Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
  • H01J37/32—Gas-filled discharge tubes
  • H01J37/32009—Arrangements for generation of plasma specially adapted for examination or treatment of objects, e.g. plasma sources
  • H01J37/32082—Radio frequency generated discharge
  • H01J37/32091—Radio frequency generated discharge the radio frequency energy being capacitively coupled to the plasma
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
  • H01J37/32—Gas-filled discharge tubes
  • H01J37/32009—Arrangements for generation of plasma specially adapted for examination or treatment of objects, e.g. plasma sources
  • H01J37/32082—Radio frequency generated discharge
  • H01J37/32137—Radio frequency generated discharge controlling of the discharge by modulation of energy
  • H01J37/32146—Amplitude modulation, includes pulsing
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
  • H01J37/32—Gas-filled discharge tubes
  • H01J37/32009—Arrangements for generation of plasma specially adapted for examination or treatment of objects, e.g. plasma sources
  • H01J37/32422—Arrangement for selecting ions or species in the plasma
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
  • H01J37/32—Gas-filled discharge tubes
  • H01J37/32431—Constructional details of the reactor
  • H01J37/32697—Electrostatic control
  • H01J37/32706—Polarising the substrate
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
  • H01J37/32—Gas-filled discharge tubes
  • H01J37/32431—Constructional details of the reactor
  • H01J37/32715—Workpiece holder
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
  • H01J2237/248—Components associated with the control of the tube
  • H01J2237/2485—Electric or electronic means
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
  • H01J37/32—Gas-filled discharge tubes
  • H01J37/32431—Constructional details of the reactor
  • H01J37/32697—Electrostatic control

Definitions

• TITLE A METHOD OF CONTROLLING THE SWITCHED MODE ION ENERGY
• the present disclosure relates generally to plasma processing.
• the present invention relates to methods and apparatuses for plasma-assisted etching, deposition, and/or other plasma-assisted processes.
• the substrate is a dielectric, however, a non-varying voltage is ineffective to place a voltage across the surface of the substrate.
• an AC voltage e.g., high frequency
• the conductive plate or chuck
• the AC field induces a voltage on the surface of the substrate.
• the substrate attracts electrons, which are light relative to the mass of the positive ions; thus many electrons will be attracted to the surface of the substrate during the positive part of the cycle.
• the surface of the substrate will be charged negatively, which causes ions to be attracted toward the negatively-charged surface.
• the impact dislodges material from the surface of the substrate— effectuating the etching.
• the invention may be characterized as a method for establishing one or more plasma sheath voltages.
• the method may comprise providing a modified periodic voltage function to a substrate support of a plasma chamber.
• the substrate support can be coupled to a substrate that is configured for processing in the plasma.
• the modified periodic voltage function can comprise a periodic voltage function modified by an ion current compensation, Ic.
• the modified periodic voltage function can comprise pulses and a portion between the pulses.
• the pulses can be a function of the periodic voltage function, and a slope of the portion between the pulses can be a function of the ion current compensation, Ic
• the method can further comprise accessing an effective capacitance value, C l5 that represents at least a capacitance of the substrate support.
• the method finally can identify a value of the ion current compensation, Ic, that will result in a defined ion energy distribution function of ions reaching a surface of the substrate, where the identifying is a function of the effective capacitance, C l5 a slope, dVo/dt, of the portion between the pulses.
• the invention may be described as a method for biasing a plasma so as to achieve a defined ion energy at a surface of a substrate within a plasma processing chamber.
• the method may include applying a modified periodic voltage function comprising a periodic voltage function modified by an ion current compensation to a substrate support.
• the method may further include sampling at least one cycle of the modified periodic voltage function to generate voltage data points.
• the method may further include estimating a value of a first ion energy at the substrate surface from the voltage data points.
• the method may include adjusting the modified periodic voltage function until the first ion energy equals the define ion energy.
• the invention may be characterized as a method to achieve an ion energy distribution function width.
• the method may include providing a modified periodic voltage function to a substrate support of a plasma processing chamber.
