Patent Publication Number: US-2015083586-A1

Title: Deposition apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a deposition apparatus using an arc discharge. 
     2. Description of the Related Art 
     As a method of forming a protection film for a medium such as a hard disk, there is a CVD method using a reactive gas such as C 2 H 2  or C 2 H 4 . Recently, a thinner protection film of carbon or the like deposited on a magnetic recording layer is required to further shorten the head flying height and the spacing distance between a magnetic read head and the magnetic recording layer of a medium, and improve the drive characteristic. 
     However, the limitation of the thickness of the carbon protection film deposited by CVD is said to be 2 to 3 nm owing to its characteristic. As a technique replacing CVD, attention has been paid to a film deposition method (vacuum arc deposition) which uses an arc discharge and can form a thinner carbon protection film. Vacuum arc deposition can deposit a harder carbon protection film with a lower hydrogen content in comparison with CVD, and has the possibility of decreasing the film thickness to about 1 nm. 
     For example, Japanese Patent Laid-Open No. 2010-202899 discloses a film deposition apparatus including a striker configured to form an arc spot on a target and emit target ions and electrons by an arc discharge, an anode unit configured to maintain an arc, an anode coil configured to form a flow of electrons between targets, and a filter unit configured to guide target ions and electrons to a process chamber. 
     At an arc spot (location where an arc is generated), electrons and ions are generated. In addition, a liquid or solid target material also emerges, which is called a droplet. In general, the droplet needs to be prevented from reaching a material to be deposited and entering a film. Various methods for implementing this have been proposed. 
     Examples are a method of bending a plasma path twice or more so that a droplet traveling from a target does not reach a substrate (for example, Japanese Patent Laid-Open No. 2010-202899 and U.S. Pat. No. 6,031,239), and a method of narrowing part of a plasma path to remove a droplet (for example, Japanese Patent No. 4889957). 
     It is generally considered that there are droplets in the micron size or larger and droplets in the submicron size. Droplets in the micron size or larger have a size of several μm or larger, and reach a material to be deposited while mostly repeating collision and reflection by the wall surface of a plasma path. As for droplets in the micron size or larger, the above-described problem can be substantially solved by devising the shape of an internal shield. 
     Submicron-size droplets have a size of several nm to several μm or less. Some such droplets are charged and attracted by a plasma, or tangled in lines of magnetic force, and reach a material to be deposited. The most effective means for removing submicron-size droplets are considered to be, a method of bending a plasma path twice or more and shaking droplets off a plasma or lines of magnetic force by centrifugal force, and a method of applying, to the wall surface of a plasma path, a potential at which droplets are attracted, thereby removing the droplets. 
     However, the structure in which the plasma path is bent twice or more complicates the shape and makes maintenance difficult. In the method of applying a potential, the deposition rate decreases. Thus, there is room for improvement. 
     SUMMARY OF THE INVENTION 
     The present inventors have conceived a new droplet removal method by paying attention to the facts that bending a plasma path twice or more is a very effective means for removing submicron-size droplets and the plasma is transported along lines of magnetic force. According to this method, permanent magnets are helically arranged at a linear magnetic field generation means, or a coil having a central axis at a position decentered from the central axis of the magnetic field generation means is arranged to form the magnetic field of a plasma path into not a linear shape but a helical shape. Centrifugal force always acts on electrons, ions, and droplets passing through the helical path, thereby removing only heavy droplets. 
     The present invention has been made in consideration of the aforementioned problems, and realizes a deposition apparatus which has a simpler shape and good maintainability and can remove droplets without decreasing the deposition rate. 
     In order to solve the aforementioned problems, the present invention provide a deposition apparatus comprising: a source unit having a function of generating a plasma by an arc discharge; and a filter unit configured to transport the plasma generated by the source unit toward a material to be deposited, wherein the filter unit includes a duct configured to transport the plasma, a magnetic field formation unit configured to form, in the duct, a magnetic field for transporting the plasma, and a magnetic field bending unit configured to generate a magnetic force for bending the magnetic field formed by the magnetic field formation unit. 
