Plasma chamber with high frequency RF signal and slave low frequency RF signal to upper electrode for plasma process control

Abstract

A system including a plasma chamber with an upper electrode above a lower electrode. A first low frequency radio frequency (RF) generator is electrically coupled to the lower electrode to supply a first low frequency RF signal at a frequency and a first phase. A second low frequency RF generator is electrically coupled to the upper electrode to supply a second low frequency RF signal at the first frequency and a second phase. A phase controller determines a phase offset between the first and second low frequency RF signals based on a predetermined time period related to an occurrence of a maximum of the first low frequency RF signal and an occurrence of a minimum of the second low frequency RF signal, wherein the second phase is based on the phase offset. A high frequency RF generator is electrically coupled the upper electrode to supply a high frequency RF signal.

Description

LAM2P121 l.P / 11810-1WOPLASMA CHAMBER WITH HIGH FREQUENCY RF SIGNAL AND SLAVE LOW FREQUENCY RF SIGNAL TO UPPER ELECTRODE FOR PLASMA PROCESS CONTROLTECHNICAL FIELD

[0001] The present embodiments relate to semiconductor fabrication, and more specifically to systems and methods for controlling plasma density (i.e., achieving plasma uniformity) at the edge of a substrate using a capacitively coupled plasma chamber providing a high frequency radio frequency (RF) signal and a low frequency RF signal to an upper electrode. The low frequency RF signal delivered to the upper electrode is slaved to a bias signal delivered to a lower electrode, such that a frequency is locked and a phase offset is applied to promote generation and delivery of negative species to a substrate.BACKGROUND OF THE DISCLOSURE

[0002] Many modern semiconductor chip fabrication processes such as plasma etching processes are performed within a plasma processing chamber in which a substrate, e.g., wafer, is supported on an electrostatic chuck (ESC). In plasma etching processes, the wafer is exposed to a plasma generated within a plasma processing volume. Plasma contains various types of radicals, electrons, as well as positive and negative ions. The chemical reactions of the various radicals, electrons, positive ions, and negative ions are used to etch features, surfaces and materials of a wafer.

[0003] For example, when a process gas is supplied into the plasma processing chamber, one or more radio frequency (RF) signals provide power that are applied to one or more coils and electrodes of the plasma processing chamber to form an electric field. The process gas is turned into plasma by the RF signals, thereby performing plasma etching on a predetermined layer disposed on the wafer. Unfortunately, during wafer processing, the plasma non-uniformity arising from plasma generation zones may result in ions striking the wafer with a non-vertical direction (e.g., ion tilt angles) occurring all across the wafer and along the extreme edge of the wafer which may cause tilted etch features in the wafer.

[0004] It is in this context that embodiments of the disclosure arise.SUMMARY

[0005] The present embodiments relate to plasma processing systems for controlling plasma density and on-wafer process performance using a capacitively coupled plasma chamber providing to an upper electrode a high frequency radio frequency (RF) signal and a low frequency RF signal that is slaved to a bias signal delivered to a lower electrode, such that a frequency is locked and a phase offset is applied. Several inventive embodiments of the present disclosure are described below.LAM2P121 l.P / 11810-1WO

[0006] Embodiments of the present disclosure provide for a system. The system including a plasma chamber configured for generating plasma, wherein the plasma chamber includes a lower electrode located within an electrostatic chuck (ESC). The system including an upper electrode disposed above the lower electrode. The system including a first low frequency radio frequency (RF) generator electrically coupled to the lower electrode and configured to supply a first low frequency RF signal to the lower electrode at a low frequency and a first phase. The system including a second low frequency RF generator electrically coupled to the upper electrode and configured to supply a second low frequency RF signal to the upper electrode at the low frequency and a second phase. The system including a phase controller configured to determine a phase offset between the first low frequency RF signal and the second low frequency RF signal based on a predetermined time period that is related to an occurrence of a maximum of the first low frequency RF signal and an occurrence of a minimum of the second low frequency RF signal, wherein the phase controller sets the second phase based on the phase offset. The system including a high frequency RF generator electrically coupled the upper electrode and configured to supply a high frequency RF signal to the upper electrode.

[0007] Other embodiments of the present disclosure provide for a method. The method including supplying a high frequency RF signal to an upper electrode. The method including supplying a first low frequency RF signal to a lower electrode at a low frequency and a first phase, wherein a plasma chamber configured for generating the plasma includes the lower electrode located within an electrostatic chuck (ESC). The method including supplying a second low frequency signal to the upper electrode at the low frequency and a second phase, wherein the upper electrode is disposed over the lower electrode in the plasma chamber. The method including determining a phase offset between the first low frequency RF signal and the second low frequency RF signal based on a predetermined time period that is related to an occurrence of a maximum of the first low frequency RF signal and an occurrence of a minimum of the second low frequency RF signal, wherein the second phase is set based on the phase offset.

[0008] These and other advantages will be appreciated by those skilled in the art upon reading the entire specification and the claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The embodiments may best be understood by reference to the following description taken in conjunction with the accompanying drawings.

[0010] FIG. 1 illustrates an embodiment of a capacitively coupled plasma processing system utilized for etching operations configured for supplying a high frequency RF signal and a low frequency RF signal that is slaved to a bias signal in order to control plasma density and anLAM2P121 l.P / 11810-1WO amount and / or the flux of negatively charged species entering the plasma sheath at the substrate, in accordance with one embodiment of the present disclosure.

[0011] FIG. 2 illustrates the operation of a capacitively coupled plasma processing system and voltage waveforms of a top sheath and a bottom sheath, wherein the voltage waveform of the bottom sheath is offset in phase from the voltage waveform of the top sheath, in accordance with one embodiment of the present disclosure.

[0012] FIG. 3 illustrates a dual frequency match circuit providing tuning for a high frequency RF signal and a low frequency RF signal that is slaved to a bias signal of the capacitively coupled plasma processing system of FIG. 1, in accordance with one embodiment of the present disclosure.

[0013] FIG. 4 is a flow chart illustrating steps in a method for controlling plasma density and an amount and / or flux of negatively charged species entering the plasma sheath at the substrate using a capacitively coupled plasma processing system utilized for etching operations configured for supplying a high frequency RF signal and a low frequency RF signal that is slaved to a bias signal, in accordance with one embodiment of the present disclosure.DETAILED DESCRIPTION

[0014] Although the following detailed description contains many specific details for the purposes of illustration, anyone of ordinary skill in the art will appreciate that many variations and alterations to the following details are within the scope of the present disclosure.Accordingly, the aspects of the present disclosure described below are set forth without any loss of generality to, and without imposing limitations upon, the claims that follow this description.