• the method may further include sampling at least two voltages from the non-sinusoidal waveform at a first time and at a second time.
• the method can additionally include calculating a slope of the at least two voltages as dV/dt.
• the method may include comparing the slope to a reference slope known to correspond to an ion energy distribution function width.
• the method may include adjusting the modified periodic voltage function so that the slope approaches the reference slope.
• Another aspect of the disclosure can be characterized as an apparatus comprising a power supply, an ion current compensation component, and a controller.
• the power supply can provide a periodic voltage function having pulses and a portion between the pulses.
• the ion current compensation component can modify a slope of the portion between the pulses to form a modified periodic voltage function.
• the modified period voltage function can be configured for providing to a substrate support for processing in a plasma processing chamber.
• the controller can be coupled to the switch-mode power supply and the ion current compensation component.
• the controller can also be configured to identify a value of the ion current compensation that if provided to the substrate support, would result in a defined ion energy distribution function of ions reaching a surface of the substrate.
• Yet another aspect of the disclosure can be characterized as a non-transitory, tangible computer readable storage medium, encoded with processor readable instructions to perform a method for monitoring an ion current of a plasma configured to process a substrate.
• the method can include sampling a modified periodic voltage function given an ion current compensation having a first value, and sampling the modified periodic voltage function given the ion current compensation having a second value.
• the method further can include determining a slope of the modified periodic voltage function as a function of time based on the first and second sampling.
• the method also determines a slope of the modified periodic voltage function as a function of time based on the first and second sampling.
• the method finally can include calculating a third value of the ion current compensation, based on the slope, at which a constant voltage on the substrate will exist for at least one cycle of the modified periodic voltage function.
• FIG. 1 illustrates a block diagram of a plasma processing system in accordance with one implementation of the present invention
• FIG. 2 is a block diagram depicting an exemplary embodiment of the switch- mode power system depicted in FIG. 1;
• FIG. 3 is a schematic representation of components that may be utilized to realize the switch-mode bias supply described with reference to FIG. 2;
• FIG. 4 is a timing diagram depicting two drive signal waveforms;
• FIG. 5 is a graphical representation of a single mode of operating the switch mode bias supply, which effectuates an ion energy distribution that is concentrated at a particular ion energy;
• FIG. 6 are graphs depicting a bi-modal mode of operation in which two separate peaks in ion energy distribution are generated
• FIGS. 7 A and 7B are is are graphs depicting actual, direct ion energy
• FIG. 8 is a block diagram depicting another embodiment of the present invention.
• FIG. 9A is a graph depicting an exemplary periodic voltage function that is modulated by a sinusoidal modulating function
• FIG. 9B is an exploded view of a portion of the periodic voltage function that is depicted in FIG. 9A;
• FIG. 9C depicts the resulting distribution of ion energies, on time-averaged basis, that results from the sinusoidal modulation of the periodic voltage function
• FIG. 9D depicts actual, direct, ion energy measurements made in a plasma of a resultant, time averaged, IEDF when a periodic voltage function is modulated by a sinusoidal modulating function;
• FIG. 10A depicts a periodic voltage function is modulated by a sawtooth modulating function
• FIG. 10B is an exploded view of a portion of the periodic voltage function that is depicted in FIG. 10A;
• FIG. IOC is a graph depicting the resulting distribution of ion energies, on a time averaged basis, that results from the sinusoidal modulation of the periodic voltage function in FIGS. 10A and 10B;
• FIG. 11 are graphs showing IEDF functions in the right column and associated modulating functions in the left column;
• FIG. 12 is a block diagram depicting an embodiment in which an ion current compensation component compensates for ion current in a plasma chamber
• FIG. 13 is a diagram depicting an exemplary ion current compensation component
• FIG. 14 is a graph depicting an exemplary voltage at node Vo depicted in FIG.
• FIGS. 15A-15C are voltage waveforms as appearing at the surface of the substrate or wafer responsive to compensation current
• FIG. 16 is an exemplary embodiment of a current source, which may be implemented to realize the current source described with reference to FIG. 13;
• FIGS. 17 A and 17B are block diagrams depicting other embodiments of the present invention.
