Patent Publication Number: US-9837249-B2

Title: Radial waveguide systems and methods for post-match control of microwaves

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent application is a continuation of U.S. patent application Ser. No. 15/063,849, filed on Mar. 8, 2016, which is a continuation of, and claims the benefit of priority to, pending U.S. patent application Ser. No. 14/221,132, filed on Mar. 20, 2014. Both of the above-identified patent applications are hereby incorporated by reference for all purposes. 
    
    
     TECHNICAL FIELD 
     The present disclosure is in the field of microwaves. More specifically, embodiments that utilize radial waveguides and associated control systems to provide control of microwaves in a plasma process chamber are disclosed. 
     BACKGROUND 
     Semiconductor processing often generates plasmas to create ionized and/or energetically excited species for interaction with semiconductor wafers themselves, or other processing related materials (e.g., photoresist). To create and/or maintain a plasma, one or more radio frequency (RF) and/or microwave generators are typically utilized to generate oscillating electric and/or magnetic fields. The same fields, and/or DC fields, may also be utilized to direct the ionized and/or energetically excited species to the semiconductor wafer(s) being processed. Various known methods are often utilized to match an impedance of a power source (the RF generator) to a load (the plasma) so that power from the RF generator is delivered to the plasma without significant reflection of power back to the RF generator. This is for reasons of energy efficiency as well as to protect electrical components of the RF generator from damage. Particularly when microwave energy is utilized, reflected power is usually directed to a dummy load where it is dissipated as heat, which must then be removed. Thus, reflected power results in a two-fold waste of energy: the energy utilized to generate the power, and the energy utilized to remove the waste heat. 
     SUMMARY 
     In an embodiment, a system provides post-match control of microwaves in a radial waveguide. The system includes the radial waveguide and a signal generator that provides a first microwave signal and a second microwave signal. The first and second microwave signals have a common frequency. The signal generator adjusts a phase offset between the first and second microwave signals in response to a digital correction signal. The system also includes a first electronics set and a second electronics set. Each of the first and second electronics sets amplifies a respective one of the first and second microwave signals to provide a respective first or second amplified microwave signal, transmits the respective first or second amplified microwave signal into the radial waveguide, and matches an impedance of the respective first or second amplified microwave signal to an impedance presented by the radial waveguide. The system also includes at least two monitoring antennas disposed at least 30 degrees about a circumference of the radial waveguide from locations at which the first and second electronics sets transmit the respective first and second amplified microwave signals into the radial waveguide. A signal controller receives analog signals from the at least two monitoring antennas, determines the digital correction signal based at least on the analog signals from the at least two monitoring antennas, and transmits the digital correction signal to the signal generator. 
     In an embodiment, a system for plasma processing of a workpiece includes a process chamber configured to create a plasma for the plasma processing, and a radial waveguide, adjacent to the process chamber, configured to generate microwaves for transmission to the process chamber to supply energy for the plasma. The system also includes a signal generator that provides a first microwave signal and a second microwave signal, the first and second microwave signals having a common frequency. The signal generator adjusts a phase offset between the first and second microwave signals in response to a digital correction signal. The system also includes a first electronics set and a second electronics set. Each of the first and second electronics sets amplifies a respective one of the first and second microwave signals to provide an amplified microwave signal, transmits the amplified microwave signal into the radial waveguide, and matches an impedance of the amplified microwave signal to an impedance presented by the radial waveguide. The system also includes at least two monitoring antennas disposed at least 30 degrees about a circumference of the radial waveguide from locations at which the first and second electronics sets transmit the respective first and second amplified microwave signals into the radial waveguide. A signal controller receives analog signals from the at least two monitoring antennas, determines the digital correction signal based at least on the analog signals from the at least two monitoring antennas, and transmits the digital correction signal to the signal generator. The first electronics set includes a tuner that matches the impedance of the first amplified microwave signal to the impedance presented by the radial waveguide, a dummy load, and a circulator that shunts power reflected back from the radial waveguide toward the first electronics set, into the dummy load. The signal generator adjusts the phase offset, and the tuner matches the impedance, concurrently with one another. 
     In an embodiment, a method for controlling a plasma within a process chamber includes generating, with a signal generator, a first microwave signal and a second microwave signal, the first and second microwave signals having a common frequency and a phase offset therebetween that is determined at least in part by the signal generator responding to a digital correction signal. The method also includes amplifying the first and second microwave signals to provide respective first and second amplified microwave signals, and transmitting the first and second amplified microwave signals into a radial waveguide proximate the process chamber such that microwaves propagate from the radial waveguide into the process chamber to provide energy for the plasma. The method also includes generating analog signals with at least two monitoring antennas disposed at least 30 degrees about a circumference of the radial waveguide from locations at which the first and second electronics sets transmit the respective first and second amplified microwave signals into the radial waveguide, determining the digital correction signal based at least on the analog signals from the at least two monitoring antennas, and transmitting the digital correction signal to the signal generator. 
