Plasma non-uniformity detection

Abstract

A method for detecting plasma non-uniformity in a radio frequency plasma processing system includes generating a plasma in a reaction chamber of the radio frequency plasma processing system and detecting electrical signals from the plasma in a frequency range from a frequency of the radio frequency power sustaining the plasma to approximately ten times the frequency with a plurality of sensors azimuthally positioned about an axis of symmetry of the chamber of the radio frequency plasma processing system. The method further includes comparing waveforms of the electrical signals obtained from the plasma by the plurality of sensors and determining when plasma non-uniformity occurs based on a comparison of the electrical characteristics of the plasma detected by each of the plurality of sensors.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Application No. 62959-644, filed January 10, 2020, and U.S. Nonprovisional Patent Application No. 17-145-202, filed January 8, 2021, the contents of which are incorporated herein by reference. Summary of the Invention [Problem to be solved by the invention]

[0002] Radio frequency (RF) plasma processes are widely used in semiconductor manufacturing for etching various types of films, depositing thin films at low to medium process temperatures, and performing surface treatment and cleaning. Such processes are characterized by the use of plasma, i.e., partially ionized gases that are used to generate neutral species and ions from precursors in a reaction chamber, provide energy for ion bombardment, and / or perform other operations. Control of plasma density during such processes is challenging, and non-uniformity of the plasma in the reaction chamber affects the uniformity and yield of wafer processing of integrated circuits or other devices being manufactured. [Means for solving the problem]

[0003] Non-uniform plasma density in a reaction chamber can cause non-uniform etch rates or specific characteristics across a substrate. In certain systems, monitoring of the uniformity of plasma density in a reaction chamber is performed using a probe. Such a probe may be exposed to a coating-dependent plasma environment and may use active electronics to infer the plasma density. Such systems may take several milliseconds or longer to respond to changes in the plasma. Optical emission spectroscopy may be used to determine the profile of plasma density in a reaction chamber, but such systems may require multiple lines of sight through the plasma and use complex analysis to infer the non-uniformity. None of these techniques are sensitive and fast enough to effectively solve the non-uniformity problem, and may be costly to implement. [Brief description of the drawings]

[0004] The present disclosure is best understood from the following detailed description when read in conjunction with the accompanying drawings, in which it is emphasized that, in accordance with standard practice in the industry, various features have not been drawn to scale, and in fact the dimensions of various features may be arbitrarily increased or decreased for clarity of discussion.

[0005] [Figure 1] 1 is a schematic side view of an RF plasma processing system according to an embodiment of the present disclosure.

[0006] [Diagram 2] 1 is a schematic side view of a plasma chamber having high bandwidth sensors mounted at various positions on an electrode according to an embodiment of the present disclosure. FIG.

[0007] [Diagram 3] FIG. 13 is a cross-sectional view of a dual plate electrode assembly having a sensor that provides a voltage signal through an electrical connector with low shunt capacitance to electrical ground in accordance with an embodiment of the present disclosure.

[0008] [Figure 4]1 is a cross-sectional view of a pedestal with an embedded high bandwidth voltage sensor according to an embodiment of the present disclosure.

[0009] [Diagram 5] FIG. 2 is a schematic side view of a pedestal according to an embodiment of the present disclosure.

[0010] [Figure 6] FIG. 13 is a top view illustrating the propagation of axisymmetric surface waves across a pedestal along which a plasma in a reaction chamber is axisymmetric in accordance with an embodiment of the present disclosure.

[0011] [Figure 7] FIG. 1 is a top view of the propagation of a transverse electromagnetic surface wave across an electrode according to an embodiment of the present disclosure.

[0012] [Figure 8] FIG. 1 is a horizontal cross-sectional view of a sensor azimuthally (about the chamber axis of symmetry) mounted in a reaction chamber according to an embodiment of the present disclosure.

[0013] [Figure 9] 1 is a vertical cross-sectional view of an electrode, an electrode base, an upper dielectric plate, a sight glass, and a sensor azimuthally mounted on a dielectric wall of a reaction chamber according to an embodiment of the present disclosure.

[0014] [Figure 10] FIG. 1 is a vertical cross-sectional view of a capacitively coupled plasma reaction chamber having several sensor array locations according to an embodiment of the present disclosure.

[0015] [Figure 11] FIG. 1 is a side cross-sectional view of a model induced plasma reaction chamber according to an embodiment of the present disclosure.

[0016] [Figure 12] 1 is a schematic partial cross-sectional side view of a RF plasma processing system having several possible sensor locations according to an embodiment of the present disclosure.

[0017] [Figure 13] 1 is a schematic partial cross-sectional view including a dielectric wall of an RF plasma processing system in which a sensor is mounted on a dielectric surface proximate an inductively coupled antenna according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Illustrative examples of the claimed subject matter are disclosed below. For clarity, not all features of an actual implementation are described herein. It is understood that in the development of any such actual implementation, numerous implementation-specific decisions may be made to achieve the developer's particular goals, such as compliance with system-related and business-related constraints that vary from implementation to implementation. It is further understood that such a development effort, even if complex and time-consuming, would be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.

[0019] Furthermore, as used herein, the article "a" is intended to have its ordinary meaning in the patent art, i.e., "one or more." The term "about" herein, when applied to a value, generally means within the tolerance of the device used to generate the value, and in some instances means ±10%, ±5% or ±1%, unless expressly specified otherwise. Additionally, the term "approximately" herein means, for example, majority, nearly all, all, or an amount having a range of about 51% to about 100%. Additionally, the examples herein are intended to be illustrative only and are presented for discussion and not by way of limitation.

[0020] 1, a schematic side view of an RF plasma processing system 100 according to an embodiment of the present disclosure is shown. The RF plasma processing system 100 includes a first RF generator 105 and a second RF generator 110, a first impedance match network 115, a second impedance match network 120, a sheath 125, a plasma power supply such as a showerhead 130 or equivalent power supply element such as an electrode, and a pedestal 135. As used herein, a plasma power supply may refer to any device that introduces power to generate a plasma and may include, for example, the showerhead 130 and / or other types of electrodes, antennas, etc.

[0021] The RF plasma processing system 100 may have one or more RF generators 105, 110 that provide power to the reaction chamber 140 through one or more impedance matching networks 115, 120. RF power flows from the first RF generator 105 through the impedance matching network 115 to the plasma in the reaction chamber 140, to the showerhead 130 or sidewalls, to an electrode other than the showerhead 130, or to an inductive antenna (not shown) that electromagnetically provides power to the plasma, and then the power flows from the plasma to ground and / or the pedestal 135 and / or the second impedance matching network 120. Typically, the first impedance matching network 115 compensates for variations in the load impedance in the reaction chamber 140 by adjusting a reactive component, e.g., a variable capacitor, in the first impedance matching network 115 such that the combined impedance of the showerhead 130 and the first impedance matching network 115 is equal to the output impedance of the first RF generator 105, e.g., 50Ω. Additionally, the reflected power can be modified by adjusting the frequency within about ±10% of the RF power. The term "about" as used herein acknowledges that in practice some inaccuracy to the ranges or values ​​may be experienced and still obtain satisfactory results. Such inaccuracies may result, for example, from loss or degradation of calibration or from drift during operation. In these circumstances, however, the expressed ranges or values ​​are nominal target values ​​for the operating conditions in use.

[0022] In a particular example, the first RF generator 105 may provide power at an RF frequency between about 400 KHz and 150 MHz, while the second RF generator 110 coupled to the pedestal 135 may provide power at an RF frequency lower than that of the first RF generator 105, although in a particular implementation the second RF generator 110 may not provide power at an RF frequency lower than that of the first RF generator 105. Typically, the frequencies of the first RF generator 105 and the second RF generator 110 are such that the first RF generator 105 is at an RF frequency that is neither an integer multiple nor an integer fraction of the frequency of the second RF generator 110. One or more of the first RF generator 105 and the second RF generator 110 may adjust the frequency to modify the reflected power.

