System and method for using low frequency harmonics in a bias radio frequency supply to control uniformity of plasma process results across a substrate

Abstract

To reduce non-uniformity of plasma.SOLUTION: First, second, third, and fourth radio frequency (RF) signal generators are provided, the second and third frequencies being different specified harmonics of the first frequency, and the fourth frequency being at least two orders of magnitude greater than the first frequency. An impedance matching system controls impedances to the first, second, third, and fourth RF signal generators. A control module is programmed to control A) a first phase difference between the first and second RF signals, B) a second phase difference between the first and third RF signals, C) a first voltage difference between the first and second RF signals, and D) a second voltage difference between the first and third RF signals. The first and second phase differences and the first and second voltage differences collectively control the plasma sheath voltage as a function of time.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] 1. Field of Disclosure

[0002] The present disclosure relates to semiconductor device manufacturing. [Background technology]

[0003] 2. Description of Related Technology

[0004] In the fabrication of semiconductor devices such as integrated circuits, memory cells, and the like, a series of manufacturing operations are performed to define features on a semiconductor wafer (hereinafter "wafer"). The wafer contains integrated circuit devices in the form of multi-level structures defined on a silicon substrate. At the substrate level, transistor devices with diffusion regions are formed. At subsequent levels, wiring metallization lines are patterned and electrically connected to the transistor devices to define the desired integrated circuit devices. Additionally, patterned conductive layers are insulated from other conductive layers by dielectric materials.

[0005] Many modern semiconductor chip manufacturing processes involve the generation of a plasma from which ionic and / or radical components are derived for use in directly or indirectly affecting changes on the surface of a substrate exposed to the plasma. For example, various plasma-based processes can be used to etch material from a substrate surface, deposit material onto a substrate surface, or modify material already present on the substrate surface. Plasma is often generated by applying radio frequency (RF) power to a process gas in a controlled environment such that the process gas is energized and transformed into the desired plasma. The characteristics of the plasma and the corresponding process results on the substrate are affected by many process parameters, including, but not limited to, the material composition of the process gas, the flow rate of the process gas, the geometric characteristics of the plasma generation region and surrounding structures, the temperature of the process gas and surrounding materials, the frequency of the applied RF power, the magnitude of the applied RF power, and the temporal manner in which the RF power is applied, among others. Therefore, it is important to understand, monitor, and / or control some of the process parameters that can affect the characteristics of the generated plasma and the corresponding process results on the substrate. It is in this context that the present disclosure is made. Summary of the Invention

[0006] In one exemplary embodiment, a radio frequency (RF) signal delivery system for a plasma processing system is disclosed. The RF signal delivery system includes a first RF signal generator configured to generate a first RF signal having a first frequency. The RF signal delivery system also includes a second RF signal generator configured to generate a second RF signal having a second frequency. The second frequency is a specified harmonic of the first frequency. The RF signal delivery system also includes a third RF signal generator configured to generate a third RF signal having a third frequency. The third frequency is a specified harmonic of the first frequency. The third frequency and the second frequency are different specified harmonics of the first frequency. The RF signal delivery system also includes a fourth RF signal generator configured to generate a fourth RF signal having a fourth frequency. The fourth frequency is at least two orders of magnitude greater than the first frequency.

[0007] In one exemplary embodiment, a method for operating an RF signal delivery system for a plasma processing system is disclosed. The method includes operating a first RF signal generator to generate a first RF signal having a first frequency at an output of the first RF signal generator. The method also includes operating a second RF signal generator to generate a second RF signal having a second frequency at an output of the second RF signal generator. The second frequency is a specified harmonic of the first frequency. The method also includes operating a third RF signal generator to generate a third RF signal having a third frequency at an output of the third RF signal generator. The third frequency is a specified harmonic of the first frequency. The third frequency and the second frequency are different specified harmonics of the first frequency. The method also includes operating a fourth RF signal generator to generate a fourth RF signal having a fourth frequency at an output of the fourth RF signal generator. The fourth frequency is at least two orders of magnitude greater than the first frequency. The method also includes operating an impedance matching system to control impedances at an output of the first RF signal generator, an output of the second RF signal generator, an output of the third RF signal generator, and an output of the fourth RF signal generator. The first RF signal, the second RF signal, the third RF signal, and the fourth RF signal are transmitted through the impedance matching system to a radio frequency supply input of the plasma processing system to cause generation of plasma in the plasma processing system. The method also includes operating a control module to control a first phase difference between the second RF signal and the first RF signal. The method also includes operating the control module to control a second phase difference between the third RF signal and the first RF signal. The method also includes operating the control module to control a first voltage difference between the second RF signal and the first RF signal. The method also includes operating the control module to control a second voltage difference between the third RF signal and the first RF signal. The first phase difference, the second phase difference, the first voltage difference, and the second voltage difference collectively control a plasma sheath voltage as a function of time in the plasma processing system.

[0008] Other aspects and advantages of the present invention will become more apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the invention. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 illustrates an RF signal delivery system including a low-frequency RF signal generator and a high-frequency RF signal generator, according to some embodiments.

[0010] [Figure 2] FIG. 1 is a diagram of a frequency adjustment process, according to some embodiments.

[0011] [Figure 3] 3A-3C show various plots of normalized voltage and normalized current as a function of time measured at the output of the impedance matching system when the RF signal generating system is operating according to the frequency adjustment process of FIG. 2 in accordance with some embodiments.

[0012] [Figure 4] FIG. 1 illustrates an example of injecting higher harmonic frequency signals along with a fundamental (base) frequency signal to generate a non-sinusoidal waveform shape, according to some embodiments.

[0013] [Figure 5A] FIG. 1 illustrates a composite signal waveform that is a combination of a fundamental (base) frequency signal, a third harmonic frequency signal of the fundamental (base) frequency signal, and a fifth harmonic frequency signal of the fundamental (base) frequency signal, according to some embodiments.

[0014] [Figure 5B] FIG. 1 illustrates a composite signal waveform that is a combination of a fundamental (base) frequency signal, a second harmonic frequency signal of the fundamental (base) frequency signal, and a fourth harmonic frequency signal of the fundamental (base) frequency signal, according to some embodiments.

[0015] [Figure 5C] FIG. 1 illustrates a composite signal waveform that is a combination of a fundamental (base) frequency signal, a second harmonic frequency signal of the fundamental (base) frequency signal, and a third harmonic frequency signal of the fundamental (base) frequency signal, according to some embodiments.

[0016] [Figure 6] FIG. 2 illustrates a sinusoidal reference low frequency RF signal along with its harmonic frequency signal components according to some embodiments.

[0017] [Figure 7] FIG. 1 illustrates a substantially rectangular-shaped composite low-frequency RF signal formed by combining phase-matched third and fifth harmonic frequency signals with a fundamental (base) frequency signal, according to some embodiments.

[0018] [Figure 8] FIG. 1 illustrates a slanted rectangular shaped composite low frequency RF signal formed by combining phase-shifted third and fifth harmonic frequency signals with a fundamental (base) frequency signal in accordance with some embodiments.

[0019] [Figure 9] 9A-9C show plots of average film thickness versus radial position across a substrate obtained by performing etching processes according to the frequency adjustment process of FIG. 2 , each etching process using a different one of the reference sinusoidal low-frequency RF signal of FIG. 6 , the composite rectangular shaped low-frequency RF signal of FIG. 7 , and the composite ramped rectangular shaped low-frequency RF signal of FIG. 8 , in accordance with some embodiments.

[0020] [Figure 10]FIG. 10 illustrates various waveform shapes that can be obtained by combining a third harmonic frequency signal and a fifth harmonic frequency signal with a fundamental (base) frequency signal and shifting the phase of the third and fifth harmonic frequency signals by various amounts relative to the phase of the fundamental (base) frequency signal, according to some embodiments.

[0021] [Figure 11] 2 illustrates an RF signal delivery system including the low frequency RF signal generator and the high frequency RF signal generator described with respect to FIG. 1, and further including multiple harmonic frequency RF signal generators, according to some embodiments.

[0022] [Figure 12] 1 illustrates an exemplary configuration of an impedance matching system, according to some embodiments.

[0023] [Figure 13A] FIG. 1 is a diagram of a CCP processing system according to some embodiments of the present disclosure.

[0024] [Figure 13B] FIG. 1 is a diagram of an ICP processing system, according to some embodiments of the present disclosure.

[0025] [Figure 13C] FIG. 1 is a top view of a coil, according to some embodiments.

[0026] [Figure 13D] FIG. 2 is a diagram of a control module, according to some exemplary embodiments.

[0027] [Figure 14] 1 is a flowchart of a method for operating a radio frequency signal generator system for a plasma processing system, according to some embodiments. DETAILED DESCRIPTION OF THE INVENTION

[0028] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. However, as will be apparent to one skilled in the art, embodiments of the present disclosure may be practiced without some or all of these specific details. In other instances, well-known process operations have not been described in detail in order to avoid unnecessarily obscuring the present disclosure.

[0029] In the semiconductor industry, semiconductor substrates can undergo manufacturing processes in various types of plasma chambers, such as capacitively coupled plasma (CCP) and inductively coupled plasma (ICP) processing chambers. In both CCP and ICP processing chambers, radio frequency (RF) power is used to energize a process gas to convert it into a plasma within a plasma processing region to which the substrate is exposed. Reactive and / or charged species within the plasma interact with the substrate to modify the state of the substrate, for example, by modifying materials present on the substrate, depositing material on the substrate, or removing / etching material from the substrate. CCP and ICP processing chambers are equipped with one or more electrodes and / or antennas that receive RF power to generate a plasma within the plasma processing region. CCP and ICP processing chambers also are equipped with one or more electrodes that receive RF power and / or direct current (DC) power to generate a bias voltage at the substrate to attract charged species from the plasma toward the substrate.

[0030] 1 shows an RF signal delivery system 100 including a low-frequency RF signal generator 101 and a high-frequency RF signal generator 102, according to some embodiments. Each of the low-frequency RF signal generator 101 and the high-frequency RF signal generator 102 is connected to provide an RF signal to a plasma processing system 150 through an impedance matching system 115. In various embodiments, the plasma processing system 150 is either a CCP processing system or an ICP processing system. In various embodiments, the RF signal delivery system 100 is connected to an electrode or an antenna (coil) in the plasma processing system 150 through the impedance matching system 115.

[0031] The low frequency RF signal generator 101 is configured to generate a low frequency RF signal of controlled amplitude and frequency and transmit the low frequency RF signal from an output 110 of the low frequency RF signal generator 101 through / along electrical conductor 113 to an input 117 of an impedance matching system 115. The low frequency RF signal then travels from an output 123 of the impedance matching system 115 through / along an RF feed structure 160 to an electrode or antenna within the plasma processing system 150.

[0032] Similarly, high frequency RF signal generator 102 is configured to generate a high frequency RF signal of controlled amplitude and frequency and transmit the high frequency RF signal from output 171 of high frequency RF signal generator 102 through / along electrical conductor 173 to input 175 of impedance matching system 115. The high frequency RF signal then travels from output 123 of impedance matching system 115 through / along RF feed structure 160 to an electrode or antenna within plasma processing system 150.

[0033] The impedance matching system 115 includes a combination of capacitors and inductors configured and connected in an electrical circuit to match the impedance at the output 110 of the low-frequency RF signal generator 101 to a design impedance (typically 50 ohms). The impedance matching system 115 also includes a combination of capacitors and inductors configured and connected in an electrical circuit to match the impedance at the output 171 of the high-frequency RF signal generator 102 to a design impedance (typically 50 ohms). The impedance matching system 115 also includes a network interface controller (NIC) 139, which enables the impedance matching system 115 to send data to and receive data from systems external to the impedance matching system 115. Examples of the NIC 139 include a network interface card, a network adapter, etc. In various embodiments, the NIC 139 is configured to operate according to one or more network communication protocols and associated physical layers, such as Ethernet and / or EtherCAT, among others.

[0034] The low-frequency RF signal generator 101 includes an oscillator 103 for generating an RF signal. The oscillator 103 is an electronic circuit that generates a periodically oscillating electrical signal, such as a sinusoidal electrical signal having a specified frequency within the RF range. In some embodiments, the oscillator 103 is a low-frequency oscillator capable of oscillating within a frequency range extending from approximately 50 kilohertz (kHz) to approximately 3 megahertz (MHz). In some embodiments, the oscillator 103 is configured to generate a low-frequency RF signal within a frequency range extending from approximately 330 kHz to approximately 440 kHz. In some embodiments, the oscillator 103 is configured to generate a low-frequency RF signal of approximately 400 kHz. The output of the oscillator 103 is connected to the input of a power amplifier 105. The power amplifier 105 operates to amplify the low-frequency RF signal generated by the oscillator 103 and transmit the amplified low-frequency RF signal to an output 110 of the low-frequency RF signal generator 101 through the output of the power amplifier 105.

[0035] The low-frequency RF signal generator 101 also includes a control system 109 configured to provide control of all operational aspects of the low-frequency RF signal generator 101. In some embodiments, the control system 109 includes a processor, a data storage device, an input / output interface, and a data bus through which the processor, data storage device, and input / output interface communicate data with each other. The control system 109 is connected to provide control of the oscillator 103, as shown by connection 104. The control system 109 is also connected to provide control of the power amplifier 105, as shown by connection 106. The control system 109 also includes a NIC 111, which enables the control system 109 to transmit data to and receive data from systems external to the low-frequency RF signal generator 101. Examples of the NIC 111 include a network interface card, a network adapter, etc. In various embodiments, the NIC 111 is configured to operate according to one or more network communication protocols and associated physical layers, such as Ethernet and / or EtherCAT, among others.

[0036] It should be understood that the control system 109 is connected and configured to control essentially any aspect of the low-frequency RF signal generator 101. It should also be understood that the control system 109 may be connected and configured to monitor essentially any physical and / or electrical state, condition, and / or parameter at essentially any location within the low-frequency RF signal generator 101. The control system 109 is also configured to command the operation of the low-frequency RF signal generator 101 according to one or more defined algorithms. For example, the control system 109 is configured to operate the low-frequency RF signal generator 101 by executing input and control instructions / programs. The input and control instructions / programs include a target RF power setpoint and a target frequency setpoint, among other parameters associated with the operation and control of the low-frequency RF signal generator 101.