• FIG. 18 is a block diagram depicting yet another embodiment of the present invention.
• FIG. 19 is a block diagram depicting still another embodiment of the present invention.
• FIG. 20 is a block diagram input parameters and control outputs that may be utilized in connection with the embodiments described with reference to FIGS. 1-19;
• FIG. 21 is a block diagram depicting yet another embodiment of the present invention.
• FIG. 22 is a block diagram depicting yet another embodiment of the present invention.
• FIG. 23 is a block diagram depicting yet another embodiment of the present invention.
• FIG. 24 is a block diagram depicting yet another embodiment of the present invention.
• FIG. 25 is a block diagram depicting yet another embodiment of the present invention.
• FIG. 26 is a block diagram depicting yet another embodiment of the present invention.
• FIG. 27 is a block diagram depicting yet another embodiment of the present invention.
• FIG. 28 illustrates a method according to an embodiment of this disclosure
• FIG. 29 illustrates another method according to an embodiment of this disclosure.
• FIG. 30 illustrates one embodiment of a method of controlling an ion energy distribution of ions impacting a surface of a substrate
• FIG. 31 illustrates methods for setting the IEDF and the ion energy
• FIG. 32 illustrates two modified periodic voltage function waveforms delivered to the substrate support according to one embodiment of this disclosure
• FIG. 33 illustrates an ion current waveform that can indicate plasma source instability or changes in the plasma density
• FIG. 34 illustrates an ion current, 3 ⁇ 4, of a modified periodic voltage function waveform having a non-cyclical shape
• FIG. 35 illustrates a modified periodic voltage function waveform that can indicate faults within the bias supply
• FIG. 36 illustrates a modified periodic voltage function waveform that can be indicative of a dynamic change in the system capacitance
• FIG. 37 illustrates a modified periodic voltage function waveform that may be indicative of changes in plasma density
• FIG. 38 illustrates a sampling of ion current for different process runs, where drift in the ion current can indicate system drift
• FIG. 39 illustrates a sampling of ion current for different process parameters.
• FIG. 40 illustrates two bias waveforms monitored without a plasma in the chamber
• FIG. 41 illustrates two bias waveforms that can be used to validate a plasma process
• FIG. 42 illustrates a number of power supply voltages and ion energy plots showing the relationship between the power supply voltage and ion energy
• FIG. 43 illustrates one embodiment of a method of controlling an ion energy distribution of ions impacting a surface of a substrate
• FIG. 44 illustrates various waveforms at different points in the systems herein disclosed
• FIG. 45 illustrates the effects of making a final incremental change in ion current compensation, Ic, in order to match it to ion current 3 ⁇ 4;
• FIG. 46 illustrates selection of ion energy;
• FIG. 47 illustrates selection and expansion of the ion energy distribution function width
• FIG. 48 illustrates one pattern of the power supply voltage, Vps, that can be used to achieve more than one ion energy level where each ion energy level has a narrow IEDF width;
• FIG. 49 illustrates another pattern of the power supply voltage, Vps, that can be used to achieve more than one ion energy level where each ion energy level has a narrow IEDF width;
• FIG. 50 illustrates one combination of power supply voltages, Vps, and ion current compensation, I c , that can be used to create a defined IEDF.
• FIG. 1 An exemplary embodiment of a plasma processing system is shown generally in FIG. 1.
• a plasma power supply 102 is coupled to a plasma processing chamber 104 and a switch-mode power supply 106 is coupled to a support 108 upon which a substrate 110 rests within the chamber 104.
• a controller 112 that is coupled to the switch-mode power supply 106.
• the plasma processing chamber 104 may be realized by chambers of substantially conventional construction (e.g., including a vacuum enclosure which is evacuated by a pump or pumps (not shown)).
