Plasma processing with broadband RF waveforms

Abstract

A plasma system includes a plasma apparatus including: a plasma chamber; a susceptor configured to hold a substrate in the chamber; and a radio frequency (RF) electrode configured to excite a plasma in the chamber; an electromagnetic (EM) circuit block coupled to the RF electrode, the EM circuit block comprising: a function generator configured to output a broadband RF waveform, the EM power of the waveform being distributed within a range of frequencies; the broadband amplifier is coupled to the output end of the function generator, and the working frequency range of the amplifier comprises the frequency range; and a broadband impedance matching network having an input coupled to an output of the broadband amplifier and an output coupled to a terminal of the RF electrode, an operating frequency range of the broadband impedance matching network including the frequency range; and a controller configured to adjust an input parameter of the EM circuit block.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of U.S. Non-Provisional Application No. 17 / 865,225, filed on July 14, 2022, which is incorporated herein by reference.

[0003] This application is related to U.S. application No. 16 / 572,708 (US 11,170,981 B2) filed on September 17, 2019 (Agent Case No.: TEL-190559US01), U.S. application No. 16 / 717,024 (US11,295,937 B2) filed on December 17, 2019 (Agent Case No.: TEL-190559US02), U.S. application No. 17 / 498,063 (Agent Case No.: TEL-190559US03) filed on October 11, 2021, and U.S. application No. 17 / 012,168 (US11,348,761 B2) (Agent Case No.: TEL-200041US01) filed on September 4, 2020, which are incorporated herein by reference in their entirety. Technical Field

[0004] The present invention generally relates to a system for plasma processing and, in a particular embodiment, to a system for plasma processing utilizing a broadband radio frequency (RF) waveform. Background Art

[0005] Integrated circuits (ICs) are networks of circuit components within a monolithic structure, including electronic devices and interconnects that comprise complex three-dimensional structures with nanoscale features. Plasma processing is widely used in IC manufacturing. Typically, these structures are formed by sequentially depositing and patterning various layers using photolithography and etching. Plasma deposition and etching processes used to manufacture components at technology nodes below 10 nm require nearly atomic-scale dimensional control on 300 mm wafers. Many relevant structural features, such as line edge roughness (LER), sidewall angle at high aspect ratios, film thickness, liner conformality, void-free fill, and etch selectivity, are affected by plasma properties; therefore, precise plasma control is essential. Scaling makes it difficult to achieve the precision required within the constraints of using simple continuous wave (CW) RF signals to excite the plasma. To overcome some of these obstacles, innovative processing methods, including cyclic processes, have been developed. These methods may require complex, time-varying plasma properties to improve process capabilities. Complex and dynamic processing requires sophisticated RF waveforms to excite a plasma with the desired properties. Typically, two RF waveforms are applied simultaneously to two electrodes or superimposed on a single electrode. The RF power of the superimposed waveform is distributed over a certain frequency range. Clearly, plasma systems using broadband RF waveforms facilitate innovative plasma processing, and further development of broadband plasma systems is needed to successfully deploy new processes. Summary of the Invention

[0006] A plasma system includes a plasma apparatus, the plasma apparatus comprising: a plasma chamber; a susceptor configured to hold a substrate in the chamber; and a radio frequency (RF) electrode configured to excite plasma in the chamber; an electromagnetic (EM) circuit block coupled to the RF electrode, the EM circuit block including: a function generator configured to output a broadband RF waveform having an EM power distribution within a frequency range; a broadband amplifier coupled to an output of the function generator, the amplifier having an operating frequency range including the frequency range; and a broadband impedance matching network having an input coupled to an output of the broadband amplifier and an output coupled to a terminal of the RF electrode, the broadband impedance matching network having an operating frequency range including the frequency range; and a controller configured to adjust input parameters of the EM circuit block.

[0007] A plasma system includes: a plasma device; a dual-channel electromagnetic (EM) circuit block, the dual-channel EM circuit block including: a first EM circuit block comprising a first function generator, a first broadband amplifier, and a first broadband impedance matching network, wherein the first EM circuit block outputs a first broadband RF waveform coupled to the plasma device, the EM power of the first broadband RF waveform being distributed within a first frequency range; and a second EM circuit block comprising a second function generator, a second broadband amplifier, and a second broadband impedance matching network, wherein the second EM circuit block outputs a second broadband RF waveform coupled to the plasma device, the EM power of the second broadband RF waveform being distributed within a second frequency range, the second range being different from the first range; and a controller configured to adjust a plurality of input parameters of the EM circuit block.

[0008] A method of operating a plasma processing system includes: outputting a broadband radio frequency (RF) waveform at an output of a function generator; coupling the output of the function generator to an input of a broadband amplifier; outputting an amplified broadband RF waveform at the output of the broadband amplifier; coupling the output of the broadband amplifier to a source terminal of a first RF tube; coupling a load terminal of the first RF tube to an input terminal of a broadband impedance matching network, the load terminal being opposite the source terminal; and coupling the output of the broadband impedance matching network to a terminal of an RF electrode of a plasma device using a second RF tube, the coupling providing EM power at the RF electrode, the EM power igniting plasma in a plasma chamber of the plasma device. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] For a more complete understanding of the present invention and its advantages, reference will now be made to the following description taken in conjunction with the accompanying drawings, in which:

[0010] Figure 1A A schematic diagram of a broadband plasma system according to some embodiments is shown, the schematic diagram including a cross-sectional view of a plasma device and a block diagram of an electromagnetic (EM) system providing EM power to the plasma device;

[0011] Figure 1B illustrates a cross-sectional view of a VI sensor showing example voltage pickups and current pickups according to some embodiments;

[0012] Figure 1C A circuit schematic illustrating an example reactive circuit for a broadband impedance matching network according to some embodiments;

[0013] Figure 2A schematic diagram of a broadband plasma system according to some embodiments is shown, the schematic diagram including a cross-sectional view of a plasma device and a block diagram of an electromagnetic (EM) system providing EM power to the plasma device;

[0014] Figure 3 A schematic diagram of a broadband plasma system according to some embodiments is shown, the schematic diagram including a cross-sectional view of a plasma device and a block diagram of an electromagnetic (EM) system providing EM power to the plasma device;

[0015] Figure 4 shows a schematic diagram of a broadband plasma system according to some embodiments, the schematic diagram including a cross-sectional view of a plasma device and a block diagram of an electromagnetic (EM) system providing EM power to the plasma device; and

[0016] Figure 5 A flow chart of a method for processing a substrate according to some embodiments is shown. DETAILED DESCRIPTION

[0017] The present disclosure describes embodiments of a system for plasma processing in which a broadband radio frequency (RF) waveform can be used to ignite a plasma. The broadband RF waveform has electromagnetic (EM) power distributed over a range of frequencies within the RF frequency band. The plasma processing system includes a plasma device for igniting a plasma to process a substrate, an EM circuit block for providing EM power to the plasma device, and a controller for adjusting input parameters of the EM circuit block. In embodiments of the present disclosure, the EM power provided to the plasma device can be provided as a broadband arbitrary RF waveform, including continuous wave (CW) RF, pulsed RF, DC, pulsed DC, high-frequency rectangular (e.g., square wave) or triangular (e.g., sawtooth) pulse trains, or a combination or superposition of more than one such waveform.

[0018] Typically, plasma processing involves physically and / or chemically modifying the exposed surface of a substrate using energetic particles (e.g., ions and radicals) excited by electrons in a plasma. As mentioned in the Background section, a broadband plasma system is a processing platform that provides the flexibility to implement various innovative techniques such as simultaneous deposition and etching, cyclic processes that alternate between deposition and etching, or isotropic and anisotropic etching, as well as adaptive processing that dynamically adjusts the plasma as different materials are exposed to the plasma during processing. To implement such dynamic plasma processes, the plasma system must excite a plasma with plasma properties that change in a sequence necessary to achieve the set of process conditions specified for the process. In order to excite a plasma with accurate and dynamically adjustable properties, it may be necessary to apply complex broadband RF waveforms using a broadband plasma system.

