Patent Publication Number: US-2023154728-A1

Title: Methods and Systems for Controlling Radiofrequency Pulse-Initiation Power Spike for Plasma Sheath Stabilization

Description:
BACKGROUND 
     1. Field of the Disclosure 
     The present disclosure relates to semiconductor device fabrication. 
     2. Description of the Related Art 
     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 (“wafers” hereafter). The wafer includes integrated circuit devices in the form of multi-level structures defined on a silicon substrate. At a substrate level, transistor devices with diffusion regions are formed. In subsequent levels, interconnect metallization lines are patterned and electrically connected to the transistor devices to define a desired integrated circuit device. Also, patterned conductive layers are insulated from other conductive layers by dielectric materials. 
     Many modern semiconductor chip fabrication processes include generation of a plasma from which ions and/or radical constituents are derived for use in either directly or indirectly affecting a change on a 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 a material already present on a substrate surface. The plasma is often generated by applying radiofrequency (RF) power to a process gas in a controlled environment, such that the process gas becomes energized and transforms into the desired plasma. The characteristics of the plasma are affected by many process parameters including, but not limited to, material composition of the process gas, flow rate of the process gas, geometric features of the plasma generation region and surrounding structures, temperatures of the process gas and surrounding materials, frequency of the RF power applied, magnitude of the RF power applied, and temporal manner in which the RF power is applied, among others. Therefore, it is of interest to understand, monitor, and/or control some of the process parameters that may affect the characteristics of the generated plasma, particularly with regard to delivery of the RF power to the plasma generation region. It is within this context that the present disclosure arises. 
     SUMMARY 
     In an example embodiment, a method is disclosed for controlling a plasma within a plasma processing chamber. The method includes supplying multiple, sequential pulses of RF power to an electrode of the plasma processing chamber. Each of the pulses of RF power includes a first duration over which a first RF power profile exists, immediately followed by a second duration over which a second RF power profile exists. The first RF power profile has greater RF power than the second RF power profile. The first duration is less than the second duration. And, the sequential pulses of RF power are separated from each other by a third duration. 
     In an example embodiment, a controller is programmed to control a plasma within a plasma processing chamber. The controller includes program instructions stored in a computer memory that when executed direct supplying of multiple, sequential pulses of RF power to an electrode of the plasma processing chamber. Each of the pulses of RF power includes a first duration over which a first RF power profile exists, immediately followed by a second duration over which a second RF power profile exists. The first RF power profile has greater RF power than the second RF power profile. The first duration is less than the second duration. And, the sequential pulses of RF power are separated from each other by a third duration. 
     In an example embodiment, an RF signal generation system is configured to control a plasma within a plasma processing chamber. The RF signal generation system includes an RF signal generator configured to generate RF signals at or near a set frequency. The RF signal generation system also includes a first direct current voltage supply connected to a voltage input of the RF signal generator. The RF signal generation system also includes a second direct current voltage supply switchably connected to the voltage input of the RF signal generator. The RF signal generation system also includes a controller configured and connected to control each of the RF signal generator, the first direct current voltage supply, and the second direct current voltage supply. The voltage supplied to the voltage input of the RF signal generator by the first and second direct current voltage supplies controls an amplitude of the RF signals generated by the RF signal generator. 
     In an example embodiment, a method is disclosed for controlling a plasma within a plasma processing chamber. The method includes supplying multiple, sequential pulses of primary RF power to a primary electrode of the plasma processing chamber. Each of the pulses of primary RF power includes a first duration over which a first primary RF power profile exists, immediately followed by a second duration over which a second primary RF power profile exists. The first primary RF power profile has greater RF power than the second primary RF power profile. The first duration is less than the second duration. And, the sequential pulses of primary RF power are separated from each other by a third duration. The method also includes supplying multiple, sequential pulses of bias RF power to a bias electrode of the plasma processing chamber. Each of the pulses of bias RF power includes a fourth duration over which a first bias RF power profile exists, immediately followed by a fifth duration over which a second bias RF power profile exists. The first bias RF power profile has greater RF power than the second bias RF power profile. The fourth duration is less than the fifth duration. And, the sequential pulses of bias RF power are separated from each other by a sixth duration. 
     Other aspects and advantages of the invention will become more apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1 A  shows a vertical cross-section view of a plasma processing system for use in manufacturing semiconductor wafers, in accordance with some embodiments. 
         FIG.  1 B  shows a top view of the plasma processing system of  FIG.  1 A , in accordance with some embodiments. 
         FIG.  2    shows an example arrangement of the control system, in accordance with some embodiments. 
         FIG.  3 A  shows a square-shaped RF power pulse profile that may be supplied by the bias RF signal generator to the bias electrode to generate the bias voltage, in accordance with some embodiments. 
         FIG.  3 B  shows the square-shaped RF power pulse profile of  FIG.  3 A , with an initial spike of RF power associated with the initial masking time of the bias RF signal generator, in accordance with some embodiments. 
         FIG.  4    shows an RF power pulse profile that includes RF pulse-initiation power spiking, in accordance with some embodiments. 
         FIG.  5    shows an RF power pulse profile that represents dual-level RF power pulsing in which the RF power is pulsed between a first set non-zero power level P 1  and a set power level P 2 , with the first RF power profile p 1  having the set power level P 3 , in accordance with some embodiments. 
         FIG.  6    shows an RF power pulse profile that represents single-level RF power pulsing in which the RF power is pulsed between zero and a set power level P 1 , with a first RF power profile p 1  that exceeds the set power level P 1  and is non-constant, in accordance with some embodiments. 
         FIG.  7    shows an RF power pulse profile that represents single-level RF power pulsing in which the RF power is pulsed between zero and a set power level P 1 , with a first RF power profile p 1  that exceeds the set power level P 1  and is non-constant, in accordance with some embodiments. 
         FIG.  8 A  shows the RF power pulse profile of  FIG.  4    with frequency variation applied over the pulse duration, in accordance with some embodiments. 
         FIG.  8 B  shows an example frequency control function in which the frequency of the signals that are generated by the bias RF signal generator or primary RF signal generator is substantially constant over time, in accordance with some embodiments. 
         FIG.  8 C  shows an example frequency control function in which the frequency of the signals that are generated by the bias RF signal generator or primary RF signal generator increases monotonically over time, in accordance with some embodiments. 
         FIG.  8 D  shows an example frequency control function in which the frequency of the signals that are generated by the bias RF signal generator or primary RF signal generator decreases monotonically over time, in accordance with some embodiments. 
         FIG.  8 E  shows an example frequency control function in which the frequency of the signals that are generated by the bias RF signal generator or primary RF signal generator varies in a non-linear manner over time, in accordance with some embodiments. 
         FIG.  9    shows an example arrangement of an RF signal generation system that implements dual DC power supplies for RF pulse-initiation power spike generation, in accordance with some embodiments. 
         FIG.  10    shows a diagram of the voltage output by the first DC voltage supply as a function of time to generate the RF power pulse profile of  FIG.  4   , in accordance with some embodiments. 
         FIG.  11    shows a diagram of the voltage output by the second DC voltage supply as a function of time to generate the RF power pulse profile of  FIG.  4   , in accordance with some embodiments. 
         FIG.  12    shows a diagram of the sum of the voltages output by the first DC voltage supply and the second DC voltage supply as a function of time to generate the RF power pulse profile of  FIG.  4   , in accordance with some embodiments. 
         FIG.  13    shows a diagram of the activation of the RF signal generator as a function of time to generate the RF power pulse profile of  FIG.  4   , in accordance with some embodiments. 
         FIG.  14    shows a flowchart of a method for controlling a plasma within a plasma processing chamber, in accordance with some embodiments. 
         FIG.  15    shows a flowchart of a method for controlling a plasma within a plasma processing chamber, in accordance with some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, numerous specific details are set forth in order to provide an understanding of embodiments of the present disclosure. It will be apparent, however, to one skilled in the art that 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 not to unnecessarily obscure the present disclosure. 
