Impedance transformation in radio frequency assisted plasma production

Abstract

SOLUTION: To provide an apparatus for providing signals to a device, which may include one or more radio frequency signal generators and an electrically small transmission line that couples signals from the one or more RF signal generators to a fabrication chamber, and may further include a reactive circuit that transforms an impedance of the electrically small transmission line from a region of relatively high impedance sensitivity to a region of relatively low impedance sensitivity.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] Incorporation by Reference A PCT application is being filed concurrently herewith as part of this application, and each application identified in that concurrently filed PCT application to which this application claims benefit or priority is incorporated herein by reference in its entirety for all purposes. [Background technology]

[0002] The background and context discussion contained herein is provided solely for the purpose of generally presenting the contents of the present disclosure. Much of the present disclosure presents work by the inventors, and merely because such work is described in the Background section or presented as context elsewhere herein does not mean that such work is admitted to be prior art.

[0003] The fabrication of semiconductor wafers used to form integrated circuits can include many diverse processing steps. In certain processing steps, which may occur after various materials have been deposited on a semiconductor wafer, material may be etched away to allow additional materials, such as metals, to be deposited. Such deposition may involve the formation of conductive traces, transistor gates, vias, circuit elements, and the like. However, in at least some instances, semiconductor fabrication processes, such as those involving plasma-based etching, plasma-enhanced atomic layer deposition, or other processes, uncontrollable process variations can result in lower yields, costs, semiconductor layout and mask redesigns, and the like. In some cases, such uncontrollable process variations can result in variations in the energy coupled into the fabrication chamber utilized to form the plasma. Therefore, techniques for improving control in plasma-based wafer etching and / or plasma-enhanced atomic layer deposition, or other fabrication processes, remain an area of ​​active investigation. Summary of the Invention

[0004] In one aspect, an apparatus for providing a signal to a device is provided, the apparatus including one or more radio frequency (RF) signal generators, one or more electrically-small transmission lines that couple signals from one or more of the RF signal generators to a fabrication chamber, and a reactive circuit that transforms the impedance of each of the electrically-small transmission lines from a region having a first impedance sensitivity to a region having a second impedance sensitivity.

[0005] In some embodiments, the reactive circuit includes at least a series reactance. In some embodiments, the reactive circuit includes at least a shunt susceptance. In some embodiments, the reactive circuit includes at least a series reactance and a shunt susceptance. In some embodiments, the region of relatively high impedance sensitivity corresponds to a region in impedance space where the real part of the impedance corresponds to a value greater than approximately 100 ohms. In some embodiments, the region of relatively low impedance sensitivity corresponds to a region in impedance space where the real part of the impedance corresponds to a value less than approximately 100 ohms. In some embodiments, the impedance-transforming reactive circuit avoids the possibility of a resonant transmission line at any frequency lower than the frequency of the signals from one or more of the RF signal generators. In some embodiments, the electrically small transmission line corresponds to a transmission line that transforms the impedance from the region of relatively high impedance sensitivity to the region of relatively low impedance sensitivity without experiencing transmission line resonance at frequencies lower than the frequency of the signals generated by the RF signal generators in the medium of the transmission line. In some embodiments, the resistive losses of the electrically small transmission line combined with the losses of the reactive circuitry represent less than about 20%. In some embodiments, the resistive losses of the electrically small transmission line represent less than 10%.

[0006] In another aspect, an apparatus is provided that includes an electrically small transmission line that couples signals from one or more of the RF signal generators to a fabrication chamber, and a reactive circuit that transforms an impedance of the electrically small transmission line from a region of relatively high impedance sensitivity to a region of relatively low impedance sensitivity, the reactive circuit operative to move an impedance control point in a direction opposite to a direction moved by a length of the transmission line.

[0007] In some embodiments, the electrically small transmission line corresponds to a transmission line that moves the impedance control point from a region of relatively high impedance sensitivity to a region of relatively low impedance sensitivity without passing through a transmission line resonance at frequencies lower than the frequency of the signal generated by the RF signal generator in the medium of the transmission line. In some embodiments, the reactive circuit includes a series capacitive reactance. In some embodiments, the reactive circuit includes at least a shunt inductive susceptance. In some embodiments, the reactive circuit includes a series capacitive reactance and a shunt inductive susceptance. In some embodiments, the resistive losses of the electrically small transmission line combined with the losses of the reactive circuit amount to less than about 20%. In some embodiments, the resistive losses of the electrically small transmission line amount to less than 10%.

[0008] In another aspect, an integrated circuit fabrication chamber is provided, the integrated circuit fabrication chamber including a plurality of integrated circuit fabrication stations, one or more input ports for coupling radio frequency (RF) signals to at least one of the plurality of integrated circuit fabrication stations, an electrically small transmission line coupling a signal from one or more of the RF signal generators to the fabrication chamber, and a reactive circuit transforming an impedance of the electrically small transmission line from a region of relatively high impedance sensitivity to a region of relatively low impedance sensitivity.

[0009] In some embodiments, the region of relatively high impedance sensitivity corresponds to a region in impedance space where the real part of the impedance corresponds to values ​​greater than about 100 ohms. In some embodiments, the region of relatively low impedance sensitivity corresponds to a region in impedance space where the real part of the impedance corresponds to values ​​less than about 100 ohms. In some embodiments, the region having a first impedance sensitivity corresponds to a region having low impedance sensitivity, and the region having a second impedance sensitivity corresponds to a region having high impedance sensitivity. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 illustrates a substrate processing apparatus for depositing films on semiconductor substrates using any number of processes.

[0011] [Figure 2] FIG. 2 is a block diagram illustrating various components of a system utilized to perform a semiconductor fabrication process, according to one embodiment.

[0012] [Figure 3] FIG. 3 is a diagram illustrating power versus time profiles of radio frequency (RF) power coupled into stations of a multi-station integrated circuit fabrication chamber, according to one embodiment.

[0013] [Figure 4] FIG. 4 illustrates an RF matching unit coupled to a load (ZL) through transmission lines of different lengths, along with corresponding impedance plots in impedance space, according to one embodiment.

[0014] [Figure 5A] FIG. 5A illustrates impedance sensitivity at control points of an RF matching unit for various lengths of transmission line, according to one embodiment. [Figure 5B]FIG. 5B illustrates impedance sensitivity at control points of an RF matching unit for various lengths of transmission line, according to one embodiment.

