Abstract:
Electron beam-confining electromagnets of an electron beam generator are aligned with an electron beam axis, each of the electromagnets being folded to define a main section and a pair of angled wing sections disposed at respective angles relative to said main section, and a conductor wound around the edge.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part of U.S. patent application Ser. No. 13/097,800, filed Apr. 29, 2011 entitled APPARATUS FOR FORMING A MAGNETIC FIELD AND METHODS OF USE THEREOF, by Gary Leray et al., which claims benefit of U.S. Provisional Application Ser. No. 61/405,970, filed Oct. 22, 2010 entitled APPARATUS FOR FORMING A MAGNETIC FIELD AND METHODS OF USE THEREOF, by Gary Leray, et al. 
     
    
     BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    Embodiments of the present invention generally relate to plasma enhanced substrate processing. 
         [0004]    2. Background Discussion 
         [0005]    Plasma enhanced substrate processing is commonly used, for example, in the manufacture of semiconductor devices and integrated circuits. Such processing generally includes introducing a process gas into a process chamber having a substrate, such as a semiconductor wafer, disposed therein and applying sufficient energy to the process gas to form a plasma over the substrate. The plasma contains dissociated and ionized components as well as neutral components that operate to assist the process being performed on the substrate (such as deposition, etching, and the like). Although the constituents of the plasma are beneficial for assisting or carrying out the process on the substrate, unconstrained plasma components may impinge on the substrate and/or chamber components causing damage. In addition, plasma non-uniformities may lead to non-uniform processing of substrates. 
         [0006]    To control the plasma, conventional process chambers may include a magnetic field-forming device configured to produce a magnetic field within the process chamber to constrain plasma components. However, the magnetic field produced by such conventional configurations typically comprise non-parallel and non-planar magnetic field lines, resulting in non-uniform plasma confinement, and therefore, non-uniform processing of the substrate. 
       SUMMARY 
       [0007]    A plasma reactor includes a processing chamber, an electron source having an electron emission axis extending into the processing chamber, and a pair of electron beam-confining electromagnets aligned with the electron emission axis. Each of the electromagnets includes a conductor coiled around a closed boundary, the closed boundary comprising an edge folded to define a main section and a pair of angled wing sections disposed at respective angles relative to the main section, the boundary defining an aperture through which the electron emission axis extends. The conductor is confined in a zone along the edge of the frame defining an aperture extending between opposite edges of the frame, the electron beam axis extending through the aperture of one of the electromagnets. 
         [0008]    In a further aspect, there are provided first and second DC current sources coupled to first and second ones of the electromagnets respectively, and a controller governing the first and second DC current sources. 
         [0009]    In one embodiment, the electron beam source provides an electron beam having a width less than a distance between opposing edges of the angled wing sections. In a related embodiment, the width of the electron beam exceeds a width of the main section. 
         [0010]    In a related embodiment, the angled wing sections are folded about respective fold axes which are parallel to an axis of symmetry of the chamber. 
         [0011]    In a further embodiment, each of the pair of electromagnets extends around portion of a periphery of the chamber. In one aspect, the pair of electromagnets defines respective portions of a polygon within which a circular boundary of the processing chamber is inscribed. 
         [0012]    In a further embodiment, each angled wing section of one of the electromagnets is separated by a gap from the corresponding angled wing section of the other one of the electromagnets. 
         [0013]    In accordance with a related embodiment, there is provided respective pairs of side electromagnets extending at least partially across respective ones of the gaps, each of the side electromagnets extending from a corresponding one of the angled wing sections into the gap. 
         [0014]    In one aspect, each one of the pair of side electromagnets extends across the entirety of the corresponding one of the gaps. 
         [0015]    Each of the side electromagnets is oriented at an angle relative to the electron emission axis. 
         [0016]    In one embodiment, the pair of electromagnets and the side electromagnets together define a complete polygon within which a circular boundary of the processing chamber is inscribed. 
         [0017]    The reactor may further include respective DC current sources coupled to respective ones of the side electromagnets. In a related aspect, the DC current sources are such that current flow direction along a top edge of each electromagnet is co-directional with current flow along the top edge of the corresponding one of the folded wing sections. 
         [0018]    In a related aspect, the electron beam source extends partially into the aperture. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    So that the manner in which the exemplary embodiments of the present invention are attained can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings. It is to be appreciated that certain well known processes are not discussed herein in order to not obscure the invention. 
           [0020]      FIG. 1  depicts a schematic side view of a process chamber having an apparatus for controlling a plasma in accordance with some embodiments of the present invention. 
           [0021]      FIG. 2  is a top view of an apparatus for controlling a plasma in accordance with some embodiments of the present invention. 
           [0022]      FIGS. 3 and 3A  depict side views of an apparatus for controlling a plasma in accordance with some embodiments of the present invention. 
           [0023]      FIGS. 4 and 4A  respectively depict a schematic side view and cross section along line  4 A- 4 A of a coil for use with an apparatus for controlling a plasma in accordance with some embodiments of the present invention. 
           [0024]      FIGS. 5A-5C  depicts a graph showing top views of magnetic field lines superimposed over a substrate in accordance with some embodiments of the present invention. 
           [0025]      FIG. 6  depicts a method performed in a process chamber in accordance with some embodiments of the present invention. 
           [0026]      FIG. 7  depicts a plasma reactor employing a pair of folded electromagnets. 
