Wideband sensor for electromagnetic waves

Abstract

A wideband sensor for a radio frequency plasma processing system includes a capacitive pickup for an electrical potential disposed on a conductive component of a reaction chamber, the wideband sensor also including leads with a circuit, the leads connecting the pickup to a connector attached to an electrically grounded plate proximate the pickup having an electrical resistance of the circuit and a capacitance to electrical ground of the connector such that the pickup voltage differs from the surface voltage of the conductive component by less than 5%, and an attenuator circuit connected to the connector, the attenuator circuit including at least one current-limiting resistor in series from the attenuator input to the attenuator output, the wideband sensor having detection in a radio frequency range of about 10 kHz to at least about 1 GHz for radio frequency potential measurements in a radio frequency plasma processing system.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Patent Application No. 62 / 959,611, filed January 10, 2020, and U.S. Non-Provisional Patent Application No. 17 / 144,983, filed January 10, 2021, the contents of which are incorporated herein by reference. [Background technology]

[0002] Radio frequency (RF) plasma-enhanced processing is widely used in semiconductor manufacturing to etch different types of films, deposit thin films at low to moderate processing temperatures, and perform surface treatment and cleaning. Such processes are characterized by the use of plasma, i.e., partially ionized gases, which are used to generate neutral species and ions from precursors in a reaction chamber, provide energy for ion bombardment, and / or perform other actions. Controlling the plasma density during such processes presents challenges, and plasma non-uniformity within the reaction chamber can affect wafer processing uniformity and the yield of manufactured integrated circuits or other devices. Summary of the Invention

[0003] Non-uniform plasma density within a reaction chamber can cause non-uniform etch rates or specific characteristics across a substrate. In certain systems, this is done using a probe to monitor the uniformity of plasma density within the reaction chamber. Such probes may be exposed to the coating-dependent plasma environment and may use active electronics to infer plasma density. Such systems may take several milliseconds or longer to respond to changes in the plasma. Optical emission spectroscopy can also be used to determine the plasma density profile within the reaction chamber; however, such systems require multiple lines of sight through the plasma and require complex analysis to infer non-uniformity. Neither of these techniques is sensitive enough, fast enough, or costly enough to implement to effectively resolve non-uniformity issues. [Brief explanation of the drawings]

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

[0005] [Figure 1] FIG. 1 is a schematic diagram of a side view of an RF plasma processing system according to an embodiment of the present disclosure. [Figure 2] 1A-1C are schematic side views of a plasma chamber with high bandwidth sensors mounted at various locations on an electrode, according to an embodiment of the present disclosure. [Figure 3] FIG. 10 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, according to an embodiment of the present disclosure. [Figure 4] FIG. 2 is a cross-sectional view of a pedestal with an embedded high bandwidth voltage sensor according to an embodiment of the present disclosure. [Figure 5]FIG. 2 is a cross-sectional view of a pedestal with an embedded high bandwidth voltage sensor according to an embodiment of the present disclosure. [Figure 6] FIG. 2 is a cross-sectional view of a pedestal with an embedded high bandwidth voltage sensor according to an embodiment of the present disclosure. [Figure 7] FIG. 2 is a cross-sectional view of a pedestal with an embedded high bandwidth voltage sensor according to an embodiment of the present disclosure. [Figure 8] FIG. 2 is a schematic side view of a pedestal according to an embodiment of the present disclosure. [Figure 9] 1 is a top view of axisymmetric surface wave propagation across a pedestal with which the plasma in the reaction chamber is axisymmetric, according to an embodiment of the present disclosure. FIG. [Figure 10] FIG. 1B is a top view of a transverse electromagnetic surface wave propagation across an electrode according to an embodiment of the present disclosure. [Figure 11] FIG. 1 is a top cross-sectional view of a sensor mounted azimuthally (about the chamber axis of symmetry) above a reaction chamber, according to an embodiment of the present disclosure. [Figure 12] FIG. 1 is a cross-sectional side view of a sensor azimuthally attached to an electrode, electrode base, top dielectric plate, viewport, and dielectric wall of a reaction chamber according to an embodiment of the present disclosure. [Figure 13] FIG. 1 is a cross-sectional side view of a capacitively coupled plasma reaction chamber with several sensor array locations, according to an embodiment of the present disclosure. [Figure 14] FIG. 1 is a cross-sectional side view of a model inductive plasma reaction chamber according to an embodiment of the present disclosure. [Figure 15] 1 is a schematic partial cross-sectional side view of an RF plasma processing system with several possible sensor locations, according to an embodiment of the present disclosure. [Figure 16] 1 is a schematic partial cross-sectional view of an RF plasma processing system including a dielectric wall with a sensor mounted on the dielectric surface proximate to an inductively coupled antenna, according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0006] Illustrative examples of the claimed subject matter are disclosed herein. In the interest of clarity, not all features of an actual implementation are described in this specification. It is understood that the development of such an actual implementation may involve numerous implementation-specific decisions to achieve developer-specific goals, including compliance with system- and business-related constraints, which will 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.

[0007] Furthermore, as used herein, the article "a" is intended to have its ordinary meaning in the patent art, i.e., "one or more." As used herein, the term "about" when applied to a value generally means within the tolerance of the equipment used to generate the value, or in some instances, to the extent of 10%, or to the extent of 5%, or to the extent of 1%, unless otherwise specified. Furthermore, as used herein, the term "substantially" means, for example, most, or almost all, or all, or an amount in the range of about 51% to about 100%. Additionally, the examples herein are for illustrative purposes only and are presented for discussion purposes, not as limitations.

[0008] 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 matching network 115, a second impedance matching network 120, a sheath 125, a plasma power device such as a showerhead 130 or equivalent powering element such as an electrode, and a pedestal 135. As used herein, a plasma power device 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, as well as antennas.

[0009] The RF plasma processing system 100 may include one or more RF generators 105, 110 that supply power to a reaction chamber 140 through one or more impedance matching networks 115, 120. RF power flows from a first RF generator 105 through the impedance matching network 115 to a plasma in the reaction chamber 140, a showerhead 130 or sidewall, an electrode other than the showerhead 130, or an inductive antenna (not shown) that electromagnetically supplies power to the plasma. Here, power flows from the plasma to a ground and / or pedestal 135 and / or a second impedance matching network 120. Generally, the first impedance matching network 115 compensates for variations in load impedance in the reaction chamber 140 so 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., 50 ohms, by adjusting a reactive component, e.g., a variable capacitor, in the first impedance matching network 115. Additionally, adjusting the frequency within about a ten percent range of the RF power can modify the reflected power.

[0010] In particular embodiments, the first RF generator 105 may provide power at an RF frequency between approximately 400 kHz and 150 MHz, while the second RF generator 110 connected to the pedestal 135 may provide power at an RF frequency lower than the RF frequency of the first RF generator 105. However, in certain implementations, the second RF generator 110 may not provide power at an RF frequency lower than the RF frequency of the first RF generator 105. Typically, the frequencies of the first and second RF generators 105, 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. Also, one or more of the first and second RF generators 105, 110 may adjust their frequency to modify reflected power.

[0011] The impedance matching networks 115, 120 are designed to adjust their internal reactive elements so that the load impedance matches the source impedance. While low reflected power is generally considered positive, embodiments of the present disclosure may be configured such that the supplied power is maintained within the reaction chamber 140 and reflected toward the first and second RF generators 105, 110, and the reflected power is relatively high. The associated impedance matching networks 115, 120 monitor the forward and reflected power to and from the reaction chamber 140 and use a motor-driver system to adjust an adjustable reactive element, such as a vacuum variable capacitor. In certain embodiments, an electronically controlled capacitor, such as a pin diode, can be used for the electronic variable capacitor. The impedance matching networks 115, 120 may include circuitry for measuring the signal phase and magnitude to determine the level 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 changed until the reflected power is minimized, for example, by less than about 5 watts and / or less than about 1 percent over the period, or in certain embodiments, by less than 1 watt. Additionally, the frequency may be adjusted within about a 10 percent range of the RF power to correct for the reflected power. Typically, harmonic frequency signals are not measured, including reflected power at harmonic frequencies.