[0019] Plasma properties, such as plasma density, ion energy and angular distribution, electron temperature (Te), and the ratio of radical to ion flux, depend not only on the RF power and frequency, but also on the details of the waveform. RF waveforms are selected to achieve the desired plasma properties and can be applied in a specific order, for example, to change the plasma during a cycle. As mentioned above, broadband waveforms can include pulsed RF, a superposition of sinusoidal RF and DC or pulsed DC, RF pulses of multiple frequencies, and non-sinusoidal waveforms (such as sawtooth and square waves). Different RF waveforms can be applied to different electrodes that are coupled to the plasma ignited in the plasma processing chamber. For example, a first electrode can be coupled to a pulsed sinusoidal waveform at a high RF frequency, while a second electrode is coupled to a low-frequency sinusoidal waveform superimposed on a pulsed DC waveform.

[0020] Traditionally, plasmas are excited by a CW RF signal provided at a single frequency. In contrast, an arbitrary RF waveform can be a broadband RF waveform with a power spectrum spanning a certain frequency range. The superposition of two waveforms with power spectral densities in two corresponding frequency bands has a combined power spectral density that is the superposition of the two frequency bands. The power of the superimposed waveform can be distributed across the broadband formed by the superposition of the two overlapping frequency bands. In some cases, for example, the superposition of a low RF frequency bias waveform on a high RF frequency source waveform can carry power in non-overlapping frequency bands. Some other waveforms (such as modulated sine waves, e.g., amplitude-modulated or frequency-modulated waveforms) distribute their power across a certain frequency band.

[0021] Figure 1A A schematic representation of an example broadband plasma system 100 is shown. The example broadband plasma system 100 includes an example plasma device 110, an example EM circuit block 120 that provides EM power to the plasma device 110, and a controller 140 for adjusting input parameters of the EM circuit block 120. The controller 140 can be a microcontroller, a processor, or other programmable circuit and can be programmed accordingly, for example, by storing instructions in a memory that can be executed by the processing circuitry of the controller 140. In addition, the plasma system 100 includes a voltage and current (V1) sensor 128, a V1 analysis circuit 130, and a DC bias generation circuit 132. The controller 140 can also adjust the DC bias generation circuit 132. The plasma device 110 is shown in cross-section, and the EM circuit block 120 is illustrated as a block diagram.

[0022] The plasma apparatus 110 includes a main vacuum chamber (referred to as the plasma chamber 102) and a gas flow system coupled to the plasma chamber 102. The gas flow system is equipped with sensors, valves, pumps, and the like to control the pressure and flow of gas through the chamber 102. The gas flow system is configured to flow a mixture of process gas and carrier gas through a gas inlet 104 of the chamber 102 and remove excess gas and gaseous byproducts through an exhaust port 106 of a vacuum pump coupled to the gas flow system. A susceptor 108 configured to hold a substrate 112 (e.g., a semiconductor wafer) is included in the plasma apparatus 110. The susceptor 108 and substrate 112 are shown positioned within the plasma chamber 102, where the substrate 112 is processed. The substrate 112 can be loaded from a load lock 114 through a load window 115 and positioned on the susceptor 108 for processing. Typically, the temperature of the substrate 112 is controlled during processing by an external temperature control system 116 that includes heating and cooling hardware, such as a liquid cooling column 117 coupled to the pedestal 108 .

[0023] The apparatus 110 further includes RF electrodes configured to receive EM power to excite the gas discharge plasma. Figure 1A In the illustrated example, the plasma apparatus 110 is configured to ignite a direct plasma within the chamber 102 using electrodes configured to provide EM power to the plasma via capacitive coupling. Typically, when the plasma apparatus 110 is in a capacitively coupled plasma (CCP) configuration, a disk-shaped electrode is used to ignite the plasma in the chamber 102. In some embodiments, the RF electrode is a disk-shaped electrode in the upper portion of the chamber 102, referred to as the upper electrode 118. In the embodiments described herein, the pedestal 108 can function as both a substrate holder and a disk-shaped RF electrode (sometimes referred to as a lower electrode). To function as an RF electrode, the pedestal 108 is configured to include a disk-shaped conductive portion, which is generally located at the top of the pedestal and in contact with the substrate 112. The diameter of the lower electrode (which is the conductive portion of the pedestal 108) (not explicitly shown) is approximately the same as the diameter of the upper electrode 118, or in some embodiments, is relatively smaller.

[0024] In some other embodiments, a direct plasma may be ignited using the plasma apparatus 110 in an inductively coupled plasma (ICP) configuration, wherein the electrode supplying EM source power to the plasma is an antenna positioned outside the plasma chamber 102. The antenna may have various shapes, such as a helical coil-shaped electrode placed on an insulating (e.g., quartz) window in the ceiling of the plasma chamber 102 or a helical coil wrapped around an insulating portion of a curved sidewall of the cylindrical plasma chamber 102.

[0025] Typically, the conductive portions of the walls of the plasma chamber are coupled to a reference potential (referred to as ground). In various embodiments, the upper electrode 118 and the lower electrode (i.e., the pedestal 108) can be coupled to a waveform that provides EM source power or a waveform that provides EM bias power. Typically, the EM source power is used to ignite the plasma, while the EM bias power is used to tailor the plasma properties of the gas discharge. Additionally, the electrodes can be coupled to a DC bias or a pulsed DC bias. In some configurations (e.g., Figure 1A In the configuration shown), the electrodes of device 110 (e.g., base 108) can be grounded or floating.

[0026] Figure 1A The example EM circuit block 120 of the example broadband plasma system 100 schematically shown in FIG includes an adjustable function generator 122, a broadband amplifier 124, and an adjustable broadband impedance matching network 126. As described in detail below, the EM circuit block 120 provides a high-power broadband RF waveform at the upper electrode 118 of the plasma device 110 to excite the plasma in the chamber 102. The adjustable function generator can be an arbitrary function generator or even an arbitrary waveform generator, which can generate non-periodic waveforms.

[0027] It should be noted that in block diagrams of EM circuit blocks, the various components are schematically connected by straight lines. However, in physical systems, high-power RF waveforms may be coupled using a coaxial RF tube. The RF waveform in the RF tube refers to the RF voltage waveform and the RF current waveform, where the voltage is the potential of the inner conductor of the RF tube relative to the annular outer conductor, and the current is the current in the inner conductor, which is equal and opposite to the current in the outer conductor. Typically, the outer conductor (also called the shield) is coupled to ground (reference potential). The voltage and current are related by an impedance over a length comparable to the wavelength of the EM wave in the RF tube, which is generally frequency-dependent and position-dependent.

[0028] like Figure 1AAs shown, the signal path begins at function generator 122, coupling a low-power RF waveform to the input of amplifier 124. The signal path for the high-power, amplified RF waveform is a first RF transistor (schematically shown by a line) from the output of amplifier 124 to the input of impedance matching network 126. A second RF transistor, starting at the output of impedance matching network 126, couples the RF waveform to the terminals of upper electrode 118. As explained in further detail below, the impedance of impedance matching network 126 can be adjusted to adjust the high-power, broadband RF waveform at the terminals of upper electrode 118, thereby maximizing the EM power thereat. Generally, the impedance depends not only on the components of impedance matching network 126 (e.g., the adjustable inductor and capacitor), but also on the spectrum (i.e., frequency) of the broadband RF waveform. Therefore, the RF waveform at the terminals of upper electrode 118 is adjusted by synchronously configuring the variable inductor and capacitor of impedance matching network 126 and the spectrum of the broadband RF waveform output by adjustable function generator 122 by sending appropriate control signals from controller 140.

[0029] Function generator 122 can generate arbitrary waveforms in the RF range using appropriate digital and analog circuitry, such as oscillators, pulse generators, modulators, and combiners. DC bias generation circuit 132 can generate a constant DC bias or a pulsed DC bias waveform using, for example, a DC power supply and a chopper driven by a pulse train from a pulse generator. As explained above, while the power spectral density of a CW sinusoidal signal is concentrated at a single frequency, the power carried by more complex waveforms is distributed over a frequency band. In various embodiments, the frequency can be from about 100 kHz to about 300 MHz. The power spectrum of waveforms used to provide EM source power is typically at the higher end of this range, e.g., from about 10 MHz to about 300 MHz, while the power spectral density of waveforms providing EM bias power is typically in a frequency band falling within the lower frequency range of about 100 kHz to about 13 MHz.

