Abstract:
A RF source and method are disclosed which inductively create a plasma within an enclosure without an electric field or with a significantly decreased creation of an electric field. A ferrite material with an insulated wire wrapped around its body is used to efficiently channel the magnetic field through the legs of the ferrite. This magnetic field, which flows between the legs of the ferrite can then be used to create and maintain a plasma. In one embodiment, these legs rest on a dielectric window, such that the magnetic field passes into the chamber. In another embodiment, the legs of the ferrite extend into the processing chamber, thereby further extending the magnetic field into the chamber. This ferrite can be used in conjunction with a PLAD chamber, or an ion source for a traditional beam line ion implantation system.

Description:
BACKGROUND 
     A plasma processing apparatus generates a plasma in a chamber which can be used to treat a workpiece supported by a platen in a process chamber. In some embodiments, the chamber in which the plasma is generated is the process chamber. Such plasma processing apparatus may include, but not be limited to, doping systems, etching systems, and deposition systems. In some plasma processing apparatus, ions from the plasma are attracted towards a workpiece. In a plasma doping apparatus, ions may be attracted with sufficient energy to be implanted into the physical structure of the workpiece, e.g., a semiconductor substrate in one instance. 
     In other embodiments, the plasma may be generated in one chamber, which ions are extracted from, and the workpiece is treated in a different process chamber. One example of such a configuration may be a beam line ion implanter where the ion source utilizes an inductively coupled plasma (ICP) source. The plasma is generally a quasi-neutral collection of ions (usually having a positive charge) and electrons (having a negative charge). The plasma has an electric field of about 0 Volts per centimeter in the bulk of the plasma. 
     Turning to  FIG. 1 , a block diagram of one exemplary plasma processing apparatus  100  is illustrated. The plasma processing apparatus  100  includes a process chamber  102  defining an enclosed volume  103 . A gas source  104  provides a primary dopant gas to the enclosed volume  103  of the process chamber  102  through the mass flow controller  106 . A gas baffle  170  may be positioned in the process chamber  102  to deflect the flow of gas from the gas source  104 . A pressure gauge  108  measures the pressure inside the process chamber  102 . A vacuum pump  112  evacuates exhausts from the process chamber  102  through an exhaust port  110 . An exhaust valve  114  controls the exhaust conductance through the exhaust port  110 . 
     The plasma processing apparatus  100  may further includes a gas pressure controller  116  that is electrically connected to the mass flow controller  106 , the pressure gauge  108 , and the exhaust valve  114 . The gas pressure controller  116  may be configured to maintain a desired pressure in the process chamber  102  by controlling either the exhaust conductance with the exhaust valve  114  or a process gas flow rate with the mass flow controller  106  in a feedback loop that is responsive to the pressure gauge  108 . 
     The process chamber  102  may have a chamber top  118  that includes a first section  120  formed of a dielectric material that extends in a generally horizontal direction. The chamber top  118  also includes a second section  122  formed of a dielectric material that extends a height from the first section  120  in a generally vertical direction. The chamber top  118  further includes a lid  124  formed of an electrically and thermally conductive material that extends across the second section  122  in a horizontal direction. 
     The plasma processing apparatus further includes a source  101  configured to generate a plasma  140  within the process chamber  102 . The source  101  may include a RF source  150  such as a power supply to supply RF power to either one or both of the planar antenna  126  and the helical antenna  146  to generate the plasma  140 . The RF source  150  may be coupled to the antennas  126 ,  146  by an impedance matching network  152  that matches the output impedance of the RF source  150  to the impedance of the RF antennas  126 ,  146  in order to maximize the power transferred from the RF source  150  to the RF antennas  126 ,  146 . 
     In some embodiments, the planar antenna  126  and helical antenna  146  comprise a conductive material wound in a spiraling pattern. For example,  FIG. 2A  shows one embodiment of a traditional planar antenna  126 , while  FIG. 2B  shows a second embodiment.  FIG. 3  shows a traditional helical antenna  146 . 