[0023] The impedance matching networks 115, 120 are designed to make adjustments to their internal reactive elements so that the load impedance matches the source impedance. Generally, low reflected power is considered positive, but embodiments of the present disclosure ensure that the delivered power is maintained within the reaction chamber 140, that power is reflected back towards the first RF generator 105 and the second RF generator 110, and that even when the reflected power is relatively high, the associated impedance matching networks 115, 120 can monitor the forward and reflected power to and from the reaction chamber 140 and make adjustments to the variable reactor elements, e.g., vacuum variable capacitors, through the use of a motor drive system. In certain embodiments, electronically controlled capacitors, such as pin diodes for electronic variable capacitors, may be used. The impedance matching networks 115, 120 may include circuitry to measure the phase and magnitude of the signal to determine the levels of forward and reflected power from the intended load. Thus, embodiments of the present disclosure may be effective even when the amount of reflected power is high. If there is a significant amount of reflected power at the primary frequency, the capacitor is varied until the reflected power is minimized, for example, to less than about 5 W and / or less than about 1% for the period, or in certain embodiments, less than 1 W. Generally, harmonic frequency signals, including reflected power at harmonic frequencies, are not measured. Additionally, the frequency may be adjusted within about ±10% of the RF power, which may modify the reflected power.

[0024] Although the RF plasma processing system 100 has many advantages, historically, maintaining control of plasma density through a multi-step process has been a challenge. Design tolerances on the order of, for example, 1% non-uniformity with density ranges on the same order of magnitude relative to a nominal value remain a challenge. Also, to achieve optimal integrated circuit (IC) yields on a wafer-by-wafer basis with scaling to below about 3 nm and thickening to below about 10 nm, the uniformity of the plasma and neutral species must be tightly controlled to the 1% level or even lower. Non-uniform plasma density or average density that deviates beyond a desired range from a desired value in the reaction chamber can be caused by slow changes in the chamber, changes in the RF circuitry, or rapid growth (on the order of less than a millisecond) of parasitic or secondary plasma, thereby resulting in non-uniformity of nanoscale features across the processed wafer due to non-uniformity in etch rate.

[0025] Because even a 1% etch rate difference across a wafer can cause yield problems for advanced technologies, and it often takes a significant amount of time to complete wafer processing to see yield loss, there is a need to quickly and accurately detect non-uniform plasma density in a reaction chamber or plasma density that deviates from a desired range in a time period that may need to be less than about 1 millisecond to avoid irreversible deviations on the wafer from the desired feature profile.

[0026] Those skilled in the art will appreciate that electromagnetic (EM) surface waves may propagate on surfaces within the RF powered plasma in the reaction chamber 140. These surface waves have appreciable energy at both the fundamental RF drive frequency and the RF harmonics. The average power and power distribution of the harmonics are factors that affect plasma density and non-uniformity. Here, a harmonic profile is defined as a spectrum of surface waves with frequencies that are integer multiples of the fundamental drive frequency of the RF plasma-based reaction chamber 140. For example, if a 2 MHz RF drive power is provided to the reaction chamber 140, the injected power will generate surface waves at that frequency that propagate along the interface between the plasma and the surface of the inner reaction chamber 140. The reflected wave power can be modified by adjusting the frequency by about ±10% of the RF power. Harmonic surface waves at integer multiple frequencies may also be generated. For example, a 2 MHz electromagnetic wave may generate surface waves at 4 MHz, 6 MHz, or 8 MHz. Odd and even harmonics (2nd, 3rd, 4th, 5th, etc.) may be present, but in some instances the odd harmonics may dominate.

[0027] Aspects of the present disclosure may provide sensor locations relative to the reaction chamber 140 and its components that allow for detection and analysis of RF surface waves to determine fundamental and harmonic amplitudes and phases at multiple points within or adjacent to the reaction chamber 140. The waves may be detected by sensing RF voltage or current at fundamental and harmonic frequencies on the surface of the chamber components. In some embodiments, a sensor for voltage has a pickup configured on or adjacent to the surface of the electrode, pedestal base, chamber wall or strap, and a conductive line that transmits a signal from the pickup to a connector or cable. A current sensor may have a conductive element that includes one or more loops or partial loops or line conductors, one end of the conductive element being at a reference potential that may be a local electrical ground.

[0028] Multiple sensors, e.g., two or more sensors, may be positioned on certain chamber components, described in more detail below, at different angles about the axis of symmetry of the chamber to measure surface voltages or currents associated with such surface waves. The angle measured from a reference point of the chamber about the axis of symmetry is defined herein as the azimuthal angle. In some embodiments, such sensors may be positioned at approximately the same distance from the axis of symmetry of the chamber.

[0029] The sensors may be mounted at various locations on or with respect to the reaction chamber and / or its components. For example, the sensors may be mounted on the surface of an electrode, such as the pedestal 135 and / or the showerhead 130. The sensors may be mounted on the pedestal of an electrode, either in a vacuum or outside a vacuum environment. The sensors may be mounted inside or outside one or more metal and dielectric wall areas of the reaction chamber 140 in the chamber, or on an antenna that may be used to inductively power the plasma. The sensors may be located on or in proximity to a passive antenna that may be used to sense electromagnetic waves proximate to the boundary of the plasma, or on a number of conductive buses or straps that connect the first impedance matching network 115 or the second impedance matching network 120 to an electrode, such as the pedestal 135 and / or the showerhead 130, an antenna, or other components that transfer power to the plasma in the reaction chamber 140. The sensors may be connected to an electrical ground, whereby the sensors can pick up signals from various components of the RF plasma processing system 100 as they propagate across the surfaces of the respective components.

[0030] A spectrum of RF harmonics is generated at the electrode-plasma interface, e.g., sheath 125 in FIG. 1, and waves propagate in all directions such that both the amplitude and phase of all wave components vary with the position of the electrode or support. Such waves propagate along the inner surface of metal walls adjacent to the plasma and through any dielectric walls that may be adjacent to the plasma. The amplitude and phase of such waves change in response to changes in the plasma, e.g., plasma density and inhomogeneity, with response times on the order of a few microseconds or less. Furthermore, the frequency and phase distributions of the RF harmonic surface waves propagating at the electrode-plasma interface determine the frequency and phase distributions of the harmonic surface waves propagating at the electrode-based surfaces, surfaces or walls connected to the electrode or plasma-wall interface towards the impedance matching network 115, 120. The amplitudes and phases of the fundamental and harmonic signals at different sensor positions allow the determination of the azimuthally symmetric and asymmetric parts of the total EM wave field for each frequency.

[0031] In the case of an inductive plasma, signals from the plasma, e.g., fundamental and harmonic waves, may propagate back to the antenna and then to an impedance matching network that powers the antenna. The frequency and phase distribution of the fundamental and harmonic RF waves may be monitored on microsecond or faster time scales using such surface mounted sensors and compared at specified ranges and phase relationships as an indication of plasma asymmetry or changes in plasma density or conductivity. Signals from such sensors may be transmitted by cables or the like to detectors that analyze the frequency components of the signal to produce values ​​of the amplitude and phase of each frequency component at each sensor location.

[0032] In a particular implementation, the amplitude and phase of the detected RF harmonic components may be rapidly determined by circuitry (detectors) in the signal analysis section, which may be a separate metal box or chassis, or may be in or connected to the impedance matching network 115, 120. Such amplitude and phase may be used to determine the state of the plasma, including radial distribution and asymmetry, by applying algorithms and plasma non-uniformity calibration. The signal from the sensor may be Fourier analyzed by dedicated circuitry (detectors) fast enough to perform virtually continuous spectrum analysis, updated as frequently as possible, and resulting in a high speed data stream. For example, for a 13.56 MHz plasma output, it may take less than 50 microseconds to process 512 periods in Fourier analysis, allowing the state of the plasma to be updated at a rate of 10 KHz for a pulsed plasma when each element of the pulse occurs at 5 KHz.

[0033] The results of the dedicated Fourier analysis of the fundamental and harmonics may be stored in a separate storage medium that can be read and / or written by the analysis processor associated with the signal analysis section. Either the stored results or the real-time signal may be sent to a high-speed calculation processor to determine the asymmetry parameters for each of the fundamental and harmonics. The asymmetry parameters may be compared to pre-stored values ​​in a separate storage medium (or a different storage medium) using an algorithm (which may be stored in a separate storage medium or a different storage medium) in order to very quickly recognize a "plasma fault" condition. The analysis processor may then send appropriate commands to the first RF generator 105 and the second RF generator 110, more than two RF generators in certain implementations, and impedance matching networks associated with these generators when appropriate, for example, to continue the process under the current conditions or to make necessary changes in the process conditions. In certain implementations, three, four or more RF generators may be used. The first RF generator 105 and the second RF generator 110 may then continue, stop, change the power supplied, change the frequency of the RF power by about ±10% to correct the reflected power, or in any other suitable manner - for example, respond to a transition to a reduced power mode or a pulsed mode, or command certain corrective action, such as triggering an alarm, shutting off power, etc., to avoid improper wafer processing during a plasma disturbance or other unacceptable condition.

