Abstract:
A magnetron source for producing a magnetic field near a surface of a target in a deposition system include a first magnet, a second magnet separated by a gap from the first magnet along a first direction, and a target holder configured to hold the target in the gap between the first magnet and the second magnet. The target includes a sputtering surface from which target material can be sputtered and deposited on a substrate. The target holder is so configured that the sputtering surface is substantially parallel to the first direction and the first magnet and the second magnet can produce a magnetic field near a surface of the target.

Description:
TECHNICAL FIELD  
       [0001]     This application relates to apparatus for depositing material on a substrate.  
       BACKGROUND  
       [0002]     Material deposition on large substrates or multiple substrates held by a large holder is widely used in window glass coating, flat panel display manufacturing, coating of flexible films, hard disk coating, industrial surface coating, semiconductor wafer processing, and other applications. In such a deposition system, the magnetron source, the target, and the substrate can be transported relative to each other. At least one dimension of a target needs to be larger than a dimension of the substrate such that the substrate can be fully covered by the material sputtered off the target.  
         [0003]     Different designs exist in the conventional deposition systems for large substrates. But the designs all have different drawbacks. In the first example, as shown in  FIGS. 1A-1D , a deposition system  100  includes a long narrow rectangular target  110  over a large substrate  115  in a vacuum chamber  120 . A magnetron  130  is held behind the target  110 . The substrate  115  can be transported in the direction  150  relative to the target  110  and the magnetron  130  to receive a uniform deposition across the top surface of the substrate  115 . The magnetron  130  is stationary relative to the target  110 . The deposition system  100  can also includes a power supply  140  that can produce an electric bias between the target and walls of the vacuum chamber  120 .  
         [0004]     The magnetron  130  includes a magnetic pole  132  of a first polarity and a magnetic pole  135  of an opposite polarity to the first. The magnetron  120  can produce magnetic flux outside of the sputtering surface  112  on the lower side of the target  110  as shown in  FIG. 1B . A close loop magnetic field track can be formed outside of the sputtering surface  112  for trapping the electrons and thus enhancing the plasma near the sputtering surface  112 . More electrons are trapped near the maximum magnetic field produced by the magnetron  130  parallel to the sputtering surface  112 . The locations having the maximum magnetic field strength form a close loop that can guide the migration path for the free electrons. The closed-loop magnetic field enhances the ionization efficiency of the sputtering gas and lowers the operating pressure during sputter deposition. The enhanced sputtering due to magnetic field can produce an erosion pattern over the sputtering surface  112  after repeated sputtering operations, as shown in  FIG. 1D .  
         [0005]     The drawback of the deposition system  100  is that the magnetron  130  is stationary relative to the target  110  during the depositions, which produces non-uniform erosion on the sputtering surface  112  of the target  110 . The non-uniform erosion can result in low target utilization and re-deposition of sputtered target materials on the areas of the sputtering surface  112  having low magnetic field strength. Some of the accumulated materials can fall off the target  110  and land undesirable particle deposition on the substrate  115 .  
         [0006]     Another conventional deposition system  200  is shown in  FIGS. 2A and 2B . The deposition system  200  includes a large target  210 , a vacuum chamber  220 , and a magnetron  230  on the back side (opposite to the sputtering surface  212 ) of the large target  210 . The magnetron  230  can scan across along the direction  250 . The substrate  215  is held over a substrate holder  217 . The substrate  215  remains stationary during the deposition for target with dimensions larger than the substrate, and can have a relative movement to the target  210  for smaller target.  
         [0007]     Although the scanning of the magnetron  230  relative to target  210  can improve the target utilization and prevent target material re-deposition, the deposition system  200  has the disadvantages of using a large and thus expensive target. In addition, the areas of the target  210  at the ends of the scanning direction can only be reached by a single track of the magnetron  230 , while the middle section of the target  210  is scanned by both tracks of the magnetron. This limitation lowers the sputter rate near the edges of the target  210  resulting in non-uniform deposition over the substrate  115 .  