[0037] The low frequency RF signal generator 101 also includes a voltage / current (V / I) sensor 107 connected to an output 110 of the low frequency RF signal generator 101. The V / I sensor 107 is connected to a control system 109, as shown by connection 108. In this configuration, the V / I sensor 107 provides the control system 109 with real-time measurements of the voltage and current present on the output 110 of the low frequency RF signal generator 101. In some embodiments, the V / I sensor 107 is located within the low frequency RF signal generator 101.

[0038] The high-frequency RF signal generator 102 includes an oscillator 177 for generating an RF signal. The oscillator 177 is an electronic circuit that generates a periodically oscillating electrical signal, such as a sinusoidal electrical signal, having a specified frequency within the RF range. In some embodiments, the oscillator 177 is a high-frequency oscillator capable of oscillating within a frequency range extending from approximately 10 MHz to approximately 130 MHz. In some embodiments, the oscillator 177 is configured to generate a high-frequency RF signal within a frequency range extending from approximately 57 MHz to approximately 63 MHz. In some embodiments, the oscillator 177 is configured to generate a high-frequency RF signal of approximately 60 MHz. The output of the oscillator 177 is connected to the input of a power amplifier 179. The power amplifier 179 operates to amplify the high-frequency RF signal generated by the oscillator 177 and transmit the amplified high-frequency RF signal to the output 171 of the high-frequency RF signal generator 102 through the output of the power amplifier 179.

[0039] The high-frequency RF signal generator 102 also includes a control system 181 configured to provide control of all operational aspects of the high-frequency RF signal generator 102. In some embodiments, the control system 181 includes a processor, a data storage device, an input / output interface, and a data bus through which the processor, data storage device, and input / output interface communicate data with each other. The control system 181 is connected to provide control of the oscillator 177, as shown by connection 178. The control system 181 is also connected to provide control of the power amplifier 179, as shown by connection 180. The control system 181 also includes a NIC 183, which enables the control system 181 to send data to and receive data from systems external to the high-frequency RF signal generator 102. Examples of the NIC 183 include a network interface card, a network adapter, etc. In various embodiments, the NIC 183 is configured to operate according to one or more network communication protocols and associated physical layers, such as Ethernet and / or EtherCAT, among others.

[0040] It should be understood that the control system 181 is connected and configured to control essentially any aspect of the high frequency RF signal generator 102. It should also be understood that the control system 181 may be connected and configured to monitor essentially any physical and / or electrical state, condition, and / or parameter at essentially any location within the high frequency RF signal generator 102. The control system 181 is also configured to command the operation of the high frequency RF signal generator 102 according to a defined algorithm. For example, the control system 181 is configured to operate the high frequency RF signal generator 102 by executing input and control instructions / programs. The input and control instructions / programs include a target RF power setpoint and a target frequency setpoint, among other parameters associated with the operation and control of the high frequency RF signal generator 102.

[0041] The high frequency RF signal generator 102 also includes a voltage / current (V / I) sensor 185 connected to the output 171 of the high frequency RF signal generator 102. The V / I sensor 185 is connected to the control system 181, as shown by connection 182. In this configuration, the V / I sensor 185 provides the control system 181 with real-time measurements of the voltage and current present on the output 171 of the high frequency RF signal generator 102. In some embodiments, the V / I sensor 185 is located within the high frequency RF signal generator 102.

[0042] In some embodiments, the control system 109 of the low frequency RF signal generator 101 is programmed to determine the real-time reflection coefficient (or gamma (Γ)) at the output 110 of the low frequency RF signal generator 101, where Γ=V r / V f and V r is the complex amplitude of the reflected RF signal, and V f is the complex amplitude of the forward RF signal. In some embodiments, the control system 109 of the low frequency RF signal generator 101 is also programmed to determine a voltage standing wave ratio (VSWR) at the output 110 of the low frequency RF signal generator 101, where VSWR=|V max | / |V min |=(1+|Γ|) / (1-|Γ|), and |V max |=|V f |+|V r | and |V min |=|V f |-|V r|. Minimization of the reflected RF power associated with the low-frequency RF signal generated by the low-frequency RF signal generator 101 occurs when the reflection coefficient at the output 110 of the low-frequency RF signal generator 101 is as close to zero as possible. Also, minimization of the reflected RF power associated with the low-frequency RF signal generated by the low-frequency RF signal generator 101 occurs when the VSWR at the output 110 of the low-frequency RF signal generator 101 is as close to one as possible, where one is the smallest possible value for VSWR. In some embodiments, the control system 109 is programmed to use the real-time measured voltage at the output 110 of the low-frequency RF signal generator 101 to calculate the real-time reflection coefficient and / or VSWR at the output 110 of the low-frequency RF signal generator 101. The real-time reflection coefficient and / or VSWR at the output 110 of the low-frequency RF signal generator 101, determined using voltage measurements taken within the low-frequency RF signal generator 101, may be used as a feedback signal to minimize the reflection coefficient as close to zero as possible and / or minimize the VSWR as close to one as possible.

[0043] Similarly, in some embodiments, the control system 181 of the high frequency RF signal generator 102 is programmed to determine the reflection coefficient (or gamma (Γ)) and VSWR at the output 171 of the high frequency RF signal generator 102. Minimization of the reflected RF power associated with the high frequency RF signal generated by the high frequency RF signal generator 102 occurs when the reflection coefficient at the output 171 of the high frequency RF signal generator 102 is as close to zero as possible. Also, minimization of the reflected RF power associated with the high frequency RF signal generated by the high frequency RF signal generator 102 occurs when the VSWR at the output 171 of the high frequency RF signal generator 102 is as close to one as possible, where one is the smallest possible value for VSWR. In some embodiments, the control system 181 is programmed to use the real-time measured voltage at the output 171 of the high frequency RF signal generator 102 to calculate the real-time reflection coefficient and / or VSWR at the output 171 of the high frequency RF signal generator 102. The real-time reflection coefficient and / or VSWR at the output 171 of the high frequency RF signal generator 102, determined using voltage measurements taken within the high frequency RF signal generator 102, may be used as a feedback signal to minimize the reflection coefficient as close to zero as possible and / or minimize the VSWR as close to one as possible at the output 171 of the high frequency RF signal generator 102. The real-time reflection coefficient and / or VSWR at the output 171 of the high frequency RF signal generator 102, determined using voltage measurements taken within the high frequency RF signal generator 102, may also be used to determine the reflected RF power at the output 171 of the high frequency RF signal generator 102.

[0044] A control module 163 of the plasma processing system 150 is connected to the control system 109 of the low-frequency RF signal generator 101 via a NIC 152 and a NIC 111, as shown by connection 143. The control module 163 is connected to the control system 181 of the high-frequency RF signal generator 102 via a NIC 152 and a NIC 183, as shown by connection 144. The control module 163 is connected to the impedance matching system 115 via a NIC 152 and a NIC 139, as shown by connection 145. The NIC 152 enables the control module 163 to send data to and receive data from systems external to the control module 163. Examples of the NIC 152 include a network interface card, a network adapter, etc. In various embodiments, the NIC 152 is configured to operate according to one or more network communication protocols and associated physical layers, such as Ethernet and / or EtherCAT, among others.

[0045] In some embodiments, the control module 163 is programmed to direct the operation of the low-frequency RF signal generator 101 and the high-frequency RF signal generator 102 according to a frequency adjustment process. The frequency adjustment process automatically adjusts the operating frequency of the low-frequency RF signal generator 101 around a target frequency of the low-frequency signal to minimize reflected power at the output 110 of the low-frequency RF signal generator 101. The frequency adjustment process also automatically adjusts the operating frequency of the high-frequency RF signal generator 102 around a target frequency of the high-frequency signal to minimize reflected power at the output 171 of the high-frequency RF signal generator 102. In the frequency adjustment process, the operating frequency of the high-frequency RF signal generator 102 is separately adjusted around the target frequency of the high-frequency signal in each of a plurality of time bins that collectively span one complete period of the low-frequency signal generated by the low-frequency RF signal generator 101, and the multiple time bins (of the high-frequency RF signal generator 102) and corresponding separate operating frequency adjustments repeat in turn across each period of the low-frequency signal generated by the low-frequency RF signal generator 101.

[0046] FIG. 2 shows a diagram of a frequency adjustment process according to some embodiments. An upper plot 201 shows a curve 203 of voltage measured as a function of time at the output 110 of the low-frequency RF signal generator 101. The curve 203 represents the low-frequency signal generated by the low-frequency RF signal generator 101. The low-frequency signal is a sinusoidal signal characterized by a repeating period. In the upper plot 201, a given period of the low-frequency signal begins at point P1 and ends at point P3, with point P2 representing a half-period position. In the example of FIG. 2, the low-frequency signal period begins at point P1, where the low-frequency signal crosses the zero voltage level in a positive direction. This starting position of the low-frequency signal period is referred to herein as the low-frequency signal's positive-going zero-voltage crossing. The half-period position occurs at point P2, where the low-frequency signal crosses the zero voltage level in a negative direction. The low-frequency signal period also ends at point P3, where the low-frequency signal again crosses the zero voltage level in a positive direction. The period of the low-frequency signal is divided into a number of time bins B1 through B(N), where N is the total number of time bins. The example in Figure 2 shows that the period of the low-frequency signal is divided into 20 (N=20) time bins B1 through B20. The first time bin B1 of the number of time bins B1 through B(N) begins at a positive-going zero-voltage crossing of one complete period of the low-frequency signal. The last time bin B(N) of the number of time bins B1 through B(N) ends at the next positive-going zero-voltage crossing of one complete period of the low-frequency signal.

[0047] It should be understood that the 20 time bins (N=20) in FIG. 2 are shown as an example. In other embodiments, the number of time bins B1-B(N) may be set such that N is less than or greater than 20. The example in FIG. 2 also shows that each of the time bins B1-B(N) covers an equal amount of time. However, in other embodiments, different time bins among the time bins B1-B(N) may be defined to cover different amounts of time. For example, if a higher resolution adjustment of the frequency of the high-frequency signal generated by the high-frequency RF signal generator 102 is required along a particular portion of the period of the low-frequency signal generated by the low-frequency RF signal generator 101, some of the time bins B1-B(N) along the particular portion of the period of the low-frequency signal may be defined to cover a smaller amount of time.

[0048] 2 also includes a lower plot 205 illustrating the adjustment of the operating frequency of the high-frequency RF signal generator 102 in each of a plurality of time bins B1-B20 that collectively span one complete period of the low-frequency signal generated by the low-frequency RF signal generator 101. The operating frequency of the high-frequency RF signal generator 102 is set to an adjusted frequency during each of the plurality of time bins B1-B20. The adjusted operating frequency of the high-frequency RF signal generator 102 in any given one of the plurality of time bins B1-B(N) is set independently and separately from the other ones of the plurality of time bins B1-B(N). In some embodiments, the adjusted frequency of a given one of the plurality of time bins B1-B(N) is adjusted by a frequency adjustment amount (f adj ) are integer multiples of the frequency adjustment amount (f adj ) around the target frequency (HF0). As shown in FIG. 2, the adjusted frequency of a given one of the time bins B1-B20 varies with the frequency adjustment amount (f adj) is an integer multiple of the frequency adjustment amount (f). In some embodiments, the integer multiple is -4, -3, -2, -1, 0, +1, +2, +3, or +4. However, in other embodiments, an integer multiple less than -4 and / or greater than +4 may be used. Also, in some embodiments, the integer multiple is replaced by a fractional multiple. Also, in some embodiments, the frequency adjustment amount (f adj ) is set as the target frequency of the low-frequency signal generated by the low-frequency RF signal generator 101. In the example of FIG. 2, if the target frequency of the low-frequency signal generated by the low-frequency RF signal generator 101 is 400 kHz, the bin level operating frequency of the high-frequency RF signal generator 102 is set as −4(f adj ) is HF0-1600kHz, and -3(f adj ) is HF0-1200kHz, and -2(f adj ) is HF0-800kHz, and -1(f adj ) is HF0-400kHz, and 0(f adj ) is HF0, and +1(f adj ) is HF0+400kHz, and +2(f adj ) is HF0+800kHz, and +3(f adj ) is HF0+1200kHz, and +4(f adj ) is HF0+1600 kHz. The operating frequency of the high frequency RF signal generator 102 for a given one of the plurality of time bins B1 to B(N), for example, the frequency adjustment amount (f adj ) is empirically determined as the frequency adjustment that minimizes the reflected RF power at the output 171 of the high frequency RF signal generator 102 during a given one of the multiple time bins B1-B(N). adj ) is set to a determined amount of frequency that differs from the target frequency of the low frequency signal generated by the low frequency RF signal generator 101.

[0049] The adjusted frequency of the high-frequency RF signal generator 102 over multiple time bins B1-B(N) is repeated for each period of the low-frequency signal generated by the low-frequency RF signal generator 101. Periodically, a frequency adjustment process readjusts (redetermines) the adjusted frequency of the high-frequency RF signal generator 102 over multiple time bins B1-B(N) to ensure that reflected RF power at the output 171 of the high-frequency RF signal generator 102 is minimized as much as possible. In some embodiments, the frequency adjustment process is implemented by programming the control module 163, which in turn directs the operation of the control system 109 in the low-frequency RF signal generator 101 and the control system 181 in the high-frequency RF signal generator 102.

[0050] 3 shows various plots of normalized voltage and normalized current as a function of time measured at output 123 of impedance matching system 115 when RF signal generation system 100 is operating according to the frequency adjustment process of FIG. 2 , in accordance with some embodiments. Referring again to FIG. 1 , a voltage / current (V / I) sensor 195 is connected to output 123 of impedance matching system 115. V / I sensor 195 is connected to control module 163, as shown by connection 196. In this configuration, V / I sensor 195 provides control module 163 with real-time measurements of the voltage and current present at output 123 of impedance matching system 115. The various plots shown in FIG. 3 correspond to voltage and current measurements taken by V / I sensor 195 at output 123 of impedance matching system 115.