[0034] The location of the sensor for detecting (the electric and magnetic fields of) the surface waves and characterizing the surface waves may be, in some embodiments, on the peripheral surface (bare or covered by a dielectric) of the pedestal 135 outside the area covered by the wafer. For example, if the reaction chamber 140 processes a circular wafer with a radius of 150 mm, the pedestal mounted sensor may be located at a radius greater than 150 mm from the center of the wafer, possibly under an annular peripheral dielectric to control edge effects. The sensor may additionally or alternatively be located on the surface or periphery of the showerhead 130 facing the wafer, or on the base of the pedestal 135 or on the surface of the base of the showerhead 130, whether these locations are within or outside the vacuum process environment. The sensor may be located at various other locations, described in detail below, and may be continuously or periodically monitored to provide uniformity of the process plasma.

[0035] Using sensors outside the vacuum process environment, such as sensors in one or more of the impedance match networks 115, 120, the base of the pedestal 135 and / or a strap or bus connecting the base to the showerhead 130, may eliminate the need to send signals through a vacuum feedthrough or transmission cable within the vacuum envelope of the reaction chamber 140. Sensors in such locations may provide near-continuous monitoring of fundamental and harmonic EM waves. This may enable the RF plasma processing system 100 to continuously provide plasma density uniformity and determine within a very short period of time whether a fault condition has occurred or proper wafer or substrate processing continues.

[0036] In certain exemplary embodiments, the present disclosure may provide an apparatus and method for detecting deviations of a plasma from a desired "process window" in an RF plasma processing system 100. The RF plasma processing system 100 may include a reaction chamber 140, which may include a showerhead 130 for injecting reactive gases into the reaction chamber 140, which may include a wafer support pedestal 135. However, in other implementations, the showerhead 130 may not inject gases into the reaction chamber 140. In some embodiments, the showerhead 130 may be mounted with its center approximately near an axis of symmetry of the reaction chamber 140 and may include a number of sensors positioned at selected orientations about the axis of symmetry. Additionally or alternatively, such sensors may be positioned on a wafer-facing surface in a peripheral region of the showerhead 130 to detect and measure EM surface waves propagating while the wafer is being processed.

[0037] Additionally, in some embodiments, there may be multiple sensors attached to the exterior surface of the wafer support pedestal 135 outside the area occupied by the wafer to detect both the amplitude and phase of the RF harmonics and the fundamental surface waves. Such sensors may be exposed to the plasma or may be covered by a dielectric cover or a dielectric and metal cover. Additionally or alternatively, sensors may be located at the periphery of the pedestal 135 base, inside or outside the vacuum vessel and / or below the plane defined by the wafer. In some implementations, sensors may be located on the pedestal base to detect surface electromagnetic waves propagating towards or away from the wafer support area of ​​the pedestal and surface electromagnetic waves propagating on the surface of the pedestal base. In certain embodiments, the sensors may be mounted close to the wafer plane (e.g., less than 10 cm).

[0038] Alternatively, the sensor may be attached to a portion of the pedestal 135 that is metal or other conductive material and that is located outside the vacuum region of the reaction chamber 140 under atmospheric conditions. Sensors located outside the vacuum region may be attached to a region of the pedestal 135 at a radius from the pedestal symmetry axis that is at least 50% of the maximum radius of the pedestal 135 or more than 75% of the maximum radius of the pedestal 135. Such a sensor may be positioned near - within a few centimeters in some embodiments - a vacuum seal, e.g., an O-ring, for the support pedestal 135. In some embodiments, the sum of the radial and axial propagation distances from the edge of the wafer to the sensor may be less than about 25 cm, or less than about 15 cm or about 10 cm in some embodiments. Particular locations and orientations of sensors according to embodiments of the present disclosure are discussed in detail below.

[0039] Turning now to FIG. 2, a schematic side view of a plasma chamber with high impedance sensors attached at various locations on the electrodes in accordance with an embodiment of the present disclosure is shown. Each of the two components that function as electrodes, i.e., the pedestal 235 and the showerhead 230 or other equivalent powered element, may use a separate RF generator 205 or 210 and impedance match network 215 and 220. Alternatively, the electrodes may have multiple generators and match networks that provide power thereto. Arrows 245 along the surface of the pedestal 235 indicate the inner radial direction of RF current and power flow from the lower (bias) RF generator 210 electrically connected to the pedestal 235 via the impedance match network 220. The generated electric field contributes to the formation of a plasma (not shown) between the electrodes and the outer radial backflow of current and power indicated by arrows 250 along the underside of the showerhead 235 or other powered element, and ultimately to the selective grounding circuit of the impedance match network 215 for the showerhead 230 or other powered element.

[0040] In certain embodiments, a reaction chamber 240 having RF power from first and second RF generators 205 and 210 and impedance match networks 215, 220 may have sensors 255 at the periphery of a pedestal 235 that may be covered by a dielectric material 260. A communication line 265 may transmit signals from each of the sensors 255, which in some embodiments may be approximately equidistant from the pedestal axis of symmetry, to a Fourier analysis circuit (not shown) that calculates the amplitude and phase of both the fundamental and harmonic frequency surface waves acquired by each sensor 255.

[0041] In some implementations, the Fourier analysis circuitry may calculate the magnitude and phase of the fundamental and higher harmonics of a periodic electromagnetic surface waveform. The magnitude and phase of the resulting series, known as a Fourier series, arise from the relationship between functions in the time domain and functions in the frequency domain.

[0042] Additionally, some of the disclosed matching network 220 embodiments may include a signal analysis section 275 or appendage of the matching network 220 that is separate and RF decoupled from the RF power processing and impedance matching circuits or components of the matching network 220. The signal analysis section 275 may include Fourier analysis circuitry (detectors) to analyze the sensor signal and provide digital amplitude and phase of the RF fundamental and harmonics. The signal analysis section 275 may include a high speed digital logic or calculation processor to analyze the relative magnitude and phase of the signal at harmonic frequencies and derive quantitative parameters characterizing the relative magnitude and relative phase of the axisymmetric and non-axisymmetric harmonic components at each frequency. Additionally, in some embodiments, the disclosed matching network 220 may be connected via a very high speed network to the second RF generator 210 as well as to a controller (not shown) for the reaction chamber 240 or RF plasma processing system 200 in which the sensor 255 is located. In some embodiments, the disclosed enhanced impedance matching network 220 may be capable of sending commands to the first RF generator 205 and transmitting calculated parameters to a process chamber controller and / or a tool control system.

[0043] Additionally, another first RF generator 205 and impedance match network 215 may be electrically coupled to another electrode, which may be the showerhead 230 of the reaction chamber 240. In one embodiment, the first RF generator 205 may operate at a different frequency than the second RF generator 210, which may not be an integer multiple of the frequency of the second RF generator 210.

[0044] Similarly, the impedance match network 215 may monitor the reflected power from the electrode and process chamber 240 and make adjustments if there is significant reflected power from the electrode. In some embodiments, the second RF generator 210 may be a 400 KHz RF generator, a 2 MHz RF generator, a 13.56 MHz RF generator, etc., while the first RF generator 205 may operate at a somewhat higher frequency. In some embodiments, the first RF generator 205 may operate at a frequency greater than 25 MHz, such as 60 MHz, 100 MHz, or higher.

[0045] In one embodiment, the primary function of the first RF generator 205 may be to power the reaction chamber 240 to generate a plasma between the showerhead 230 or another power source, such as an electrode, and the pedestal 235 to generate reactive species such as fluorine, chlorine, and compositions thereof, and to accelerate ions from the generated plasma to impact a wafer placed on the pedestal 235.

[0046] A set of sensors 280 may be disposed on the upper electrode or showerhead 230 facing the lower electrode surface or pedestal 235, having a bandwidth greater than about 10 times the frequency of the highest frequency RF generator connected to that electrode. In some embodiments, each of these may have an impedance greater than about 100 Ω, and in some embodiments, greater than 500 Ω. The sensors 280 may be voltage sensors or current sensors, or may combine both capabilities in a single package, for example, a current sensor may include one or more segments of wire that may be covered by an electrostatic shield.