[0015] Generally speaking, the various embodiments of the present disclosure describe plasma processing systems for controlling plasma density for achieving higher substrate processing rates and increasing the amount and / or flux of negatively charged species to the substrate to minimize substrate charging effects, which leads to improved on-wafer performance. In particular, in a capacitively coupled plasma processing system, a high frequency radio frequency (RF) signal and a low frequency RF signal are supplied to an upper electrode. A frequency of the low frequency RF signal is locked to a frequency of a bias signal delivered to a lower electrode. A phase of the low frequency RF signal is offset from the phase of the bias signal to promote generation and delivery of negative species to the substrate. In that manner, plasma density of positive ions is controlled, especially at the edge of the substrate, and increases plasma uniformity across the substrate.

[0016] Advantages of the various embodiments, disclosing plasma processing systems, including a capacitively coupled plasma chamber delivering a high frequency RF signal and a low frequency RF signal slaved to a bias signal to an upper electrode, include increased plasmaLAM2P121 l.P / 11810-1WO uniformity at the edge of the substrate and across the entirety of the substrate. This may be caused by decoupling of the high frequency RF signal from the lower electrode. Another advantage is realized because the upper electrode is floated, when receiving the high frequency RF signal and the low frequency RF signal that is slaved to the bias signal, such that there is an increase in the flux of negative species to the substrate. More particularly, offsetting a phase of the low frequency RF signal to the upper electrode from the phase of the bias signal by a desired value promotes the travel of the negative species (e.g., electrons and negative ions) to the substrate, wherein the negative species can be used to discharge buildup of positive charge accumulated in features, such as along sides and / or at bottoms of trenches or wells and / or holes formed in the substrate. For example, this reduces and / or eliminates undesired lateral etching of the features. In another advantage, by supplying the high frequency RF signal to the upper electrode, as opposed to delivering a high frequency RF signal to the lower electrode, the efficiency of delivery of the high frequency RF signal is increased, such that less power is required (e.g., up to a factor of 10) when compared to delivering the RF signal to the lower electrode. Furthermore in still another advantage, because the upper electrode is floated, when receiving the high frequency RF signal and the low frequency RF signal that is slaved to the bias signal, an increase in plasma density of positive ions is realized, which leads to increased etching.

[0017] With the above general understanding of the various embodiments, example details of the embodiments will now be described with reference to the various drawings. Similarly numbered elements and / or components in one or more figures are intended to generally have the same configuration and / or functionality. Further, figures may not be drawn to scale but are intended to illustrate and emphasize novel concepts. It will be apparent, that the present embodiments 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 not to unnecessarily obscure the present embodiments.

[0018] Throughout the specification the terms substrate and wafer may be used interchangeably. Generally, plasma processing may be performed on a substrate and / or wafer to etch features on a surface, or to deposit layers on the surface of the substrate and / or wafer.

[0019] FIG. 1 illustrates an embodiment of a capacitively coupled plasma processing system utilized for etching operations configured for supplying a high frequency RF signal and a low frequency RF signal that is slaved to a bias signal in order to control plasma density and an amount and / or the flux of negatively charged species entering the plasma sheath at the substrate, in accordance with one embodiment of the present disclosure. Generally, exemplary capacitively coupled plasma (CCP) processing system 100 can be utilized for operationsLAM2P121 l.P / 11810-1WO including etching and / or depositing films, such as for operations used to perform plasma processing of a substrate 120.

[0020] In particular, FIG. 1 illustrates an exemplary embodiment of the plasma processing system 100 utilized for etching operations that is configured as a CCP processing system, and includes a CCP plasma process chamber 102 that is configured for generating plasma 130. The plasma process chamber 102 includes a substrate support or pedestal, such as an electrostatic chuck (ESC) 118. In embodiments, the ESC may have several circular rings with different material types to achieve a certain capacitive coupling between the ESC and / or a powered edge ring 126. A lower electrode 122 may be embedded within the ESC 118. One or more power sources may be coupled to components of the plasma processing system 100. A substrate 120 may be placed on the pedestal for processing, wherein the substrate or wafer 120 is processed to make one or more semiconductor chips.

[0021] Facing the pedestal is an upper electrode 124 that is disposed over the lower electrode 122. Between the upper electrode 124 and the lower electrode 122 is a gap forming a processing volume within which a plasma 130 may be formed. As shown, the upper electrode 124 may be configured as an inner electrode, that may also be referred to as the main electrode. An upper outer electrode 123 may surround the upper inner electrode 124, and may be shaped as a ring. The upper outer electrode 123 surrounds the inner electrode in a horizontal direction. In addition, an optional dielectric (not shown) may be configured to separate the upper inner electrode 124 and the upper outer electrode 123, wherein the dielectric may be shaped as a ring. In one embodiment, the upper inner electrode 124 is floating, and is further configured to receive dual frequency RF power. In another embodiment, the upper outer electrode 123 may be grounded.

[0022] In one embodiment, the upper electrode 124 is of a similar diameter as the substrate 120. In another embodiment, the upper electrode 124 has an outer diameter that is greater than the outer diameter of the substrate 120. For example, the outer diameter of the upper electrode is greater than the outer diameter of the substrate by at least 5 to 20 percent. Furthermore, the upper electrode 124 is bigger than the ESC 118, in one embodiment.

[0023] A bias signal generated by a bias power generator 160 A provides a bias voltage to the lower electrode 122. In some embodiments, the bias power generator may supply a bias signal that is RF and may be pulsed. In still other embodiments, the bias power generator may supply a bias signal that is direct current (DC) and may be pulsed. As such, the bias signal may be a DC signal, RF signal, mixed RF and DC signal, or a mixed RF signal. In one embodiment, as shown the bias power generator is a low frequency RF generator 160A that is electrically coupled to the lower electrode 122. In particular, the low frequency RF generator 160A is configured to supplyLAM2P121 l.P / 11810-1WO a low frequency RF signal to the lower electrode at a low frequency and a first phase. In some embodiments, the RF frequency for the bias signal may range between 5 megahertz (MHz), or higher, to as low as 400 kilohertz (kHz), or lower. For purposes of illustration, the bias signal may be generated at a frequency of 400 kilohertz (kHz).