[0012] While RF plasma processing systems 100 have many advantages, they have historically been challenged in maintaining control of plasma density throughout multi-step processes. For example, design tolerances of non-uniformity on the order of 1% remain a challenge, even for density ranges on the same order relative to the nominal value. As feature sizes shrink to less than approximately 3 nm and layer thicknesses become less than approximately 10 nm, achieving optimal integrated circuit (IC) yields on every wafer requires tight control of plasma and neutral uniformity, down to the 1% level and even less. Non-uniform plasma density, or average densities that deviate from desired values ​​beyond desired ranges within a reaction chamber, can be caused by slow chamber variations, RF circuit variations, or rapid growth (on the order of less than 1 millisecond) of parasitic or secondary plasmas, which can lead to non-uniform etch rates and therefore non-uniform nanoscale features across processed wafers.

[0013] Because even a one percent etch rate difference across a wafer can cause yield issues for advanced technologies, and because it often takes a significant amount of time to complete wafer processing to confirm yield loss, non-uniform plasma densities or plasma densities that deviate from the desired range within the reaction chamber must be detected quickly and accurately in a period that may need to be less than about one millisecond to avoid irreversible deviation of the wafer from the desired feature profile.

[0014] Those skilled in the art will understand that electromagnetic (EM) surface waves can propagate on surfaces within the RF-driven plasma in the reaction chamber 140. These surface waves have significant energy at both the fundamental RF driving frequency and RF harmonics. The average power and power distribution of the harmonics are sensitive functions of plasma density and nonuniformity. Herein, a harmonic profile is defined as the spectrum of surface waves with frequencies that are integer multiples of the fundamental driving frequency of the RF plasma-based reaction chamber 140. For example, if a 2 MHz RF driving 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 internal reaction chamber 140 surface. Adjusting the frequency in the range of 10 percent of the RF power may thereby modify the reflected 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, 6, or 8 MHz. Both odd and even harmonics (2nd, 3rd, 4th, 5th, etc.) may be present, although in some embodiments odd harmonics may dominate.

[0015] Aspects of the present disclosure provide sensor locations around the reaction chamber 140 and its components that can detect and analyze RF surface waves to find the amplitude and phase of fundamental and harmonic waves at multiple points within or adjacent to the reaction chamber 140. The fundamental and harmonic waves can be detected by sensing RF voltage or current at the fundamental and harmonic frequencies on the surface of the chamber components. In some embodiments, sensors for voltage may include pickups configured on the surface of an electrode, pedestal base, chamber wall, or strap, and adjacent conductors that transmit signals from the pickup to a connector or cable. Current sensors may include a conductive element including one or more loops, partial loops, or linear conductors, with one end of the conductive element at a reference potential, which may be the local electrical ground.

[0016] Multiple sensors, e.g., two or more sensors, may be located on particular chamber components, described in detail below, at different angles about the chamber axis of symmetry to measure surface voltages or currents associated with such surface waves, where the angle measured from a reference point of the chamber about the axis of symmetry is defined as the azimuthal angle. In some embodiments, such sensors may be located at approximately the same distance from the chamber axis of symmetry.

[0017] The sensors may be mounted at various locations in or around 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 base of an electrode, either in a vacuum or outside of a vacuum environment. The sensors may be mounted within the chamber, on one or more metal wall surfaces of the reaction chamber 140, inside or outside wall regions containing dielectric materials, or on antennas that can be used to inductively power the plasma. The sensors may also be located near the plasma boundary, or on multiple conductive buses or straps that connect the first or second impedance matching networks 115, 120 to electrodes, such as the pedestal 135 and / or the showerhead 130, antennas, or other components that transfer power to the plasma in the reaction chamber 140, or on passive antennas that can sense nearby EM waves. The sensors may also be connected to electrical ground, allowing the sensors to receive signals from different parts of the RF plasma processing system 100 as the signals propagate along the surfaces of the respective components.

[0018] A spectrum of RF harmonics is generated at the electrode-plasma interface, e.g., sheath 125 in Figure 1. Because RF harmonics propagate in all directions, both the amplitude and phase of all wave components vary with position on the electrode or support base. These RF harmonics also propagate along the inner surfaces 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 plasma changes, e.g., plasma density and inhomogeneities, with response times on the order of a few microseconds or less. Furthermore, the frequency and phase distribution of RF harmonic surface waves propagating at the electrode-plasma interface determines the frequency and phase distribution of RF harmonic surface waves propagating along the surface of the electrode base toward the electrode or plasma-wall interface, or the surface impedance matching network 115, 120 connected to the wall. The amplitude and phase of the fundamental and harmonic signals at different sensor locations allow us to determine which portions of the total EM wave field at each frequency are azimuthally symmetric and which portions are asymmetric.

[0019] 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 distributions of both the fundamental and harmonic RF waves can be monitored on microsecond and longer timescales using such surface-mounted sensors and compared to specified range and phase relationships as indicators of plasma asymmetry or changes in plasma density or electrical conductivity. The signals from such sensors may be transmitted by cable or otherwise to a detector that analyzes the component frequencies of the signal and generates amplitude and phase values ​​for each frequency component at each sensor location.

[0020] In certain implementations, the amplitude and phase of the detected RF harmonic components can be rapidly determined by circuitry (detectors) within the signal analysis component, which may be a separate metal box or chassis, or part of or connected to the impedance matching networks 115, 120. Such amplitude and phase can be used to determine the plasma's status, including its radial distribution and asymmetry, by applying algorithms and plasma nonuniformity calibration. The signal from the sensor is then Fourier-analyzed by dedicated circuitry (detectors) fast enough to perform virtually continuous spectral analysis, updating as frequently as possible to generate a high-speed data stream. For example, for a 13.56 MHz plasma power, 512 periods can take less than 50 microseconds to process with Fourier analysis; for a pulsed plasma where each element of the pulse occurs at 5 kHz, this allows the plasma status to be updated at a rate of 10 kHz.

[0021] The results of the dedicated Fourier analysis of the fundamental and harmonics may be stored in a separate storage medium, which is read and / or written by an 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 asymmetry parameters for each of the fundamental and harmonics. The asymmetry parameters may be compared to previously stored values ​​in the separate storage medium (or a different storage medium) using an algorithm (which may also be stored in the separate storage medium or a different storage medium) to very quickly recognize a "plasma fault" condition. The analysis processor may then send appropriate commands, for example, to continue the process under current conditions or to make the necessary changes to the process conditions to the first and second RF generators 105, 110, and in certain implementations, two or more RF generators and, if appropriate, the impedance matching networks associated with these generators. In certain implementations, three, four, or more RF generators may be used. The first and second RF generators 105, 110 may then respond by continuing, stopping, varying the power provided, changing the frequency by about 10 percent of the RF power to modify the reflected power, or in any other appropriate manner, such as entering a low power or pulse mode to avoid improper wafer processing during plasma failure or other unacceptable condition, or may command certain corrective action, such as triggering an alarm, shutting down power, etc.

[0022] In some embodiments, the location of the sensor for detecting and characterizing the surface waves (electric and magnetic fields) may be on the peripheral surface (bare or covered by a dielectric) of the pedestal 135 outside the area covered by the wafer. For example, when the reaction chamber 140 processes circular wafers with a 150 mm radius, the pedestal-mounted sensor may be located at a radius greater than 150 mm from the wafer center, and in some cases, it may be located under the annular peripheral dielectric to control edge effects. Additionally or alternatively, the sensor may be located on or around the surface of the showerhead 130 facing the wafer, or on the base of the pedestal 135 or the surface of the base of the showerhead 130, regardless of whether these locations are inside or outside the vacuum process environment. Sensors can also be located in various other locations, described in detail below, and can be continuously or periodically monitored to provide process plasma uniformity.

[0023] By using sensors outside the vacuum process environment, for example, in a strap or bus connecting the base to one or more of the impedance match networks 115, 120, the base of the pedestal 135 and / or showerhead 130 may not require passing signals through a vacuum feedthrough or installing transmission cables within the vacuum volume of the reaction chamber 140. Sensors in such locations can substantially continuously monitor fundamental and harmonic EM waves. This allows the RF plasma processing system 100 to continuously provide plasma density uniformity and determine within a very short time whether a fault condition has occurred or whether proper wafer or substrate processing will continue.