     Additional embodiments and features are set forth in part in the description that follows, and in part will become apparent to those skilled in the art upon examination of the specification or may be learned by the practice of the invention. The features and advantages of the invention may be realized and attained by means of the instrumentalities, combinations, and methods described in the specification. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure may be understood by reference to the following detailed description taken in conjunction with the drawings briefly described below, wherein like reference numerals are used throughout the several drawings to refer to similar components. It is noted that, for purposes of illustrative clarity, certain elements in the drawings may not be drawn to scale. Specific instances of an item may be referred to by use of a numeral in parentheses (e.g., monitoring antennas  311 ( 1 ),  311 ( 2 )) while numerals without parentheses refer to any such item (e.g., monitoring antennas  311 ). In instances where multiple instances of an item are shown, only some of the instances may be labeled, for clarity of illustration. 
         FIG. 1  schematically illustrates major elements of a single wafer, semiconductor wafer processing system, according to an embodiment. 
         FIGS. 2A and 2B  are schematic cross-sections illustrating selected structure of a radial waveguide and a process chamber of the single wafer, semiconductor wafer processing system of  FIG. 1 . 
         FIG. 3  is a schematic diagram of major components of a system for providing microwaves to a plasma chamber utilizing a radial waveguide, in an embodiment. 
         FIG. 4  is a schematic diagram of major components of a system that provides post-match control of microwaves in a radial waveguide, in an embodiment. 
         FIG. 5  is a schematic diagram of major components of a system that provides post-match control of microwaves in a radial waveguide, in an embodiment. 
         FIG. 6  is a schematic diagram of major components of a system that provides post-match control of microwaves in a radial waveguide, in an embodiment. 
         FIG. 7  is a schematic diagram of a region within the system that provides post-match control of microwaves in a radial waveguide of  FIG. 6 . 
         FIG. 8  schematically illustrates a radial waveguide that is powered by four electronics sets and is monitored by four monitoring antennas, in an embodiment. 
         FIG. 9  is a schematic diagram illustrating implementations of the signal controller and dual phase signal generator shown in  FIG. 4 , in an embodiment. 
         FIG. 10  illustrates exemplary operation of a first portion of an in-phase and quadrature-phase (IQ) demodulator shown in  FIG. 9 . 
         FIG. 11  is a schematic diagram of major components of a system that provides post-match control of microwaves in a radial waveguide, in an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  schematically illustrates major elements of a plasma processing system  100 , according to an embodiment. System  100  is depicted as a single wafer, semiconductor wafer processing system, but it will be apparent to one skilled in the art that the techniques and principles herein are applicable to a plasma processing system for any type of workpiece (e.g., items that are not necessarily wafers or semiconductors). Processing system  100  includes a housing  110  for a wafer interface  115 , a user interface  120 , a process chamber  130 , a controller  140  and one or more power supplies  150 . Process chamber  130  includes one or more wafer pedestals  135 , upon which wafer interface  115  can place a workpiece  50  (e.g., a wafer, but could be a different type of workpiece) for processing. A radio frequency generator (RF Gen)  165  supplies power to create a plasma within process chamber  130 . Specifically, RF Gen  165  powers a radial waveguide  167  that may be disposed above or below process chamber  130 , and is shown in  FIG. 2  as above chamber  130 . Process chamber  130  is proximate radial waveguide  167 , and is bounded adjacent to radial waveguide  167  by a plate  169  that is formed of a material that is permeable to electromagnetic fields but not to air or process gases utilized in chamber  130 . Thus, plate  169  can support a pressure difference between radial waveguide  167  and chamber  130 , while allowing microwaves within radial waveguide  167  to propagate into chamber  130 . Plate  169  may be formed, for example, of ceramic. The elements shown as part of system  100  are listed by way of example and are not exhaustive. Many other possible elements, such as: pressure and/or flow controllers; electrodes, magnetic cores and/or other electromagnetic apparatus; mechanical, pressure, temperature, chemical, optical and/or electronic sensors; viewing and/or other access ports; and the like may also be included, but are not shown for clarity of illustration. Internal connections and cooperation of the elements shown within system  100  are also not shown for clarity of illustration. In addition to RF generator  165 , other representative utilities such as gases  155 , vacuum pumps  160 , and/or general purpose electrical power  170  may connect with system  100 . Like the elements shown in system  100 , the utilities shown as connected with system  100  are intended as illustrative rather than exhaustive; other types of utilities such as heating or cooling fluids, pressurized air, network capabilities, waste disposal systems and the like may also be connected with system  100 , but are not shown for clarity of illustration. 