[0047] In some embodiments, the sensors 280 have an electrical connection to a Fourier analysis circuit in the signal analysis section 285 of the impedance matching network 215. The Fourier analysis circuit may output the amplitude and phase of the different frequency components from each of the sensors 280 and compare the amplitude and phase of the frequency components of the other sensors 280 and / or with reference levels stored in memory. Analysis of the signals in some embodiments may include artificial intelligence (AI) employing pattern recognition or learning algorithms of the amplitude and / or phase, which may use neural networks or conventional digital algorithmic processing of the signals from the sensors 280.

[0048] Signal processing by Fourier analysis circuitry to find fundamental and harmonic component signals of both amplitude and phase may be performed in less than about 10 microseconds for each of the sensor signals, and in a preferred embodiment, in less than 1 microsecond. The separate signal analysis section 285 of the impedance matching network 215 may incorporate at least one computational or logic processor having substantial computational power with very high speed (<1 ns cycle time) circuitry employing very high speed logic ICs. In some embodiments, the processor of the signal analysis section 285 is programmable to allow a supplier or user of the processing chamber 240 to provide or implement proprietary algorithms or analysis software of the computational "platform" provided to the impedance matching network 215.

[0049] In some embodiments, the software program for calculating the parameters from the signal amplitude and phase and another logic algorithm for determining the impact on the process uniformity of deviations from acceptable plasma conditions may reside in a removable "plug-in" component with data storage and connection to the signal processing section. This software or logic calculates the degree of deviation of the RF electromagnetic surface wave spectrum from the nominal operating conditions or characteristics of the proper operating conditions. Based on this, a processor associated with the controller may "decide" to take corrective action or terminate the process within about 1 millisecond before a wafer is misprocessed. In some embodiments, a quantitative determination of the expected impact of the deviation on the uniformity or other characteristics of the process may be made within about 500 microseconds of occurrence so that corrective action can be initiated within 1 millisecond. Additionally, actions may be taken to avoid loss of wafer or substrate yield in order to minimize or eliminate damage to the wafer or substrate currently being processed in the reaction chamber 240.

[0050] The evaluation and / or decision made in the signal analysis section 285 of the impedance matching network 215 may, in some embodiments, be made by a very high speed computing or analysis system using algorithms present in a plug-in storage and / or removable data processing device. In yet another embodiment, the evaluation and decision made in the signal analysis section 285 may be made using an analog or neural net type processor. Such decision may further use decision algorithms that may be present in the removable storage or processing device. Corrective action instructions may then be sent quickly from the section 275 of the impedance matching network 215 over high speed data lines to the RF generator 205 to temporarily interrupt, change or terminate the power or RF frequency to the plasma. This ensures that factory management can quickly take or plan corrective action for the process chamber 240 and the RF plasma processing system 200.

[0051] 2 also shows a set of sensors 290 that are configured on the exterior surface of the pedestal 295 of the showerhead 230 under atmospheric conditions and outside the vacuum region within the reaction chamber 240. In some embodiments, additional sensors 296 may be attached to the pedestal base 297 and connected by high speed signal cables to the disclosed signal processing section 275 of the impedance match network 220 in the same manner as the sensors 290. The sensors 296 located outside the vacuum environment of the reaction chamber 240 are significantly less expensive and less difficult to integrate into information and processing networks since no vacuum feed is required.

[0052] The sensors 255 may be arranged in several configurations to sense the voltage and / or current on the surface of the pedestal 235 and may be covered and protected from the plasma by a dielectric cover 260. Sensors of this type and location are in close proximity to the wafer and / or substrate and therefore may have the advantage of sensitivity in detecting certain modes of EM surface waves that are indicative of plasma asymmetries, which are an important type of plasma non-uniformity. These in-chamber sensors 255 may use communication lines passing through the vacuum wall via feedthroughs or wireless communication links operating at optical or low frequencies in some embodiments.

[0053] In general, the phase and amplitude patterns of each frequency of the EM surface waves on the surfaces of the showerhead 230 and pedestal 235 may be determined by analysis of signals from any of the groups of voltage, current, phase, or combination sensors 255, 280, 290, and 296. In general, EM surface waves of a given frequency will generate voltage and current signals that have a phase relationship with signals of other frequencies. The magnitude of the voltage at each frequency and point is the sum of the voltages from all waves of that frequency originating from all points across the electrode surface. For axisymmetric electrode surfaces where power is symmetrically delivered and the plasma is axisymmetric, axisymmetric surface wave modes result from the superposition of waves from all parts of the electrode and other surfaces of the reaction chamber 240. In general, a perfectly symmetric plasma in a symmetric chamber with a symmetric electrode centered on the axis of symmetry of the chamber will have a line of symmetry of equal phase and amplitude primarily in the form of a circle centered on the center of the pedestal 235.

[0054] Turning to FIG. 3, a cross-sectional view of a dual plate electrode assembly with a broadband sensor that provides a voltage signal to the periphery of the electrode and electrical ground via an electrical connector with low shunt capacitance according to an embodiment of the present disclosure is shown. In some embodiments, an electrode such as a showerhead 330 may have two conductive plates 331, 332 arranged generally parallel and centered with a shape generally the same as a substrate or wafer. The surface of the first plate 331 facing away from the second plate 332 may be exposed to the vacuum environment and plasma. The first plate 331 is spaced from the second plate 332 by a distance that is the length of the dielectric standoff support 333. The first plate 331 may have an embedded sensor 334 with a puck or pickup being a conductive material and a surface generally coplanar with the surface of the first plate 331 facing away from the second plate 332 of the first plate 331.

[0055] In some embodiments, the sensors 334 may be attached to the first plate 331 surrounded by a dielectric 336 having a low dielectric constant, such as quartz or other suitable material. In some embodiments, the dielectric 336 may have a dielectric constant less than 5, and in some embodiments, the dielectric constant may be less than 2 for inorganic materials such as quartz-based aerogels. The sensors 334 may have a high bandwidth extending from 100 KHz to at least 10 times the highest drive frequency connected to the chamber, which may be 300 MHz or more, and may be capable of sensing surface voltage, surface current, or both. The sensitivity of the sensors 334 in some embodiments may vary by less than 30% over a range of frequencies of harmonics of the main fundamental RF frequency used in the reaction chamber. In some embodiments, at least one lead 337 from each sensor is connected to an inner conductor 338 of a vacuum electrical signal feedthrough 339 having a base 341 attached to the electrically grounded second plate 215. In some embodiments, the leads from each sensor may be connected directly to a ground plane and a circuit board in a location similar to 332 that has one detection circuit for each sensor to determine the amplitude and phase for each frequency component.

[0056] The inner conductor 338 of the feedthrough 339 may have a small shunt capacitance, for example 5 picofarads (pf, in some embodiments less than 2pf), to the base 341 of the feedthrough 339 attached to the grounded second plate 332, such that the total shunt capacitance from the sensor 334 + lead 337 + feedthrough 339 to ground is less than 5pf, and in some embodiments less than 3pf. In some embodiments, the output from the base 341 attached to the grounded second plate 332 may be connected to an attenuator (not shown). In some embodiments, the attenuator may have an electrical resistor with a resistance value greater than about 100 Ω. A shunt resistor to ground 405 may be in parallel with the electrical resistor 404. The resistance of the shunt resistor may be, for example, 50 Ω, or alternatively, may be equal to the impedance of a cable connecting the attenuator to a communication network or a controller of the plasma chamber. If a detector is placed in place of the connector as shown in FIG. 3, the signal output from the detector, which is the amplitude and phase of the voltage or current at each frequency of the sensor, may be transmitted to an analysis processor which may be in a section of the matching network.

[0057] Each sensor 334 may measure the voltage or current amplitude of the coupled electromagnetic surface wave modes having as components the fundamental and harmonic frequencies of all the RF generators powering the plasma. The fundamental and harmonic frequencies range from about 10 KHz to as much as about 500 MHz or more. In other embodiments, the sensors may measure voltages at fundamental and harmonic frequencies ranging from about 100 KHz to about 1 GHz.

[0058] FIG. 4 is a cross-sectional view of a pedestal with an embedded wideband voltage sensor according to an embodiment of the present disclosure. The voltage sensor 401 may be attached to an electrode such as the pedestal 400. In some embodiments, the sensor 401 may be connected to an electrical ground 406 through a resistor. The tip or puck of the sensor 401 may have a lead 402 surrounded by a dielectric 403 (which may optionally be air or vacuum). In some embodiments, the lead 402 from the sensor 401 may pass through an attenuator such as resistor(s) 404 having a shunt resistance 405 that in some embodiments is about 50 Ω and may be connected to an electrical ground 406. Such resistors 404 may be non-inductive and may have a resistance in the range between about 100 Ω and about 100,000 Ω. In some embodiments, the resistance may be between about 500 Ω and about 10,000 Ω. The resistor 405 may be non-inductive.