[0024] In certain exemplary implementations, the present disclosure may provide apparatus and methods 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. The reaction chamber 140 includes a showerhead 130 for injecting reactant gases into the reaction chamber 140 and may also 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 near an approximate axis of symmetry of the reaction chamber 140 and equipped with multiple sensors positioned at selected azimuthal angles about the axis of symmetry. Additionally or alternatively, such sensors may be positioned on the wafer-facing surface of the showerhead 130 in a peripheral region to detect and measure EM surface waves propagating while the wafer is being processed.

[0025] Additionally, in some embodiments, there may be multiple sensors mounted on the exterior surface of the wafer support pedestal 135, outside the area occupied by the wafer, to detect both the amplitude and phase of RF harmonic and fundamental surface waves. Such sensors may be exposed to the plasma or covered with a dielectric or dielectric-metal cover. Additionally or alternatively, sensors may be positioned around the periphery of the pedestal 135 base, inside or outside the evacuated volume, and / or below the plane determined by the wafer. In some implementations, sensors may be positioned on the pedestal base to detect surface electromagnetic waves propagating toward the wafer support region of the pedestal or at the surface of the pedestal base. In certain embodiments, sensors may be mounted close to the wafer surface (e.g., less than 10 centimeters).

[0026] Alternatively, the sensor may be mounted on a portion of the pedestal 135 that is made of metal or another conductive material and located outside the vacuum region of the reaction chamber 140 at atmospheric conditions. Sensors located outside the vacuum region may be mounted on a region of the pedestal 135 at a radius from the pedestal symmetry axis that is at least 50% of the maximum pedestal 135 radius, or greater than 75% of the maximum pedestal 135 radius. Such a sensor, in some embodiments, may be located near the support pedestal 135, for example, within a few centimeters of a vacuum seal for an O-ring. 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 in some embodiments, less than about 15 cm, or even about 10 cm. Specific locations and orientations of sensors according to embodiments of the present disclosure are discussed in detail below.

[0027] Referring to FIG. 2, a schematic side view of a plasma chamber with high-impedance sensors attached to various locations on the electrodes is shown, according to an embodiment of the present disclosure. Each of the two components functioning as electrodes—the pedestal 235 and the showerhead 230, or equivalent other powered element—can use a separate RF generator 205 or 210 and impedance matching networks 215 and 220. Alternatively, the electrode may have multiple generators and matching networks powering it. Arrow 245 along the surface of the pedestal 235 indicates the inward radial flow of RF current and power from the bottom (bias) RF generator 210, which is electrically connected to the pedestal 235 via the impedance matching network 220. The generated electric field along the underside of the showerhead 235 or other powered element, and ultimately along the selective ground circuitry in the impedance matching network 215 for the showerhead 230 or other powered element, contributes to the formation of a plasma (not shown) between the electrodes and the radially outward counterflow of current and power, indicated by arrow 250.

[0028] In certain embodiments, a reaction chamber 240 having RF power from first and second RF generators 205, 210 and impedance match networks 215, 220 may include sensors 255 around the periphery of a pedestal 235, which may be covered by a dielectric 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 received by each sensor 255.

[0029] In some implementations, the Fourier analysis circuitry can calculate the magnitude and phase of the fundamental and higher harmonics of a periodic electromagnetic surface waveform. The resulting series of magnitudes is called a Fourier series, and their phases are derived from the relationship between the time-domain and frequency-domain functions.

[0030] Additionally, some embodiments of the disclosed matching network 220 include a signal analysis section 275, or adjunct to the matching network 220, that is separate and RF-isolated from the RF power processing and impedance matching circuitry or components of the matching network 220. The signal analysis section 275 may include a Fourier analysis circuit (detector) for analyzing the sensor signal and generating digital amplitudes and phases of the RF fundamental and harmonics. The signal analysis section 275 may also include a high-speed digital logic or computational processor for analyzing the relative magnitudes and phases of the signal at harmonic frequencies and deriving quantitative parameters characterizing the relative magnitudes of the axially symmetric and non-axially symmetric harmonic components at each frequency and their relative phases. Furthermore, in some embodiments, the disclosed matching network 220 may be connected via a very high-speed network to the second RF generator 210 and to a controller (not shown) of 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 communicating its calculated parameters to a process chamber controller and / or a tool control system.

[0031] Additionally, another first RF generator 205 and impedance match network 215 may also be electrically coupled to another electrode, which may be a showerhead 230, within the reaction chamber 240. In one implementation, the first RF generator 205 may operate at a different frequency than the second RF generator 210, although that frequency may not be an integer multiple of the frequency of the second RF generator 210.

[0032] Similarly, the impedance match network 215 can monitor the reflected power from the electrode and the process chamber 240 and make adjustments if there is a large reflected power from the electrode. In some embodiments, the second RF generator 210 can be a 400 kHz RF generator, a 2 MHz RF generator, or a 13.56 MHz RF generator, or others, while the first RF generator 205 can operate at a somewhat higher frequency. In some embodiments, the first RF generator 205 can operate at a frequency greater than 25 MHz, for example, 60 MHz, 100 MHz, or higher.

[0033] In one embodiment, the primary function of the first RF generator 205 is to supply power to the reaction chamber 240 to generate a plasma between the showerhead 230 or another power source, such as an electrode and the pedestal 235, both of which generate reactive species such as fluorine, chlorine, and compositions thereof, and to accelerate ions from the generated plasma to bombard a wafer positioned on the pedestal 235.

[0034] A set of sensors 280 may be located on the upper electrode surface, i.e., showerhead 230, facing the lower electrode, i.e., pedestal 235, and have 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 ohms, and in some embodiments, greater than 500 ohms. Sensors 280 may be voltage or current sensors, or may combine both functions 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.

[0035] In some embodiments, the sensors 280 have electrical connections to a Fourier analysis circuit within the signal analysis section 285 of the impedance matching network 215. The Fourier analysis circuit can output the amplitude and phase of different frequency components from each of the sensors 280 and compare them to the other sensors 280 and / or reference levels stored in memory. Analysis of the signals in some embodiments may include artificial intelligence (AI) using pattern recognition of amplitude and / or phase, or learning algorithms that may use neural networks or conventional digital algorithmic processing of the signals from the sensors 280.

[0036] Signal processing by Fourier analysis circuitry to find fundamental and harmonic component signals of both amplitude and phase can be performed in less than about 10 microseconds, and in preferred embodiments, in 1 microsecond or less for each of the sensor signals. The isolated signal analysis section 285 of the impedance match network 215 can incorporate at least one computational or logic processor having substantial computing power with ultra-fast (<1 ns cycle time) circuitry using ultra-fast logic ICs. In some embodiments, the processor in the signal analysis section 285 is programmable, so that suppliers or users of the process chamber 240 can provide or implement their own algorithms or analysis software on the computing "platform" provided by the impedance match network 215.

[0037] In some embodiments, software programs for calculating parameters from the signal amplitude and phase, and additional logic algorithms for determining the impact on process uniformity of deviations from acceptable plasma conditions, may reside in a removable "plug-in" component that includes data storage and connects to the signal processing compartment. This software or logic calculates the range of deviations in the RF electromagnetic surface wave spectrum from the characteristics of nominal or proper operating conditions. Based on this, a processor associated with the controller can "decide" on corrective action or termination of the process within approximately 1 millisecond before a wafer is erroneously processed. In some embodiments, a quantitative determination regarding the expected effect of the deviation on process uniformity or other characteristics can be made within approximately 500 microseconds of occurrence, so that remedial action can be initiated within 1 millisecond. Furthermore, action can be taken to ensure minimal or no damage to the wafer or substrate currently being processed in the reaction chamber 240, thereby avoiding yield loss for that wafer or substrate.