     According to the present invention, droplets can be removed by shaking off, by centrifugal force, charged droplets passing through a plasma path. Also, the apparatus arrangement has a relatively simple shape, and the maintainability can be improved. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments (with reference to the attached drawings). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional view showing the schematic arrangement of a film deposition apparatus according to an embodiment of the present invention; 
         FIG. 2  is a sectional view showing the arrangement of the filter unit of the film deposition apparatus in  FIG. 1 ; 
         FIGS. 3A and 3B  are side views showing the arrangement of the source unit of the film deposition apparatus in  FIG. 1  when viewed from two directions; 
         FIG. 3C  is a sectional view taken along a line I-I in  FIG. 3B ; 
         FIG. 4  is a block diagram showing the schematic arrangement of the power supply system of the film deposition apparatus according to the embodiment; 
         FIG. 5  is a block diagram showing the schematic arrangement of the control system of the film deposition apparatus according to the embodiment; 
         FIG. 6  is a view showing the arrangement of the permanent magnets of the filter unit according to the embodiment; and 
         FIGS. 7A to 7C  are views showing a simple magnetic field simulation result of the filter unit according to the embodiment. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     An exemplary embodiment of the present invention will now be described in detail with reference to the accompanying drawings. Note that the constituent elements described in the embodiment are merely examples. The technical scope of the present invention is determined by the scope of claims and is not limited by the following individual embodiment. 
     An embodiment in which a film deposition apparatus according to the present invention is applied to a film deposition apparatus configured to form a protection film on a substrate serving as a material to be deposited by using vacuum arc deposition. 
     &lt;Apparatus Arrangement&gt; First, the arrangement of the film deposition apparatus according to the embodiment of the present invention will be explained with reference to  FIG. 1  to  FIGS. 3A to 3C . 
     In  FIG. 1 , a film deposition apparatus  100  according to the embodiment includes a process chamber  101  which loads a substrate  1  on which a 3-nm or less protection film of a target material (for example, carbon) is deposited, a filter unit  110  coupled to the process chamber  101  so as to communicate inside, and a source unit  120  coupled to the filter unit  110  so as to communicate inside. Insulating members  2  are arranged at the coupling portions between the process chamber  101  and the filter unit  110  and between the filter unit  110  and the source unit  120  so that an electrically insulating state is held at each portion. Although carbon is used as the target material, the target material is not limited to carbon and for example, Ti or TiN is also usable. 
     The filter unit  110  includes one or more transport pipes  111  which form a guide path (duct)  110   a  bent at 90° and hold the inside of the guide path  110   a  in a vacuum state, filter coils  112  which form a magnetic field for transporting electrons and target ions on the atmospheric side or vacuum side of the transport pipes  111 , and a magnetic field formation unit such as a permanent magnet. The guide path  110   a  is constituted by coupling one or more transport pipes  111 . The filter coil  112  is arranged all around the outer side (atmospheric side) of each transport pipe  111 . The guide path  110   a  guides, toward the substrate  1 , electrons and target ions generated by the source unit  120 , and removes a carbon particle of a large particle size serving as a particle. A voltage application unit such as a voltage application terminal  113  is arranged on the transport pipe  111 . When there are two or more transport pipes  111 , each transport pipe  111  can be set to an electrically conductive state or can be set to an electrically insulating state by arranging an insulating member at each coupling portion. Either state can be selected. 
     In the embodiment, six pairs of (12) permanent magnets  114  are arranged as magnetic field bending units on the outer surface of the transport pipes  111  on the atmospheric side. The positional relationship between the filter unit  110  and each permanent magnet  114  will be described later. 
     The source unit  120  includes an anode unit  130 , cathode target unit  140 , and anode coil  131   a . The source unit  120  maintains an arc discharge by maintaining an electron current or ion current between the anode unit  130  and the cathode target unit  140 . 
     As shown in detail in  FIGS. 3A to 3C , the anode unit  130  includes an anode  131 , anode feeding unit  132 , anode feeding terminal  133 , striker  134 , and anode housing  135 . 
     The striker  134  comes into contact with the surface of the cathode target unit  140  at a predetermined timing to generate an arc discharge on the target surface. Electrons and target ions emitted from an arc spot on the cathode target unit  140  are converted into a plasma and guided to the process chamber  101 . The cathode target unit  140  is also driven to rotate to a predetermined angle. Localization of an arc spot is prevented by relatively moving the position at which the striker  134  contacts the cathode target unit  140 . Note that the arc spot is a location where an arc is generated on a target. 
