System and method for controlling an LF RF pulse generator to enhance selectivity

Abstract

Systems and methods are described for controlling a low frequency (LF) radio frequency (RF) pulse generator to enhance selectivity. One method includes controlling the LF RF pulse generator to generate a plurality of rectangular pulses interspersed with a plurality of rectangular sub-pulses, each of the plurality of rectangular pulses having a first sub-pulse width greater than a second sub-pulse width of each of the plurality of rectangular sub-pulses.

Description

[Technical Field]

[0001] The present embodiment relates to a system and method for controlling a low frequency (LF) radio frequency (RF) pulse generator to enhance selectivity. [Background technology]

[0002] A plasma tool contains multiple radio frequency (RF) generators. The RF generators are connected to a plasma chamber through matchers. A wafer is placed inside the plasma chamber for processing. The RF generators generate RF signals and feed the RF signals to matchers. The matchers match the output impedance to the input impedance and output the RF signals to the plasma chamber. The RF signals are used to generate plasma for processing the wafer. However, etching the desired layer of the wafer while preserving the mask layer on the wafer can be challenging.

[0003] The background description provided herein is intended to present the contents of the present disclosure generally. Work by the presently named inventors within the scope of what is described in this Background section, as well as aspects of the description that may not otherwise be considered prior art at the time of filing, are not admitted, expressly or impliedly, as prior art against the present disclosure. Summary of the Invention

[0004]

[0006] Embodiments of the present disclosure provide systems, apparatus, methods, and computer programs for controlling a low frequency (LF) radio frequency (RF) generator to enhance selectivity. It should be understood that the present embodiments can be implemented in various ways, such as a process, an apparatus, a system, a device, or a method recorded on a computer-readable medium. Some embodiments are described below.

[0005] In one embodiment, sub-pulses are introduced between the peaks of the pulses to generate ions with lower energy, which improves mask selectivity.

[0006] In one embodiment, a method of controlling an LF RF pulse generator to enhance selectivity is described. The method includes controlling the LF RF pulse generator to generate a plurality of rectangular pulses interspersed with a plurality of rectangular sub-pulses. Each of the plurality of rectangular pulses has a first sub-pulse width greater than a second sub-pulse width of each of the plurality of rectangular sub-pulses. The act of controlling the LF RF pulse generator includes controlling the LF RF pulse generator to generate one of the plurality of rectangular pulses, determining whether a predetermined amount of time has elapsed since controlling the LF RF pulse generator to generate one of the plurality of rectangular pulses, and, upon determining that the predetermined amount of time has elapsed, controlling the LF RF pulse generator to generate one of the plurality of rectangular sub-pulses. The act of controlling the LF RF pulse generator to generate the plurality of rectangular sub-pulses enhances selectivity.

[0007] In one embodiment, a controller for controlling an LF RF pulse generator to enhance selectivity is described. The controller includes a processor that controls the LF RF pulse generator to generate a plurality of rectangular pulses interspersed with a plurality of rectangular sub-pulses. Each of the plurality of rectangular pulses has a first sub-pulse width greater than a second sub-pulse width of each of the plurality of rectangular sub-pulses. To control the LF RF pulse generator, the processor controls the LF RF pulse generator to generate one of the plurality of rectangular pulses. To further control the LF RF pulse generator, the processor determines whether a predetermined amount of time has elapsed since the LF RF pulse generator was controlled to generate one of the plurality of rectangular pulses. To further control the LF RF pulse generator, the processor controls the LF RF pulse generator to generate one of the plurality of rectangular sub-pulses when it determines that the predetermined amount of time has elapsed. The controller includes a memory device connected to the processor.

[0008] In one embodiment, a plasma system is described. The plasma system includes an LF RF pulse generator. The plasma system further includes a plasma chamber connected to the LF RF pulse generator via an RF cable. The plasma system includes a controller connected to the LF RF pulse generator. The controller controls the LF RF pulse generator to generate a plurality of rectangular pulses interspersed with a plurality of rectangular sub-pulses. Each of the plurality of rectangular pulses has a first sub-pulse width greater than a second sub-pulse width of each of the plurality of rectangular sub-pulses. To control the LF RF pulse generator, the controller controls the LF RF pulse generator to generate one of the plurality of rectangular pulses. Further, to control the LF RF pulse generator, the controller determines whether a predetermined amount of time has elapsed since the LF RF pulse generator was controlled to generate one of the plurality of rectangular pulses. Furthermore, to control the LF RF pulse generator, the controller controls the LF RF pulse generator to generate one of the plurality of rectangular sub-pulses upon determining that the predetermined amount of time has elapsed.

[0009] Some advantages of the systems and methods for controlling an LF RF pulse generator described herein include providing increased selectivity. Increased selectivity is achieved by introducing sub-pulses between pulses of a rectangular pulse waveform generated by an LF RF generator. The sub-pulses result in an increased number of low energy ions. With an increase in low energy ions, selectivity increases. Furthermore, the combination of pulses and sub-pulses of a rectangular pulse waveform provides a balance between achieving etch rate and achieving selectivity.

[0010] Other aspects will become apparent from the following detailed description taken in conjunction with the accompanying drawings. [Brief explanation of the drawings]

[0011] The embodiments will be best understood by referring to the following description taken in conjunction with the accompanying drawings.

[0012] [Figure 1] FIG. 1 is a diagram of one embodiment of a system for controlling a low frequency (LF) radio frequency (RF) pulse generator to enhance selectivity.

[0013] [Figure 2A] FIG. 2A is a graph illustrating one embodiment of a clock signal.

[0014] [Figure 2B] FIG. 2B is a graph illustrating one embodiment of a rectangular pulse waveform.

[0015] [Figure 2C] FIG. 2C is a graph illustrating a rectangular pulse waveform to provide an example of increasing peak value of each sub-pulse of the rectangular pulse waveform with decreasing sub-pulse width.

[0016] [Figure 2D] FIG. 2D is a graph illustrating a rectangular pulse waveform to provide an example of a decrease in peak value of each sub-pulse of the rectangular pulse waveform with increasing sub-pulse width.

[0017] [Figure 3] FIG. 3 is a block diagram of one embodiment of a system illustrating a method for controlling an LF RF pulse generator.

[0018] [Figure 4] FIG. 4 is a diagram of one embodiment of a system illustrating control of an LF RF pulse generator by a processor of a controller.

[0019] [Figure 5] FIG. 5 is a graph illustrating the increase in selectivity with increasing voltage of the sub-pulses of a rectangular pulse waveform.

[0020] [Figure 6]FIG. 6 is a graph illustrating the change in voltage at the bottom plasma sheath with the introduction of multiple sub-pulses of a rectangular pulse waveform. DETAILED DESCRIPTION OF THE INVENTION

[0021] The following embodiments describe systems and methods for controlling a low frequency (LF) radio frequency (RF) pulse generator to enhance selectivity. It will be apparent that the embodiments may be practiced without some or all of these specific details. In other instances, well-known operations have not been described in detail in order to avoid unnecessarily obscuring the embodiments.

[0022] 1 is a diagram of one embodiment of a system 100 for controlling an LF RF pulse generator 104 to enhance selectivity. System 100 includes a function generator 102, an LF RF pulse generator 104, and a plasma chamber 106. Examples of function generator 102 include a desktop computer, a laptop computer, a tablet, a smartphone, and a controller.