[0015] [Figure 6A] FIG. 6A illustrates the use of electrically small transmission lines and reactive components arranged to transform the impedance of a control point from a relatively high impedance sensitivity region of impedance space to a relatively low impedance sensitivity region of impedance space, in accordance with one embodiment. [Figure 6B] FIG. 6B illustrates the use of electrically small transmission lines and reactive components arranged to transform the impedance of a control point from a relatively high impedance sensitivity region of impedance space to a relatively low impedance sensitivity region of impedance space, in accordance with one embodiment.

[0016] [Figure 7] FIG. 7 is a circuit diagram of a transmission line model according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0017] In certain embodiments or implementations, impedance transformation in radio frequency (RF)-assisted plasma generation can be utilized in various semiconductor fabrication processes, such as plasma-based wafer fabrication. Impedance transformation can provide the ability to more easily control the RF power delivered to one or more stations of a multi-station process chamber in a manner that allows dynamic adjustment to various loads presented by the stations of the process chamber. Such dynamic adjustment provides the real-time ability to match the impedance of the load presented by the plasma in the station to the source impedance of one or more RF generators, even when such loads can increase or decrease significantly over the course of the fabrication process. Thus, the RF power delivered to individual stations can be increased, and the RF power reflected from the RF generators can be reduced.

[0018] Certain embodiments or implementations can be utilized in many wafer fabrication processes, such as various plasma-enhanced atomic layer deposition (ALD) processes, various plasma-enhanced chemical vapor deposition (CVD) processes, or on-the-fly during a single deposition process. In certain implementations, the RF power matching network utilizes a simplified circuit topology to accommodate load changes at any signal frequency, such as medium frequencies (e.g., frequencies between 300 kHz and 3 MHz), high frequencies (e.g., frequencies between 3 MHz and 30 MHz), and very high frequencies (e.g., frequencies between 30 MHz and 300 MHz). However, in other implementations, the RF power matching network may operate at any signal frequency, for example, relatively low frequencies, such as 50 kHz to 300 kHz, as well as higher signal frequencies, such as frequencies above 300 MHz.

[0019] It should be noted that while certain embodiments described herein may show and / or describe electrically small transmission lines and reactive elements for use with four process chamber stations, in other embodiments a fewer number of process chamber stations may be utilized, such as one, two, or three stations. In other embodiments, electrically small transmission lines and reactive elements may be utilized with a greater number of process chamber stations, such as five, six, seven, eight, ten, twelve, or any other number of process chamber stations.

[0020] The manufacture of semiconductor devices typically involves depositing one or more thin films on planar or non-planar substrates in an integrated fabrication process. In some aspects of the integrated process, it may be useful to deposit a thin film that conforms to the substrate topography. One type of reaction that is useful in some cases involves chemical vapor deposition (CVD). In a typical CVD process, gas-phase reactants are simultaneously introduced into stations of a reaction chamber and undergo a gas-phase reaction. The reaction products deposit on the surface of the substrate. The reaction may be driven by a plasma, in which case the process may be referred to as a plasma-enhanced chemical vapor deposition (PECVD) reaction. As used herein, the term CVD is intended to include PECVD unless otherwise specified. CVD processes have certain drawbacks that make them less suitable in some situations. For example, mass transport limitations in CVD gas-phase reactions can cause a "breadloafing" deposition effect, which refers to thicker deposition on top surfaces (e.g., the top surface of a gate stack) and thinner deposition on concave surfaces (e.g., the bottom corners of a gate stack). Additionally, because some dies may have regions of different device densities, mass transport effects across the substrate surface can result in thickness variations within the die and within the wafer. These thickness variations can result in overetching of some areas and underetching of others, which can reduce device performance and die yield. Another problem associated with CVD processes is that the processes are often unable to form conformal films over high aspect ratio features. As device dimensions continue to shrink, this challenge becomes increasingly problematic.

[0021] In another example, some deposition processes involve multiple film deposition cycles, each generating a distinct film thickness. For example, in atomic layer deposition (ALD), thin layers of film, used in repetitive and sequential materials, can be considered to involve multiple cycles of deposition. As device and feature sizes continue to shrink in the semiconductor industry and three-dimensional device structures become more common in integrated circuit (IC) design, the ability to deposit thin conformal films (films of material that have a uniform thickness relative to the shape of the underlying structure, even if non-planar) continues to gain importance. ALD is a film formation technique well-suited for the deposition of conformal films due to the fact that a single ALD cycle deposits a single thin layer of material, the thickness of which is limited by the amount of one or more film precursor reactants that can adsorb (i.e., form an adsorption-limiting layer) on the substrate surface prior to the film-forming chemical reaction itself. Multiple ALD cycles can then be used to build up a film of the desired thickness, and because each layer is thin and conformal, the resulting film substantially conforms to the shape of the underlying device structure. In certain embodiments, each ALD cycle includes the following steps:

[0022] Exposing the substrate surface to a first precursor.

[0023] Purging the reaction chamber in which the substrate is located.

[0024] Activation of a reaction at the substrate surface, typically utilizing a plasma and / or a second precursor.

[0025] Purging the reaction chamber in which the substrate is located.

[0026] The duration of an ALD cycle may typically be less than 25 seconds, or less than 10 seconds, or less than 5 seconds. The plasma exposure step (or steps) of an ALD cycle may be of short duration, such as 1 second or less in duration.

[0027] FIG. 1 illustrates a substrate processing apparatus for depositing films on semiconductor substrates using any number of processes. The apparatus 100 of FIG. 1 utilizes a single processing station 102 of a process chamber with a single substrate holder 108 (e.g., pedestal) within an interior volume that can be maintained under vacuum by a vacuum pump 118. A gas delivery system 101 and a showerhead 106 are also fluidly coupled to the process chamber for delivering (for example) film precursors, carrier and / or purge gases and / or process gases, secondary reactants, etc. Equipment for generating plasma within the process chamber is also illustrated in FIG. 1. The apparatus illustrated schematically in FIG. 1 can be particularly adapted for performing plasma-enhanced CVD.

[0028] For simplicity, the processing apparatus 100 is illustrated as a separate process station (102) in a process chamber for maintaining a low-pressure environment. However, as described herein, it will be understood that multiple process stations can be included in a common process tool environment, for example, within a common reaction chamber. For example, FIG. 2 illustrates an embodiment of a multi-station processing tool, which is described in more detail below. Furthermore, it will be understood that in some embodiments, one or more hardware parameters of the processing apparatus 100, including those described in more detail herein, can be programmatically adjusted by one or more system controllers.

[0029] The process chamber station 102 is in fluid communication with a gas delivery system 101 for delivering process gases, which may include liquids and / or gases, to a distribution showerhead 106. The gas delivery system 101 includes a mixing vessel 104 for blending and / or conditioning the process gases for delivery to the showerhead 106. One or more mixing vessel inlet valves 120 can control the introduction of the process gases into the mixing vessel 104.