[0030] The waveform at the output of function generator 122 is coupled to the input of broadband amplifier 124. In some embodiments, broadband amplifier 124 is a linear power amplifier that provides high output power of approximately 50W to approximately 10kW and has low harmonic distortion, such that the waveform of the input signal is preserved in the amplified output signal. Typically, linear amplifiers exhibit a tradeoff between bandwidth and power amplification, which makes it difficult and expensive to provide a single channel with both high bandwidth and high power amplification. For example, consider a plot of power gain (GP) versus frequency (f) for an amplifier, where GP is a constant GP0 up to a cutoff frequency fC (the bandwidth of the amplifier), beyond which GP typically decreases at a rate of 20dB / decade. While GP and fC can be adjusted via a negative feedback loop, the product (GP0 fC) is fixed. Thus, while a wide bandwidth amplifier (100 kHz to 300 MHz) can be used for both the EM bias power and the EM source power, the wider frequency range comes at the expense of lower power gain or loss of linearity, which requires that the gain be constant across the frequency range. Therefore, in the embodiments described in the present disclosure, the operating frequency range of a wideband amplifier (e.g., amplifier 124 in EM circuit block 120) includes either a lower frequency range of EM bias power (which may be 100 kHz to 13 MHz) or a higher frequency range of EM source power (which may be 10 MHz to 300 MHz), rather than the wider frequency range (100 kHz to 300 MHz) over which a plasma apparatus may use EM power (including both EM source power and EM bias power) to process a substrate. In one or more embodiments, the wideband amplifier 124 may be implemented as a wideband RF power amplifier, such as described in Application No. 16 / 572,708 (e.g., Figure 2 , Figure 6) (Agent Case No.: TEL-190559US01).

[0031] Figure 1A The illustrated example plasma device 110 uses EM source power provided by a broadband impedance matching network 126 and a DC bias provided by a DC bias generating circuit 132. In this example, the device 110 does not use EM bias power. Figure 1A In the illustrated block diagram, the broadband amplifier 124 may be designed to operate in a frequency band suitable for amplifying the EM source waveform without distortion (eg, a frequency band of 10 MHz to 300 MHz).

[0032] In the broadband plasma system described in the present disclosure, an adjustable function generator (such as the function generator 122 in the example plasma system 100) generates a periodic function, such as a sine wave whose characteristics (such as amplitude and frequency) can be adjusted during the process. For example, the function generator can output a frequency-modulated waveform, that is, a sine wave whose instantaneous frequency f changes periodically from a low value to a high value with a period TP. This means that f is periodically adjusted from (fC-Δf) to (fC+Δf), where fC is the center frequency and Δf is the frequency deviation around fC. The bandwidth BW of this waveform can be approximated by Carson's formula: BW=2(Δf+1 / TP). For example, if fC=13.56MHz, Δf=1MHz, and TP=10μs, then BW=2.2MHz, and the power distribution is within the frequency range of 12.46MHz to 14.46MHz. In another example, the function generator 122 can generate a rectangular or triangular (e.g., sawtooth) pulse train whose characteristics (such as ramp rate, pulse height, period, and duty cycle) can be adjusted during the process. The bandwidth of the pulse train will depend on its timing characteristics.

[0033] It should be noted that experiments conducted by the inventors have revealed that if the instantaneous frequency does not vary smoothly; for example, if f is abruptly changed in discrete steps (such as in a step function), the resulting gas discharge plasma may flicker (turn on and off) in an uncontrolled manner. Flickering increases process variability, which is undesirable. On the other hand, if the modulation function smoothly varies f, such as in a triangular or sinusoidal function, flickering can be avoided. Therefore, in the embodiments described in this disclosure, a function generator, for example, is used to generate a signal for supplying power to a plasma device (e.g., plasma device 110), wherein the signal processing circuitry adjusts the signal frequency relatively smoothly. In contrast, digital signal generators typically use circuitry that adjusts the signal frequency in abrupt steps. In some embodiments, analog signal processing techniques can be used to achieve smooth frequency changes. In addition to smoothly varying f, function generators and analog signal generators can provide smooth power adjustments without flickering. On the other hand, digital signal generators typically have stepped power adjustments, which can also cause flickering.

[0034] Plasma systems (e.g. Figure 1A The plasma system 100 in FIG. 1 is similar to a simple power system including a power supply, a load, a transmission line, and an impedance matching network.

[0035] The power source is a broadband amplifier (e.g., broadband amplifier 124) considered to be an ideal power source in series with a source impedance equal to the output impedance of the amplifier. Typically, the output impedance is a standard impedance, such as 50Ω. The load is a plasma device (e.g., plasma device 100), where the load impedance is the impedance between the terminals of the RF electrode (e.g., upper electrode 118) to which power is delivered and ground.

[0036] In a plasma system, the transmission line can be a coaxial first RF tube, which can be approximated by a lossless transmission line and modeled as a two-port network, namely, an input port and an output port. One end of the first RF tube (referred to as the source end) is the input port coupled to the output of a broadband amplifier. The characteristic impedance of the RF tube can be selected to be the same as the output impedance of the amplifier (e.g., 50Ω). The output port is the opposite end of the first RF tube and is referred to as the load end. In the plasma system described in the present disclosure, the load end is coupled to the input of a broadband impedance matching network. The output of the impedance matching network is coupled to the load at a terminal of an RF electrode of the plasma device through a second RF tube, where the load impedance is the impedance between the terminal and ground. As further explained below, the length of the second RF tube is relatively short, so that the RF tube is ideally connected. In other words, the input impedance of the short RF tube measured at one end is equal to the impedance of the connection at the opposite end, and the length of the short tube is relatively short relative to the wavelength of the EM wave in the RF tube.

[0037] The purpose of inserting an impedance matching network between the load impedance of the first RF tube and the load terminal is to adjust the impedance at the load terminal so that as much power as possible is transferred from the power source to the load. A broadband impedance matching network with variable circuit components enables efficient power transfer across the frequency range of the power spectrum of a broadband RF waveform. An example broadband impedance matching network is described in further detail below.

[0038] In the plasma system 100, the output of the amplifier 124 is coupled to the input of the impedance matching network 126 via a first RF tube, and the output of the impedance matching network 126 is coupled to the terminal of the upper electrode 118 of the plasma device 110 via a second RF tube, as shown in FIG. Figure 1A The output terminals of the impedance matching network 126 are positioned close to the terminals of the upper electrode 118 to avoid any transmission line impedance in the signal path after the impedance matching network 126. In general, the impedance of the RF tube of length l is small enough to be negligible if l < λ / 8, where λ is the representative wavelength of the broadband RF waveform in the RF tube. It should be noted that the system design should ensure that a short second RF tube is used between the impedance matching network and the electrode, especially when the second RF tube carries high-frequency (short λ) EM source power, such as Figure 1A The situation in the plasma system 100 in FIG.

[0039] Figure 1A The VI sensor 128 in the plasma system 100 includes a VI sensor assembly including a voltage pickup and a current pickup for sensing a time-varying electric field (E field) and a time-varying magnetic field (H field), respectively. In the plasma system 100, the VI sensor 128 is positioned such that its voltage pickup and current pickup are located at a position along the second RF tube that couples the impedance matching network 126 to the upper electrode 118, as shown in FIG. Figure 1A Here, a short RF tube is used for the signal path. This allows the VI sensor 128 to be placed close to the terminals of the upper electrode 118 so that the measured RF voltage waveform and RF current waveform are similar to the corresponding waveforms at the terminals of the upper electrode 118.

[0040] For illustrative purposes, Figure 1B An example VI sensor assembly is shown, for example, as described in co-pending application 17 / 514,815 filed on October 29, 2021 (Attorney Docket No.: TEL-210198US01) Figure 3 C, which co-pending application is incorporated herein by reference in its entirety.

