Abstract:
In one aspect of the invention, a sputter source is provided. The sputter source includes a target source affixed to a bottom plate of the sputter source. A plurality of magnets spaced apart from each other is included. The plurality of magnets is disposed above a surface of the bottom plate, wherein a surface of the target source is profiled such that the target source has a minimum thickness aligned with an axis of each of the plurality of magnets and a maximum thickness aligned with an axis of a gap defined between each of the plurality of magnets. A method of processing a substrate is also included.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure generally relates to the field of thin film deposition apparatus and methods and more particularly to a sputter target source. 
       BACKGROUND 
       [0002]    Physical vapor deposition (PVD) is commonly used within the semiconductor industry, as well as within solar, glass coating, and other industries, for depositing thin films over a substrate. Sputter deposition is a physical vapor deposition (PVD) method of depositing thin films by sputtering, that is ejecting material from a source target by high-energy particle bombardment, which then deposits onto a substrate such as a silicon wafer. 
         [0003]    The targets composed of ferromagnetic materials are relatively thin, as compared to targets of non-ferromagnetic material, due to the ferromagnetic material&#39;s shunting effect of the magnetic field. That is, the magnetic strength at the target surface must be strong enough to ignite and sustain a plasma, and the shunting effect of the magnetic field by the ferromagnetic material restricts the thickness for the target. Due to the high magnetic permeability and the fact that magnetic lines of force decrease drastically relative to target thickness, ferromagnetic targets are thinner than non-ferromagnetic targets in order to permit a sufficient magnetic field to permeate the target surface. Ferromagnetic targets may be 0.25 inches or less, which is substantially thinner than a thickness of non-ferromagnetic targets. Thin targets have an inherently short target life and have to be changed frequently, causing down time for the tools processing the substrates, which in turn impacts throughput and efficiency in a fabrication facility. 
         [0004]    What is needed is the ability to have a thicker ferromagnetic target to increase the time between replacement of targets and where the thicker target allows for a sufficient magnetic field to ignite and sustain a plasma. 
       SUMMARY 
       [0005]    Embodiments of the present invention provide a profiled sputter target that enables sufficient magnetic field penetration. Several inventive embodiments of the present invention are described below. 
         [0006]    In one aspect of the invention, a sputter source is provided. The sputter source includes a target source affixed to the front end of the sputter source. A plurality of magnets arranged to form a magnetron with two magnet tracks of opposing polarities, N-(north) and S-(south) tracks, for the igniting and sustaining of a closed-loop plasma is included. The plurality of magnets is disposed behind a bottom surface of the target, wherein the front sputtering surface of the target source is profiled such that the target source has a minimum thickness aligned with the N- and S-track magnets and a maximum thickness aligned with gap defined between the N- and S-track magnets. 
         [0007]    In another aspect of the invention a method of processing a substrate is provided. The method includes depositing a layer of material onto the substrate by a sputtering process. While depositing the layer, the method includes applying a magnetic field through a target having a profiled surface, the profiled surface configured so that the target has a minimum thickness aligned with the N- and S-track magnets and a maximum thickness aligned with gap defined between the N- and S-track magnets. 
         [0008]    Other aspects of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The present invention will be readily understood by the following detailed description in conjunction with the accompanying drawings. Like reference numerals designate like structural elements. 
           [0010]      FIGS. 1A and 1B  are simplified schematic cross sectional diagrams illustrating prior art configurations for sputter sources. 
           [0011]      FIG. 2  is a simplified schematic diagrams illustrating a target erosion profile and corresponding alignment with the magnetron source disposed behind the target. 
           [0012]      FIG. 3  is a simplified schematic diagram illustrating how a profiled target source assembly is optimized in accordance with some embodiments of the invention. 
           [0013]      FIG. 4  is a simplified schematic diagram illustrating an alternative configuration for a profiled target source in accordance with some embodiments of the invention. 
           [0014]      FIG. 5  is a simplified schematic diagram illustrating an alternative configuration for a profiled target source in accordance with some embodiments of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    The embodiments described herein provide a method and apparatus related to sputter deposition processing. It will be obvious, however, to one skilled in the art, that the present invention may be practiced without some or all of these specific details. In other instances, well known process operations have not been described in detail in order not to unnecessarily obscure the present invention. 