         [0008]     Yet another conventional deposition system  300  is shown in  FIG. 3 . The deposition system  300  includes a circular target  310 , a stationary magnetron  330 , a substrate  315  that can be transported along one direction, and a vacuum chamber  320 . The circular target  310  can rotate around the magnetron  330  by a rotational mechanism to expose different areas of the circular target  310  the magnetic fields of the magnetron  310  so that the target materials can be sputtered at the sputtering surface  312 . The erosion pattern can be more uniform due the circular movement of the target  310 . The high cost of the single-piece circular target  312  is a significant disadvantage in the deposition system  300 . Moreover, target material is often is sprayed on the backing plate  313 , which reduces the quality of the deposition material. The vacuum seal of the rotational transport mechanism is also an engineering challenge. System reliability can be reduced due to unreliable vacuum sealing at the rotational transport mechanism.  
         [0009]     Another disadvantage of the conventional deposition systems is that they are not suitable for thick target, especially the ones comprising magnetic or ferromagnetic materials. The magnetic fields produced by the magnetrons cannot penetrate the thick target. The limitation in the target thickness reduces the amount of materials that can be deposited for each target change-over.  
         [0010]     Yet another disadvantage of the conventional deposition systems is that the target width has to be large enough to accommodate at least one magnetic field loop. In practice, the target width is typically more than 3 inches wide. This will increase target cost and increase system size.  
         [0011]     Yet another disadvantage of the conventional deposition systems is that the deposition is made only on one side of the substrate. A double-sided conventional deposition system  400  requires two opposing magnetrons  430   a  and  430   b  and two associated targets  410   a  and  410   b  in a vacuum chamber  420  as shown in  FIG. 4 . There can be two separate substrates  415   a  and  415   b , or two deposition surfaces of a single substrate.  
       SUMMARY  
       [0012]     Implementations of the system may include one or more of the following. In one aspect, the present invention relates to a magnetron source for producing a magnetic field near a surface of a target in a deposition system, comprising:  
         [0013]     a first magnet;  
         [0014]     a second magnet separated by a gap from the first magnet along a first direction; and  
         [0015]     a target holder configured to hold the target in the gap between the first magnet and the second magnet, wherein the target comprises a sputtering surface from which target material can be sputtered and deposited on a substrate, and wherein the target holder is so configured that the sputtering surface is substantially parallel to the first direction and the first magnet and the second magnet can produce a magnetic field near a surface of the target.  
         [0016]     In another aspect, the present invention relates to a magnetron source for producing a magnetic field near a surface of a target in a deposition system, comprising:  
         [0017]     a first magnet that forms a first close loop;  
         [0018]     a second magnet that forms a second close loop, wherein the second magnet is separated by a gap from the first magnet along a first direction, and wherein the first magnet and the second magnet comprise opposite magnetic polarities; and  
         [0019]     a target holder configured to hold one or more targets in the gap between the first magnet and the second magnet, wherein each of the targets comprises a sputtering surface from which target material can be sputtered and deposited on a substrate, and wherein the target holder is so configured that the sputtering surface is substantially parallel to the first direction and the first magnet and the second magnet can produce a magnetic field near a surface of the one or more targets.  
         [0020]     In another aspect, the present invention relates to a deposition system, comprising:  
         [0021]     a magnetron source, comprising: 
        a first magnet; and     a second magnet separated by a gap from the first magnet along a first direction;        
 
         [0024]     a target holder configured to hold a target in the gap between the first magnet and the second magnet, wherein the target comprises a sputtering surface from which target material can be sputtered and deposited on a substrate, and wherein the target holder is so configured that the sputtering surface is substantially parallel to the first direction and the first magnet and the second magnet can produce a magnetic field near the sputtering surface of the target; and  
         [0025]     a substrate holder configured to hold a substrate that is adapted to receive materials sputtered of the sputtering surface of target.  