     Turning back to  FIG. 1 , the plasma processing apparatus may also include a bias power supply  190  electrically coupled to the platen  134 . The plasma processing system may further include a controller  156  and a user interface system  158 . The controller  156  can be or include a general-purpose computer or network of general-purpose computers that may be programmed to perform desired input/output functions. The controller  156  may also include communication devices, data storage devices, and software. The user interface system  158  may include devices such as touch screens, keyboards, user pointing devices, displays, printers, etc. to allow a user to input commands and/or data and/or to monitor the plasma processing apparatus via the controller  156 . A shield ring  194  may be disposed around the platen  134  to improve the uniformity of implanted ion distribution near the edge of the workpiece  138 . One or more Faraday sensors such as Faraday cup  199  may also be positioned in the shield ring  194  to sense ion beam current. 
     In operation, the gas source  104  supplies a primary dopant gas containing a desired dopant for implantation into the workpiece  138 . The source  101  is configured to generate the plasma  140  within the process chamber  102 . The source  101  may be controlled by the controller  156 . To generate the plasma  140 , the RF source  150  resonates RF currents in at least one of the RF antennas  126 ,  146  to produce an oscillating magnetic field. The oscillating magnetic field induces RF currents into the process chamber  102 . The RF currents in the process chamber  102  excite and ionize the primary dopant gas to generate the plasma  140 . 
     The bias power supply  190  provides a pulsed platen signal having a pulse ON and OFF periods to bias the platen  134  and hence the workpiece  138  to accelerate ions  109  from the plasma  140  towards the workpiece  138 . The ions  109  may be positively charged ions and hence the pulse ON periods of the pulsed platen signal may be negative voltage pulses with respect to the process chamber  102  to attract the positively charged ions. The frequency of the pulsed platen signal and/or the duty cycle of the pulses may be selected to provide a desired dose rate. The amplitude of the pulsed platen signal may be selected to provide a desired energy. 
       FIG. 4  shows a block diagram of a conventional ion implanter  300 . Of course, many different ion implanters may be used. The conventional ion implanter may comprise an ion source  302  that may be biased by a power supply  301 . The system may be controlled by controller  320 . The operator communicates with the controller  320  via user interface system  322 . The ion source  302  is typically contained in a vacuum chamber known as a source housing (not shown). The ion implanter system  300  may also comprise a series of beam-line components through which ions  10  pass. The series of beam-line components may include, for example, extraction electrodes  304 , a 90° magnet analyzer  306 , a first deceleration (D 1 ) stage  308 , a 70° magnet collimator  310 , and a second deceleration (D 2 ) stage  312 . Much like a series of optical lenses that manipulate a light beam, the beam-line components can manipulate and focus the ion beam  10  before steering it towards a workpiece or wafer  314 , which is disposed on a workpiece support  316 . 
     In operation, a workpiece handling robot (not shown) disposes the workpiece  314  on the workpiece support  316  that can be moved in one or more dimensions (e.g., translate, rotate, and tilt) by an apparatus, sometimes referred to as a “roplat” (not shown). Meanwhile, ions are generated in the ion source  302  and extracted by the extraction electrodes  304 . The extracted ions travel in a beam-like state along the beam-line components and implanted on the workpiece  314 . After implanting ions is completed, the workpiece handling robot may remove the workpiece  314  from the workpiece support  316  and from the ion implanter  300 . 
     The ion source  302  may be an inductively coupled plasma (ICP) ion source. In some embodiments, such as in  FIGS. 5A-B , the ion source  302  may comprise a rectangular enclosure, having an extraction slit  335  on one side  337 . In certain embodiments, the side  336  opposite the extraction slit  335  may be made of a dielectric material, such as alumina, such that a planar antenna  338  may be placed against the dielectric wall  336  to create a plasma within the enclosure  302 . The enclosure  302  also has a top surface  339 , a bottom surface  341 , and two endwalls  338 ,  340 . 