• the plasma excitation in the chamber 104 may be by any one of a variety of sources including, for example, a helicon type plasma source, which includes magnetic coil and antenna to ignite and sustain a plasma 114 in the reactor, and a gas inlet may be provided for introduction of a gas into the chamber 104.
• the exemplary plasma chamber 104 is arranged and configured to carry out plasma-assisted etching of materials utilizing energetic ion bombardment of the substrate 110, and other plasma processing (e.g., plasma deposition and plasma assisted ion implantation).
• the plasma power supply 102 in this embodiment is configured to apply power (e.g., RF power) via a matching network (not shown)) at one or more frequencies (e.g., 13.56 MHz) to the chamber 104 so as to ignite and sustain the plasma 114.
• frequencies e.g., 13.56 MHz
• the present invention is not limited to any particular type of plasma power supply 102 or source to couple power to the chamber 104, and that a variety of frequencies and power levels may be may be capacitively or inductively coupled to the plasma 114.
• a dielectric substrate 110 to be treated (e.g., a semiconductor wafer), is supported at least in part by a support 108 that may include a portion of a conventional wafer chuck (e.g., for semiconductor wafer processing).
• the support 108 may be formed to have an insulating layer between the support 108 and the substrate 110 with the substrate 110 being capacitively coupled to the platforms but may float at a different voltage than the support 108.
• the substrate 110 and support 108 are conductors, it is possible to apply a non-varying voltage to the support 108, and as a consequence of electric conduction through the substrate 110, the voltage that is applied to the support 108 is also applied to the surface of the substrate 110. [0019] When the substrate 110 is a dielectric, however, the application of a non- varying voltage to the support 108 is ineffective to place a voltage across the treated surface of the substrate 110.
• the exemplary switch-mode power supply 106 is configured to be controlled so as to effectuate a voltage on the surface of the substrate 110 that is capable of attracting ions in the plasma 114 to collide with the substrate 110 so as to carry out a controlled etching and/or deposition of the substrate 110, and/or other plasma-assisted processes.
• embodiments of the switch-mode power supply 106 are configured to operate so that there is an insubstantial interaction between the power applied (to the plasma 114) by the plasma power supply 102 and the power that is applied to the substrate 110 by the switch-mode power supply 106.
• the power applied by the switch-mode power supply 106 is controllable so as to enable control of ion energy without substantially affecting the density of the plasma 114.
• many embodiments of the exemplary switch-mode supply 106 depicted in FIG. 1 are realized by relatively inexpensive components that may be controlled by relatively simple control algorithms. And as compared to prior art approaches, many embodiments of the switch mode power supply 106 are much more efficient; thus reducing energy costs and expensive materials that are associated with removing excess thermal energy.
• One known technique for applying a voltage to a dielectric substrate utilizes a high-power linear amplifier in connection with complicated control schemes to apply power to a substrate support, which induces a voltage at the surface of the substrate.
• This technique has not been adopted by commercial entities because it has not proven to be cost effective nor sufficiently manageable.
• the linear amplifier that is utilized is typically large, very expensive, inefficient, and difficult to control.
• linear amplifiers intrinsically require AC coupling (e.g., a blocking capacitor) and auxiliary functions like chucking are achieved with a parallel feed circuit which harms AC spectrum purity of the system for sources with a chuck.
• Another technique that has been considered is to apply high frequency power (e.g., with one or more linear amplifiers) to the substrate.
• This technique has been found to adversely affect the plasma density because the high frequency power that is applied to the substrate affects the plasma density.
• the switch-mode power supply 106 depicted in FIG. 1 may be realized by buck, boost, and/or buck-boost type power technologies. In these embodiments, the switch-mode power supply 106 may be controlled to apply varying levels of pulsed power to induce a potential on the surface of the substrate 110.
• the switch-mode power supply 106 is realized by other more sophisticated switch mode power and control technologies.
• the switch-mode power supply described with reference to FIG. 1 is realized by a switch-mode bias supply 206 that is utilized to apply power to the substrate 110 to effectuate one or more desired energies of the ions that bombard the substrate 110.
