinions  27 ,  28  and  29  are disposed in such a manner that the pinions  27 ,  28  and  29  are engaged with the racks  24   b ,  25   b  and  26   b.    
     In addition, second linking bars  31 ,  32  and  33  which extend in the transfer direction are provided, and racks  31   a ,  32   a  and  33   a , which are engaged with the pinions  27 ,  28  and  29 , respectively, are disposed in the second linking bars  31 ,  32  and  33 . 
     The moveable plates  16   a ,  16   b  and  16   c  of the second thickness distribution correcting member  12  are also linked by a linking mechanism similar to that constructed to include racks and pinions as in the first thickness distribution correcting member  11 . More specifically, racks  16   a   1 ,  16   b   1  and  16   c   1  are provided in the moveable plates  16   a ,  16   b  and  16   c , and pinions  21 A,  22 A and  23 A corresponding to the pinions  21 ,  22  and  23 , respectively, and pinions  27 A,  28 A and  29 A corresponding to the pinions  27 ,  28  and  29 , respectively, are provided. In addition, first linking bars  24 A,  25 A and  26 A corresponding to the first linking bars  24 ,  25  and  26  are also provided. The second linking bars  31 ,  32  and  33  are also provided with racks  31   b ,  32   b  and  33   b , respectively, which are engaged with the pinions  27 A,  28 A and  29 A, respectively. 
     The second linking bars  31 ,  32  and  33  are also provided with additional racks  31   c ,  32   c  and  33   c  at the ends thereof, and pinions  34 ,  35  and  36  which are engaged with the racks  31   c ,  32   c  and  33   c  are provided. The pinions  34 ,  35  and  36  are individually linked with rotating units such as motors or other suitable devices. 
     In the construction shown in FIG. 4 that defines a plate driving mechanism, the moveable plates  14   a ,  14   b  and  14   c  and the moveable plates  16   a ,  16   b  and  16   c  can be moved symmetrically by rotating each of the pinions  34 ,  35  and  36 . For example, when the pinion  34  is rotated in a direction shown by the arrow in the figure, the pair of movable plates  14   a  and  16   a  are moved in a direction away from the target  9 , that is, backward. When the pinion  34  is rotated in the direction reverse to the direction shown by the arrow, the movable plates  14   a  and  16   a  are moved closer to each other by the same amount. 
     In addition, the pair of movable plates  14   b  and  16   b  and the pair of movable plates  14   c  and  16   c  can also be moved in a similar manner by rotating the pinions  35  and  36 , respectively. 
     The above-described pinions  34 ,  35  and  36  can be rotated by driving motors that are individually connected thereto. As schematically shown in FIG. 5, in the present preferred embodiment, dial-type switches  41 ,  42  and  43  for driving the motors are provided on the exterior surface of the sputtering apparatus  1 . Each of the switches  41  is used to drive the motor for rotating the pinion  34 . In addition, each of the switches  42  is used to drive the motors for rotating the pinion  35 , and each of the switches  43  is used to drive the motors for rotating the pinion  36 . 
     Thus, the moveable plates  14   a ,  14   b  and  14   c  and the moveable plates  16   a ,  16   b  and  16   c  can be moved symmetrically by operating the switches  41 ,  42  and  43 . 
     Accordingly, in the present preferred embodiment, the moveable plates  14   a ,  14   b  and  14   c  and  16   a ,  16   b  and  16   c  of the thickness distribution correcting members  11  and  12  can be moved symmetrically during the deposition process while the low-pressure condition is maintained. 
     In the example shown in FIGS. 3A and 3B, three moveable plates  14   a ,  14   b  and  14   c  and three moveable plates  16   a ,  16   b  and  16   c , which are arranged in the vertical direction, are preferably used. However, more than four moveable plates may also be provided when the thickness distribution needs to be corrected more precisely. For example, as shown in FIG. 6, the first and the second thickness distribution correcting members  11  and  12  may each be provided with nine moveable plates  44   a  to  44   i  and  46   a  to  46   i . In the modification shown in FIG. 6, the vertical dimension of the moveable plates  44   a ,  44   i ,  46   a , and  46   i , which are disposed at the ends, are different from that of the other moveable plates  44   b  to  44   h  and  46   b  to  46   h . Thus, the vertical dimensions, that is, widths, of the moveable plates are not necessarily the same, and vertical dimensions of some of the moveable plates may differ from those of the other moveable plates. 