[0051] 3 includes an upper plot 301 illustrating normalized voltage as a function of time measured at the output 123 of the impedance matching system 115, including normalized voltages associated with various harmonics of the low-frequency RF signal generated by the low-frequency RF signal generator 101, in accordance with some embodiments. The upper plot 301 shows a curve 303 representing the normalized voltage as a function of time at the output 123 of the impedance matching system 115 corresponding to a full-bandwidth combination of low-frequency RF signals associated with the low-frequency RF signal generated by the low-frequency RF signal generator 101. The full-bandwidth combination of low-frequency RF signals includes the fundamental (base) low-frequency RF signal generated by the low-frequency RF signal generator 101 and all harmonic frequency signals associated with the fundamental (base) low-frequency RF signal. The upper plot 301 also shows a curve 305 representing the normalized voltage as a function of time at the output 123 of the impedance matching system 115 corresponding to only the fundamental (base) low-frequency RF signal generated by the low-frequency RF signal generator 101. The upper plot 301 also shows a curve 307 representing a normalized voltage as a function of time at the output 123 of the impedance matching system 115, corresponding to a second harmonic frequency of the fundamental (base) low frequency RF signal generated by the low frequency RF signal generator 101. It should be understood that the second harmonic of the fundamental (base) low frequency RF signal corresponding to the curve 307 is sourced downstream of the output 123 of the impedance matching system 115 and is not generated by the low frequency RF signal generator 101. The upper plot 301 also shows a curve 309 representing a normalized voltage as a function of time at the output 123 of the impedance matching system 115, corresponding to a third or higher harmonic frequency of the fundamental (base) low frequency RF signal generated by the low frequency RF signal generator 101. It should be understood that the third or higher harmonics of the fundamental (base) low frequency RF signal corresponding to the curve 309 are sourced downstream of the output 123 of the impedance matching system 115 and are not generated by the low frequency RF signal generator 101.

[0052] 3 also includes a lower plot 311 showing normalized current as a function of time measured at the output 123 of the impedance matching system 115 for a high-frequency RF signal generated by the high-frequency RF signal generator 102 and for various harmonic frequencies of the high-frequency RF signal, according to some embodiments. For reference, the lower plot 311 includes a subplot 313 showing curve 303 (shown in the upper plot 301) corresponding to the full-bandwidth combination of low-frequency RF signals associated with the low-frequency RF signal generated by the low-frequency RF signal generator 101. The lower plot 311 includes a subplot 315 showing curve 316 representing normalized current as a function of time at the output 123 of the impedance matching system 115 corresponding to the full-bandwidth combination of high-frequency RF signals associated with the high-frequency RF signal generated by the high-frequency RF signal generator 102. The full-bandwidth combination of high-frequency RF signals includes the fundamental (base) high-frequency RF signal generated by the high-frequency RF signal generator 102 and all harmonic frequency signals associated with the fundamental (base) high-frequency RF signal. 3, the high-frequency RF signal has a fundamental (base) frequency of 60 MHz, and the low-frequency RF signal has a fundamental (base) frequency of 400 kHz. Thus, the normalized current curve 316 corresponding to the high-frequency RF signal cycles approximately 150 times faster than the voltage curve 303 corresponding to the low-frequency RF signal. Thus, as shown in FIG. 3, on the scale of a single period of the low-frequency RF signal curve 303, the high-frequency RF signal curve 316 traces out a substantially solid region.

[0053] The lower plot 311 also includes a subplot 317 that shows a curve 318 that represents a normalized current as a function of time at the output 123 of the impedance matching system 115, corresponding to only the fundamental (base) high-frequency RF signal generated by the high-frequency RF signal generator 102. The lower plot 311 also includes a subplot 319 that shows a curve 320 that represents a normalized current as a function of time at the output 123 of the impedance matching system 115, corresponding to a second harmonic frequency of the fundamental (base) high-frequency RF signal generated by the high-frequency RF signal generator 101. It should be understood that the second harmonic of the fundamental (base) high-frequency RF signal corresponding to curve 320 is sourced downstream of the output 123 of the impedance matching system 115 and is not generated by the high-frequency RF signal generator 102. The lower plot 311 also includes a subplot 321 that shows a curve 322 representing a normalized current as a function of time at the output 123 of the impedance matching system 115, corresponding to the third harmonic frequency of the fundamental (base) high frequency RF signal generated by the high frequency RF signal generator 101. It should be understood that the third harmonic of the fundamental (base) high frequency RF signal corresponding to the curve 322 is sourced downstream of the output 123 of the impedance matching system 115 and is not generated by the high frequency RF signal generator 102.

[0054] The lower plot 311 also includes a subplot 323 that shows a curve 324 representing a normalized current as a function of time at the output 123 of the impedance matching system 115, corresponding to a fourth harmonic frequency of the fundamental (base) high frequency RF signal generated by the high frequency RF signal generator 101. It should be understood that the fourth harmonic of the fundamental (base) high frequency RF signal corresponding to the curve 324 is sourced downstream of the output 123 of the impedance matching system 115 and is not generated by the high frequency RF signal generator 102. The lower plot 311 also includes a subplot 325 that shows a curve 326 representing a normalized current as a function of time at the output 123 of the impedance matching system 115, corresponding to a fifth harmonic frequency of the fundamental (base) high frequency RF signal generated by the high frequency RF signal generator 101. It should be understood that the fifth harmonic of the fundamental (base) high frequency RF signal corresponding to the curve 326 is sourced downstream of the output 123 of the impedance matching system 115 and is not generated by the high frequency RF signal generator 102. The lower plot 311 also includes a subplot 327 that shows a curve 328 representing normalized current as a function of time at the output 123 of the impedance matching system 115, corresponding to the sixth harmonic frequency of the fundamental (base) high frequency RF signal generated by the high frequency RF signal generator 101. It should be understood that the sixth harmonic of the fundamental (base) high frequency RF signal corresponding to curve 328 is sourced downstream of the output 123 of the impedance matching system 115 and is not generated by the high frequency RF signal generator 102.

[0055] Curve 303 of upper plot 301 (and subplot 313) shows that the normalized voltage as a function of time at output 123 of impedance match system 115, corresponding to the full bandwidth combination of the low-frequency RF signal associated with the low-frequency RF signal generated by low-frequency RF signal generator 101, exhibits a deviation in slope in the time domain 310 as the voltage approaches a zero voltage level in a positive direction. The deviation in slope of curve 303 in the time domain 310 is caused by an increase in plasma density caused by secondary electrons generated by ions at the substrate. The maximum electron flux and plasma density maximum are delayed from the maximum sheath voltage (point A) due to ion inertia. The deviation in slope of curve 303 in the time domain 310 also occurs with higher amplitudes of higher-order harmonic frequency signals associated with the fundamental (base) low-frequency RF signal generated by low-frequency RF signal generator 101.

[0056] Furthermore, as shown in subplots 319, 321, 323, 325, and 327, the higher-order harmonic signals associated with the fundamental (base) high-frequency RF signal generated by the high-frequency RF signal generator 102 are not uniformly distributed throughout a given period of the low-frequency RF signal generated by the low-frequency RF signal generator 101. Figure 3 shows that deviations in the slope of the voltage curve 303 within the time domain 310 correlate to higher amplitudes of the higher-order harmonic signals associated with the fundamental (base) high-frequency RF signal generated by the high-frequency RF signal generator 102. For example, the lower plot 311 outlines the time domain 310 across subplots 315, 317, 319, 321, 323, 325, and 327. As shown in time region 310 in subplots 319, 321, 323, 325, and 327, the normalized current associated with the higher harmonics of the fundamental (base) high frequency RF signal increases substantially at the onset of plasma density increase due to secondary electrons and is maintained throughout the duration of plasma sheath collapse. Also shown in time region 310 in subplot 317, the normalized current corresponding to the fundamental (base) frequency of the high frequency RF signal drops significantly and rapidly at the onset of plasma sheath collapse at substrate level.

[0057] The plasma sheath potential is equal to the difference between the RF voltage applied to the plasma and the measured plasma potential. Standing waves in the plasma sheath potential occur for a short period within the time window 310 at or near the onset of plasma sheath collapse. These standing waves are believed to be due to the generation of higher harmonics of the fundamental high-frequency RF signal. They are also believed to be a cause of nonuniformity in plasma process results across a substrate. For example, in plasma etching processes, standing waves in the plasma sheath potential are believed to be a contributor to center-to-middle (C / M) etch rate nonuniformity across a substrate, where center refers to the center of a circular substrate and middle refers to the mid-radius location between the center and the peripheral edge of the circular substrate. In some high aspect ratio (HAR) etching applications, the C / M etch rate nonuniformity across a substrate is a global tilt problem related to an offset in the bottom critical dimension (BCD) of HAR features formed across the substrate. More specifically, the ions that reach the bottom of the HAR structure are highly energetic ions. Therefore, to effectively etch the HAR feature, the highly energetic ions must exit the plasma sheath and travel to the etch front at the bottom of the HAR feature. Because the highly energetic ions exit the plasma sheath at or near the maximum sheath potential driven by the low-frequency RF signal generated by the low-frequency RF signal generator 101, perturbations in the sheath potential (such as the standing waves in the sheath potential described above) affect the generation and distribution of highly energetic ions across the substrate, which in turn manifests as a form of C / M etch rate nonuniformity that adversely affects the formation of HAR features, particularly within the central region of the substrate compared to intermediate radius regions of the substrate. When integrated over time, the standing waves in the sheath potential that occur at or near the onset of plasma sheath collapse during each period of the low-frequency RF signal cause less overall etching near the central region of the substrate compared to the intermediate radius regions of the substrate.

[0058] Also, a deviation in the slope of voltage curve 303 within time domain 310 is unfavorable because the deviation in slope is for a duration during which the plasma sheath voltage is low enough to allow for collapse of the plasma sheath at substrate level. In other words, it is more advantageous for time domain 310 to have a shorter duration in order to reduce the duration of plasma sheath collapse in a given period of the low frequency RF signal generated by low frequency RF signal generator 101.

[0059] Disclosed herein are systems and methods for mitigating the impact on C / M etch rate nonuniformity caused by plasma sheath collapse during each period of the low-frequency RF signal generated by the low-frequency RF signal generator 101 when operating according to the frequency adjustment process of FIG. 2 . Because the low-frequency RF signal has a much higher voltage than the high-frequency RF signal, the plasma sheath potential is more responsive to the low-frequency RF signal than to the high-frequency RF signal. For example, in some implementations of the frequency adjustment process of FIG. 2 , the low-frequency RF signal has a peak voltage of approximately 5 kilovolts (kV), and the high-frequency RF signal has a peak voltage of approximately 300 volts (V) to approximately 500 V. Thus, the plasma sheath potential is driven by the low-frequency RF signal, while the plasma density is driven by the high-frequency RF signal. Therefore, the low-frequency RF signal is more effective than the high-frequency RF signal for adjusting the plasma sheath impedance. Also, due to the significant voltage difference between the low-frequency RF signal and the high-frequency RF signal, it is impractical to significantly change the plasma sheath voltage by varying the high-frequency RF signal. When the low voltage causes the plasma sheath potential to collapse within a given period of the low frequency RF signal, different shapes of the plasma sheath voltage waveform can be obtained as a function of time by varying the phase and / or voltage of the high harmonic frequency signals associated with the fundamental (base) low frequency RF signal generated by the low frequency RF signal generator 101. Because variations in the high harmonic frequency signals associated with the fundamental (base) low frequency RF signal cause variations in the plasma sheath potential, the high harmonic frequency signals associated with the fundamental (base) low frequency RF signal can be used to control the plasma sheath potential and the corresponding coupling of the high frequency RF signal to the plasma.

[0060] 2, by manipulating the phase and / or voltage of the higher harmonic frequency signals related to the fundamental low frequency RF signal, the waveform shape of the full bandwidth low frequency RF signal voltage can be varied as a function of time to cause an increase in the time integral of the plasma sheath voltage, which in turn provides improved plasma process result uniformity across the substrate, e.g., reduced C / M etch rate non-uniformity. Also, by varying the waveform shape of the full bandwidth low frequency RF signal voltage as a function of time, the coupling of the high frequency RF signal into the plasma can be correspondingly varied as a function of time.

[0061] In some embodiments, when operating according to the frequency adjustment process of Figure 2, one or more higher harmonic frequency signals related to the fundamental (base) low frequency RF signal are introduced (supplied to the plasma) with respective phase shifts and voltage settings to interfere with signals having the same harmonic frequency generated in the plasma. This interference caused by the introduced harmonic frequency signals helps to counteract and / or reduce the effect that the corresponding harmonic frequency plasma generating signals have on the deviation in slope of the full bandwidth low frequency RF signal curve 303 in the time domain 310, as shown in Figure 3, which in turn helps to reduce non-uniformity in plasma process results across the substrate due to the integrated effect of the collapse of the plasma sheath potential with each period of the low frequency RF signal.

[0062] In some embodiments, when operating according to the frequency adjustment process of Figure 2, the waveform of the full-bandwidth low-frequency RF signal is generated to have a non-sinusoidal shape so that the plasma sheath collapse duration within each period of the low-frequency RF signal is shortened. Reducing the plasma sheath collapse duration within each period of the low-frequency RF signal changes the proportion of the low-frequency RF signal period during which harmonic frequencies of the fundamental low-frequency signal are generated by the plasma, thereby changing the amount of time during which standing waves are generated in the plasma sheath potential, and thus changing the amount of time during which energetic ions are non-uniformly distributed across the substrate. Because shortening the plasma sheath collapse duration within each period of the low-frequency RF signal reduces the fundamental frequency of the low-frequency RF signal, e.g., from about 400 kHz to about 50 kHz, and the total duration of each period of the fundamental low-frequency RF signal correspondingly increases, this shortening has an increasingly greater impact on reducing plasma process result non-uniformity across the substrate.