       FIGS. 2A and 2B  are schematic cross-sections illustrating selected structure of radial waveguide  167  and process chamber  130 ,  FIG. 1 .  FIG. 2A  is a vertical cross-section of radial waveguide  167 , process chamber  130  and a workpiece  50  therein. A broken line  2 B- 2 B′ indicates a further cross-sectional view illustrated in  FIG. 2B . Radial waveguide  167  is a substantially cylindrical and closed shape, except for slots  168  formed in an undersurface thereof that allow microwaves to propagate into process chamber  130 , ports for providing and/or measuring microwaves, and other minor penetrations (such ports and penetrations are not shown in  FIGS. 2A / 2 B). Slots  168  may for example form a radial line slot antenna. Process chamber  130  is substantially radially symmetric along a common axis with radial waveguide  129 . Microwaves propagate from radial waveguide  167  into process chamber  130  through slots  168  and through plate  169  to provide energy for igniting and/or maintaining plasma  60 . Pedestal  135  is configured to present a workpiece  50  to plasma  60  for processing. Process chamber  130  may include ports and/or mechanical openings (not shown) for insertion and/or withdrawal of workpiece  50 , introduction of gases to form plasma  60 , removal of plasma and gaseous reaction products, sensors, viewing and the like. 
       FIG. 3  is a schematic diagram of major components of a system  200  for providing microwaves to a plasma chamber utilizing a radial waveguide, in an embodiment. A radial waveguide  210  of system  200  may be utilized for example as radial waveguide  167 ,  FIG. 1 . In general, system  200  powers radial waveguide  210  at two locations noted as P and Q in  FIG. 3 , with locations P and Q being driven roughly π/2 out of phase with one another by electronics sets  225 ( 1 ),  225 ( 2 ) described below. Radial waveguide  210  is thus considered a “dual driven” radial waveguide; the dual driven mode of operation provides high microwave energy density derived from two sets of driving electronics rather than a single set operating at double the power. Use of two (or more) sets of driving electronics, each operating at lower power than a single set at high power, may be advantageous. An electronics set operating at higher power may require components having higher voltage, current, or heat dissipation ratings that may be much more expensive or difficult to obtain than components for lower power sets. For example, microwave field effect transistors (FETs) of low cost and high quality have recently become available for use in electronics sets  225  herein, but high voltage, current, and/or power dissipation versions of such FETs may remain costly or difficult to obtain. 
     Operation of system  200  is best understood as starting with a dual phase signal generator  215  that provides two microwave signals  220 ( 1 ),  220 ( 2 ) that are at the same frequency, but are π/2 out of phase with one another. Microwave signals  220 ( 1 ),  220 ( 2 ) drive circuits that are referred to as a first set  225 ( 1 ) and a second set  225 ( 2 ). Each set  225 ( 1 ),  225 ( 2 ) begins with a solid state amplifier  230  that boosts the power of respective microwave signals  220 ( 1 ),  220 ( 2 ) to create amplified microwave signals  235 ( 1 ),  235 ( 2 ). Solid state amplifiers  230  may include one or more microwave FETs, as discussed above. Each amplified microwave signal  235 ( 1 ),  235 ( 2 ) passes into and through a circulator  240  that serves to protect the respective solid state amplifiers  230  from power reflections from radial waveguide  210 . Circulators  240  thus pass input power from solid state amplifiers  230  into respective tuners  250 , while shunting any power that is reflected back into dummy loads  245 . 
     Tuners  250  adjust impedance seen by the amplified microwave signals  235 ( 1 ),  235 ( 2 ) so as to match an impedance presented by components such as converters  255 , radial waveguide  260  and an adjacent process chamber (e.g., process chamber  130 ,  FIG. 1 , not shown in  FIG. 3 ). Tuners  250  may be, for example, three-pole stub tuners. The amplified, tuned signals then pass through respective coaxial-to-waveguide converters  265  and into radial waveguide  210  at respective waveguides with radiating apertures  270 . 
     As part of the tuning required to achieve acceptable impedance matching, tuners  250  can change the phase of signals passed toward radial waveguide  210 , such that although the signals are supplied at positions that are exactly π/2 out of phase around the circumference of radial waveguide  210 , the signals themselves may no longer be exactly π/2 out of phase. That is, instead of exciting a symmetric, circular polarization mode in radial waveguide  210 , an asymmetric, ellipsoidally polarized mode may be excited. This asymmetry in the microwave configuration can lead, in turn, to process aberrations in an adjacent process chamber. For example, an asymmetric microwave configuration can lead to a correspondingly asymmetric plasma and consequently to local skews in depth of plasma etching. 
     Embodiments herein recognize that as wafer sizes grow larger and the geometries produced in semiconductor fabrication grow smaller, the need for uniformity control of all aspects of the processing environment around the wafer increases. Therefore, embodiments herein adjust the microwave configuration that generates the plasma, not only to match impedance, but also to adjust phase and/or amplitude after impedance is matched, for improved symmetry of the plasma generated around the wafer. Even when careful attention is paid to symmetry of a process chamber, placement of a wafer in the process chamber, and the like, asymmetries in a plasma can arise from many causes (e.g., mechanically asymmetric ports, sensors, wafer placement, wafer flats, cabling length and the like) such that control of phase and/or amplitude, in addition to impedance matching, may provide an extra and useful degree of freedom for improving uniformity in plasma processing. 