       FIG.  1 A  shows a vertical cross-section view of a plasma processing system  100  for use in manufacturing semiconductor wafers, in accordance with some embodiments.  FIG.  1 B  shows a top view of the plasma processing system of  FIG.  1 A , in accordance with some embodiments. The vertical cross-section view of  FIG.  1 A  is referenced as View A-A in  FIG.  1 B . In the semiconductor industry, semiconductor substrates can undergo fabrication operations in an inductively coupled plasma (ICP) plasma processing chamber, such as the plasma processing system  100 . The ICP processing chamber can also be referred to as a transformer coupled plasma (TCP) processing chamber. For ease of discussion herein, the ICP processing chamber will be used to refer to both ICP and TCP processing chambers. It should be understood that the plasma processing system  100  represents essentially any type of ICP processing chamber in which RF signals are transmitted from a coil  101  disposed outside a processing chamber  103  to a process gas within the processing chamber  103  to generate a primary plasma  105  within a plasma processing volume  106  of the processing chamber  103 , where the primary plasma  105  is used to affect a change in a condition of a substrate  107  held in exposure to constituents of the primary plasma  105 .  FIG.  1 A  shows the coil  101  from which RF signals are transmitted into the plasma processing volume  106  to generate the primary plasma  105  within the plasma processing volume  106  in exposure to a substrate  107 . The coil  101  is also referred to as a primary electrode. 
     In some embodiments, the substrate  107  is a semiconductor wafer undergoing a fabrication procedure. However, it should be understood that in various embodiments, the substrate  107  can be essentially any type of substrate that is subjected to a plasma-based fabrication process. For example, in some embodiments, the term substrate  107  as used herein can refer to substrates formed of sapphire, GaN, GaAs or SiC, or other substrate materials, and can include glass panels/substrates, metal foils, metal sheets, polymer materials, or the like. Also, in various embodiments, the substrate  107  as referred to herein may vary in form, shape, and/or size. For example, in some embodiments, the substrate  107  referred to herein may correspond to a 200 mm (millimeters) semiconductor wafer, a 300 mm semiconductor wafer, or a 450 mm semiconductor wafer. Also, in some embodiments, the substrate  107  referred to herein may correspond to a non-circular substrate, such as a rectangular substrate for a flat panel display, or the like, among other shapes. 
     The plasma processing volume  106  of the processing chamber  103  is formed within a surrounding structure  109  and below an upper window structure  111  and above a substrate support structure  113 . In some embodiments, the surrounding structure  109  is formed of an electrically conductive material, such as a metal, that is mechanically and chemically compatible with the environment and materials present within the plasma processing volume  106  during operation of the plasma processing system  100 . In these embodiments, the surrounding structure  109  can be electrically connected to a reference ground potential  115 . The processing chamber  103  includes a door  151  through which the substrate  107  can be moved into and removed from the plasma processing volume  106 . 
     The substrate support structure  113  is configured to support the substrate  107  in a secure manner in exposure to the primary plasma  105  generated within the plasma processing volume  106 . In some embodiments, the substrate support structure  113  is an electrostatic chuck that includes one or more clamp electrode(s)  117  to which electric power can be supplied by a clamping power supply  119  through an electrical connection  121 . The electric power supplied to the one or more clamp electrode(s)  117  generates an electrostatic field for clamping the substrate  107  onto the substrate support structure  113 . In various embodiments, the clamping power supply  119  can be configured to supply either RF power, direct current (DC) power, or a combination of both RF power and DC power to the one or more clamp electrode(s)  117 . In the embodiments in which the clamping power supply  119  is configured to supply RF power, the clamping power supply  119  further includes an impedance matching circuit through which the RF power is transmitted to ensure that the RF power is not unacceptably reflected from the one or more clamp electrode(s)  117 . In these embodiments, the impedance matching circuit within the clamping power supply  119  includes an arrangement of capacitors and/or inductors. 
     The substrate support structure  113  can also include a bias electrode  123  to which RF bias power can be supplied to generate a bias voltage (V b ) at the substrate  107  level within the plasma processing volume  106 . The RF power transmitted from the bias electrode  123  into the plasma processing volume  106  is referred to as the bias RF power. In some embodiments, the bias RF power is generated by a bias RF signal generator  125  and is transmitted through an electrical connection  127  to an impedance matching circuit  129 , and then transmitted from the impedance matching circuit  129  through a transmission rod  131  to the bias electrode  123 . The transmission rod  131  is electrically insulated from the surrounding structure  109  of the processing chamber  103 . The impedance matching circuit  129  includes an arrangement of capacitors and/or inductors configured to ensure that an impedance seen by the bias RF signal generator  125  at the transmission rod  131  is sufficiently close to a load impedance for which the bias RF signal generator  125  is designed to operate, so that RF signals generated and transmitted by the bias RF signal generator  125  will be transmitted into the plasma processing volume  106  in an efficient manner, i.e., without unacceptable reflection. 
     The plasma processing system  100  operates by flowing one or more process gases from a process gas supply  133  through an arrangement of fluid conveyance structures  135  into the plasma processing volume  106 , and by applying RF power from the coil  101  to the one or more process gases to transform the one or more process gases into the primary plasma  105  in exposure to the substrate  107 , in order to affect a change in material or surface condition on the substrate  107 . The used process gases and other materials that result from processing of the substrate  107  are exhausted from the plasma processing volume  106  through one or more exhaust ports  147 , as indicated by the arrows  149 . The coil  101  is disposed above the upper window structure  111 . In the example of  FIGS.  1  and  2   , the coil  101  is formed as a radial coil assembly, with the shaded parts of the coil  101  turning into the page of the drawing and with the unshaded parts of the coil  101  turning out of the page of the drawing.  FIG.  1 B  shows a top view of the example coil  101  of  FIG.  1 A , in accordance with some embodiments of the present invention. It should be understood, however, that in other embodiments the coil  101  can be of essentially any configuration that is suitable for transmitting RF power through the upper window structure  111  and into the plasma processing volume  106 . In various embodiments, the coil  101  can have any number of turns and any cross-section size and shape (circular, oval, rectangular, trapezoidal, etc.) as required to provide the necessary transmission of RF signals through the upper window structure  111  into the plasma processing volume  106 . 
     Also, in some embodiments, a return electrical connection  145  extends from the coil  101  to the matching circuitry  141 . 
     The RF power transmitted from the coil  101  into the plasma processing volume  106  is referred to as the plasma primary RF power. The plasma primary RF power is generated by a primary RF signal generator  137  and is transmitted through an electrical connection  139  to an impedance matching circuit  141 , and through an electrical connection  143  to the coil  101 . The matching circuit  141  includes an arrangement of capacitors and/or inductors configured to ensure that an impedance seen by the primary RF signal generator  137  at the coil  101  is sufficiently close to a load impedance for which the primary RF signal generator  137  is designed to operate, so that RF signals supplied to the coil  101  by the primary RF signal generator  137  will be transmitted into the plasma processing volume  106  in an efficient manner without unacceptable reflection. 
     It should be understood that the coil  101  of  FIGS.  1  and  2    is presented by way of example. In some embodiments, the coil  101  can include multiple zones, with each zone spanning a specified corresponding radial extent above the upper window structure  111 . In these embodiments, the RF power supplied to each zone of the coil  101  is independently controlled. Also, it should be understood that the number of turns (about the center of the upper window structure  111 ) of the example coil  101  of  FIGS.  1  and  2    is presented by way of example. In various embodiments, the coil  101  can have any number of turns and any cross-section size and shape (circular, oval, rectangular, trapezoidal, etc.) as required to provide the necessary transmission of RF signals through the upper window structure  111  into the plasma processing volume  106 . 
     The plasma processing system  100  has certain advantages in plasma process control in various plasma-based semiconductor fabrication applications, such as in plasma etching, by way of example. The plasma processing system  100  provides for separate control of plasma density (ion flux/radical flux) and ion energy. Specifically, the plasma density can be controlled to a certain extent by the plasma primary RF power that is transmitted from the coil  101  through the upper window structure  111  into the plasma processing volume  106 . And, the ion energy can be controlled by the bias voltage (V b ) that is generated at the substrate level by the bias RF power transmitted from the bias electrode  123  into the plasma processing volume  106 . Separate control of plasma density (which directly correlates to ion flux and radical flux) and ion energy is particularly useful in some semiconductor fabrication applications. For example, in patterning applications where high plasma density is needed to obtain a required etch rate and where low ion energy is required to reduce damage to one or more materials present on the substrate, such as photoresist material. It should be understood that in addition to patterning applications, many other plasma-based semiconductor fabrication applications can also benefit from separate control of plasma density and ion energy. 