     The striker  134  is set to the same potential as that of the anode  131 . The insulating member  2  is interposed between the anode housing  135  and the anode feeding unit  132  to hold an electrically insulating state. The striker  134  is configured to be drivable by transmitting the driving force of a striker driving motor  134   a  via a striker driving motor coupling  134   b , striker driving motor shaft  134   c , striker driving motor gear  134   d , striker driving motor power transmission gear  134   e , and striker feeding/driving shaft  134   i . A striker feeding terminal  134   g , striker feeding unit  134   f , and striker feeding brush  134   h  are connected to the striker feeding/driving shaft  134   i . By arranging the striker feeding brush  134   h  in contact with the striker feeding/driving shaft, power can be fed to the striker  134 . The insulating member  2  is interposed between the striker feeding/driving shaft  134   i  and the anode housing  135  to hold an electrically insulating state. In addition, a magnetic fluid  134   j  is interposed between the insulating member  2  and the striker feeding/driving shaft  134   i . This structure makes it possible to drive the striker  134  and feed power without electrically connecting the striker feeding/driving shaft  134   i  and anode housing  135 . 
     The striker  134  is constituted by an arm unit  134   k  and chip unit  134   l , and is desirably made of a material that is durable at a high temperature and large current. For example, the arm unit  134   k  is made of molybdenum, and the chip unit  134   l  is made of graphite. The arm unit and chip unit may be integrated. 
     The cathode target unit  140  includes a cylindrical or disk-like carbon graphite cathode target  141 , cathode target feeding unit  142 , cathode target feeding terminal  143 , and cathode target housing  144 . The cathode target  141  is configured to be rotatable by transmitting the driving force of a cathode target rotation motor  141   a  via a cathode target rotation motor coupling  141   b , cathode target rotation motor shaft  141   c , cathode target rotation motor gear  141   d , cathode target rotation motor power transmission gear  141   e , cathode target rotation shaft  141   f , and cathode target bracket  141   h . Also, the cathode target  141  is configured to receive power by connecting it to the cathode target feeding unit  142 , a cathode target feeding brush  142   a , and the cathode target feeding terminal  143 . Further, the insulating member  2  is interposed between the cathode target rotation shaft  141   f  and the cathode target housing  144  to hold an electrically insulating state. In addition, a magnetic fluid  141   g  is interposed between the insulating member  2  and the cathode target rotation shaft  141   f . This structure makes it possible to rotate the cathode target  141  and feed power without electrically connecting the cathode target rotation shaft  141   f  and cathode target housing  144 . 
     In the above-described arrangement, when the striker  134  and cathode target  141  contact each other, the anode  131  and cathode target  141  are short-circuited to generate an arc. 
     A negative voltage is applied from an arc power source (not shown) to the cathode target  141 , and a positive voltage is applied to the striker  134  and anode  131 , thereby forming a flow of electrons between the cathode target  141  and the anode  131  along a magnetic field generated by the anode coil  131   a.    
     Electrons generated at the arc spot serve as arc maintenance electrons and ion transport electrons. The arc maintenance electrons are electrons which are obtained by guiding some of electrons generated on the target surface by the magnetic field of the anode coil  131   a , and flow into the anode  131 . The arc maintenance electrons are used to heat an arc spot by supplying a current between the cathode target  141  and the anode  131  in order to maintain a plasma arc generated at the cathode target  141 . 
     The ion transport electrons are electrons for causing target ions to reach the substrate  1 , and attract ions by using the Coulomb force of electrons. The ion transport electrons are guided toward the substrate  1  by a magnetic field generated by the filter unit  110 . 
     With the above-described arrangement, target ions are attached to and stacked on the surface of the substrate  1  inside the process chamber  101 , thereby depositing a protection film. 
     &lt;Power Supply System&gt; The arrangement of the power supply system of the film deposition apparatus according to the embodiment will be described with reference to even  FIG. 4 . 