       FIG. 4  is a schematic diagram of major components of a system  300  that provides post-match control of microwaves in a radial waveguide, in an embodiment. System  300  may be utilized to excite a plasma in an adjacent plasma chamber. In general, system  300  has many of the same components as, and works similarly to, system  200  ( FIG. 3 ). However, system  300  independently adjusts amplitude of, and/or a phase offset between, microwave signals  320 ( 1 ) and  320 ( 2 ) to control phase at points P and Q, for example to be utilized as a degree of freedom for optimizing process uniformity. 
     In system  300 , a radial waveguide  210  may be utilized for example as radial waveguide  167 ,  FIG. 1 . System  300  powers radial waveguide at two locations noted as P and Q in  FIG. 1 , with locations P and Q being driven roughly π/2 out of phase with one another. Like system  200 , operation of system  300  can be understood starting with a dual phase signal generator  315  that provides microwave signals  320 ( 1 ),  320 ( 2 ) that are at the same frequency. However, dual phase signal generator  315  receives a correction signal  313  from a signal controller  312  that provides information for adjustment of signals  320 ( 1 ),  320 ( 2 ). For example, correction signal  313  may direct dual phase signal generator  315  to provide a corrected or targeted phase offset between microwave signals  320 ( 1 ),  320 ( 2 ). Thus, in system  300 , microwave signals  320 ( 1 ),  320 ( 2 ) may be out of phase with one another by π/2, or by π/2 plus or minus the target phase difference, such that a measured phase difference at points P and Q is as intended, as discussed below. In another example, correction signal  313  may direct dual phase signal generator  315  to boost and/or attenuate one or both of microwave signals  320 ( 1 ),  320 ( 2 ). 
     At this point, it should be noted that signal generator  315  is termed a “dual phase signal generator” herein, but considering that other embodiments may be driven at more than two points by a signal generator that generates more than two signals of identical frequency and differing phase (see, e.g.,  FIG. 8 ) it is understood that the “dual phase” aspect is for convenient reference. Furthermore, in embodiments, signal generator  315  may control amplitude of signals  320 , as well as phase thereof. Thus, dual phase signal generator  315  is simply a specific case of a “signal generator” as discussed elsewhere herein. 
     Like system  200 , microwave signals  320 ( 1 ),  320 ( 2 ) drive respective solid state amplifiers  230  that boost power to create amplified microwave signals  335 ( 1 ),  335 ( 2 ), which in turn pass into and through circulators  240 . Circulators  240  pass amplified microwave signals  335 ( 1 ),  335 ( 2 ) into respective tuners  250  while shunting any power reflected back into dummy loads  245 . Tuners  250  adjust impedance seen by the amplified microwave signals  335 ( 1 ),  335 ( 2 ) so as to match an impedance presented by components such as converters  255 , radial waveguide  260  and an adjacent process chamber (e.g., process chamber  130 ,  FIG. 1 , not shown in  FIG. 4 ). The amplified, tuned signals then pass through respective coaxial-to-waveguide converters  265  and into radial waveguide  210  at respective waveguides with radiating apertures  270 . 
     Monitoring antennas  311 ( 1 ) and  311 ( 2 ), disposed proximate to points P and Q respectively, provide analog signals to signal controller  312  through their respective connections  318 ( 1 ) and  318 ( 2 ), capturing any phase offset introduced by tuners  250 . Monitoring antennas  311  may monitor either an electrical field or a magnetic field component of microwaves in radial waveguide  210 . When electrical fields are monitored, it is appreciated that metal of radial waveguide  210  may reduce electrical fields in close proximity thereto, such that care should be taken to locate monitoring antennas  311  far enough from radial waveguide  210  to provide sufficient sensitivity. Signal controller  312  receives signals from monitoring antennas  311 ( 1 ) and  311 ( 2 ) through their respective connections  318 ( 1 ) and  318 ( 2 ) and determines amplitude of, and a phase offset between, signals at points P and Q. For example, signal controller  312  may perform in-phase and quadrature-phase demodulation (IQ demodulation) to measure amplitude and phase offset of the signals from monitoring antennas  311 ( 1 ) and  311 ( 2 ) (see also  FIG. 9 ). Signal controller  312  then utilizes the measured phase offset and/or amplitudes to calculate and provide a corresponding digital correction signal  313  to dual phase signal generator  315 . Digital correction signal  313  may be chosen to be a desired phase offset (e.g., a value of π/2) or an offset from an assumed, desired phase difference (e.g., a correction factor that is zero when the desired phase difference is attained). Alternatively, digital correction signal may be chosen to adjust amplitude of one or both of microwave signals  320 ( 1 ),  320 ( 2 ). Dual phase signal generator  315  then provides microwave signals  320 ( 1 ) and  320 ( 2 ) with a phase offset and/or amplitudes such that when the microwave signals propagate through the system, the phase offset between points P and Q is driven to the desired phase difference, and/or the amplitudes measured at points P and Q are as desired. 