[0041] Figure 1B A cutaway view of an example VI sensor assembly 150 is shown, comprising a conductive voltage pickoff 152 held by an insulating voltage pickoff holder 154 and a conductive current pickoff 156 supported by an insulating annular mandrel 158. For clarity, Figure 1B The second RF tube is not shown: its inner conductor will be a cylindrical conductor passing through the hole 160 , and the annular outer conductor will comprise the top and bottom conductive covers of the sensor assembly 150 . Figure 1B The conductive cover and the inner and outer conductors of the second RF tube are not shown.

[0042] The voltage pickup 152 is a ring surrounding the inner conductor that generates, through capacitive coupling, a signal proportional to the radial E-field between the inner and outer conductors of the second RF tube.

[0043] The current pickup 156 is a wire that passes through the hollow passage 162 and is wound around a circular axis inside the annular mandrel 158, as shown in FIG. Figure 1BTypically, the H-field has a negligible effect on the signal output of voltage pickup 152, but the perturbation of the radial E-field on current pickup 156 cannot be ignored. Therefore, an E-field shielding scheme is included in sensor assembly 150. E-field shielding is provided by conductive protrusions on the top and bottom covers of sensor assembly 150, which can be positioned within slots 164 and 166, respectively. These conductive protrusions are grounded by being part of the top and bottom covers; thus, they are part of the grounded outer conductor of the second RF tube. The grounded conductive protrusions shield current pickup 156 from the E-field, but not from the H-field, because the insulating walls of slots 164 and 166 prevent any ground current from flowing into these two conductive protrusions. Therefore, current pickup 156 is a semi-ring inside the second RF tube that senses the time-varying H-field circulating around the inner conductor through inductive coupling.

[0044] In this example, the voltage pickup 152 and the current pickup 156 are positioned symmetrically about the center axis of the second RF tube (ie, the center axis of the aperture 160). The symmetry provides higher measurement accuracy by taking advantage of the cancellation of some parasitic voltages and currents induced in the conductive pickups.

[0045] Reference again Figure 1A The measured RF voltage waveform and RF current waveform are transmitted from the VI sensor 128 to the VI analysis circuit 130 using, for example, a coaxial cable.

[0046] The VI analysis circuit 130 may include an amplifier (e.g., a differential amplifier) ​​coupled to its input to receive and amplify the incoming RF voltage and current waveforms from the VI sensor. The amplified waveforms may be analyzed by the VI analysis circuit 130, which may include electronic circuitry configured to extract relevant electrical characteristics from the RF voltage and current waveforms and output an electronic feedback signal encoding the extracted electrical characteristics. The electrical characteristics extracted from the properties of the RF voltage and current waveforms may include peak and rms values ​​of voltage and current, instantaneous frequency, instantaneous power, average power, and power spectral density (from harmonic analysis). The electronic circuitry for performing the analysis and extraction may be implemented as a separate signal processor, such as a programmable digital signal processor. The feedback signal from the output buffer of the VI analysis circuit 130 may be coupled to an input port of the controller 140 for process monitoring and / or feedback control, as further described below.

[0047] In some embodiments, the DC bias (or pulsed DC) from the DC bias generating circuit 132 may also be superimposed on the waveform at the terminal of the upper electrode 118, as shown in FIG. Figure 1A Schematically shown in .

[0048] exist Figure 1AIn the example shown, the load impedance is the impedance between the terminals of the upper electrode 118 and ground, and therefore, when plasma is present in the chamber 102, the load impedance includes the impedance of the plasma. It is not uncommon to have a large mismatch between the source impedance (i.e., the output impedance of the amplifier 124) and the load impedance. Therefore, it is common practice to insert an impedance matching network in the signal path between the load terminal of the first coaxial RF tube and the load. Without the impedance matching network 126, the mismatch could result in undesirably low power being delivered to the plasma device 110.

[0049] When f is low, λ is large, and if l < λ / 8, the wave nature of the EM signal in the RF tube can be neglected, and the RF tube can be approximated by an ideal connection. However, as f increases, λ shrinks, so it may be wrong to neglect the fact that the EM signal in the RF tube is an EM wave. In other words, the RF tube must be modeled like a waveguide, along which the transmitted EM wave propagates from the source to the load, and the reflected wave (reflected at the load) propagates in the opposite direction. The ratio of the amplitude of the reflected wave to the amplitude of the transmitted wave is called the reflection coefficient Γ. If there is a large mismatch between the source and load impedances, the magnitude of the reflection coefficient (|Γ|) can be significantly higher, resulting in poor power transfer to the plasma device 110. In addition, interference between the transmitted wave and the undesired reflected wave can lead to standing wave patterns, which in some cases can damage the amplifier 124. An impedance matching network 126 is used to suppress reflections and standing wave modes in the first RF tube to efficiently transfer EM power to a load impedance, i.e., the impedance between the terminals of the RF electrode (e.g., the upper electrode 118) to which the power is delivered and ground. As described in further detail below, the broadband impedance matching network in embodiments of the plasma system includes variable inductors and capacitors to adjust the impedance of the matching network to achieve efficient power transfer across the frequency range of the power spectrum of the broadband RF waveform by suppressing reflections at the load end of the first RF tube such that |Γ| ≤ 0.6.

[0050] Typically, an impedance matching network includes only approximately lossless circuit components (e.g., approximately ideal inductors, capacitors, and switches) to avoid undesirable resistive power losses in the impedance matching network. In this disclosure, a circuit approximated by an ideal inductor, capacitor, and switch network is referred to as a reactive circuit. For a particular circuit topology and a particular selection of reactive components, the impedance of the matching network is a specific reactance function XM(f). Other impedances in the power system are the output impedance of the amplifier 124, the transmission line impedance, and the load impedance (which includes the plasma impedance). Typically, the power delivered to a given load impedance depends on the various impedances in the power system. Optimizing the power delivered to the load impedance means optimizing the impedance of the impedance matching network, i.e., the reactance function XM(f). In other words, the purpose of selecting the inductance and capacitance of the matching network is to maximize the power delivered to the load (i.e., the plasma device 110, including the plasma) for a given broadband RF waveform (e.g., the output of the function generator 122).

[0051] In conventional single-frequency (or narrowband) systems, impedance matching involves designing an impedance matching network during the development process. After the inductors and capacitors of the impedance matching network are selected so that the power delivered to the load is maximized at the operating frequency (or the center frequency of the narrowband), the reactive elements are changed only within a narrow range during processing to compensate for minor changes in plasma processing conditions.

[0052] In broadband systems (such as Figure 1A In a broadband system such as plasma system 100, the operating frequency can be intentionally varied by discrete amounts, for example, during different cycles of a cyclic process. Alternatively, a broadband system such as plasma system 100 can utilize an RF waveform with a continuously varying frequency, such as a frequency modulated sinusoidal waveform. Thus, broadband impedance matching network 126 includes one or more variable reactive components.

[0053] For illustrative purposes, Figure 1C An example reactive circuit for forming the matching network 126 is shown, for example, as described in FIG. 29 of application Ser. No. 17 / 12,168, filed Sep. 4, 2020, which is incorporated herein by reference.

[0054] Figure 1CA schematic diagram of an example reactance circuit 170 is shown that includes three variable capacitors C1, C2, and C3 and two variable inductors L1 and L2. As explained above, because the reactive components C1, C2, C3, L1, and L2 may change during processing, reactance circuit 170 can be implemented as a broadband impedance matching network 126. In addition, reactance circuit 170 includes two three-terminal switches S1 and S2, which provide additional control variables for adjusting the reactance of reactance circuit 170. It should be noted that the variable capacitors and inductors may include switched capacitors and switched inductors that include multiple two-terminal switches, as explained in further detail below.

[0055] like Figure 1A As shown, an impedance matching network 126 is inserted in the signal path between the output of the amplifier 124 and the terminal of the upper electrode 118. As mentioned above, the first RF tube can couple the output of the amplifier 124 to the input of the impedance matching network 126 (by Figure 1C The output of the impedance matching network 126 (indicated by the arrow on the left side of the reactance circuit 170) Figure 1C The reactance circuit 170 (indicated by the box arrow to the right of the reactance circuit 170) can be coupled to the terminal of the upper electrode 118 through a shorter second RF tube. The inventors have demonstrated that in a plasma system, |Γ|≤0.6 in the operating frequency range of 13.56 MHz to 220 MHz, where the reactance circuit 170 has been implemented for a broadband impedance matching network.