[0030] Some reactants may be stored in liquid form prior to vaporization and subsequent delivery to process chamber station 102. The embodiment of FIG. 1 includes a vaporization point 103 for vaporizing the liquid reactant provided to mixing vessel 104. In some embodiments, vaporization point 103 may be a heated liquid injection module. In some other embodiments, vaporization point 103 may be a heated vaporizer. In still other embodiments, vaporization point 103 may be eliminated from the process station. In some embodiments, a liquid flow controller (LFC) may be provided upstream of vaporization point 103 to control the mass flow rate of the liquid vaporized and delivered to process station 102.

[0031] The showerhead 106 delivers process gases and / or reactants (e.g., film precursors) to the substrate 112 at the process stations, the flow of which is controlled by one or more valves (e.g., valves 120, 120A, 105) upstream of the showerhead. In the embodiment shown in FIG. 1 , the substrate 112 is shown positioned below the showerhead 106 and resting on a pedestal 108. The showerhead 106 may have any suitable shape and may have any suitable number and arrangement of ports for delivering process gases to the substrate 112. In some embodiments with more than one station, the gas delivery system 101 includes valves or other flow control structures upstream of the showerhead that can independently control the flow of process gases and / or reactants to each station, such that gases can flow to one station but not to another station. Additionally, the gas delivery system 101 may be configured to independently control the process gases and / or reactants delivered to each station in a multi-station apparatus such that the gas compositions provided to different stations are different, e.g., such that the partial pressures of gas components may vary between stations simultaneously.

[0032] Volume 107 is located below showerhead 106. In some implementations, pedestal 108 can be raised or lowered to expose substrate 112 to volume 107 and / or to change the volume of volume 107. Optionally, pedestal 108 can be lowered and / or raised during portions of the deposition process to adjust process pressure, reactant concentrations, etc. within volume 107.

[0033] 1 , the showerhead 106 and pedestal 108 are electrically coupled to a radio frequency power source 114 and a matching network 116 to provide power to the plasma generator. In some implementations, the plasma energy can be controlled (e.g., via a system controller having appropriate machine-readable instructions and / or control logic) by controlling one or more of the process station pressure, gas concentration, RF power source, etc. For example, the radio frequency power source 114 and the matching network 116 can be operated at any suitable power to form a plasma having a desired composition of radical species. Similarly, the RF power source 114 can provide RF power at any suitable frequency or group of frequencies, and power.

[0034] In some implementations, plasma ignition and maintenance conditions are controlled by appropriate hardware and / or appropriate machine-readable instructions in a system controller, which can provide control instructions via a series of input / output control (IOC) instructions. In one example, instructions for setting plasma conditions for igniting or maintaining the plasma are provided in the form of a plasma activation recipe of a process recipe. In some cases, process recipes may be arranged sequentially, such that all instructions for a process are executed simultaneously with that process. In some implementations, instructions for setting one or more plasma parameters may be included in a recipe preceding a plasma process. For example, a first recipe may include instructions for setting the flow rates of inert (e.g., helium) and / or reactant gases, instructions for setting a plasma generator to a power set point, and time delay instructions for the first recipe. A second, subsequent recipe may include instructions for enabling the plasma generator and time delay instructions for the second recipe. A third recipe may include instructions for disabling the plasma generator and time delay instructions for the third recipe. It will be understood that these recipes may be further subdivided and / or iterated in any appropriate manner within the scope of this disclosure.

[0035] In some deposition processes, plasma strikes last on the order of several seconds or more in duration. In certain embodiments described herein, much shorter plasma strikes can be applied during a processing cycle. These can be on the order of less than 50 milliseconds, with 25 milliseconds being a specific example.

[0036] For simplicity, the processing apparatus 100 is illustrated in Figure 1 as a separate station (102) of a process chamber for maintaining a low-pressure environment. However, it can be understood that multiple process stations can be included in a multi-station processing tool environment, such as that shown in Figure 2, which illustrates a schematic diagram of one embodiment of a multi-station processing tool.

[0037] The processing apparatus 200 employs an integrated circuit fabrication chamber 263 that includes multiple fabrication process stations, each of which can be used to perform a processing operation on a substrate held on a wafer holder, such as pedestal 108 of FIG. 1, at a particular process station. In the embodiment of FIG. 2, the integrated circuit fabrication chamber 263 is shown as having four process stations 251, 252, 253, and 254, and four cables 266 that provide RF power to each of the four process stations through input port 267. Other similar multi-station processing apparatuses may have a greater or lesser number of process stations, depending on the implementation, e.g., desired level of parallel wafer processing, size / space constraints, cost constraints, etc. Also shown in FIG. 2 is a substrate handler robot 275 that operates under the control of a system controller 290 and can be configured to move substrates from a wafer cassette (not shown in FIG. 2) from a loading port 280 into the integrated circuit fabrication chamber 263 and to one of the process stations 251, 252, 253, and 254.

[0038] FIG. 2 also illustrates one embodiment of a system controller 290 used to control the process conditions and hardware states of the processing tool 200. The system controller 290 can include one or more memory devices, one or more mass storage devices, and one or more processors. The one or more processors can include a central processing unit, analog and / or digital input / output connections, stepper motor controller boards, etc. In some embodiments, the system controller 290 controls all activity of the processing tool 200. The system controller 290 executes system control software that can be stored in a mass storage device, loaded into a memory device, and executed on the system controller's hardware processor. The software executed by the system controller's 290 processor can include instructions for controlling the timing, mixture of gases, fabrication chamber and / or station pressures, fabrication chamber and / or station temperatures, wafer temperature, substrate pedestal, chuck and / or susceptor position, number of cycles performed on one or more substrates, and other parameters of a particular process performed by the processing tool 200. These programmed processes may include various types of processes, including, but not limited to, processes related to determining the amount of buildup on surfaces inside the chamber, processes related to depositing a film on a substrate, including cycle numbers, and processes related to cleaning the chamber. The system control software that may be executed by one or more processors of the system controller 290 may be configured in any suitable manner. For example, various process tool component subroutines or control objects may be written to control the operation of process tool components necessary to perform various tool processes.

[0039] In some embodiments, software for execution via the processor of the system controller 290 may include input / output control (IOC) sequence instructions for controlling the various parameters described above. For example, deposition of a substrate and each stage of a deposition cycle may include one or more instructions for execution by the system controller 290. Instructions for setting process conditions for an ALD / CFD deposition process stage may be included in the corresponding ALD / CFD deposition recipe stage. In some implementations, recipe steps may be arranged in sequence such that all instructions for a process step are executed simultaneously with that process step.