• a switch-mode bias supply 206 that is utilized to apply power to the substrate 110 to effectuate one or more desired energies of the ions that bombard the substrate 110.
• an ion energy control component 220, an arc detection component 222, and a controller 212 that is coupled to both the switch-mode bias supply 206 and a waveform memory 224.
• the controller 212 which may be realized by hardware, software, firmware, or a combination thereof, may be utilized to control both the power supply 202 and switch-mode bias supply 206.
• the power supply 202 and the switch-mode bias supply 206 are realized by completely separated functional units.
• the controller 212, waveform memory 224, ion energy control portion 220 and the switch-mode bias supply 206 may be integrated into a single component (e.g., residing in a common housing) or may be distributed among discrete components.
• the switch-mode bias supply 206 in this embodiment is generally configured to apply a voltage to the support 208 in a controllable manner so as to effectuate a desired (or defined) distribution of the energies of ions bombarding the surface of the substrate. More specifically, the switch-mode bias supply 206 is configured to effectuate the desired (or defined) distribution of ion energies by applying one or more particular waveforms at particular power levels to the substrate. And more particularly, responsive to an input from the ion energy control portion 220, the switch-mode bias supply 206 applies particular power levels to effectuate particular ion energies, and applies the particular power levels using one or more voltage waveforms defined by waveform data in the waveform memory 224. As a consequence, one or more particular ion bombardment energies may be selected with the ion control portion to carry out controlled etching of the substrate (or other forms of plasma processing).
• the switch-mode power supply 206 includes switch components 226', 226" (e.g., high power field effect transistors) that are adapted to switch power to the support 208 of the substrate 210 responsive to drive signals from corresponding drive components 228', 228". And the drive signals 230', 230" that are generated by the drive components 228', 228" are controlled by the controller 212 based upon timing that is defined by the content of the waveform memory 224.
• switch components 226', 226" e.g., high power field effect transistors
• the controller 212 in many embodiments is adapted to interpret the content of the waveform memory and generate drive-control signals 232', 232", which are utilized by the drive components 228', 228" to control the drive signals 230', 230" to the switching components 226', 226" .
• drive-control signals 232', 232" which are utilized by the drive components 228', 228" to control the drive signals 230', 230" to the switching components 226', 226" .
• two switch components 226', 226" which may be arranged in a half- bridge configuration, are depicted for exemplary purposes, it is certainly contemplated that fewer or additional switch components may be implemented in a variety of architectures (e.g., an H-bridge configuration).
• the controller 212 in this embodiment is configured, responsive to an arc in the plasma chamber 204 being detected by the arc detection component 222, to carry out arc management functions.
• the controller 212 alters the drive-control signals 232', 232" so that the waveform applied at the output 236 of the switch mode bias supply 206 extinguishes arcs in the plasma 214.
• the controller 212 extinguishes arcs by simply interrupting the application of drive-control signals 232', 232" so that the application of power at the output 236 of the switch-mode bias supply 206 is interrupted.
• FIG. 3 it is a schematic representation of components that may be utilized to realize the switch-mode bias supply 206 described with reference to FIG. 2.
• the switching components Tl and T2 in this embodiment are arranged in a half-bridge (also referred to as or totem pole) type topology.
• R2, R3, CI, and C2 represent a plasma load
• CIO is an effective capacitance (also referred to herein as a series capacitance or a chuck capacitance)
• C3 is an optional physical capacitor to prevent DC current from the voltage induced on the surface of the substrate or from the voltage of an electrostatic chuck (not shown) from flowing through the circuit.
• CIO is referred to as the effective capacitance because it includes the series capacitance (or also referred to as a chuck capacitance) of the substrate support and the electrostatic chuck (or e-chuck) as well as other capacitances inherent to the application of a bias such as the insulation and substrate.
• LI is stray inductance (e.g., the natural inductance of the conductor that feeds the power to the load).
• V2 and V4 represent drive signals (e.g., the drive signals 230', 230"output by the drive components 228', 228" described with reference to FIG. 2), and in this embodiment, V2 and V4 can be timed (e.g., the length of the pulses and/or the mutual delay) so that the closure of Tl and T2 may be modulated to control the shape of the voltage output Vout, which is applied to the substrate support.