         [0016]    The embodiments described herein provide techniques to minimize the downtime of a sputter deposition tool by extending the life of a target source. In some embodiments a profiled target source is provided. The profiled target source has a surface with varying thicknesses across the surface. A first thickness is substantially aligned with N-track magnets, which may be referred to as magnet tracks of a first pole, and S-track magnets which may be referred to as magnet tracks of a second pole, providing a magnetic field permeating the target source. A second thickness is substantially aligned with an axis of a gap defined between the N- and S-track magnets providing the magnetic field. The second thickness is greater than the first thickness. In some embodiments, a smooth transition is provided between the first thickness and the second thickness. With the profiled target, the magnetic field is able to permeate a ferromagnetic target source, such as cobalt, nickel or iron, in order to sustain and ignite a plasma due to the proximity of the magnet to the first thickness of the target source. In some embodiments, the target material has a magnetic permeability of greater than 1.0. In addition, the life of the target source is extended as the portion of the target that erodes quicker is correlated to the second thickness. It should be further appreciated that the embodiments may be applied to any film composition being deposited including but not limited to conductive films, dielectric films, etc. 
         [0017]      FIGS. 1A and 1B  are simplified schematic cross sectional diagrams illustrating prior art configurations for sputter sources. Magnetic shunt plate  104  is affixed to one end of magnets  100  and  102 . The other end of S-track magnet  100  and N-track magnet  102  is disposed over target backing plate  108 . Non-ferromagnetic target  106  is affixed to an opposing surface of backing plate  108  in  FIG. 1A , while ferromagnetic target  112  is affixed to an opposing surface of backing plate  108  in  FIG. 1B . It should be appreciated that target backing plate  108  and targets  106  or  112  can be replaced with a so-called monolithic target without a separate backing plate although targets of ferromagnetic materials usually have a separate backing plate to allow greater target thickness. A magnetic field is generated between magnets  100  and  102 . In  FIG. 1A  the magnetic field efficiently permeates through non-ferromagnetic target  106 , as illustrated by magnetic field lines  110 . However, in  FIG. 1B  the magnetic field is shunted by ferromagnetic target  112 , as illustrated by magnetic field lines  114 . Thus, the thickness of 2-10 mm for ferromagnetic target  112  is significantly less than the thickness of 2-50 mm for non-ferromagnetic target  106  in order to ignite and sustain a plasma for a sputtering process. A thin ferromagnetic target is usually bonded to a backing plate to satisfy the mechanical strength requirement for a target. 
         [0018]      FIG. 2  is a simplified schematic diagrams illustrating a target erosion profile and corresponding alignment with the magnetron sources disposed behind the target. It should be appreciated that top portion of  FIG. 2  depicts the surface of the target source  200  with a typical erosion profile for a target with initially uniform thickness, while the bottom portion of  FIG. 2  illustrates the configuration and alignment of annular magnets disposed behind the target source. The erosion profile illustrated in the top portion of  FIG. 2  depicts an annular erosion groove  202  that experiences a greater amount of erosion than a remainder of the target surface after processing. Erosion groove  202  is substantially aligned with gap  201  defined between center magnet  204  and outer annular magnet  206 . Outer peripheral region of the surface of target source  200  has significantly more of the target material remaining, i.e., is thicker, as compared to the amount of material remaining in erosion groove  202 . However, due to the depletion of the material in erosion groove  202 , the target is no longer useful and changing of the target is necessary, which incurs downtime for the sputter tool. 