[0056] Variable capacitors C1, C2, and C3 can be implemented in several ways. A mechanically variable capacitor may include a movable portion, such as a plate of a tuning capacitor. For example, the distance and / or overlapping area of ​​the two plates of capacitor C1 can be adjusted by a suitable mechanical structure. An electrically variable capacitor such as a varactor diode can be used as the variable capacitor C1, wherein the width of the depletion layer varies due to the bias voltage across a metal oxide semiconductor (MOS) capacitor or a pn junction diode. Another method for implementing the electrically variable capacitor C1 may be to use an array comprising a plurality of switched capacitors connected in parallel. Each switched capacitor includes a capacitor and a two-terminal switch connected in series. The capacitance of capacitor C1 can be adjusted by controlling the state of the two-terminal switches of the plurality of switched capacitors. In some embodiments, the capacitance of the variable capacitors (e.g., C1, C2, and C3) may be able to vary in the range of about 3 pF to about 4000 pF.

[0057] The variable inductors L1 and L2 can also be implemented in several ways. For example, similar to the electrically variable capacitor C1 implemented by a switched capacitor array, the variable inductor L1 can be implemented as an array of switched inductors connected in series. Each switched inductor includes an inductor and a two-terminal switch connected in parallel. The inductance of the inductor L1 can be adjusted by controlling the state of the two-terminal switches of the multiple switched inductors. Alternatively, the variable inductor L1 can have its inductance changed by mechanical movement. For example, the coupling between the magnetic core and the coil of the first inductor L1 can be adjusted by a suitable mechanical structure. In some embodiments, the inductance of the variable inductors (e.g., L1 and L2) can be able to vary in the range of about 50nH to about 20μH.

[0058] Similar to broadband amplifiers, the broadband impedance matching network in embodiments of the present disclosure is designed for an operating frequency range, which can be a higher frequency range of approximately 10 MHz to approximately 300 MHz or a lower frequency range of approximately 100 kHz to approximately 13 MHz. The broadband impedance matching network 126 is designed for the waveform of the EM source power; therefore, the impedance matching network 126 covers the frequency range of 10 MHz to 300 MHz. However, for the waveform of the EM bias power, an impedance matching network covering the lower frequency range of 100 kHz to 13 MHz will be used.

[0059] Adjustments to the impedance matching network 126 can be made using Figure 1A The controller 140 is schematically shown in FIG. The controller 140 can be configured to transmit control signals to adjust the inductance and capacitance of the variable inductor and capacitor of the broadband impedance matching network 126, thereby adjusting the waveform at the load terminal (the terminal of the upper electrode 118 in the plasma device 110). In addition, the controller 140 can make more precise adjustments to the impedance of the impedance matching network 126 by adjusting the waveform (e.g., frequency) of the broadband RF waveform at the function generator 122. The functions of the controller 140 will be explained in further detail below.

[0060] As mentioned above, the VI sensor 128 can be positioned in the portion of the RF tube between the output of the impedance matching network 126 and the terminals of the electrode 118 to measure the RF voltage and current waveforms delivered to the plasma device 110 and transmit this data to the VI analysis circuit 130. The VI analysis circuit 130 can be configured to extract relevant electrical characteristics from the waveforms and output an electronic feedback signal encoding the extracted electrical characteristics. The feedback signal from the VI analysis circuit 130 can be coupled to the controller 140 for process monitoring and / or feedback control. The electrical characteristics received from the VI analysis circuit 130 can be stored in a memory device and processed by a processor. Based on the feedback, the processor can instruct the controller 140 to generate appropriate control signals, which are transmitted to various components of the EM circuit block 120 and the DC bias generation circuit 132 to adjust the RF voltage and current waveforms, as well as the impedance between the output of the broadband amplifier 124 of the impedance matching network 126 and the load, including the plasma.

[0061] As described above, the controller 140 is used to adjust input parameters of an EM circuit block (e.g., EM circuit block 120) and an optional DC bias generation circuit (e.g., DC bias generation circuit 132) by transmitting control signals to corresponding input ports of the EM circuit block and the optional DC bias generation circuit, thereby adjusting the broadband RF waveform at the terminals of the RF electrodes of the plasma device 110.

[0062] like Figure 1A As shown, in the plasma system 100, the controller 140 can generate and transmit a plurality of control signals to adjust input parameters of the EM block 120 and the DC bias generation circuit 132, thereby regulating a broadband RF waveform including an RF voltage waveform and an RF current waveform at the terminals of the upper electrode 118. The controller 140 can include a processor and a memory device in which data and encoded instructions for the processor can be stored. The data includes process recipes and electrical characteristics decoded from feedback signals output from the VI analysis circuit 130, which are received at input ports of the controller 140, such as Figure 1A These instructions, when executed by the processor, retrieve the data from the memory device and generate the appropriate control signals mentioned above based on the data.

[0063] exist Figure 1AIn the illustrated example embodiment, the first, second, and third output ports of the controller 140 are configured to transmit first, second, and third control signals, respectively, to synchronously adjust input parameters of the function generator 122, the broadband amplifier 124, and the broadband impedance matching network 126. In addition, a fourth control signal may be generated and transmitted from the fourth output port to adjust input parameters of the DC bias generation circuit 132, such as Figure 1A As shown. In some embodiments, the DC bias generation circuit 132 may be optional. Each control signal is transmitted from the controller 140 and coupled to an input port of the EM circuit block 120 or the optional DC bias generation circuit 132 using, for example, a coaxial cable. Collectively, these control signals synchronously adjust input parameters of the EM circuit block 120 and the DC bias generation circuit 132 to adjust the broadband RF waveform that provides EM power to the plasma device 110. For example, a first control signal transmitted to the function generator 122 can adjust the spectrum (i.e., frequency) of the RF waveform; a second control signal transmitted to the broadband amplifier 124 can adjust its power gain to adjust the amplitude of the RF waveform; and a third control signal transmitted to the broadband impedance matching network 126 can adjust the phase relationship between the RF voltage waveform and the RF current waveform to adjust the EM power delivered at the terminals of the upper electrode 118. In some embodiments, when the DC bias generation circuit 132 is used, a fourth control signal transmitted to the DC bias generation circuit 132 can adjust a DC bias superimposed on the RF waveform, such as the DC voltage, pulse frequency, and duty cycle of the DC pulses.

[0064] Some adjustments are process-specific and are specified in a process recipe stored in a memory device of the controller 140. For example, the plasma system 100 may perform a cyclic process that alternates between an etch cycle and a deposition cycle, wherein the operating frequency, DC bias, and RF source power may be specified differently for the two cycles in the cyclic process. In addition to adjusting the power gain of the amplifier 124 and the output voltage of the DC bias generation circuit 132, performing this process may also require appropriate synchronization adjustments to the function generator 122 and the broadband impedance matching network 126 to tune for the change in operating frequency at the beginning of each cycle of the cyclic process. Thus, the controller 140 may retrieve instructions from the recipe, execute these instructions using a processor to transmit control signals to adjust the variable inductor and / or capacitor in the broadband impedance matching network 126, and simultaneously transmit the control signals to the frequency selector in the function generator 122 at the times specified in the instructions in the recipe.

[0065] In addition to intentional changes in the waveform (e.g., changes specified by a recipe), random variations may also occur during processing. As explained above, while the plasma is maintained in the chamber 102, the load impedance includes the plasma. Because plasma properties may vary during the plasma process, the load impedance may also typically vary during the process, resulting in undesirable and random variations in the waveform carrying the EM power from the EM circuit block 120 to the plasma device 110. Therefore, the controller 140 may make additional adjustments to the process control to perform waveform tuning and feedback control.