         [0026]     In another aspect, the present invention relates to a deposition system, comprising:  
         [0027]     a plurality of magnetron sources, each comprising: 
        a first magnet; and     a second magnet separated by a gap from the first magnet along a first direction;        
 
         [0030]     one or more target holder configured to hold the target in the gap between the first magnet and the second magnet of each of the magnetron source, wherein the target comprises a sputtering surface from which target material can be sputtered and deposited on a substrate, and wherein the target holder is so configured that the sputtering surface is substantially parallel to the first direction and the first magnet and the second magnet in the magnetron source can produce a magnetic field near the sputtering surface of the target; and  
         [0031]     a transport mechanism configured to move the substrate relative to one or more target holders to allow different areas of the substrate to receive materials sputtered of the sputtering surfaces of the targets.  
         [0032]     Embodiments may include one or more of the following advantages. The disclosed deposition system can provide uniform depositions over a large substrate. The disclosed magnetron source can improve target utilization and reduce target cost by reducing the uneven erosion pattern in the target.  
         [0033]     The disclosed deposition system can improve magnetic field uniformity on sputtering surface of the target surface and produce high and controllable deposition rate across substrate. Moreover, the disclosed deposition system can significantly reduce the contamination resulted from re-deposition of target materials in the conventional deposition systems.  
         [0034]     The disclosed deposition system can generate high sputtering rate for magnetic and ferromagnetic target materials. Furthermore, the disclosed system can utilize thick target materials.  
         [0035]     The disclosed magnetron source can reduce the footprint of the deposition system. The deposition system is suitable for double-sided depositions.  
         [0036]     The details of one or more embodiments are set forth in the accompanying drawings and in the description below. Other features, objects, and advantages of the invention will become apparent from the description and drawings, and from the claims.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0037]      FIG. 1A  illustrates a cross section of a conventional deposition system.  
         [0038]      FIG. 1B  is a cross sectional view of the conventional deposition system of  FIG. 1A .  
         [0039]      FIG. 1C  is a bottom perspective view of the magnetron source in the conventional deposition system of  FIG. 1A .  
         [0040]      FIG. 1D  is a bottom perspective view of the target and the erosion pattern on the target in the conventional deposition system of  FIG. 1A .  
         [0041]      FIG. 2A  illustrates a cross section of another conventional deposition system.  
         [0042]      FIG. 2B  is a cross sectional view of the conventional deposition system of  FIG. 2A .  
         [0043]      FIG. 3  illustrates a perspective view of yet another conventional deposition system.  
         [0044]      FIG. 4  is a cross-sectional view of a conventional deposition system for double sided deposition.  
         [0045]      FIG. 5A  illustrates a deposition system in accordance with the present invention.  
         [0046]      FIG. 5B  illustrates a magnetron source and the associated target in the deposition system of  FIG. 5A .  
         [0047]      FIG. 6  illustrates a deposition system having a magnetron source including one or more electric conductor coils.  
         [0048]      FIG. 7  shows a deposition system capable of providing a plurality of targets over or under a substrate.  
         [0049]      FIG. 8  shows magnetron sources and targets comprising multiple materials for a magnetron. 
     
    
     DETAILED DESCRIPTION  
       [0050]     A deposition system  500  in accordance with the present invention is shown in  FIG. 5A . A magnetron source and a target  530  and one or more targets  510   a - 510   c  are shown in  FIG. 5B . The deposition system  500  includes one or more targets  510   a ,  510   b ,  510   c ,  510   d , a magnetron source  530 , a substrate  515  that can be transported along the direction  550 , and a vacuum chamber  520 . The magnetron source  530  can comprise a pair of magnets  530   a  and  531   a  above the substrate  515 . The magnet  530   a  can be of a “North” polarity and the magnet  531   a  of “South” polarity, which produces magnetic flux lines from the magnet  530   a  to magnet  531   a  as shown in  FIG. 5A . Similarly, a pair of magnets  530   b  and  531   b  is positioned under the substrate  515 . Both pairs of magnets  530   a / 531   a  and  530   b / 531   b  can produce magnetic field lines having components substantially parallel to the sputtering surfaces  512   a  and  512   b . The magnetron source  530  also includes two vertical pairs of magnets  530   c / 531   c  and  530   d / 531   d  (not shown for clarity reasons) of opposing polarities in each pair. The magnets  530   a ,  530   b ,  530   c , and  530   d  of the “North” polarity can form a close loop. Similarly the magnets of the “South” polarity in the magnets  531   a ,  531   b ,  531   c , and  531   d  can also form a close loop. Each pair of the magnets  530   a / 531   a ,  530   b / 531   b ,  530   c / 531   c , or  530   d / 531   d  can also be connected on the outer rim by ferromagnetic material, which can enhance the magnetic field strengths near the sputtering surfaces  512   a - d.    