         [0019]      FIG. 3  is a simplified schematic diagram illustrating how a profiled target source assembly is optimized in accordance with some embodiments of the invention. The target source assembly includes a magnet shunt plate  104  having magnets  102  and  100  affixed to a surface of the plate. Magnets  100  and  102  are disposed behind a surface of backing plate  108 . In one embodiment magnet  100  may be referred to as a center magnet while magnet  102  may be referred to as an annular outer magnet. Target source  112  is affixed to an opposing surface of backing plate  108 . In the top portion of  FIG. 3  the erosion profile  300  of a prior art flat target  112  after sputter processing is illustrated by erosion groove or erosion depth  302 . Magnetic flux lines  114  emanating from magnets  102  to magnet  100  permeates through ferromagnetic target source  112 . Erosion depth  302  and erosion depth profile  304  are illustrated below the target and magnetron assembly of  FIG. 3  for explanatory purposes. In some embodiments, the area depicted by erosion groove  302  is inverted in order to define the profiled shape of a target source. That is, the profiled target source is further illustrated as target backing plate  108  with a profiled target source  306  affixed thereto in the lower section of  FIG. 3 . The profiled target source includes a portion  308  which is a substantially uniformly thick portion, and portion  310  which is a profiled portion of the target material. For example, portion  310  may be defined by the inverted area of erosion groove  302 . Portion  308  may be defined by the minimum target material, typical 0.5-2 mm, which is required to be left behind at the end of target life to prevent accidental sputtering of target backing material  108 . It should be appreciated that the thickest portion, i.e., the maximum thickness of the surface profile, of the profiled target material is substantially aligned with a gap defined between S-track magnets  100  and N-track magnets  102 , while the thinnest portion, i.e., the minimum thickness of the surface profile, is substantially aligned with S-track magnets  100  and N-track magnets  102 . A complete illustration of the two portions  308  and  310  of the profiled target material is illustrated as profiled target source  306 . As mentioned above, target source  306  is configured with a minimum thickness aligned with the S-track and N-track magnets of the magnetron assembly and a maximum thickness aligned with gaps between the S-track and N-track magnets. It should be further appreciated that target source  306  gradually transitions between the regions of minimum thickness and maximum thickness, i.e., the transition is a smooth transition. Sharper transitions are possible in alternative embodiments. Processing of a substrate with the profiled target source and the magnet configuration illustrated in  FIG. 3  results in a longer life for the target source. That is, the maximum thickness regions of profiled target  306  are eroded at a faster rate than the minimum thickness regions, thereby resulting in a substantially flat target profile  312  at the end of target life. End-of-life target profile  312  is desirably comparable to  308 , i.e., the minimum target material required to be left behind at the end of target life to prevent accidental sputtering of target backing material  108 . Due to the profiled target source, the life of the target is extended in order to minimize the downtime of the tool. It should be appreciated that magnets  100  and  102  may be rotatable around an axis in some embodiments of the invention, or scanned two-dimensionally (X,Y) in other embodiments of the invention. 
         [0020]      FIG. 4  is a simplified schematic diagram illustrating an alternative configuration for a profiled target source in accordance with some embodiments of the invention. It should be appreciated that while  FIG. 3  illustrates a symmetrical design where rotation of the magnets may be incorporated,  FIGS. 4 and 5  illustrate designs where rotation is likely not incorporated. Region  400  and region  404  illustrate regions of a profiled target aligned with a corresponding magnet disposed above the profiled target. Region  402  illustrates a gap between the corresponding magnets. Thus, the profiled target of  FIG. 4  would have a maximum thickness corresponding to region  402  and a minimum thickness corresponding to region  400  and region  404 . 
         [0021]      FIG. 5  is a simplified schematic diagram illustrating an alternative configuration for a profiled target source in accordance with some embodiments of the invention. Region  500  and region  504  illustrate regions of a profiled target aligned with a corresponding magnet disposed above the profiled target. Region  502  illustrates a gap between the corresponding magnets. The profiled target of  FIG. 5  has a maximum thickness corresponding to region  502  and a minimum thickness corresponding to region  500  and region  504 . In some embodiments, the transition between the maximum and minimum thicknesses of  FIGS. 4 and 5  is a transition as illustrated with reference to  FIG. 3 . The profiles of  FIGS. 3-5  are illustrated for exemplary purposes and not meant to be limiting as any suitable profile where the thickness of the target is correlated to the magnet placement as described above may be integrated with a sputter source as described herein. 
         [0022]    Although the foregoing invention has been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications can be practiced within the scope of the appended claims. Accordingly, the present embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalents of the appended claims. In the claims, elements and/or steps do not imply any particular order of operation, unless explicitly stated in the claims.