[0038] The evaluation and / or determination made in the signal analysis section 285 of the impedance matching network 215 can, in some embodiments, be performed by a very fast computing or analysis system using algorithms resident on plug-in storage and / or removable data processing devices. In yet other embodiments, the evaluation and determination made in the signal analysis section 285 can be performed using analog or neural net-type processors. Such determinations can further utilize decision algorithms that may reside on removable storage or processing devices. Corrective action instructions can then be quickly transmitted over high-speed data lines from the section 275 of the impedance matching network 215 to the RF generator 205, thereby temporarily interrupting, changing, or terminating power or modifying the RF frequency to the plasma. This ensures that factory management can quickly implement or plan corrective actions for the process chamber 240 and RF plasma processing system 200.

[0039] 2 shows a set of sensors 290 configured on the exterior surface of the base 295 of the showerhead 230, outside the vacuum region within the reaction chamber 240 at atmospheric conditions. In some embodiments, additional sensors 296 may be mounted on a pedestal base 297 and connected to the disclosed signal processing section 275 of the impedance matching network 220 by high-speed signal cables, similar to the sensors 290. Sensors 296 located outside the vacuum environment of the reaction chamber 240 are substantially less expensive and less difficult to integrate into information and processing networks, since a vacuum supply is not required.

[0040] The sensors 255 may be arranged in several configurations to sense 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, due to their proximity to the wafer and / or substrate, may have the advantage of sensitivity in detecting certain modes of EM surface waves that are indicative of plasma asymmetries, which are important types of plasma non-uniformity. These in-chamber sensors 255 may use communication lines that pass through the vacuum wall via feed-throughs, or in some embodiments, use wireless communication links operating at optical or lower frequencies.

[0041] 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 can be determined by analyzing signals from any of the groups of voltage, current, phase, or combination sensors 255, 280, 290, and 296. Generally, EM surface waves of a particular frequency generate voltage and current signals that have phase relationships 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 supplied symmetrically and the plasma is axisymmetric, axisymmetric surface wave modes result from the superposition of waves from all parts of the electrode and other surfaces within the reaction chamber 240. In general, a perfectly symmetric plasma in a symmetric chamber with symmetric electrodes centered on the chamber's axis of symmetry will have a line of symmetry of equal phase and amplitude, primarily in the form of a circle centered at the center of the pedestal 235.

[0042] Referring to FIG. 3 , a cross-sectional view of a dual-plate electrode assembly having a wide-bandwidth sensor that provides a voltage signal through an electrical connector with low shunt capacitance to the surrounding area of ​​the electrode and electrical ground is shown, according to an embodiment of the present disclosure. In some embodiments, an electrode, such as a showerhead 330, may include two conductive plates 331, 332 arranged substantially parallel, aligned at their centers, and having a shape generally similar to that of 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 separated from the second plate 332 by a distance equal to the length of a dielectric standoff support 333. The first plate 331 may have an embedded sensor 334 whose puck or pickup is a conductive material and whose surface is substantially flush with the surface of the first plate 331 facing away from the second plate 332.

[0043] In some embodiments, the sensors 334 may be surrounded by a dielectric 336 having a low dielectric constant, such as quartz or some other suitable material, and attached to the first plate 331. In some embodiments, the dielectric 336 may have a dielectric constant less than 5, and in some embodiments, inorganic materials such as quartz-based aerogels may have a dielectric constant less than 2. The sensors 334 may have a high bandwidth ranging from 100 kHz to at least 10 times the highest driving frequency connected to the chamber, which may be as high as or higher than 300 MHz, 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 the 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 the inner conductor 338 of a vacuum electrical signal feedthrough 339, the base 341 of which is attached to the electrically grounded second plate 215. In some embodiments, the leads from each sensor can be connected directly to a circuit board located similar to 332, one for each sensor, that contains the ground plane and detector circuitry to determine the amplitude and phase of each frequency component.

[0044] The inner conductor 338 of the feedthrough 339 can have a small shunt capacitance, such as less than 5 pico-Farads, and in some embodiments, less than 2 pico-Farads, relative to the base 341 of the feedthrough 339 attached to the grounded second plate 332, so that the total shunt capacitance from the sensor 334, lead wire 337, and feedthrough 339 to ground must be less than 5 pico-Farads, and in some embodiments, less than 3 pico-Farads. 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 include an electrical resistor having a resistance greater than about 100 ohms. In parallel with the electrical resistor 404 may be a shunt resistor to ground 405. The resistance of the shunt resistor may be, for example, 50 ohms, or may be equal to the impedance of a cable connecting the attenuator to a communications network or a plasma chamber controller. If the detector is placed in the connector as shown in Figure 3 instead, the signal output from the detector will be the amplitude and phase of the voltage or current at each frequency of that sensor and may be sent to the analysis processor and into the matching network section.

[0045] Each sensor 334 may measure the combined electromagnetic surface wave mode voltage or current amplitude, including the fundamental and harmonic frequencies of all RF generators powering the plasma, ranging from about 10 kHz to about 500 MHz or greater. In other embodiments, the sensors may measure voltages at fundamental and harmonic frequencies ranging from about 100 kHz to about 1 GHz.

[0046] FIG. 4 shows 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 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 be air or a vacuum, as appropriate). In some embodiments, the lead 402 from the sensor 401 may pass through an attenuator, such as a resistor 404 with a shunt resistor 405, which in some embodiments may be approximately 50 ohms, and may be connected to electrical ground 406. Such a resistor 404 may be non-inductive and may have a resistance ranging from approximately 100 ohms to approximately 100,000 ohms. In some embodiments, the resistance may be between approximately 500 ohms and approximately 10,000 ohms. The resistor 405 may also be non-inductive.

[0047] Additionally, the dielectric 403 should be generally non-magnetic and have a low-loss tangent, less than about 0.01 in some embodiments, or less than about 0.001 in other embodiments. The shunt capacitance between the tip of the sensor 401 and the lead 402 to the ground electrode should be less than about 5 pico-Farads, or less than about 2 pico-Farads in some embodiments, so that the reactance between the sensor 401 and the pedestal 400 or electrode should be greater than about 100 ohms at 300 MHz. The purpose of such low shunt capacitance is to reduce loading of the surface wave by the sensor 401, thereby absorbing minimal wave energy and allowing the wave to propagate as if the sensor 401 were not present. Under such conditions, the detected surface potential will not be significantly different from that present on the electrode without such a sensor 401.

[0048] FIG. 5 illustrates a cross-sectional view of a pedestal with an embedded wideband voltage sensor according to an embodiment of the present disclosure. In this embodiment, the pedestal 1400 can include an embedded wideband pickup 1405 disposed within the pedestal 1400. The embedded wideband pickup 1405 can be substantially flush with the surface of the pedestal 1400 or, in certain embodiments, embedded in the surface of the pedestal. The pickup 1405 can include a variety of shapes, such as circular, oblong, square, rectangular, etc. The pickup 1405 can also include a variety of sizes, such as a substantially circular design with a diameter of about 1 centimeter, less than 1 centimeter, 2 centimeters, or more than 2 centimeters. Stated another way, the pickup 1405 can have an area of ​​less than 1 centimeter, about 1 centimeter, about 2 centimeters, or more than 2 centimeters.

[0049] A lead 1410 may be connected to the pickup 1405 to transfer the signal from the pickup 1405 to a coaxial cable 1415 or another type of cable that can be used to receive the signal from the lead 1410 and transfer the signal to other aspects of the system. In certain embodiments, the lead may be connected to a first resistor 1420. The first resistor 1420 may limit the flow of radio frequency current in the lead 1410, thereby limiting the drain of the pickup 1405. After the first resistor 1420, a ground connector 1425 may be connected to the lead 1410. Before the first resistor 1420, the lead 1410 may be connected to a shunt 1427 that is connected to the pedestal 1400.

[0050] Following the first resistor 1420, a second resistor 1430 may be positioned or otherwise connected to the lead 1410. The second resistor 1430 is relatively smaller than the first resistor 1420, thereby avoiding suppression of radio frequency current flowing from the pickup 1405. Because the lead 1410 is connected to the coaxial cable 1415, a third resistor 1435 may be positioned or otherwise connected to one of the lead 1410 and / or the coaxial cable 1415. The third resistor 1435 may include, for example, a 50 ohm shunt resistor that can eliminate or reduce reflections of radio frequency waves returning from the detector (now shown separately).

