Abstract:
A magnetron source for producing a magnetic field near a sputtering target in a vacuum deposition system includes a first group of sequentially positioned individual magnets of a first magnetic polarity, and a second group of sequentially positioned individual magnets of a second magnetic polarity opposite to the first magnetic polarity. The first group of magnets and the second group of magnets are so configured that electrons can be trapped near the sputtering surface of the sputtering target in the regions between the first group of magnets and the second group of magnets.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS  
       [0001]     This application is related to commonly assigned U.S. patent application Ser. No. 11/185,241, titled “Single-process-chamber deposition system” by Guo, filed Jul. 20, 2005 and U.S. patent application Ser. No. 11/212,142, titled “Vacuum processing and transfer system” by Guo et al, filed Aug. 26, 2005, the contents of which are incorporated herein by reference. 
     
    
     TECHNICAL FIELD  
       [0002]     This application relates to apparatus for depositing material on substrate in a vacuum environment.  
       BACKGROUND  
       [0003]     Physical vapor deposition (PVD) is a process of sputtering materials off a target and depositing the sputtered materials on a substrate. The sputtering target and the substrate are positioned inside a vacuum envelope that can be filled with low-pressure gas such as Argon, Nitrogen, or Oxygen. Magnetrons are used in physical vapor deposition (PVD) to reduce the operating vacuum pressure and bias voltage by trapping energetic electrons in the magnetic field and hence increasing the path length of the electrons. The lengthened electron path increases the probability of ionizing gas atoms in the vacuum chamber and hence increases the plasma density. Magnetrons are typically placed behind the sputtering target.  
         [0004]     A magnetron can include one or more pieces of magnets each consisting of two opposite magnetic poles. Inside the vacuum chamber, electrons can be trapped by the magnetic fields between the opposite magnetic poles of a magnet and form a plasma gas near the target surface. The attractive forces on the electrons are proportional to the tangential component of the magnetic field that is parallel to the target surface. The tangential component of the magnetic field reaches its maximum near the mid point between the two poles of a magnet. As a result, more electrons are trapped and form a higher density plasma near the mid regions between the opposite poles of a magnet. More target materials are thus sputter removed in the mid regions between the opposite poles of the magnets, resulting in uneven removal of target materials from the sputtering target.  
         [0005]      FIG. 1  illustrates the erosion pattern in a target  100  by a circular magnetron  110  (although the magnetron can also be of other shapes). The sputtering occurs over the upper surface of the target  100 . The magnetron  110  is placed behind the back surface of the target  100 . The magnetron  110  includes two magnetic poles of opposite polarities: a circular shaped magnetic pole  120  in the center and a circular shaped magnetic pole  130  near the rim of the target  100 . The magnetic field lines  115  are arc shaped as shown spanning between the two magnetic poles  120  and  130 . After repeated sputtering operations, the uneven removal of the target material forms an erosion grove  140  between the two magnetic poles.  
         [0006]     The uneven erosion can cause a target unusable even when there is still substantial target material left in a target. The shortened target life results in material waste and higher maintenance costs. In order to address the uneven erosion problem, some magnetron designs utilize the shape of the magnetic track to optimize the erosion profile. The improvement by these designs is limited because they still tend to leave large areas without magnetic track on the target surface. There is therefore a need to further reduce the erosion unevenness in the sputtering target in PVD systems.  
       SUMMARY  
       [0007]     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 sputtering target in a vacuum deposition system including a first group of sequentially positioned individual magnets of a first magnetic polarity, and a second group of sequentially positioned individual magnets of a second magnetic polarity opposite to the first magnetic polarity. The first group of magnets and the second group of magnets are so configured that electrons can be trapped near the sputtering surface of the sputtering target in the regions between the first group of magnets and the second group of magnets.  
         [0008]     In another aspect, the present invention relates to a method for producing a magnetic field near the sputtering surface of a sputtering target in a vacuum deposition system, including positioning a first group of sequentially positioned individual magnets of a first magnetic polarity near a surface of the sputtering target opposite to the sputtering surface of the sputtering target, positioning a second group of sequentially positioned individual magnets of a second magnetic polarity opposite to the first magnetic polarity near the surface of the sputtering target opposite to the sputtering surface of the sputtering target, trapping electrons near the sputtering surface of the sputtering target in the regions between the first group of magnets and the second group of magnets, and sputtering target material off the sputtering target.  