     In another embodiment, a helical antenna  350  is wrapped around the endwalls  338 ,  340  and the top surface  339  and bottom surface  341  of the ion source  302 . 
     One drawback of conventional plasma processing is the creation of metals within the chamber. These metals are generally generated by ions bombarding the walls of the dielectric window of the plasma-generating source at high energy. In inductively coupled RF plasmas, there is a capacitive component due to the high voltages on the RF coil. This capacitive component creates an electric field that is responsible for the metal generation in the RF source. Therefore, there is a need for an RF source which produces the magnetic field necessary for inductively generating a plasma without the associated electrical field or with a significantly decreased associated electrical field. 
     SUMMARY 
     A RF source and method are disclosed which inductively create a plasma within an enclosure without the associated electric field or with a significantly decreased creation of an electric field. A ferrite material is used to create a magnetic field. An insulated wire is wrapped around the body of the ferrite, which creates a magnetic field between the legs of the ferrite. This magnetic field can then be used to create a plasma. In one embodiment, these legs rest on a dielectric window, such that the magnetic field passes into the chamber. In another embodiment, the legs of the ferrite extend into the processing chamber, thereby further extending the magnetic field into the chamber. This RF source can be used in conjunction with a PLAD chamber, or an ion source for a traditional beam line ion implantation system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding of the present disclosure, reference is made to the accompanying drawings, in which like elements are referenced with like numerals, and in which: 
         FIG. 1  is a block diagram of a plasma processing apparatus of the prior art; 
         FIGS. 2A-B  illustrate planar antenna of the prior art; 
         FIG. 3  illustrates a helical antenna of the prior art; 
         FIG. 4  is a block diagram of a ion implantation apparatus; 
         FIG. 5A  is a front view of one embodiment of an ICP source; 
         FIG. 5B  is a rear view of the embodiment of  FIG. 5A ; 
         FIG. 6  is a cross-sectional view of an embodiment of the transformer coupled RF source resting on a dielectric window; 
         FIG. 7A  is a cross-sectional view of an embodiment of the transformer coupled RF source extending into the plasma processing chamber; 
         FIG. 7B  is a cross-sectional view of an embodiment of the transformer coupled RF source resting on a dielectric window with separate ferrite extensions on the opposite side of the window; 
         FIG. 8  is top view of a first embodiment of the transformer coupled RF source of  FIG. 6  or  FIG. 7 ; 
         FIG. 9  is a top view showing several RF sources of  FIG. 8  positioned on a dielectric window; 
         FIG. 10  is a cross-sectional view of a PLAD chamber showing the embodiment of  FIG. 9 ; 
         FIG. 11  is a top view of a second embodiment of the transformer coupled RF source of  FIG. 7 ; and 
         FIG. 12  shows a perspective view of an ion source for a beam line implanter using the embodiment of  FIG. 11 . 
     
    
    
     DETAILED DESCRIPTION 
     As described above, traditional ICP ion sources typically produce an electrical field, due to the capacitance introduced due to the high voltages in the antennas  126 ,  146 . 
     As shown in cross-section in  FIG. 6 , the RF source  490  uses a mechanism, where a coil  410  is would around ferrite  400 , which is u-shaped in this instance. The ferrite  400  has a main body  420 , around which the coil  410  is wound, and two legs  430  extending perpendicularly from the ends of the main body  420 . An alternating current is passed through the coil  410 , which may be an insulated wire in one instance. The current in the coil  410  creates a magnetic field in the ferrite  400 . This alternating current has a frequency, such as between 50 kHz and 50 MHz. The magnitude of the current may vary, based on the amount of power that is dedicated to creating this field. In addition, the strength of the magnetic field is also a function of the spacing between the legs  430 , and this parameter affects the amount of power required to create the desired magnetic field. 
     The ferrite can be constructed from various materials. In some embodiments, the choice of material is related to the frequency of the alternating current. For example, manganese zinc ferrites are preferably used for frequencies up to 500 kHz, while nickel zinc ferrites can be used for higher frequencies. 
