# Patent

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

## Abstract

A system provides post-match control of microwaves in a radial waveguide. The system includes the radial waveguide, and a signal generator that provides first and second microwave signals that have a common frequency. The signal generator adjusts a phase offset between the first and second signals in response to a correction signal. The system also includes first and second electronics sets, each of which amplifies a respective one of the first and second microwave signals. The system transmits the amplified, first and second microwave signals into the radial waveguide, and matches an impedance of the amplified microwave signals to an impedance presented by the waveguide. The system also includes at least two monitoring antennas disposed within the waveguide. A signal controller receives analog signals from the monitoring antennas, determines the digital correction signal based at least on the analog signals, and transmits the correction signal to the signal generator.

## Background
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 within 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 a signal controller that 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 singal 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 within 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 schematically illustrates a radial waveguide that is powered by four electronics sets and is monitored by four monitoring antennas, in an embodiment.
FIG. 6 is a schematic diagram illustrating implementations of the signal controller and dual phase signal generator shown in FIG. 4, in an embodiment.
FIG. 7 illustrates exemplary operation of a first portion of an IQ demodulator shown in FIG. 6.
FIG. 8 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 2B-2B′ 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/2B). 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.
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 FIG. 4. For example, FIG. 5 schematically illustrates a system 500 having 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. 5, 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. 5 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. 6 is a schematic diagram illustrating implementations of signal controller 312 and dual phase signal generator 315, in an embodiment. The embodiment illustrated in FIG. 6 could support any of the systems shown in FIG. 4 directly, and the principles now explained can be duplicated or otherwise modified in ways that will be readily apparent to support the system illustrated in FIG. 5.
In the embodiment illustrated in FIG. 6, 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. 3-4 or radial waveguide 510, FIG. 5, 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 (Xni2+Xnq2)}. The IQ demodulation of each of the signals proceeds in parallel such that for each interval, IQ demodulator 606 provides corresponding digital signals X1i, X1q, X2i, X2q, as shown.
FIG. 7 illustrates exemplary operation of a first portion 606(a) of IQ demodulator 606 that processes a signal received from connection 318(1) to yield X1i and X1q; 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 X2i and X2q. 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. 7 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 2πfIF/fs, where fs is a sampling frequency of clock 602 (40 MHz in this example), fIF 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 X1i and X1q. 
In certain embodiments, digital low pass filters 634(a) and 634(b) can be utilized to eliminate high frequency digital noise from X1i and X1q. Typical cutoff values of digital low pass filters 634(a) and 634(b) are for example 1 kHz.
Returning to FIG. 6, from IQ demodulator 606, digital outputs X1i, X1q, X2i and X2q 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 Vout1 and Vout2. 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 FIG. 4, 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. 8 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 and 300, (FIGS. 3-4). 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. 8 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 and 500 (FIGS. 4, 5)).
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.

## Claims

1. A system that provides post-match control of microwaves in a radial waveguide, comprising:
the radial waveguide;
a signal generator that provides a first microwave signal and a second microwave signal, the first and second microwave signals having a common frequency, wherein the signal generator adjusts a phase offset between the first and second microwave signals in response to a digital correction signal;
a first electronics set and a second electronics set, wherein each of the first and second electronics sets:
amplifies a respective one of the first and second microwave signals to provide respective first and second amplified microwave signals,
transmits the respective one of the first and second amplified microwave signals into the radial waveguide, and
matches an impedance of the respective one of the first and second amplified microwave signals to an impedance presented by the radial waveguide;

at least two monitoring antennas disposed within the radial waveguide; and
a signal controller that:
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.

2. The system that provides post-match control of microwaves in a radial waveguide as recited in claim 1, further comprising:
a target input device configured to provide a target parameter to the signal controller;
and wherein:
the signal controller determines the digital correction signal based on the analog signals from the at least two monitoring antennas and the target parameter.