[0023] The function generator 102 includes a processor 108 and a memory device 110. By way of example, the processor 108 may be an application specific integrated circuit (ASIC), a central processing unit (CPU), a field programmable gate array (FPGA), a programmable logic device (PLD), an integrated controller, or a microcontroller. Examples of the memory device 110 include a read-only memory (ROM) and a random access memory (RAM). Illustratively, the memory device 144 is a flash memory or a redundant array of independent disks (RAID). The processor 108 is connected to the memory device 110.

[0024] An example of an LF RF pulse generator 104 is a machine that periodically generates multiple high-voltage nanosecond pulses. Illustratively, the LF RF pulse generator 104 is a nanosecond pulser. Each high-voltage nanosecond pulse may be referred to herein as a pulse or sub-pulse. Examples of low frequencies include frequencies in the range of 10 kilohertz (kHz) to 800 kHz. Illustratively, a low frequency is a baseline frequency of 400 kHz. Further illustratively, the frequency of operation of the LF RF pulse generator 104 is 400 kHz. An example of a baseline frequency is the fundamental frequency.

[0025] The plasma chamber 106 includes a substrate support 112, such as an electrostatic chuck (ESC). The plasma chamber 106 further includes an upper electrode 114, which is disposed above the substrate support 112 and forms a gap 118 between the upper electrode 114 and the substrate support 112. The upper electrode 114 faces the substrate support 112. A substrate S is disposed on the upper surface of the substrate support 112. Examples of the substrate S include a semiconductor wafer and a substrate stack. For example, the substrate stack includes one or more layers, such as a mask layer, a metal layer, and an oxide layer.

[0026] The lower electrode 116 is embedded in the substrate support 112 and is formed of a metal such as aluminum or an aluminum alloy. The substrate support 112 is formed of a metal and a ceramic such as aluminum oxide (Al2O3). The upper electrode 114 is made of a metal. One example of the plasma chamber 112 is a capacitively coupled plasma (CCP) chamber. The upper electrode 114 is connected to ground potential.

[0027] The processor 108 is connected to the LF RF pulse generator 104 via a transfer cable 120, and the output 122 of the LF RF pulse generator 104 is connected to the lower electrode 116 via an RF cable 122 and an RF transmission line 126. Examples of transfer cables include a cable that allows serial transfer of data, a cable that allows parallel transfer of data, or a cable that allows transfer of data using the Universal Serial Bus (USB) protocol. By way of example, the control signals sent from the processor 108 to the LF RF pulse generator 104 include data or information. By way of example, the RF cable 122 is a high-voltage RF cable to facilitate the transfer of high-voltage nanosecond pulses. Illustratively, the RF cable 122 is a coaxial cable.

[0028] One example of an RF transmission line includes an RF rod surrounded by an RF tunnel with an insulator between the RF rod and the RF tunnel. The RF rod, RF tunnel, and insulator are components of an RF transmission line. Another example of an RF transmission line includes a combination of one or more RF straps, an RF rod, an insulator, and an RF tunnel. In this example, one or more RF straps are connected to the RF rod. Also in this example, the RF rod is surrounded by an insulator, and the insulator is surrounded by the RF tunnel.

[0029] As an example, there is no matcher between the LF RF pulse generator 104 and the plasma chamber 106. For example, there is no matcher between the RF cable 124 and the RF transmission line 126. An example of a matcher is an impedance matching circuit or an impedance matching network. For example, a matcher is a series of circuit components, such as capacitors, inductors, and resistors. The circuit components are connected to each other. For example, two of the circuit components are connected to each other in series or parallel. The matcher matches the impedance of a load, such as the plasma chamber 106, connected to the output of the matcher to the impedance of a source connected to the input of the matcher.

[0030] The processor 108 generates a recipe signal 130 and transmits the recipe signal 130 to the LF RF pulse generator 104 via the transfer cable 120. The recipe signal 130 includes information about a rectangular pulse waveform 132. The rectangular pulse waveform 132 is sometimes referred to herein as an interspersed waveform. The rectangular pulse waveform 132 includes multiple pulses 132A and 132B interspersed with multiple sub-pulses 134A and 134B. For example, the sub-pulse 134A is located between two adjacent pulses 132A and 132B. The pulses 132A and 132B are adjacent to each other, with no pulse between the two pulses 132A and 132B. As another example, the sub-pulse 134A immediately follows the pulse 132A. Also, the pulse 132B immediately follows the sub-pulse 134A, and the sub-pulse 134B immediately follows the pulse 132B. The pulses of rectangular pulse waveform 132 are sometimes referred to herein as rectangular pulses, and the sub-pulses of rectangular pulse waveform 132 are sometimes referred to herein as rectangular sub-pulses.

[0031] As an example, the rectangular pulse waveform 132 is not a sinusoidal signal. In this example, the envelope, such as the power level, of the sinusoidal signal is constant or substantially constant. For example, the power levels, such as the maximum amplitudes, of the sinusoidal signal envelopes have power amounts within a predetermined range, such as within ±10% of each other. In this example, the rectangular pulse waveform 132 has an envelope for the RF voltage ringing of the rectangular pulse waveform 132 that is different from the envelope of any pulse of the rectangular pulse waveform 132 or the envelope of any sub-pulse of the rectangular pulse waveform 132. For further example, the envelope of the RF voltage ringing is less than 10% of the envelope of the pulse preceding the RF voltage ringing. As yet another further example, the envelope of the pulse is greater than 100% of the envelope of the RF voltage ringing immediately following the pulse. As yet another further example, the envelope of the RF voltage ringing is less than 10% of the envelope of the sub-pulse preceding the RF voltage ringing. As yet another further example, the envelope of a sub-pulse is greater than 100% of the envelope of the RF voltage ringing immediately following the sub-pulse. As another example, a sinusoidal signal does not have pulses with rectangular envelopes and does not have sub-pulses with rectangular envelopes. Also, in this example, the sinusoidal signal does not have RF voltage ringing.

[0032] For example, the information about the rectangular pulse waveform 132 includes a first subpulse width (SPW) of each pulse of the rectangular pulse waveform 132, such as pulses 132A and 132B, and a second subpulse width of each subpulse of the rectangular pulse waveform 132, such as subpulses 134A and 134B. For example, the second subpulse width is smaller than the first subpulse width. For example, the second subpulse width is at least 10% smaller than the first subpulse width. For example, the second subpulse width is between 10% and 90% smaller than the first subpulse width. For further example, the second subpulse width is between 10% and 90% of the first subpulse width. The information also includes a phase delay, such as a period or time interval, after which the first subpulse width is modified to the second subpulse width. For example, the phase delay includes a period during which RF voltage ringing occurs immediately after the first subpulse width. Additionally, the information about the rectangular pulse waveform 132 includes the frequency of occurrence of the pulses of the rectangular pulse waveform 132, such as pulses 132A and 132B.

[0033] The LF RF pulse generator 104 includes a controller, which includes a processor and a memory device. The processor of the LF RF pulse generator 104 is connected to the memory device of the LF RF pulse generator 104. The processor of the LF RF pulse generator 104 receives information about the rectangular pulse waveform 132 from the processor 108 and stores the information in the memory device of the LF RF pulse generator 104.

[0034] Additionally, processor 130 generates a trigger signal 134 and transmits the trigger signal 134 to LF RF pulse generator 104 via transmission cable 120. In response to receiving trigger signal 134, the processor of LF RF pulse generator 104 accesses information regarding rectangular pulse waveform 132 from a memory device of LF RF pulse generator 104 and controls signal components of LF RF pulse generator 104 to generate rectangular pulse waveform 132 based on the information.