         [0051]     The magnets  530   a - d  and magnets  531   a - d  can comprise permanent magnets such as rare earth magnets, or ceramic magnet. They can be connected using a ferromagnetic material such as a 400 series stainless steel and a Mu-metal. In the present specification, as described below, the magnets  530   a - d  can also include electric conductor coils or electromagnets that can generate magnetic flux similar to the permanent magnetic materials.  
         [0052]     The targets  510   a - 510   c  and target  510   d  (not shown in  FIG. 5B  for clarity reasons) are sandwiched between the two closed looped magnets of opposing polarities. The cross section of the target  510   a - 510   d  can also take other shapes such as curved surface, non-orthogonal sidewalls, and non-flat sputtering surfaces. The vacuum chamber  520  is at ground potential or is positively biased. The substrate  515  can be at ground potential of independently biased. The magnets  530   a - 530   d  can be held at ground potential or positively biased as part of the anode. The targets  510   a - 510   d  are insulated from the vacuum chamber  520  and negatively biased during the deposition forming a continuous electrical field around the loop. The targets  510   a - 510   d  can be separated from each other each independently biased, or biased by the same power supply. The sputtering rate from each of the four targets can therefore be individually varied. The targets  510   a - 510   d  can also be connected or formed by a single target piece of material, which is biased a single power supply. The negatively biased targets  510   a - 510   d  attract and accelerate positive ions to sputter materials off the sputtering surface  512   a - 512   d  of the targets  510   a - 510   d  which can be subsequently deposited on the substrate  515 .  
         [0053]     The typical dimension for large substrate is 1 to 2 meters on one side. For example, an 8th generation flat panel substrate is approximately 2.2×2.4 meters. The lengths of the long targets  510   a  and  510   b  are typically at least 0.1 meters longer than the smaller dimension of the substrate. The lengths of the short targets  510   c  and  510   d  are typically at least 0.1 meter longer than the thickness of the substrate and substrate holder.  
         [0054]     The electric biases can be provided by power supplies  540   a  and  540   b . The power supplies  540   a  and  540   b  can also provide Alternative Current (AC) or Radio Frequency (RF) in addition to DC power supply.  
         [0055]     The substrate  515  is transported horizontally through the close loops formed by the magnets  530   a - 530   d  and the targets  510   a - 510   d  such that the top and bottom surfaces of the substrate  515  can be respectively exposed to the sputtering surfaces  512   a  and  512   b.    
         [0056]     An advantageous feature of the deposition system  500  is that the targets  510   a - 510   d  are held between the oppositely poled pairs of magnets  530   a - 530   d . The North and South poled magnets are displaced along the horizontal direction. The sputtering surfaces  521   a  and  512   b  are substantially parallel to the horizontal direction. The magnetic field flux as shown in  FIG. 5A  thus has a large component parallel to the sputtering surfaces  512   a  and  512   b . The large tangential component of the magnetic fields can apply strong Lorentz forces to bend the paths of the electrons that are repelled at high velocity by the negative bias of the sputtering surfaces  512   a - 512   d . The electrons can be curved back to the target  530   a - 530   d  before they again bounce away from the targets. This bouncing-pulling cycle can repeat many times until the electrons lose the kinetic energy and the Lorentz force becomes insignificant.  
         [0057]     The sputtering off target  512   a  and  512   b  depends on uniformity of the magnetic field strength on the surface. It is relative easy to have consistent magnetic field by using the same type of permanent magnets or electric conductor coil. The sputtering off the targets  512   c  and  512   d  can deposit materials along the edges of the substrate  515  or used to fine tune to the deposition uniformity over the upper and lower surfaces of the substrate  515 .  