           [0027]      FIGS. 7A and 7B  are top and end views of one of the folded electromagnets of  FIG. 7 . 
           [0028]      FIGS. 7C and 7D  are top and end views of the other one of the folded electromagnets of  FIG. 7 . 
           [0029]      FIG. 7E  is a top view the reactor of  FIG. 7 . 
           [0030]      FIG. 7F  is an orthographic projection corresponding to  FIG. 7E  and depicting insertion of an electron beam source into an aperture of an electromagnet. 
           [0031]      FIG. 8  depicts a graph of electron flux lines of an electron beam in a processing region of the plasma reactor of  FIG. 7 . 
           [0032]      FIG. 9  depicts a plasma reactor having a pair of folded electromagnets flanked by side electromagnets. 
           [0033]      FIG. 9A  is a top view corresponding to  FIG. 9 . 
           [0034]      FIG. 9B  is a side view of a side electromagnet of  FIG. 9 . 
           [0035]      FIG. 9C  is another top view depicting an alternative mode for controlling electron flux distribution. 
           [0036]      FIG. 10  is a simplified orthographic projection depicting current flow direction in each electromagnet of  FIG. 9 , in accordance with one mode. 
           [0037]      FIG. 11  depicts a graph of electron flux lines of an electron beam in a processing region of the plasma reactor of  FIG. 9 , showing an improved electron distribution. 
       
    
    
       [0038]    To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation. It is to be noted, however, that the appended drawings illustrate only exemplary embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
       DETAILED DESCRIPTION 
       [0039]    Embodiments of the present invention generally relate to an apparatus for controlling a plasma and methods of use thereof. Embodiments of the inventive apparatus and methods may advantageously allow for substantially planar and parallel magnetic field to be formed in multiple directions, thereby providing an increased flexibility in plasma processing. In addition, the inventive apparatus provides a coil configuration of comparatively small volume about a process chamber as opposed to conventional coil configurations (e.g. a Helmholtz coil configuration). Embodiments of the inventive apparatus and methods may further advantageously more uniformly constrain a plasma formed within a process chamber, thereby leading to more uniform processing results. 
         [0040]      FIG. 1  depicts a process chamber  100  suitable for use with an apparatus for forming a magnetic field in accordance with some embodiments of the present invention. Exemplary process chambers may include the DPS®, ENABLER®, ADVANTEDGE™, or other process chambers, available from Applied Materials, Inc. of Santa Clara, Calif. Other suitable process chambers may similarly be used. 
         [0041]    The process chamber  100  generally comprises a chamber body  101  defining an inner volume  103  that may include a processing volume  105 . The processing volume  105  may be defined, for example, between a substrate support pedestal  124  disposed within the process chamber  100  for supporting a substrate  122  thereupon during processing and one or more gas inlets, such as a showerhead  102  and/or nozzles  106  provided at desired locations. In some embodiments, the substrate support pedestal  124  may include a mechanism that retains or supports the substrate  122  on the surface of the substrate support pedestal  124 , such as an electrostatic chuck, a vacuum chuck, a substrate retaining clamp, or the like (not shown). In some embodiments, the substrate support pedestal  124  may include mechanisms for controlling the substrate temperature (such as heating and/or cooling devices, not shown) and/or for controlling the species flux and/or ion energy proximate the substrate surface. 
         [0042]    For example, in some embodiments, the substrate support pedestal  124  may include an RF bias electrode  142 . The bias electrode  142  may be coupled to one or more bias power sources (one bias power source  128  shown) through one or more respective matching networks (matching network  126  shown). The one or more bias power sources may provide RF or DC energy in a pulsed or continuous mode. For example, in some embodiments, the one or more bias power sources may be capable of producing up to 12,000 W of RF energy at a desired frequency, such as about 2 MHz, or about 13.56 MHz, or about 60 MHz, or the like. In some embodiments, two or more bias power sources may be provided for coupling RF power through respective matching networks to the RF bias electrode  142  at respective frequencies of, for example, any of the frequencies discussed above. One or more of the bias power sources may provide either continuous or pulsed power. In some embodiments, the one or more bias power sources  128  may be a DC or pulsed DC source. 
         [0043]    The substrate  122  may enter the process chamber  100  via an opening  144  in a wall  145  of the chamber body  101 . The opening  144  may be selectively sealed via a slit valve  146 , or other mechanism for selectively providing access to the interior of the chamber through the opening  144 . The substrate support pedestal  124  may be coupled to a lift mechanism (not shown) that may control the position of the substrate support pedestal  124  between a lower position suitable for transferring substrates into and out of the chamber via the opening  144  and a selectable upper position suitable for processing. The process position may be selected to maximize process uniformity for a particular process. When in at least one of the elevated processing positions, the substrate support pedestal  124  may be disposed above the opening  144  to provide a symmetrical processing region. 
         [0044]    The showerhead  102  and/or nozzles  106  may be coupled to a gas supply  104  for providing one or more process gases into the processing volume  105  of the process chamber  100 . Although only two nozzles  106  are shown in  FIG. 1  disposed on the walls  145  of the chamber body  101 , additional or alternative gas nozzles or inlets may be disposed in the ceiling  149  or on the walls  145  of the chamber body  101  or at other locations suitable for providing gases as desired to the process chamber  100 , such as the base of the process chamber  100 , the periphery of the substrate support pedestal  124 , or the like. An exhaust system  140  comprising a vacuum pump (not shown) may be coupled to the process chamber  100  for pumping out the exhaust gases from the inner volume  103 . 