     Most of the magnetic field created by the current passing through the coil  420  is captured by the ferrite  400 . The magnetic field lines  440  close near the distal ends of the legs  430  of the ferrite  400 , thereby creating a localized magnetic field with little to no electrical field. 
     The RF source can be positioned on a surface in several different ways. As shown in  FIG. 6 , the RF source  490  may be placed on a dielectric window  470  such that the distal ends of the legs  430  are in contact with the dielectric window  470 . Materials such as quartz and alumina may be used for this dielectric window  470 . In this embodiment, the magnetic field  440  may not extend significantly into the chamber, which is located on the opposite side of the dielectric window  470 . 
     In another embodiment, shown in  FIG. 7A , the distal ends of the legs  430  of the ferrite  400  extend beyond the wall  472 . Wall  472  does not need to be dielectric in this embodiment, since the magnetic field is generated on the opposite side of the wall  472 , within the plasma processing chamber. In fact, wall  472  may be any material, including a dielectric material or a metal, such as aluminum. In this embodiment, because of the location of the distal ends of the legs  430 , the magnetic field  440  extends further within the chamber formed by the wall  472 . The ferrite extensions  435  can be created in several ways. In one embodiment, the wall  472  is cut out, such that the distal ends of legs  430  of the ferrite  400  are placed in the cut out portions and extend through these cutouts. In this embodiment, the leg extensions  435  are preferably bonded to the wall  472 , preferably in an airtight manner. Various glues or seals, such as o-rings, may be used to create this bond. The introduction of the leg extensions  435  into the chamber may be a source of particulates. In some embodiments, the legs  430 , and specifically the leg extensions  435 , are coated with silicon to minimize the amount of contamination introduced to the chamber. 
     In another embodiment, shown in  FIG. 7B , the legs  430  of the ferrite  400  sit on the dielectric window  470 . Separate ferrite extensions  436  may be added inside the chamber formed by the dielectric window  470 , opposite each of the distal ends of the legs  430  to extend the magnetic channel inside the chamber. As described above, these separate ferrite extensions  436  may be coated with silicon to minimize contamination. 
     This RF source  490  can be formed in a variety of shapes and sizes. In some embodiments, the legs  430  are sufficiently long so that the electric field surrounding the coil  420  does not reach the window  470 . The width of the main body  410 , which determines the spacing between the legs  430  may be varied. In embodiments where the legs are spaced relatively close together, the magnetic field density is high, however it is also highly localized. In contrast, where the legs  430  are spaced apart, the magnetic density decreases, but the magnetic field is more distributed. Therefore, there is a tradeoff between power supplied to the coil  420 , the spacing between the legs  430 , and the uniformity and density of the magnetic field  440  created. 
     In one embodiment, the top view of which is shown in  FIG. 8 , the ferrite  400  is semi-circular. This shape may be used in conjunction with a plasma processing chamber  104 , such as the one shown in  FIG. 1 . In this embodiment, the ferrite may be semi-circular, with coils  450  that also follow a semi-circular path, approximately parallel to the legs. The legs (not shown) extend downward from inner edge  460  and outer edge  461 . This configuration creates a semi-circular annular magnetic field, where the field is located between the legs extending downward from edges  460 ,  461 . While a semi-circular ferrite  400  is shown, other shapes are possible, such as quarter circles, semi-oval and others. 
     As the RF source  490  of  FIG. 8  only creates a semi-circular annular magnetic field, in some embodiments, two such ferrites may be arranged to form a complete circle, as shown in  FIG. 9 . In this embodiment, two identical RF sources  490   a ,  490   b  are arranged in a circular pattern so as to create an annular magnetic field. In some embodiments, these RF sources  490   a ,  490   b  are placed atop a dielectric window  470 , such that the magnetic field permeates the dielectric window  470  and the chamber (as shown in  FIG. 6 ). In other embodiments, the legs of the RF sources  490   a ,  490   b  extend into the chamber, as shown in  FIG. 7A . In other embodiments, ferrite extensions are disposed on the dielectric window  470  in the chamber, opposite the distal ends of the legs. 