[0051] During operation, signals from electromagnetic waves in the system can generate a radio frequency voltage in the pickup 1405 through capacitive coupling. The radio frequency voltage in the pickup 1405 drives a radio frequency current down the lead 1410 with relatively little current shunt to the pedestal 1400 because the voltages are substantially the same. As the radio frequency current travels down the lead 1410, the first resistor 1420 can limit the radio frequency current in the lead 1410 from flowing to the coaxial cable 1415. The radio frequency current travels down the lead 1410 through the second resistor 1430. The second resistor 1430 can be smaller than the first resistor 1420 to avoid suppressing the radio frequency current from the pickup 1405. Before or upon entering the coaxial cable 1415, the third resistor 1435 can substantially eliminate reflections of radio frequency waves returning from the detector, which may otherwise distort the radio frequency current flowing from the lead 1410 to the coaxial cable 1415.

[0052] 6 shows a cross-sectional view of a pedestal with an embedded wideband voltage sensor according to an embodiment of the present disclosure. In this embodiment, the pedestal 1400, or any other type of electrode such as those discussed above, may include an inductive radio frequency magnetic field sensor 1401. The inductive radio frequency magnetic field sensor may include an electrostatic shield 1402 disposed within the pedestal 1400. The electrostatic shield 1402 may be disposed relatively flush with the surface of the pedestal 1400 or may be disposed slightly recessed within the surface of the pedestal 1400. The electrostatic shield 1402 may prevent damage to the inductive radio frequency magnetic field sensor 1401 and other components during plasma operation.

[0053] The inductive radio frequency magnetic field sensor 1401 may further include an inductive loop pickup 1406 disposed within the pedestal 1400 substantially below the electrostatic shield 1402. The inductive loop pickup 1406 may include one, two, three, or more loops, which may increase the current pulse and increase the accuracy of detecting the changing magnetic field in the plasma processing system. The inductive loop pickup 1406 may be connected to leads 1410, such as the leads discussed above with respect to FIG. 5.

[0054] The lead 1410 may then be connected to a first resistor 1420, such as the first resistor 1420 discussed above. In embodiments using an inductive radio frequency magnetic field sensor 1401, the first resistor 1420 may be smaller than if a capacitive sensor is used. The lead 1410 may also be connected to a shunt 1427, which is connected to the pedestal 1400. A ground connector 1425 may be connected to the lead 1410 after the first resistor 1420. A second resistor 1430 may also be positioned or otherwise connected to the lead 1410 after the first resistor 1420. The second resistor 1430 may be relatively smaller than the first resistor 1420, thereby avoiding suppression of the radio frequency current flowing from the pickup 1405. Once the lead 1410 is connected to the coaxial cable 1415, a third resistor 1435 may be placed or otherwise connected to one of the lead 1410 and / or the coaxial cable 1415. The third resistor 1435 may include, for example, a 50 ohm shunt resistor that can eliminate or reduce reflections of radio frequency waves returning from the detector (now shown separately).

[0055] During operation, induced current from the changing magnetic field within the plasma processing system above the detector can drive a radio frequency current down the lead 1410 via the inductive loop pickup 1406. The radio frequency voltage of the inductive loop pickup 1406 drives the radio frequency current into the lead 1410 with relatively little current shunt to the pedestal 1400 because the voltages are substantially the same. As the radio frequency current travels down the lead 1410, the first resistor 1420 can limit the radio frequency current in the lead 1410 from flowing to the coaxial cable 1415. The radio frequency current travels down the lead 1410 and through the second resistor 1430. The second resistor 1430 can be smaller than the first resistor 1420 to avoid suppressing the radio frequency current from the pickup 1405. Before or as it enters the coaxial cable 1415, the third resistor 1435 can substantially eliminate reflections of radio frequency waves returning from the detector, which may otherwise distort the radio frequency current flowing from the lead 1410 to the coaxial cable 1415.

[0056] FIG. 7 illustrates a cross-sectional view of a pedestal with an embedded wideband voltage sensor according to an embodiment of the present disclosure. In this embodiment, the pedestal 1400 may include an embedded primary wideband pickup 1408 disposed within the pedestal 1400. The embedded primary wideband pickup 1408 may be substantially flush with the surface of the pedestal 1400, or in certain embodiments, may be embedded in the surface of the pedestal. The primary wideband pickup 1408 may include various shapes, such as circular, oblong, square, rectangular, etc. Additionally, the primary wideband pickup 1408 may include various sizes, such as a substantially circular design with a diameter of approximately 1 centimeter, less than 1 centimeter, 2 centimeters, or more than 2 centimeters. Stated another way, the primary wideband pickup 1408 may have an area of ​​less than 1 centimeter, approximately 1 centimeter, approximately 2 centimeters, or more than 2 centimeters.

[0057] A secondary pickup 1409 may be located within the pedestal 1400 substantially below the primary wideband pickup 1408. The secondary pickup 1409 may be a wideband pickup such as the primary wideband pickup 1408, or another type of pickup sufficient to receive radio frequency current from the primary wideband pickup 1408. A lead 1410 may be connected to the secondary pickup 1409 to transfer signals from the secondary pickup 1409 to a coaxial cable 1415 or another type of cable that can be used to receive signals from the lead 1410 and transfer the signals to other aspects of the system. In certain embodiments, the lead may be connected to a first resistor 1420. The first resistor 1420 can limit the flow of radio frequency current in the lead 1410, thereby limiting the drain of the pickup 1405. A ground connector 1425 may be connected to the lead 1410 after the first resistor 1420. Before the first resistor 1420 , the lead 1410 may be connected to a shunt 1427 that is connected to the pedestal 1400 .

[0058] A second resistor 1430 may be positioned or otherwise connected to the lead 1410 after the first resistor 1420. The second resistor 1430 may be relatively smaller than the first resistor 1420, thereby avoiding suppression of radio frequency current flowing from the pickup 1405. Because the lead 1410 is connected to the coaxial cable 1415, a third resistor 1435 may be positioned or otherwise connected to one of the lead 1410 and / or the coaxial cable 1415. The third resistor 1435 may include, for example, a 50 ohm shunt resistor that can eliminate or otherwise reduce reflections of radio frequency waves returning from the detector (now shown separately).

[0059] During operation, signals from electromagnetic waves in the system can generate a radio frequency voltage in the primary wideband pickup 1408 through capacitive coupling. This allows the radio frequency current in the primary wideband pickup 1408 to capacitively drive a radio frequency current in the secondary pickup 1409. The radio frequency current in the secondary pickup 1409 has substantially the same voltage, driving the radio frequency current into the lead 1410 with relatively little current shunt to the pedestal 1400. As the radio frequency current travels down the lead 1410, the first resistor 1420 can limit the radio frequency current in the lead 1410 from flowing to the coaxial cable 1415. The radio frequency current travels down the lead 1410 and through the second resistor 1430. The second resistor 1430 can be smaller than the first resistor 1420 to avoid suppressing the radio frequency current from the pickup 1405. Before or as it enters the coaxial cable 1415, the third resistor 1435 can substantially eliminate reflections of radio frequency waves returning from the detector, which may otherwise distort the radio frequency current flowing from the lead 1410 to the coaxial cable 1415.