[0035] The rectangular pulse waveform 132 is transferred to the lower electrode 116 via the RF cable 124 and the RF transmission line 126 to provide power to the lower electrode 116. Furthermore, when one or more process gases are supplied to the gap 118 in addition to the rectangular pulse waveform 132, a plasma is struck or sustained in the gap 118 to process the substrate S. The boundaries of the plasma are defined by an upper plasma sheath 115A and a bottom plasma sheath 115B. The plasma processes the substrate S, such as a semiconductor wafer disposed on the substrate support 112. Examples of processing the substrate S include etching the substrate S, depositing one or more material layers on the substrate S, cleaning the substrate S, or sputtering the substrate S. Examples of the one or more process gases include an oxygen-containing gas, a fluorine-containing gas, and combinations thereof.

[0036] In one embodiment, the terms RF voltage ringing and RF ringing are used interchangeably herein, for example, RF ringing may also be referred to as RF voltage ringing herein.

[0037] 2A is a graph 200 illustrating one embodiment of a clock signal 202. Clock signal 202 is generated by processor 108 (FIG. 1) and transmitted to a processor of LF RF pulse generator 104 (FIG. 1) via transmission cable 120. The processor of LF RF pulse generator 104 controls signal components of LF RF pulse generator 104 in synchronization with clock signal 202.

[0038] Graph 200 plots the logic level of clock signal 202 versus time t. The logic level is plotted on the y-axis of graph 200, and time t is plotted on the x-axis of graph 200. Time t increases in the positive x-direction of the x-axis from time t0 to time t40. Time t progresses from time t0 to time t40. Note that the time interval between two consecutive times on the x-axis of graph 200 is equal to the time interval between any other two consecutive times on the x-axis. For example, a first time interval between times t0 and t5 is equal to a second time interval between times t5 and t10. As another example, the time interval between times t0 and t1 is equal to the time interval between times t1 and t2 and the time interval between times t2 and t3.

[0039] Clock signal 202 periodically transitions between logic level 1 and logic level 0. For example, during cycle n of clock signal 202, clock signal 202 is at logic level 1 from time t0 to time t5, where n is an integer greater than zero. Also during cycle n, at time t5, clock signal 202 transitions from logic level 1 to logic level 0. Further during cycle n, clock signal 202 remains at logic level 0 from time t5 to time t10. Logic levels 1 and 0 are repeated in this manner during cycle (n+1) of clock signal 202, cycle (n+2) of clock signal 202, and cycle (n+3) of clock signal 202.

[0040] Note that, as illustrated in graph 201, each cycle of clock signal 202 is also a cycle of rectangular pulse waveform 132 ( FIG. 1 ). For example, clock signal 202 and rectangular pulse waveform 132 are synchronized with each other. For example, cycle n of clock signal 202 is also cycle n of rectangular pulse waveform 132, cycle (n+1) of clock signal 202 is also cycle (n+1) of rectangular pulse waveform 132, cycle (n+2) of clock signal 202 is also cycle (n+2) of rectangular pulse waveform 132, and cycle (n+3) of clock signal 202 is also cycle (n+3) of rectangular pulse waveform 132. To further illustrate, a pulse of the rectangular pulse waveform 132 followed by successive RF voltage ringings may periodically repeat to generate cycles n, (n+2), etc. of the rectangular pulse waveform 132, and a sub-pulse of the rectangular pulse waveform 132 followed by successive RF voltage ringings may periodically repeat to generate cycles (n+1), (n+3), etc. of the rectangular pulse waveform 132.

[0041] 2B is a graph 200 illustrating one embodiment of a rectangular pulse waveform 202, which is an example of rectangular pulse waveform 132 (FIG. 1). Graph 200 plots the voltage of rectangular pulse waveform 202 versus time t. The voltage of rectangular pulse waveform 202 is plotted on the y-axis of graph 200, and time t is plotted on the x-axis of graph 200. The x-axis of graph 200 is the same as the x-axis of graph 201 (FIG. 2A). The voltage ranges from a voltage value −V6 to a voltage value V6. For example, the voltage increases from −V6 to V6.

[0042] Rectangular pulse waveform 202 has a series of pulses, such as pulse 204A and pulse 204B, interspersed with a series of sub-pulses, such as sub-pulse 206A and sub-pulse 206B. For example, pulse 204A occurs from time t0 to time t4. In this example, RF voltage ringing 208A directly follows pulse 204A. RF voltage ringing 208A occurs from time t4 to time t10. An example of RF voltage ringing is noise. Continuing the example, sub-pulse 206A occurs from time t10 to time t12, and RF voltage ringing 210A immediately follows sub-pulse 206A. RF voltage ringing 210A occurs from time t12 to time t20. Furthermore, in this example, pulse 204B occurs immediately after RF voltage ringing 210A. Pulse 204B occurs from time t20 to time t24. Also in this example, RF voltage ringing 208B immediately follows pulse 204B and occurs from time t24 to time t30. Sub-pulse 206B immediately follows RF voltage ringing 208B and occurs from time t30 to time t32. Sub-pulse 206B is immediately followed by RF voltage ringing 210B from time t32 to time t40.

[0043] Pulse 204A is an example of pulse 132A, and pulse 204B is an example of pulse 132B (FIG. 1). Each pulse, such as pulses 204A and 204B, has a first sub-pulse width 212. An example of the first sub-pulse width 212 is a time interval or period. Illustratively, the first sub-pulse width 212 of pulse 204A ranges from time t0 to time t4, and the first sub-pulse width 212 of pulse 204B ranges from time t20 to time t24. At time t0, pulse 204A has a voltage value −V4, and at time t4, pulse 204A has a voltage value −V4. Pulse 204A transitions upward from a voltage value −V4 to a voltage value V6 during the time interval from time t0 to time t2. Pulse 204A has a voltage value V6, which is a peak value, such as a maximum amplitude, of pulse 204A. Pulse 204A further transitions down from voltage value V6 to voltage value V4 during the time interval from time t2 to time t4. Pulse 204A is surrounded by a rectangular envelope 214. Similarly, pulse 204B transitions from voltage value −V6 to voltage value V4, where voltage value V4 is a peak value, and then transitions back down to voltage value −V4. Pulse 204B is also surrounded by another instance of envelope 214.

[0044] Additionally, sub-pulse 206A is an example of sub-pulse 134A, and sub-pulse 206B is an example of sub-pulse 134B (FIG. 1). Each sub-pulse, such as sub-pulses 206A and 206B, has a second sub-pulse width 216. An example of second sub-pulse width 216 is a time interval or period. Illustratively, second sub-pulse width 216 of sub-pulse 206A ranges from time t10 to time t12, and second sub-pulse width 216 of sub-pulse 206A ranges from time t30 to time t32. At time t10, sub-pulse 206A has a voltage value −V4, and at time t12, sub-pulse 206A has a voltage value −V4. Sub-pulse 206A transitions upward from a voltage value −V4 to a voltage value V0 during the time interval from time t10 to time t10.5. Sub-pulse 206A has a voltage value V0, which is the peak value, e.g., maximum amplitude, of sub-pulse 206A. Sub-pulse 206A further transitions down from voltage value V0 to a voltage value −V4 during the time interval from time t10.5 to time t11.5. Sub-pulse 206A is surrounded by a rectangular envelope 218. Similarly, sub-pulse 206B transitions from voltage value −V4 to voltage value V0, where voltage value V0 is the peak value, and then transitions back down to voltage value −V4. Sub-pulse 206B is also surrounded by another instance of envelope 218.