         [0009]     Embodiments may include one or more of the following advantages. The disclosed magnetron source improves the utilization of target materials, especially for a static magnetron. The disclosed magnetron source can lengthen the usage lifetime of the sputtering targets by increasing the uniformity of the erosion pattern, which reduces the cost for the target materials. The usage lifetime increase is especially prominent for magnetron sources that are stationary to the sputtering target during depositions.  
         [0010]     In another aspect, the disclosed magnetron source provides the flexibilities of rearranging the electron path of sputtering source or for different targets. The magnetron designs can be optimized by placing individual magnets over entire target surface, so that the erosion on any point of the target surface can be adjusted by changing corresponding individual magnets. The redistribution of individual magnets can even out the material removal from the target and can also optimize the sputtering pattern in accordance with different materials. Sputtering uniformity and efficiency are improved. Equipment cost is also reduced where different targets are required in prior art systems.  
         [0011]     In yet another aspect, the disclosed magnetron increases the ionization efficiency and increases the plasma density. This will reduce the operating pressure and lower the operating voltage, resulting in better plasma stability, higher deposition efficiency, and less chance of arcing inside the plasma.  
         [0012]     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  
       [0013]      FIG. 1  illustrates the erosion track in a typical prior art magnetron source.  
         [0014]      FIG. 2A  illustrates the layout of a magnetron source in accordance with the present invention.  
         [0015]      FIG. 2B  is a perspective view of the magnetron source in  FIG. 2A .  
         [0016]      FIG. 2C  illustrates the path of electrons for the magnetron source as shown in  FIG. 2A .  
         [0017]      FIG. 3A  illustrates a magnetron source  300  comprising ferromagnetic magnetic plates attached to the magnets of  FIG. 2A .  
         [0018]      FIG. 3A  illustrates ferromagnetic magnetic plates that can be attached to the magnets of  FIG. 2A .  
         [0019]      FIG. 3B  is a perspective view of a magnetron source  300  comprising the ferromagnetic magnetic plates of  FIG. 3A  attached to the magnets of  FIG. 2A .  
         [0020]      FIG. 4A  illustrates the layout of the individual magnets in a rectangular shaped magnetron source in accordance with another embodiment of the present invention.  
         [0021]      FIG. 4B  is a perspective view of the rectangular shaped magnetron source of  FIG. 4A . 
     
    
     DETAILED DESCRIPTION  
       [0022]      FIG. 2A  illustrates the layout of a magnetron source  200  in accordance with the present invention. The magnetron source  200  includes a plurality of individual magnets  210 A,  210 B and  220 A,  220 B,  220 C. The magnets  210 A,  210 B and the magnets  220 A,  220 B,  220 C have opposite polarities. For example, the magnets  211 A,  210 B can be of south polarity whereas the magnets  220 A,  220 B,  220 C can be of the north polarity. The magnets  210 A,  210 B,  220 A,  220 B,  220 C can take the form of a circular disk, or a polygon-shaped tablet.  
         [0023]     The magnets  210 A,  210 B are typically sequentially positioned with closer distances to each other with the group than from the magnets  220 A,  220 B,  220 C. Similarly, the magnets  220 A,  220 B,  220 C are typically closer positioned to each other with the group than from the magnets  210 . In the example shown in  FIG. 2A , the magnets  210 A,  210 B are distributed in a ring  210 A and a closely positioned lateral branch  210 B leading to the center. The magnets  220 A,  220 B,  220 C form an outer ring  220 A and an inner ring  220 B that are bridged by a linear array of magnets  220 C.  FIG. 2B  shows a perspective view of the magnetron source  200 .  