[0024] The low frequency RF signal is tuned via a low frequency RF match circuit 165. For example, the match circuit 165 operates as an impedance matching circuit, and is electrically coupled to the lower electrode 122. In general, an impedance match network matches impedances between the load (e.g., plasma chamber 102 and any connecting cabling) and a source (e.g., source RF power supply and any connecting cabling). That is, the match circuit 165 is configured to tune the low frequency RF signal that is supplied to the lower electrode 122 for purposes of impedance matching between the low frequency RF generator 160 A and at least the lower electrode 122 and / or other components of the plasma chamber 102.

[0025] The upper electrode 124 delivers RF power at dual frequencies to generate plasma 130. That is, different RF power can be delivered to the upper electrode 124 for generating plasma. In particular, the dual frequency RF power signals delivered to the upper electrode 124 can be adjusted to control plasma density and the amount and / or the flux of negatively charged species to the substrate 120, and also generate uniform plasma globally across the substrate. For example, the RF power signals are adjusted to control the plasma density of positive ions and / or flux of negative species (electrons and / or negative ions) on the substrate, such as to achieve uniform plasma density of positive ions and / or flux of negative species globally across the substrate. For example, by adjusting the RF power signals delivered to the upper electrode 124, selective control of angular ion tilt is achieved globally across the substrate, and especially at the edge of the substrate, to achieve plasma uniformity globally across the substrate, such as during etching processes.

[0026] In embodiments, the frequencies of the RF power signals to the upper electrode 124 are selectable, and are of sufficient frequency to generate plasma. In general, the RF power being supplied to the upper electrode 124 may be of sufficient frequency to generate plasma. For example, the RF frequency may range between 5 megahertz (MHz) to over 100 MHz, or higher (e.g., to over 200 MHz). In some implementations the RF frequency may range as low as 400 kilohertz (kHz), or lower. Also in embodiments, the power of the RF power signals to the upper electrode 124 are selectable, and may be similar or different.

[0027] In particular, a power signal generated by the high frequency RF power generator 170 provides a high frequency RF signal to the upper electrode 124. The high frequency RF power generator 170 is electrically coupled to the upper electrode 124 via a corresponding match circuit. A frequency of the high frequency RF signal may range between 5 megahertz (MHz) toLAM2P121 l.P / 11810-1WO over 100 MHz, or higher (e.g., to over 200 MHz). The voltage of the high frequency RF signal supplied to the upper electrode 124 may range between 1 kilovolts (kV), or lower, to about 5 kilovolts (kV), or higher. For purposes of illustration, the high frequency RF signal may be generated at a frequency of approximately 60 megahertz (MHz) that is delivered at 1.0 to 3.0 kilovolts (kV) to the upper electrode 124.

[0028] In addition, another low frequency RF generator 160B is electrically coupled to the upper electrode via a corresponding match circuit. The low frequency RF generator 160B supplies a low frequency RF signal to the upper electrode at the frequency of bias signal delivered to the lower electrode 122. That is, the low frequency RF signal delivered to the upper electrode has a frequency that is locked to the frequency of the low frequency RF signal delivered to the lower electrode 122. Because the frequency is locked, the RF frequency for the low frequency RF signal to the upper electrode 124 may range between 5 megahertz (MHz), or higher, to as low as 400 kilohertz (kHz), or lower. For purposes of illustration, the low frequency RF signal to the upper electrode 124 may be generated at a frequency of approximately 400 kilohertz (kHz).

[0029] In one embodiment, the low frequency RF generator 160B is a slave to the low frequency RF generator 160 A. In particular, the slave / phase controller 117 locks the frequency of the low frequency RF signal delivered to the upper electrode 124 to the frequency of the bias signal (i.e., the low frequency RF signal delivered to the lower electrode 122). In addition, the slave / phase controller 117 sets the phase of the low frequency RF signal delivered to the upper electrode 124, which may be offset from the phase of the RF bias signal.

[0030] In particular, the phase (e.g., a second phase) of the low frequency RF signal delivered to the upper electrode 124 is offset from the phase (e.g., a first phase) of the bias signal (i.e., the low frequency RF signal delivered to the lower electrode 122). For example, the slave / phase controller 117 is configured to determine the phase offset between the bias signal (i.e., the low frequency RF signal delivered to the lower electrode 122) and the low frequency RF signal delivered to the upper electrode 124. More particularly, the phase offset is based on a predetermined time period that is related to an occurrence of a maximum of the first low frequency RF signal and an occurrence of a minimum of the second low frequency RF signal, wherein the phase controller sets the second phase based on the phase offset. The phase offset is described in more detail in relation to FIG. 2.

[0031] As shown, a dual frequency match circuit 300 is electrically coupled to the upper electrode 124, with corresponding match circuits each operating as an impedance match network for an RF power signal at a corresponding frequency. For example, the dual frequency match circuit 300 includes a high frequency RF match circuit 310 configured to tune the highLAM2P121 l.P / 11810-1WO frequency RF signal, and a low frequency RF match circuit 320 configured to tune the low frequency RF signal. In general, an impedance match network matches impedances between the load (e.g., plasma chamber 102 and any connecting cabling) and a source (e.g., source RF power supply and any connecting cabling). As such, one or more RF power signals at one or more frequencies are output from the dual frequency match circuit 300 to the upper electrode 124.

[0032] A frequency controller 335 is configured to reduce negative effects resulting from the delivery of dual frequency RF power to the upper electrode 124, including reduced power to the chamber and / or decreased plasma uniformity. For example, the low frequency RF signal may adversely affect the high frequency RF signal. As such, the frequency controller 335 is configured to address the issue when delivering dual frequency RF power to the upper electrode. In particular, the frequency controller 335 may operate as a bin controller to adjust the frequency (i.e., apply a frequency offset) of the high frequency RF signal during each period or cycle (e.g., apply a frequency offset to a corresponding bin of the cycle) of the low frequency RF signal to achieve higher power and / or increased plasma uniformity. For example, each period or cycle of the low frequency RF signal is separated into a plurality of bins, wherein each bin is of equal or different time periods to other bins. In addition, the frequency controller 335 may operate as a blank controller to blank (i.e., turn off) the high frequency RF signal at one or more bins of the period or cycle.