[0045] By controlling the first sub-pulse width 212, the envelope 214 becomes square or achieves a smaller rectangular shape. As an example, the first sub-pulse width 212 ranges from 10 nanoseconds (ns) to 500 ns, and the rise time of each pulse of the rectangular pulse waveform 202 is approximately 50 ns. Illustratively, each pulse of the rectangular pulse waveform 202 has a rise time ranging from 40 ns to 60 ns. If the envelope 214 changes to a square, each of the pulses 204A and 204B becomes a rectangular pulse, such as a square pulse. Note also that with a rectangular envelope 214, the pulses 204A and 204B are sometimes referred to herein as rectangular pulses.

[0046] Similarly, by controlling the second sub-pulse width 216, the envelope 218 can be shaped as a square or a smaller rectangle. As an example, the second sub-pulse width 216 can range from 5 ns to 250 ns, and the rise time of each pulse of the rectangular pulse waveform 202 can be approximately 25 ns. By way of example, each sub-pulse of the rectangular pulse waveform 202 can have a rise time ranging from 20 ns to 30 ns. If the envelope 218 is changed to a square, each of the sub-pulses 206A and 206B can become a rectangular pulse, such as a square pulse. It should also be noted that with a rectangular envelope 218, the pulses 206A and 206B are sometimes referred to herein as rectangular pulses.

[0047] Each RF voltage ringing, such as RF voltage ringing 208A and RF voltage ringing 208B, associated with an individual predecessor pulse of rectangular pulse waveform 202 has a ringing width 220, which is greater than first subpulse width 212. Ringing width 220 is a time interval greater than first subpulse width 212. Each RF voltage ringing associated with an individual predecessor pulse is a series of micropulses, each with an amplitude less than that of the predecessor pulse. For example, pulse 204A has a maximum amplitude of V6, and RF voltage ringing 208A has a maximum amplitude of V4. Each micropulse of RF voltage ringing associated with an individual predecessor pulse also has a micropulse width less than first subpulse width 212 of the predecessor pulse. An example of a micropulse width, as described herein, is the time interval between occurrences of micropulses of rectangular pulse waveform 202. An example of an amplitude, as described herein, is the maximum amplitude or peak-to-peak amplitude.

[0048] Additionally, the micropulse width of the RF voltage ringing associated with each preceding pulse is outside of the first subpulse width 212. For example, the micropulse width is substantially less than the first subpulse width 212. As another example, the micropulse width decreases as the RF voltage ringing 208A or 208B progresses.

[0049] Similarly, each RF voltage ringing, such as RF voltage ringing 210A and RF voltage ringing 210B, associated with each leading sub-pulse of rectangular pulse waveform 202 has a ringing width 222 that is greater than second sub-pulse width 216. Ringing width 222 has a greater time interval than second sub-pulse width 216. Each RF voltage ringing associated with each leading sub-pulse is a series of micro-pulses, each with an amplitude that is less than the amplitude of the leading sub-pulse. For example, sub-pulse 206A has a maximum amplitude of V0, and RF voltage ringing 210A has a maximum amplitude of -V3.5. Each micro-pulse of RF voltage ringing associated with each leading sub-pulse also has a micro-pulse width that is less than second sub-pulse width 216 of the leading sub-pulse.

[0050] Additionally, the micropulse width of the RF voltage ringing associated with each preceding sub-pulse is outside the range of the second sub-pulse width 216. For example, the micropulse width is substantially less than the second sub-pulse width 216. As another example, the micropulse width decreases as the RF voltage ringing 210A or 210B progresses.

[0051] Note that, as an example, second sub-pulse width 216 is smaller than first sub-pulse width 212. For example, second sub-pulse width 216 is at least 10% smaller than first sub-pulse width 212. For example, second sub-pulse width 216 is 10% to 80% smaller than first sub-pulse width 212.

[0052] The rectangular pulse waveform 202 also has a pulse width 224, which is the width between the maximum amplitudes of two successive pulses of the rectangular pulse waveform 202. For example, the pulse width 224 is the time interval between time t2 when pulse 204A has a voltage value V6 and time t22 when the successive or adjacent pulse 204B has a voltage value V6.

[0053] Note that pulse width 224 occurs between any two alternating ones of cycles n, (n+1), (n+2), and (n+3). For example, pulse width 224 between cycles n and (n+2) is equal to pulse width 224 between cycles (n+2) and (n+4) (not shown) of clock signal 201 ( FIG. 2A ). As another example, pulse width 224 between cycles n and (n+2) is within ±10% of pulse width 224 between cycles (n+2) and (n+4). Pulse width 224 provides the low frequency of rectangular pulse waveform 202. For example, the low frequency is the inverse of pulse width 224.

[0054] It should also be noted that controlling first sub-pulse width 212, ringing width 220, and pulse width 224 controls pulse width 226. Pulse width 226 is the width between the maximum amplitudes of two consecutive sub-pulses of rectangular pulse waveform 202. For example, pulse width 226 is the time interval between time t10.5 when sub-pulse 206A has a voltage value V and time t30.5 when sub-pulse 206B has a voltage value V. It should further be noted that the sub-pulses of rectangular pulse waveform 202 increase the amount of low-energy ions in the plasma formed in gap 118 (FIG. 1).

[0055] 2C is a graph 250 illustrating a rectangular pulse waveform 252 to provide an example of an increase in the peak value of each sub-pulse of rectangular pulse waveform 202 (FIG. 2A) with a decrease in second sub-pulse width 216 (FIG. 2A). Square pulse waveform 252 is another example of rectangular pulse waveform 132 (FIG. 1). Graph 250 plots the voltage of rectangular pulse waveform 252 versus time t. The voltage of rectangular pulse waveform 252 is plotted on the y-axis of graph 250, and time t is plotted on the x-axis of graph 250. The x-axis of graph 250 is the same as the x-axis of graph 201 (FIG. 2A), and the y-axis of graph 250 is the same as the y-axis of graph 200 (FIG. 2B).

[0056] The rectangular pulse waveform 252 is the same as the rectangular pulse waveform 202 ( FIG. 2B ), except that the rectangular pulse waveform 252 has a smaller third sub-pulse width 258 compared to the second sub-pulse width 216. When the third sub-pulse width 258 is smaller than the second sub-pulse width 216, the peak voltages of the sub-pulses of the rectangular pulse waveform 252, such as sub-pulse 254A and sub-pulse 254B, are greater than the peak voltages of the sub-pulses of the rectangular pulse waveform 202. For example, the peak voltage of the sub-pulses of the rectangular pulse waveform 252 is V3, which is greater than the peak voltage V0 of the sub-pulses of the rectangular pulse waveform 202. The third sub-pulse width 258 is the duration during which each of the sub-pulses of the rectangular pulse waveform 252, such as sub-pulse 254A and sub-pulse 254B, occurs.

[0057] Sub-pulse 254A extends from time t10 to time t11, and sub-pulse 254B extends from time t30 to time t31. Also, at time t10, sub-pulse 254A has a voltage value -V4. Sub-pulse 254A transitions upward from the voltage value -V4 to a peak voltage V3. The upward transition occurs from time t10 to time t10.5, and the peak voltage V3 is achieved by sub-pulse 254A at time t10.5. Sub-pulse 254A transitions downward from the peak voltage to a voltage value -V4, which occurs at time t11. The downward transition occurs from time t10.5 to time t11. Similarly, sub-pulse 254B extends from time t30 to time t31, and achieves a peak voltage V3 at time t30.5.