• the transistors used to realize the switching components Tl and T2 are not ideal switches, so to arrive at a desired waveform, the transistor-specific characteristics are taken into consideration. In many modes of operation, simply changing the timing of V2 and V4 enables a desired waveform to be applied at Vout.
• the switches Tl, T2 may be operated so that the voltage at the surface of the substrate 110, 210 is generally negative with periodic voltage pulses approaching and/or slightly exceeding a positive voltage reference.
• the value of the voltage at the surface of the substrate 110, 210 is what defines the energy of the ions, which may be characterized in terms of an ion energy distribution function (IEDF).
• IEDF ion energy distribution function
• the pulses at Vout may be generally rectangular and have a width that is long enough to induce a brief positive voltage at the surface of the substrate 110, 210 so as to attract enough electrons to the surface of the substrate 110, 210 in order to achieve the desired voltage(s) and corresponding ion energies.
• the periodic voltage pulses that approach and/or slightly exceed the positive voltage reference may have a minimum time limited by the switching abilities of the switches Tl, T2.
• the generally negative portions of the voltage can extend so long as the voltage does not build to a level that damages the switches. At the same time, the length of negative portions of the voltage should exceed an ion transit time.
• Vbus in this embodiment defines the amplitude of the pulses measured at Vout, which defines the voltage at the surface of the substrate, and as a consequence, the ion energy.
• Vbus may be coupled to the ion energy control portion, which may be realized by a DC power supply that is adapted to apply a DC signal or a time- varying waveform to Vbus.
• the pulse width, pulse shape, and/or mutual delay of the two signals V2, V4 may be modulated to arrive at a desired waveform at Vout (also referred to herein as a modified periodic voltage function), and the voltage applied to Vbus may affect the characteristics of the pulses.
• the voltage Vbus may affect the pulse width, pulse shape and/or the relative phase of the signals V2, V4.
• FIG. 4 shown is a timing diagram depicting two drive signal waveforms that may be applied to Tl and T2 (as V2 and V4) so as to generate the period voltage function at Vout as depicted in FIG. 4.
• the timing of the two gate drive signals V2, V4 may be controlled.
• the two gate drive signals V2, V4 may be applied to the switching components Tl, T2 so the time that each of the pulses is applied at Vout may be short compared to the time T between pulses, but long enough to induce a positive voltage at the surface of the substrate 110, 210 to attract electrons to the surface of the substrate 110, 210.
• the gate voltage level between the pulses it is possible to control the slope of the voltage that is applied to Vout between the pulses (e.g., to achieve a substantially constant voltage at the surface of the substrate between pulses).
• the repetition rate of the gate pulses is about 400 kHz, but this rate may certainly vary from application to application.
• waveforms that may be used to generate the desired (or defined) ion energy distributions may be defined, and the waveforms can be stored (e.g., in the waveform memory portion described with reference to FIG. 1 as a sequence of voltage levels).
• the waveforms can be generated directly (e.g., without feedback from Vout); thus avoiding the undesirable aspects of a feedback control system (e.g., settling time).
• the graphs in FIG. 5 depict a single mode of operating the switch mode bias supply 106, 206, which effectuates an ion energy distribution that is concentrated at a particular ion energy.
• the voltage applied at Vbus is maintained constant while the voltages applied to V2 and V4 are controlled (e.g., using the drive signals depicted in FIG. 3) so as to generate pulses at the output of the switch-mode bias supply 106, 206, which effectuates the corresponding ion energy distribution shown in FIG. 5.
• the potential at the surface of the substrate 110, 210 is generally negative to attract the ions that bombard and etch the surface of the substrate 110, 210.
• the periodic short pulses that are applied to the substrate 110, 210 (by applying pulses to Vout) have a magnitude defined by the potential that is applied to Vbus, and these pulses cause a brief change in the potential of the substrate 110, 210 (e.g., close to positive or slightly positive potential), which attracts electrons to the surface of the substrate to achieve the generally negative potential along the surface of the substrate 110, 210. As depicted in FIG.