     With the plasma processing system  100 , the plasma density can be increased through control of the plasma primary RF power supplied to the coil  101 , and the bias voltage (V b ) can be controlled through control of the bias RF power supplied to the bias electrode  123 . Also, the plasma primary RF power/frequency and the bias RF power/frequency may need to be controlled in different ways at the same time to achieve a desired result. For example, in some embodiments, to obtain increased plasma density in conjunction with low ion energy, the plasma primary RF power needs to be high and at the same time the bias RF power needs to be low. 
     In some fabrication applications a high density plasma is needed at the substrate  107  level to obtain an increased ion flux and/or increased radical flux near the substrate  107  to obtain an increased interaction rate on the substrate  107 , and simultaneously, a low ion energy is required at the substrate  107  level to avoid damage to material on the substrate  107  and/or to reduce directionality of the ion flux incident upon the substrate  107 , i.e., to have a more isotropic ion flux at the substrate  107  level. In these fabrication applications, the plasma density needs to be increased at the substrate  107  level without increasing the bias voltage (V b ) at the substrate  107  level. For example, in a patterning application, a photoresist material can be used to provide a protective coating over portions of the substrate  107  during an etching operation. In this situation, a high bias voltage (V b ) can increase the ion energy to the point where the ions that are incident upon the photoresist material will sputter the photoresist material off of the substrate  107 . And, because it is necessary for the photoresist material to remain through the entirety of the etching process, it is of interest to keep the bias voltage (V b ) at the substrate  107  level low, e.g., less than 200 V (volts), to avoid sputtering of the photoresist material and premature loss of the photoresist material. 
     In some situations, the plasma primary RF power transmitted from the coil  101  through the upper dielectric window  111  into the plasma processing volume  106  does not provide enough plasma density at the substrate  107  level to obtain a necessary etch rate and/or etch selectivity. One reason for this is that the density of the primary plasma  105  generated by the plasma primary RF power transmitted from the coil  101  decreases with increased distance from the coil  101 . Therefore, with increased distance between the coil  101  and the substrate support structure  113 , it becomes more difficult to obtain a required plasma density at the substrate  107  level. Also, the lower frequency of the bias RF power that is applied to the bias electrode  123  generates a DC bias voltage (V b ) on the substrate  107  without contributing much to the plasma density near the substrate  107 . Additionally, it may not be possible to simply increase the plasma primary RF power supplied to the coil  101  beyond a specified maximum amount, such as about 3 kW (kiloWatts), due to potential damage caused by overheating of the upper window structure  111 . Also, reducing the distance between the coil  101  and substrate support structure  113  may require a costly redesign of the processing chamber  103 , and potentially cause problems with regard to plasma uniformity at the substrate  107  level, and present other challenges. 
     It is possible to provide an increase in plasma density at the substrate  107  level without causing an increase in ion energy at the substrate  107  level. The bias electrode  123  can be used to transmit specially controlled RF signals into the plasma processing volume  106  to generate supplemental plasma density  154  locally at the substrate  107  level. And, in some embodiments, it is possible to generate the supplemental plasma density  154  locally at the substrate  107  level without increasing the ion energy at the substrate  107  level. The bias RF power applied at the substrate  107  level by the bias RF signal generator  125  is controlled to generate the supplemental plasma density  154  at the substrate  107  level, i.e., just above the substrate  107 . Generally, the bias voltage (V b ) generated by the RF signals supplied by the bias RF signal generator  125  is inversely proportional to the frequency (ƒ) of these RF signals (V b ∝1/ƒ). Because the bias RF power (P b ) is given by the product of the bias voltage (V b ) and the bias current (I b ), i.e., (P b =V b *I b ), when the bias voltage (V b ) is lower, the bias current (I b ) has to be correspondingly higher to have the same bias RF power (P b ). Therefore, to achieve a higher plasma density from a given bias RF power (P b ), it is necessary to have a lower bias voltage (V b ) and a correspondingly higher bias current (I b ). And, because the bias voltage (V b ) is inversely proportional to the frequency (ƒ) of the bias RF signals, in order to obtain a lower bias voltage (V b ) for a given bias RF power (P b ), the frequency (ƒ) of the bias RF signals can be increased. Therefore, to obtain an increase in the supplemental plasma density  154  generated at the substrate  107  level, while simultaneously keeping the bias voltage (V b ) low, RF signals of higher frequency (ƒ) can be supplied to the bias electrode  123 . 
     At the substrate  107  level, the effective plasma density is the sum of the plasma density generated by the plasma primary RF power and the plasma density generated by the RF signals supplied to the bias electrode  123 . In some embodiments where a higher plasma density is needed at the substrate  107  level without increasing the ion energy at the substrate  107  level, a supplemental plasma density  154  RF power is supplied to the bias electrode  123  at a high frequency (e.g., greater than or equal to about 27 MHz (megaHertz)) to generate supplemental plasma density  154  at the substrate  107  level with low bias voltage (V b ) (e.g., less than about 200 V), and a bias RF power is also supplied to the bias electrode  123  at a low frequency (e.g., less than or equal to about 15 MHz) to provide control of the bias voltage (V b ), and a plasma primary RF power is supplied to the coil  101  to generate the primary plasma  105  within the plasma processing volume  106 . 
     The plasma processing system  100  also includes a control system  153  configured and connected to control operations of the plasma processing system  100 . The control system  153  is configured and connected through a connection  155  to control the process gas supply  133 . The control system  153  is configured and connected through a connection  157  to control the primary RF signal generator  137 . The control system  153  is configured and connected through a connection  159  to control the impedance matching circuit  141 . The control system  153  is configured and connected through a connection  161  to control the bias RF signal generator  125 . The control system  153  is configured and connected through a connection  163  to control the impedance matching circuit  129 . The control system  153  is configured and connected through a connection  165  to control the clamping power supply  119 . It should be understood that in various embodiments, any of the connections  155 ,  157 ,  159 ,  161 ,  163 , and  165  can be either a wired connection, a wireless connection, an optical connection, or a combination thereof. It should be understood that in various embodiments, the control system  153  can be configured and connected to control essentially any feature of the plasma processing system  100  that lends itself to active control. Also, it should be understood that in various embodiments, the control system  153  is configured and connected to various metrology and sensors and other data acquisition devices disposed throughout the plasma processing system  100  to measure and monitor any and all parameters that are relevant to operation of the plasma processing system  100 . Also, in various embodiments, data/signal connection between the control system  153  and the various metrology and sensors and other data acquisition devices can be either a wired connection, a wireless connection, an optical connection, or a combination thereof. 
       FIG.  2    shows an example arrangement of the control system  153 , in accordance with some embodiments. In various embodiments, the control system  153  includes a processor  201 , a storage hardware unit (HU)  203  (e.g., computer memory), an input HU  205 , an output HU  207 , an input/output (I/O) interface  209 , an I/O interface  211 , a network interface controller (NIC)  213 , and a data communication bus  215 . The processor  201 , the storage HU  203 , the input HU  205 , the output HU  207 , the I/O interface  209 , the I/O interface  211 , and the NIC  213  are in data communication with each other by way of the data communication bus  215 . 
     The input HU  205  is configured to receive data communication from a number of external devices, such as from the process gas supply  133 , the primary RF signal generator  137 , the impedance matching circuit  141 , the bias RF signal generator  125 , the impedance matching circuit  129 , the clamping power supply  119 , and/or any other device within the plasma processing system  100 . Examples of the input HU  205  include a data acquisition system, a data acquisition card, etc. The output HU  207  is configured to transmit data to a number of external devices, such as to the process gas supply  133 , the primary RF signal generator  137 , the impedance matching circuit  141 , the bias RF signal generator  125 , the impedance matching circuit  129 , the clamping power supply  119 , and/or any other device within the plasma processing system  100 . An example of the output HU  207  is a device controller. Examples of the NIC  213  include a network interface card, a network adapter, etc. Each of the I/O interfaces  209  and  211  is defined to provide compatibility between different hardware units coupled to the I/O interface. For example, the I/O interface  209  can be defined to convert a signal received from the input HU  205  into a form, amplitude, and/or speed compatible with the data communication bus  215 . Also, the I/O interface  211  can be defined to convert a signal received from the data communication bus  215  into a form, amplitude, and/or speed compatible with the output HU  207 . Although various operations are described herein as being performed by the processor  201  of the control system  153 , it should be understood that in some embodiments various operations can be performed by multiple processors of the control system  153  and/or by multiple processors of multiple computing systems in data communication with the control system  153 . Also, in some embodiments, there is a user interface associated with the control system  153 . The user interface may include a display (e.g., a display screen and/or graphical software displays of the apparatus and/or process conditions) and user input devices such as pointing devices, keyboards, touch screens, microphones, etc. 