[0058] RF voltage ringing, such as RF voltage ringing 256A and RF voltage ringing 256B, is associated with each preceding sub-pulse of rectangular pulse waveform 252. For example, each sub-pulse of rectangular pulse waveform 252 is immediately followed by an RF voltage ringing. Illustratively, sub-pulse 254A precedes RF voltage ringing 256A, and sub-pulse 254B precedes RF voltage ringing 256B.

[0059] Note that the ringing width 260 of each RF voltage ringing associated with each preceding sub-pulse of the rectangular pulse waveform 252 is greater than the ringing width 222 (FIG. 2B). When the third sub-pulse width 258 is less than the second sub-pulse width 216, the ringing width 260 is greater than the ringing width 222.

[0060] 2D is a graph 270 illustrating a square pulse waveform 272 to provide an example of a decrease in peak value of each sub-pulse of square pulse waveform 202 (FIG. 2A) with an increase in second sub-pulse width 216 (FIG. 2A). Square pulse waveform 272 is yet another example of square pulse waveform 132 (FIG. 1). Graph 270 plots the voltage of square pulse waveform 272 versus time t. The voltage of square pulse waveform 272 is plotted on the y-axis of graph 270, and time t is plotted on the x-axis of graph 270. The x-axis of graph 270 is the same as the x-axis of graph 201 (FIG. 2A), and the y-axis of graph 270 is the same as the y-axis of graph 200 (FIG. 2B).

[0061] Square pulse waveform 272 is the same as square pulse waveform 202 ( FIG. 2B ), except that square pulse waveform 272 has a fourth sub-pulse width 278 that is larger compared to second sub-pulse width 216. When fourth sub-pulse width 278 is larger than second sub-pulse width 216, the peak voltages of the sub-pulses of square pulse waveform 272, such as sub-pulse 274A and sub-pulse 274B, are lower than the peak voltages of the sub-pulses of square pulse waveform 202. For example, the peak voltage of the sub-pulses of square pulse waveform 272 is −V1, which is less than the peak voltage V0 of the sub-pulses of square pulse waveform 202. Fourth sub-pulse width 272 is the period during which each of the sub-pulses of square pulse waveform 272, such as sub-pulse 274A and sub-pulse 274B, occurs.

[0062] Sub-pulse 274A extends from time t10 to time t13, and sub-pulse 274B extends from time t30 to time t33. Also, at time t10, sub-pulse 274A has a voltage value -V4. Sub-pulse 274A transitions upward from a voltage value -V4 to a peak voltage -V1. The upward transition occurs from time t10 to time t11, and the peak voltage -V1 is achieved by sub-pulse 274A at time t11. Sub-pulse 274A transitions downward from the peak voltage to a voltage value -V4, which occurs at time t13. The downward transition occurs from time t11 to time t13. Similarly, sub-pulse 274B extends from time t30 to time t33, and achieves a peak voltage -V1 at time t31.

[0063] RF voltage ringing, such as RF voltage ringing 276A and RF voltage ringing 276B, is associated with each preceding sub-pulse of rectangular pulse waveform 272. For example, each sub-pulse of rectangular pulse waveform 272 is immediately followed by an RF voltage ringing. Illustratively, sub-pulse 274A precedes RF voltage ringing 276A, and sub-pulse 274B precedes RF voltage ringing 276B.

[0064] Note that the ringing width 280 of each RF voltage ringing associated with each preceding sub-pulse of the rectangular pulse waveform 272 is less than the ringing width 222 (FIG. 2B). When the fourth sub-pulse width 278 is greater than the second sub-pulse width 216, the ringing width 280 is less than the ringing width 222.

[0065] 3 is a block diagram of an embodiment of a system 300 to illustrate a method for controlling LF RF pulse generator 104. System 300 includes controller 102 and LF RF pulse generator 104. Transmission cable 120 includes channel 302 and channel 304. An example channel includes a logical operation, such as a frequency range, for transmitting data. Illustratively, data transmitted via channel 302 is multiplexed with data transmitted via channel 304.

[0066] The processor 108 of the controller 102 executes a method 306 for controlling the LF RF pulse generator 104 to generate the rectangular pulse waveform 132. The method 306 includes an operation 308 for generating one or more instructions for the LF RF pulse generator 104 to generate pulses, such as pulse 204A and pulse 204B (FIG. 2A), periodically at a low frequency to have a pulse width 224 (FIG. 2A). The one or more instructions of operation 308 further indicate that each of the pulses, such as pulse 204A and pulse 204B, should be generated to have a first sub-pulse width 212 (FIG. 2A). For example, the one or more instructions of operation 308 include a command to generate pulse 204A having the first sub-pulse width 212. Also, in this example, the one or more instructions of operation 308 include a command to generate pulse 204B having the first sub-pulse width 212. In this example, the command to generate pulse 204B is to generate pulse 204B at the end of pulse width 224. Pulse width 224 provides a period for generating a pulse of rectangular pulse waveform 132. By way of example, pulse width 224 and first sub-pulse width 212 are received from a user via an input device such as a mouse, keyboard, keypad, touch screen, stylus, or a combination thereof. The input device is connected to processor 108 via an input / output interface.

[0067] Method 306 further includes an operation 310 of generating one or more instructions to LF RF pulse generator 104 to wait a predetermined amount of phase delay, such as ringing width 220 (FIG. 2A), after generating each individual pulse of rectangular pulse waveform 132, such as pulse 204A or pulse 204B. For example, the one or more instructions include a command to wait a predetermined amount of phase delay after generating pulse 204A and a command to wait a predetermined amount of phase delay after generating pulse 204B. The predetermined amount of phase delay is sometimes referred to herein as a predetermined amount of time.

[0068] The one or more instructions of operation 310 include a command for determining whether a predetermined amount of phase delay has elapsed since each of the pulses of the rectangular pulse waveform 132 was generated. If the predetermined amount of phase delay has not elapsed, the one or more instructions of operation 310 include a command for waiting for the predetermined amount of phase delay to elapse. On the other hand, if the predetermined amount of phase delay has elapsed, the method 306 proceeds to operation 312. As one example, the ringing width 220 is received from a user via an input device. As another example, the ringing width 220 is empirical data determined by experimentation.

[0069] Method 306 includes operation 312, in which one or more instructions are generated for LF RF pulse generator 104 to generate a respective one of the sub-pulses, such as sub-pulse 206A (FIG. 2A) or sub-pulse 206B, having a second sub-pulse width 216 (FIG. 2A) after a predetermined amount of phase delay has elapsed. The sub-pulses of operation 312 are of rectangular pulse waveform 132. For example, the one or more instructions of operation 312 include a command to generate sub-pulse 206A a predetermined amount of phase delay after pulse 204A is generated. In this example, the one or more instructions of operation 312 include a command to generate sub-pulse 206B a predetermined amount of phase delay after pulse 204B is generated.

[0070] The instructions for operations 308 and 310 are transmitted by processor 108 to LF RF pulse generator 104 over channel 302, and one or more instructions for operation 312 are transmitted by processor 108 to LF RF pulse generator 104 over channel 304. Upon receiving the instructions for operations 308, 310, and 312, the processor of LF RF pulse generator 104 stores the instructions and information related to rectangular pulse waveform 202 in a memory device of LF RF pulse generator 104.