[0040] In some embodiments, other computer software and / or programs stored on the mass storage device of the system controller 290 and / or on memory devices accessible to the system controller 290 may be used. Examples of programs or sections of programs for this purpose include a substrate positioning program, a process gas control program, a pressure control program, a heater control program, and a plasma control program. The substrate positioning program may include program code for process tool components used to load the substrate onto the pedestal 108 (of FIG. 2) and control the spacing between the substrate and other parts of the processing apparatus 200. The positioning program may include instructions for appropriately moving the substrate in and out of the reaction chamber as needed to deposit a film on the substrate and clean the chamber.

[0041] The process gas control program may include code for controlling gas composition and flow rates to stabilize the pressure in the process station, as well as code for optionally flowing gas to one or more process stations prior to deposition. In some embodiments, the process gas control program includes instructions for introducing gas during film formation on a substrate in the reaction chamber. This may include introducing gas for different cycles for one or more substrates in a batch of substrates. The pressure control program may include code for controlling the pressure in the process station by, for example, adjusting a throttle valve in the exhaust system of the process station, gas flow to the process station, etc. The pressure control program may include instructions for maintaining the same pressure during different cycles of deposition on one or more substrates during processing of a batch.

[0042] The heater control program may include code for controlling the current to the heating unit 110 (of FIG. 1) used to heat the substrate. Alternatively, the heater control program may control the delivery of a heat transfer gas (such as helium) to the substrate.

[0043] In some embodiments, there may be a user interface associated with the system controller 290. The user interface may include a display screen, a graphical software display of equipment and / or process conditions, and user input devices such as a pointing device, keyboard, touch screen, microphone, etc.

[0044] In some embodiments, the parameters adjusted by the system controller 290 may relate to process conditions. Non-limiting examples may include process gas composition and flow rates, temperature, pressure, plasma conditions, etc. These parameters may be provided to the user in the form of a recipe and may be entered using a user interface. A recipe for an entire batch of substrates may include a compensated cycle count for one or more substrates in the batch to account for thickness trends over the course of processing the batch.

[0045] Signals for monitoring the process may be provided by analog and / or digital input connections of the system controller 290 from various process tool sensors. Signals for controlling the process can be output via analog and / or digital output connections of the processing tool 200. Non-limiting examples of process tool sensors that can be monitored include mass flow controllers, pressure sensors (such as pressure gauges), thermocouples, etc. Sensors can also be included and used to monitor and determine buildup on one or more surfaces inside the chamber and / or the thickness of a material layer on a substrate within the chamber. Appropriately programmed feedback and control algorithms can be used with data from these sensors to maintain process conditions.

[0046] The system controller 290 can provide program instructions for carrying out the deposition processes described above. The program instructions can control various process parameters such as DC power levels, pressure, temperature, number of cycles per substrate, amount of deposition on at least one surface inside the chamber, etc. The instructions can control the parameters to operate the in-situ deposition of a film stack according to various embodiments described herein.

[0047] For example, the system controller may include control logic for implementing the techniques described herein (e.g., determining an amount of deposition material currently accumulated on at least an internal region within the deposition chamber, and applying the determined amount of deposition material, or a parameter derived therefrom, to a relationship between (i) the number of ALD cycles required to achieve a target deposition thickness and (ii) a variable representing the amount of accumulated deposition material), thereby obtaining a compensated number of ALD cycles, obtaining the target deposition thickness given the amount of deposition material currently accumulated on the internal region within the deposition chamber, and performing the compensated number of ALD cycles on one or more substrates in the batch of substrates. The system may also include control logic for determining when accumulation in the chamber has reached an accumulation limit, and, in response to that determination, stopping processing of the batch of substrates and initiating cleaning of the chamber interior.

[0048] 2 , the controller may further control and / or manage the operation of an RF subsystem 295, which may generate and communicate RF power to integrated circuit fabrication chamber 263 via radio frequency input port 267. As described further herein, such operations may involve determining upper and lower thresholds for RF power delivered to integrated circuit fabrication chamber 263, determining the actual (e.g., real-time) level of RF power delivered to integrated circuit fabrication chamber 263, RF power activation / deactivation times, RF power on / off durations, operating frequencies, etc.

[0049] In certain embodiments, integrated circuit fabrication chamber 263 may include input ports in addition to input port 267 (additional input ports not shown in FIG. 2 ). Thus, integrated circuit fabrication chamber 263 may utilize eight RF input ports. In certain embodiments, process stations 251-254 of integrated circuit fabrication chamber 165 may each utilize a first and second input port, where the first input port may transmit a signal having a first frequency and the second input port may transmit a signal having a second frequency. The use of dual frequencies may improve plasma characteristics, thereby achieving deposition rates within certain limits and / or more easily controlled deposition rates. Dual frequencies may also produce other desirable results beyond those described herein. In certain embodiments, frequencies between about 300 kHz and about 300 MHz may be utilized.

[0050] 2, RF power from RF signal source 276 may be split into four output channels, which may be coupled to corresponding ones of input ports 267 of integrated circuit fabrication chamber 263. In at least certain embodiments, it may be useful for the RF power from RF signal source 276 to be split into relatively equal portions (such as about +1%). Thus, in one example, if RF signal source 276 provides 1000 W of output power, about 250 W (+1%) is delivered to each of input ports 267 of fabrication chamber 263.

[0051] FIG. 3 illustrates a power versus time profile of RF power coupled to stations of a multi-station integrated circuit fabrication chamber, according to one embodiment. In FIG. 3, the vertical axis represents delivered power, which corresponds to the total power delivered to the fabrication chamber by an RF distribution unit, such as single-input RF distribution unit 289 (of FIG. 2). As illustrated by the variation profile of the total power input, the power delivered to the single-input RF distribution unit can be subject to significant fluctuations, which may include, for example, fluctuations of up to 100 W, 150 W, or 200 W. While FIG. 3 illustrates the total power input along with the power input profiles for the first and second process stations (Sta1 and Sta2), in other embodiments, power may be coupled to a greater number of stations in a multi-station fabrication chamber, such as three stations, four stations, five stations, etc.

[0052] Fluctuations in the power delivered to a single input RF distribution unit can occur in response to significantly different RF loads corresponding to individual stations of a multi-station integrated circuit fabrication chamber 263. For example, during transitions occurring within a station of the fabrication chamber 263, such as during purging of gases utilized during an atomic layer deposition process, the RF load impedance presented by an individual station (e.g., one of stations 251, 252, 253, 254) may increase. In some cases, during the purge portion of an atomic layer deposition cycle in which precursor gases are purged or exhausted from the process station, the load impedance presented by a particular station may increase significantly. Such an increase in load impedance may operate to reduce the power coupled to the process station. In contrast, during the portion of an atomic layer delivery cycle in which a certain amount of precursor gas is injected into the fabrication chamber, the input impedance presented by a particular station of a multi-station fabrication chamber may decrease significantly.