[0063] FIG. 4 illustrates an example of injecting a higher-order harmonic frequency signal along with a fundamental (base) frequency signal to generate a non-sinusoidal waveform shape, according to some embodiments. In FIG. 4, the fundamental (base) frequency signal has a waveform represented by curve 401, which has a sinusoidal shape. Third and fifth harmonic frequency signals of the fundamental (base) frequency are combined with the fundamental (base) frequency signal to generate a waveform represented by curve 403, which has a rectangular shape. If the waveforms corresponding to curves 401 and 403 are considered to represent different waveforms of a full-bandwidth low-frequency RF signal generated according to the frequency adjustment process of FIG. 2, FIG. 4 demonstrates how using a rectangular-shaped waveform for the full-bandwidth low-frequency RF signal can help shorten the plasma sheath potential collapse time and increase the time of low-voltage plasma sheath per period compared to using a sinusoidal waveform for the full-bandwidth low-frequency RF signal. 3 where plasma sheath breakdown occurs, sinusoidal curve 401 is shown to have an estimated sheath breakdown duration 405. Also, rectangular curve 403 is shown to have an estimated sheath breakdown duration 407. It is clearly evident that estimated sheath breakdown duration 407 of rectangular curve 403 is less than estimated sheath breakdown duration 405 of sinusoidal curve 401. Therefore, to reduce the sheath breakdown duration per period of the full-bandwidth low-frequency RF signal, waveform shaping of the full-bandwidth low-frequency RF signal can be achieved by combining higher-order harmonic frequency signals of the fundamental frequency signal with the fundamental frequency signal.

[0064] In some embodiments, when operating according to the frequency adjustment process of FIG. 2 , the waveform of the full-bandwidth low-frequency RF signal is generated such that the negative half of each period of the full-bandwidth low-frequency RF signal has a longer duration than the positive half of each period of the full-bandwidth low-frequency RF signal. The plasma sheath potential is greatest during the negative half of each period of the full-bandwidth low-frequency RF signal. Thus, if the waveform of the full-bandwidth low-frequency RF signal is configured to spend more time in the negative half of the period than in the positive half of the period, the plasma sheath potential will be greater for more of the time. Also, if the plasma sheath potential is greater for more of the time, the harmonic frequencies of the fundamental high-frequency RF signal will have less overall adverse effect on the plasma sheath potential and correspondingly less adverse effect on the uniformity of plasma process results across the substrate.

[0065] 5A, 5B, and 5C collectively illustrate examples of how higher-order harmonic frequency signals can be combined with a fundamental (base) frequency signal to generate a non-sinusoidal, periodic waveform shape in which the negative half of each period is longer than the positive half of each period, according to some embodiments. FIG. 5A illustrates a composite signal waveform 501 that is a combination of a fundamental (base) frequency signal, a third harmonic frequency signal of the fundamental (base) frequency signal, and a fifth harmonic frequency signal of the fundamental (base) frequency signal, according to some embodiments. For reference, FIG. 5A also illustrates an ideal square wave signal waveform 502. A comparison of the composite signal waveform 501 and the ideal square wave signal waveform 502 illustrates that combining a fundamental (base) frequency signal with corresponding signals having third and fifth harmonic frequencies of the fundamental (base) frequency results in a composite signal waveform 501 having an approximate square wave shape. In the example of Figure 5A, the fundamental (base) frequency signal, the third harmonic frequency signal of the fundamental (base) frequency signal, and the fifth harmonic frequency signal of the fundamental (base) frequency signal are each phase-matched with one another and have substantially equal amplitudes. The negative half of a given period of the composite signal waveform 501 has a duration D NH-135 The positive half of a given period of the composite signal waveform 501 has duration D PH-135In the composite signal waveform 501, the negative half of the period has a duration D NH-135 is the duration of the positive half of the period D PH-135 Thus, a composite signal waveform, such as waveform 501, formed by combining a fundamental (base) frequency signal with both a phase-matched third harmonic frequency signal of the fundamental (base) frequency signal and a phase-matched fifth harmonic frequency signal of the fundamental (base) frequency signal has a period defined by negative and positive half-cycles of equal duration.

[0066] A particular harmonic frequency signal can be combined with a fundamental (base) frequency signal to generate a composite signal waveform having a period defined by negative and positive half cycles of different durations. FIG. 5B illustrates a composite signal waveform 503 that is a combination of a fundamental (base) frequency signal, a second harmonic frequency signal of the fundamental (base) frequency signal, and a fourth harmonic frequency signal of the fundamental (base) frequency signal, according to some embodiments. FIG. 5B also illustrates an ideal square wave signal waveform 504 for reference. Comparing the composite signal waveform 503 with the ideal square wave signal waveform 504 shows that combining the fundamental (base) frequency signal with corresponding signals having second and fourth harmonic frequencies of the fundamental (base) frequency results in a composite signal waveform 503 having an approximate square wave shape. In the example of FIG. 5B, the fundamental (base) frequency signal, the second harmonic frequency signal of the fundamental (base) frequency signal, and the fourth harmonic frequency signal of the fundamental (base) frequency signal are each phase-matched and have substantially equal amplitudes. The negative half of a given period of the composite signal waveform 503 is of duration D NH-124 The positive half of a given period of the composite signal waveform 503 has duration D PH-124 In the composite signal waveform 503, the negative half of the period has a duration D NH-124 is the duration of the positive half of the period D PH-124Thus, a composite signal waveform, such as waveform 503, formed by combining a fundamental (base) frequency signal with both a phase-matched second harmonic frequency signal of the fundamental (base) frequency signal and a phase-matched fourth harmonic frequency signal of the fundamental (base) frequency signal has a period in which the negative half-cycle has a longer duration than the positive half-cycle.

[0067] FIG. 5C illustrates a composite signal waveform 505 that is a combination of a fundamental (base) frequency signal, a second harmonic frequency signal of the fundamental (base) frequency signal, and a third harmonic frequency signal of the fundamental (base) frequency signal, according to some embodiments. FIG. 5C also illustrates an ideal square wave signal waveform 506 for reference. Comparing the composite signal waveform 505 to the ideal square wave signal waveform 506 shows that combining the fundamental (base) frequency signal with corresponding signals having second and third harmonic frequencies of the fundamental (base) frequency results in a composite signal waveform 505 that has an approximate square wave shape. In the example of FIG. 5C , the fundamental (base) frequency signal, the second harmonic frequency signal of the fundamental (base) frequency signal, and the third harmonic frequency signal of the fundamental (base) frequency signal are each phase-matched to one another and have substantially equal amplitudes. The negative half of a given period of the composite signal waveform 505 is of duration D NH-123 The positive half of a given period of the composite signal waveform 505 has duration D PH-123 In the composite signal waveform 505, the negative half of the period has a duration D NH-123 is the duration of the positive half of the period D PH-123 Therefore, a composite signal waveform, such as waveform 505, formed by combining a fundamental (base) frequency signal with both a phase-matched second harmonic frequency signal of the fundamental (base) frequency signal and a phase-matched third harmonic frequency signal of the fundamental (base) frequency signal has a period in which the negative half-cycle has a longer duration than the positive half-cycle. Also, the duration D of the negative half of the period of composite signal waveform 505 is NH-123 is the duration D of the negative half of the period of the composite signal waveform 503 of FIG. 5B NH-124As shown in Figures 5A, 5B, and 5C, different harmonic frequency signals can be combined with a fundamental (base) frequency signal to generate composite waveforms of different shapes that are unique in terms of the duration of the negative half cycles relative to the duration of the positive half cycles in the composite waveform.

[0068] 6, 7, and 8 collectively illustrate examples of how higher-order harmonic frequency signals of a base low-frequency RF signal can be generated and combined with the base low-frequency RF signal to generate a non-sinusoidal, periodic waveform for the full-bandwidth low-frequency RF signal when operating according to the frequency adjustment process of FIG. 2 , according to some embodiments. FIG. 6 illustrates a sinusoidal reference low-frequency RF signal 602 along with its harmonic frequency signal components, according to some embodiments. FIG. 6 includes subplot 601 illustrating a full-bandwidth version of the reference low-frequency RF signal 602 used in the frequency adjustment process of FIG. 2 , according to some embodiments. Subplot 603 illustrates a base frequency component signal 602A of the full-bandwidth version of the reference low-frequency RF signal 602. Subplot 605 illustrates a component signal 602B including second and third harmonic frequencies of the full-bandwidth version of the reference low-frequency RF signal 602. Subplot 607 shows a component signal 602C that includes the fourth, fifth, and sixth harmonic frequencies of the full bandwidth version of reference low frequency RF signal 602. Subplot 609 shows a component signal 602D that includes the seventh and higher harmonic frequencies of the full bandwidth version of reference low frequency RF signal 602. For reference, Figure 6 also shows line 604 that corresponds to the time when collapse of the sheath potential occurs, which corresponds to the time region 310 in Figure 3 where deviations in slope of curve 303 occur.

[0069] FIG. 7 illustrates a substantially rectangular-shaped composite low-frequency RF signal 702 formed by combining phase-matched third and fifth harmonic frequency signals with a fundamental (base) frequency signal, according to some embodiments. FIG. 7 includes subplot 701 illustrating a full-bandwidth version of the composite low-frequency RF signal 702 used in the frequency adjustment process of FIG. 2 , according to some embodiments. The composite low-frequency RF signal 702 is formed by combining a 400 kHz fundamental (base) frequency signal with both a 1.2 MHz third harmonic frequency signal and a 2 MHz fifth harmonic frequency signal. The total power of the composite low-frequency RF signal 702 is distributed as follows: 80% comes from the 400 kHz fundamental (base) frequency signal, 15% comes from the 1.2 MHz third harmonic frequency signal, and 5% comes from the 2 MHz fifth harmonic frequency signal. Subplot 703 illustrates the fundamental (base) frequency component signal 702A of the full-bandwidth version of the composite low-frequency RF signal 702. Subplot 705 shows component signal 702B, which includes the second and third harmonic frequencies of the full-bandwidth version of composite low-frequency RF signal 702. Subplot 707 shows component signal 702C, which includes the fourth, fifth, and sixth harmonic frequencies of the full-bandwidth version of composite low-frequency RF signal 702. Subplot 709 shows component signal 702D, which includes the seventh and higher harmonic frequencies of the full-bandwidth version of composite low-frequency RF signal 702. For reference, Figure 7 also shows line 704, which corresponds to the time when collapse of the sheath potential occurs, which corresponds to time region 310 in Figure 3 where deviations in slope of curve 303 occur.

[0070] FIG. 8 illustrates a slanted rectangular-shaped composite low-frequency RF signal 802 formed by combining phase-shifted third and fifth harmonic frequency signals with a fundamental (base) frequency signal, according to some embodiments. FIG. 8 includes a subplot 801 illustrating a full-bandwidth version of the composite low-frequency RF signal 802 used in the frequency adjustment process of FIG. 2 , according to some embodiments. The composite low-frequency RF signal 802 is formed by combining a 400 kHz fundamental (base) frequency signal with both a 1.2 MHz third harmonic frequency signal and a 2 MHz fifth harmonic frequency signal, each of which is phase-shifted by 30 degrees relative to the fundamental (base) frequency signal. The total power of the composite low-frequency RF signal 802 is distributed as follows: 80% comes from the 400 kHz fundamental (base) frequency signal, 15% comes from the 1.2 MHz third harmonic frequency signal, and 5% comes from the 2 MHz fifth harmonic frequency signal. Subplot 803 shows a fundamental (base) frequency component signal 802A of the full-bandwidth version of the composite low-frequency RF signal 802. Subplot 805 shows a component signal 802B including second and third harmonic frequencies of the full-bandwidth version of the composite low-frequency RF signal 802. Subplot 807 shows a component signal 802C including fourth, fifth, and sixth harmonic frequencies of the full-bandwidth version of the composite low-frequency RF signal 802. Subplot 809 shows a component signal 802D including seventh and higher harmonic frequencies of the full-bandwidth version of the composite low-frequency RF signal 802. For reference, FIG. 8 also shows line 804 corresponding to the time at which collapse of the sheath potential occurs, which corresponds to time region 310 in FIG. 3 where deviations in slope of curve 303 occur.

[0071] 6, the composite square-shaped low-frequency RF signal 702 of FIG. 7, and the composite ramped square-shaped low-frequency RF signal 802 of FIG. 8 each have a corresponding effect on the plasma sheath potential within the time domain of the low-frequency RF signal period, e.g., the time domain 310 in which the plasma sheath potential collapses. Thus, the reference sinusoidal low-frequency RF signal 602 of FIG. 6, the composite square-shaped low-frequency RF signal 702 of FIG. 7, and the composite ramped square-shaped low-frequency RF signal 802 of FIG. 8 each have a corresponding effect on the uniformity of the plasma process results across the substrate. FIG. 9 shows a plot of average film thickness versus radial position across a substrate obtained by performing etch processes according to the frequency adjustment process of FIG. 2, in accordance with some embodiments, where each etch process uses a different one of the reference sinusoidal low-frequency RF signal 602 of FIG. 6, the composite square-shaped low-frequency RF signal 702 of FIG. 7, and the composite ramped square-shaped low-frequency RF signal 802 of FIG. 8. The data shown in Figure 9 was obtained by subjecting a silicon substrate, on which a blanket silicon oxide film had been deposited, to a 60-second etching process using the frequency adjustment process of Figure 2. Here, a high-frequency RF signal was applied at 60 MHz and 3.5 kW, and a low-frequency RF signal was applied at 12.5 kW as either the reference sinusoidal low-frequency RF signal 602 of Figure 6, the composite rectangular-shaped low-frequency RF signal 702 of Figure 7, or the composite ramped rectangular-shaped low-frequency RF signal 802 of Figure 8. Figure 9 demonstrates that the waveform shape of the low-frequency RF signal used in the frequency adjustment process of Figure 2 has an effect on the uniformity of plasma process results across the substrate, including the effect on center-middle etch rate uniformity.