[0033] In particular, the bin / blank frequency controller 335 is configured to define a plurality of bins for a period or cycle of the low frequency of the low frequency RF signal delivered to the upper electrode. As described previously, the low frequency is locked to the frequency of the RF bias signal delivered to the lower electrode. Further, the bin / blank frequency controller 335 is configured to apply a plurality of frequency offsets to a high frequency of the high frequency RF signal delivered to the upper electrode 124 for the plurality of bins to improve plasma uniformity and / or increase RF power delivered through the upper electrode 124. In one embodiment, the frequency controller 335 directs the bin / blank circuit 330 in the high frequency RF match circuit 310 to apply the plurality of frequency offsets to the frequency of the high frequency RF signal delivered to the upper electrode over the plurality of bins in each period or cycle of the low frequency RF signal delivered to the upper electrode 124. In one embodiment, the frequency controller 335 directs the bin / blank circuit 330 to effectively turn the high frequency RF signal off as an output from the dual frequency match circuit 300.

[0034] The plasma process chamber 102 also includes the edge ring 126, such as a tunable edge sheath (TES) ring, which surrounds the ESC 118 and / or the lower electrode 122. As an example, the edge ring 126 is fabricated from a conductive material, such as silicon, boron doped single crystalline silicon, silicon carbide, an alloy of silicon, or a combination thereof. InLAM2P121 l.P / 11810-1WO embodiments, the edge ring 126 has an annular body, such as a circular body, or ring-shaped body, or dish-shaped body. As an illustration, the edge ring 126 has an inner radius and an outer radius, and the inner radius is greater than a radius of the ESC 118. The edge ring 126 performs many functions including positioning the substrate 120 on the ESC 118, confining plasma to an area above the substrate 120, protecting the ESC 118 from erosion by ions of the plasma, and shielding underlying components of the plasma chamber 102 from being damaged by ions of the plasma. Further, the edge ring is configured to improve performance at the edge of the substrate. For example, by varying an amount of the power coupled to the edge ring, plasma density of the plasma at the edge region, sheath uniformity of the plasma at the edge region; etch rate uniformity of the plasma at the edge region, and ion tilt at which the substrate is etched in the edge region may be controlled. The power supplied to the edge ring 126 may be generated by TES power source (not shown) that is configured for generating RF power, wherein the TES power source may be electrically coupled to the edge ring 126 through a coupling ring 127, and optionally via a match circuit (not shown).

[0035] In addition, plasma processing chamber 102 of FIG. 1 may optionally include a C- shroud 150 that extends from the upper electrode 124 and / or upper outer electrode 123, and / or an extension (not shown), to the ESC 118 including the lower electrode 122 to provide additional plasma containment. The C-shroud may have a plurality of apertures to allow gas and byproducts to flow out of the C-shroud. The C-shroud may be grounded. In other embodiments, the plasma processing chamber may be configured differently to include confinement rings (not shown) for confining plasma 130 during etching operations.

[0036] In another embodiment, gas source(s) 114 are connected to the plasma process chamber 102 and are configured to inject the desired process gas(es) into the plasma process chamber 102. As an example of plasma formation, after providing one or more bias signals (e.g., RF and / or DC and / or continuous and / or pulsed) to the ESC 118 and injecting process gas(es) into the plasma process chamber 102, plasma 130 is then formed between the upper electrode 124 (and optionally the upper outer electrode 123) and the ESC 118. The plasma 130 can be used to etch the surface of the substrate 120. Although not shown, pumps are connected to the plasma chamber 102 to enable vacuum control and removal of gaseous byproducts from the plasma chamber during operational plasma processing.

[0037] In some embodiments, the system may include a controller 116 that is used for controlling various components of the plasma processing system 100 A. In one example, the controller 116 can be connected to the plasma generators (e.g., low frequency RF generator 160B, high frequency RF generator 170, TES power source (not shown), bias power source (low frequency RF generator 160 A), to the gas source(s) 114 that are coupled to the plasma processLAM2P121 l.P / 11810-1WO chamber 102, and to other components. The controller 116 may also control the slave controller 117 and / or one or more match circuits. The controller 116 includes a processor, memory, software logic, hardware logic and input and output subsystems from communicating with, monitoring and controlling the plasma processing system 100. In some embodiments, the controller 116 includes one or more recipes including multiple set points and various operating parameters (e.g., voltage, current, frequency, pressure, flow rate, power levels, temperature, timing parameters, process gases, mechanical movement of the substrate 120, etc.) for operating the plasma processing system 100 A. For example, depending on the processing being performed, the controller 116 manages the delivery of process gases delivered from the gas source(s) 114 to achieve a designed processing condition, such as to etch features and / or deposit or form films over the substrate 120. The chosen gases are then distributed in a space volume defined between the top electrode 101 A and the substrate 120 resting over the ESC 118.

[0038] In one embodiment, the plasma processing system 100 of FIG. 1 may be configured for negative ion control. Gases (e.g., fluorocarbons, etc.) introduced into the CCP plasma process chamber 102 can produce significant quantities of negative species (i.e., electrons and / or negative ions). Normally, negative species remain trapped within the plasma 130 due to the effects of a top sheath near the upper electrode 124 and a bottom sheath near the ESC 118 and / or the substrate 120. The top and bottom sheaths are generally electron free and act as potential barriers for plasma negative species, and normally act to pass positive ions and RF displacement currents (i.e., towards the substrate 120). That is, typically negative ions do not reach the surface of the substrate 120 and are trapped in the plasma 130 due to potentials of the top and bottom sheaths.

[0039] However, negative ions can play a significant role in surface charge control and etch rates for dielectric etch processes. Specifically, the plasma processing system 100 may be configured to pass high energy negative ions and / or electrons generated at expanding sheath at electrode 124 across the plasma bulk to reach the surface of the lower electrode 122 (i.e., the surface of the substrate 120). In particular, the dual frequency RF power supplied to the upper electrode 124 of the CCP plasma process chamber provide for negative ions and energetic electrons to escape from the plasma 130 due to high top sheath potentials. That is, the high frequency RF generator controls the ion flux (e.g., generation of electrons, positive and negative ions), and the low frequency RF generator controls the ion and electron energy, such that the plasma processing system 100 may increase the number of negative ions and / or electrons that reach the substrate for processing. In that manner, the negative ions and / or electrons may act to discharge the buildup of positive charge on the surface of the substrate 120, such as at the bottom of a well or trench feature. In addition, the high frequency RF signal may be used toLAM2P121 l.P / 11810-1WO increase plasma density, with the low frequency RF bias signal used to increase the ion energy, as previously introduced, such as for faster etching. As such, features with higher aspect ratios may be built without introducing abnormalities, such as sidewall distortion (e.g., mouse bites).