         [0045]    In some embodiments, the process chamber  100  may utilize an electron beam generator  115  to generate an electron beam  121  to ignite a process gas (e.g. a process gas provided by gas supply  104 ) to form a plasma in the processing volume  105 . For example, in such embodiments the process chamber  100  may comprise a cathode  112  disposed on a wall  145  of the chamber body  101  and configured to produce electrons having an adequate amount of energy to ignite the process gas. 
         [0046]    An anode  113  may be disposed on a wall  145  opposite the cathode  112  and configured to attract the electrons produced by the cathode  112 . 
         [0047]    The electron beam generator  115  may be disposed at any position within the process chamber  100  to provide the electron beam  121  at a suitable distance from the substrate  122  to perform a desired process. For example, in some embodiments, the electron beam generator  115  may be positioned such that a distance  118  between a central axis  119  of the electron beam  121  and an upper surface of the substrate  122  may be about 1 cm to about 30 cm. In some embodiments, the distance  118  may be selected to adjust the plasma density in an area  123  proximate the substrate. For example, as the distance  118  between the central axis  119  of the electron beam  121  and the substrate  122  decreases the density of the plasma in the area  123  proximate the substrate  122  may increase. Alternatively, as the distance  118  between the central axis  119  of the electron beam  121  and the substrate  122  increases, the density of the plasma in the area  123  proximate the substrate  122  may decrease. 
         [0048]    A magnetic field forming device  148  (described more fully below with respect to  FIGS. 2-4 ) is disposed proximate the walls  145  of the chamber body  101  and configured to form a magnetic field  117  having magnetic field lines that are substantially planar and substantially parallel to facilitate control over the plasma formed in the processing volume  105 . The magnetic field forming device  148  generally comprises a plurality of coils  110  positioned symmetrically about a central axis  150  of the process chamber  100 . The magnetic field forming device  148  may comprise any amount of coils  110  suitable for forming a magnetic field (i.e., magnetic field  117 ) having the desired shape and orientation. 
         [0049]    One or more power supplies  138  may be coupled to the plurality of coils  110  to selectively provide an electric current through one or more of the plurality of coils  110  to produce the desired magnetic field  117  within the process chamber  100 . In operation, the magnetic field  117  confines at least some of the electrons (negatively charged particles) of the electron beam  121  and/or the plasma, thereby facilitating control over the plasma. 
         [0050]    In some embodiments, a shield  108  may be disposed around the plurality of coils  110  to shield other equipment (e.g., controllers, process chambers, other fabrication equipment, or the like) from the magnetic field  117 . The shield  108  may comprise any material suitable to impede the magnetic field  117 , such as a metal, for example stainless steel. In addition, the shield  108  may have any suitable geometry (e.g., size and shape) that provides the desired shielding effect. For example, in some embodiments, the shield  108  may be sized to cover an outer facing surface  109  of the plurality of coils  110 . The shield  108  may be continuous and extend from coil to coil, or alternatively, the shield  108  may comprise a plurality of discrete elements disposed proximate each individual coil (or groups of coils). The shield  108  may be in direct contact with the coils or may be spaced apart from the coils. 
         [0051]    The magnetic field forming device  148  may be disposed at any position about the process chamber  100  to provide the magnetic field  117 , and therefore control the plasma, in a suitable location with respect to the substrate  122 . For example, in some embodiments, the magnetic field forming device  148  may be positioned such that a distance  120  between a central axis  114  of the magnetic field  117  and the substrate  122  may be about 1 cm to about 30 cm In some embodiments, the distance  120  may be selected to adjust the plasma density in an area  123  proximate the substrate. For example, as the distance  120  between the central axis  114  of the magnetic field  117  and the substrate  122  decreases the density of the plasma in the area  123  proximate the substrate  122  may increase. Alternatively, as the distance  120  between the central axis  114  of the magnetic field  117  and the substrate  122  increases, the density of the plasma in the area  123  proximate the substrate  122  may decrease. 
         [0052]    In addition, the position of the magnetic field forming device  148  and the electron beam generator  115  may be selected to adjust a distance  116  between the central axis  114  of the magnetic field  117  and the central axis  119  of the electron beam  121 . In some embodiments, by varying the distance  116  between the central axis  114  of the magnetic field  117  and the central axis  119  of the electron beam  121 , the amount of electrons of the electron beam  121  confined to a given plane may be adjusted. In some embodiments, the inventors have observed as the distance  116  between the central axis  114  of the magnetic field  117  and the central axis  119  of the electron beam  121  is decreased more of the electrons of the electron beam  121  are confined to a given plane, thus increasing the confinement (and reducing or eliminating divergence) of the electron beam  121 , thereby preventing electrons from the electron beam  121  from impinging on the substrate  122 . For example, in some embodiments the distance  116  between the central axis  114  of the magnetic field  117  and the central axis  119  of the electron beam  121  may be up to about a thickness of the electron beam  121 . 