     The process chamber  101  is grounded. The filter unit  110  is connected to a filter power supply or current measurement unit (not shown) via the voltage application terminal  113 . The anode unit  130  is connected to an arc power supply  150  via the anode feeding terminal  133 . The striker  134  is connected to the arc power supply  150  via the striker feeding terminal  134   g . The cathode target unit  140  is connected to the negative electrode side of the arc power supply  150  via the cathode target feeding terminal  143 . The anode unit  130  and striker  134  are connected to the positive side of the arc power supply  150  to have the same potential. The cathode target unit  140  is connected to the negative side of the arc power supply  150 . The arc power supply  150  is desirably of a current supply control type, but may be of a voltage application control type. In this embodiment, a current and voltage will be generically called power herein. 
     Note that the circuit may be constituted using a plurality of power supplies because a circuit configured to generate a potential difference between the anode unit  130  and the cathode target unit  140  generates an arc discharge between the anode unit  130  and the cathode target unit  140 . An example is a circuit in which one terminal of the first power supply is grounded, its other terminal is connected to the anode unit  130 , one terminal of the second power supply is connected to the cathode target unit  140 , and its other terminal is grounded. 
     The striker  134  according to the embodiment is connected to the arc power supply  150  parallel to the anode unit  130 . However, series wiring of connecting the striker  134  to the anode unit  130  is also possible. If powers supplied to the striker  134  and anode unit  130  are substantially the same, a power supply for supplying power to the striker  134  and a power supply source for supplying power to the anode unit  130  may be separate. The embodiment assumes that when power is supplied to the anode unit  130  in generating an arc, power is similarly supplied to even the striker  134 . 
     &lt;Control System&gt; The schematic arrangement of the control system of the film deposition apparatus according to the embodiment will be described with reference to  FIG. 5 . 
     As shown in  FIG. 5 , the film deposition apparatus according to the embodiment includes a main control device  500  which comprehensively controls the overall apparatus, and an arc control device  501  which controls generation of an arc. The main control device  500  and arc control device  501  include a storage unit such as a memory, an arithmetic processing unit such as a CPU, and a communication unit. The arc control device  501  controls power supply by the arc power supply  150  serving as a power application device  503  in accordance with a control signal received from the main control device  500 . In addition, the arc control device  501  controls rotation of the motors  134   a  and  141   a  serving as a striker driving device  504 . Note that the power application device  503  includes a resistance meter for measuring a resistance value between the striker  134  and the cathode target unit  140 . The striker driving device  504  also includes a sensor, such as an encoder, which detects the rotational speed and torque of the striker driving motor  134   a  and those of the cathode target rotation motor  141   a  of the cathode target unit  140 . 
     &lt;Permanent Magnet of Filter Unit&gt; Next, the arrangement and function of the permanent magnets of the filter unit in the film deposition apparatus according to the embodiment will be explained with reference to  FIGS. 2 ,  6 , and  7 A to  7 C. 
       FIG. 6  shows the arrangement of the permanent magnets of the filter unit according to the embodiment. 
     As shown in  FIGS. 2 and 6 , the filter coils  112 , and six permanent magnet pairs  114 A to  114 F are arranged on the transport pipe  111  according to the embodiment. Each of the permanent magnet pairs  114 A to  114 F generates a magnetic field in a direction perpendicular to the direction of a magnetic field generated by the filter coil  112 , and is formed from two paired permanent magnets so that opposite polarities face each other. The permanent magnet pairs  114 A to  114 F are arranged by rotating every other pair by 90° in the same direction using, as the central axis, a direction G1 of a magnetic field generated by the filter coil  112 . Although a samarium-based magnet is applied as the permanent magnet in the embodiment, a ferrite- or neodymium-based magnet is also usable. 
     In the embodiment, the volume of each of the two permanent magnet pairs  114 C and  114 D at the center is set to be double the volume of each of the four remaining permanent magnet pairs  114 A,  114 B,  114 E, and  114 F, out of the six permanent magnet pairs  114 A to  114 F, so that a synthetic magnetic field G2 of the filter coil  112  and permanent magnet  114  becomes a helical magnetic field as symmetrical as possible with respect to the central axis G1 of the coil. By doubling the volumes of permanent magnets of the same type, the magnetic force is doubled. 