[0040] In particular, the slave / phase controller 117 can be configured to control the phases of the low frequency RF generators 160 A and 160B, such that the low frequencies delivered to the upper electrode 124 and the lower electrode 122 have a phase difference controlled by the slave / phase controller 117. In particular, the slave / phase controller 117 adjusts the phase and power of the low frequency RF signal delivered to the upper electrode 124 to have the described phase difference from the RF bias signal (i.e., low frequency RF signal delivered to the lower electrode 122). That is, the low frequency RF signal delivered to the upper electrode 124 has the same frequency as the RF bias signal, but with the desired phase difference and power level. As will be described below, the phase difference allows for negative ions and / or electrons born at the top sheath to travel through the plasma 130 to the surface of the substrate, and escaping the bottom sheath. The phase difference is set in such a manner to increase generation of both positive and negative ions and / or electrons, and is selected depending on which species is more desired. For example, when the signals are out-of-phase (i.e., 180 degrees), there is more generation of negative ions and / or electrons that are reaching the surface of substrate, whereas when the signals are in phase (i.e., zero degrees), there is more generation of positive ions. In general, the phase difference is selected such that the minimum voltage value of the low frequency RF signal delivered to the lower electrode 122 (and as reflected in the voltage waveform of the bottom sheath) follows a maximum voltage value of the low frequency RF signal delivered to the upper electrode 124 (and as reflected in the voltage waveform of the top sheath).

[0041] FIG. 2 illustrates the operation of a CCP processing system (e.g., plasma processing system 100) and voltage waveforms of a top sheath and a bottom sheath, wherein the voltage waveform of the bottom sheath is offset in phase from the voltage waveform of the top sheath, in accordance with one embodiment of the present disclosure. The CCP plasma process chamber includes an upper electrode 124 and a lower electrode 122 receiving independently generated RF power, wherein the low frequency RF signals to the upper and lower electrodes are shown. The high frequency RF signal supplied to the upper electrode 124 is not shown for ease of description. Depending on the selected phase offset, flux of both positive and negative ions may be increased and delivered to the surface of the substrate. In particular, FIG. 2 illustrates an etching process for etching including an increase in negative ion generation.

[0042] In particular, the low frequency RF signal supplied to the upper electrode 124 is offset in phase from the RF bias signal to the lower electrode 122, such that negative ions and / orLAM2P121 l.P / 11810-1WO electrons born at the top sheath travel through the plasma 212 and approach the surface of the substrate 120 when the bottom sheath potential is at its minimum, or near its minimum. The CCP plasma process chamber 102 produces an increase in the flux of negative ions and / or electrons, having a broad energy distribution, which are delivered to the surface of the substrate 120 without having to extinguish the plasma 130. A transit time defines the time needed for negative ions and / or electrons born at the top sheath to cross the plasma 130 and the bottom sheath to reach the surface of the substrate 120. The goal is to have the negative ions reach the bottom sheath when the bottom sheath is at the lowest RF potential, or at its weakest to repel the negative ions and / or electrons back to the plasma 130. The phase offset or difference is set such that the negative ions and / or electrons are bom at the upper electrode 124 and / or within the top sheath when the upper electrode 124 is at its maximum potential, wherein the potential 208 of the top sheath mirrors the potential of the upper electrode 124. Also, the phase offset is set such that the negative ions and / or electrons reach the substrate 120 after traveling through the plasma 130 when the potential 214 of the lower electrode 122 is at a minimum, wherein the potential 214 of the bottom sheath mirrors the potential of the lower electrode 122. Because the potentials are mirrored, the boundary 208 of the top sheath changes as the potential 206 of the top sheath 206 changes, and the boundary 216 of the bottom sheath changes as the potential 214 of the bottom sheath 214 changes. FIG. 2 shows the voltage or potential waveforms of the top and bottom sheaths at one time in the RF power cycle (i.e., time during a period of the low frequency RF signals).

[0043] Substrate 120 has a top layer 220 where the etching is performed. The top layer 220 includes a mask layer on top of the surface of the substrate 120 that contains the features to be etched. For example, contact holes 224 are the areas that do not have mask material and where etching is desired.

[0044] Time difference 202 shows the time required for the negative ions and / or electrons (e.g., born at the top sheath) to go from the top sheath to the bottom sheath. In one embodiment, a predetermined time period (e.g., time difference 202) used for determine the phase offset includes a travel time required for negative ion(s) and / or electrons formed near a top plasma sheath adjacent to the upper electrode to travel a predetermined distance towards the lower electrode, wherein the negative ions and / or electrons are formed at the occurrence of the maximum of the low frequency RF signal supplied to the upper electrode 124. In another embodiment, the distance 210 between the upper electrode 124 and substrate 120 is used to calculate the traveling time for the negative ions and / or electrons, as an approximation for the distance between the top sheath and the bottom sheath. In still another embodiment, the distance used to calculate the traveling time is the distance between the top sheath, when the upperLAM2P121 l.P / 11810-1WO electrode 124 and / or the bottom sheath is at their maximum potential, and the bottom sheath, when the bottom sheath is at the lowest potential.

[0045] As the negative ions and / or electrons are accelerated onto the surface of the substrate 120, some of the negative ions and / or electrons will enter contact holes 224 in the top surface of the substrate 120 to perform the etching. For example, the negative ions and / or electrons penetrate into the contact holes and neutralize any positive charge accumulated at the bottom of the contact holes.

[0046] A discussion of negative ion control in a capacitively coupled plasma chamber is provided in commonly owned patent application Serial No. 13 / 188,421, filed on July 21, 2011, entitled “Negative Ion Control for Dielectric Etch,” which issued into U.S. Patent No. 9,117,767 with issue date of August 25, 2015, the disclosure of which is herein incorporated by reference in its entirety.

[0047] FIG. 3 illustrates a dual frequency match circuit 300 providing tuning for a high frequency RF signal supplied to an upper electrode 124, and a low frequency RF signal supplied to the upper electrode, that is slaved to a bias signal of the plasma processing system 100 of FIG. 1, in accordance with one embodiment of the present disclosure. For example, the dual frequency match circuit 300 may be electrically coupled to the upper electrode 124 and corresponding RF power generators.

[0048] The dual frequency match circuit 300 includes a high frequency RF match circuit 310 configured to tune the high frequency RF signal, and a low frequency RF match circuit 320 configured to tune the low frequency RF signal, each operating as an impedance match network for an RF power signal at a corresponding frequency. As such, one or more RF power signals at one or more frequencies are output from the dual frequency match circuit 300 to the upper electrode 124. In general, an impedance match network matches impedances between the load (e.g., plasma chamber 102 and any connecting cabling) and a source (e.g., source RF power supply and any connecting cabling). Each of the high frequency RF match circuit 310 and the low frequency RF match circuit 320 may be controllable by one or more of the controllers 116, 117, and / or 335.