[0066] Figure 2 Shows something similar to the reference above Figure 1A A schematic representation of another broadband plasma system 200 of the example plasma system 100 is depicted. In the plasma system 200, the EM circuit block 120 supplies EM source power to the plasma device 110 at the pedestal 108. As described above, the conductive portion (lower electrode) of the pedestal 108 may be an RF electrode for exciting the plasma in the chamber 102. Figure 2 In the example embodiment of FIG, the upper electrode 118 is present but is not coupled to an RF or DC power source. In some embodiments, the upper electrode may not be present if it is not needed. Figure 2 As shown, if the upper electrode 118 is present but not used, it may be floating (open circuit) or grounded (ie, coupled to a reference potential), or coupled to a chamber wall, which may be coupled to ground.

[0067] Figure 3 and Figure 4 An embodiment of a plasma system is shown in which an EM circuit block uses several broadband RF waveforms to provide EM power to a plasma device. Figure 3 and Figure 4 The plasma system 300 and the plasma system 400 shown in FIG. 3 are examples of plasma systems in which two broadband RF waveforms are simultaneously generated for the referenced Figure 1A An example of an embodiment of powering the plasma device 110 is described: a high frequency RF waveform provides EM source power, and a low frequency RF waveform provides EM bias power.

[0068] The two broadband RF waveforms are generated using two single-channel EM circuit blocks to accommodate the wide frequency range (100 kHz to 300 MHz) typically used for RF waveforms carrying EM source power and EM bias power in plasma systems. As explained above, linear amplifiers exhibit a tradeoff between bandwidth and power amplification, which makes it difficult and expensive to include a linear power amplifier in a plasma system that has both high bandwidth (100 kHz to 300 MHz) and high power amplification (output power between 50 W and 10 kW). Therefore, while a plasma system could include a multi-channel broadband amplifier for amplifying multiple broadband RF waveforms within a smaller frequency range (e.g., a range of 100 kHz to 13 MHz for EM bias power, or a range of 10 MHz to 300 MHz for EM source power), it may be advantageous to use two single-channel EM circuit blocks, one for EM source power and the other for EM bias power, because a dual-channel broadband amplifier that can provide high power with low distortion over a wide frequency range for the various RF waveforms used simultaneously in plasma processing is expensive.

[0069] Figure 3 and Figure 4 Example plasma systems 300 and 400 are shown, wherein the corresponding EM circuit blocks 350 and 450 are dual-channel EM circuit blocks comprising two single-channel EM circuit blocks, each channel being used for a broadband RF waveform. The first EM circuit block 120 can be used for a higher-frequency broadband RF waveform, and the second EM circuit block 320 can be used for a lower-frequency broadband RF waveform. Each single-channel EM circuit block includes a function generator, a broadband amplifier, and a broadband impedance matching network. Although in the embodiments of the present disclosure, each dual-channel EM circuit block uses two function generators (one for each channel), it should be understood that in some other embodiments, a single dual-channel function generator can be used instead of two function generators.

[0070] Figure 3 The plasma system 300 is shown, which includes the plasma device 110 and a dual-channel EM circuit block 350, which includes a first EM circuit block 120 for supplying a higher frequency EM source power and a second EM circuit block 320 for supplying a lower frequency EM bias power. It should be noted that the first EM circuit block 120 is the same as the one described above with reference to FIG. Figure 1A and Figure 2 The higher frequency EM circuit block 120 is described identically.

[0071] As mentioned above Figure 1AAs explained, the higher frequency first EM circuit block 120 includes a function generator 122, a high frequency broadband amplifier 124, and a high frequency broadband impedance matching network 126. The second EM circuit block 320 also includes a function generator 322 similar to function generator 122, but as a lower frequency system, second EM circuit block 320 has a low frequency broadband amplifier 324 and a low frequency broadband impedance matching network 326. Function generator 122 outputs a higher frequency broadband RF waveform that can be amplified by high frequency broadband amplifier 124, while function generator 322 is configured to output a lower frequency broadband RF waveform that can be amplified by low frequency broadband amplifier 324.

[0072] like Figure 3 As shown, the upper electrode 118 and the pedestal 108 receive power to ignite the plasma in the plasma chamber 102. Note that in addition to supporting the substrate, the pedestal 108 is also configured to function as an RF electrode. As explained above, to function as an RF electrode, the pedestal 108 is configured to include a disk-shaped conductive portion that is generally located at the top of the pedestal in contact with the substrate 112. The pedestal 108 in the plasma system 300 is similar to the pedestal 108 described above with reference to FIG. Figure 2 1. The pedestal 108 in the plasma system 200 is depicted. In this example embodiment (plasma system 300), the upper electrode 118 is used to couple EM source power to the plasma, while the pedestal 108 is used to couple EM bias power to the plasma. Thus, a higher-frequency, first EM circuit block 120 is shown supplying power at the terminals of the upper electrode 118. In contrast, EM bias power is supplied at the pedestal 108 by a lower-frequency, second EM circuit block 320.

[0073] The plasma system 300 includes a first VI sensor 128 and a first VI analysis circuit 130 to sense the RF voltage waveform and the RF current waveform coupled to the upper electrode 118 (similar to Figure 1A In addition, there is a second VI sensor 328 and a second VI analysis circuit 330 to sense the RF voltage waveform and RF current waveform coupled to the pedestal 108 (similar to Figure 2 The electrical characteristics extracted from the various waveforms by the VI analysis circuits 130 and 330 are transmitted to the controller 140 for storage and feedback control. The controller 140 is used to synchronously adjust the input parameters of the first EM circuit block 120, the second EM circuit block 320, and the DC bias generation circuits 132 and 332.

[0074] Figure 4A plasma system 400 is shown that includes a plasma device 110 and an EM circuit block 450. Similar to the dual-channel EM circuit block 350, the dual-channel EM circuit block 450 also includes a higher-frequency first EM circuit block 120 for supplying EM source power and a lower-frequency second EM circuit block 320 for supplying EM bias power. However, unlike the EM circuit block 350, the EM source power and the EM bias power are superimposed in the EM circuit block 450 by using, for example, the same RF tube for both the EM source power and the EM bias power. The superimposed waveforms are coupled to the plasma device 110 at the terminals of the pedestal 108. The pedestal 108 uses the superimposed EM power to couple power to the plasma ignited in the chamber 102.

[0075] In the example plasma system 400, the upper electrode 118 is not used to couple EM power to Figure 4 The plasma in the plasma chamber 102 is shown. Figure 2 As explained, in some embodiments, if an upper electrode is not required, then the upper electrode may not be present. Figure 4 As shown, if the upper electrode 118 is present but not used, it can be floating (open circuit) or grounded (i.e., coupled to a reference potential), or coupled to a chamber wall, which can be coupled to ground, similar to plasma system 200 (see Figure 2 ). In addition, since the upper electrode 118 is not coupled to any power source, the plasma system 400 uses only one VI sensor 128 and VI analysis circuit 130 to sense and analyze the RF voltage waveform and RF current waveform supplied to the pedestal 108. Similarly, the plasma system 400 can include only one DC bias generation circuit 132 coupled to the pedestal 108.

[0076] For processing substrates (e.g. Figures 1A to 4 The method 500 of the substrate 112 in FIG. Figure 5 In the flowchart shown. Figure 5 In a method 500 described in the flowchart of FIG. 1 , a substrate is processed using a plasma ignited in a plasma device using EM power carried in a broadband RF waveform and coupled to the plasma via electrodes of the plasma device. EM circuitry delivers EM power carried in the broadband RF waveform to terminals of each electrode.

[0077] As indicated at block 510, a function generator configured to generate various arbitrary waveforms (as described above with reference to FIG) is used, for example. Figure 1A The broadband RF waveform output by the function generator is coupled to the input port of the broadband linear power amplifier, such as Figure 5As indicated by box 512 in .

[0078] In block 520, a broadband linear power amplifier (as described above with reference to Figure 1A The broadband amplifier 124 described above is used to amplify the broadband RF waveform. The broadband amplifier outputs the amplified waveform. As a linear power amplifier, the output of the broadband amplifier has high power compared to the output of the function generator, and the waveform maintains high fidelity (i.e., low distortion).