         [0053]    Referring to  FIG. 2 , in some embodiments, the plurality of coils  110  may comprise eight coils  210   a - h  disposed about the central axis  150  of the process chamber  100 . In such embodiments, the eight coils  210   a - h  may be arranged in a symmetrical pattern wherein each of the eight coils  210   a - h  is offset by an angle  212  of about 45 degrees from a respective adjacent coil of the eight coils  210   a - h . In some embodiments, each coil may have a substantially similar size, shape, and strength (e.g., number of turns of wire forming the coil). 
         [0054]    In operation, subsets of the plurality of coils  110  may be utilized to form the magnetic field  117  having a desired shape and orientation in a desired vector direction. For example, in some embodiments, six coils (i.e., coils  210   b ,  210   c ,  210   d ,  210   f ,  210   g ,  210   h ) of the eight coils  210   a - h  may be utilized to form the magnetic field  117 . For example, in such embodiments, a first current may be provided to a first group of coils (primary coils  220 ) comprising two coils  210   c ,  210   g  to generate the magnetic field  117  having magnetic field lines  230  oriented in a vector direction  214 . 
         [0055]    The first current may flow in opposite directions with respect to the opposing coils. For example, the first current may be applied in a first direction  206  about a first coil (e.g., coil  210   c ) of the primary coils  220  and in a second direction  207  opposite the first direction  206  about a second coil (e.g., coil  210   g ) of the primary coils  220 . The arrows depicting the first direction  206  and the second direction  207  schematically indicate the general direction of current flow across the top of the respective coils. Since the coils  210   c  and  210   g  are opposing, the first direction  206  and the second direction  207  both are illustratively moving down the page in the frame of reference of  FIG. 2 . Alternatively, the opposing coils may be wound in opposite directions to cause the current to flow in opposite directions. 
         [0056]    A second current may be concurrently provided to a second group of coils (secondary coils  224 ) adjacent to the first group of coils (for example, four coils  210   b ,  210   d ,  210   f ,  210   h ) to cause the magnetic field lines to be substantially planar and substantially parallel throughout a region of the magnetic field disposed above substrate support of the process chamber. For example, the magnetic field lines created by the second group of coils may compress the magnetic field lines created by the first group of coils with respect to a direction  215  perpendicular to the vector direction  214 . The second current may be applied in the first direction  206  about secondary coils adjacent to the primary coil that also has current flowing in the first direction (e.g., primary coil  210   c  and secondary coils  210   b ,  210   d ). The second current may be applied in the second direction  207  about secondary coils adjacent to the primary coil that also has current flowing in the second direction (e.g., primary coil  210   g  and secondary coils  210   f ,  210   h ). By providing the plurality of coils  110  in the manner and operation described above, the inventors have observed that the desired magnetic field  117  may be formed using the magnetic field forming device  148  configured in a comparatively small volume about a process chamber as opposed to conventional coil configurations (e.g. a Helmholtz coil configuration). 
         [0057]    In some embodiments, a ratio of the first current to the second current may be varied to control the shape and/or contours of the magnetic field lines  230  within the magnetic field  117  in the plane parallel to the substrate  122  to compensate for plasma effects. For example, the ratio of the first current to the second current may be about 2:1 to about 1:5. In some embodiments, the inventors have observed if the ratio is higher towards the first current, the magnetic field lines  230  in the plane parallel to the substrate  122  may be convex (i.e., divergent). Alternatively, in some embodiments, if the ratio is higher towards the second current, the magnetic field lines  230  in the plane parallel to the substrate  122  may be concave (i.e., convergent). 
         [0058]    For example,  FIGS. 5A-5C  respectively depict top views of the shape of magnetic field lines created at three different ratios of the first current to the second current.  FIG. 5A  depicts a graph  510  showing a top view of magnetic field lines  502  superimposed over a substrate  504  where the ratio of the first current to the second current is about 1:1. As shown in  FIG. 5A , the magnetic field lines  502  are generally parallel over the predominant portion of the substrate  504 , although the magnetic field lines  502  near the outer edges, or outer region, of the magnetic field are slightly curved outward (e.g., concave). The magnetic field lines  502  proximate the outer region of the magnetic field may have a greater radius of curvature than that of the magnetic field lines  502  proximate a central axis of the magnetic field. 
         [0059]      FIG. 5B  depicts a graph  520  showing a top view of magnetic field lines  506  superimposed over a substrate  504  where the ratio of the first current to the second current is about 2:1. As shown in  FIG. 5B , the magnetic field lines  506  are generally parallel over the predominant portion of the substrate  504 , and the magnetic field lines  506  near the outer edges, or outer region, of the magnetic field are much less curved (e.g., concave). 
         [0060]      FIG. 5C  depicts a graph  530  showing a top view of magnetic field lines  508  superimposed over a substrate  504  where the ratio of the first current to the second current is about 1:5. As shown in  FIG. 5C , the magnetic field lines  508  are generally parallel over the predominant portion of the substrate  504 , and the magnetic field lines  508  near the outer edges, or outer region, of the magnetic field are slightly curved inward (e.g., convex). 