[0049] In particular, the low frequency RF match circuit 320 of the dual frequency match circuit 300 is configured to tune the low frequency RF signal that is supplied to the upper electrode 124 for purposes of impedance matching between the low frequency RF generator 160B and at least the upper electrode 124 and / or other components of the plasma chamber 102. As shown, the low frequency RF match circuit 320 includes an input node 321, configured to receive the low frequency RF signal. Inductor (L2) is coupled between the input node 321 and node 322. For purposes of illustration, inductor (L2) may be 77 microhenries (pH) in size,LAM2P121 l.P / 11810-1WO though it may be smaller or larger. Variable capacitor (C5) and capacitor (C6) are coupled in parallel, as shunt capacitors, between node 322 and common node 324, such as ground. For purposes of illustration, variable capacitor (C5) may range between 40 to 2,000 picofarads (pF), though it may range smaller or larger. Variable capacitor (C5) may be set to address the stray capacitance of the upper electrode 124, and may be adjusted via controllers 116, 117 and / or 335. For purposes of illustration, capacitor (C6) may be 500 picofarads (pF) in size, though it may be smaller or larger. Capacitor (C7) is coupled between nodes 322 and 323, and may act as a blocking capacitor. For purposes of illustration, capacitor (C7) may be 2.0 or 5.4 nanofarads (nF) in size, though it may be smaller or larger. Capacitor (C8) is coupled between node 323 and node 324, such as ground. For purposes of illustration, capacitor (C8) may be 300 picofarads (pF) in size, though it may be smaller or larger. Inductor (L3) is coupled between node 323 and output node 350. For purposes of illustration, inductor (L3) may be 2.8 microhenries (pH) in size, though it may be smaller or larger. The circuit combination of the capacitor (C8) and inductor (L3) operates to filter out the high frequency RF signal provided to input node 311. In that manner, the high frequency RF signal does not couple with the low frequency RF match circuit 320.

[0050] A voltage (V) sensor system 329 measures the voltage and / or current at the output of resistor (Rl), wherein the resistor (Rl) is electrically coupled between node 323 and the input to the V sensor system 329. For purposes of illustration, resistor (Rl) may be 100 megaohms in size, though it may be smaller or larger. In addition, voltage DC (VDC) sensor system 328 measures the voltage and / or current at the output of resistor (R2), wherein inductor (L4) and resistor (R2) are coupled in series between the output node 350 and the VDC sensor system 328. For purposes of illustration, inductor (L4) may be 5.0 microhenries (pH) in size, though it may be smaller or larger. For purposes of illustration, resistor R2 may be 99.5 megaohms in size, though it may be smaller or larger.

[0051] Also, the high frequency RF match circuit 310 of the dual frequency match circuit 300 is configured to tune the high frequency RF signal that is supplied to the upper electrode 124 for purposes of impedance matching between the high frequency RF generator 170 and at least the upper electrode 124 and / or other components of the plasma chamber 102. As shown, the high frequency RF match circuit 310 includes an input node 311, configured to receive the high frequency RF signal, that is electrically coupled to an output node 350 via a capacitor (C3) in series, wherein the output node 350 passes the tuned high frequency RF signal to the upper electrode 124. For purposes of illustration, series capacitor (C3) may be 50 or 90 picofarads (pF) in size, though it may be smaller or larger. Also, inductor (LI), variable capacitor (Cl), and capacitor (C2) are coupled in parallel, as shunt capacitors, between the input node 311 andLAM2P121 l.P / 11810-1WO another common node 312, such as ground. One or more of the inductor (LI), capacitor (Cl), and capacitor (C2) in a circuit combination may operate to filter out the low frequency RF signal provided to input node 321, such that the low frequency RF signal does not coupled with the high frequency RF match circuit 310. For purposes of illustration, inductor (LI) may be 1.0 microhenries (pH) in size, though it may be smaller or larger. For purposes of illustration, variable capacitor (Cl) may range between 25 to 250 picofarads (pF) in size, though it may range smaller or larger. For purposes of illustration, capacitor (C2) may be 120 picofarads (pF) in size, though it may be smaller or larger. Variable capacitor (C4) is coupled between the output node 350 and node 312, such as ground. For purposes of illustration, variable capacitor (C4) may range between 3.0 to 30 picofarads (pF) in size, though it may range smaller or larger. Variable capacitor (C4) may be controlled by the bin / blank frequency controller 335 for purposes of offsetting the frequency (i.e., providing a frequency offset) of the high frequency RF signal provided at the input node 311 at one or more bins for controlling plasma uniformity, as previously described. Also, variable capacitor (C4) may be controlled by the bin / blank frequency controller 335 to perform blanking of the high frequency RF signal provided at the input node 311 at one or more bins for controlling plasma uniformity, as previously described.

[0052] With the detailed description of the system 100 of FIGS. 1-3, flow diagram 400 of FIG. 4 illustrating steps in a method for controlling plasma density and an amount of negatively charged species entering the plasma sheath at the substrate using a capacitively coupled plasma processing system utilized for etching operations configured for supplying a high frequency RF signal and a low frequency RF signal that is slaved to a bias signal, in accordance with one embodiment of the present disclosure. In particular, the operations performed in the flow diagram may be implemented by one or more of the previously described components of the plasma processing system 100.

[0053] At 410, the method including supplying a high frequency RF signal to an upper electrode. For example, a high frequency RF generator is configured to generate the high frequency RF signal. The high frequency RF signal that is supplied to the upper electrode is tuned using the dual match circuit for purposes of impedance matching between the high frequency RF generator and at least the upper electrode, and / or other components of the CCP plasma process chamber.

[0054] As such, dual frequency RF power is delivered to the upper electrode to generate plasma. The dual frequency RF power signals delivered to the upper electrode can be adjusted to control plasma density over the substrate and / or at the edge of the substrate, and also generate uniform plasma globally across the substrate. For example, the RF power signals are adjusted to control the plasma density of positive ions and / or flux of negative species (electrons and / orLAM2P121 l.P / 11810-1WO negative ions) on the substrate, such as to achieve uniform plasma density of positive ions and / or flux of negative species globally across the substrate.

[0055] In embodiments, the frequencies of the RF power signals to the upper electrode 124 are selectable, and are of sufficient frequency to generate plasma. For example, the RF frequency may range between 5 megahertz (MHz) to over 100 MHz, or higher (e.g., to over 200 MHz), and in some implementations the RF frequency may range as low as 400 kilohertz (kHz), or lower. Also in embodiments, the power of the RF power signals to the upper electrode 124 are selectable, and may be similar or different.