[0059] Additionally, the dielectric 403 is generally non-magnetic and has a low loss tangent, in some embodiments less than about 0.01, or in other embodiments less than about 0.001. The shunt capacitance between the tip of the sensor 401 and the lead 402 to the ground electrode is less than about 5 pf, or in some embodiments less than about 2 pf, such that the reactance between the sensor 401 and the electrode of the pedestal 400 is greater than about 100 Ohms at 300 MHz. The purpose of such low shunt capacitance is to reduce loading of the surface waves by the sensor 401 so as to minimize wave energy absorption and allow the waves to propagate as if the sensor 401 were not present. Under such conditions, the detected surface potential does not differ significantly from the potential at the electrode without such a sensor 401.

[0060] Turning to FIG. 5, a schematic side view of a pedestal with associated RF and control components is shown according to an embodiment of the present disclosure. The power supply circuit of the pedestal 501 includes an RF power generator 405 and an impedance matching network 506. High speed signal lines, e.g., cables 511, 512, carry signals from the sensors 502, 503 to sections that may be within or attached to the impedance matching network 506 in some embodiments. High speed lines 513 of a data network take information from the impedance matching network 506 to a reaction chamber or generator controller(s) 514 or to a tool or factory (not shown). The sensors 502, 503 are mounted on or near the base 504 of the pedestal 501, which may be inside or outside the vacuum region of the reaction chamber.

[0061] In some embodiments, there may be a signal analysis section associated with the impedance matching network 506, for example, a fault detection section 510. The signal analysis section 510 may be electrically and / or RF isolated from certain components of the impedance matching network 506, such as the vacuum capacitors and high voltage electronics. The signal analysis section 510 receives signals from the sensors 502, 503 via cables 511, 112. The signal analysis section 510 directs the signals from each sensor 502, 503 to an internal circuit, referred to as a detector, which may include electronic components such as transistors and passive components. In an alternative embodiment where the amplitude and phase are found directly adjacent to the sensor for each frequency component, the signals coming to the signal analysis section may be the amplitude and phase for each frequency component rather than the raw signal.

[0062] Each detector (not shown) in section 510 may perform RF spectrum analysis of the signals from one sensor 502, 503 or from a group of sensors analyzed in parallel. The analysis may include time averaging of the group of sensors signals or the signals of one or more sensors 502, 503 for noise reduction. In some embodiments, there may be an output from each detector of the signals acquired by each sensor 502, 503, e.g., amplitude and phase for each of the fundamental and harmonic frequency components. The output from each detector may be input to an analog-to-digital converter for each harmonic signal to produce digitized values ​​for both the amplitude and phase of each measured harmonic.

[0063] These digital amplitude and phase values ​​for each frequency component and each sensor may be input with little delay, e.g., less than 10 microseconds, to a high speed digital processor in a signal analysis section associated with the disclosed impedance matching network. The digital processor may analyze both the amplitude and phase information of the fundamental and each harmonic from the sensor to determine the relative magnitudes of various surface wave modes, including axially symmetric and non-axially symmetric modes, for both the fundamental and the harmonics. Various non-axially symmetric modes may exist for each frequency component, one or more of which may be indicative of plasma non-uniformity.

[0064] In some embodiments, such non-axisymmetric modes may be quickly identified by algorithms present in the plug-in. A reference database correlating the magnitude of the non-axisymmetric modes with the % plasma non-uniformity may also be present in this plug-in or removable processor. The digital processor may calculate the rate of change of the amplitude of the wave modes and the rate of increase of the amplitude of one or more wave modes to determine the likelihood of an impending failure. One indication of the magnitude of a non-axisymmetric mode at a given frequency may be the difference between the phase of the surface waves of the given frequency at various sensor locations having the same radial distance from the center of a circular electrode symmetrically arranged in an axisymmetric chamber. Alternatively, a second indication of a non-axisymmetric mode may be the difference between the amplitude of the surface waves of the given frequency at various sensor locations having the same radial distance from the center of a circular electrode symmetrically arranged in an axisymmetric chamber.

[0065] A matching network 506 with an insulating section 510 containing a multi-channel detector system (not shown) can perform simultaneous Fourier analysis, digitization and recording of the voltage amplitude and phase of the propagating EM wave at various locations on the pedestal 501. Due to inherent noise, each determined voltage amplitude and phase may be averaged over a short time interval, averaged over a group of sensors 502, 503 to make a relative magnitude determination, or averaged in time over a relatively large number of pulses, if desired.

[0066] A showerhead, pedestal, or other power delivery element such as an electrode with a group or array of sensors may be used as a test system to generate data that characterizes and records the spectral and spatial patterns of EM wave modes during RF processing and their relationship to various non-uniformities in plasma density. These data may be analyzed offline by engineers in some embodiments to characterize and classify the behavior of the plasma and enter into a database that may be stored in a plug-in storage device that may be connected to a matching network section or other controller or monitoring system.

[0067] The relationship between the amplitude and phase pattern characteristics of the non-axisymmetric and axisymmetric EM modes and the process and plasma non-uniformities or deviations from proper conditions may be stored in a plug-in that connects to the disclosed signal analysis section of the matching network. In implementations where the RF plasma processing system may be used as a production tool, plasma and process non-uniformities may thereby be rapidly detected as the chamber operation is monitored. For example, a sensor of the disclosed type shown in FIG. 4 configured as shown in FIG. 2 may be incorporated into an RF plasma system as shown in FIG. 1.

[0068] To determine whether the process plasma may have experienced a plasma fault condition, an analysis processor in a signal analysis section associated with the impedance matching network may calculate parameters based in part on the magnitude of the non-axisymmetric EM modes for each of a pre-specified set of harmonics of the drive frequency of some electrodes or antennas. The processor in some embodiments may compare these parameters to reference ranges in a database. Such a reference database may reside in a plug-in connected to the signal analysis section, which may be a section of the impedance matching network or an associated section therewith.

[0069] The database may store parameters characterizing various plasma conditions to help determine how severe the plasma deviation from an acceptable "process window" is. In some embodiments, the analysis may include a comparison of the phase of each harmonic from all sensors or groups thereof at a given distance from the center of the electrode. The change in such phase for a sensor or group of sensors for any orientation may be a measure of the asymmetry of the generation and / or propagation of that harmonic mode, and therefore may be a measure of the asymmetry and non-uniformity of the plasma. In some embodiments, the analysis may include a calculation of the difference in amplitude between sensors or groups of sensors at a given distance from the axis of symmetry. The change in such amplitude for adjacent sensors or groups of sensors in a range of orientations may be a measure of the asymmetry of the generation and / or propagation of that harmonic mode, and therefore may be a measure of the asymmetry and non-uniformity of the plasma.

[0070] Quantitative measures of asymmetry for each of the set of harmonics, parameters, may be stored in the plug-in unit and transmitted to the chamber and tool controllers over a data network. Additionally, trends and rates of increase in parameters may be calculated and compared to baseline values ​​and criteria in a database as part of the process of determining whether a fault condition occurs. In some embodiments, when such a fault condition occurs, algorithms and criteria that may be stored in the plug-in may be executed in a processor present in the compartment to determine a course of remedial or preventative action. Such actions may be rapidly transmitted to the RF generator and / or the chamber and / or tool controller.

[0071] In some embodiments, all such databases of parameters, algorithms, criteria, and specifications for comparing parameters, parameter change rates, and parameter increase rates may reside in a data storage device or removable processor that may be connected to a port that may be an input / output port of the signal analysis section. Analysis of the surface wave modes based on the signals from the sensor and the parameters derived therefrom may be performed very quickly by the processor, and any fault declarations and corrective action commands may be sent to the RF generator and reported to the controller for the chamber or system over a network within 5 milliseconds of occurrence. In some embodiments, the fault condition and specified corrective action commands may be sent to the generator within 1 millisecond.

[0072] In some embodiments, many types of plasma deviations from the desired plasma uniformity may be detected quickly enough that tool or chamber controllers may take action to correct the plasma disturbance condition before a wafer or substrate is misprocessed. In some situations, the specified remedial action may be in the form of RF power, e.g., continuous wave (CW) or pulsed, or powered off completely for a short period of time, or processing of the current wafer may be stopped and the wafer may be stored for later processing or disposal, or the reaction chamber may be powered down for maintenance. Thus, the reflected power may be altered by adjusting the frequency within a range of about ±10% of the RF power.