         [0061]    Returning to  FIG. 2 , in some embodiments, the magnitude of the magnetic field  117  may be varied by to tune the uniformity of a plasma formed within the process chamber  100 . In some embodiments, the magnitude of the magnetic field  117  may be varied by increasing or decreasing the first current and second current. Alternatively, or in combination, the magnitude of the magnetic field  117  may be varied by increasing or decreasing an amount of a conductor wound about a core (e.g. a number of turns) when constructing of the plurality of coils  110  (for example, as described below with respect to  FIG. 4 .) In some embodiments, the magnetic field  117  may comprise a magnitude of about 44 to 52 Gauss, or in some embodiments about 60 to 70 Gauss. In some embodiments, by increasing or decreasing the magnitude of the magnetic field  117 , a radius of the circular motion of the electrons formed in the plasma with respect to a plane perpendicular to the magnetic field  117  (i.e., the Larmor radius) may be increased or decreased. For example, as the magnitude of the magnetic field  117  is increased, the Larmor radius may decrease which reduces the electron divergence due to collisions with other particles. 
         [0062]    Although the above embodiments are described with respect to forming a magnetic field  117  having magnetic field lines  230  orientated in vector direction  214 , it is to be noted that the magnetic field  117  may be formed in other directions by utilizing any six of the eight coils  210   a - h  in a manner similar to that described above. 
         [0063]    Referring to  FIGS. 3 and 3A , in some embodiments, a height  302  of the plurality of coils  110  may be varied to adjust a magnetic field line  230  divergence (i.e., the density of magnetic field lines) in a given volume  304  about the electron beam  121 . For example, the inventors have observed that as the height  302  of the plurality of coils  110  increases, the magnetic field line  230  divergence in a given volume around the substrate decreases, resulting in the magnetic field line  230  becoming increasingly parallel proximate the electron beam  121 , for example such as depicted in  FIG. 3 . Alternatively, as the height  302  of the plurality of coils  110  decreases, the magnetic field line  230  divergence in a given volume around the substrate increases, resulting in the magnetic field line  230  becoming less parallel proximate the electron beam  121 , for example such as depicted in  FIG. 3A . 
         [0064]    The plurality of coils  110  may comprise any shape suitable to produce the desired magnetic field  117 . For example, in some embodiments, the plurality of coils  110  may be a rectangular toroid, as depicted in  FIGS. 4-4A . In some embodiments, each coil of the plurality of coils  110  may comprise a conductor  402  (e.g., a wire comprising copper) wound in a desired shape a number of times (e.g., turns or windings). The conductor  402  is covered by an insulating layer (not shown) to electrically isolate adjacent portions of the conductor  402  between turns. For example,  FIGS. 4-4A  illustratively depict the conductor  402  having three layers (e.g.,  406 ,  408 ,  410 ) with each layer having five turns of the conductor  402  (as shown in the cross-sectional side view of  FIG. 4A ). The size, number, and spacing of the conductor  402  and the layers  406 ,  408 ,  410  in the figures are not drawn to scale and simplified for illustrative purposes. Other numbers of turns, layers, geometries, etc. may be used as required to provide a desired magnetic field shape and strength. In some embodiments, the conductor  402  may be wound about an optional core  404 . 
         [0065]    In some embodiments, the core  404  may comprise a ferromagnetic material (e.g., cobalt (co), iron (Fe), nickel (Ni), or the like). The number of turns or windings of the conductor  402  may be varied to increase or decrease the magnitude of the magnetic field produced by the plurality of coils  110 . 
         [0066]      FIG. 6  depicts a method performed in a process chamber in accordance with some embodiments of the present invention. The method  600  may be performed in any suitable process chamber comprising a plurality of coils having substantially similar dimensions disposed symmetrically about an exterior of the process chamber with respect to a central axis of the process chamber, for example such as the process chamber  100  comprising the magnetic field forming device  148  described above with respect to  FIG. 1 . 
         [0067]    In some embodiments, the method  600  may be utilized to create a magnetic field to confine a plasma formed within a process chamber. Accordingly, in some embodiments, the method  600  may comprise forming a plasma within the process chamber. The plasma may be formed at any time during the method  600 , for example such as the beginning of the method  600  at  602 , at the end of the method  600  at  608 , or at any time between. 
         [0068]    In embodiments where the method  600  is performed in a process chamber similar to the process chamber  100  described above, to form the plasma a process gas may be supplied from the gas supply  104  to the processing volume  105  of the process chamber  100  via the showerhead  102  and/or nozzles  106 . The process gas may be any process gas suitable to perform a desired process. Following the introduction of the process gas to the process chamber  100 , the plasma may be formed by igniting the process gas via an electron beam  121  supplied by the electron beam generator  115 , for example, as discussed above. 
         [0069]    Next, at  604 , a first current is provided to two opposing coils selected from the plurality of coils to create a magnetic field in a first vector direction. The two coils may be any two coils disposed on directly opposing sides of the magnetic field forming device to provide the magnetic field in a desired vector direction, as discussed above. The amount of current provided to the two coils  210   c ,  210   g  may be any amount suitable to produce the magnetic field  117  having a desired magnitude. In some embodiments, the amount of current required may be dictated by the size (e.g., the height  302  described in  FIG. 3 ) and construction (e.g., insulated conductor  402 , core  404 , of the like, described in  FIG. 4 ) of each of the eight coils  210   a - h.    
         [0070]    At  606 , a second current may be concurrently provided to coils adjacent to the two opposing coils (selected at  604 ) to form a magnetic field having a plurality of magnetic field lines that are substantially planar and substantially parallel, as discussed above. The magnetic field lines may further be substantially planar and substantially parallel throughout a region of the magnetic field disposed above substrate support  124  of the process chamber  100 . 