     Optionally, a target input device  314  may provide one or more target parameters  316  to signal controller  312 . Target input device  314  may be implemented in a variety of ways, such as by physical switches providing an output that is received directly by signal controller  312 , or as a part of system management hardware and software that acquires the target parameters from a user interface (e.g., a keyboard, other buttons, or a graphical user interface (GUI)). Target parameters  316  may include, for example, a desired phase difference as measured at monitoring antennas  311 ( 1 ) and  311 ( 2 ), or amplitude adjustments to either or both of microwaves driven into radial waveguide  210 . Target parameters  316  can be utilized by signal controller  312  along with the analog signals from monitoring antennas  311 ( 1 ) and  311 ( 2 ), to generate digital correction signal  313 . For example, when a target phase difference is utilized, digital correction signal  313  may be generated first based on the signals from monitoring antennas  311 ( 1 ) and  312 ( 1 ), after which digital correction signal  313  may be adjusted by adding or subtracting target parameter  316 . Once digital correction signal  313  is transmitted, dual phase signal generator  315  provides signals  320 ( 1 ) and  320 ( 2 ) with a corresponding offset until the phase offset between points P and Q is driven according to the target parameter, and digital correction signal  313  is driven to its target value, or zero. In another example, when a target amplitude adjustment is utilized, dual phase signal generator  315  can adjust amplitude of either or both of signals  320 ( 1 ),  320 ( 2 ) in response thereto. 
     Optional target input device  314  provides a useful, independent degree of freedom for optimizing a semiconductor processing system that includes system  300  or other systems with a similar capability, as disclosed herein. For example, the corresponding semiconductor processing system may be optimized by processing (e.g., etching) wafers, which may have test patterns printed thereon. Each wafer could be processed with identical processing parameters except for a different target parameter entered into target input device  314 . The performance of the system could be evaluated by measurements of the wafers that are indicative of performance of the etch system (e.g., etch rate, selectivity, linewidth change due to etch, and the like) as well as system monitors (e.g., system stabilization times, endpoint detection parameters, etc.) An optimized value of the target parameter could then be selected, based on the wafer measurements, the system monitors and/or a combination thereof. 
     It will be understood by one skilled in the art that while signal controller  312  cooperates with dual phase signal generator  315  to adjust phase of microwave signals  320 ( 1 ) and  320 ( 2 ), tuners  250  also continue to adjust impedance matching to minimize reflected power. Thus, system  300  does not sacrifice impedance matching, but rather provides the additional capability of phase and/or amplitude adjustment for the dual driven radial waveguide, to optimize plasma symmetry in an adjacent process chamber. That is, in embodiments, signal generator  315  adjusts the phase offset, and tuners  250  provide the impedance matching, concurrently with one another during the operation of system  300 . In other embodiments, signal generator  315  adjusts the amplitude, and tuners  250  provide the impedance matching, concurrently with one another during the operation of system  300 . 
       FIG. 5  is a schematic diagram of major components of a system  400  that provides post-match control of microwaves in a radial waveguide, in an embodiment. System  400  may be utilized to excite a plasma in an adjacent plasma chamber. In general, system  400  has many of the same components as, and works similarly to, systems  200  ( FIG. 3 ) and  300  ( FIG. 4 ). However, system  400  places monitoring antennas  411 ( 1 ) and  411 ( 2 ) at locations that are 180 degrees across radial waveguide  210  from points P and Q. The locations of monitoring antennas  411 ( 1 ) and  411 ( 2 ) may enable the signals returned to signal controller  312  to include effects of radial waveguide  210  that are not readily monitored by monitoring antennas located at points P and Q (e.g., like monitoring antennas  311 ,  FIG. 4 ). That is, in system  300 , monitoring antennas  311 ( 1 ) and  311 ( 2 ) will receive very strong signals directly from waveguides with radiating apertures  270  such that effects introduced by other features (e.g., minor asymmetries) of radial waveguide  210 , and/or feedback effects from an adjacent plasma chamber, may not have much effect on the received signals. Placing monitoring antennas  411 ( 1 ) and  411 ( 2 ) at points within radial waveguide  210  that are distant from points P and Q (for example, points that are at least 30 degrees offset from points P and/or Q) increases the usefulness of the phase match capabilities of system  400  by including such effects. Those skilled in the art will appreciate that placing monitoring antennas  411 ( 1 ) and  411 ( 2 ) 180 degrees across radial waveguide  210  from points P and Q respectively may simplify calculation of digital correction signal  313  (e.g., signals expected when monitoring antennas  411 ( 1 ) and  411 ( 2 ) are 180 degrees across radial waveguide  210  from points P and Q leads to the expectation that phase of signals detected thereby will be π out of phase with the respective signals at points P and Q). 