[0073] In certain embodiments, upon detection of a plasma fault condition, the disclosed signal analysis section associated with the matching network may command appropriate corrective actions to be taken by the RF generator and / or in some embodiments by the matching network. For example, the RF process generator may initiate a termination process to terminate processing of the wafer in response to signals measured by the showerhead and / or pedestal sensors. In specific embodiments, the frequency may be adjusted, i.e., increased or decreased, within a range of about one tenth to ten percent. Alternatively, the power, e.g., pulsed power, may be interrupted by the RF plasma processing deposition system to stop or pulse the plasma such that the secondary plasma is stopped or significantly reduced. In some embodiments, after a very short interruption, the specified remedial action may provide that processing can then continue. In certain embodiments, the remedial action may be determined, for example, through machine learning and / or programmed remedial programs based on yield data or other wafer diagnostics.

[0074] Turning to FIG. 6, a top view of axisymmetric surface wave propagation across a pedestal where the plasma of a reaction chamber according to an embodiment of the present disclosure is axisymmetric is shown. In FIG. 6, the circle 601 is a curve with constant phase and amplitude for the fundamental and harmonic frequency components of the axisymmetric surface wave modes. The circle is concentric with the electrode. These modes are highly dominant when the chamber, electrode and plasma are all axisymmetric and concentric. The propagation vector 602 of the surface wave at any frequency is radial. The wave propagates towards and away from the center, and as the wave propagates, such waves inject power into the plasma.

[0075] Turning now to FIG. 7, a top view of transverse electromagnetic surface wave propagation across an electrode according to an embodiment of the present disclosure is shown. In FIG. 7, the lines of constant phase and equal amplitude 701, 704 for a particular single non-axisymmetric mode are nearly straight and parallel regardless of the fundamental frequency or its harmonics. Such surface waves may be detected by sensors located at the pedestal or showerhead of the RF plasma deposition apparatus. This mode may be referred to as "transverse", meaning that the direction of propagation is from one side to the other or both left and right of the central plane across the electrode surface, as seen by the propagation vectors 705, 707. There may also be other non-axisymmetric modes where the lines of constant phase are curves with a center of curvature offset from the center of the electrode. The detector measurements for each frequency can be decomposed into a sum of the axisymmetric modes and (often a small number of) non-axisymmetric modes that reflect the major inhomogeneities of the plasma. Typically, the decomposition allows for the identification of a transverse mode component and / or one main "off-center" or offset radial mode, either of which is characteristic of the plasma inhomogeneity configuration. Correlation of plasma non-uniformity configurations to specific non-axisymmetric modes is performed prior to production processing as part of a database build that may reside in a plug-in unit or elsewhere.

[0076] Turning now to FIG. 8, a top view of one exemplary azimuth sensor arrangement for a reaction chamber according to an embodiment of the present disclosure is shown. In this embodiment, multiple sensors 800 may be azimuthally arranged around one or more components of the reaction chamber and / or in the reaction chamber itself. As briefly mentioned above, multiple sensors 800, which in this embodiment may be four, may be arranged at various angles about the chamber axis of symmetry 805 and at specific chamber components such as the showerhead and / or pedestal to measure surface voltages or currents associated with surface waves, in this case at 90 degree intervals, but in some embodiments may be at irregular intervals in azimuth.

[0077] The sensors 800 may include passive sensors 800 that acquire a changing electric potential or a magnetic field. The sensors 800 may be positioned in various orientations to detect EM waves having various types of propagation modes relative to the chamber axis of symmetry 805. The sensors 800 may be positioned at equidistant locations around the chamber axis of symmetry 805 and / or components of the reaction chamber or the reaction chamber itself. Similarly, the sensors 800 may be positioned diametrically opposite each other such that the spacing between the sensors 800 and the axis of symmetry is approximately the same. For example, the distance between sensors 800-1 and 800-2 is approximately the same as the distance between 800-3 and 800-4. Similarly, each sensor 800 is positioned at the same distance from the chamber axis of symmetry 805. Examples of spacing and locations of the sensors 800 are discussed in more detail below.

[0078] As shown, the sensors 800 are positioned at diametrically opposed locations. For example, sensor 800-1 is diametrically opposed to sensor 800-3, while sensor 800-2 is diametrically opposed to sensor 800-4. The sensors 800 may find waveform differences for non-axisymmetric plasmas and therefore on different sides of the reaction chamber and / or components thereof, and provide notification as described above when waveform differences occur so that remedial or preventative measures can be taken. For example, if sensors 800-1 and 800-4 detect and report waveform differences from diametrically opposed locations, such differences may provide an indication that harmonics are out of phase or have different amplitudes, thereby indicating that plasma non-uniformities and asymmetries exist. Such waveform differences occur when there is a difference in the relative phase or amplitude of one or more harmonics of signals acquired by diametrically opposed detectors.

[0079] In certain embodiments, four sensors 800 may be used, as shown in FIG. 8. However, in other embodiments, a different number of sensors 800 may be used, such as 6, 8, 12, 14, 16, 18, 20 or more sensors 800. In some embodiments, the azimuth angles between the sensors may not be equal, and yet the same characteristics of the non-azimuthally symmetric plasma mode may be observed by the sensors. In certain implementations, it may be beneficial to have between 6 and 12 sensors 800. With a larger number of sensors 800, more data may be collected, thereby enhancing the ability to discriminate against noise and the sensitivity for identifying non-uniformities. However, increasing the number of sensors 800 may slow down data processing, so that remedial and preventative measures may occur more slowly. Those skilled in the art will appreciate that balancing the number of sensors 800 with the desired level of granularity of the data allows for optimizing the RF plasma process. Thus, it may be beneficial to increase the number of sensors 800 as the speed at which data can be processed increases with increasing computing power. In certain embodiments, certain sensors 800 may be selectively turned off and on, thereby allowing the controller to access certain desired data. For example, in a system having eight sensors, four of the sensors may be selected to be turned off, thereby reducing the amount of data generated. In other embodiments, additional sensors may be added or removed from the operation, thereby changing the amount of data generated.

[0080] The sensor 800 may include various types of sensors, both circular and other geometric shapes. In a particular embodiment, the sensor 800 has a resolution of approximately 0.1 cm 2 and about 10cm 2 The sensor 800 may be circular with an area between 0.1 mm and 0.2 mm. The sensor 800 may further include a surface insulator layer or coating to protect the sensor 800 from the plasma or reactive species of the reaction chamber, and may include other optional coatings and layers such as a Faraday shield for the current sensor, an aluminum coating, etc.

[0081] Turning now to FIG. 9, a vertical cross-sectional view of sensors azimuthally mounted in a reaction chamber according to an embodiment of the present disclosure is shown. In this embodiment, the reaction chamber 940 has an axis of symmetry 905 that extends longitudinally from the center of the showerhead 930 through the pedestal 935. In other embodiments, the axis of symmetry 905 may extend longitudinally from the center of another electrode, such as an antenna. Multiple sensors 900 may be azimuthally positioned at various locations around and within the reaction chamber 940, as well as around or relative to specific components, such as the showerhead 930 and / or the pedestal 935. Because FIG. 9 is a cross-section, only two sensors 900 are shown for each location, although more sensors 900 may be used during the RF plasma monitoring process, as discussed in detail with respect to FIG. 8.

[0082] In certain implementations, the sensor 900-1 may be positioned around the edge or periphery of the showerhead 930. In such implementations, the sensor 900-1 may be positioned at least partially or completely embedded within the showerhead 900-1, and the outer surface of the sensor 900-1 may be coated with an insulating layer to protect the sensor 900-1 from the environment within the reaction chamber 940. In such embodiments, two or more sensors 900-1 may be positioned azimuthally around the edge of the showerhead 930, preferably four or more sensors, thereby enabling detection of non-uniformities and asymmetries in the RF plasma processing.

[0083] In other embodiments, the sensor 900-2 may be disposed along the edge of the pedestal 935 within the vacuum of the reaction chamber 940. As described above with respect to the sensor 900-1, the sensor 900-2 may be partially or completely embedded in the pedestal 935, and the sensor 900-2 may or may not include an insulating layer disposed on its outer surface. Furthermore, in some embodiments, the sensor 900-2 may have a dielectric protection covering the sensor 900-2. In addition to the sensor 900-2 disposed around the pedestal 935 within the vacuum, other sensors 900-3 and 900-4 may be disposed around the pedestal 935 outside the vacuum of the reaction chamber 940. Such sensors 900-3 and 900-4 may be disposed on a metal surface along the pedestal 935 and / or its base portion. The sensor 900 may be disposed on the pedestal 935 or other support structure associated therewith.