[0071] Upon receiving the trigger signal 134, the processor of the LF RF pulse generator 104 accesses instructions for operations 308, 310, and 312 and information regarding the rectangular pulse waveform 202 from a memory device of the LF RF pulse generator 104 and controls the signal components of the LF RF pulse generator 104 to generate the rectangular pulse waveform 132 in accordance with the instructions and information regarding the rectangular pulse waveform 202. The rectangular pulse waveform 132 is sent from the signal components via RF cable 124 for delivery to the plasma chamber 106 (FIG. 1).

[0072] Method 306 includes operation 314 of generating one or more instructions to modify second sub-pulse width 216. For example, processor 108 generates a command to decrease second sub-pulse width 216 to third sub-pulse width 258 (FIG. 2C). As another example, processor 108 generates a command to increase second sub-pulse width 216 to fourth sub-pulse width 278 (FIG. 2D). The one or more instructions of operation 314 are generated upon receiving input to modify second sub-pulse width 216 from an input device. The input to modify second sub-pulse width 216 is generated by the input device upon one or more selections made by a user via the input device. The input received from the input device includes second sub-pulse width 216 or third sub-pulse width 258. Processor 108 transmits the one or more instructions of operation 314 to a processor of LF RF pulse generator 104 via channel 304. Upon receiving the one or more instructions of operation 314, LF RF pulse generator 104 modifies second sub-pulse width 216 to another sub-pulse width, such as third sub-pulse width 258 or fourth sub-pulse width 278, and outputs another rectangular pulse waveform, such as rectangular pulse waveform 252 (FIG. 2C) or rectangular pulse waveform 272 (FIG. 2D).

[0073] In one embodiment, one or more instructions for operation 308 are transmitted by processor 108 to LF RF pulse generator 104 via channel 302, and instructions for operations 310 and 312 are transmitted by processor 108 to LF RF pulse generator 104 via channel 304.

[0074] 4 is a diagram of one embodiment of a system 400 to illustrate control of LF RF pulse generator 104 by processor 108 of controller 102 (FIG. 1). System 400 includes controller 102 and LF RF pulse generator 104. LF RF pulse generator 104 includes signal components 402 and controller 404. Signal components 402 include voltage source and regulator 406, power storage 408, and switch and transformer system 410. As an example, RF voltage ringing as described herein is noise due to one or more of signal components 402.

[0075] An example of a voltage source and regulator 302 includes a combination of a voltage source, such as a direct current (DC) voltage source, and a voltage regulator, such as a variable resistor. The voltage source is connected to the voltage regulator. An example of a switch and transformer system 410 includes a combination of a switch, such as a solid-state switch, and a transformer. An example of a solid-state switch is a single transistor or a group of transistors. The solid-state switch is connected to a transformer. In one example, the transformer includes a primary winding and a secondary winding. In one example, the power storage unit 408 includes a capacitor.

[0076] The controller 404 includes a processor 412 and a memory device 414. The processor 412 is coupled to the memory device 414. As another example, the controller 404 is an ASIC or a PLD.

[0077] The processor 108 of the controller 102 is connected to a processor 412 via a transfer cable 120. The processor 412 is connected to the switches of the switch-transformer system 410. The voltage regulator of the voltage source-regulator 302 is connected to a power storage unit 408.

[0078] Furthermore, the power storage unit 408 is connected to a transformer, and the switch is connected to the transformer. For example, the power storage unit 408 is connected to a first end of a primary winding, and the switch is connected to a second end of the primary winding. The secondary winding of the transformer is connected to the RF cable 138.

[0079] Upon receiving the instructions for operations 308, 310, and 312 and information regarding the rectangular pulse waveform 202 in the recipe signal 130 from the processor 108, the processor 412 stores the instructions and information in a memory device 414. The voltage source generates a voltage signal and provides the voltage signal to a voltage regulator. The voltage regulator adjusts the voltage signal, such as maintaining the voltage signal to match a predetermined voltage signal, and outputs an adjusted voltage signal and sends the adjusted voltage signal to the power storage unit 408. The power storage unit 408 stores charge according to the adjusted voltage signal.

[0080] Further, in response to receiving the trigger signal 134 from the processor 108 of the controller 102, the processor 412 accesses the first sub-pulse width 212 (FIG. 2B) and the instructions of operations 308 and 310 (FIG. 3) from the memory device 414. To control the signal component 402 according to the one or more instructions of operation 308, the processor 412 generates an ON command signal and sends the ON command signal to the switch. Upon receiving the ON command signal, the switch is turned ON, and a switch current signal generated to discharge the charge stored in the power storage unit 408 is supplied to the primary winding of the transformer for the first sub-pulse width 212. The secondary winding transforms, such as by increasing or decreasing the voltage magnitude of the switch current signal to a different amount, and outputs the transformed voltage magnitude to initiate generation of the pulse 204A (FIG. 2B). The transformed voltage magnitude is that of the pulse 204A.

[0081] At the end of the first sub-pulse width 212 period, the processor 412 generates an OFF command signal and sends the OFF command signal to the switch. Upon receiving the OFF command signal, the switch turns OFF and stops supplying the switch current signal to the primary winding. When the supply of the switch current signal stops, the voltage applied by the switch current signal decreases, reducing the voltage across the primary winding. As the voltage across the primary winding decreases, the transformed voltage amount decreases, terminating the generation of the pulse 204A and outputting the reduced transformed voltage amount. The reduced transformed voltage amount is that of the RF voltage ringing 208A (FIG. 2A).

[0082] To control the signal component 402 based on the one or more instructions of operation 310, the processor 412 determines whether a predetermined amount of phase delay has occurred since the off command signal was sent from the processor 412 to the switch based on the timing provided by the clock signal 202. Upon determining that the predetermined amount of phase delay has occurred, the processor 412 accesses the one or more instructions of operation 312 and the second sub-pulse width 216 from the memory device 414 to control the signal component 402 based on the one or more instructions of operation 312.

[0083] To control the signal component 402 based on the one or more instructions of operation 312, the processor 412 generates an on command signal and sends the on command signal to the switch. Upon receiving the on command signal, the switch is turned on, and a switch current signal generated to discharge the charge stored in the power storage unit 408 is supplied to the primary winding of the transformer for the duration of the second sub-pulse width 216. The secondary winding transforms, such as by increasing or decreasing the voltage magnitude of the switch current signal to a different amount, and outputs the transformed voltage magnitude, thereby initiating the generation of the sub-pulse 206A (FIG. 2B). The transformed voltage magnitude is the voltage of the sub-pulse 206A.

[0084] At the end of the period of the second sub-pulse width 216, the processor 412 generates an OFF command signal and sends the OFF command signal to the switch. Upon receiving the OFF command signal in operation 312, the switch turns OFF and stops supplying the switch current signal to the primary winding. When the supply of the switch current signal stops, the voltage applied by the switch current signal decreases, reducing the voltage across the primary winding. When the voltage across the primary winding decreases, the transformed voltage amount decreases, terminating the generation of the sub-pulse 206A and outputting the reduced transformed voltage amount. The reduced transformed voltage amount is that of the RF voltage ringing 210A (FIG. 2A).