[0072] As shown in the example of Figure 8, when higher-order harmonic frequency signals of a fundamental (base) low-frequency RF signal are generated and combined with the fundamental (base) low-frequency RF signal to generate a composite periodic waveform for the full-bandwidth low-frequency RF signal, the phases of the higher-order harmonic signals can be adjusted to obtain different waveform shapes. Figure 10 shows various waveform shapes obtained by combining a third harmonic frequency signal and a fifth harmonic frequency signal with the fundamental (base) frequency signal and shifting the phases of the third and fifth harmonic frequency signals by various amounts relative to the phase of the fundamental (base) frequency signal, according to some embodiments. Figure 10 shows a sinusoidal reference signal 1001 corresponding to Equation 1. Figure 10 also shows a square-shaped waveform signal 1003 corresponding to Equation 2, where A 400kHz is the relative power of the fundamental (base) frequency component, and B 1.2MHz is the relative power of the third harmonic frequency component, and C 2MHz is the relative power of the fifth harmonic frequency component. FIG. 10 also shows ramped rectangular waveform signals 1005A-1005F corresponding to Equation 3, where A 400kHz is the relative power of the fundamental (base) frequency component, and B 1.2MHz is the relative power of the third harmonic frequency component, and C 2MHz where Δφ is the relative power of the fifth harmonic frequency component, and (Δφ) is the phase shift between the fundamental (base) frequency component and each of the third and fifth harmonic frequency components. Specifically, waveform signal 1005A corresponds to a 6 degree phase shift (Δφ). waveform signal 1005B corresponds to a 9 degree phase shift (Δφ). waveform signal 1005C corresponds to a 12 degree phase shift (Δφ). waveform signal 1005D corresponds to a 15 degree phase shift (Δφ). waveform signal 1005E corresponds to a 20 degree phase shift (Δφ). waveform signal 1005F corresponds to a 30 degree phase shift (Δφ). In some embodiments, ramped square waveforms such as 1005A-1005F, for example, may be utilized to compensate for charging during a low frequency RF signal period.

[0073] Formula 1: Y=A 400kHz sinφ

[0074] Formula 2: Y=A 400kHz sin(φ)+B 1.2MHz sin(3φ)+C 2MHz sin(5φ)

[0075] Formula 3: Y=A 400kHz sin(φ)+B 1.2MHz sin(3φ-(360-(3Δφ))) +C 2MHz sin(5φ-(360-(5Δφ)))

[0076] 11 illustrates an RF signal delivery system 1100 including the low-frequency RF signal generator 101 and high-frequency RF signal generator 102 described with respect to FIG. 1 , and further including multiple harmonic frequency RF signal generators 1101-1 through 1101-N, according to some embodiments. In some embodiments, the number (N) of harmonic frequency RF signal generators is two (N=2). However, in other embodiments, the number (N) of harmonic frequency RF signal generators is greater than two (N>2). Each harmonic frequency RF signal generator 1101-1 through 1101-N is configured to generate an RF signal that is a particular harmonic frequency of the fundamental (base) low-frequency RF signal generated by the low-frequency RF signal generator 101. The harmonic frequency RF signals generated by harmonic frequency RF signal generators 1101-1 through 1101-N are combined with the fundamental low-frequency RF signal generated by low-frequency RF signal generator 101 in impedance matching system 1115 to generate a composite low-frequency RF signal waveform for use in the frequency adjustment process of FIG. 2, such as composite low-frequency RF signal waveforms 702 and 802 described above with respect to FIGS. 7 and 8, respectively.

[0077] Each of the harmonic frequency RF signal generators 1101-1 to 1101-N is configured similarly to the low-frequency RF signal generator 101. Each of the harmonic frequency RF signal generators 1101-1 to 1101-N includes an oscillator 1103-x, where x ranges from 1 to N, for generating an RF signal. The oscillator 1103-x is an electronic circuit that generates a periodically oscillating electrical signal, such as a sinusoidal electrical signal, having a specified frequency within the RF range. The oscillator 1103-x is capable of oscillating at a harmonic frequency of the operating frequency of the oscillator 103 of the low-frequency RF signal generator 101. The output of the oscillator 1103-x is connected to the input of a power amplifier 1105-x, where x ranges from 1 to N. The power amplifier 1105-x operates to amplify the RF signal generated by the oscillator 1103-x and transmit the amplified RF signal to the output 1110-x of the harmonic frequency RF signal generator 1101-x through the output of the power amplifier 1105-x, where x is 1 to N.

[0078] Each harmonic frequency RF signal generator 1101-x also includes a control system 1109-x configured to provide control of all operational aspects of the harmonic frequency RF signal generator 1101-x, where x ranges from 1 to N. In some embodiments, the control system 1109-x includes a processor, a data storage device, an input / output interface, and a data bus through which the processor, data storage device, and input / output interface communicate data with each other. The control system 1109-x is connected to provide control of an oscillator 1103-x, as indicated by connection 1104-x, where x ranges from 1 to N. The control system 1109 is also connected to provide control of a power amplifier 1105-x, as indicated by connection 1106-x, where x ranges from 1 to N. The control system 1109-x also includes a NIC 1111-x, which enables the control system 1109-x to send data to and receive data from systems external to the harmonic frequency RF signal generators 1101-x, where x ranges from 1 to N. Examples of the NIC 1111-x include network interface cards, network adapters, etc. In various embodiments, the NIC 1111-x is configured to operate according to one or more network communication protocols and associated physical layers, such as Ethernet and / or EtherCAT, among others. The control module 163 of the plasma processing system 150 is also connected to the control system 1109-x of each harmonic frequency RF signal generator 1101-x via the NIC 152 and the NIC 1111-x, as shown by connection 1143-x, where x ranges from 1 to N.

[0079] It should be understood that the control system 1109-x is connected and configured to control essentially any aspect of the harmonic frequency RF signal generator 1101-x. It should also be understood that the control system 1109-x can be connected and configured to monitor essentially any physical and / or electrical state, condition, and / or parameter at essentially any location within the harmonic frequency RF signal generator 1101-x. The control system 1109-x is also configured to command the operation of the harmonic frequency RF signal generator 1101-x according to a prescribed algorithm. For example, the control system 1109-x is configured to operate the harmonic frequency RF signal generator 1101-x by executing input and control instructions / programs. The input and control instructions / programs include, among other parameters associated with the operation and control of the harmonic frequency RF signal generator 1101-x, a target RF power setpoint and a target frequency setpoint. In some embodiments, the control system 1109-x of each harmonic frequency RF signal generator 1101-x is connected to the control system 109 of the low frequency RF signal generator 101 such that each harmonic frequency RF signal generator 1101-x operates as a slave system to the low frequency RF signal generator 101 operating as a master system.

[0080] The harmonic frequency RF signal generator 1101-x also includes a voltage / current (V / I) sensor 1107-x connected to an output 1110-x of the harmonic frequency RF signal generator 1101-x, where x ranges from 1 to N. The V / I sensor 1107-x is connected to a control system 1109-x, as shown by connection 1108-x, where x ranges from 1 to N. In this configuration, the V / I sensor 1107-x provides real-time measurements of the voltage and current present on the output 1110-x of the harmonic frequency RF signal generator 1101-x to the control system 1109-x. In some embodiments, the V / I sensor 1107-x is located within the harmonic frequency RF signal generator 1101-x.

[0081] Each harmonic frequency RF signal generator 1101-x is configured to generate a harmonic frequency RF signal of controlled amplitude and frequency and transmit the harmonic frequency RF signal from an output 1110-x of the harmonic frequency RF signal generator 1101-x through / along a corresponding conductor 1113-x to a corresponding input 1117-x of an impedance matching system 1115, where x ranges from 1 to N. The impedance matching system combines the harmonic frequency RF signal generated by the harmonic frequency RF signal generator 1101-x with the fundamental low-frequency RF signal generated by the low-frequency RF signal generator 1101 to generate a composite low-frequency RF signal waveform, which travels from an output 123 of the impedance matching system 115 through / along an RF feed structure 160 to an electrode or antenna within the plasma processing system 150.

[0082] 12 shows an exemplary configuration of an impedance matching system 1115 according to some embodiments. Input 117, through which a fundamental (base) frequency RF signal is transmitted from low-frequency RF signal generator 101, is connected to impedance control circuit 1202, which includes capacitor 1201, inductor 1203, inductor 1205, capacitor 1207, capacitor 1211, and capacitor 1213. Input 117 is connected to a first terminal of capacitor 1201. A second terminal of capacitor 1201 is connected to a first terminal of inductor 1203. A second terminal of inductor 1203 is connected to a first terminal of inductor 1205. A second terminal of inductor 1205 is connected to pre-output node 1204. A first terminal of capacitor 1207 is connected to both the second terminal of capacitor 1201 and the first terminal of inductor 1203. A second terminal of capacitor 1207 is connected to a reference ground potential 1209. A first terminal of capacitor 1211 is connected to both the second terminal of inductor 1203 and the first terminal of inductor 1205. A second terminal of capacitor 1211 is connected to the reference ground potential 1209. A first terminal of capacitor 1213 is connected to both the second terminal of inductor 1205 and the pre-output node 1204. A second terminal of capacitor 1213 is connected to the reference ground potential 1209.

[0083] Input 1117-1, through which the harmonic frequency RF signal is transmitted from harmonic frequency RF signal generator 1101-1, is connected to impedance control circuit 1206-1, which includes capacitor 1215-1, inductor 1217-1, inductor 1219-1, capacitor 1221-1, capacitor 1223-1, and capacitor 1225-1. Input 1117-1 is connected to a first terminal of capacitor 1215-1. A second terminal of capacitor 1215-1 is connected to a first terminal of inductor 1217-1. A second terminal of inductor 1217-1 is connected to a first terminal of inductor 1219-1. A second terminal of inductor 1219-1 is connected to a pre-output node 1204. In addition, the first terminal of capacitor 1221-1 is connected to both the second terminal of capacitor 1215-1 and the first terminal of inductor 1217-1. The second terminal of capacitor 1221-1 is connected to the reference ground potential 1209. The first terminal of capacitor 1223-1 is connected to both the second terminal of inductor 1217-1 and the first terminal of inductor 1219-1. The second terminal of capacitor 1223-1 is connected to the reference ground potential 1209. The first terminal of capacitor 1225-1 is connected to both the second terminal of inductor 1219-1 and the pre-output node 1204. The second terminal of capacitor 1225-1 is connected to the reference ground potential 1209.

[0084] In some embodiments, each input 1117-1 through 1117-N of the impedance matching system 1115, through which a given harmonic frequency RF signal is transmitted from a corresponding harmonic frequency RF signal generator 1101-1 through 1101-N, is connected to a corresponding impedance control circuit 1206-1 through 1206-N configured like impedance control circuit 1206-1. Thus, the input 1117-N through which the harmonic frequency RF signal is transmitted from the Nth harmonic frequency RF signal generator 1101-N is connected to impedance control circuit 1206-N, which includes capacitor 1215-N, inductor 1217-N, inductor 1219-N, capacitor 1221-N, capacitor 1223-N, and capacitor 1225-N. Input 1117-N is connected to a first terminal of capacitor 1215-N. The second terminal of capacitor 1215-N is connected to the first terminal of inductor 1217-N. The second terminal of inductor 1217-N is connected to the first terminal of inductor 1219-N. The second terminal of inductor 1219-N is connected to pre-output node 1204. In addition, the first terminal of capacitor 1221-N is connected to both the second terminal of capacitor 1215-N and the first terminal of inductor 1217-N. The second terminal of capacitor 1221-N is connected to reference ground potential 1209. The first terminal of capacitor 1223-N is connected to both the second terminal of inductor 1217-N and the first terminal of inductor 1219-N. The second terminal of capacitor 1223-N is connected to reference ground potential 1209. A first terminal of the capacitor 1225-N is connected to both the second terminal of the inductor 1219-N and the pre-output node 1204. A second terminal of the capacitor 1225-N is connected to the reference ground potential 1209.

[0085] An input 175, through which a high-frequency RF signal is transmitted from the high-frequency RF signal generator 102, is connected to an impedance control circuit 1208, which includes a capacitor 1227, an inductor 1229, an inductor 1231, and a capacitor 1233. The input 175 is connected to a first terminal of the capacitor 1227. A second terminal of the capacitor 1227 is connected to a first terminal of the inductor 1229. A second terminal of the inductor 1229 is connected to the final output node 1210. A first terminal of the inductor 1231 is connected to the input 175, a first terminal of the capacitor 1227, and a first terminal of the capacitor 1233. A second terminal of the inductor 1231 is connected to the reference ground potential 1209. A first terminal of the capacitor 1233 is connected to the input 175, a first terminal of the inductor 1231, and a first terminal of the capacitor 1227. The second terminal of the capacitor 1233 is connected to the reference ground potential 1209 .

[0086] The pre-output node 1204 is connected to a first terminal of an output inductor 1235. A second terminal of the output inductor 1235 is connected to a final output node 1210. The final output node is connected to the output 123 of the impedance matching system 1115, which is connected to the RF feed structure 160 of the plasma processing system 150. In some embodiments, voltage and / or current measurements of the composite low-frequency RF signal waveform are taken at the pre-output node 1204. In these embodiments, the output inductor 1235 is provided to prevent the high-frequency RF signal at the final output node 1210 from interfering with the voltage and / or current measurements taken at the pre-output node 1204. It should be understood that the configuration of the impedance matching system 1115 shown in FIG. 12 is provided by way of example. In other embodiments, the impedance matching system 1115 may be configured differently using different combinations of capacitors and inductors to ensure that the impedance seen at the output 110 of the low-frequency RF signal generator 101 is substantially close to the designed operating impedance, and that the impedance seen at each output 1110-x of the harmonic frequency RF signal generators 1101-x is substantially close to the designed operating impedance, and that the impedance seen at the output 171 of the high-frequency RF signal generator 102 is substantially close to the designed operating impedance.