     In some embodiments, the discontinuities in the magnetic field between RF sources  490   a ,  490   b  may be undesirable, and may cause plasma non-uniformity. In such embodiments, third and fourth smaller RF sources  491   a ,  491   b  may be inserted within the circle created by RF sources  490   a ,  490   b , as shown in  FIG. 9 . These RF sources  491   a ,  491   b  are preferably concentric with RF sources  490   a ,  490   b  and are arranged so that the openings between them are rotated a quarter turn from the openings between RF sources  490   a ,  490   b . As described above, these RF sources  490 ,  491  may sit atop a dielectric window  470 , as shown in  FIG. 6 , or may extend into the plasma processing chamber, as shown in  FIG. 7 . Of course, other variations, dimensions, or rotations than that illustrated in  FIG. 9  are possible. 
       FIG. 10  shows the RF sources  490  of  FIG. 9  used in conjunction with a plasma processing chamber  500 . As described in conjunction with  FIG. 1 , the plasma processing chamber  500  has a gas inlet  510 , a baffle  170 , a platen  134 , and an exhaust port  110 . In one embodiment, the RF sources  400  may be disposed on dielectric windows  520 . The dielectric windows  520  may extend along a vertical direction at an oblique angle relative to the chamber walls  521 , as shown in  FIG. 10 . In other embodiments, the dielectric windows  520  may be perpendicular to the chamber walls  521 . 
     In another embodiment, the legs  430  of the ferrites may extend through the windows  520  into the chamber  500 . In this embodiment, the windows  520  need not be constructed of dielectric material. Although the windows  520  are shown as slanted, other embodiments are possible. For example, in another embodiment, the RF sources  490  may replace the antennas  126 ,  146  shown in  FIG. 1 . 
       FIG. 11  shows a top view of a second embodiment of the RF source  690 . In this embodiment, the main body  620  of the ferrite  600  is straight, rather than semi-circular. Coils  610  are wound around the main body  620 . The main body  620  has two edges  601 ,  602 , which are approximately parallel to the path of the coils  610 . The legs (not shown) extend downward from these edges  601 ,  602 . 
       FIG. 12  shows a perspective view of an ion source, such as that shown in  FIGS. 5A-B , being used in conjunction with RF source  690 . In this embodiment, the RF source  690  is placed on a dielectric window  650  on the side of the rectangular enclosure  302  directly opposite extraction slit  335 . The ferrite  600  may be roughly the same length as the rectangular enclosure  302 . Since the magnetic field created between legs  430  is uniform along the length of the main body  620 , the resulting plasma density within the rectangular enclosure  302  should likewise be uniform across the length of the enclosure  302 . In another embodiment, the ferrite  600  may be positioned such that the legs  430  extend into the rectangular enclosure  302 , as shown in  FIG. 7A . In this embodiment, the top surface  650  does not need to be a dielectric material. In another embodiment, ferrite extensions are used to extend the ferrite legs into the chamber, as shown in  FIG. 7B . In this embodiment, the top surface is a dielectric material. 
     The present disclosure is not to be limited in scope by the specific embodiments described herein. Indeed, other various embodiments of and modifications to the present disclosure, in addition to those described herein, will be apparent to those of ordinary skill in the art from the foregoing description and accompanying drawings. Thus, such other embodiments and modifications are intended to fall within the scope of the present disclosure. Further, although the present disclosure has been described herein in the context of a particular implementation in a particular environment for a particular purpose, those of ordinary skill in the art will recognize that its usefulness is not limited thereto and that the present disclosure may be beneficially implemented in any number of environments for any number of purposes. Accordingly, the claims set forth below should be construed in view of the full breadth and spirit of the present disclosure as described herein.