     Next, the manner in which the thickness distribution of the thin film is controlled by the sputtering apparatus  1  will be described below with reference to FIGS. 7 to  9 . 
     FIGS. 7 to  9  are schematic diagrams which show thickness distributions of thin films which are formed on substrates using five moveable plates  54   a  to  54   e  and five moveable plates  56   a  to  56   e.    
     In FIG. 7A, in the moveable plates  54   a  to  54   e  and  56   a  to  56   e , the moveable plates  54   b  and  56   b  that are positioned second from the top are moved so that the gap therebetween is reduced. In this case, as shown in FIG. 7B, the thickness of the thin film is reduced at a portion corresponding to the moveable plates  54   b  and  56   b.    
     In contrast, when the moveable plates  54   b  and  56   b  are moved so that the gap therebetween is increased as shown in FIG. 8A, the thickness of the thin film formed on the substrate is increased at a portion corresponding to the moveable plates  54   b  and  56   b  as shown in FIG.  8 B. 
     Accordingly, it is understood that the thickness of the thin film can easily be adjusted by controlling the gaps between the moveable plates  54   a  to  54   e , and  56   a  to  56   e . For example, the thickness of the thin film formed on the substrate can be varied as shown in FIG. 9B by changing the gaps between the pairs of the moveable plates such as the moveable plates  54   a  and  56   a , etc., variously as shown in FIG.  9 A. In other words, the thickness of the thin film formed on the substrate can be adjusted by adjusting the gaps between the moveable plates  54   a  to  54   e  and  56   a  to  56   e  in accordance with the regional differences thereof. Thus, the thin film having uniform thickness is achieved. 
     In this case, the moveable plates  54   a  to  54   e  and the moveable plates  56   a  to  56   e  move in pairs, and every two moveable plates forming a pair are moved symmetrically to each other about the center of the target  9  as described above. 
     Since all of the pairs of moveable plates are moved symmetrically to each other, the thickness distribution of the thin film is controlled with high accuracy. 
     In the above-described sputtering apparatus disclosed in Japanese Unexamined Patent Application Publication No. 9-125240, only the gaps between the correction plates are changed. In other words, the correction plates are not moved symmetrically. Accordingly, the thickness distribution cannot be controlled with high accuracy since the relationship between the change of the gap sizes and the change of the thickness distribution cannot be achieved. 
     In contrast, in the sputtering apparatus of preferred embodiments of the present invention, the moveable plates that oppose each other are symmetrically moved in pairs as described above. Accordingly, when the gaps between the moveable plates are varied, the relationship between the change of the gap sizes and the change of the thickness distribution is achieved. Thus, the thickness distribution is controlled with high accuracy. 
     As shown in FIG. 10 by a schematic sectional view, in the sputtering apparatus of the present preferred embodiment, nozzles  61  of ambient gas injection pipes  60  are preferably disposed in such a manner that an ambient gas is ejected at the centers of the targets  9  and  10 . The gas uniformly flows over the surfaces of the targets  9  and  10 . In addition, since the gas is injected for each of the targets  9  and  10  separately, the amounts of the ambient gas that flow around the targets  9  and  10  are approximately the same. Accordingly, the thickness of the thin film is reliably and accurately adjusted by the thickness distribution correcting members  11  and  12 . 
     Although a separate gas injection pipe is provided for each of the targets in FIG. 1, a plurality of injection pipes may also be provided for each target. 
     While preferred embodiments of the invention have been disclosed, various modes of carrying out the principles disclosed herein are contemplated as being within the scope of the following claims. Therefore, it is understood that the scope of the invention is not to be limited except as otherwise set forth in the claims.