[0087] The harmonic frequency RF signal generators 1101-1 through 1101-N can be used to manipulate the frequency and phase of the harmonic frequency RF signal that is combined with the fundamental (base) frequency RF signal to generate a particular composite low-frequency RF signal that serves to favorably influence the portion of the plasma sheath where the plasma potential collapses so as to maintain and / or improve the coupling of the high-frequency RF signal to the plasma and thereby reduce non-uniformity of corresponding plasma process results across the substrate. It should be understood that each of the harmonic frequency RF signal generators 1101-1 through 1101-N can be independently controlled to enable control of both the phase difference and the voltage difference between each harmonic frequency RF signal and the fundamental (base) low-frequency RF signal. Also, while the examples of FIGS. 7 and 8 demonstrate the combination of the first (fundamental), third, and fifth harmonics to generate a composite low-frequency RF signal waveform, it should be understood that in various embodiments, essentially any combination of two or more harmonics can be combined with the first (fundamental) harmonic to generate a composite low-frequency RF signal waveform having particular characteristics. In some embodiments, a composite low-frequency RF signal waveform can be generated to provide a higher plasma sheath potential than would be achievable using a sinusoidal low-frequency RF signal at the same power level.

[0088] As mentioned above, in various embodiments, the plasma processing system 150 is either a CCP processing system or an ICP processing system. FIG. 13A shows an exemplary vertical cross-sectional view of a CCP processing system 150A according to some embodiments of the present disclosure. The CCP processing system 150A includes a chamber 1301 within which a plasma processing region 1302 resides. Within the plasma processing region 1302, a plasma 1323 (represented by the dashed oval region) is generated to impinge on the substrate 1305 in a controlled manner to affect a change to the substrate 1305. In various manufacturing processes, the change to the substrate 1305 can be a change in the material or surface state on the substrate 1305. For example, in various manufacturing processes, the change to the substrate 1305 can include one or more of etching material from the substrate 1305, depositing material on the substrate 1305, or modifying material present on the substrate 1305. In some embodiments, the substrate 1305 is a semiconductor wafer undergoing a manufacturing procedure. However, it should be understood that in various embodiments, the substrate 1305 can be essentially any type of substrate amenable to plasma-based manufacturing processes. For example, in some embodiments, the substrate 1305 referred to herein can be a substrate formed of silicon, sapphire, GaN, GaAs, or SiC, or other substrate materials, and may include a glass panel / substrate, metal foil, metal sheet, polymeric material, etc. Also, in various embodiments, the substrate 1305 referred to herein can vary in form, shape, and / or size. For example, in some embodiments, the substrate 1305 referred to herein can correspond to a 200 mm (millimeter) diameter semiconductor wafer, a 300 mm diameter semiconductor wafer, or a 450 mm diameter semiconductor wafer, among other semiconductor wafer sizes. Also, in some embodiments, the substrate 1305 referred to herein can correspond to a non-circular substrate, such as a rectangular substrate for a flat panel display, etc., among other shapes.

[0089] The plasma processing region 1302 within the CCP processing chamber 1301 is connected to a process gas supply system 1304 such that one or more process gases can be controlled to be supplied to the plasma processing region 1302, as represented by line 1306. It should be understood that the process gas supply system 1304 includes one or more process gas sources and an arrangement of valves and mass flow controllers to enable providing one or more process gases to the plasma processing region 1302 at controlled flow rates and flow times. Also, in various embodiments, the one or more process gases are delivered to the plasma processing region 1302 in both a temporally and spatially controlled manner relative to the substrate 1305. In various embodiments, the CCP processing system 150A operates by the process gas supply system 1304 delivering one or more process gases into the plasma processing region 1302 to cause changes in the material or surface state on the substrate 1305, and by applying RF power to the one or more process gases to convert the one or more process gases into a plasma 1323 that impinges on the substrate 1305.

[0090] The CCP processing chamber 1301 includes a substrate support structure 1303 on which a substrate 1305 is positioned and supported during processing operations. In some embodiments, an electrode 1307 is disposed within the substrate support structure 1303 to provide for transmitting RF power from the electrode 1307 through the plasma processing region 1302 to generate a plasma 1323 and / or control ion energy. The electrode 1307 is connected to receive RF power through an RF feed structure 160, which is connected to the RF signal supply system 1100 via an impedance match system 1115. The RF feed structure 160 is an electrically conductive member. In some embodiments, the RF feed structure 160 includes an electrically conductive rod. Impedance matching system 1115 includes an arrangement of capacitors and inductors configured to ensure that the impedance seen at the output of RF signal generators 101, 102, and 1101-1 to 1101-N in RF signal supply system 1100 is sufficiently close to the design impedance (typically 50 ohms) that the RF signal generators are designed to operate with, so that the RF power generated and transmitted by RF signal generators 101, 102, and 1101-1 to 1101-N is transmitted into plasma processing region 1302 as efficiently as possible, e.g., with minimal reflections.

[0091] Also, in some embodiments, the CCP processing chamber 1301 may include an upper electrode 1315. In various embodiments, the upper electrode 1315 can either provide an electrical ground electrode or can be used to transmit RF power into the plasma processing region 1302. For example, in some embodiments, the upper electrode 1315 is connected to a reference ground potential 1308 such that the upper electrode 1315 provides a return path for the RF signal transmitted from the electrode 1307 into the plasma processing region 1302. Alternatively, in some embodiments, the upper electrode 1315 is connected to receive RF power through an RF feed structure 1317, which is connected to an example RF signal delivery system 1100 via an example impedance match system 1115.

[0092] In some embodiments, a heater assembly 1325 is disposed within the substrate support structure 1303 to provide temperature control for the substrate 1305. The heater assembly 1325 is electrically connected to receive power through an electrical connection 1327, where power is provided from a power source 1331 through electrical connection 1337 to an RF filter 1329 and through the RF filter 1329 to the electrical connection 1327. In some embodiments, the power source 1331 is an alternating current (AC) power source. In some embodiments, the power source 1331 is a direct current (DC) power source. In some embodiments, the heater assembly 1325 includes a plurality of electrical resistive heating elements. The RF filter 1329 is configured to prevent RF power from entering the power source 1331 while allowing current to pass between the power source 1331 and the electrical connection 1327.

[0093] Additionally, in some embodiments, a bias voltage control system 1365 is connected to the substrate support structure 1303 in the CCP processing chamber 1301. In some embodiments, the bias voltage control system 1365 is connected to one or more bias voltage electrodes disposed in the substrate support structure 1303 to control the bias voltage present at the substrate 1305. The bias voltage may be controlled to control the energy and directionality of the charged components of the plasma 1323 by attracting the charged components of the plasma toward the substrate 1305. For example, the bias voltage control system 1365 may operate to accelerate ions in the plasma 1323 toward the substrate 1305 to perform anisotropic etching on the substrate 1305.

[0094] FIG. 13B shows an exemplary vertical cross-sectional view of an ICP processing system 150B in accordance with some embodiments of the present disclosure. The ICP processing system 150B may also be referred to as a transformer-coupled plasma (TCP) processing system. For ease of description herein, the term "ICP processing system" is used to refer to both ICP and TCP processing systems. The ICP processing system 150B includes a chamber 1351 within which a plasma processing region 1352 resides. Within the plasma processing region 1352, a plasma 1323 (represented by the dashed oval region) is generated to impinge on the substrate 1305 in a controlled manner to affect changes to the substrate 1305. In various manufacturing processes, the changes to the substrate 1305 may be changes in the material or surface state on the substrate 1305. For example, in various manufacturing processes, the changes to the substrate 1305 may include one or more of etching material from the substrate 1305, depositing material on the substrate 1305, or modifying material present on the substrate 1305. It should be understood that the ICP processing chamber 1351 can be any type of ICP processing chamber in which RF power is transferred from a coil 1355 located outside the ICP processing chamber to process gases within the ICP processing chamber 1351 to generate a plasma 1323 within the plasma processing region 1352. An upper window structure 1353 is provided to enable transfer of RF power from the coil 1355 through the upper window structure 1353 into the plasma processing region 1352 of the ICP processing chamber 1351.

[0095] A plasma processing region 1352 within the ICP processing chamber 1351 is connected to a process gas supply system 1304 so that one or more process gases can be controlled to be supplied to the plasma processing region 1352, as represented by line 1306. The ICP processing system 150B operates by the process gas supply system 1304 flowing one or more process gases into the plasma processing region 1352 to cause a change in the material or surface state on the substrate 1305, and by applying RF power from a coil 1355 to the one or more process gases to convert the one or more process gases into a plasma 1323 that impinges on the substrate 1305.

[0096] The coil 1355 is disposed above the upper window structure 1353. In the example of FIG. 13B , the coil 1355 is formed as a radial coil assembly, with the shaded portions of the coil 1355 winding into the page and the unshaded portions of the coil 1355 winding out of the page. FIG. 13C shows a top view of the coil 1355, according to some embodiments. However, it should be understood that in other embodiments, the coil 1355 can have essentially any configuration suitable for transmitting RF power through the upper window structure 1353 and into the plasma processing region 1352. In various embodiments, the coil 1355 can have any number of turns and any cross-sectional size and shape (circular, oval, rectangular, trapezoidal, etc.) appropriate to provide the desired transmission of RF power through the upper window structure 1353 and into the plasma processing region 1352. In some embodiments, the coil 1355 is connected to an example of an RF signal delivery system 1100 through an RF power structure 1361 via an impedance matching system 1115. Also, in some embodiments, the ICP processing chamber 1351 may include an electrode 1307, an RF power structure 160, an impedance matching system 1115, and an RF signal delivery system 110, as described above with respect to FIG.

[0097] Also, in some embodiments, the ICP processing chamber 1351 can include a heater assembly 1325 disposed within the substrate support structure 1303 to provide temperature control for the substrate 1305. As described with respect to the ICP processing chamber 1301 of Figure 13A, the heater assembly 1325 of the ICP processing chamber 1351 is electrically connected to receive power through electrical connection 1327, where power is provided from a power source 1331 through electrical connection 1337 to an RF filter 1329 and through the RF filter 1329 to the electrical connection 1327. Also, in some embodiments, a bias voltage control system 1365 is connected to the substrate support structure 1303 in the ICP processing chamber 1351.

[0098] The control module 163 is configured and connected to provide control of plasma process operations performed by the CCP processing system 150A and by the ICP processing system 150B. In some embodiments, the control module 163 is implemented as a combination of computer hardware and software. The control module 163 may be configured and connected to provide control of essentially any system or component associated with the CCP processing system 150A and / or the ICP processing system 150B. For example, the control module 163 may be configured and connected to control the process gas supply system 1304, the RF signal supply system 1100, the impedance matching system 1115, the power supply 1331 for the heater assembly 1325, the bias voltage control system 1365, and / or any other system or component.

[0099] The control module 163 may also be connected and configured to receive signals from various components, sensors, and monitoring devices associated with the CCP processing system 150A and the ICP processing system 150B. For example, the control module 163 may be connected and configured to receive electrical measurement signals, e.g., voltage and / or current, and RF measurement signals, from one or more of the substrate support structure 1303, the RF feed structure 160, the RF feed structure 1317, the RF feed structure 1361, and the electrical connection 1327, as well as from any other structure or component within the CCP processing system 150A and the ICP processing system 150B. The control module 163 may also be connected and configured to receive temperature and pressure measurement signals from within the plasma processing regions 1302 and 1352 of the CCP processing chamber 1301 and the ICP processing chamber 1351, respectively. Additionally, in some embodiments, the control module 163 may be configured and connected to receive, process, and respond to optically measured signals within the CCP processing chamber 1301 and the ICP processing chamber 1351.

[0100] It should be understood that the control module 163 may be connected and configured to control essentially any active or controllable device associated with the operation of the CCP processing system 150A and the ICP processing system 150B. It should also be understood that the control module 163 may be connected and configured to monitor essentially any physical and / or electrical state, condition, and / or parameter at essentially any location within the CCP processing system 150A and the ICP processing system 150B. The control module 163 may also be configured to command the operation of various components in a synchronized, scheduled manner to perform a prescribed plasma processing operation on the substrate 1305. For example, the control module 163 may be configured to operate the CCP processing system 150A and the ICP processing system 150B by executing process inputs and control instructions / programs. The process inputs and control instructions / programs may include process recipes having time-dependent commands for parameters such as power levels, timing parameters, process gases, mechanical movement of the substrate 1305, etc., as needed to achieve a desired process result on the substrate 1305. In some embodiments, the control module 163 is programmed to direct the operation of the CCP processing system 150A and / or the ICP processing system 150B according to the frequency adjustment process of FIG.

[0101] 13D shows a diagram of control module 163, according to some example embodiments. Control module 163 includes a processor 1381, a storage hardware unit (HU) 1383 (e.g., memory), an input HU 1371, an output HU 1375, an input / output (I / O) interface 1373, an I / O interface 1377, a NIC 152, and a data communication bus 1385. The processor 1381, the storage HU 1383, the input HU 1371, the output HU 1375, the I / O interface 1373, the I / O interface 1377, and the NIC 152 are in data communication with each other via the data communication bus 1385. Examples of input HUs 1371 include a mouse, a keyboard, a stylus, a data acquisition system, a data acquisition card, etc. Examples of output HUs 1375 include a display, a speaker, a device controller, etc. Examples of NICs 152 include a network interface card, a network adapter, etc. In various embodiments, NIC 152 is configured to operate according to one or more communication protocols and associated physical layers, such as Ethernet and / or EtherCAT, among others. Each of I / O interfaces 1373 and 1377 is defined to provide compatibility between different hardware units coupled to the I / O interface. For example, I / O interface 1373 may be defined to convert signals received from input HU 1371 to a format, amplitude, and / or rate compatible with data communication bus 1385. I / O interface 1377 may also be defined to convert signals received from data communication bus 1385 to a format, amplitude, and / or rate compatible with output HU 1375. While various operations described herein are performed by processor 1381 of control module 163, it should be understood that in some embodiments, various operations may be performed by multiple processors of control module 163 and / or by multiple processors of multiple computing systems connected to control module 163.