         [0058]     The trapping of the fast moving electrons at the sputtering surfaces can enhances the plasma ionization efficiency. The closed loop arrangement of the targets can ensure the fast-moving electrons to be contained in the close loop. Since most electrons are trapped near the sputtering surfaces  512   a - 512   d , most of the sputtering occurs at the surfaces sputtering surfaces  512   a - d , that is, the target surfaces that are facing the substrate  515 . Since the magnetic field is perpendicular to the side surfaces of the targets  510   a - 510   d , the electrons cannot be effectively trapped near those surfaces. The plasma density and the sputtering erosion are low on the target sidewalls.  
         [0059]     By arranging the “North” and the “South” poled magnets, a substantially uniform magnetic field can be formed in the tangential directions relative to the sputtering surfaces  512   a - d . The uniform magnetic field can ensure full target surface erosion and even erosion across target surface, which in turn produces a high target material utilization.  
         [0060]     In another embodiment, the substrate  515  can be replaced by a two substrates for single sided deposition. The upper substrate receives deposition material on its upper surface. The lower substrate receives deposition material on its lower surface. This configuration thus allows parallel depositions on two substrate pieces which doubles the throughput comparing to a single-substrate processing.  
         [0061]     In another embodiment, the magnets  530   a - d  and  531   a - d  in deposition system  500  can be replaced by a pair of electric conductor coils  630   a  and  630   b  (or electromagnets) in deposition system  600 , shown in  FIG. 6 . The electric conductor coils  630   a  and  630   b  are disposed along the two sides of the close looped targets. The electric conductor coils  630   a  and  630   b  can be applied with electric currents to produce “North” and “South” magnetic polarities and substantially uniform magnetic flux  660  in the close loop and near the sputtering surfaces  612   a  and  612   b  of the targets  610   a - 610   d . A single electric conductor coil  630   a  or  630   b  can also produce a substantially magnetic flux parallel to the target surface and achieve similar results as two or more electric coil.  
         [0062]     In another embodiment, a deposition system  700  can include a plurality of targets  710   a ,  711   a ,  712   a  and  713   a  that are positioned above a substrate and a plurality of targets  710   b ,  711   b ,  712   b  and  713   b  below the substrate (not shown for clarity reasons) in a vacuum chamber  720 . A plurality of electric conductor coils or permanent magnets  730 - 734  can be alternatively positioned between the targets  710   a / 713   a  through  713   a / 713   b  to produce a uniform magnetic field in the vacuum chamber  720  and near the sputtering surfaces. Shields can be added between the adjacent targets  710   a - 713   b  to minimize the cross contamination on the substrate  715 .  
         [0063]     The substrate  715  can be transported in the horizontal direction. In one embodiment, the targets  710   a - 713   b  can comprise substantially the same target material. The substrate  715  is transported only by a short distance that is approximately the separation between the adjacent targets to produce uniform deposition over the substrate  715 . The shortened travel distance by the substrate  715  reduces the foot print of the deposition system  700 . In another embodiment, different target materials can be included in targets  710   a - 713   b  to enable availability of depositions of different coating compositions in one vacuum pump down of the vacuum chamber  720 .  
         [0064]     In another embodiment, targets  810  and  811  can each be positioned between electric conductor coils  830   a  and  830   b . The target  810  includes two different portions  810   a  and  811   a  that can be made of different materials. The target  811  includes three different portions  810   b ,  811   b  and  812   b  that can be made of different materials. The different materials in a target can allow the deposition of materials of different compositions over the upper surface or the lower surface of a substrate.  
         [0065]     It is understood that the disclosed system and methods are not limited to the specific description in the specification. For example, the disclosed system is suitable for material depositions on large or small substrates. In addition, the substrate can be heated and/or applied with an electric bias voltage. The deposition system can also include a vacuum load locks and a cleaning chamber for cleaning the substrate. The substrate transport mechanism can also take various forms without deviating from the spirit of the specification.