         [0071]    The amount of current provided to the four coils  210   b ,  210   d ,  210   f ,  210   h  may be any amount suitable to produce the magnetic field  117  having a desired shape. In some embodiments, a ratio of the first current to the second current may be varied to adjust the shape and/or contours of the magnetic field lines  230  within the magnetic field  117 , as discussed above. 
         [0072]    In some embodiments, during processing of the substrate  122 , the orientation of the magnetic field  117  may be changed to alter the orientation of the plasma. In such embodiments, the current supplied to the selected coils (e.g., the two coils (e.g., coils  210   c ,  210   g ) and the four coils (e.g., coils  210   b ,  210   d ,  210   f ,  210   h )) may be stopped and then the respective currents may be applied to another six of the eight coils  210   a - h  in a manner similar to that described above. In such embodiments, the direction of the electron beam  121  may also be similarly changed to ensure the electron beam  121  remains parallel with the magnetic field lines  230  of the magnetic field  117 . 
         [0073]    After providing the second current at  606 , the method  600  generally ends, unless the step of  608  is performed. In embodiments where a plasma is formed within the process chamber, the magnetic field  117  magnetically confines the electrons of the electron beam  121  and/or the plasma (as discussed above), thereby facilitating control over the plasma, thus facilitating control over the plasma assisted process. In such embodiments, following the end of the method  600 , a plasma assisted process (e.g., an etch, deposition, anneal process, or the like) may also be terminated. 
         [0074]    Returning to  FIG. 1 , a controller  130  may be coupled to the process chamber  100  to facilitate control over the process chamber  100 . The controller  130  may be one of any form of general-purpose computer processor that can be used in an industrial setting for controlling various chambers and sub-processors. The memory  136 , or computer-readable medium of the CPU  132  may be one or more of readily available memory such as random access memory (RAM), read only memory (ROM), floppy disk, hard disk, or any other form of digital storage, local or remote. The support circuits  134  are coupled to the CPU  132  for supporting the processor in a conventional manner. These circuits include cache, power supplies, clock circuits, input/output circuitry and subsystems, and the like. 
         [0075]    The inventive methods disclosed herein may generally be stored in the memory  136  as a software routine that, when executed by the CPU  132 , causes the process chamber  101  to perform processes of the present invention. The software routine may also be stored and/or executed by a second CPU (not shown) that is remotely located from the hardware being controlled by the CPU  132 . Some or all of the method of the present invention may also be performed in hardware. As such, the invention may be implemented in software and executed using a computer system, in hardware as, e.g., an application specific integrated circuit or other type of hardware implementation, or as a combination of software and hardware. The software routine, when executed by the CPU  132 , transforms the general purpose computer into a specific purpose computer (controller) that controls the chamber operation such that the methods disclosed herein are performed. 
         [0076]      FIG. 7  depicts a plasma reactor having an electron beam generator  650  as a plasma source that produces plasma from process gases within a processing chamber  652 . The electron beam  654  produced by the electron beam generator  650  is confined along a straight path by the magnetic field produced by a pair of electromagnets  656  and  658  facing one another. A workpiece support  653  is disposed within the processing chamber  652  for holding a workpiece or wafer in a support plane at least approximately parallel to the direction of the electron beam  654 . 
         [0077]    Referring to  FIGS. 7A and 7B , the electromagnet  656  consists a continuous conductive winding  660  extending along the periphery of a folded rectangular frame  662  shown in dashed line. A controlled electric current source  657  is coupled to the winding  660 . The rectangular frame  662  is folded along folds  670 - 1  and  670 - 2  defining a base  672  and a pair of folded wings  674 - 1  and  674 - 2  extending from opposite sides of the base  672 . Each folded wing  674 - 1  and  674 - 2  is disposed at a fold angle A relative to the base  672 . In one embodiment, the plane of the base  672  is orthogonal to the direction of the electron beam  654 . 
         [0078]    As shown in  FIG. 7B , the conductive winding  660  is confined within a folded annular region  676  conforming to the folded rectangular frame  662 . The folded annular region  676  of  FIG. 7B  defines an opening or aperture  678  through which the electron beam generator  650  faces toward the processing chamber  652 , as will be described below. The aperture  678  is bounded in width between the outer edges of the wings  674 - 1  and  674 - 2 . The electron beam  654  has a width up to the width of the aperture  678  and may therefore exceed the width of the base  672 . This corresponds to the widened electron beam source  650 ′ indicated in dashed line in  FIG. 7E . This aspect allows for a large electron beam width, a significant advantage. 
         [0079]    Referring now to  FIGS. 7C and 7D , the electromagnet  658  consists a continuous conductive winding  664  extending along the periphery of a folded rectangular frame  666  shown in dashed line. A controlled electric current source  659  is coupled to the winding  664 . The rectangular frame  666  is folded at folds  671 - 1  and  671 - 2  defining a base  673  and a pair folded wings  675 - 1  and  675 - 2  extending from opposite sides of the base  673 . Each folded wing  675 - 1  and  675 - 2  is disposed at a fold angle A relative to the base  673 . In one embodiment, the plane of the base  673  is orthogonal to the direction of the electron beam  654 . 