[0053] As shown in FIG. 3 , the RF power coupled to Station 1 (Sta1) combined with the RF power coupled to Station 2 (Sta2) sums to a total power input. Thus, although not shown in FIG. 3 , it can be understood that as the total power input increases, the power coupled to each station of the multi-station fabrication chamber can increase proportionally. Additionally, as the total power input decreases, the power coupled to each station of the multi-station fabrication chamber can decrease proportionally. However, it can also be understood that as the total power input to the multi-station fabrication chamber decreases while the power coupled to a particular station (e.g., Sta1) increases, the power coupled to one or more other stations (e.g., Sta2) can decrease, thereby maintaining a substantially constant total power input.

[0054] In the example of FIG. 3 , which may relate to a multi-station fabrication chamber having two process stations (Sta1 and Sta2), if the total power input is held stable, e.g., at 100% of its nominal level, the power coupled to an individual station of the multi-station fabrication chamber may remain at, e.g., approximately 50% of its nominal value. However, as also shown in FIG. 3 , in some cases, the RF power coupled to a particular station (e.g., Sta1) may increase, perhaps for a short period of time, in response to a decrease in load impedance due, for example, to the conversion of a gaseous precursor to an ionized plasma material. In response to an increase in RF power at Sta1, the RF power coupled to Sta2 may decrease by an amount corresponding to a similar short-term increase, so that the increase sums to the total power input. However, as shown in FIG. 3 , the total power input to the fabrication chamber may decrease from time to time, which may occur in response to a mismatch between the output impedance of the RF generator and the input impedance of the fabrication chamber. Under such circumstances, as the total power input decreases and the power to an individual station (e.g., Sta1) increases, the power coupled to a different station (e.g., Sta2) may approach the lower threshold shown in FIG. 3 .

[0055] In certain embodiments, it may be undesirable for the power coupled to an individual station to approach or reach a particular lower threshold. In some cases, in response to power flow to a station in a multi-station fabrication chamber below the lower threshold, the station may present a high-impedance load. Accordingly, the power coupled to other stations in the multi-station fabrication chamber may increase, which may undesirably increase the plasma density at the other fabrication stations. In some cases, such increased power consumption at a station in a multi-station integrated circuit fabrication chamber may cause arcing or other abnormal plasma events. In some cases, power coupling below a threshold level may further result in deposition rate imbalances occurring within the multi-station fabrication chamber. Thus, for example, if the power coupled to a station falls below the lower threshold in Sta2, it may be necessary to extend the fabrication process in Sta2. Such extension may include additional cycles, such as atomic layer deposition cycles, or may involve other additional processing and / or measurement to determine whether such a reduction in power has adversely affected the quality of the fabricated wafers.

[0056] Therefore, it may be useful to ensure that the RF power coupled from an RF generator (such as RF signal source 276) is maintained at a consistent, relatively high level to reduce the incidence of power flow below a lower threshold. Accordingly, an output port, such as the output port of single-input RF distribution unit 289 of FIG. 2, may be equipped with a matching unit (not shown in FIG. 2) that can operate without user input to insert a reactive component (e.g., series capacitance, series inductance, shunt capacitance, shunt inductance) into the input signal path from RF signal source 276. In some cases, single-input RF distribution unit 289 may utilize one or more computer processors coupled to one or more memory circuits to enable execution of a set of computer-implemented instructions (e.g., an algorithm) that can operate to dynamically insert a reactive component into the signal path from RF signal source 276.

[0057] FIG. 4 illustrates a load impedance (Z) through a first or second length of transmission line, along with a corresponding impedance plot in representative impedance space, according to one embodiment. L ) is coupled to the RF matching unit.

[0058] In FIG. 4, diagram 401 shows that RF signal source 276 is shown providing an input to single-input RF distribution unit 289. As previously described herein, single-input RF distribution unit 289 may utilize reactive components (e.g., series capacitance, series inductance, shunt capacitance, shunt inductance), shown in FIG. 4 as Cser and Cshu. The values ​​of reactive components Cser and Cshu may be controlled via a computer so as to be dynamically adjusted according to the various loads presented by the individual stations of multi-station integrated circuit fabrication chamber 263. The load impedance presented by the individual stations of fabrication chamber 263 is shown in FIG. 4 as Z L 4, additional load impedances are presented by other stations (e.g., Sta1, Sta2, Sta3, etc.) in fabrication chamber 263. In certain embodiments, individual station loads Z L may correspond to a load with a relatively small real part and a relatively large imaginary part. In the particular example of FIG. L The impedance measured at this plane can be characterized as having a real impedance value of about 1 to 10 ohms and an imaginary impedance value of about 10 to 40 ohms.

[0059] In certain embodiments, an electrically short cable 266, such as a coaxial cable about 35 inches to about 45 inches (about 89 cm to about 114 cm), can be utilized to couple the single input RF distribution unit 289 to the input ports of the stations of a multi-station integrated circuit fabrication chamber. Thus, in the example of FIG. 4, Z LThe load impedance presented by Z L plane to a control point at the output port of the single-input RF distribution unit 289. L 402) through a fraction of a wavelength at the signal frequency, the load transforms to an impedance value corresponding to an impedance having a real component of approximately 25-50 ohms and a reactive component of approximately 100-200 ohms. Representative impedance space 402 shows point (1) rotating through path (2), which corresponds to approximately a fraction of one wavelength to reach point (3).

[0060] 4 can be understood to include regions of relatively low impedance sensitivity (corresponding to areas of the representative impedance space where the real and imaginary components of the impedance are less than about 100 ohms). The representative impedance space 402 can also include regions of relatively high impedance sensitivity (corresponding to areas of the impedance space where the real and imaginary components of the impedance are greater than about 100 ohms). Thus, the load impedance Z L When the plane of is rotated, the impedance Z L 4. It can be appreciated that this has the effect of transforming the load impedance Z from regions of low impedance sensitivity, such as regions corresponding to relatively low real and imaginary impedances (e.g., reactance to resistance ratios < 2.5), to regions of high impedance sensitivity, such as regions corresponding to relatively high real and imaginary impedances (e.g., reactance to resistance ratios > 2.5). However, as will be further explained in connection with FIG. 5A, in some cases it may be necessary to determine precise values ​​for reactive components such as Cser and Cshu of FIG. 4, thereby adjusting the load impedance Z LIt can be difficult to arrive at a capacitive reactance or inductive susceptance that provides a conjugate match or other type of match that operates to provide maximum power flow into the power supply and minimum reflected power.