[0085] After sending the OFF command signal at the end of the second sub-pulse width period, processor 412 accesses pulse width 224 from memory device 414 and determines, based on the one or more instructions of operation 308 and pulse width 224, whether the period of pulse width 224 (FIG. 2B) occurred after the ON command signal to generate pulse 204A was sent to the switch. If processor 412 determines that pulse width 224 occurred after the ON command to generate pulse 204A was sent, processor 412 determines to generate an ON command signal to generate pulse 204B (FIG. 2A). In this manner, the pulses and sub-pulses of rectangular pulse waveform 202 are repeated.

[0086] Furthermore, upon receiving one or more instructions of operation 314 (FIG. 3) to modify second sub-pulse width 216 to another sub-pulse width, processor 412 stores the other sub-pulse width in memory device 414 and determines whether an end of RF voltage ringing associated with the respective preceding pulse has occurred. For example, processor 412 determines whether an end of a predetermined amount of phase delay of ringing width 220 has occurred, occurring immediately after pulse 204B (FIG. 2B), based on clock signal 202. Upon determining that an end of the predetermined amount of phase delay of ringing width 220 has occurred, processor 412 accesses the other sub-pulse width from memory device 414 and generates on and off command signals based on the other sub-pulse width. The on and off command signals are generated in the same manner as the on and off command signals for generating second sub-pulse width 216, except that the off command signal for the other sub-pulse width is generated at the end of the period of the other sub-pulse width.

[0087] In one embodiment, instead of generating one or more instructions for generating second sub-pulse width 216, one or more instructions for generating other sub-pulse widths, such as third sub-pulse width 258 or fourth sub-pulse width 278, are generated by processor 108. The one or more instructions for generating the other sub-pulse widths are transmitted from processor 108 to processor 412 via transmission cable 120. Processor 412 generates on and off command signals and applies the on and off command signals to control signal component 402 to generate sub-pulses having the other sub-pulse widths in the same manner as it applies the on and off command signals to control signal component 402 to generate each of the sub-pulses having second sub-pulse width 216.

[0088] FIG. 5 is a graph 500 illustrating that selectivity, such as mask selectivity, increases with increasing voltage of the sub-pulses of the rectangular pulse waveform 202 (FIG. 2B). One example of mask selectivity is the ratio of the rate at which a mask layer of the substrate S is etched to the rate at which a layer or feature of the substrate S desired to be etched is etched. Graph 500 plots the etch rate of the substrate S (FIG. 1) on a first y-axis, the selectivity on a second y-axis, and the kilovolts (kV) of the sub-pulses of the rectangular pulse waveform 202. As illustrated in graph 500, increasing the voltage, such as the peak voltage, of the sub-pulses of the rectangular pulse waveform 202 increases the mask selectivity, while the process rate, such as the etch rate, remains approximately constant. In this manner, mask selectivity is controlled by increasing or decreasing the voltage of the sub-pulses of the rectangular pulse waveform 202.

[0089] 6 is a graph 600 illustrating the change in voltage at the bottom plasma sheath 115B (FIG. 1) with the introduction of sub-pulses of a rectangular pulse waveform 202 (FIG. 2B). Graph 600 plots the voltage at the bottom plasma sheath 115B versus time t. When sub-pulses of a rectangular pulse waveform 202 are included in addition to pulses of the rectangular pulse waveform 202, a decrease in the voltage at the bottom plasma sheath 115B is observed compared to when only pulses are used with the rectangular pulse waveform. In this manner, the voltage at the bottom plasma sheath 115B is controlled using the sub-pulses of the rectangular pulse waveform 202.

[0090] It should be noted that although the above embodiments have been described with reference to rectangular pulse waveforms, in some embodiments the terms triangular pulse waveform, sawtooth pulse waveform, and rectangular pulse waveform are used interchangeably herein.

[0091] Broadly speaking, in various embodiments, a controller is defined as an electronic device having various integrated circuits, logic, memory, and / or software that receives instructions, issues instructions, controls operations, enables cleaning operations, enables endpoint measurements, etc. Integrated circuits include chips in the form of firmware that store program instructions, digital signal processors (DSPs), chips defined as (ASICs), PLDs, and / or one or more microprocessors or microcontrollers that execute program instructions (e.g., software). Program instructions are instructions communicated to the controller in the form of various individual settings (or program files) that define parameters, factors, variables, etc. for performing a particular process on or for a semiconductor wafer or for a system. In some embodiments, the program instructions are part of a recipe defined by a process engineer to accomplish one or more processing steps during the manufacture of one or more layers, materials, metals, oxides, silicon, silicon dioxide, surfaces, circuits, and / or dies of a wafer.

[0092] In various embodiments, examples of systems to which the methods may be applied include, but are not limited to, a plasma etch chamber or module, a deposition chamber or module, a spin rinse chamber or module, a metal plating chamber or module, a cleaning 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, 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 semiconductor processing system associated with or used in the fabrication and / or manufacturing of semiconductor wafers.

[0093] It is further noted that in some embodiments, the operations described above apply to several types of plasma chambers, such as plasma chambers including inductively coupled plasma (ICP) reactors, transformer-coupled plasma chambers, conductor tools, dielectric tools, and plasma chambers including electron cyclotron resonance (ECR) reactors. For example, one or more RF generators are connected to an inductor in an ICP reactor. Example shapes of the inductor include a solenoid, a dome-shaped coil, a flat-shaped coil, and the like.

[0094] Some embodiments also relate to hardware units or apparatus for performing these operations, where the apparatus is specifically made for a special purpose computer. When defined as a special purpose computer, the computer is operable for a special purpose, but also performs other processes, programs, or routines that do not belong to the special purpose.

[0095] One or more embodiments may also be fabricated as computer-readable code on a non-transitory computer-readable medium. The non-transitory computer-readable medium is any data storage hardware unit, such as a memory device, that stores data, which is subsequently read by a computer system. Examples of non-transitory computer-readable media include hard drives, network-attached storage (NAS), ROM, RAM, compact disc ROMs (CD-ROMs), CD-recordables (CD-Rs), CD-rewritables (CD-RWs), magnetic tape, and other optical and non-optical data storage hardware units. In some embodiments, the non-transitory computer-readable medium comprises a computer-readable tangible medium distributed over network-coupled computer systems so that the computer-readable code is stored and executed in a distributed fashion.

[0096] Although the method operations described above have been described in a particular order, it should be understood that in various embodiments, other housekeeping operations may be performed between operations, the method operations may be arranged to occur at slightly different times, may be distributed in a system that allows the method operations to occur at various intervals, or may be performed in an order different from that described above.

[0097] It is further noted that in one embodiment, one or more features from any of the above-described embodiments may be combined with one or more features of any other of the above-described embodiments without departing from the scope set forth in the various embodiments described in this disclosure.

[0098] 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 may be practiced within the scope of the appended claims. The present embodiments are therefore to be considered as illustrative and not restrictive, and the embodiments are not to be limited to the details given herein.

Claims

1. 1. A method for controlling a low frequency (LF) radio frequency (RF) pulse generator to enhance selectivity, comprising: controlling the LF RF pulse generator to generate a plurality of rectangular pulses interspersed with a plurality of rectangular sub-pulses, each of the plurality of rectangular pulses having a first sub-pulse width greater than a second sub-pulse width of each of the plurality of rectangular sub-pulses, wherein controlling the LF RF pulse generator comprises: controlling the LF RF pulse generator to generate one of the plurality of rectangular pulses; determining whether a predetermined amount of time has elapsed since controlling the LF RF pulse generator to generate the one of the plurality of rectangular pulses; controlling the LF RF pulse generator to generate one of the plurality of rectangular sub-pulses upon determining that the predetermined amount of time has elapsed; The method, wherein controlling the LF RF pulse generator to generate the plurality of rectangular sub-pulses enhances the selectivity.