     The control system  153  can be configured to execute computer programs including sets of instructions for controlling operation of the process gas supply  133 , the primary RF signal generator  137 , the impedance matching circuit  141 , the bias RF signal generator  125 , the impedance matching circuit  129 , the clamping power supply  119 , and/or any other controllable device within the plasma processing system  100 . Also, computer programs stored on memory devices associated with the control system  153  may be employed in some embodiments. Software for directing operation of the control system  153  may be designed or configured in many different ways. Computer programs for directing operation of the control system  153  to in turn direct operation of the plasma processing system  100  can be written in any conventional computer readable programming language: for example, assembly language, C, C++, Pascal, Fortran or others. Compiled object code or script is executed by the processor  201  to perform the tasks identified in the program. 
     Generally speaking, the control system  153  is defined as electronics having various integrated circuits, logic, memory, and/or software that receive instructions, issue instructions, and control operations. The integrated circuits may include chips in the form of firmware that store program instructions, digital signal processors (DSPs), chips defined as application specific integrated circuits (ASICs), and/or one or more microprocessors, or microcontrollers that execute program instructions (e.g., software). Program instructions may be instructions communicated to the control system  153  in the form of various individual settings (or program files), defining operational parameters for operating the plasma processing system  100  to carrying out a prescribed process on the substrate  107 . 
     In conductor etch applications where the primary plasma  105  chemistry is highly electronegative and a high bias voltage (V b ) is supplied in a pulsed manner, it is very difficult to push out and stabilize the plasma  105  sheath when the bias RF signal generator  125  is turned on to supply RF power to the bias electrode  123 .  FIG.  3 A  shows a square-shaped RF power pulse profile  301  that may be supplied by the bias RF signal generator  125  to the bias electrode  123  to generate the bias voltage (V b ), in accordance with some embodiments. The square-shaped RF power pulse profile  301  includes a series of pulses of RF power in accordance with a set cycle duration d 303 . Each pulse of RF power has an essentially square shape. Each pulse of RF power goes from a power level of about zero to a power level P 1 . Each pulse of RF power has a pulse duration d 301 . The duration between successive RF power pulses is an interpulse duration d 302 . During each interpulse duration d 302 , the RF power goes from a power level of P 1  to a lower power level (e.g., to a power of about zero). The set cycle duration d 303  is the sum of the pulse duration d 301  and the interpulse duration d 302 . 
     Use of the square-shaped RF power pulse profile  301  as shown in  FIG.  3 A  presents a timing problem, because the process of getting RF energy into the plasma  105  starts slowly and takes time to complete. Consider that there is a significant change in the impedance of the plasma processing volume  106  between having the plasma  105  present therein and not having the plasma  105  present, or rather one may say between having a plasma  105  sheath and not having a plasma  105  sheath. Further consider that there are heavy ions within the plasma  105  that have to be pushed away from the bias electrode  123  in order to stabilize the plasma  105  sheath. It takes a significant amount of energy and time to move these heavy ions. At the beginning of an RF power pulse, the bias RF signal generator  125  and corresponding impedance matching circuit  129  will operate as though they are pushing RF power into the plasma  105  sheath, because that is the last thing they were doing at the end of the previous RF power pulse. However, at the beginning of each RF power pulse, the bias RF signal generator  125  and corresponding impedance matching circuit  129  are actually pushing RF power into a badly mismatched load. Therefore, at the beginning of the RF power pulse, not much RF power can be pushed from the bias RF signal generator  125  and corresponding impedance matching circuit  129  into the plasma  105 . It is a slow process to get RF power into the plasma  105  at the beginning of the RF power pulse, because the RF energy initially enters the plasma  105  at a slow rate due to impedance mismatch, and then as the plasma  105  sheath begins to build in, the bias RF signal generator  125  and corresponding impedance matching circuit  129  become impedance tuned to allow more and more RF energy to enter the plasma  105 . 
     Therefore, the process of getting RF energy from the bias RF signal generator  125  and corresponding impedance matching circuit  129  into the plasma  105  during a square-shaped RF power pulse starts slowly and takes time to complete. For this reason, in certain applications, such as in conductor etch applications where the primary plasma  105  chemistry is highly electronegative and high bias voltage (V b ) is supplied in a pulsed manner, the square-shaped RF power pulse profile  301  may not be usable. Instead, what is needed is a high amplitude, short duration RF power spike at the start of each RF pulse in order to quickly establish and stabilize the plasma  105  sheath near the bias electrode  123 . In some cases, without such a high amplitude, short duration RF power spike at the start of each RF pulse, the plasma  105  sheath will not stabilize over the RF power pulse duration d 301 . 
     The bias RF signal generator  125  has an initial masking time when the bias RF signal generator  125  operates in an open loop control mode. During this initial masking time, there can be a naturally large initial spike of RF power, depending on the cabling configuration, the operating frequency of the bias RF signal generator  125 , and the impedance seen by the bias 
     RF signal generator  125 .  FIG.  3 B  shows the square-shaped RF power pulse profile  301  of  FIG.  3 A , with an initial spike of RF power  303  associated with the initial masking time of the bias RF signal generator  125 , in accordance with some embodiments. More specifically, at the beginning of each square-shaped pulse of RF power, an initial spike of RF power  303  occurs due the bias RF signal generator  125  operating in the open loop control mode. After the initial spike of RF power  303 , the RF power settles to the power level P 1  set for the RF power pulse profile  301 . The magnitude and duration of the initial spike of RF power  303  is dependent upon the cabling configuration (between the bias RF signal generator  125  and the impedance matching circuit  129 , and between the impedance matching circuit  129  and the bias electrode  123 ), the operating frequency of the bias RF signal generator  125 , the impedance seen by the bias RF signal generator  125 , and the chemistry of the plasma  105 . It should be understood that the initial spike of RF power  303  at the beginning of each RF power pulse is not controlled. Therefore, although the initial spike of RF power  303  can be helpful in accelerating the establishment and stabilization of the plasma  105  sheath at the beginning of each RF power pulse, the initial spike of RF power  303  cannot be relied upon for that purpose. 
     In some embodiments, an attempt is made to maximize the initial spike of RF power  303  that occurs due to the natural response to the bias RF signal generator  125  operating in open loop control mode. More specifically, an example approach includes finding a particular cable length and/or a particular frequency setpoint of the bias RF signal generator  125  that will cause the impedance that the bias RF signal generator  125  sees at the instant of the start of the 
     RF power pulse to be where the RF power output is the highest, with the bias RF signal generator  125  operating in the natural open loop control mode. For example, a certain cabling configuration and setpoint frequency of the bias RF signal generator  125  can be determined to maximize the initial spike of RF power  303 . This approach can cause the initial spike of RF power  303  to be several times higher than the actual power level (P 1 ) setpoint of the RF power pulse and can be up to two times the stated full scale power of the bias RF signal generator  125 . Therefore, it should be understood that attempts to maximize the initial spike of RF power  303  with the bias RF signal generator  125  operating in open loop control mode can be dangerous and can even cause destruction of the bias RF signal generator  125 . Also, the optimal cable length and/or optimal setpoint frequency can change from one substrate  107  process recipe to another, and can change with just a tweaking of some substrate  107  process recipe parameter(s). Therefore, it is of interest to develop a controlled approach for initially spiking the RF power at the beginning of each RF power pulse. 