[0061] 5A and 5B illustrate the impedance sensitivity at the control point of an RF matching unit corresponding to transmission lines of various lengths, according to one embodiment. As illustrated in FIG. 5A, determining the real and imaginary components necessary to produce a match, such as a conjugate match, can help determine whether load impedances located in regions of high impedance sensitivity may be problematic, resulting in a low reflection coefficient. Thus, transforming an impedance, such as through an electrically short transmission line (at frequencies between 10 and 100 MHz), can result in undesirably high standard deviations in the impedance introduced by resistive and reactive circuit elements. Therefore, efforts to match such loads may require multiple iterations, as resistive and reactive elements are inserted into the matching network, tested to determine the effect of the insertion of such elements on the reflection coefficient (or voltage standing wave ratio), and then adjusted and remeasured to drive the reflection coefficient below a threshold. Such an impedance transformation is performed by determining the load impedance Z at point (1). L is shown in the representative impedance space 402 of Figure 4 in a region of low impedance sensitivity. Rotation of point (1) through path (2) in the representative impedance space results in a load impedance Z to point (3) in a region of high impedance sensitivity. L This results in the conversion of

[0062] However, referring again to FIG. 4 in a representative impedance space 403, the use of RF cables (266) having greater electrical lengths at frequencies between about 10 MHz and about 100 MHz results in a load impedance Z LThe impedance space 403 shown in FIG. 4 can operate to transform a point (1) from a first region of low-impedance sensitivity to a second region of low-impedance sensitivity. As shown in FIG. 4, the rotation from point (1) through path (4) to reach point (5) corresponds to an impedance transformation from a point within the region of low-impedance sensitivity to a second point within the region of low-impedance sensitivity. The length of path (4) corresponds to the number of wavelengths represented by 10 to 20 cables at operating frequencies between 10 MHz and 100 MHz. In an example such as FIG. 4 (lower right portion), a 15-foot (457.2 cm) coaxial cable transmission line represents a wavelength slightly longer than a half wavelength. It can also be appreciated that such a rotation through path (4) avoids the possibility of providing a conjugate match within the region of high-impedance sensitivity.

[0063] Figure 5B shows the uncertainty in the real and imaginary impedances corresponding to point (5) shown in representative impedance space 403 (of Figure 4). As shown in Figure 5B, the uncertainty surrounding point (5) corresponds to a relatively low standard deviation in the impedance introduced by the reactive elements to provide the conjugate match. Matching such a load may therefore require only a single measurement of the reflection coefficient followed by the insertion of appropriate resistive and / or reactive circuit elements to drive the measured reflection coefficient to a value below a threshold.

[0064] However, it should be noted that in addition to regions of low and high impedance sensitivity, the representative impedance spaces 402 and 403 of Figure 4 may include areas of resonance and anti-resonance. For example, referring to impedance space 403, the load impedance (Z) from point (1) to point (5) through an electrically long (e.g., about 10 feet to about 20 feet (about 305 cm to about 610 cm)) coaxial cable is L ) corresponds to the resonance and anti-resonance points where the impedance space intersects. For example, the load impedance Z LThe transformation of (6) is shown as a crossover point, which may theoretically correspond to a point of infinite impedance. At such a point, the voltage present in the transmission line (e.g., a coaxial cable) may increase to a relatively high value while the current decreases to a relatively low value. Such a high value of voltage generated in the transmission line in response to passing through the anti-resonance point (6) may cause breakdown of the dielectric of the coaxial cable and / or result in other undesirable consequences.

[0065] It should be noted that in certain embodiments, impedance transformation can occur from a region having a first impedance sensitivity to a region having a second impedance sensitivity.

[0066] The path (4) shown in the representative impedance space 403 further crosses or passes through a point (7) that could theoretically represent a point of zero impedance. At such a point, the voltage present in the transmission line (e.g., a coaxial cable) may decrease to a very low or negligible value while the current increases to a very high value. Such a high value of current may cause excessive heating of the coaxial cable, which may damage the coaxial cable and / or the RF signal source 276.

[0067] Furthermore, aside from passing through resonance (e.g., high current / low voltage) and anti-resonance (e.g., high voltage / low current) points, the use of longer cables, such as 15-foot (457.2 cm) cables, can result in other undesirable consequences, such as increased resistive losses. Additionally, the use of longer cables can raise cabling concerns, and excess cable length must be coiled, tucked, or set aside to avoid interference with other equipment associated with the fabrication chamber. For example, such coiling of excess cable length can cause parasitic effects in which adjacent sections of the coiled cable interact with each other, resulting in increased capacitance that can in turn affect the characteristic impedance (Z0) of the cable.

[0068] Therefore, for the reasons stated above, it may be desirable to utilize electrically small transmission lines (e.g., about 10 to 50 inches (about 25 to 127 cm) of coaxial cable) rather than electrically long transmission lines (e.g., about 10 to 20 feet (about 305 cm to about 610 cm) of coaxial cable). In this context, the term "electrically small" refers to a transmission line that transforms impedance from a region of relatively high impedance sensitivity to a region of relatively low impedance sensitivity without passing through a resonance of the transmission line or an anti-resonance of the transmission line at a frequency lower than the frequency of the signal generated by the RF signal generator in the medium of the transmission line. Thus, by way of example, a 40-inch (101.6 cm) transmission line transmitting a signal having a frequency between 1 MHz and 50 MHz would have a load impedance Z from point (1) to point (3) in representative impedance space. L The transform of the 15-foot (457.2 cm) transmission line carrying a signal with a frequency between approximately 1 MHz and 50 MHz can be classified as electrically small in that it does not pass through the anti-resonance point (6). On the other hand, a 15-foot (457.2 cm) transmission line carrying a signal with a frequency between approximately 1 MHz and 50 MHz has a load impedance Z from point (1) to point (5) in typical impedance space. L can be classified as electrically non-small in that the transformation of

[0069] 6A and 6B illustrate the use of electrically small transmission lines and reactive components arranged to transform the impedance of a control point from a relatively high impedance sensitivity region of impedance space to a relatively low impedance sensitivity region of impedance space, in accordance with one embodiment.