[0056] At 420, the method including supplying a first low frequency RF signal to a lower electrode at a low frequency and a first phase. For example, a first low frequency RF generator is configured to generate the first low frequency RF signal, which may be an RF bias signal. For purposes of illustration, the frequency of the first low frequency RF signal may be 400 kilohertz, as previously described. In particular, a CCP plasma process chamber configured for generating plasma includes the lower electrode that is located within an ESC. The first low frequency RF signal that is supplied to the lower electrode is tuned for purposes of impedance matching between the first low frequency RF generator and at least the lower electrode and / or other components of the CCP plasma process chamber.

[0057] At 430, the method including supplying a second low frequency signal to the upper electrode at the low frequency and a second phase. For example, a second low frequency RF generator is configured to generate the second low frequency RF signal. The frequency of the second low frequency RF signal delivered to the upper electrode has a frequency that is locked to the frequency of the first low frequency RF signal that is delivered to the lower electrode. For example, the second low frequency RF generator may be a slave to the first low frequency RF generator, and is configured for locking frequencies. The second low frequency RF signal that is supplied to the upper electrode is tuned using a dual match circuit electrically coupled to upper electrode for purposes of impedance matching between the second low frequency RF generator and at least the upper electrode and / or other components of the CCP plasma process chamber.

[0058] In one embodiment, the upper electrode is disposed over the lower electrode in the CCP plasma process chamber. In another embodiment, the upper electrode is extended in a horizontal direction beyond an outer diameter of the lower electrode, such that the upper electrode is larger in diameter than the lower electrode and / or ESC. In still another embodiment, the upper electrode is floating.

[0059] In one embodiment, the upper electrode is configured as an upper inner electrode and an upper outer electrode. The upper inner electrode, that is configured to receive the second lowLAM2P121 l.P / 11810-1WO frequency RF signal, is floating, and the upper outer electrode is electrically coupled to ground, in one embodiment.

[0060] At 440, the method including determining a phase offset between the first low frequency RF signal and the second low frequency RF signal. In particular, the phase of the second low frequency RF signal delivered to the upper electrode is offset from the phase of the first low frequency RF signal delivered to the lower electrode. The phase offset is based on a predetermined time period that is related to an occurrence of a maximum of the first low frequency RF signal and an occurrence of a minimum of the second low frequency RF signal, wherein the second phase of the second low frequency RF signal is set based on the phase offset. For example, the predetermined time period used to determine the phase offset includes a travel time required for negative ion(s) and / or electrons formed near a top plasma sheath adjacent to the upper electrode to travel a predetermined distance towards the lower electrode. In that manner, negative ions or / and electrons that are formed in or near the top sheath at the occurrence of the maximum of the low frequency RF signal supplied to the upper electrode 124 are able to pass through the bulk plasma and strike the surface of the substrate for purposes of enhancing the etching of features. In particular, electrons and / or negative ions are able to travel to the bottom of trenches or slits and / or wells or holes to discharge positive charges and / or positive ions in those areas. This increases the aspect ratio of the features.

[0061] In one embodiment, the high frequency RF signal supplied to the upper electrode is modified to increase power and / or efficiency when delivering the high frequency RF signal. In particular, frequency of the high frequency RF signal may be adjusted during one or more bins of a period or cycle of the low frequency RF signal provided as an RF bias signal to the lower electrode. In particular, the method includes defining a plurality of bins for a period of the frequency of the first low frequency RF signal and the second low frequency RF signal. That is, each period or cycle of the low frequency RF signal delivered to the lower electrode and / or the upper electrode (since they are in a master / slave relationship) is separated into a plurality of bins, wherein each bin is of equal or different time periods to other bins. In addition, the method includes applying a plurality of frequency offsets to a high frequency of the high frequency RF signal delivered to the upper electrode for the plurality of bins to improve plasma uniformity and / or increase RF power delivered through the upper electrode. In particular, a plurality of frequency offsets is applied to the frequency (e.g., base frequency) of the high frequency RF signal delivered to the upper electrode over the plurality of bins in each period or cycle of the low frequency RF signal delivered to the upper electrode and / or the lower electrode (as they are in a master / slave relationship). In one embodiment, for at least one of the plurality of bins, the high frequency RF signal delivered to the upper electrode is off.LAM2P121 l.P / 11810-1WO

[0062] In embodiments, a substrate positioning program may include program code for controlling chamber components that are used to load the substrate onto a pedestal or chuck and to control the spacing between the substrate and other parts of the chamber such as a gas inlet and / or target, which may be implemented by control system or controller 150 of FIG. 1. In some implementations, a controller is part of a system, which may be part of the abovedescribed examples. Such systems can comprise semiconductor processing equipment, including a processing tool or tools, chamber or chambers, a platform or platforms for processing, and / or specific processing components (a substrate pedestal, a gas flow system, etc.). These systems may be integrated with electronics for controlling their operation before, during, and after processing of a semiconductor wafer or substrate. The controller, depending on the processing requirements and / or the type of system, may be programmed to control any of the processes disclosed herein, and process implemented for operating a plasma chamber. Program instructions may be instructions communicated to the controller in the form of various individual settings (or program files), defining operational parameters for carrying out a particular process on or for a semiconductor substrate or to a system. The operational parameters may, in some embodiments, be part of a recipe defined by process engineers to accomplish one or more processing steps during the fabrication of one or more layers, materials, metals, oxides, silicon, silicon dioxide, surfaces, circuits, and / or dies of a wafer.

[0063] The controller, in some implementations, may be a part of or coupled to a computer that is integrated with, coupled to the system, otherwise networked to the system, or a combination thereof. For example, the controller may be in the “cloud” of all or a part of a fab host computer system, which can allow for remote access of the substrate processing. The computer may enable remote access to the system to monitor current progress of fabrication operations, examine a history of past fabrication operations, examine trends or performance metrics from a plurality of fabrication operations, to change parameters of current processing, to set processing steps to follow a current processing, or to start a new process. In some examples, a remote computer (e.g., a server) can provide process recipes to a system over a network, which may include a local network or the Internet.