         [0080]    As shown in  FIG. 7D , the conductive winding  664  is confined within a folded annular region  677  conforming to the folded rectangular frame  666 . The folded annular region  677  of  FIG. 7D  defines an opening or aperture  679  through which a beam dump  736  ( FIG. 7 ) receives the electron beam  654 . The aperture  679  is bounded in width between the outer edges of the wings  675 - 1  and  675 - 2 . The electron beam  654  may have a width up to the width of the aperture  679 , allowing for a large electron beam width. 
         [0081]      FIG. 7E  shows how the wings  674 - 1 ,  674 - 2 ,  675 - 1  and  675 - 2  are folded toward the processing chamber  652 . The folded electromagnets  656  and  658  in one embodiment are mirror images of one another and together define an axis of symmetry coinciding with an axis of symmetry of the processing chamber  652 . Current flow in the conductive windings  660  and  664  is along the same rotational direction about an axis coinciding with the direction of the electron beam  654 . In the illustrated example, the current flow in the conductive windings  660  and  664  is clockwise when viewed along the electron beam direction of travel. Thus, viewed along the direction of the electron beam  654 , current flow along the top edge of each electromagnet  656 ,  658  is from left to right, while current flow along the bottom edge is from right to left. 
         [0082]      FIG. 7F  is a view showing how the electron beam generator  650  faces the processing chamber  652  through the aperture  678  of the electromagnet  656 . In some embodiments, the electron beam generator  650  extends partially through the aperture  678 . 
         [0083]    Referring again to  FIG. 7 , the processing chamber  652  has a cylindrical side wall  702 , a floor  704  and a ceiling  706 . A workpiece support or pedestal  653  supports a workpiece  710 , such as a semiconductor wafer, the pedestal  653  being movable in the axial (e.g., vertical) direction. A gas distribution plate  712  is integrated with or mounted on the ceiling  706 , and receives process gas from a process gas supply  714 . A vacuum pump  716  evacuates the chamber through a passage in the floor  704 . A processing region  718  is defined between the workpiece  710  and the gas distribution plate  712 . Within the processing region  718 , the process gas is ionized to produce a plasma for processing of the workpiece  710 . 
         [0084]    The plasma is generated in the processing region  718  by the electron beam  654  from the electron beam generator or source  650 . The electron beam source  650  in one embodiment includes a plasma generation chamber  722  spaced from the processing chamber  652  and having a conductive enclosure  724 . The conductive enclosure  724  has a gas inlet  725 . An electron beam source gas supply  727  is coupled to the gas inlet  725 . The conductive enclosure  724  has an opening  724   a  facing the processing region  718  through an opening  702   a  in the sidewall  702 . 
         [0085]    The electron beam source  650  in the illustrated embodiment includes an extraction grid  726  adjacent the opening  724   a , and an acceleration grid  728  adjacent the extraction grid  726  and facing the processing region  718 . Either or both the extraction grid  726  and the acceleration grid  728  may be formed as either a conductive mesh or a slotted electrode, for example, and are herein referred to generically as grids. Electrical contact to the extraction grid  726  is provided by a conductive ring  726   a  surrounding the extraction grid. Electrical contact to the acceleration grid  728  is provided by a conductive ring  728   a  surrounding the acceleration grid  728 . The extraction grid  726  and the acceleration grid  728  are mounted with insulators  730 ,  732 , respectively, so as to be electrically insulated from one another and from the conductive enclosure  724 . However, the acceleration grid  728  is in electrical contact with the side wall  702  of the chamber  652 . The openings  724   a  and  702   a  and the extraction and acceleration grids  726 ,  728  can be mutually congruent, generally, and define a thin wide flow path for an electron beam  654  into the processing region  718 . The width of the flow path is about the diameter of the workpiece  710  (e.g., 300 mm) or more, while the height of the flow path is less than about two inches. 
         [0086]    The electron beam flows across the processing region  718  over the workpiece  710 , and is absorbed on the opposite side of the processing region  718  by the beam dump  736 . The beam dump  736  is a conductive body having a shape adapted to capture the wide thin electron beam. The beam dump  736  may be coupled to ground through a shunt resistor  738 . 
         [0087]    A negative terminal of a plasma D.C. discharge voltage supply  740  is coupled to the conductive enclosure  724 , and a positive terminal of the voltage supply  740  is coupled to the extraction grid  726 . A negative terminal of an electron beam acceleration voltage supply  742  is connected to the extraction grid  726 , and a positive terminal of the voltage supply  742  is connected to the ground. In one embodiment the acceleration grid  728  is grounded. The acceleration voltage supply  742  is connected across the extraction grid  726  and the acceleration grid  728 . In one embodiment, plasma is generated within the chamber  722  of the electron beam source  650  by a D.C. gas discharge produced by power from the voltage supply  740 . Electrons are extracted from the plasma in the chamber  722  through the extraction grid  726  and the acceleration grid  728  to produce an electron beam that flows into the processing chamber  652 . Electrons are accelerated to energies corresponding to the voltage provided by the acceleration voltage supply  742 . 
         [0088]    The electron beam source  650  has been described as a D.C. gas discharge plasma source. In other embodiments, the electron beam source  650  may embody any other suitable plasma source, such as a capacitively coupled plasma source, an inductively coupled plasma source or a toroidal plasma source. 