[0102] Disclosed herein is an RF signal delivery system (1100) for a plasma processing system (150). The RF signal delivery system (1100) includes a first RF signal generator (101) configured to generate a first RF signal having a first frequency (LF1) at an output (110) of the first RF signal generator (101). The RF signal delivery system (1100) also includes a second RF signal generator (1101-1) configured to generate a second RF signal having a second frequency (LF2) at an output (1110-1) of the second RF signal generator (1101-1). The second frequency (LF2) is a specified harmonic of the first frequency (LF1), i.e., LF2≈(LF1*n), where n is an integer greater than 1. The RF signal delivery system (1100) also includes a third RF signal generator (1101-2) configured to generate a third RF signal having a third frequency (LF3) at an output (1110-2) of the third RF signal generator (1101-2). The third frequency (LF3) is a specified harmonic of the first frequency (LF1), i.e., LF3 ≈ (LF1 * n), where n is an integer greater than 1. The third frequency (LF3) and the second frequency (LF2) are different specified harmonics of the first frequency (LF1). The RF signal delivery system (1100) also includes a fourth RF signal generator (102) configured to generate a fourth RF signal having a fourth frequency (HF) at an output (171) of the fourth RF signal generator (102). The fourth frequency (HF) is at least two orders of magnitude greater than the first frequency (LF1).

[0103] The RF signal supply system (1100) also includes an impedance matching system (1115) having a first input (117) connected to the output (110) of the first RF signal generator (101), a second input (1117-1) connected to the output (1110-1) of the second RF signal generator (1101-1), a third input (1117-2) connected to the output (1110-2) of the third RF signal generator (1101-2), and a fourth input (175) connected to the output (171) of the fourth RF signal generator (102). The impedance matching system (1115) has an output (123) connected to the RF supply input (160) of the plasma processing system (150). The impedance matching system (1115) is configured to control impedance at the output (110) of the first RF signal generator (101), the output (1110-1) of the second RF signal generator (1101-1), the output (1110-2) of the third RF signal generator (1101-2), and the output (171) of the fourth RF signal generator (102).

[0104] The RF signal supply system (1100) also includes a control module (163) programmed to control a first phase difference (Δφ1) between the second RF signal having the second frequency (LF2) and the first RF signal having the first frequency (LF1). The control module (163) is also programmed to control a second phase difference (Δφ2) between the third RF signal having the third frequency (LF3) and the first RF signal having the first frequency (LF1). The control module (163) is also programmed to control a first voltage difference (ΔV1) between the second RF signal having the second frequency (LF2) and the first RF signal having the first frequency (LF1). The control module (163) is also programmed to control a second voltage difference (ΔV2) between the third RF signal having the third frequency (LF3) and the first RF signal having the first frequency (LF1). The first phase difference (Δφ1), the second phase difference (Δφ2), the first voltage difference (ΔV1), and the second voltage difference (ΔV2) are set to collectively control the plasma sheath voltage / potential as a function of time within the plasma processing system (150) and correspondingly control process result uniformity across a substrate (1305) within the plasma processing system (150).

[0105] In some embodiments, the first frequency (LF1) is within a range extending from about 330 kHz to about 440 kHz, and the fourth frequency (HF) is within a range extending from about 57 MHz to about 63 MHz. In some embodiments, the first frequency (LF1) is about 400 kHz, the second frequency (LF2) is about 1.2 MHz, the third frequency (LF3) is about 2.0 MHz, and the fourth frequency (HF) is about 60 MHz. In some embodiments, the first phase difference (Δφ1) is about 30 degrees, and the second phase difference (Δφ2) is about 30 degrees. In some embodiments, the first voltage difference (ΔV1) is set so that the power of the second RF signal having the second frequency (LF2) is within a range ranging from about 17% to about 20% of the power of the first RF signal having the frequency (LF1), and the second voltage difference (ΔV2) is set so that the power of the third RF signal having the frequency (LF3) is within a range ranging from about 5% to about 8% of the power of the first RF signal having the frequency (LF1). In some embodiments, the second frequency (LF2) and the third frequency (LF3) are each an integer multiple of the first frequency (LF1) that is greater than one.

[0106] In some embodiments, the second RF signal generator (1101-1) is connected as a slave to the first RF signal generator (101) so that the second frequency (LF2) tracks in real time as an integer multiple of the first frequency (LF1) and so that a first phase difference (Δφ1) between the second RF signal having the second frequency (LF2) and the first RF signal having the first frequency (LF1) is maintained in real time. Also in these embodiments, the third RF signal generator (1101-2) is connected as a slave to the first RF signal generator (101) so that the third frequency (LF3) tracks in real time as an integer multiple of the first frequency (LF1) and so that a second phase difference (Δφ2) between the third RF signal having the third frequency (LF3) and the first RF signal having the first frequency (LF1) is maintained in real time.

[0107] In some embodiments, the first phase difference (Δφ1), the first voltage difference (ΔV1), the second phase difference (Δφ2), and the second voltage difference (ΔV2) are collectively set to control etch rate uniformity across a substrate (1305) in the plasma processing system (150). In some embodiments, the first phase difference (Δφ1), the first voltage difference (ΔV1), the second phase difference (Δφ2), and the second voltage difference (ΔV2) are collectively set to increase the plasma sheath voltage / potential over a greater percentage of the period of the first RF signal having the first frequency (LF1). In some embodiments, the first phase difference (Δφ1), the first voltage difference (ΔV1), the second phase difference (Δφ2), and the second voltage difference (ΔV2) are collectively set to generate a substantially rectangular periodic waveform as a combination of the first RF signal having the first frequency (LF1), the second RF signal having the second frequency (LF2), and the third RF signal having the third frequency (LF3). In some embodiments, the first phase difference (Δφ1), the first voltage difference (ΔV1), the second phase difference (Δφ2), and the second voltage difference (ΔV2) are collectively set to provide a maximum plasma sheath voltage / potential that is greater than that achievable from the first RF signal having the first frequency (LF1) alone. In some embodiments, a first RF signal having a first frequency (LF1), a second RF signal having a second frequency (LF2), and a third RF signal having a third frequency (LF3) are combined to form a periodic waveform, each period of the periodic waveform having a negative half and a positive half, and the first phase difference (Δφ1), the first voltage difference (ΔV1), the second phase difference (Δφ2), and the second voltage difference (ΔV2) are collectively set such that the negative half of each period of the periodic waveform is longer than the positive half of each period of the periodic waveform.

[0108] In some embodiments, the impedance matching system (1115) includes a first impedance control circuit (1202) connected between a first input (117) of the impedance matching system (1115) and an output (123) of the impedance matching system (1115). The impedance matching system (1115) also includes a second impedance control circuit (1206-1) connected between a second input (1117-1) of the impedance matching system (1115) and the output (123) of the impedance matching system (1115). The impedance matching system (1115) also includes a third impedance control circuit (1206-2) connected between a third input (1117-2) of the impedance matching system (1115) and the output (123) of the impedance matching system (1115). The impedance matching system (1115) also includes a fourth impedance control circuit (1208) connected between a fourth input (175) of the impedance matching system (1115) and an output (123) of the impedance matching system (1115).

[0109] FIG. 14 shows a flowchart of a method for operating a radio frequency signal generator system for a plasma processing system according to some embodiments. For purposes of explanation, some of the operations appear sequentially in the flowchart of FIG. 14, but it should be understood that the operations of FIG. 14 may be performed substantially simultaneously. The method includes an operation 1401 for operating a first RF signal generator (101) to generate a first RF signal having a first frequency (LF1) at an output (110) of the first RF signal generator (101). The method also includes an operation 1403 for operating a second RF signal generator (1101-1) to generate a second RF signal having a second frequency (LF2) at an output (1110-1) of a second RF signal generator (1101-2). The second frequency (LF2) is a specified harmonic of the first frequency (LF1), i.e., LF2≈(LF1*n), where n is an integer greater than 1. The method also includes an operation 1405 for operating the third RF signal generator (1101-2) to generate a third RF signal having a third frequency (LF3) at an output (1110-2) of the third RF signal generator (1101-2). The third frequency (LF3) is a specified harmonic of the first frequency (LF1), i.e., LF3 ≈ (LF1 * n), where n is an integer greater than 1. The third frequency (LF3) and the second frequency (LF2) are different specified harmonics of the first frequency (LF1). The method also includes an operation 1407 for operating the fourth RF signal generator (102) to generate a fourth RF signal having a fourth frequency (HF) at an output (171) of the fourth RF signal generator (102). The fourth frequency (HF) is at least two orders of magnitude greater than the first frequency (LF1).

[0110] The method also includes an operation 1409 for operating an impedance matching system (1115) to control impedances at the output (110) of the first RF signal generator (101), the output (1110-1) of the second RF signal generator (1101-1), the output (1110-2) of the third RF signal generator (1101-2), and the output (171) of the fourth RF signal generator (102). A first RF signal having a first frequency (LF1), a second RF signal having a second frequency (LF2), a third RF signal having a third frequency (LF3), and a fourth RF signal having a fourth frequency (HF) are transmitted through the impedance matching system (1115) to a radio frequency supply input (160) of the plasma processing system (150) causing generation of a plasma (1323) in the plasma processing system (150). The impedance matching system (1115) operates to combine a first RF signal having a first frequency (LF1), a second RF signal having a second frequency (LF2), a third RF signal having a third frequency (LF3), and a fourth RF signal having a fourth frequency (HF) on the output of the impedance matching system (1115).

[0111] The method also includes operation 1411 for operating the control module (163) to control a first phase difference (Δφ1) between the second RF signal having the second frequency (LF2) and the first RF signal having the first frequency (LF1). Operation 1411 also includes operating the control module (163) to control a second phase difference (Δφ2) between the third RF signal having the third frequency (LF3) and the first RF signal having the first frequency (LF1). Operation 1411 also includes operating the control module (163) to control a first voltage difference (ΔV1) between the second RF signal having the second frequency (LF2) and the first RF signal having the first frequency (LF1). Operation 1411 also includes operating the control module (163) to control a second voltage difference (ΔV2) between the third RF signal having the third frequency (LF3) and the first RF signal having the first frequency (LF1). The first phase difference (Δφ1), the second phase difference (Δφ2), the first voltage difference (ΔV1), and the second voltage difference (ΔV2) collectively control a plasma sheath voltage / potential as a function of time in the plasma processing system (150). In some embodiments, the plasma sheath voltage / potential is used to control process result uniformity across a substrate (1305) in the plasma processing system (150).

[0112] In some embodiments of the method, the first frequency (LF1) is within a range extending from approximately 340 kHz to approximately 440 kHz, the fourth frequency (HF) is within a range extending from approximately 57 MHz to approximately 63 MHz, and each of the second frequency (LF2) and the third frequency (LF3) is a respective integer multiple of the first frequency (LF1) that is greater than 1. In some embodiments of the method, the first frequency (LF1) is approximately 400 kHz, the second frequency (LF2) is approximately 1.2 MHz, the third frequency (LF3) is approximately 2.0 MHz, and the fourth frequency (HF) is approximately 60 MHz. In some embodiments of the method, the first phase difference (Δφ1) is approximately 30 degrees, and the second phase difference (Δφ2) is approximately 30 degrees. In some embodiments of the method, the first voltage difference (ΔV1) is controlled so that the power of the second RF signal having the second frequency (LF2) is within a range ranging from about 17% to about 20% of the power of the first RF signal having the frequency (LF1), and the second voltage difference (ΔV2) is controlled so that the power of the third RF signal having the frequency (LF3) is within a range ranging from about 5% to about 8% of the power of the first RF signal having the frequency (LF1).

[0113] In some embodiments of the method, the second RF signal generator (1101-1) operates as a slave to the first RF signal generator (101) such that the second frequency (LF2) tracks in real time as an integer multiple of the first frequency (LF1) and such that a first phase difference (Δφ1) between the second RF signal having the second frequency (LF2) and the first RF signal having the first frequency (LF1) is maintained in real time. Also in these embodiments of the method, the third RF signal generator (1101-2) operates as a slave to the first RF signal generator (101) such that the third frequency (LF3) tracks in real time as an integer multiple of the first frequency (LF1) and such that a second phase difference (Δφ2) between the third RF signal having the third frequency (LF3) and the first RF signal having the first frequency (LF1) is maintained in real time.

[0114] In some embodiments, the first phase difference (Δφ1), the second phase difference (Δφ2), the first voltage difference (ΔV1), and the second voltage difference (ΔV2) are collectively set to control etch rate uniformity across a substrate (1305) in the plasma processing system (150). In some embodiments, the first phase difference (Δφ1), the second phase difference (Δφ2), the first voltage difference (ΔV1), and the second voltage difference (ΔV2) are collectively set to increase the plasma sheath voltage / potential over a greater percentage of a period of the first RF signal having the first frequency (LF1). In some embodiments, the first phase difference (Δφ1), the first voltage difference (ΔV1), the second phase difference (Δφ2), and the second voltage difference (ΔV2) are collectively controlled so that the combination of the first RF signal having the first frequency (LF1), the second RF signal having the second frequency (LF2), and the third RF signal having the third frequency (LF3) generates a substantially rectangular periodic waveform. In some embodiments, the first phase difference (Δφ1), the first voltage difference (ΔV1), the second phase difference (Δφ2), and the second voltage difference (ΔV2) are collectively controlled to provide a maximum plasma sheath voltage / potential that is greater than that achievable from the first RF signal having the first frequency (LF1) alone. In some embodiments, a first RF signal having a first frequency (LF1), a second RF signal having a second frequency (LF2), and a third RF signal having a third frequency (LF3) are combined to form a periodic waveform, each period of the periodic waveform having a negative half and a positive half, and the first phase difference (Δφ1), the first voltage difference (ΔV1), the second phase difference (Δφ2), and the second voltage difference (ΔV2) are collectively controlled such that the negative half of each period of the periodic waveform is longer than the positive half of each period of the periodic waveform.