[0060] 8, a schematic side view of a pedestal with associated RF and control components is shown, according to an embodiment of the present disclosure. The pedestal 501 power supply circuitry includes an RF generator 505 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, in some embodiments, may be within or connected to the impedance matching network 506. High-speed lines 513 of a data network take information from the impedance matching network 506 to a controller 514 for the reaction chamber, generator, or tool or factory (not shown). The sensors 502, 503 are mounted at or near the base 504 of a 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, e.g., fault detection, section 510 associated with impedance matching network 506. Signal analysis section 510 may be electrically and / or RF isolated from certain components, such as the vacuum capacitors and high voltage electronics of impedance matching network 506. Signal analysis section 510 may be connected to cables 511, 512 , 503。 Signal analysis section 510 then directs the signal from each sensor 502, 503 to an internal circuit, which may be called a detector, and which may include electronic components such as transistors and passive components. In an alternative embodiment, where the amplitude and phase are seen directly adjacent the sensor for each frequency component, the signal coming into 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 signal from one sensor 502, 503, or from a group of sensors that may be analyzed in parallel. The analysis may include averaging the signals of the group of sensors, or one or more sensors 502, 503, over time for noise reduction. In some embodiments, there may be an output from each detector of amplitude and phase for each frequency component, e.g., fundamental and harmonics, of the signal acquired by each sensor 502, 503. The output from each detector may then be input to an analog-to-digital converter for each harmonic signal to generate digitized values ​​of both the amplitude and phase of each measured harmonic.

[0063] These digital amplitude and phase values ​​for each frequency component and sensor can be input with little to no 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 analyzes both the amplitude and phase information for the fundamental and each harmonic from the sensor to determine the relative magnitudes of various surface wave modes, including axially symmetric and non-axisymmetric modes, for both the fundamental and the harmonics. Different non-axisymmetric modes may exist for each frequency component, one or more of which may be indicative of plasma inhomogeneity.

[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 mode with the percentage of plasma non-uniformity may also reside in this plug-in or removable processor. The digital processor may also calculate the rate of change of the wave mode amplitude and the acceleration of the amplitude of one or more wave modes to determine the likelihood of impending failure. One measure of the magnitude of a non-axisymmetric mode at a given frequency may be the difference between the phase of a given frequency surface wave at different sensor locations symmetrically positioned in an axisymmetric chamber and having the same radial distance from the center of the circular electrode. Alternatively, a second indicator of a non-axisymmetric mode may be the difference between the amplitude of a given frequency surface wave at different sensor locations symmetrically positioned in an axisymmetric chamber and having the same radial distance from the center of the circular electrode.

[0065] A matching network 506 with an isolated section 510 containing a multi-channel detector system (not shown) can simultaneously Fourier analyze, digitize, and record the voltage amplitude and phase of the propagating EM waves at various locations on the pedestal 501. Due to inherent noise, each determined voltage amplitude and phase can be averaged over a short time interval if desired, and can also be averaged over groups of sensors 502, 503 to determine relative magnitude or time averages over a relatively large number of pulses.

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

[0067] The relationship between the amplitude and phase pattern characteristics of non-axisymmetric and axisymmetric EM modes and process and plasma nonuniformities 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 manufacturing tool, plasma and process nonuniformities may thereby be rapidly detected when chamber operation is monitored. For example, a sensor of the disclosed type shown in FIG. 4, configured as shown in FIG. 2, may be retrofitted to an RF plasma system such as that 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 set of pre-specified harmonics of the drive frequency of some electrodes or antennas. The processor in some embodiments may then 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 within the impedance matching network or a section associated with the impedance matching network.

[0069] The database can store parameters characterizing various plasma conditions to help determine how severe a plasma deviation from an acceptable "process window" is and how severe it is. In some embodiments, the analysis can 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 variance of such phases for a sensor or group of sensors for any azimuthal angle can be a measure of the asymmetry of the generation and / or propagation of that harmonic mode, and thus, the asymmetry and non-uniformity of the plasma. In some embodiments, the analysis can include a calculation of the difference in amplitude between sensors or groups of sensors at a given distance from the axis of symmetry. The variance of such amplitudes for sensors or groups of adjacent sensors within a range of azimuthal angles can be a measure of the asymmetry of the generation and / or propagation of that harmonic mode, and thus, the asymmetry and non-uniformity of the plasma.

[0070] Parameters that are quantitative measurements of the asymmetry of each of the set of harmonics may then be stored in the plug-in unit and transmitted to the chamber and tool controllers via a data network. Additionally, trends and accelerations of the parameters may be calculated and compared to reference values ​​and criteria in a database as part of the process of determining whether a fault condition has occurred. In some embodiments, when such a fault condition occurs, algorithms and criteria that may be stored in the plug-in may be executed by a processor in the compartment to determine a course of remedial or preventative action. Such actions may then be rapidly transmitted to the RF generator and / or chamber and / or tool controller.

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

[0072] In some embodiments, many types of plasma deviations from the desired plasma uniformity can be detected quickly enough that a tool or chamber controller can take action to correct the plasma fault condition before a wafer or substrate is accidentally processed. In some situations, the specified corrective action may be to briefly change the RF power format (e.g., continuous wave (CW) or pulsed), to turn off the power completely for a short period of time, to stop processing the current wafer and then store or discard the wafer for processing, or to shut down the reaction chamber for maintenance. Thus, adjusting the frequency within a 10 percent range of the RF power may correct the reflected power.

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

[0074] Referring to Figure 9, a top view of axisymmetric surface wave propagation across a pedestal where the plasma in the reaction chamber is axisymmetric is shown in accordance with an embodiment of the present disclosure. 9 In Fig. 6, circle 601 is a curve of constant phase and amplitude for the fundamental and harmonic frequency components of an axisymmetric surface wave mode. The circle is concentric with the electrode. These modes are most dominant when the electrode and plasma are all axisymmetric and coaxial within the chamber. The propagation vectors 602 of a surface wave at any frequency are radial. The waves propagate toward and away from the center, and as they propagate, such waves inject power into the plasma.

[0075] Referring to FIG. 10, a top view of transverse electromagnetic surface wave propagation across an electrode is shown, according to an embodiment of the present disclosure. 10In Fig. 7, the lines of constant phase and equal amplitude of a specific single non-axisymmetric mode 701-704 are nearly straight and parallel, whether at the fundamental frequency or its harmonic frequencies. Such surface waves can be detected by sensors located on the pedestal or showerhead of an RF plasma deposition system. This mode is sometimes called "transverse," meaning that the direction of propagation is from one side to the other across the electrode surface, or both left and right of the center plane, as seen in propagation vectors 705-707. Other non-axisymmetric modes may exist, where the lines of constant phase may be curves with centers of curvature displaced from the center of the electrode. Detector readings per frequency can be decomposed into the sum of the axially symmetric mode and (often a few) non-axisymmetric modes, which reflect the primary inhomogeneity of the plasma. Typically, the decomposition allows for the identification of a transverse mode component and / or one primary "off-center" or displaced radial mode, either of which is characteristic of the plasma inhomogeneity configuration. Correlation of plasma non-uniformity configurations with specific non-axisymmetric modes is performed prior to production processing as part of building a database that may reside in a plug-in unit or elsewhere.

[0076] Referring to FIG. 11 , a top view of one preferred azimuthal sensor arrangement for a reaction chamber is shown, according to an embodiment of the present disclosure. In this embodiment, multiple sensors 800 may be azimuthally arranged around one or more components of the reaction chamber and / or within the reaction chamber itself. As briefly discussed above, the multiple sensors 800, which may be four in this embodiment, may be arranged at different angles around 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, they are spaced at 90-degree intervals, but in some embodiments, they may be spaced at irregular azimuthal intervals.

[0077] The sensors 800 may include passive sensors 800 that receive varying electrical potentials or magnetic fields. The sensors 800 may be positioned at different azimuthal angles relative to the chamber axis of symmetry 805 to detect EM waves having different types of propagation modes. The sensors 800 may be positioned at equidistant locations around the chamber axis of symmetry 805 and / or components within 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 may be approximately the same. For example, the distance between sensors 800-1 and 800-2 is approximately the same as the distance between sensors 800-3 and 800-4. Similarly, each sensor 800 is positioned the same distance from the chamber axis of symmetry 805. For example, the spacing and location of the sensors 800 are discussed in more detail below.

[0078] As shown, 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. Thus, sensors 800 for non-axisymmetric plasmas may detect waveform differences on different sides of the reaction chamber and / or its components and, when waveform differences occur, provide notification as described above, thereby enabling corrective or preventative action. For example, if sensors 800-1 and 800-4 sense and report waveform differences from their diametrically opposed locations, such differences may indicate that harmonics are out of phase or have different amplitudes. This may thereby indicate plasma nonuniformity and asymmetry. Such waveform differences occur when there is a difference between the diametrically opposed detectors in the relative phase or amplitude of one or more harmonics in the signals received by the opposite sensors.