[0084] In yet another embodiment, the sensor 900-5 may be located and / or otherwise integrated into the sidewall of the reaction chamber 940. In such an embodiment where the wall is dielectric, the sensor 900-5 may be located on the outer chamber wall 915 outside the reaction chamber 940 or may be integrated into the sidewall such that the sensor 900-5 is within the vacuum of the reaction chamber 940. In the case of a metal wall, the sensor must expose the pickup to the inner surface of the wall so that it can sense the EM field inside the chamber. Another sensor 900-6 may be located on a sight glass 920 located along the outer chamber wall 915. In such an embodiment, the sight glass sensor 900-6 may be located outside the vacuum of the reaction chamber 940 or may be located inside the reaction chamber 940.

[0085] In yet another embodiment, the sensor 900-7 may be disposed in a dielectric located around the showerhead 930, for example, while in other embodiments, the sensor 900-7 may be disposed in a dielectric located around the pedestal 935. Although specific locations of the sensor 900 are discussed herein, the sensor 900 may be disposed in a variety of other locations within and around the reaction chamber 940. For example, the sensor 900 may be disposed inside or outside a dielectric wall near an antenna or other component. The sensor 900 may be disposed in a variety of other locations inside a metal wall of the reaction chamber 940.

[0086] In certain embodiments, a combination of sensors 900-1 through 900-7 may be used to more accurately monitor the RF plasma process. For example, a sensor 900-1 around the edge of the showerhead 930 may be combined with a sensor 900-2 around the edge of the pedestal 935. Similarly, a combination of a sensor 900-5 outside the reaction chamber 940 may be combined with sensors 900-1 / 900-2 located within the reaction chamber 940. In yet other embodiments, 3, 4, 5, 6, 7 or more variations of the combination of sensor 900 locations may be used to further optimize the monitoring of the RF plasma process.

[0087] Turning now to FIG. 10, a vertical cross section of a model reaction chamber is shown according to an embodiment of the present disclosure. In this embodiment, exemplary positions of sensors 1000 are shown positioned at multiple azimuth angles around the lower electrode, which in this example is a pedestal 1035. Similar to the sensors 1000 described above with respect to FIG. 9, FIG. 10 shows the sensors 1000 positioned at various positions. Sensor 1000-1 is positioned around the outer edge of the pedestal 1035. Sensor azimuth positions shown as 1000-2 are positioned around the perimeter within the reaction chamber 1040, and sensor azimuth position 1000-3 is positioned around the perimeter outside the reaction chamber 1040 adjacent to the sight glass.

[0088] In this embodiment, twelve sensors 1000 are shown at each location, however, other embodiments may use fewer and greater numbers of sensors 1000. Also, in addition to the sensor 1000 locations explicitly shown, other sensor 1000 locations may be used to further enhance RF plasma processing.

[0089] 11, a schematic vertical cross-sectional view of a reaction chamber according to an embodiment of the present disclosure is shown. In this embodiment, a sensor 1100 is shown disposed around the antenna of an inductively coupled plasma source 1105. Thus, the sensor 1100 can sense RF current or voltage from a plasma source disposed within the reaction chamber 1140.

[0090] 12, a partial cross section of an RF plasma processing system according to an embodiment of the present disclosure is shown. In this embodiment, RF plasma processing system 1200 includes a pedestal 1235. Pedestal 1235 includes a sensor 1240 disposed along a top outer edge of pedestal 1235. As discussed above, sensor 1240 may be located on the top outer edge, embedded within pedestal 1235, or alternately positioned around the outer edge of either the vacuum or vacuum of the reaction chamber.

[0091] The RF plasma processing system 1200 also includes a circuit 1245 connected to the sensor 1240 via a communication line 1250. When the sensor 1240 receives sensed data from the RF plasma processing system 1200, the data may be transmitted to the circuit 1245 for processing. Because the circuit 1245 is relatively close to the sensor 1240, the time required to transfer the sensed data therebetween may be reduced. Thus, initial calculations regarding the electrical properties sensed by the sensor 1240 may be performed more quickly and then transferred to other components 1255 of the RF plasma processing system 1200. The other components 1255 may include, for example, an RF generator, an impedance matching network, a fault detection section, an operation controller for a reaction chamber, an operation controller for a tool, a plug-in device, a signal analysis section, or other component(s) connected to the RF plasma processing system 1200.

[0092] Any of the components of 1200, 1255, or other components not shown, can adjust aspects of the RF plasma processing system 1200 to correct a disturbance detected by the sensor 1240 and at least partially addressed in the circuitry 1245. The circuitry 1245 may be located in the pedestal 1235 outside the vacuum of the reaction chamber in an isolated configuration to protect the circuitry 1245 from conditions within the reaction chamber. In other embodiments, the circuitry 1245 may be located in the base of the pedestal 1235 or in other areas proximate to the pedestal 1235.

[0093] 12 shows a cross-section of components of RF plasma processing system 1200, one skilled in the art will appreciate that the circuits 1245 may be located at approximately the same radius at various azimuth angles around the pedestal 1235. Thus, a separate circuit 1245 may be available for each sensor 1240, or the sensors 1240 may be connected to a centralized circuit 1245 located at one or more selected locations around and / or within the pedestal 1235.

[0094] 13, a partial cross-sectional view of an inductively coupled RF plasma processing system is shown in accordance with an embodiment of the present disclosure. A sensor 1340 is shown configured proximate to the inductive antenna 1330 and may be mounted on the exterior or interior of a dielectric wall (not shown) adjacent to the antenna.

[0095] In a particular embodiment, a method of the present application can provide for detection of plasma non-uniformity in an RF plasma processing system. The method may include generating a plasma in a reaction chamber of the RF plasma processing system and detecting electrical signals from the plasma in a frequency range from a frequency of a RF power sustaining the plasma to about 10 times the frequency with a plurality of sensors arranged azimuthally about an axis of symmetry of the chamber of the RF plasma processing system. The electrical signals may include at least one of a voltage and a current generated by an electromagnetic surface wave.

[0096] In operation, the method may further include comparing waveforms of electrical signals acquired from the plasma by the multiple sensors and determining when plasma non-uniformity occurs based on a comparison of the electrical properties of the plasma detected by each of the multiple sensors. In certain implementations, the comparing may include comparing amplitudes of at least one radio frequency harmonic picked up by at least two different sensors. In certain implementations, the comparing may include comparing phases of at least one radio frequency harmonic acquired by at least two sensors separated by an azimuth angle of at least 90 degrees about the chamber axis of symmetry. In yet another embodiment, the method may include determining azimuth variations of signals from the multiple sensors that increase in time over a period of time greater than 10 microseconds.

[0097] Determining may further include Fourier analyzing signals from the plurality of sensors at different azimuth angles and comparing the change in at least one of the amplitude and phase of the one or more frequency components for the plurality of sensors to a reference value in a plasma control database. Determining that a non-uniformity has occurred may consist in finding an increase over a time period of at least 100 microseconds, and / or determining may include calculating the plasma non-uniformity from an azimuth change in the amplitude and phase of at least one harmonic of the frequency of the radio frequency power sustaining the plasma. Aspects of the present disclosure may further include the non-uniformity comprising a variation in plasma density as a function of orientation about an axis of symmetry of the chamber.

[0098] In operation, aspects of the disclosure may include a method of detecting plasma non-uniformity in a radio frequency plasma processing system. The method may include generating a plasma in the radio frequency plasma processing system. The method may further include detecting electrical signals from the plasma at multiple frequencies that are integer multiples of at least one radio frequency excitation frequency using multiple broadband radio frequency sensors azimuthally positioned about a chamber axis of symmetry of the radio frequency plasma processing system. Particular implementations may include determining asymmetry of the plasma based on detecting at least one azimuthal variation of multiple detected frequency components of the electrical signals.