       FIG. 6  is a schematic diagram of major components of a system  500  that provides post-match control of microwaves in a radial waveguide, in an embodiment. System  500  may be utilized to excite a plasma in an adjacent plasma chamber. In general, system  500  has many of the same components as, and works similarly to, systems  200 ,  300  and  400  ( FIGS. 3-5 ). However, system  500  includes monitoring antennas  511 ( 1 ) and  511 ( 2 ) that measure independent components of magnetic fields, H z  and H θ  respectively. Monitoring antennas  511 ( 1 ) and  511 ( 2 ) are shown at a region A that is across radial waveguide  210  from point P, as shown in  FIG. 6 , but because antennas  511 ( 1 ) and  511 ( 2 ) provide signals that relate to magnetic field components H z  and H θ  that are independent of one another, they may be located at other locations and still provide phase offset information that is useful for providing post-match control. 
       FIG. 7  is a schematic diagram of region A,  FIG. 6 . A radial direction r, azimuthal direction θ and axial direction z of a cylindrical coordinate system useful for describing the positions of antennas  511  and the directions of magnetic fields detected thereby, are shown. Monitoring antenna  511 ( 1 ) includes a loop that is horizontally oriented and is thus responsive to magnetic field H z . Monitoring antenna  511 ( 2 ) includes a loop that is vertically oriented and is thus responsive to magnetic field H θ . Each of monitoring antennas  511 ( 1 ),  511 ( 2 ) connects with a respective coaxial cable  518 ( 1 ) or  518 ( 2 ), as shown. Cables  518 ( 1 ) and  518 ( 2 ) transmit signals from antennas  511 ( 1 ) and  511 ( 2 ) to signal controller  312 , as shown in  FIG. 6 . Monitoring antennas  511 ( 1 ) and  511 ( 2 ) may be disposed relatively close to one another in order to simplify calculations of phase offsets therebetween. For example, as shown in  FIG. 7 , monitoring antennas  511 ( 1 ) and  511 ( 2 ) may be disposed atop one another in the z direction, and/or within about 3 degrees of one another in the azimuthal direction θ. 
     Embodiments that provide post-match control of microwaves in a radial waveguide are not limited to the cases of two microwave generating electronics sets and two antennas that are illustrated in  FIGS. 4-6 . For example,  FIG. 8  schematically illustrates a radial waveguide  510  that is powered by four electronics sets,  525 ( 1 ) through  525 ( 4 ) and is monitored by four monitoring antennas,  555 ( 1 ) through  555 ( 4 ). As shown in  FIG. 8 , electronics sets  525  are disposed at 90 degree intervals about a periphery of radial waveguide  510 , with monitoring antennas  555  disposed at midpoints therebetween. While two monitoring antennas  555  disposed orthogonally to one another are theoretically sufficient to evaluate whether a microwave distribution within radial waveguide  510  is symmetrical, four antennas  555  and corresponding correction factors for four electronics sets  525  may be utilized to provide further degrees of freedom in process control. Electronics sets  525  are driven by a signal generator that provides four microwave signals of the same frequency but different phases (e.g., analogous to operation of dual phase signal generator  315 ) that receives correction factors from a quad signal controller (e.g., analogous to signal controller  312 ). An optional target input device (analogous to target input device  314 ) may provide target parameters applicable to any of the signals driven by the signal generator and/or the signals detected by any of the monitoring antennas  555 . The locations of electronics sets  525  and monitoring antennas  555  shown in  FIG. 8  may simplify calculation of expected phase of microwaves monitored at the monitoring antennas, and corresponding digital correction factors to be applied to the microwave signals that are input to the electronics sets, but other arrangements will be apparent to those skilled in the art. Also, similar embodiments may utilize more or fewer electronics sets  525  and/or monitoring antennas  555 , with appropriate adjustments to input of target parameters and/or calculation of signals driven by a corresponding signal generator. A semiconductor processing system that includes radial waveguide  510 , electronics sets  525  and monitoring antennas  555  may be optimized in a manner analogous to the procedure described above in connection with  FIG. 4 , except that multiple target parameters may be implemented and evaluated, alone and/or in combination with one another. 
       FIG. 9  is a schematic diagram illustrating implementations of signal controller  312  and dual phase signal generator  315 , in an embodiment. The embodiment illustrated in  FIG. 9  could support any of the systems shown in  FIGS. 4, 5 and 6  directly, and the principles now explained can be duplicated modified in ways that will be readily apparent to support the system illustrated in  FIG. 8 . 