[0070] As shown in FIG. 6A, an electrically long (e.g., 15 ft (457.2 cm)) cable exhibits a load impedance (Z) that represents the load presented by the process stations of the multi-station integrated circuit fabrication chamber 263. L ) is utilized to transform the load impedance (Z L) can be transformed from a first point in the region of low impedance sensitivity to a second point in the region of low impedance sensitivity. Such control can be effected via a computer-controlled matching network (e.g., via execution of a suitable algorithm) in the single-input RF distribution unit 289. However, as previously mentioned, the use of electrically long (e.g., 15 ft (457.2 cm)) cables or other transmission lines that allow passage through resonance or anti-resonance points in representative impedance space can have undesirable consequences, such as increased resistive losses, changes in parasitic capacitance, and cable routing / housing issues.

[0071] Therefore, to avoid the above drawbacks, electrically small cables can be utilized in conjunction with appropriate reactive circuitry to transform the load impedance from a plane corresponding to the input port of a station of a multi-station fabrication chamber to a desired control point. Certain embodiments can overcome the disadvantages of using electrically small cables, such as transforming the load impedance from a region of low impedance sensitivity to a region of high impedance sensitivity. Thus, in FIG. 6B, the load impedance (Z L) is shown as being transformed from point (1) to point (2A). As previously described herein, such a transformation corresponds to a transformation of the impedance from a region of low impedance sensitivity to a region of high impedance sensitivity. However, with the insertion of a lumped element shunt inductor (e.g., L1 in FIG. 6B ), the impedance at the control point of the single RF distribution unit is moved within the representative impedance space through the path formed by the insertion of L1. It can therefore be appreciated that such a transformation of the impedance at the control point may be desirable in that such a transformation helps avoid the need for matching in the high impedance sensitivity portion of the impedance space. As shown in FIG. 6B , additional transformation of the load impedance from an area of ​​high impedance sensitivity to an area of ​​low impedance sensitivity can be achieved by using a lumped element series reactance, such as the insertion of C1 in the circuit. It can be appreciated that the insertion of such a reactance results in a movement of the control point, such as from point (3A) to point (4) in the impedance space of FIG. 6B .

[0072] Thus, in certain embodiments, electrically small transmission lines can be utilized to couple RF distribution units to input ports to stations of a multi-station fabrication chamber. The use of such electrically small transmission lines can avoid various drawbacks, such as the potential for conjugate matching in areas of high impedance sensitivity. Such electrically small transmission lines can be utilized in conjunction with the insertion of circuit elements that provide capacitive reactance or inductive susceptance. The use of such circuit elements assists in transforming impedance from areas of high impedance sensitivity back to areas of low impedance sensitivity. Furthermore, the use of such electrically small transmission lines with appropriate inductive / capacitive circuit elements, which can be coupled as series or shunt devices, can provide relatively low resistive losses and reduced capacitive coupling, such as between adjacent segments of longer, possibly coiled, transmission lines, avoiding cabling concerns. In certain embodiments, the use of electrically small transmission lines (e.g., 10- to 50-inch (25.4 cm to 127 cm) coaxial cables) can reduce the resistive losses of the transmission lines to a minimal amount, e.g., less than 5%, 10%, or 15%. In addition, the insertion of various circuit elements, such as shunt inductors and series capacitors, can introduce resistive losses. The combined losses, including transmission line losses and losses from the various circuit elements, can be kept below nominal levels, for example, below about 20%.

[0073] 6B utilizes the insertion of a shunt inductor to provide the inductive susceptance and a series capacitor to provide the capacitive reactance, other embodiments may utilize different circuit topologies, and thus may include various combinations of capacitive, inductive, and resistive elements, transmission line lengths, etc., according to particular impedance transformation requirements.

[0074] FIG. 7 is a circuit diagram of a transmission line model according to one embodiment.

[0075] In Figure 7, a series inductance (L) and a shunt capacitance (C) are shown. The lumped elements of Figure 7 contrast with the lumped elements of Figure 6B, in which a series capacitance (C1) and a shunt inductance (L1) are utilized. Thus, the lumped circuit elements of Figure 6B represent the inverse (or reverse) of the standard transmission line model of Figure 7.

[0076] In the foregoing detailed description, numerous specific details are set forth to provide a thorough understanding of the presented embodiments or implementations. The disclosed embodiments or implementations may be practiced without some or all of these specific details. In other instances, well-known process operations have not been described in detail so as not to unnecessarily obscure the disclosed embodiments or implementations. While the disclosed embodiments or implementations have been described in conjunction with specific embodiments or implementations, it will be understood that such description is not intended to limit the disclosed embodiments or implementations.

[0077] The foregoing detailed description has been directed to particular embodiments or implementations for the purpose of illustrating the disclosed aspects. However, the teachings herein can be applied and implemented in many different ways. In the foregoing detailed description, reference is made to the accompanying drawings. The disclosed embodiments or implementations have been described in sufficient detail to enable those skilled in the art to practice the embodiments or implementations, but it should be understood that these examples are not limiting. Other embodiments or implementations may be used, and changes can be made to the disclosed embodiments or implementations without departing from their spirit and scope. In addition, the conjunction "or" is intended herein in an inclusive sense where appropriate, unless otherwise expressly stated; for example, it should be understood that the phrase "A, B, or C" is intended to include the possibilities of "A," "B," "C," "A and B," "B and C," "A and C," and "A, B, and C."

[0078] In this application, the terms “semiconductor wafer,” “wafer,” “substrate,” “wafer substrate,” and “partially fabricated integrated circuit” are used interchangeably. Those skilled in the art will understand that the term “partially fabricated integrated circuit” can refer to a silicon wafer in any of many stages of integrated circuit fabrication. Wafers or substrates used in the semiconductor device industry may typically include diameters of 200 mm, 300 mm, or 450 mm. The foregoing detailed description assumes that embodiments or implementations are practiced on wafers or in conjunction with processes related to the formation or fabrication of wafers. However, the claimed subject matter is not so limited. Workpieces may be of various shapes, sizes, and materials. In addition to semiconductor wafers, other workpieces that may utilize the claimed subject matter may include various products, such as printed circuit boards or fabrications of printed circuit boards.