[0064] Without limitation, example systems may include a plasma etch chamber or module, a deposition chamber or module, a spin-rinse chamber or module, a metal plating chamber or module, a clean chamber or module, a bevel edge etch chamber or module, a physical vapor deposition (PVD) chamber or module, a chemical vapor deposition (CVD) chamber or module, a plasma enhanced chemical vapor deposition (PECVD) chamber or module, an atomic layer deposition (ALD) chamber or module, an atomic layer etch (ALE) chamber or module, an ion implantation chamber or module, a track chamber or module, and any other semiconductorLAM2P121 l.P / 11810-1WO processing systems that may be associated or used in the fabrication and / or manufacturing of semiconductor wafers.

[0065] The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.

[0066] Although the foregoing embodiments have been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications can be practiced within the scope of the appended claims. Accordingly, the present embodiments are to be considered as illustrative and not restrictive, and the embodiments are not to be limited to the details given herein, but may be modified within their scope and equivalents of the claims.

Claims

LAM2P121 l.P / 11810-1WOCLAIMS1. A system, comprising: a plasma chamber configured for generating plasma, wherein the plasma chamber includes a lower electrode located within an electrostatic chuck (ESC); an upper electrode disposed above the lower electrode; a first low frequency radio frequency (RF) generator electrically coupled to the lower electrode and configured to supply a first low frequency RF signal to the lower electrode at a low frequency and a first phase; a second low frequency RF generator electrically coupled to the upper electrode and configured to supply a second low frequency RF signal to the upper electrode at the low frequency and a second phase; a phase controller configured to determine a phase offset between the first low frequency RF signal and the second low frequency RF signal based on a predetermined time period that is related to an occurrence of a maximum of the first low frequency RF signal and an occurrence of a minimum of the second low frequency RF signal, wherein the phase controller sets the second phase based on the phase offset; and a high frequency RF generator electrically coupled the upper electrode and configured to supply a high frequency RF signal to the upper electrode.

2. The system of claim 1, a dual match circuit electrically coupled to the upper electrode, wherein the dual match circuit is configured to tune the second low frequency RF signal that is supplied to the upper electrode for purposes of impedance matching between the second low frequency RF generator and at least the upper electrode, wherein the dual match circuit is configured to tune the high frequency RF signal that is supplied to the upper electrode for purposes of impedance matching between the high frequency RF generator and at least the upper electrode.

3. The system of claim 1, further comprising: an impedance matching circuit electrically coupled to the lower electrode and configured to tune the first low frequency RF signal that is supplied to the lower electrode for purposes of impedance matching between the first low frequency RF generator and at least the lower electrode.

4. The system of claim 1, wherein the first low frequency RF generator is a master device, wherein the second low frequency RF generator is a slave device.LAM2P121 l.P / 11810-1WO5. The system of claim 1, wherein the upper electrode includes an upper inner electrode and an upper outer electrode, wherein the upper inner electrode is floating and receives the second low frequency RF signal and the high frequency RF signal, wherein the upper outer electrode is electrically coupled to ground.

6. The system of claim 1, wherein the predetermined time period includes a travel time required for a negative species formed near a top plasma sheath adjacent to the upper electrode to travel a predetermined distance towards the lower electrode, wherein the negative species are formed at the occurrence of the maximum of the first low frequency RF signal.

7. The system of claim 6, wherein the negative species includes at least one of negative ions and electrons.

8. The system of claim 1, wherein the low frequency of the first low frequency RF signal and the second low frequency RF signal is 400 kilohertz, wherein a high frequency of the high frequency RF signal is 60 megahertz.

9. The system of claim 1, wherein the upper electrode extends in a horizontal direction beyond an outer diameter of the lower electrode.

10. The system of claim 2, further comprising: a frequency controller configured to define a plurality of bins for a period of the low frequency of the first low frequency RF signal and the second low frequency RF signal, wherein the frequency controller applies a plurality of frequency offsets to a high frequency of the high frequency RF signal for the plurality of bins to improve plasma uniformity.

11. The system of claim 10, wherein the frequency controller directs the dual match circuit to apply the plurality of frequency offsets.

12. The system of claim 10, wherein for at least one of the plurality of bins, the high frequency RF signal is off.

13. A method, comprising: supplying a high frequency radio frequency (RF) signal to an upper electrode;LAM2P121 l.P / 11810-1WO supplying a first low frequency RF signal to a lower electrode at a low frequency and a first phase, wherein a plasma chamber configured for generating plasma includes the lower electrode located within an electrostatic chuck (ESC); supplying a second low frequency signal to the upper electrode at the low frequency and a second phase, wherein the upper electrode is disposed over the lower electrode in the plasma chamber; and determining a phase offset between the first low frequency RF signal and the second low frequency RF signal based on a predetermined time period that is related to an occurrence of a maximum of the first low frequency RF signal and an occurrence of a minimum of the second low frequency RF signal, wherein the second phase is set based on the phase offset.

14. The method of claim 13, further comprising: tuning the second low frequency RF signal that is supplied to the upper electrode using a dual match circuit electrically coupled to upper electrode for purposes of impedance matching between the second low frequency RF generator and at least the upper electrode; and tuning high frequency RF signal that is supplied to the upper electrode using the dual match circuit for purposes of impedance matching between the high frequency RF generator and at least the upper electrode.

15. The method of claim 13, further comprising: tuning the first low frequency RF signal that is supplied to the lower electrode for purposes of impedance matching between the first low frequency RF generator and at least the lower electrode.

16. The method of claim 13, wherein the upper electrode includes an upper inner electrode and an upper outer electrode, the method further comprising: floating the upper inner electrode that is configured to receive the second low frequency RF signal and the high frequency RF signal; and electrically coupling the upper outer electrode to ground.

17. The method of claim 13, further comprising: defining the predetermined time period as a travel time required for negative species formed near a top plasma sheath adjacent to the upper electrode to travel a predetermined distance towards the lower electrode, wherein the negative species are formed at the occurrence of the maximum of the first low frequency RF signal.

18. The method of claim 17, wherein the negative species includes at least one of negative ions and electrons.LAM2P121 l.P / 11810-1WO19. The method of claim 13, wherein the low frequency of the first low frequency RF signal and the second low frequency RF signal is 400 kilohertz, wherein a high frequency of the high frequency RF signal is 60 megahertz.

20. The method of claim 13, further comprising: extending the upper electrode in a horizontal direction beyond an outer diameter of the lower electrode.

21. The method of claim 13, defining a plurality of bins for a period of the frequency of the first low frequency RF signal and the second low frequency RF signal; and applying a plurality of frequency offsets to a high frequency of the high frequency RF signal for the plurality of bins to improve plasma uniformity.

22. The method of claim 21, wherein for at least one of the plurality of bins, the high frequency RF signal is off.

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