         [0089]    In some instances, the magnetic field produced by the electromagnets  656  and  658  of  FIG. 7  can be non-uniform. In such cases, plasma production and transport are non-uniform, leading to significant plasma non-uniformity in the processing chamber  652 . Along a direction transverse to the central axis of the electromagnets  656 ,  658 , the magnetic field lines curve. Since the electrons follow the magnetic field lines, beam electrons follow a curved trajectory and electron flux density in the electron beam decreases with distance from the central axis of the electron beam  654 , as shown in the graph of  FIG. 8 . In addition, due to curvature in the magnetic fields lines, electrons in the electron beam follow a path that twists up and down. As a result of these effects, plasma is produced non-uniformly, which detracts from process uniformity in the processing chamber  652 . 
         [0090]      FIG. 9  depicts an embodiment in which the foregoing problem is solved, by the addition of side electromagnets  681 ,  682 ,  683 ,  684  between the electromagnets  656  and  658 . Referring to  FIG. 9A , the side electromagnets  681  and  682  extend from the outer edges of the folded wings  674 - 1  and  674 - 2  respectively in a direction generally tangential to the edge of the processing chamber  652 . The side electromagnets  683  and  684  extend from the outer edges of the folded wings  675 - 1  and  675 - 2  respectively in a direction generally tangential to the edge of the processing chamber  652 . In the illustrated embodiment, each of the of side electromagnets  681 ,  682 ,  683 ,  684  is rectangular in shape and supported on an individual rectangular frame and are identical design.  FIG. 9B  illustrates the structure of the side electromagnet  681 , which is typical all four side electromagnets  681 ,  682 ,  683 ,  684 . The side electromagnet  681  consists of an elongate conductor  681 - 1  wound around the outer edge of a rectangular frame  681 - 2 . 
         [0091]    Each side electromagnet  681 ,  682 ,  683 ,  684  extends about half the distance of each gap D separating opposing pairs of the folded wings  674 - 1 ,  675 - 1  and  674 - 2 ,  675 - 2 . Each side electromagnet  681 ,  682 ,  683 ,  684  may be articulated at an angle “B” relative to the direction of the electron beam  654 , as indicated in  FIG. 9A . The angle B can be changed to optimize electron beam uniformity or minimize curvature of the magnetic field. 
         [0092]      FIG. 9C  depicts another way of optimizing uniformity or minimizing magnetic field curvature, by shifting the location of each pair of side electromagnets  681 ,  682 ,  683 ,  684  relative to the axis of symmetry of the processing chamber  652 . 
         [0093]    Referring now to  FIG. 10 , the current flow direction (indicated by arrows) along the top edge of each side electromagnet  681 ,  682  is the same as the direction of current flow along the top edge of the adjacent folded wing  674 - 1 ,  674 - 2  respectively. Similarly, the current flow direction along the top edge of each side electromagnet  683 ,  684  is the same as the direction of current flow along the top edge of the adjacent folded wing  675 - 1 ,  675 - 2  respectively. Respective current sources  691 ,  692 ,  693 ,  694  are separately controlled and connected to respective ones of the side electromagnets  681 ,  682 ,  683 ,  684 .  FIG. 9B  shows how the current source  691  is connected to opposite ends of the coiled conductor  681 - 2  of the side electromagnet  681 . 
         [0094]    In the mode depicted in  FIG. 10 , the current sources  657 ,  659 ,  691 ,  692 ,  693 ,  694  are controlled to provide current flow in each electromagnet  656 ,  658 ,  681 ,  682 ,  683 ,  684  such that net current flow viewed along the direction of electron beam propagation is clockwise. Thus, viewed along the direction of the electron beam  654 , current flow along the top edge of the electromagnet  656  and its side electromagnets  681 ,  682  is from left to right, while current flow along the bottom edge is from right to left. Similarly, viewed along the direction of the electron beam  654 , current flow along the top edge of the electromagnet  658  and its side electromagnets  683 ,  684  is from left to right, while current flow along the bottom edge is from right to left. 
         [0095]    By exciting the side electromagnets  681 ,  682 ,  683 ,  684  with appropriate currents, they produce a magnetic field that opposes or compensates for the magnetic field curvatures produced by the electromagnets  656  and  658 , and so achieve a more uniform distribution in the electron beam  654  (as illustrated in the graph of  FIG. 11 ) and of plasma in the processing chamber  652 . In addition, as the resulting magnetic field lines have less curvature, the up/down twisting of the beam electrons is also minimized. The side electromagnets  681 ,  682 ,  683 ,  684  provide the following variable parameters to optimize the performance: their length “L”, the angle B, current magnitude, and current direction. These variable parameters enhance control of the magnetic field distribution. By shaping the magnetic field using the side electromagnets  681 ,  682 ,  683 ,  684 , the etch uniformity can also be improved. The magnetic field can be optimized electrically by separately powering the electromagnets  656 ,  658  and the side electromagnets  681 ,  682 ,  683 ,  684  and controlling the ratio of their electromagnet coil currents. 
         [0096]    In the illustrated embodiment, the electromagnets  656 ,  658  and the side electromagnets  681 ,  682 ,  683 ,  684  together form a polygon or at least a portion of a polygon within which the circular boundary of the processing chamber is at least approximately inscribed. The polygon may be irregular in that not all sides are of the same length. In some embodiments, the opposing pairs of side magnets touch one another so that the polygon is closed. In other embodiments there is a gap G between each pair of opposing side magnets, and the polygon is not closed. Such differences are affected by the angle A and length L of the different side electromagnets  681 ,  682 ,  683 ,  684 . 
         [0097]    While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.