[0079] Unless the context of this disclosure clearly requires otherwise, throughout the description and claims, words like "comprises," "comprising," and the like should be construed in an inclusive sense, i.e., "including but not limited to," rather than an exclusive or exhaustive sense. Words using the singular or plural generally also include the plural or singular, respectively. When the word "or" is used in reference to a list of two or more items, the word covers all of the following interpretations of the word: any of the items in the list, all of the items in the list, and any combination of the items in the list. The term "embodiment" refers to an embodiment of the technologies and methods described herein, as well as a physical object that embodies the structure and / or incorporates the technologies and / or methods described herein. The present disclosure can also be realized in the following manner, for example. Application example 1: 1. An apparatus for providing a signal to a device, comprising: one or more radio frequency (RF) signal generators; one or more electrically small transmission lines coupling signals from one or more of said RF signal generators to a fabrication chamber; a reactive circuit that transforms the impedance of each of the electrically small transmission lines from a region having a first impedance sensitivity to a region having a second impedance sensitivity; An apparatus comprising: Application example 2: The device of Application Example 1, The apparatus, wherein the reactive circuit comprises at least a series reactance. Application example 3: The device of Application Example 1, The apparatus, wherein the reactive circuit comprises at least a shunt susceptance. Application example 4: The device of Application Example 1, The apparatus, wherein the reactive circuit comprises at least a series reactance and a shunt susceptance. Application example 5: The device of Application Example 1, The region of relatively high impedance sensitivity corresponds to a region in impedance space where the real part of the impedance corresponds to a value greater than about 100 ohms. Application example 6: The device of Application Example 1, The region of relatively low impedance sensitivity corresponds to a region in impedance space where the real part of the impedance corresponds to a value less than about 100 ohms. Application example 7: The device of Application Example 1, The apparatus, wherein the reactive circuit that transforms the impedance avoids the possibility of a resonant transmission line at any frequency lower than the frequency of the signals from one or more of the RF signal generators. Application example 8: The device of Application Example 1, the electrically small transmission line corresponds to a transmission line that transforms impedance from the region of relatively high impedance sensitivity to the region of relatively low impedance sensitivity without going through a transmission line resonance at a frequency lower than the frequency of the signal generated by the RF signal generator in a medium of the transmission line. Application example 9: The device of Application Example 1, The apparatus, wherein resistive losses in the electrically small transmission line combined with losses in the reactive circuitry amount to less than about 20%. Application example 10: The device of Application Example 1, The apparatus, wherein the resistive losses of the electrically small transmission line are less than 10%. Application example 11: an electrically small transmission line that couples signals from one or more of the RF signal generators to the fabrication chamber; a reactive circuit that transforms the impedance of the electrically small transmission line from a region of relatively high impedance sensitivity to a region of relatively low impedance sensitivity, the reactive circuit operating to move an impedance control point in a direction opposite to that moved by a length of transmission line; An apparatus comprising: Application example 12: The device of Application Example 11, The apparatus, wherein the electrically small transmission line corresponds to a transmission line that moves the impedance control point from the region of relatively high impedance sensitivity to the region of relatively low impedance sensitivity without going through a transmission line resonance at a frequency lower than the frequency of the signal generated by the RF signal generator in a medium of the transmission line. Application example 13: The device of Application Example 11, The apparatus, wherein the reactive circuit comprises a series capacitive reactance. Application 14: The device of Application Example 11, The apparatus, wherein the reactive circuit comprises at least a shunt inductive susceptance. Application example 15: The device of Application Example 11, The apparatus, wherein the reactive circuit comprises a series capacitive reactance and a shunt inductive susceptance. Application 16: The device of Application Example 11, The apparatus, wherein resistive losses in the electrically small transmission line combined with losses in the reactive circuitry amount to less than about 20%. Application 17: The device of Application Example 12, The apparatus, wherein the resistive losses of the electrically small transmission line are less than 10%. Application 18: 1. An integrated circuit fabrication chamber comprising: a plurality of integrated circuit fabrication stations; one or more input ports for coupling radio frequency (RF) signals to at least one of the plurality of integrated circuit fabrication stations; an electrically small transmission line coupling signals from one or more of the RF signal generators to the fabrication chamber; a reactive circuit that transforms the impedance of the electrically small transmission line from a region of relatively high impedance sensitivity to a region of relatively low impedance sensitivity; 1. An integrated circuit fabrication chamber comprising: Application 19: The device of Application Example 18, The apparatus, wherein the region of relatively high impedance sensitivity corresponds to a region in impedance space where the real part of the impedance corresponds to a value greater than about 100 ohms. Example 20: The device of Application Example 18, The region of relatively low impedance sensitivity corresponds to a region in impedance space where the real part of the impedance corresponds to a value less than about 100 ohms. Example 21: The device of Application Example 1, The region having a first impedance sensitivity corresponds to a region having a low impedance sensitivity, and the region having a second impedance sensitivity corresponds to a region having a high impedance sensitivity.

Claims

1. 1. An apparatus for providing a signal to a device, comprising: one or more electrically small transmission lines coupling signals from one or more RF signal generators to the fabrication chamber, wherein one electrically small transmission line of the one or more electrically small transmission lines corresponds to a transmission line that transforms impedance from a first impedance sensitivity region to a second impedance sensitivity region without passing through a transmission line resonance at a predetermined frequency; a reactive circuit that transforms the impedance of each of the one or more electrically small transmission lines from the region having the first impedance sensitivity to the region having the second impedance sensitivity; An apparatus comprising:

2. 10. The apparatus of claim 1, The apparatus, wherein the reactive circuit comprises at least a series reactance.

3. 10. The apparatus of claim 1, The apparatus, wherein the reactive circuit comprises at least a shunt susceptance.

4. 10. The apparatus of claim 1, The apparatus, wherein the reactive circuit comprises at least a series reactance and a shunt susceptance.

5. 10. The apparatus of claim 1, The apparatus, wherein the region having the first impedance sensitivity corresponds to a region of relatively high impedance sensitivity in impedance space, the real part of the impedance corresponding to a value greater than about 100 ohms.

6. 10. The apparatus of claim 1, The apparatus, wherein the region having the second impedance sensitivity corresponds to a region of relatively low impedance sensitivity in impedance space, the real part of the impedance corresponding to a value less than about 100 ohms.

7. 10. The apparatus of claim 1, The apparatus, wherein the reactive circuit that transforms the impedance avoids the possibility of a resonant transmission line at any frequency lower than a frequency of the signals from the one or more RF signal generators.

8. 10. The apparatus of claim 1, The apparatus, wherein resistive losses in the electrically small transmission line combined with losses in the reactive circuitry amount to less than about 20%.

9. 10. The apparatus of claim 1, The apparatus, wherein the resistive losses of the electrically small transmission line are equal to or less than 10%.

10. 10. The apparatus of claim 1, The apparatus wherein the reactive circuit operates to move an impedance control point in a direction opposite to that moved by a length of transmission line.

11. 10. The apparatus of claim 1, the resistive losses of one of the one or more electrically small transmission lines combined with losses in the reactive circuit represent less than about 20%.

12. 10. The apparatus of claim 1, The apparatus, wherein a resistive loss of one electrically small transmission line of the one or more electrically small transmission lines represents less than 10%.

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