         [0024]     The magnets  210 A,  210 B and the magnets  220 A,  220 B,  220 C are positioned close enough with each group to form a continuous path along which the tangential component of the magnetic field reaches its maximum. As such, more electrons are trapped in the areas between the two groups of individual magnets.  FIG. 2C  illustrates the path  250  of electrons in magnetron source  200 . The electron path  250  is produced along the track of magnetic field between the barriers formed by the oppositely poled magnets  210 A,  210 B and magnets  220 A,  220 B,  220 C. The electrons can bounce back and forth from the target surface and traverse along the path  250  until they lose most of their kinetic energies. The path  250  as shown forms a close loop to allow electrons to move continuously along the path  250 . Abrupt end in magnetic track or the electron path  250  is avoided to prevent loss of electrons and plasma.  
         [0025]     An advantage of the invented magnetron source  200  is that the number of the individual magnets, the spacing between the individual magnets, the number of rings in the distribution of the individual magnets, the size of the individual magnets, and the spacing between the two polarity groups of magnets can all easily be optimized to maximize target utilization, improve deposition uniformity, and improve plasma stability. As shown in  FIG. 2A , the magnets  210 A and  220 B can include larger magnets at the ends of the lines to enhance the magnetic field strength in ending areas where larger open areas are involved. In addition, the magnetic strength at any point of the target and hence the erosion depth can be adjusted by changing the corresponding magnets nearby. This greatly increases the flexibility in the magnetron design.  
         [0026]     Furthermore, various above described parameters can also be optimized in the magnetron source  200  specific to different the types of target materials to accommodate the difference in sputtering yield, scattering of sputtered materials with the gas atoms before reaching substrate, and angular sputtering distribution. For example, when the sputtering target material is changed, the individual magnets can be re-positioned using the same magnetron source  200 , which can significantly reduce equipment development cost.  
         [0027]     To optimize the erosion depth and maximize target utilization, the individual magnets  210 A,  210 B and  220 A,  220 B,  220 C can be distributed to form a long electron path  250  and cover as much target surface as possible. More rings can be included in the distribution of the magnets  210 A,  210 B and  220 A,  220 B,  220 C. A larger target surface area can be more evenly sputtered, which is highly desirable especially for the stationary magnetrons. In addition, the operating vacuum pressure and the bias voltage can also be lowered. Furthermore, the width of the magnetic field track can slightly vary along the electron path  250 , which can further even out the erosion pattern and fill all available space above target surface.  
         [0028]     In another embodiment, a ferromagnetic material can be attached to a group of magnets of the same polarity to reduce the magnetic field variation.  FIG. 3A  shows two continuous pieces of ferromagnetic plates  310  and  320  that are shaped to cover the magnets  210 A,  210 B and magnets  220 A,  220 B,  220 C, respectively.  FIG. 3B  is a perspective view of a magnetron source  300  that comprises the ferromagnetic plates  310  and  320  respectively attached to the individual magnets  210 A,  210 B and individual magnets  220 A,  220 B,  220 C. Examples of the ferromagnetic material can include 400-series stainless steel, Mu-metal, etc.  
         [0029]     In another embodiment, the magnetron sources  200  and  300  can be held stationary relative to the sputtering target or mounted on a rotation plate that can rotate relative to the sputtering target during the vacuum deposition. The distribution of the individual magnets can be optimized relative the rotation parameters to further reduce the uneven erosion in the target.  
         [0030]     The invented magnetron source can be formed in other than circular shapes such as rectangles, polygons, or irregular shapes.  FIG. 4A  and  FIG. 4B  show a top view and a perspective view of a rectangular shaped magnetron source  400 . The magnetron source  400  includes two groups of the individual magnets  410  and  420  that have a rectangular (e.g. square) outer boundary. The magnets  410  and  420  are distributed sequentially positioned in horizontal rows and vertical columns, forming a close-loop magnetic track between the two opposite polarity groups. Similar to previously described, the number, the sizes, the magnetic strength, and the spacing between individual magnets  410  and  420  can be optimized to minimize the erosion pattern.  
         [0031]     In another embodiment, the distribution of individual magnets can be moved between different configurations during the lifetime of a target to further even out the residual uneven erosion in the target. For example, a magnetic track can be moved in a new configuration over the area where the magnets used to be positioned in the previous configuration. Material sputtering can thus catch up in the under-sputtered area on the target.