[0115] In the above embodiments, multiple harmonic frequency signals are combined with a fundamental (base) frequency signal to create a composite low-frequency RF signal waveform for use in the frequency adjustment process of Figure 2, in which a high-frequency RF signal is applied with a composite low-frequency RF signal waveform to generate a plasma for processing a semiconductor substrate. In some embodiments, either alternatively or additionally, passive approaches may be implemented to manipulate one or more harmonic frequency signals of the fundamental (base) low-frequency RF signal to create a designed low-frequency RF signal waveform for use in the frequency adjustment process of Figure 2. For example, in some embodiments of passive approaches, one or more RF signal filters may be disposed within and / or around the plasma processing chamber 150 along with various RF signal transmission paths to manipulate one or more harmonic frequency signals of the fundamental (base) low-frequency RF signal to create a designed low-frequency RF signal waveform for use in the frequency adjustment process of Figure 2. Also, in some embodiments, the impedances of various chamber components within various RF signal transmission paths within and / or around the plasma processing chamber 150 may be designed to contribute to the manipulation of one or more harmonic frequency signals of the fundamental (base) low frequency RF signal to create a designed low frequency RF signal waveform for use in the frequency adjustment process of FIG.

[0116] In some embodiments, an RF signal filter is configured to filter and / or alter the phase of specific harmonic frequency signals relative to the phase of the fundamental (base) low-frequency RF signal. In various embodiments, the RF signal filter may be implemented in either the low-frequency RF signal generator 101 or the impedance matching system 115 / 1115. In a passive approach, the objective is to control the phase difference between one or more harmonic frequency signals and the corresponding fundamental (base) frequency signal to achieve a desired shape of the designed low-frequency RF signal waveform and, therefore, a desired plasma sheath voltage / potential behavior as a function of time, which has a beneficial effect on plasma process result uniformity control across the substrate. In a passive approach, impedance control is implemented within the RF transmission line to affect the phase control of the targeted low-frequency harmonic signals and, therefore, achieve the desired shape of the designed low-frequency RF signal waveform. In some embodiments, the phase of specific low-frequency harmonic signals may also be filtered / altered electrically or by adjusting some impedance along the RF signal transmission line, such as in the plasma processing chamber 1301 / 1351.

[0117] For example, an impedance control device, such as a variable capacitor or other device, is connected between the electrode and a reference ground potential to vary the impedance to ground seen by a particular harmonic frequency signal of the low-frequency RF signal, which in turn varies the phase of that particular harmonic frequency signal and correspondingly varies the shape of the designed low-frequency RF signal waveform used in the frequency adjustment process of Figure 2. For example, with reference to Figure 13A, in some embodiments, a variable capacitor or other impedance control device is connected between the electrode 1315 and the reference ground potential 1308 to vary the phase of one or more particular harmonic frequency signals and correspondingly vary the shape of the designed low-frequency RF signal waveform used in the frequency adjustment process of Figure 2. It should be understood that in various embodiments, one or more impedance control devices may be installed at designated locations within the RF signal transmission path to achieve a desired effect on the phase of one or more harmonic frequency signals of the fundamental (base) low-frequency RF signal generated by the low-frequency RF signal generator 101 to achieve a desired shape of the designed low-frequency RF signal waveform and, in turn, a desired plasma sheath voltage / potential behavior as a function of time, which has a beneficial effect on plasma process result uniformity control across the substrate.

[0118] It should be understood that the embodiments described herein may employ various computer-implemented operations involving data stored in computer systems. These operations are operations requiring physical manipulation of physical quantities. Any of the operations described herein that form part of the embodiments are useful machine operations. The embodiments also relate to hardware units or apparatus for performing these operations. An apparatus may be specially constructed for a special purpose computer. When defined as a special purpose computer, the computer may also perform other processes, program execution, or routines that are not part of its special purpose while still being capable of operations for that special purpose. In some embodiments, operations may be processed by a general-purpose computer selectively activated or configured by one or more computer programs stored in computer memory, cache, or retrieved over a network. If the data is retrieved over a network, the data may be processed by other computers on the network, e.g., a cloud of computing resources.

[0119] Various embodiments described herein may be fabricated as computer-readable code on a non-transitory computer-readable medium. A non-transitory computer-readable medium is any data storage hardware unit that can store data, which can then be read by a computer system. Examples of non-transitory computer-readable media include hard drives, network-attached storage (NAS), ROM, RAM, compact disc ROM (CD-ROM), CD-recordable (CD-R), CD-rewritable (CD-RW), magnetic tape, and other optical and non-optical data storage hardware units. A non-transitory computer-readable medium may include a computer-readable tangible medium that is distributed across network-coupled computer systems so that the computer-readable code is stored and executed in a distributed manner.

[0120] Although the above disclosure includes some details for purposes of clarity of understanding, it will be apparent that certain changes and modifications can be made within the scope of the appended claims. For example, it should be understood that one or more features from any embodiment disclosed herein can be combined with one or more features of any other embodiment disclosed herein. Therefore, the present embodiments should be considered illustrative and not limiting, and the claims should not be limited to the details provided herein, but may vary within the scope and equivalents of the described embodiments.

Claims

1. 1. A radio frequency (RF) signal delivery system for a plasma processing system, comprising: a first RF signal generator configured to generate a first RF signal having a first frequency; a second RF signal generator configured to generate a second RF signal having a second frequency, the second frequency being a designated harmonic of the first frequency; a third RF signal generator configured to generate a third RF signal having a third frequency, the third frequency being a designated harmonic of the first frequency, and the third frequency and the second frequency being different designated harmonics of the first frequency; a fourth RF signal generator configured to generate a fourth RF signal having a fourth frequency, the fourth frequency being at least two orders of magnitude greater than the first frequency; 1. An RF signal delivery system for a plasma processing system, comprising:

2. 10. The RF signal delivery system for a plasma processing system of claim 1, comprising: an impedance matching system having a first input connected to the output of the first RF signal generator, a second input connected to the output of the second RF signal generator, a third input connected to the output of the third RF signal generator, and a fourth input connected to the output of the fourth RF signal generator, the impedance matching system having an output connectable to an RF supply input of the plasma processing system and configured to control impedance at the output of the first RF signal generator, the output of the second RF signal generator, the output of the third RF signal generator, and the output of the fourth RF signal generator; a first phase difference between the second RF signal and the first RF signal; a second phase difference between the third RF signal and the first RF signal; a first voltage difference between the second RF signal and the first RF signal; a second voltage difference between the third RF signal and the first RF signal; a control module programmed to control the Furthermore, An RF signal supply system for a plasma processing system, wherein the first phase difference, the second phase difference, the first voltage difference, and the second voltage difference collectively control a plasma sheath voltage as a function of time within the plasma processing system.

3. 3. The RF signal delivery system for a plasma processing system of claim 2, wherein the plasma sheath voltage is used to control process result uniformity across a substrate in the plasma processing system.

4. 10. The RF signal supply system for a plasma processing system of claim 1, wherein the first frequency is in a range extending from about 330 kilohertz (kHz) to about 440 kHz, and the fourth frequency is in a range extending from about 54 megahertz (MHz) to about 63 MHz.

5. 5. The RF signal supply system for a plasma processing system of claim 4, wherein the first frequency is about 400 kilohertz (kHz), the second frequency is about 1.2 megahertz (MHz), the third frequency is about 2.0 MHz, and the fourth frequency is about 60 MHz.

6. 6. The RF signal supply system for a plasma processing system of claim 5, wherein the first phase difference is about 30 degrees and the second phase difference is about 30 degrees.

7. 6. The RF signal supply system for a plasma processing system of claim 5, wherein the first voltage difference is set such that the power of the second RF signal is within a range ranging from about 17% to about 20% of the power of the first RF signal, and the second voltage difference is set such that the power of the third RF signal is within a range ranging from about 5% to about 8% of the power of the first RF signal.

8. 2. The RF signal supply system for a plasma processing system of claim 1, wherein each of the second frequency and the third frequency is a respective integer multiple greater than one of the first frequency.

9. 2. The RF signal delivery system for a plasma processing system of claim 1, wherein the second RF signal generator is connected as a slave to the first RF signal generator such that the second frequency tracks in real time as an integer multiple of the first frequency and such that the first phase difference between the second RF signal and the first RF signal is maintained in real time; and a third RF signal generator connected as a slave to the first RF signal generator such that the third frequency tracks the first frequency in real time as an integer multiple of the first frequency and such that the second phase difference between the third RF signal and the first RF signal is maintained in real time.

10. 2. The RF signal supply system for a plasma processing system of claim 1, wherein the first phase difference, the first voltage difference, the second phase difference, and the second voltage difference are collectively set to control etch rate uniformity across a substrate in the plasma processing system.

11. 2. The RF signal supply system for a plasma processing system of claim 1, wherein the first phase difference, the first voltage difference, the second phase difference, and the second voltage difference are collectively set to increase a plasma sheath voltage over a greater percentage of a period of the first RF signal.

12. 2. The RF signal supply system for a plasma processing system of claim 1, wherein the first phase difference, the first voltage difference, the second phase difference, and the second voltage difference are collectively set to generate a substantially rectangular periodic waveform as a combination of the first RF signal, the second RF signal, and the third RF signal.

13. 2. The RF signal supply system for a plasma processing system of claim 1, wherein the first phase difference, the first voltage difference, the second phase difference, and the second voltage difference are collectively set to provide a maximum plasma sheath voltage greater than that achievable from the first RF signal alone.

14. 2. The RF signal supply system for a plasma processing system of claim 1, wherein the first RF signal, the second RF signal, and the third RF signal are combined to form a periodic waveform, each period of the periodic waveform having a negative half and a positive half, and the first phase difference, the first voltage difference, the second phase difference, and the second voltage difference are collectively set such that the negative half of each period of the periodic waveform is longer than the positive half of each period of the periodic waveform.

15. 2. The RF signal supply system for a plasma processing system of claim 1, wherein the impedance matching system includes a first impedance control circuit connected between the first input of the impedance matching system and the output of the impedance matching system, the impedance matching system includes a second impedance control circuit connected between the second input of the impedance matching system and the output of the impedance matching system, the impedance matching system includes a third impedance control circuit connected between the third input of the impedance matching system and the output of the impedance matching system, and the impedance matching system includes a fourth impedance control circuit connected between the fourth input of the impedance matching system and the output of the impedance matching system.

16. 1. A method for operating a radio frequency signal delivery system for a plasma processing system, comprising: operating a first RF signal generator to generate a first RF signal having a first frequency at an output of the first RF signal generator; operating a second RF signal generator to generate a second RF signal having a second frequency at an output of the second RF signal generator, the second frequency being a specified harmonic of the first frequency; operating a third RF signal generator to generate a third RF signal having a third frequency at an output of the third RF signal generator, the third frequency being a designated harmonic of the first frequency, and the third frequency and the second frequency being different designated harmonics of the first frequency; operating a fourth RF signal generator to generate a fourth RF signal having a fourth frequency at an output of the fourth RF signal generator, the fourth frequency being at least two orders of magnitude greater than the first frequency; operating an impedance matching system to control impedances at the output of the first RF signal generator, the output of the second RF signal generator, the output of the third RF signal generator, and the output of the fourth RF signal generator, wherein the first RF signal, the second RF signal, the third RF signal, and the fourth RF signal are transmitted through the impedance matching system to a radio frequency supply input of the plasma processing system causing generation of a plasma in the plasma processing system; a first phase difference between the second RF signal and the first RF signal; a second phase difference between the third RF signal and the first RF signal; a first voltage difference between the second RF signal and the first RF signal; a second voltage difference between the third RF signal and the first RF signal; wherein the first phase difference, the second phase difference, the first voltage difference, and the second voltage difference collectively control a plasma sheath voltage as a function of time in the plasma processing system; A method comprising:

17. 15. The method of claim 14, wherein the plasma sheath voltage is used to control process result uniformity across a substrate in the plasma processing system.

18. 17. The method of claim 16, wherein the first frequency is in a range extending from about 330 kilohertz (kHz) to about 440 kHz, the fourth frequency is in a range extending from about 54 megahertz (MHz) to about 63 MHz, and each of the second and third frequencies is a respective integer multiple of the first frequency that is greater than one.

19. 17. The method of claim 16, wherein the first frequency is approximately 400 kilohertz (kHz), the second frequency is approximately 1.2 megahertz (MHz), the third frequency is approximately 2.0 MHz, and the fourth frequency is approximately 60 MHz.

20. 20. The method of claim 19, wherein the first phase difference is about 30 degrees and the second phase difference is about 30 degrees.

21. 20. The method of claim 19, wherein the first voltage difference is controlled such that the power of the second RF signal is within a range ranging from about 17% to about 20% of the power of the first RF signal, and the second voltage difference is controlled such that the power of the third RF signal is within a range ranging from about 5% to about 8% of the power of the first RF signal.

22. 17. The method of claim 16, wherein the second RF signal generator operates as a slave to the first RF signal generator such that the second frequency tracks in real time as an integer multiple of the first frequency and such that the first phase difference is maintained in real time; wherein the third RF signal generator operates as a slave to the first RF signal generator such that the third frequency tracks the first frequency as an integer multiple in real time and such that the second phase difference is maintained in real time.

23. 17. The method of claim 16, wherein the first phase difference, the second phase difference, the first voltage difference, and the second voltage difference are collectively controlled to control etch rate uniformity across a substrate in the plasma processing system.

24. 17. The method of claim 16, wherein the first phase difference, the second phase difference, the first voltage difference, and the second voltage difference are collectively controlled to increase plasma sheath voltage over a greater percentage of a period of the first RF signal.

25. 17. The method of claim 16, wherein the first phase difference, the first voltage difference, the second phase difference, and the second voltage difference are collectively controlled such that a combination of the first RF signal, the second RF signal, and the third RF signal produces a substantially rectangular periodic waveform.

26. 17. The method of claim 16, wherein the first phase difference, the first voltage difference, the second phase difference, and the second voltage difference are collectively controlled to provide a maximum plasma sheath voltage greater than achievable from the first RF signal alone.

27. 17. The method of claim 16, wherein the first RF signal, the second RF signal, and the third RF signal combine to form a periodic waveform, each period of the periodic waveform having a negative half and a positive half, and the first phase difference, the first voltage difference, the second phase difference, and the second voltage difference are collectively controlled such that the negative half of each period of the periodic waveform is longer than the positive half of each period of the periodic waveform.

28. 17. The method of claim 16, wherein the impedance matching system operates to combine the first RF signal, the second RF signal, the third RF signal, and the fourth RF signal onto the output of the impedance matching system.

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