     In the embodiment illustrated in  FIG. 9 , signal controller  312  includes a control clock (CLK)  602  that generates a 40 MHz waveform and a high frequency clock (HCLK)  604  that generates a 2.449 GHz waveform. Clock  602  serves to provide a gating time signal for successive demodulations. Clock  604  provides a reference frequency for dual phase signal generator  315  (e.g., a frequency at which radial waveguide  167 ,  FIGS. 2A and 2B , radial waveguide  210 ,  FIGS. 3-7  or radial waveguide  510 ,  FIG. 8 , is driven to support a plasma powered thereby) and can therefore provide the same reference frequency for IQ demodulation purposes. Given these understandings of how clocks  602  and  604  are utilized, the exact frequencies of clocks  602  and  604  are not critical and may be different in other embodiments. In particular, a higher speed of clock  602  will force more frequent repetition of the calculations discussed below, leading to faster plasma adjustment and settling times for an entire system, but will increase system power requirements and may lead to a need for higher performance versions of components  606  and  608  discussed below. A lower speed of clock  602  may increase plasma adjustment and settling time achievable by the system but may reduce system power requirements and may allow use of lower performance versions of components  606  and  608 . 
     Signal controller  312  also includes an IQ demodulator  606  and a microcontroller  608  executing software  609 . At intervals established by clock  602 , an IQ demodulator  606  performs IQ demodulation of each of the signals provided through connections  318 ( 1 ) and  318 ( 2 ), and generates therefrom a digital in-phase signal Xni and a digital quadrature phase signal Xnq, where n is 1 or 2 corresponding to connections  318 ( 1 ) and  318 ( 2 ) respectively. Digital in-phase and quadrature-phase signals Xni and Xnq characterize the corresponding received signal in that Xni is the real part of signal n, and Xnq is the imaginary part of signal n. A phase φn of signal n is given by φn=tan (Xni/Xnq) and an amplitude An of signal n is given by An=√{square root over (Xni 2 +Xnq 2 )}. The IQ demodulation of each of the signals proceeds in parallel such that for each interval, IQ demodulator  606  provides corresponding digital signals X 1   i , X 1   q , X 2   i , X 2   q , as shown. 
       FIG. 10  illustrates exemplary operation of a first portion  606 ( a ) of IQ demodulator  606  that processes a signal received from connection  318 ( 1 ) to yield X 1   i  and X 1   q ; it is understood that IQ demodulator  606  also has a second portion that performs similar processing with respect to a signal received from connection  318 ( 2 ) to yield X 2   i  and X 2   q . An optional bandpass filter  620  may be utilized to clean up the signal from connection  318 , especially to eliminate harmonics of the main received frequency, which in this example is around 2.450 GHz. An exemplary passband of filter  620  might be, for example, 2.45 GHz±0.05 GHz; in embodiments, the width of the passband could be considerably higher, up to perhaps 20% of the received frequency and not necessarily centered about the received frequency. Demodulation proceeds by mixing the signal from connection  318 ( 1 ) with the signal from clock  604  to generate an intermediate frequency (IF) signal. It should be understood from the discussion above and further below that the clock  604  frequency will be related to the frequency produced by signal generator  315  and propagated into radial waveguide  210  to produce a usable IF signal. In the present example clock  604  operates at 2.449 GHz while dual phase signal generator  315  produces a 2.450 GHz signal, thus yielding a 1 MHz IF signal. FIG.  10  labels parts of portion  606 ( a ) of demodulator  606  as “HF” (high frequency), “IF” and “DIGITAL” for easy understanding of the signals being processed in each part. 
     In certain embodiments, in the IF part of portion  606 ( a ) a bandpass or lowpass filter  624  cleans up the signal from mixer  622 . An exemplary passband of filter  620  might be, for example, 0 Hz (if lowpass) or 0.5 MHz (if bandpass) to around 2 MHz. An analog to digital converter  626  converts the IF signal to a digital sample on intervals determined from clock  602 ; further processing takes place in the digital part of portion  606 ( a ). 
     Copies  628 ( a ).  628 ( b ) of the digital sample are mixed with values corresponding to cos(ωn) and −sin(ωn), where ω is defined as 2πf IF /f s , where f s  is a sampling frequency of clock  602  (40 MHz in this example), f IF  is the microwave signal frequency projected to the IF band (1 MHz in this example). The cos(ωn) and −sin(ωn) values are generated from a read-only-memory (ROM)  630  at the clock  602  sampling frequency, and are multiplied with copies  628 ( a ),  628 ( b ) at digital mixers  632 ( a ),  632 ( b ) to form the resulting digital outputs X 1   i  and X 1   q.    
     In certain embodiments, digital low pass filters  634 ( a ) and  634 ( b ) can be utilized to eliminate high frequency digital noise from X 1   i  and X 1   q . Typical cutoff values of digital low pass filters  634 ( a ) and  634 ( b ) are for example 1 kHz. 