       FIG.  4    shows an RF power pulse profile  401  that includes RF pulse-initiation power spiking, in accordance with some embodiments. It should be understood that the RF power pulse profile  401  can be applied equally to operation of the bias RF signal generator  125  and to operation of the primary RF signal generator  137 . More specifically, when the bias RF signal generator  125  is being operated in a pulsed mode, the RF power pulse profile  401  can be used. Also, when the primary RF signal generator  137  is being operated in a pulsed mode, the RF power pulse profile  401  can be used. The RF power pulse profile  401  includes multiple, sequential pulses of RF power  401 A,  401 B,  401 C, etc., in accordance with a set cycle duration d 405 . Each pulse of RF power  401 A,  401 B,  401 C, etc., includes a first duration d 401  over which a first RF power profile p 1  exists, immediately followed by a second duration d 402  over which a second RF power profile p 2  exists. The first RF power profile p 1  has a greater RF power than the second RF power profile p 2 . In the example of  FIG.  4   , the first RF power profile p 1  has an RF power level of P 2 , and the second RF power profile p 2  has an RF power level of P 1 . Also, the first duration d 401  of the first RF power profile p 1  is less than the second duration d 402  of the second RF power profile p 2 . Each pulse of RF power  401 A,  401 B,  401 C, etc., has a pulse duration d 404 , which is the sum of the duration of the first duration d 401  of the first RF power profile p 1  and the second duration d 402  of the second RF power profile p 2 . Also, the sequential pulses of RF power  401 A,  401 B,  401 C, etc., are separated from each other by a third duration d 403 , referred to as the interpulse duration d 403 . The set cycle duration d 405  is the sum of the pulse duration d 404  and the interpulse duration d 403 . 
     The first RF power profile p 1  defines an RF pulse-initiation power spike. By way of the first RF power profile p 1 , the RF pulse-initiation power spike is controllable in terms of power and time. The power level P 2  and duration d 401  of the first RF power profile p 1  is set to accelerate establishment and stabilization of the plasma  105  sheath at the beginning of each RF power pulse  401 A,  401 B,  401 C, etc. Therefore, it should understood that the first RF power profile p 1  is defined to put more RF energy into the plasma  105  at the beginning of generation of the plasma  105  (as the plasma  105  sheath initially builds in). The RF power pulse profile  401  can be used in many different plasma processing operations for semiconductor device fabrication, and is particular useful in plasma-based etching of a conductor material and/or a carbon-based hardmask material on the substrate  107 . 
     In the example RF power pulse profile  401 , the first RF power profile p 1  is a substantially constant first RF power at the set power level P 2 , and the second RF power profile p 2  is a substantially constant second RF power at the set power level P 1 , and during the interpulse duration d 403  between successive pulses  401 A,  401 B,  401 C, etc., the RF power is essentially zero. In some embodiments, when the bias RF signal generator  125  is operated in accordance with the RF power pulse profile  401 , the impedance matching circuit  129  is optimized for the conditions present during the second RF power profile p 2 . In other embodiments, when the bias RF signal generator  125  is operated in accordance with the RF power pulse profile  401 , the impedance matching circuit  129  is optimized for the conditions present during the first RF power profile p 1 . In some embodiments, when the primary RF signal generator  137  is operated in accordance with the RF power pulse profile  401 , the impedance matching circuit  141  is optimized for the conditions present during the second RF power profile p 2 . In other embodiments, when the primary RF signal generator  137  is operated in accordance with the RF power pulse profile  401 , the impedance matching circuit  141  is optimized for the conditions present during the first RF power profile p 1 . 
     In some embodiments, a sum of the first duration d 401  of the first RF power profile p 1  and the second duration d 402  of the second RF power profile p 1  and the interpulse duration d 403  is less than or equal to about  10  milliseconds. Or, in other words, in some embodiments, the set cycle duration d 405  is less than or equal to about 10 milliseconds. In some embodiments, a sum of the first duration d 401  of the first RF power profile p 1  and the second duration d 402  of the second RF power profile p 1  is less than one-half of the set cycle duration d 405 . Or, in other words, in some embodiments, the pulse duration d 404  is less than one-half of the set cycle duration d 405 . Or, in other words, in some embodiments, a sum of the first duration d 401  of the first RF power profile p 1  and the second duration d 402  of the second RF power profile p 1  is less than the interpulse duration d 403 . In some embodiments, the first duration d 401  of the first RF power profile p 1  is within a range extending from about 10 microseconds to about 100 microseconds, or within a range extending from about 20 microseconds to about 80 microseconds, or within a range extending from about 40 microseconds to about 50 microseconds. In some embodiments, the first duration d 401  of the first RF power profile p 1  is about 5% to about 25% of a sum of the first duration d 401  of the first RF power profile p 1  and the second duration d 402  of the second RF power profile p 2 . In some embodiments, the first duration d 401  of the first RF power profile p 1  is about  1 0% to about 15% of a sum of the first duration d 401  of the first RF power profile p 1  and the second duration d 402  of the second RF power profile p 2 . In an example embodiment, the bias RF signal generator  125  is operated to provide an RF pulse-initiation power spike of about 1000 Watts for about 10 to about 100 microseconds at the beginning of each bias RF power pulse  401 A,  401 B,  401 C, etc., followed by a steady RF bias power level of about 500 W for the remainder of each bias RF power pulse  401 A,  401 B,  401 C, etc. In an example embodiment of the RF power pulse profile  401 , the set power level P 1  (of the second RF power profile p 2 ) is 3000 Watts (W), and the set power level P 2  (of the first RF power profile p 1 ) is within a range extending from about 5000 W to about 6000 W. In another example embodiment of the RF power pulse profile  401 , the set power level P 1  (of the second RF power profile p 2 ) is 500 Watts (W), and the set power level P 2  (of the first RF power profile p 1 ) is within a range extending from about 1000 W to about 2000 W. The term “about” as used herein represents plus or minus 10%. It should be understood that the above-described values for the set power levels P 1  and P 2  of the RF power pulse profile  401  are provided by way of example. In other embodiments of the RF power pulse profile  401 , the set power levels P 1  and P 2  are set as needed, such as to achieve a desired plasma control effect, or other result. 
     The rail voltage supply for the bias RF signal generator  125  or the primary RF signal generator  137  mainly controls the absolute amount of maximum RF power that can be output. An additional amount of rail voltage can be provided to the bias RF signal generator  125  or the primary RF signal generator  137  at the beginning of the RF power pulse  401 A,  401 B,  401 C, etc., to generate the RF pulse-initiation power spike in accordance with the first RF power profile p 1 . In some embodiments, the additional amount of rail voltage used to generate the RF pulse-initiation power spike at the beginning of each RF power pulse  401 A,  401 B,  401 C, etc., is provided by an additional voltage supply device (DC power supply) connected within the bias RF signal generator  125  or the primary RF signal generator  137 , as the case may be. In some embodiments, the additional voltage supply device can be switchably connected to the rail voltage supply for the bias RF signal generator  125  or the primary RF signal generator  137  to provide temporal control of the rail voltage supply in order to comply with the first RF power profile p 1 . 
     In addition to having the additional voltage supply device, the output of the extant rail voltage supply for the bias RF signal generator  125  or the primary RF signal generator  137  can be increased during the first RF power profile p 1  to give a small boost in power. But, the amount of power added by increasing the output of the extant rail voltage supply for the bias RF signal generator  125  or the primary RF signal generator  137  is less than what is needed and is less than what is provided by the additional voltage supply device. Also, in some embodiments, during the first RF power profile p 1 , the power limits can be fully removed from the bias RF signal generator  125  or the primary RF signal generator  137  to create an “ignition state” in which the RF generator is allowed to frequency tune in order to reduce reflected power with maximum power output. 
     The RF power pulse profile  401  of  FIG.  4    represents single-level RF power pulsing in which the RF power is pulsed between zero and a set power level P 1 , with the first RF power profile p 1  having the set power level P 2 .  FIG.  5    shows an RF power pulse profile  501  that represents dual-level RF power pulsing in which the RF power is pulsed between a first set non-zero power level P 1  and a set power level P 2 , with the first RF power profile p 1  having the set power level P 3 , in accordance with some embodiments. In the dual-level RF power pulsing of  FIG.  5   , the RF power during the third duration (interpulse duration) d 403  is a substantially constant RF power level P 1  that is greater than zero. In an example embodiment of the RF power pulse profile  501 , the set power level P 1  (of the interpulse duration d 403 ) is 500 W, and the set power level P 2  (of the second RF power profile p 2 ) is 3000 W, and the set power level P 3  (of the first RF power profile p 1 ) is within a range extending from about 5000 W to about 6000 W. In an example embodiment of the RF power pulse profile  501 , the set power level P 1  (of the interpulse duration d 403 ) is 100 W, and the set power level P 2  (of the second RF power profile p 2 ) is 500 W, and the set power level P 3  (of the first RF power profile p 1 ) is within a range extending from about 1000 W to about 2000 W. It should be understood that the above-described values for the set power levels P 1 , P 2 , and P 3  of the RF power pulse profile  501  are provided by way of example. In other embodiments of the RF power pulse profile  501 , the set power levels P 1 , P 2 , and P 3  are set as needed, such as to achieve a desired plasma control effect, or other result. 