     The magnetic force is doubled to make helical a plasma path formed by the phase magnetic field G1 and the magnetic field G2 obtained by synthesizing two magnetic fields generated by the permanent magnets. More specifically, the plasma path is made helical by bending lines of magnetic force by the two, first and second permanent magnet pairs  114 A and  114 B, and bending them by double force by the two, third and fourth permanent magnet pairs  114 C and  114 D in a direction opposite to that of the first and second pairs. 
     Since the permanent magnets  114  are arranged with respect to the filter coils  112  in this manner, the magnetic field G1 generated by the coils  112 , and the synthetic magnetic field G2 of magnetic fields generated by the permanent magnets  114  can be formed to bend lines of magnetic force, as represented by the magnetic field G2 in  FIG. 6 . If the magnetic field strengths and orientations of the coils  112  and permanent magnets  114  are known, the angle of the magnetic field by the synthetic magnetic field G2 is given by: 
       θ=tan −1 (Bm/Bc)  (1)
 
     where Bm is the magnetic field strength of the permanent magnet, and Bc is the magnetic field strength of the electromagnet. From equation (1), the number of turns of the coil, its current, and the size and arrangement of the permanent magnet can be obtained. 
     This result reveals that the permanent magnet  114  influences the line G1 of magnetic force of the coil  112  to bend the line G1 of magnetic force of the coil. Further, electrons and ions in a plasma move along lines of magnetic force while holding a Larmor radius determined by their energies and weights with respect to lines of magnetic force. When helical lines of magnetic force as shown in  FIG. 6  are generated, the plasma path also becomes helical, similar to the line G2 of magnetic force. 
     This is applied to vacuum arc deposition. When a plasma generated in the arc discharge unit (the surface of the cathode target unit  140 ) flies close to the permanent magnet pair  114 A of the filter unit  110 , the plasma path is also bent along bent lines of magnetic force. At this time, centrifugal force acts on electrons, ions, and droplets in the plasma, shaking them off the plasma in at a ratio of electron&lt;ion&lt;droplet based on a physical law formula regarding centrifugal force: F=mv2/r. 
     In this manner, the plasma passes through the filter unit  110  in which a helical plasma path is formed by the permanent magnets  114 . The number of droplets in the plasma becomes relatively small, reducing particles in a film stacked on a material to be deposited. By using the filter unit  110  in which the permanent magnets  114  are arranged, as in the embodiment, the filter unit  110  need not be bent twice or more, greatly improving the maintainability. Since the particle removal method of applying a voltage to the filter unit  110  to capture droplets need not be employed, neither a device nor power supply for supplying power to the filter unit  110  need be used, and the cost can therefore be reduced. 
       FIGS. 7A to 7C  show a simple magnetic field simulation result of the filter unit according to the embodiment. 
     The filter unit  110  according to the embodiment has a shape obtained by bending a linear filter unit shown in  FIGS. 7A to 7C  directly at 90°. 
     As described above, according to the embodiment, droplets in a plasma can be removed by the helical magnetic field G2 of the filter unit  110 . A plasma containing less droplets can reach a material to be deposited. Particles in a film stacked on the material to be deposited can be reduced, and the maintainability can be improved. 
     Note that the magnet which bends the plasma path according to the embodiment may be constituted by an electromagnet instead of a permanent magnet, or a combination of a permanent magnet and electromagnet. When an electromagnet is used, a plasma which less changes can be obtained by adjusting the application power in accordance with the progress of erosion of the cathode target unit  140 . 
     Although the embodiment uses six pairs of permanent magnets, a combination of magnets can be changed as long as a helical magnetic field can be formed. For example, many permanent magnets may be helically arrayed around the outer surface of the filter unit while rotating them clockwise or counterclockwise by 90°. In this case, the number of times of bending can be adjusted in accordance with the number of magnets. 
     Note that the effects of the embodiment are not limited to a helical magnetic field. Even when a meandering magnetic field is generated, the same effects as those described above can be obtained. As magnets when generating a meandering magnetic field, at least three pairs of permanent magnets are arranged while rotating each pair at 180°. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2013-200493, filed Sep. 26, 2013 which is hereby incorporated by reference herein in its entirety.