     Returning to  FIG. 9 , from IQ demodulator  606 , digital outputs X 1   i , X 1   q , X 2   i  and X 2   q  pass to microcontroller  608 , that generates correction signal  313  therefrom. Microcontroller  608  executes software  609  (which may be stored in nontransitory, computer-readable media that forms part of microcontroller  608 , or may be external to microcontroller  608 ) to generate correction signal  313 . Software  609  is implemented to generate correction signal  313  in cooperation with operation of dual phase signal generator  315 . For example, if default operation of dual phase signal generator  315  is to generate signals  320 ( 1 ) and  320 ( 2 ) with a phase offset of π/2, the default value of correction signal  313  may be zero; alternatively, dual phase signal generator  315  may expect correction signal  313  to completely specify a phase offset between signals  320 ( 1 ) and  320 ( 2 ), in which case the default value of correction signal  313  may be π/2. Also, when optional target input device  314  is implemented, microcontroller  608  receives target parameter  316  therefrom, and software  609  implements adjustments to correction signal  313  based on target parameter  316 . 
     Dual phase signal generator  315  receives correction signal  313  from signal controller  312  (specifically, from microcontroller  608 ) and provides signals  320 ( 1 ) and  320 ( 2 ) with a phase offset indicated by correction signal  313 , at two outputs Vout 1  and Vout 2 . Dual phase signal generator  315  may include, for example, a direct digital synthesizer that generates two analog outputs, each at the nominal IF frequency discussed in connection with IQ demodulator  606 , that are subsequently mixed with the signal from clock  604  to form the frequencies of signals  320 . For example, in consistency with the examples above, the direct digital synthesizer would create analog outputs at 1 MHz frequency that, when mixed with the 2.449 GHz frequency of clock  604 , would provide signals  320  at 2.450 GHz. Signals  320  then transmit to their respective electronics sets, as shown in each of  FIGS. 4, 5 and 6 , radiated into respective radial waveguides  210  and received back into connections  318 ( 1 ),  318 ( 2 ). 
     In embodiments, clock  604  may not be part of signal controller  312 , but may instead be part of a signal generator (e.g., dual phase signal generator  315 ) which may originate the clock  604  signal and provide an output thereof to IQ demodulator  606  for use as a reference clock. Similarly, clock  602  may also be generated by a signal controller or some other part of a system that includes signal controller  312 . 
       FIG. 11  is a schematic diagram of major components of a system  700  that provides post-match control of microwaves in a radial waveguide, in an embodiment. System  700  may be utilized, for example, to excite a plasma in an adjacent plasma chamber. In general, system  700  has many of the same components as, and works similarly to, systems  200 ,  300 ,  400  and  500  ( FIGS. 3-6 ). However, system  700  does not include monitoring antennas or a corresponding signal controller providing feedback to signal generator  315 . Instead, a target input device  714  provides an ability to provide one or more target parameters such as phase offset, amplitude adjustments, or both to signal generator  315  and/or to solid state amplifiers  230 . When target input device  714  specifies a phase offset as the target parameter, the phase offset is provided by signal generator  315  in the form of a corresponding phase offset between signals  320 ( 1 ) and  320 ( 2 ). When input device specifies amplitude as the target parameter, the corresponding effect may be provided by signal generator  315  (e.g., in the form of amplitude(s) of signals  320 ( 1 ) and/or  320 ( 2 )) or by one or both of solid state amplifiers  230  (e.g., in the form of adjusting gain of one or both of solid state amplifiers  230 , so that the resulting amplitude is provided to radial waveguide  210 ). Whether phase or amplitude is selected as the target parameter, target input device  714  allows an operator of system  700  to optimize the selected target parameter independently of actions of tuners  250 , which continue to match impedance. 
     It should be understood that an ability to set and/or adjust gain of solid state amplifiers  230  as shown in  FIG. 11  may also be utilized in embodiments wherein antennas provide feedback and a signal controller adjusts phase and/or amplitude based on the feedback, (e.g., systems  300 ,  400  and  500  ( FIGS. 4-6 )). 
     Having described several embodiments, it will be recognized by those of skill in the art that various modifications, alternative constructions, and equivalents may be used without departing from the spirit of the invention. Additionally, a number of well-known processes and elements have not been described in order to avoid unnecessarily obscuring the present invention. Accordingly, the above description should not be taken as limiting the scope of the invention. 
     Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limits of that range is also specifically disclosed. Each smaller range between any stated value or intervening value in a stated range and any other stated or intervening value in that stated range is encompassed. The upper and lower limits of these smaller ranges may independently be included or excluded in the range, and each range where either, neither or both limits are included in the smaller ranges is also encompassed within the invention, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included. 
     As used herein and in the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a process” includes a plurality of such processes and reference to “the electrode” includes reference to one or more electrodes and equivalents thereof known to those skilled in the art, and so forth. Also, the words “comprise,” “comprising,” “include,” “including,” and “includes” when used in this specification and in the following claims are intended to specify the presence of stated features, integers, components, or steps, but they do not preclude the presence or addition of one or more other features, integers, components, steps, acts, or groups.