     In the RF power pulse profile  401  of  FIG.  4   , the first RF power profile p 1  has a substantially constant RF power level P 2 . However, in some embodiments, the first RF power profile p 1  can be non-constant, i.e., can vary as a function of time.  FIG.  6    shows an RF power pulse profile  601  that represents single-level RF power pulsing in which the RF power is pulsed between zero and a set power level P 1 , with a first RF power profile p 1  that exceeds the set power level P 1  and is non-constant, in accordance with some embodiments. The RF power pulse profile  601  is essentially the same as the RF power pulse profile  401 , with the exception of the first RF power profile p 1 . The first RF power profile p 1  of the RF power pulse profile  601  initially jumps to the power level P 2 , then decreases over time from the power level P 2  to the power level P 1 . Specifically, the first RF power profile p 1  of the RF power pulse profile  601  decreases in three steps over time to go from the power level P 2  to the power level P 1 , where a first step extends over a duration d 601 , a second step extends over a duration d 603 , and a third step extends over a duration d 605 . 
     Also, in some embodiments, the first RF power profile p 1  can increase as a function of time.  FIG.  7    shows an RF power pulse profile  701  that represents single-level RF power pulsing in which the RF power is pulsed between zero and a set power level P 1 , with a first RF power profile p 1  that exceeds the set power level P 1  and is non-constant, in accordance with some embodiments. The RF power pulse profile  701  is essentially the same as the RF power pulse profile  401 , with the exception of the first RF power profile pl. The first RF power profile p 1  of the RF power pulse profile  701  increases in steps to reach the power level P 2 . Specifically, the first RF power profile p 1  of the RF power pulse profile  701  increases in two steps over time to go from a zero power level to the power level P 2 , where a first step extends over a duration d 701 , and a second step extends over a duration d 703 . It should be understood that the RF power pulse profiles  601  and  701  of  FIGS.  6  and  7   , respectively, are provided by way of example. In various embodiments, the first RF power profile p 1  that defines the RF pulse-initiation power spike can be configured in essentially anyway needed to most efficiently and/or rapidly establish and stabilize the plasma  105  sheath. 
     In some embodiments, the frequency of the signals that are generated by the bias RF signal generator  125  or primary RF signal generator  137  is a constant during an entirety of the pulse duration d 404 . More specifically, in some embodiments, the frequency of the signals that are generated by the bias RF signal generator  125  or primary RF signal generator  137  is the same during both the duration d 401  of the first RF power profile p 1  corresponding to the RF pulse-initiation power spike and the duration d 402  of the second RF power profile p 2  corresponding to the settled pulse power level. However, in some embodiments, the frequency of the signals that are generated by the bias RF signal generator  125  or primary RF signal generator  137  is varied during the pulse duration d 404 . In this manner, the frequency of the signals that are generated by the bias RF signal generator  125  or primary RF signal generator  137  can be optimized for RF power delivery to the plasma  105 . For example, consider that the impedance of the plasma  105  during the first duration d 401  of the first RF power profile p 1  may be different than the impedance of the plasma  105  during the second duration d 402  of the second RF power profile p 2 . With this consideration, the frequency of the signals that are generated by the bias RF signal generator  125  or primary RF signal generator  137  can be controlled in a first manner during the first duration d 401  of the first RF power profile p 1 , and can be controlled in a second manner during the second duration d 402  of the second RF power profile p 2 , to optimize RF power delivery to the plasma  105  during the entire pulse duration d 404 . 
       FIG.  8 A  shows the RF power pulse profile  401  of  FIG.  4    with frequency variation applied over the pulse duration d 404 , in accordance with some embodiments. In the example of  FIG.  8 A , the frequency of the signals that are generated by the bias RF signal generator  125  or primary RF signal generator  137  during the first duration d 401  of the first RF power profile p 1  correspond to a first frequency control function freq 1 {t}. And, the frequency of the signals that are generated by the bias RF signal generator  125  or primary RF signal generator  137  during the second duration d 402  of the second RF power profile p 2  correspond to a second frequency control function freq 2 {t}. Each of the first frequency control function freq 1 {t} and the second frequency control function freq 2 {t} is essentially a specification of frequency setpoint as a function of time for the bias RF signal generator  125  or primary RF signal generator  137 . In some embodiments, the frequency of the bias RF signal generator  125  or primary RF signal generator  137  can be changed/adjusted within a time of less than or equal to about 1 microsecond. Therefore, a frequency tuning resolution of each of the first frequency control function freq 1 {t} and the second frequency control function freq 2 {t} is less than or equal to about 1 microsecond. 
     The first frequency control function freq 1 {t} and the second frequency control function freq 2 {t} can be defined independently of each other, and can be either the same or different. In some embodiments, the first frequency control function freq 1 {t} and/or the second frequency control function freq 2 {t} can be a linear function with respect to time.  FIG.  8 B  shows an example frequency control function  801  (freq#{t}) in which the frequency of the signals that are generated by the bias RF signal generator  125  or primary RF signal generator  137  is substantially constant over time, in accordance with some embodiments. The frequency control function  801  (freq#{t}) is representative of the first frequency control function freq 1 {t} and/or the second frequency control function freq 2 {t}. 
       FIG.  8 C  shows an example frequency control function  803  (freq#{t}) in which the frequency of the signals that are generated by the bias RF signal generator  125  or primary RF signal generator  137  increases monotonically over time, in accordance with some embodiments. The frequency control function  803  (freq#{t}) is representative of the first frequency control function freq 1 {t} and/or the second frequency control function freq 2 {t}. In some embodiments, the frequency control function  803  (freq#{t} is a linear function, such as shown in  FIG.  8 C . However, in other embodiments, the frequency control function  803  (freq#{t}) is a monotonically increasing non-linear function. 
       FIG.  8 D  shows an example frequency control function  805  (freq#{t}) in which the frequency of the signals that are generated by the bias RF signal generator  125  or primary RF signal generator  137  decreases monotonically over time, in accordance with some embodiments. The frequency control function  805  (freq#{t}) is representative of the first frequency control function freq 1 {t} and/or the second frequency control function freq 2 {t}. In some embodiments, the frequency control function  805  (freq#{t}) is a linear function, such as shown in  FIG.  8 D . However, in other embodiments, the frequency control function  805  (freq#{t}) is a monotonically decreasing non-linear function. 
       FIG.  8 E  shows an example frequency control function  807  (freq#{t}) in which the frequency of the signals that are generated by the bias RF signal generator  125  or primary RF signal generator  137  varies in a non-linear manner over time, in accordance with some embodiments. The frequency control function  807  (freq#{t}) is representative of the first frequency control function freq 1 {t} and/or the second frequency control function freq 2 {t}. In some embodiments, the frequency control function  807  (freq#{t}) includes both a first portion in which the frequency increases with time, and a second portion in which the frequency decreases with time. 
     A potential problem with current RF generators is that the DC rail voltage of the RF generator cannot be changed fast enough to implement the first RF power profile p 1  and implement the transition to the second RF power profile p 2  on the time scale needed. In some embodiments, one way to control the DC rail voltage of the RF generator as needed to provide the RF pulse-initiation power spike (corresponding to the first RF power profile p 1 ) is to have two separately controllable DC power supplies within the RF generator. 
     In these embodiments, a first DC power supply operates to supply the necessary rail voltage to generate RF signals for the duration d 402  corresponding to the second RF power profile p 2  that follows the RF pulse-initiation power spike corresponding to the first RF power profile p 1 . Also, a second DC power supply operates to supply an additional amount of rail voltage to generate RF signals for the duration  401  of the RF pulse-initiation power spike corresponding to the first RF power profile p 1 . The additional amount of rail voltage supplied by the second DC power supply is added to the baseline amount of rail voltage supplied by the first DC power supply. The second DC power supply can be controlled on the time scale needed to generate the RF pulse-initiation power spike corresponding to the first RF power profile p 1  and then transition at the proper time to the second RF power profile p 2  of the bulk of the RF power pulse. The output of the second DC power supply is connected to a switching mechanism to control transmission of the additional amount of rail voltage to the power rail of the RF generator. In some embodiments, a capacitor or equivalent electrical device is connected to the output of the second DC power supply to enable fast switching. Also, the first and second DC power supplies are configured and connected to avoid transmission of power into each other, such as with one or more diode(s). 