[0079] In certain embodiments, FIG. 11As shown, four sensors 800 may be used. However, other embodiments may use a different number of sensors 800, such as 6, 8, 12, 14, 16, 18, 20, or more sensors 800. In some embodiments, the azimuthal angles between the sensors may not be equal, but the same characteristics of non-azimuthally symmetric plasma modes may nonetheless be observed by the sensors. In certain implementations, it may be beneficial to have between 6 and 12 sensors 800. A greater number of sensors 800 may collect more data, thereby providing enhanced ability to distinguish noise and sensitivity for recognizing non-uniformities. However, increasing the number of sensors 800 may slow data processing, thereby resulting in remedial and preventative measures occurring more slowly. Those skilled in the art will appreciate that balancing the number of sensors 800 with the desired level of data granularity can thereby optimize the RF plasma process. Therefore, as computing power increases and the speed at which data can be processed increases, it may be beneficial to increase the number of sensors 800. In certain embodiments, certain sensors 800 can be selectively turned off and on, allowing the controller to access certain required data. For example, in a system having eight sensors, four sensors can be selectively turned off to reduce the amount of data generated thereby. In other embodiments, additional sensors can be added or removed from operation, thereby changing the amount of data generated.

[0080] Additionally, sensor 800 can include various types of sensors, both circular and other shapes. In certain embodiments, sensor 800 can be circular with an area between about 0.1 square centimeters and about 10 square centimeters. Sensor 800 can further include a surface insulator layer or coating to protect sensor 800 from plasma or reactive species within the reaction chamber, and can also include other optional coatings and layers, such as a Faraday shield for a current sensor, an aluminum coating, etc.

[0081] 12, a cross-sectional side view of a sensor azimuthally mounted in a reaction chamber is shown, according to an embodiment of the present disclosure. 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 positioned azimuthally at various locations around and within the reaction chamber 940, and around or relative to particular components, such as the showerhead 930 and / or pedestal 935. 12 Although FIG. 11 is a cross-sectional view and only two sensors 900 per location are shown, more sensors 900 may be used during implementation of the RF plasma monitoring process, as will be discussed in detail with respect to FIG.

[0082] In certain embodiments, the sensor 900-1 may be located on the edge or periphery of the showerhead 930. In such implementations, the sensor 900-1 may be located on the edge or periphery of the showerhead 930. 930The sensor 900-1 may be positioned at least partially or completely embedded within the showerhead 930, 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 an embodiment, 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, sensor 900-2 may be positioned along the edge of pedestal 935 within the vacuum of reaction chamber 940. As described above with respect to sensor 900-1, sensor 900-2 may be partially or completely embedded in pedestal 935, and may or may not include an insulating layer disposed on its outer surface. Furthermore, in some embodiments, sensors 900-2 may have a dielectric protective portion covering them. In addition to sensor 900-2 positioned around pedestal 935 within the vacuum, other sensors 900-3 and 900-4 may be positioned outside the vacuum of reaction chamber 940 and around pedestal 935. Such sensors 900-3 and 900-4 may be positioned on metal surfaces along pedestal 935 and / or its base portion. Sensor 900 may also be positioned on or in relation to other support structures for pedestal 935.

[0084] In yet other embodiments, the sensor 900-5 may be positioned and / or otherwise integrated into the sidewall of the reaction chamber 940. In such embodiments where the wall is dielectric, the sensor 900-5 may be positioned outside the reaction chamber 940 on the outer chamber wall 915. Alternatively, the sensor 900-5 may be integrated into the sidewall so that it is within the vacuum of the reaction chamber 940. In the case of metal walls, the sensor should expose its pickup to the inner surface of the wall so that it can sense the EM fields within the chamber. Another sensor 900-6 may be positioned in a viewport 920 located along the outer chamber wall 915. In such embodiments, the sensor 900-6 in the viewport may be positioned outside the vacuum of the reaction chamber 940 or may be positioned within the reaction chamber 940.

[0085] In yet other embodiments, the sensor 900-7 may be positioned in a dielectric located around the showerhead 930, for example, while in other implementations, the sensor 900-7 may be positioned in a dielectric located around the pedestal 935. Although specific locations for the sensor 900 are discussed herein, the sensor 900 may be positioned in various other locations within and around the reaction chamber 940. For example, the sensor 900 may be positioned inside or outside a dielectric wall near an antenna or other component. Additionally, the sensor 900 may be positioned in various other locations within the 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 RF plasma processing. For example, sensor 900-1 around the edge of showerhead 930 may be combined with sensor 900-2 around the edge of pedestal 935. Similarly, a combination of sensor 900-5 outside of reaction chamber 940 may be combined with sensors 900-1 / 900-2 located within reaction chamber 940. In still other embodiments, a combination of three, four, five, six, seven, or more variations of sensor 900 location may be used to further optimize monitoring of RF plasma processing.

[0087] 13, a cross-sectional side view of a model reaction chamber according to an embodiment of the present disclosure is shown, illustrating the preferred location of multiple azimuthally arranged sensors 1000 arranged around the bottom electrode, which in this example is a pedestal 1035. 13 Similar to the sensor 1000 discussed above with respect to FIG. 13 shows sensors 1000 positioned at various locations. Sensor 1000-1 is positioned around the outer edge of pedestal 1035. Sensor azimuthal positions shown as 1000-2 are positioned around the inside of reaction chamber 1040, while sensor azimuthal positions 1000-3 are positioned around the perimeter of reaction chamber 1040 in the adjacent viewport.

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

[0089] 14, a schematic cross-sectional side 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] 15, a partial cross-sectional view of an RF plasma processing system is shown in accordance with an embodiment of the present disclosure. In this embodiment, the RF plasma processing system 1200 includes a pedestal 1235. The pedestal 1235 includes a sensor 1240 disposed along the upper outer edge of the pedestal 1235. As noted above, the sensor 1240 may be located on the upper outer edge embedded within the pedestal 1235, or alternatively, the sensor 1240 may be located around the outer edge either inside or outside the vacuum of the reaction chamber.

[0091] The RF plasma processing system 1200 also includes circuitry 1245 connected to the sensor 1240 via communication line 1250. The sensor 1240 receives sensed data from the RF plasma processing system 1200 so that the data can be transmitted to the circuitry 1245 for processing. Because the circuitry 1245 is relatively close to the sensor 1240, the time it takes to transfer the sensed data therebetween can be reduced. Thus, initial calculations regarding the electrical properties sensed by the sensor 1240 can be performed more quickly and then transmitted 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 components connected to the RF plasma processing system 1200.

[0092] 1255, or any other component of 1200 not shown, can then adjust aspects of RF plasma processing system 1200 to correct the fault detected by sensor 1240 and at least partially addressed within circuit 1245. Circuit 1245 may be located within pedestal 1235 outside the vacuum of the reaction chamber in an isolated structure to protect circuit 1245 from conditions within the reaction chamber. In other embodiments, circuit 1245 may be located at the base of pedestal 1235 or in other areas proximate to pedestal 1235.

[0093] 15 shows a cross-sectional view of components of RF plasma processing system 1200, and one skilled in the art will appreciate that circuits 1245 may be located at approximately the same radius at different azimuthal angles around pedestal 1235. Thus, a separate circuit 1245 may be available for each sensor 1240, or sensors 1240 may be connected to a centralized circuit 1245 located at one or more selected locations around and / or within pedestal 1235.

[0094] 16, 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 can be mounted on the exterior or interior of a dielectric wall (not shown) proximate to the antenna.