[0099] In the foregoing description, for purposes of explanation, specific nomenclature has been used to provide a thorough understanding of the present disclosure. However, it will be apparent to one skilled in the art that specific details are not required to practice the systems and methods described herein. The foregoing description of the specific embodiments has been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present disclosure to the precise forms described. Obviously, many modifications and variations are possible in light of the above teachings. The embodiments are shown and described to best explain the principles and practical application of the present disclosure and to enable those skilled in the art to best utilize the present disclosure and various embodiments with various modifications as appropriate for the particular use contemplated. It is intended that the scope of the present disclosure be defined by the following claims and their equivalents. The inventions disclosed herein include the following: [Aspect 1] 1. A system for detecting changes in a plasma in a radio frequency plasma processing system, comprising: a reaction chamber having a chamber axis of symmetry; one or more plasma power supply devices for supplying radio frequency power to the plasma in the reaction chamber; a plurality of broadband radio frequency sensors azimuthally disposed about the chamber axis of symmetry for detecting electromagnetic signals associated with the plasma in the reaction chamber; at least one detector, which is a Fourier transform processor coupled to at least one of the plurality of broadband radio frequency sensors; a computational processor coupled to the at least one detector; A system comprising: [Aspect 2] The system of embodiment 1, wherein the plurality of broadband radio frequency sensors are arranged with respect to the radio frequency plasma power supply device at three or more spaced azimuth angles centered on the chamber axis of symmetry and approximately equidistant from the chamber axis of symmetry. [Aspect 3] 2. The system of embodiment 1, further comprising one or more radio frequency generators connected to the computational processor, at least one of the radio frequency generators being adjustable in response to receiving a signal from the computational processor. [Aspect 4] The system of aspect 1, further comprising at least one radio frequency detector connected to at least one of the plurality of wideband radio frequency sensors and configured to provide a digital output to a port connected to the computational processor. [Aspect 5] 5. The system of embodiment 4, wherein the at least one detector is connected to a removable storage medium. [Aspect 6] The system of embodiment 5, wherein the storage medium includes at least one of instructions, algorithms, and data for generating an output that is an eccentricity of at least one frequency component of an electromagnetic wave. [Aspect 7] 1. A method for detecting plasma non-uniformity in a radio frequency plasma processing system, comprising: generating a plasma in a reaction chamber of the radio frequency plasma processing system; detecting electrical signals from the plasma in a frequency range from the frequency of the plasma sustaining radio frequency power to approximately ten times the frequency with a plurality of sensors arranged azimuthally about a chamber symmetry axis of the radio frequency plasma processing system; comparing waveforms of electrical signals acquired from the plasma by the plurality of sensors; determining when a plasma non-uniformity occurs based on a comparison of the electrical characteristics of the plasma sensed by each of the plurality of sensors; A method for providing the above. [Aspect 8] 8. The method of embodiment 7, wherein the comparing comprises comparing an amplitude of the at least one high frequency harmonic acquired by at least two different sensors. [Aspect 9] 8. The method of embodiment 7, wherein the comparing comprises comparing the phase of at least one high frequency harmonic acquired by at least two sensors separated by an azimuth angle of at least 90 degrees about the chamber axis of symmetry. [Aspect 10] 8. The method of embodiment 7, wherein the non-uniformity comprises a variation in plasma density as a function of orientation about the chamber axis of symmetry. [Aspect 11] 8. The method of embodiment 7, wherein the determining comprises determining an orientation variation of signals from the plurality of sensors that increases over time over a period of time greater than 10 microseconds. [Aspect 12] 8. The method of claim 7, wherein the electrical signal is at least one of a voltage and a current generated by an electromagnetic surface wave. [Aspect 13] The method of embodiment 7, wherein the determining comprises Fourier analyzing signals from the plurality of sensors at different azimuth angles from each other, and comparing changes in at least one of the amplitude and phase of one or more frequency components of the plurality of sensors with reference values ​​in a plasma control database. [Aspect 14] 14. The method of embodiment 13, wherein determining that non-uniformity has occurred consists in finding an increase over a time period of at least 100 microseconds. [Aspect 15] 8. The method of embodiment 7, wherein the determining comprises calculating the plasma non-uniformity from azimuthal changes in amplitude and phase of at least one harmonic of a frequency of a radio frequency power sustaining the plasma. [Aspect 16] 1. A method for detecting plasma non-uniformity in a radio frequency plasma processing system, comprising: generating a plasma in the radio frequency plasma processing system; detecting electrical signals from the plasma at a plurality of frequencies that are integer multiples of at least one of the RF excitation frequencies using a plurality of broadband RF sensors azimuthally arranged about a chamber axis of symmetry of the RF plasma processing system; determining an asymmetry of the plasma based on detecting an orientation variation of at least one of a plurality of detected frequency components of the electrical signal; A method for providing the above. [Aspect 17] 17. The method of embodiment 16, wherein the determining occurs in about 10 milliseconds or less. [Aspect 18] 17. The method of embodiment 16, wherein the plurality of broadband radio frequency sensors comprises at least four sensors, with at least one sensor in each azimuthal quadrant about the chamber axis of symmetry. [Aspect 19] 17. The method of embodiment 16, wherein the plurality of wideband radio frequency sensors are positioned around a plasma power device. [Aspect 20] 17. The method of embodiment 16, wherein the plurality of broadband radio frequency sensors are azimuthally positioned at approximately equal angular intervals about the chamber axis of symmetry and approximately equal distances from the chamber axis of symmetry.

Claims

1. 1. A system for detecting plasma non-uniformity in a radio frequency plasma processing system, comprising: a reaction chamber having a chamber axis of symmetry; one or more plasma power supply devices for supplying radio frequency power to the plasma in the reaction chamber; a plurality of sensors azimuthally disposed about the chamber axis of symmetry for detecting electrical signals from the plasma in a frequency range from the frequency of the radio frequency power sustaining the plasma to about ten times the frequency; at least one detector, which is a Fourier transform processor coupled to at least one of the plurality of sensors; a computational processor coupled to the at least one detector; Equipped with The system further comprises a computational processor that compares waveforms of electrical signals obtained from the plasma by the plurality of sensors and determines when plasma non-uniformity occurs based on a comparison of the electrical characteristics of the plasma detected by each of the plurality of sensors.

2. The system of claim 1 , wherein the plurality of sensors are azimuthally spaced at approximately equal angular intervals about the chamber axis of symmetry and approximately equidistant from the chamber axis of symmetry.

3. The system of claim 1 , further comprising one or more radio frequency generators coupled to the computational processor, at least one of the radio frequency generators being adjustable in response to receiving a signal from the computational processor.

4. The system of claim 1, wherein the at least one detector is configured to provide a digital output to a port connected to the computational processor.

5. The system described in claim 4, wherein at least one detector is connected to another storage medium.

6. The system of claim 5 , wherein the storage medium includes a database that stores parameters characterizing various plasma conditions.

7. 1. A method for detecting plasma non-uniformity in a radio frequency plasma processing system, comprising: generating a plasma in a reaction chamber of the radio frequency plasma processing system; detecting electrical signals from the plasma in a frequency range from the frequency of the plasma sustaining radio frequency power to approximately ten times the frequency with a plurality of sensors arranged azimuthally about a chamber symmetry axis of the radio frequency plasma processing system; comparing waveforms of electrical signals acquired from the plasma by the plurality of sensors; determining when a plasma non-uniformity occurs based on a comparison of the electrical characteristics of the plasma sensed by each of the plurality of sensors; A method for providing the above.

8. The method of claim 7 , wherein the comparing comprises comparing an amplitude of at least one high frequency harmonic acquired by at least two different sensors.

9. 8. The method of claim 7, wherein the comparing comprises comparing a phase of at least one high frequency harmonic acquired by at least two sensors separated by an azimuth angle of at least 90 degrees about the chamber axis of symmetry.

10. The method of claim 7 , wherein the non-uniformity comprises a variation in plasma density as a function of orientation about the chamber axis of symmetry.

11. The method of claim 7 , wherein said determining comprises determining an orientation variation of signals from said plurality of sensors that increases with time over a period of time greater than 10 microseconds.

12. The method of claim 7 , wherein the electrical signal is at least one of a voltage and a current generated by an electromagnetic surface wave.

13. 8. The method of claim 7, wherein the determining comprises: Fourier analyzing signals from the plurality of sensors at different azimuth angles; and comparing changes in at least one of amplitude and phase of one or more frequency components of the plurality of sensors to reference values ​​in a plasma control database.

14. 14. The method of claim 13, wherein determining that non-uniformity has occurred consists in finding an increase over a time period of at least 100 microseconds.

15. 8. The method of claim 7, wherein said determining comprises calculating plasma non-uniformity from azimuthal changes in amplitude and phase of at least one harmonic of a frequency of radio frequency power sustaining the plasma.

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