[0079] The amplified waveform at the output of the broadband amplifier is coupled to the source terminal of the first RF tube, as indicated by block 530. As described above, the first RF tube is a coaxial RF tube, which can be modeled as a lossless transmission line. As indicated by block 532, the load terminal of the first RF tube is coupled to the input terminal of the broadband impedance matching network. The load terminal of the RF tube is opposite the source terminal of the first RF tube.

[0080] A broadband impedance matching network (such as broadband impedance matching network 126 described above) includes switches, variable inductors, and variable capacitors. These components are connected in a network known as a reactance circuit, examples of which are described above. The impedance of a corresponding matching network depends on the selection of the variable inductor, variable capacitor, and switch states. Furthermore, the impedance is frequency-dependent. The controller can be programmed to set input parameters for selecting the impedance of a corresponding broadband matching network to achieve efficient power transfer from the EM circuit block to the plasma device over the frequency range of the broadband RF waveform spectrum.

[0081] Figure 5 Block 540 in the illustrated flow chart indicates that a second RF tube can be used to couple the waveform at the output of the impedance matching network to the terminals of the RF electrode. The waveform at the terminals of the RF electrode (matched for efficient power transfer to the plasma device) ignites a plasma in the plasma chamber of the plasma device.

[0082] Block 550 indicates that the broadband RF waveform at the terminals of the RF electrodes may be adjusted by a feedback loop, as shown in FIG. Figure 1A to Figure 1B described.

[0083] As mentioned above, adjustments are made using control signals from a controller that set various input parameters of the EM circuit block. The feedback signal can be based on the RF voltage waveform and the RF current waveform supplied to the electrode terminals. The RF waveform can be measured using, for example, a VI sensor. The VI sensor can be configured to measure the RF waveform by sensing the E field and H field in a short second RF tube between the output of the impedance matching network and the terminals of the RF electrode of the plasma device, as described above with reference to Figure 1A and Figure 1B The measured RF waveform can be analyzed to generate a feedback signal. Figure 1A As described, analysis can be performed in a VI analysis circuit that receives the measured RF waveform from the VI sensor. A feedback signal can be coupled from the VI analysis circuit to a controller using, for example, a coaxial cable. As described above, the controller can be used to adjust the waveform, as indicated by block 550 in the flowchart. Adjustments can be made by sending control signals from the controller to various components of the EM circuit block used to generate the broadband RF waveform.

[0084] Example 1. A plasma system includes a plasma apparatus, the plasma apparatus comprising: a plasma chamber; a susceptor configured to hold a substrate in the chamber; and a radio frequency (RF) electrode configured to ignite plasma in the chamber; an electromagnetic (EM) circuit block coupled to the RF electrode, the EM circuit block comprising: a function generator configured to output a broadband RF waveform having an EM power distribution within a frequency range; a broadband amplifier coupled to an output of the function generator, the amplifier having an operating frequency range including the frequency range; and a broadband impedance matching network having an input coupled to an output of the broadband amplifier and an output coupled to a terminal of the RF electrode, the broadband impedance matching network having an operating frequency range including the frequency range; and a controller configured to adjust an input parameter of the EM circuit block.

[0085] Example 2. The plasma system of example 1, wherein the broadband impedance matching network comprises a variable inductor.

[0086] Example 3. The plasma system of either example 1 or 2, wherein the broadband impedance matching network comprises a variable capacitor.

[0087] Example 4. The plasma system of any one of Examples 1 to 3, further comprising a first RF tube having a source terminal coupled to the output terminal of the broadband amplifier and a load terminal coupled to the input terminal of the broadband impedance matching network, the load terminal being opposite the source terminal, wherein during operation, a reflection coefficient, which is a ratio of an amplitude of a reflected EM wave to an amplitude of a transmitted EM wave, has a magnitude less than or equal to 0.6, wherein an EM wave in the first RF tube is a superposition of the transmitted EM wave propagating from the source terminal to the load terminal and the reflected EM wave propagating in an opposite direction.

[0088] Example 5. The plasma system of any one of Examples 1 to 4, wherein the operating frequency range of the broadband amplifier and the operating frequency range of the impedance matching network include a frequency range greater than or equal to 10 MHz and less than or equal to 300 MHz.

[0089] Example 6. The plasma system of any one of Examples 1 to 5, further comprising a DC bias generating circuit having an output coupled to the RF electrode, the DC bias generating circuit being configured to output a constant DC bias or a pulsed DC bias waveform.

[0090] Example 7. The plasma system of any one of Examples 1 to 6, wherein the RF electrode is a disk-shaped electrode disposed in an upper portion of the chamber.

[0091] Example 8. The plasma system of any one of Examples 1 to 7, wherein the RF electrode is a disk-shaped conductive portion of the pedestal.

[0092] Example 9. The plasma system of any one of Examples 1 to 8, wherein the RF electrode is an antenna positioned outside the plasma chamber.

[0093] Example 10. The plasma system of any one of Examples 1 to 9, further comprising: a voltage and current (VI) sensor, the VI sensor comprising a voltage pickup and a current pickup positioned at a location along a second RF tube that couples the broadband impedance matching network to the RF electrode, wherein the VI sensor is configured to measure an RF voltage waveform and an RF current waveform at the location in the second RF tube; and a VI analysis circuit configured to receive the RF voltage waveform and the RF current waveform, wherein the VI analysis circuit comprises electronic circuitry configured to extract electrical characteristics from the received RF voltage waveform and RF current waveform and output an electronic feedback signal encoding the electrical characteristics.

[0094] Example 11. The plasma system of any one of Examples 1 to 10, wherein the length of the second RF tube is less than one eighth of a representative wavelength of the RF voltage waveform and the RF current waveform.

[0095] Example 12. The plasma system of any one of Examples 1 to 11, wherein the controller comprises: an input port configured to receive the electronic feedback signal; an electronic memory; a processor; data and instructions stored in the memory, wherein the data comprises a process recipe and the electrical characteristics, and wherein the instructions, when executed by the processor, generate a control signal; and an output port configured to transmit the control signal to the input port of the EM circuit block.

[0096] Example 13. A plasma system comprising: a plasma device; a dual-channel electromagnetic (EM) circuit block, the dual-channel EM circuit block comprising: a first EM circuit block comprising a first function generator, a first broadband amplifier, and a first broadband impedance matching network, wherein the first EM circuit block outputs a first broadband RF waveform coupled to the plasma device, the first broadband RF waveform having an EM power distribution within a first frequency range; and a second EM circuit block comprising a second function generator, a second broadband amplifier, and a second broadband impedance matching network, wherein the second EM circuit block outputs a second broadband RF waveform coupled to the plasma device, the second broadband RF waveform having an EM power distribution within a second frequency range, the second range being different from the first range; and a controller configured to adjust a plurality of input parameters of the EM circuit block.

[0097] Example 14. The plasma system of Example 13, wherein the first frequency range includes a frequency range greater than or equal to 10 MHz and less than or equal to 300 MHz, and wherein the second frequency range includes a frequency range greater than or equal to 100 kHz and less than or equal to 13 MHz.

[0098] Example 15. The plasma system of either Example 13 or 14, wherein the plasma apparatus comprises a plasma chamber, an upper RF electrode, and a lower RF electrode, the lower RF electrode being a pedestal configured to support a substrate in the plasma chamber.

[0099] Example 16. The plasma system of any one of Examples 13 to 15, wherein the first broadband RF waveform and the second broadband RF waveform are coupled to different RF electrodes of the plasma device.

[0100] Example 17. The plasma system of any one of Examples 13 to 16, wherein the first broadband RF waveform and the second broadband RF waveform are coupled to a same RF electrode of the plasma device.

[0101] Example 18. A method of operating a plasma processing system, the method comprising: outputting a broadband radio frequency (RF) waveform at an output of a function generator; coupling the output of the function generator to an input of a broadband amplifier; outputting an amplified broadband RF waveform at the output of the broadband amplifier; coupling the output of the broadband amplifier to a source terminal of a first RF tube; coupling a load terminal of the first RF tube to an input terminal of a broadband impedance matching network, the load terminal being opposite the source terminal; and coupling the output of the broadband impedance matching network to a terminal of an RF electrode of a plasma device using a second RF tube, the coupling providing EM power at the RF electrode, the EM power igniting plasma in a plasma chamber of the plasma device.