       FIG.  9    shows an example arrangement of an RF signal generation system  900  that implements dual DC power supplies for RF pulse-initiation power spike generation, in accordance with some embodiments. The RF signal generation system  900  of  FIG.  9    can be used for the bias RF signal generator  125  and/or the primary RF signal generator  137 . The RF signal generation system  900  includes an RF signal generator  901  configured to generate RF signals at or near a set frequency. The RF signal generation system  900  also includes a first DC voltage supply  903  connected to a voltage input  905  of the RF signal generator  901 . In some embodiments, the first DC voltage supply  903  is connected to the voltage input  905  through a diode  913 . The diode  913  functions to protect the first DC voltage supply  903  from electrical power present at the voltage input  905  of the RF signal generator  901 . The RF signal generation system  900  also includes a second DC voltage supply  907  switchably connected to the voltage input  905  of the RF signal generator  901 . In some embodiments, a switching device  911  is connected between the second DC voltage supply  907  and the voltage input  905  of the RF signal generator  901 . In some embodiments, a capacitor  915  or equivalent electrical device is connected between the output of the second DC voltage supply  907  and a reference ground potential  917 . The capacitor  915  or equivalent electrical device ensures that the output of the second DC voltage supply  907  is electrically charged to enable fast switching of the switching device  911 . 
     The RF signal generation system  900  also includes a controller  909  configured and connected to control each of the RF signal generator  901 , the first DC voltage supply  903 , the second DC voltage supply  907 , and the switching device  911 . In some embodiments, the controller  909  is configured similar to the control system  153 . The switching device  911  is configured to control electrical connection of the second DC voltage supply  907  to the voltage input  905  of the RF signal generator  901  in accordance with control signals received from the controller  909 . The voltage supplied to the voltage input  905  of the RF signal generator  901  by the first DC voltage supply  903  and the second DC voltage supply controls an amplitude of the RF signals generated by the RF signal generator  901 . The controller  909  is configured to execute program instructions stored in a computer memory that when executed cause the controller  909  to direct the RF signal generator  901  to supply multiple, sequential pulses of RF power to an electrode ( 123 / 101 ) of the plasma processing system  100 . Each of the pulses of RF power include the first duration d 401  over which the first RF power profile p 1  exists, immediately followed by the second duration d 402  over which the second RF power profile p 2  exists. The first RF power profile p 1  has greater RF power than the second RF power profile p 2 . The first duration d 401  is less than the second duration d 402 . Also, the sequential pulses of RF power are separated from each other by the third (interpulse) duration d 403 . 
     The first RF power profile p 1  corresponds to connection of both the first DC voltage supply  903  and the second DC voltage supply  907  to the voltage input  905  of the RF signal generator  901 . The second RF power profile p 2  corresponds to connection of the first DC voltage supply  903  to the voltage input  905  of the RF signal generator  901 , without connection of the second DC voltage supply  907  to the voltage input  905  of the RF signal generator  901 . The controller  909  is configured to initiate a given pulse of RF power in accordance with the first RF power profile p 1  by directing activation of the RF signal generator  901  and by directing the switching device  911  to connect the second DC voltage supply  907  to the voltage input  905  of the RF signal generator  901 , with the first DC voltage supply  903  persistently connected to the voltage input  905  of the RF signal generator  901 . The controller  909  is configured to transition from the first RF power profile p 1  to the second RF power profile p 2  by directing the switching device  911  to disconnect the second DC voltage supply  907  from the voltage input  905  of the RF signal generator  901 . The controller  909  is configured to end the given pulse of RF power by directing deactivation of the RF signal generator  901 . 
       FIGS.  10 ,  11 , and  12    collectively show voltages supplied to the voltage input  905  of the RF signal generator  901  as a function of time.  FIG.  10    shows a diagram of the voltage output by the first DC voltage supply  903  as a function of time to generate the RF power pulse profile  401  of  FIG.  4   , in accordance with some embodiments. The voltage output by the first DC voltage supply  903  as a function of time is a substantially constant voltage V 1 .  FIG.  11    shows a diagram of the voltage output by the second DC voltage supply  907  as a function of time to generate the RF power pulse profile  401  of  FIG.  4   , in accordance with some embodiments. The voltage output by the second DC voltage supply  907  as a function of time pulses between zero and a voltage ΔV, where ΔV=V 2 -V 1 , and where V 2  is a voltage level corresponding to generation of the first RF power profile p 1 .  FIG.  12    shows a diagram of the sum of the voltages output by the first DC voltage supply  903  and the second DC voltage supply  907  as a function of time to generate the RF power pulse profile  401  of  FIG.  4   , in accordance with some embodiments. The voltage diagram of  FIG.  12    represents the voltage present at the voltage input  905  of the RF signal generator  901  as a function of time.  FIG.  13    shows a diagram of the activation of the RF signal generator  901  as a function of time to generate the RF power pulse profile  401  of  FIG.  4   , in accordance with some embodiments. The activation of the RF signal generator  901  follows the timing of the RF power pulse profile  401  of  FIG.  4    with regard to RF power pulse generation. When the RF signal generator  901  is ON, the RF signal generator  901  generates RF signals in accordance with whatever voltage is present at the voltage input  905  of the RF signal generator  901 . Therefore, over the pulse duration d 404 , the RF signal generator  901  generates RF signals in accordance with the voltage V 2  during the first duration d 401  of the first RF power profile p 1 , and generates RF signals in accordance with the voltage V 1  during the second duration d 402  of the second RF power profile p 2 . And, when the RF signal generator  901  is OFF, no RF signals are generated by the RF signal generator  901 , regardless of the voltage present at the voltage input  905  of the RF signal generator  901 . 
       FIG.  14    shows a flowchart of a method for controlling a plasma within a plasma processing chamber, in accordance with some embodiments. In some embodiments, the plasma is generated to cause etching of a conductor material and/or a carbon-based hardmask material on a substrate. The method includes an operation  1401  for supplying multiple, sequential pulses of RF power to an electrode of the plasma processing chamber. In some embodiments, the electrode is a bias electrode disposed within a substrate holder within the plasma processing chamber. In some embodiments, the electrode is a coil disposed outside a window of the plasma processing chamber. Each of the pulses of RF power include a first duration over which a first RF power profile exists, immediately followed by a second duration over which a second RF power profile exists. The first RF power profile has greater RF power than the second RF power profile. The first duration is less than the second duration. And, the sequential pulses of RF power are separated from each other by a third duration. In some embodiments, the RF power during the third duration is essentially zero. In some embodiments, the RF power during the third duration is a substantially constant RF power level greater than zero. 
     In some embodiments, a sum of the first duration over which the first RF power profile exists, and the second duration over which the second RF power profile exists, and the third duration that separates sequential pulses is less than or equal to about 10 milliseconds. In some embodiments, a sum of the first duration over which the first RF power profile exists and the second duration over which the second RF power profile exists is less than or equal to the third duration that separates sequential pulses. In some embodiments, the first duration over which the first RF power profile exists is within a range extending from about 10 microseconds to about 100 microseconds, or within a range extending from about 20 microseconds to about 80 microseconds, or within a range extending from about 40 microseconds to about 50 microseconds. In some embodiments, the first duration over which the first RF power profile exists is about 5% to about 25% of a sum of the first duration and the second duration over which the second RF power profile exists. In some embodiments, the first duration over which the first RF power profile exists is about 10% to about 15% of a sum of the first duration and the second duration over which the second RF power profile exists. 
     In some embodiments, the first RF power profile is a substantially constant first RF power, and the second RF power profile is a substantially constant second RF power. In some embodiments, the first RF power profile decreases from a first (an initial) RF power, and the second RF power profile is a substantially constant second RF power. In some embodiments, the first RF power profile increases toward a first RF power, and the second RF power profile is a substantially constant second RF power. 