2. 2. The method of claim 1, further comprising controlling the second sub-pulse width of each of the plurality of rectangular sub-pulses to modify a peak voltage associated with each of the plurality of rectangular sub-pulses.

3. 3. The method of claim 2, wherein controlling the second sub-pulse width comprises: Increasing the second sub-pulse width to increase the peak voltage; Decreasing the second sub-pulse width to decrease the peak voltage. A method comprising:

4. 2. The method of claim 1, wherein the one of the plurality of rectangular sub-pulses is located between two adjacent rectangular pulses of the plurality of rectangular pulses for the plurality of rectangular pulses interspersed with the plurality of rectangular sub-pulses.

5. 2. The method of claim 1, wherein the one of the plurality of rectangular pulses is a first rectangular pulse, the plurality of rectangular pulses includes a second rectangular pulse, the one of the plurality of rectangular sub-pulses is a first rectangular sub-pulse, and the plurality of rectangular sub-pulses includes a second rectangular sub-pulse; For the plurality of rectangular pulses interspersed with the plurality of rectangular sub-pulses, the first rectangular pulse is followed by a first RF ringing, the first RF ringing is followed by the first rectangular sub-pulse, the first rectangular sub-pulse is followed by a second RF ringing, the second RF ringing is followed by the second rectangular pulse, the second rectangular pulse is followed by a third RF ringing, the third RF ringing is followed by the second rectangular sub-pulse, and the second rectangular sub-pulse is followed by a fourth RF ringing. method.

6. 2. The method of claim 1, wherein controlling the LF RF pulse generator to generate the plurality of rectangular pulses is performed by a controller connected to the LF RF pulse generator.

7. 2. The method of claim 1, wherein the plurality of rectangular sub-pulses includes a first rectangular sub-pulse and a second rectangular sub-pulse, the first rectangular sub-pulse being followed by noise, and the second RF sub-pulse being followed by noise.

8. 2. The method of claim 1, wherein each of the plurality of pulses is non-sinusoidal and each of the plurality of rectangular sub-pulses is non-sinusoidal.

9. 1. A controller for controlling a low frequency (LF) radio frequency (RF) pulse generator to enhance selectivity, comprising: a processor configured to control the LF RF pulse generator to generate a plurality of rectangular pulses interspersed with a plurality of rectangular sub-pulses, each of the plurality of rectangular pulses having a first sub-pulse width greater than a second sub-pulse width of each of the plurality of rectangular sub-pulses, and to control the LF RF pulse generator, the processor controlling the LF RF pulse generator to generate one of the plurality of rectangular pulses; determining whether a predetermined amount of time has elapsed since the LF RF pulse generator was controlled to generate said one of said plurality of rectangular pulses; a processor configured to control the LF RF pulse generator to generate one of the plurality of rectangular sub-pulses upon determining that the predetermined amount of time has elapsed; a memory device coupled to said processor; A controller comprising:

10. 10. The controller of claim 9, wherein the processor is configured to control the second sub-pulse width of each of the plurality of rectangular sub-pulses to modify a peak voltage associated with each of the plurality of rectangular sub-pulses.

11. 11. The controller of claim 10, wherein to control the second sub-pulse width, the processor: Increasing the second sub-pulse width to increase the peak voltage; The width of the second sub-pulse is decreased to decrease the peak voltage. The controller is configured as follows:

12. 10. The controller of claim 9, wherein the one of the plurality of rectangular sub-pulses is located between two adjacent rectangular pulses of the plurality of rectangular pulses for the plurality of rectangular pulses interspersed with the plurality of rectangular sub-pulses.

13. 10. The controller of claim 9, wherein the one of the plurality of rectangular pulses is a first rectangular pulse, the plurality of rectangular pulses includes a second rectangular pulse, the one of the plurality of rectangular sub-pulses is a first rectangular sub-pulse, and the plurality of rectangular sub-pulses includes a second rectangular sub-pulse; For the plurality of rectangular pulses interspersed with the plurality of rectangular sub-pulses, the first rectangular pulse is followed by a first RF ringing, the first RF ringing is followed by the first rectangular sub-pulse, the first rectangular sub-pulse is followed by a second RF ringing, the second RF ringing is followed by the second rectangular pulse, the second rectangular pulse is followed by a third RF ringing, the third RF ringing is followed by the second rectangular sub-pulse, and the second rectangular sub-pulse is followed by a fourth RF ringing. controller.

14. 10. The controller of claim 9, wherein the processor is connected to the LF RF pulse generator via a transfer cable.

15. 10. The controller of claim 9, wherein the plurality of rectangular sub-pulses includes a first rectangular sub-pulse and a second rectangular sub-pulse, the first rectangular sub-pulse being followed by noise, and the second RF sub-pulse being followed by noise.

16. 10. The controller of claim 9, wherein each of the plurality of pulses is non-sinusoidal and each of the plurality of rectangular sub-pulses is non-sinusoidal.

17. 1. A plasma system comprising: a low frequency (LF) radio frequency (RF) pulse generator; a plasma chamber connected to the LF RF pulse generator via an RF cable; a controller connected to the LF RF pulse generator; Equipped with The controller is configured to control the LF RF pulse generator to generate a plurality of rectangular pulses interspersed with a plurality of rectangular sub-pulses, each of the plurality of rectangular pulses having a first sub-pulse width greater than a second sub-pulse width of each of the plurality of rectangular sub-pulses, and to control the LF RF pulse generator, the controller controlling the LF RF pulse generator to generate one of the plurality of rectangular pulses; determining whether a predetermined amount of time has elapsed since the LF RF pulse generator was controlled to generate said one of said plurality of rectangular pulses; Upon determining that the predetermined amount of time has elapsed, controlling the LF RF pulse generator to generate one of the plurality of rectangular sub-pulses. It is configured as follows: Plasma system.

18. 20. The plasma system of claim 17, wherein the LF RF pulse generator is connected to the plasma chamber without using a match box between the LF RF pulse generator and the plasma chamber.

19. 18. The plasma system of claim 17, wherein the controller is configured to control the second sub-pulse width of each of the plurality of rectangular sub-pulses to modify a peak voltage associated with each of the plurality of rectangular sub-pulses, and to control the second sub-pulse width, the controller: Increasing the second sub-pulse width to increase the peak voltage; The width of the second sub-pulse is decreased to decrease the peak voltage. The plasma system is configured as follows.

20. 18. The plasma system of claim 17, wherein the one of the plurality of rectangular pulses is a first rectangular pulse, the plurality of rectangular pulses includes a second rectangular pulse, the one of the plurality of rectangular sub-pulses is a first rectangular sub-pulse, and the plurality of rectangular sub-pulses includes a second rectangular sub-pulse; for the plurality of rectangular pulses interspersed with the plurality of rectangular sub-pulses, the first rectangular pulse is followed by a first RF ringing, the first RF ringing is followed by the first rectangular sub-pulse, the first rectangular sub-pulse is followed by a second RF ringing, the second RF ringing is followed by the second rectangular pulse, the second rectangular pulse is followed by a third RF ringing, the third RF ringing is followed by the second rectangular sub-pulse, and the second rectangular sub-pulse is followed by a fourth RF ringing; each of the plurality of pulses is non-sine wave and each of the plurality of rectangular sub-pulses is non-sine wave; Plasma system.

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