[0102] Example 19. The method of Example 18 further comprises adjusting the broadband RF waveform at the terminals of the RF electrode of the plasma device via a feedback loop.

[0103] Example 20. The method of any one of Examples 18 or 19, further comprising: measuring an RF voltage waveform and an RF current waveform using a voltage pickup and a current pickup of a voltage and current (VI) sensor located at a location along the second RF tube; transmitting the RF voltage waveform and the RF current waveform to a VI analysis circuit, the VI analysis circuit comprising an electronic circuit system configured to perform analysis of the received waveforms; performing the analysis using the electronic circuit system to extract electrical characteristics from the received waveforms; outputting an electronic feedback signal encoding the electrical characteristics; and coupling the electronic feedback signal to an input port of a controller.

[0104] Example 21. The method of any one of Examples 18 to 20, further comprising: storing the electrical characteristics encoded in the feedback signal in a memory device of the controller; generating a plurality of control signals based on processing the electrical characteristics using instructions executed by a processor of the controller; transmitting each control signal to a respective input port of the function generator, the broadband amplifier, and the broadband impedance matching network; and synchronously adjusting input parameters of the function generator, the broadband amplifier, and the broadband impedance matching network based on the control signals, the adjustments adjusting a broadband RF waveform at a terminal of an RF electrode of the plasma device.

[0105] Although the present invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments, as well as other embodiments of the present invention, will be apparent to those skilled in the art by reference to the description. Accordingly, the appended claims are intended to cover any such modifications or embodiments.

Claims

1. A plasma system comprising: A plasma device, the plasma device comprising: Plasma chamber; a susceptor configured to hold a substrate in the chamber; and a radio frequency (RF) electrode configured to excite a plasma in the chamber; an electromagnetic (EM) circuit block coupled to the RF electrode, the EM circuit block comprising: a function generator configured to output a broadband RF waveform having an EM power distribution over a frequency range; a broadband amplifier coupled to an output of the function generator, the broadband amplifier having an operating frequency range including the frequency range; and a broadband impedance matching network having an input coupled to the output of the broadband amplifier and an output coupled to a terminal of the RF electrode, the broadband impedance matching network having an operating frequency range including the frequency range; and A controller is configured to adjust an input parameter of the EM circuit block.

2. The plasma system of claim 1, wherein: The broadband impedance matching network includes a variable inductor.

3. The plasma system of claim 1, wherein: The broadband impedance matching network includes a variable capacitor.

4. The plasma system of claim 1, further comprising a first RF tube having a source terminal coupled to the output terminal of the broadband amplifier and a load terminal coupled to the input terminal of the broadband impedance matching network, the load terminal being opposite to the source terminal, wherein During operation, a magnitude of a reflection coefficient, which is a ratio of an amplitude of a reflected EM wave to an amplitude of a transmitted EM wave, is less than or equal to 0.6, wherein the EM wave in the first RF tube is a superposition of the transmitted EM wave propagating from the source end to the load end and the reflected EM wave propagating in an opposite direction.

5. The plasma system of claim 1, further comprising a DC bias generating circuit having an output terminal coupled to the RF electrode, the DC bias generating circuit being configured to output a constant DC bias or a pulsed DC bias waveform.

6. The plasma system of claim 1, wherein: The RF electrode is a disk-shaped electrode disposed in the upper part of the chamber.

7. The plasma system of claim 1, wherein: The RF electrode is a disk-shaped conductive portion of the pedestal.

8. The plasma system of claim 1, wherein: The RF electrode is an antenna positioned outside the plasma chamber.

9. The plasma system of claim 1, further comprising: a voltage and current (VI) sensor comprising a voltage pickup and a current pickup placed at a location along a second RF tube that couples the broadband impedance matching network to the RF electrode, wherein the VI sensor is configured to measure an RF voltage waveform and an RF current waveform at the location in the second RF tube; and A VI analysis circuit is configured to receive the RF voltage waveform and the RF current waveform, wherein the VI analysis circuit includes an electronic circuit system configured to extract electrical characteristics from the received RF voltage waveform and the RF current waveform and output an electronic feedback signal encoding the electrical characteristics.

10. The plasma system of claim 9, wherein: The length of the second RF tube is less than one eighth of a representative wavelength of the RF voltage waveform and the RF current waveform.

11. The plasma system of claim 9, wherein: The controller includes: an input port configured to receive the electronic feedback signal; Electronic storage; processor; Data and instructions stored in this memory, Among other things, the data includes the process recipe and these electrical characteristics, and wherein the instructions, when executed by the processor, generate control signals; and An output port is configured to transmit the control signal to an input port of the EM circuit block.

12. A plasma system comprising: Plasma devices; A dual-channel electromagnetic (EM) circuit block, the dual-channel EM circuit block comprising: a first EM circuit block, the first EM circuit block comprising a first function generator, a first broadband amplifier, and a first broadband impedance matching network, wherein the first EM circuit block outputs a first broadband RF waveform coupled to the plasma device, the first broadband RF waveform having an EM power distribution within a first frequency range; and a second EM circuit block comprising a second function generator, a second broadband amplifier, and a second broadband impedance matching network, wherein the second EM circuit block outputs a second broadband RF waveform coupled to the plasma device, the second broadband RF waveform having an EM power distribution within a second frequency range, the second range being different from the first range; and A controller is configured to adjust a plurality of input parameters of the EM circuit block.

13. The plasma system of claim 12, wherein: The first frequency range includes a frequency range greater than or equal to 10 MHz and less than or equal to 300 MHz, and wherein the second frequency range includes a frequency range greater than or equal to 100 kHz and less than or equal to 13 MHz.

14. The plasma system of claim 12, wherein: The plasma apparatus includes a plasma chamber, an upper RF electrode, and a lower RF electrode, the lower RF electrode being a susceptor configured to support a substrate in the plasma chamber.

15. The plasma system of claim 14, wherein: The first broadband RF waveform and the second broadband RF waveform are coupled to different RF electrodes of the plasma device.

16. The plasma system of claim 14, wherein: The first broadband RF waveform and the second broadband RF waveform are coupled to a same RF electrode of the plasma device.

17. A method of operating a plasma processing system, the method comprising: Outputting a broadband radio frequency (RF) waveform at the output of the function generator; coupling an output of the function generator to an input of a broadband amplifier; outputting an amplified broadband RF waveform at an output terminal of the broadband amplifier; coupling the output end of the broadband amplifier to the source end of the first RF tube; coupling a load end of the first RF tube to an input end of a broadband impedance matching network, the load end being opposite to the source end; as well as An output of the broadband impedance matching network is coupled to a terminal of an RF electrode of a plasma device using a second RF tube, the coupling providing EM power at the RF electrode, the EM power exciting plasma in a plasma chamber of the plasma device.

18. The method of claim 17, further comprising adjusting the broadband RF waveform at the terminals of the RF electrode of the plasma device through a feedback loop.

19. The method of claim 17, further comprising: measuring an RF voltage waveform and an RF current waveform using a voltage pickup and a current pickup of a voltage and current (VI) sensor located at a location along the second RF tube; transmitting the RF voltage waveform and the RF current waveform to a VI analysis circuit, the VI analysis circuit comprising electronic circuitry configured to perform an analysis of the received waveforms; performing the analysis using the electronic circuit system to extract electrical characteristics from the received waveforms; outputting an electronic feedback signal encoding these electrical characteristics; as well as The electronic feedback signal is coupled to an input port of a controller.

20. The method of claim 19, further comprising: storing the electrical characteristics encoded in the feedback signal in a memory device of the controller; generating a plurality of control signals based on processing the electrical characteristics using instructions executed by a processor of the controller; transmitting each control signal to a corresponding input port of the function generator, the broadband amplifier, and the broadband impedance matching network; as well as Based on the control signals, input parameters of the function generator, the broadband amplifier, and the broadband impedance matching network are synchronously adjusted, which adjust the broadband RF waveform at the terminals of the RF electrodes of the plasma device.

Images