     In some embodiments, the method includes an optional operation  1403  for generating RF signals in accordance with a first frequency control function during the first duration to generate the first RF power profile. Also, in some embodiments, the method includes an optional operation  1405  for generating RF signals in accordance with a second frequency control function during the second duration to generate the second RF power profile. It should be understood that either or both of the optional operations  1403  and  1405  can be performed in any given embodiment. In some embodiments, a frequency tuning resolution of each of the first frequency control function and the second frequency control function is less than or equal to about 1 microsecond. 
     In some embodiments, the first frequency control function specifies a substantially constant frequency of the generated RF signals as a function of time. In some embodiments, the first frequency control function specifies a monotonically increasing frequency of the generated RF signals as a function of time. In some embodiments, the first frequency control function specifies a monotonically decreasing frequency of the generated RF signals as a function of time. In some embodiments, the first frequency control function specifies a non-linearly varying frequency of the generated RF signals as a function of time. 
     In some embodiments, the second frequency control function specifies a substantially constant frequency of the generated RF signals as a function of time. In some embodiments, the second frequency control function specifies a monotonically increasing frequency of the generated RF signals as a function of time. In some embodiments, the second frequency control function specifies a monotonically decreasing frequency of the generated RF signals as a function of time. In some embodiments, the second frequency control function specifies a non-linearly varying frequency of the generated RF signals as a function of time. 
     It should be understood that the systems and methods disclosed herein provide for generation of the RF pulse-initiation power spike. Also, it should be understood that the systems and methods disclosed herein provide for precise control of the amplitude and duration of the RF pulse-initiation power spike. Therefore, with the RF pulse-initiation power spike generation methods and systems disclosed herein, it is not necessary to attempt use of the open loop response of the RF signal generator in conjunction with frequency search and cable length adjustment to obtain an uncontrolled pulse initiation spike. 
     Also, by having a way to boost the rail voltage and/or RF drive of existing RF signal generators, and/or by creating an “ignition state” using the multi-level pulsing capabilities of existing RF signal generators, the methods and system disclosed herein provide an extra degree of control of the RF pulse-initiation power spike, which is particularly useful considering that the amplitude and duration needed in the RF pulse-initiation power spike can be different for each process recipe step. It should be understood that the methods and systems disclosed herein for generating the controlled RF pulse-initiation power spike are particularly useful when the bias RF signal generator  125  and/or primary RF signal generator  137  is/are operated in single-level pulsing mode. However, the methods and systems disclosed herein for generating the controlled RF pulse-initiation power spike are also useful when the bias RF signal generator  125  and/or primary RF signal generator  137  is/are operated in dual-level pulsing mode. And, in general, the methods and systems disclosed herein for generating the controlled RF pulse-initiation power spike are useful for the plasma striking phase of essentially any multiple phase pulse generation mode of the bias RF signal generator  125  and/or primary RF signal generator  137 . 
     In some embodiments, the methods and systems disclosed herein for generating the controlled RF pulse-initiation power spike can be used for both supply of bias RF power to the bias electrode  123  and supply of primary RF power to the coil  101 . It should be understood, however, that implementation of the methods and systems to generate the controlled RF pulse-initiation power spike for supply of bias RF power to the bias electrode  123  is/are completely independent from implementation of the methods and systems to generate the controlled RF pulse-initiation power spike for supply of primary RF power to the coil  101 , and vice-versa. Generation of the controlled RF pulse-initiation power spike is particularly useful when supplying low power pulses of the primary RF power to the coil  101 . 
       FIG.  15    shows a flowchart of a method for controlling a plasma within a plasma processing chamber, in accordance with some embodiments. The method includes an operation  1501  for supplying multiple, sequential pulses of primary RF power to a primary electrode of the plasma processing chamber. Each of the pulses of primary RF power includes a first duration over which a first primary RF power profile exists, immediately followed by a second duration over which a second primary RF power profile exists. The first primary RF power profile has greater RF power than the second primary RF power profile. The first duration is less than the second duration. And, the sequential pulses of primary RF power are separated from each other by a third duration. In some embodiments, the primary RF power level is essentially zero during the third duration. In some embodiments, the primary RF power level is a substantially constant power level greater than zero during the third duration. 
     The method also includes an operation  1503  for supplying multiple, sequential pulses of bias RF power to a bias electrode of the plasma processing chamber. Each of the pulses of bias RF power includes a fourth duration over which a first bias RF power profile exists, immediately followed by a fifth duration over which a second bias RF power profile exists. The first bias RF power profile has greater RF power than the second bias RF power profile. The fourth duration is less than the fifth duration. And, the sequential pulses of bias RF power are separated from each other by a sixth duration. In some embodiments, the bias RF power level is essentially zero during the sixth duration. In some embodiments, the bias RF power level is a substantially constant power level greater than zero during the sixth duration. 
     In some embodiments, the pulses of bias RF power are delayed relative to the pulses of primary RF power by a pulse delay amount within a range extending from about 2 microseconds to about 100 microseconds, or within a range extending from about 2 microseconds to about 5 microseconds, or of about 3 microseconds. In some embodiments, the pulse delay amount is set to enable a given pulse of primary RF power to establish a stable primary plasma condition within the plasma processing chamber before supply of a subsequent pulse of bias RF power. Also, in a dual-level primary RF power pulsing application, the impedance variation and transition of the bulk plasma between the different primary RF power levels can be significant and can require a longer delay between the primarily RF power pulse and the bias RF power pulse. This longer delay can be about 50 microseconds to about 100 microseconds. 
     In some embodiments, the method includes an optional operation  1505  for generating RF signals in accordance with a first frequency control function during the first duration to generate the first primary RF power profile. Also, in some embodiments, the method includes an optional operation  1507  for generating RF signals in accordance with a second frequency control function during the second duration to generate the primary second RF power profile. It should be understood that either or both of the optional operations  1505  and  1507  can be performed in any given embodiment. Additionally, in some embodiments, the method includes an optional operation  1509  for generating RF signals in accordance with a third frequency control function during the fourth duration to generate the first bias RF power profile. Also, in some embodiments, the method includes an optional operation  1511  for generating RF signals in accordance with a fourth frequency control function during the fifth duration to generate the second bias RF power profile. It should be understood that either or both of the optional operations  1509  and  1511  can be performed in any given embodiment. In some embodiments, a frequency tuning resolution of each of the first frequency control function, the second frequency control function, the third frequency control function, and the fourth frequency control function is less than or equal to about 1 microsecond. 
     Various embodiments described herein may also be practiced using various computer system configurations including hand-held hardware units, microprocessor systems, microprocessor-based or programmable consumer electronics, minicomputers, mainframe computers and the like. Embodiments described herein can also be practiced in distributed computing environments where tasks are performed by remote processing hardware units that are linked through a network. It should be understood that the embodiments described herein can employ various computer-implemented operations involving data stored in computer systems. These operations are those 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 a hardware unit or an apparatus for performing these operations. The apparatus may be specially constructed for a special purpose computer. 
     When defined as a special purpose computer, the computer can also perform other processing, program execution or routines that are not part of the special purpose, while still being capable of operating for the special purpose. In some embodiments, the operations may be processed by a general purpose computer selectively activated or configured by one or more computer programs stored in the computer memory, cache, or obtained over a network. When data is obtained over a network, the data may be processed by other computers on the network, e.g., a cloud of computing resources. 
     Various embodiments described herein can be implemented through process control instructions instantiated as computer-readable code on a non-transitory computer-readable medium. The non-transitory computer-readable medium is any data storage hardware unit that can store data, which can be thereafter be read by a computer system. Examples of the non-transitory computer-readable medium include hard drives, network attached storage (NAS), ROM, RAM, compact disc-ROMs (CD-ROMs), CD-recordables (CD-Rs), CD-rewritables (CD-RWs), magnetic tapes, and other optical and non-optical data storage hardware units. The non-transitory computer-readable medium can include computer-readable tangible medium distributed over a network-coupled computer system so that the computer-readable code is stored and executed in a distributed fashion. 
     Although the foregoing disclosure includes 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. For example, it should be understood that one or more features from any embodiment disclosed herein may be combined with one or more features of any other embodiment disclosed herein. Accordingly, the present embodiments are to be considered as illustrative and not restrictive, and what is claimed is not to be limited to the details given herein, but may be modified within the scope and equivalents of the described embodiments.