3. The system that provides post-match control of microwaves in a radial waveguide as recited in claim 1, wherein the first electronics set includes a tuner that matches an impedance of the first amplified microwave signal to an impedance presented by the radial waveguide;
wherein the signal generator adjusts the phase offset, and the tuner matches the impedance, concurrently with one another.

4. The system that provides post-match control of microwaves in a radial waveguide as recited in claim 1, wherein the first electronics set includes:
a dummy load; and
a circulator that shunts power reflected back from the radial waveguide toward the first electronics set, into the dummy load.

5. The system that provides post-match control of microwaves in a radial waveguide as recited in claim 1, wherein the first electronics set includes a solid state amplifier having a microwave field effect transistor that amplifies the first microwave signal to provide the first amplified microwave signal.

6. The system that provides post-match control of microwaves in a radial waveguide as recited in claim 1, wherein the monitoring antennas are disposed proximate to locations at which the first and second electronics sets transmit the respective first and second amplified microwave signals into the radial waveguide.

7. A system for plasma processing of a workpiece, comprising:
a process chamber configured to create a plasma for the plasma processing;
a radial waveguide, adjacent to the process chamber, configured to generate microwaves for transmission to the process chamber to supply energy for the plasma;
a signal generator that provides a first microwave signal and a second microwave signal, the first and second microwave signals having a common frequency, wherein the signal generator adjusts a phase offset between the first and second microwave signals in response to a digital correction signal;
a first electronics set and a second electronics set, wherein 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 respective one of the first and second amplified microwave signals into the radial waveguide to produce microwaves therein; and
matches an impedance of the respective one of the first and second amplified microwave signals to an impedance presented by the radial waveguide;

at least two monitoring antennas disposed within the radial waveguide that produce analog signals in response to the microwaves; and
a signal controller that:
receives the analog signals from the at least two monitoring antennas,
determines the digital correction signal based at least on the analog signals, and
transmits the digital correction signal to the signal generator; and wherein 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; and

the signal generator adjusts the phase offset, and the tuner matches the impedance, concurrently with one another.

8. The system for plasma processing of a workpiece as recited in claim 7, wherein the radial waveguide comprises a radial line slot antenna for transmitting the microwaves into the process chamber.

9. The system for plasma processing of a workpiece as recited in claim 8, further including a ceramic plate that bounds the process chamber adjacent to the radial line slot antenna of the radial waveguide, the ceramic plate supporting a pressure difference between the radial waveguide and the process chamber, while allowing the microwaves to propagate from the radial waveguide into the process chamber.

10. A method for controlling a plasma within a process chamber, comprising:
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;
amplifying the first and second microwave signals to provide respective first and second amplified microwave signals;
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;
generating analog signals from the microwaves with at least two monitoring antennas disposed within 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.

11. The method for controlling a plasma within a process chamber as recited in claim 10, wherein determining the digital correction signal comprises performing in-phase and quadrature-phase demodulation on each of the analog signals.

12. The method for controlling a plasma within a process chamber as recited in claim 11, wherein performing in-phase and quadrature-phase demodulation comprises:
mixing a reference high frequency signal with one of the the analog signals to generate an intermediate frequency, and
generating digital in-phase and quadrature-phase signals from the intermediate frequency.

13. The method for controlling a plasma within a process chamber as recited in claim 12, further comprising:
utilizing a microprocessor to generate the digital correction signal based on the digital in-phase and quadrature-phase signals;
and wherein generating the first microwave signal comprises:
generating an analog output at the intermediate frequency, utilizing the digital correction signal, and
mixing the analog output with the reference high frequency signal to form the first microwave signal.

14. The method for controlling a plasma within a process chamber as recited in claim 10, further comprising:
receiving a target parameter from a target input device;
and wherein determining the digital correction signal further comprises adjusting the digital correction signal according to the target parameter.

15. The method for controlling a plasma within a process chamber as recited in claim 14, wherein the target parameter is a phase difference, and adjusting the digital correction signal comprises adjusting the phase offset according to the phase difference.