[0095] The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the present disclosure. However, it will be apparent to those skilled in the art that specific details are not required to practice the systems and methods described herein. The foregoing descriptions of specific embodiments have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the disclosure to the precise forms described. Obviously, many modifications and variations are possible in light of the above teachings. The embodiments have been shown and described to best explain the principles and practical applications of the present disclosure, so as to enable those skilled in the art to best utilize the disclosure and various embodiments, with various modifications suited to the particular uses contemplated. It is intended that the scope of this disclosure be defined by the following claims and their equivalents. Some aspects of the invention are described below. [Aspect 1] 1. A broadband sensor for a radio frequency plasma processing system, comprising: a capacitive pickup for an electrical potential placed on a conductive component of the reaction chamber; a lead comprising the circuit connecting the pickup to a connector attached to an electrically grounded plate proximate the pickup having an electrical resistance of the circuit and a capacitance to electrical ground of the connector such that the pickup voltage differs from the surface voltage of the conductive component by less than 5%; and an attenuator circuit connected to said connector, said attenuator circuit comprising at least one current limiting resistor in series from the attenuator input to the attenuator output; The wideband sensor has detection within a radio frequency range of about 10 kHz to at least about 1 GHz for radio frequency potential measurements in the radio frequency plasma processing system. [Aspect 2] 2. The apparatus of claim 1, wherein the shunt capacitance from the connector to the electrical ground is less than about 50 picofarads. [Aspect 3] 2. The apparatus of claim 1, wherein the shunt capacitance from the connector to the electrical ground is less than about 5 picofarads. [Aspect 4] 2. The apparatus of claim 1, wherein the sum of the electrical resistance of the circuit connecting the pickup to the connector and the resistance within the attenuator is greater than about 50 ohms and less than about 10,000 ohms. [Aspect 5] The apparatus of aspect 1, wherein the capacitive pickup is embedded in a surface of a plasma powered electrode of the radio frequency plasma processing system, and the surface of the capacitive pickup is approximately coplanar with the surface of the plasma powered electrode. [Aspect 6] 10. The apparatus of claim 1, wherein the attenuator further comprises a shunt resistor at approximately 50 ohms connected to the electrical ground. [Aspect 7] 10. The apparatus of claim 1, wherein the broadband sensor is disposed within a dielectric component mounted proximate to an electrode. [Aspect 8] 2. The apparatus of claim 1, wherein the wideband sensor has a maximum bandwidth greater than about five times the highest driving frequency of the radio frequency plasma processing system. [Aspect 9] The device of aspect 1, wherein the capacitive pickup is mounted on or in close proximity to a surface of the dielectric component located in close proximity to the conductive component, and the gap from the capacitive pickup to the conductive component is less than about 10 mm. [Aspect 10] 1. A broadband sensor for a radio frequency plasma processing system, comprising: an inductive pickup for sensing surface currents, the inductive pickup having a first end connected to electrical ground and a wire formed in a loop with a generally vertical orientation of the loop having an azimuthal component about the reaction chamber axis of symmetry; leads connected to the inductive pickup and connector; and an attenuator circuit including an electrical resistor connected to the connector and the output of the signal cable; The wideband sensor has detection capabilities in a radio frequency range from about 10 kHz to at least about 1 GHz for radio frequency potential measurements in the radio frequency plasma processing system. [Aspect 11] 11. The apparatus of embodiment 10, wherein the impedance element comprises a resistor having at least about 10 ohms. [Aspect 12] 11. The apparatus of claim 10, wherein a shunt capacitance from the connector to the electrical ground is less than about 20 picofarads. [Aspect 13] 11. The apparatus of claim 10, wherein the radio frequency sensor is embedded in a hole in the plasma powered electrode of the radio frequency plasma processing system, and the top of the loop is approximately flush with the surface of the electrode. [Aspect 14] 11. The apparatus of embodiment 10, wherein the broadband sensor is embedded in the component located proximate to an electrode at a distance from the reaction chamber axis of symmetry that is greater than the edge of a wafer. [Aspect 15] 11. The apparatus of claim 10, wherein the impedance of the circuit connecting the second end of the loop to ground is in a range between about 10 ohms and about 5,000 ohms. [Aspect 16] 1. A broadband sensor having detection capability in the radio frequency range from about 10 kHz to at least 1 GHz for measuring radio frequency potentials in a radio frequency plasma processing chamber, comprising: a first capacitive pickup for an electrical potential occupying one of the positions parallel to, within a short distance from, and slightly below the surface of the conductive component of the RF plasma processing system; a first pickup and a second internal pickup on the other side of the first pickup from the side facing the surface of the conductive component, the side of the second pickup opposite the first pickup having (1) a first end of a second, larger capacitance, the second end of which is connected to electrical ground, and (2) a small, first capacitance to leads connecting in parallel to two nodes of an input pin of the connector; a wideband sensor comprising an attenuator circuit connected to the output of the connector, the attenuator circuit comprising at least one current limiting resistor in series from the attenuator input to the attenuator output, and an approximately 1 kOhm shunt resistor from the output of the attenuator circuit to electrical ground. [Aspect 17] 17. The wideband sensor of embodiment 16, wherein the ratio of the second capacitance to the first capacitance is at least three. [Aspect 18] 17. The wideband sensor of claim 16, wherein the resistance of the current-limiting resistor is at least 1 kOhm.

Claims

1. 1. A broadband sensor for a radio frequency plasma processing system, comprising: a capacitive pickup for detecting a potential, disposed on a conductive component of the reaction chamber; a lead including a circuit connecting the capacitive pickup to a connector attached to an electrically grounded plate adjacent the pickup, the lead configured such that the electrical resistance of the circuit and the capacitance of the connector to electrical ground result in a difference between the pickup voltage and the surface voltage of the conductive component being less than 5%; an attenuator circuit connected to said connector, said attenuator circuit comprising at least one current limiting resistor in series from the attenuator input to the attenuator output; The wideband sensor detects within a radio frequency range of 10 kHz to at least 1 GHz for radio frequency potential measurements in the radio frequency plasma processing system.

2. The wideband sensor of claim 1 , wherein the shunt capacitance from the connector to the electrical ground is less than 50 picofarads.

3. The wideband sensor of claim 1 , wherein the shunt capacitance from the connector to the electrical ground is less than 5 picofarads.

4. 2. The wideband sensor of claim 1, wherein the sum of the electrical resistance of the circuit connecting the pickup to the connector and the resistance of the current-limiting resistor in the attenuator circuit is greater than 50 ohms and less than 10,000 ohms.

5. 10. The wideband sensor of claim 1, wherein the capacitive pickup is embedded in a surface of a plasma powered electrode of the radio frequency plasma processing system, the surface of the capacitive pickup being coplanar with the surface of the plasma powered electrode.

6. The wideband sensor of claim 1 , wherein the attenuator circuit further comprises a shunt resistor at 50 ohms connected to the electrical ground.

7. The wideband sensor of claim 1 , wherein the wideband sensor is disposed within a dielectric component mounted proximate to an electrode.

8. 10. The broadband sensor of claim 1, wherein the broadband sensor has a maximum bandwidth greater than five times the highest driving frequency of the radio frequency plasma processing system.

9. 2. The wideband sensor of claim 1, wherein the capacitive pickup is mounted on or in close proximity to a surface of a dielectric component located in close proximity to the conductive component, and the gap from the capacitive pickup to the conductive component is less than 10 mm.

10. 1. A broadband sensor having detection capability in the radio frequency range from 10 kHz to at least 1 GHz for measuring radio frequency potentials in a radio frequency plasma processing chamber, comprising: a first capacitive pickup for detecting an electric potential, located parallel to and within a short distance from a surface of the conductive component of the chamber and at or below the surface of the conductive component of the RF plasma processing system; a second internal pickup on the opposite surface of the conductive component from the first capacitive pickup, the second internal pickup having a first small capacitance relative to the first capacitive pickup; a second internal pickup having (1) a first end having a second greater capacitance than the second end connected to electrical ground, and (2) leads connecting in parallel to two nodes of the input pin of the connector; a wideband sensor comprising: an attenuator circuit connected to the output of said connector, said attenuator circuit comprising at least one current limiting resistor in series from an attenuator input to an attenuator output and a 1 kOhm shunt resistor from said attenuator output to said electrical ground.

11. The wideband sensor of claim 10 , wherein the ratio of the second, larger capacitance to the first, smaller capacitance is at least three.

12. The wideband sensor of claim 10 , wherein the resistance of the current-limiting resistor is at least 1 kOhm.

Images