• the constant voltage applied to Vbus effectuates a single concentration of ion flux at particular ion energy; thus a particular ion bombardment energy may be selected by simply setting Vbus to a particular potential.
• two or more separate concentrations of ion energies may be created (e.g., see FIG. 49).
• the power supply need not be limited to a switch-mode power supply, and as such the output of the power supply can also be controlled in order to effect a certain ion energy.
• the output of the power supply whether switch-mode or otherwise, when considered without being combined with an ion current compensation or an ion current, can also be referred to as a power supply voltage, V PS .
• FIG. 6 shown are graphs depicting a bi-modal mode of operation in which two separate peaks in ion energy distribution are generated.
• the substrate experiences two distinct levels of voltages and periodic pulses, and as a consequence, two separate concentrations of ion energies are created.
• the voltage that is applied at Vbus alternates between two levels, and each level defines the energy level of the two ion energy concentrations.
• FIG. 6 depicts the two voltages at the substrate 110, 210 as alternating after every pulse (e.g., FIG. 48), this is certainly not required.
• the voltages applied to V2 and V4 are switched (e.g., using the drive signals depicted in FIG. 3) relative to the voltage applied to Vout so that the induced voltage at surface of the substrate alternates from a first voltage to a second voltage (and vice versa) after two or more pulses (e.g., FIG. 49).
• FIGS. 7 A and 7B shown are graphs depicting actual, direct ion energy measurements made in a plasma corresponding to monoenergetic and dual-level regulation of the DC voltage applied to Vbus, respectively.
• the ion energy distribution is concentrated around 80 eV responsive to a non-varying application of a voltage to Vbus (e.g., as depicted in FIG. 5).
• two separate concentrations of ion energies are present at around 85 eV and 115 eV responsive to a dual-level regulation of Vbus (e.g., as depicted in FIG. 6).
• a switch-mode power supply 806 is coupled to a controller 812, an ion-energy control component 820, and a substrate support 808 via an arc detection component 822.
• the controller 812, switch-mode supply 806, and ion energy control component 820 collectively operate to apply power to the substrate support 808 so as to effectuate, on a time-averaged basis, a desired (or defined) ion energy distribution at the surface of the substrate 810.
• FIG. 9A shown is a periodic voltage function with a frequency of about 400 kHz that is modulated by a sinusoidal modulating function of about 5 kHz over multiple cycles of the periodic voltage function.
• FIG. 9B is an exploded view of the portion of the periodic voltage function that is circled in FIG. 9A
• FIG. 9C depicts the resulting distribution of ion energies, on a time-averaged basis, that results from the sinusoidal modulation of the periodic voltage function.
• FIG. 9D depicts actual, direct, ion energy measurements made in a plasma of a resultant, time- averaged, IEDF when a periodic voltage function is modulated by a sinusoidal modulating function.
• achieving a desired (or defined) ion energy distribution, on a time-averaged basis may be achieved by simply changing the modulating function that is applied to the periodic voltage.
• a 400 kHz periodic voltage function is modulated by a sawtooth modulating function of approximately 5 kHz to arrive at the distribution of ion energies depicted in FIG. IOC on a time-averaged basis.
• the periodic voltage function utilized in connection with FIG. 10 is the same as in FIG. 9, except that the periodic voltage function in FIG. 10 is modulated by a sawtooth function instead of a sinusoidal function.
• the ion energy distribution functions depicted in FIGS. 9C and IOC do not represent an instantaneous distribution of ion energies at the surface of the substrate 810, but instead represent the time average of the ion energies.
• the distribution of ion energies will be a subset of the depicted distribution of ion energies that exist over the course of a full cycle of the modulating function.
• the modulating function need not be a fixed function nor need it be a fixed frequency. In some instances for example, it may be desirable to modulate the periodic voltage function with one or more cycles of a particular modulating function to effectuate a particular, time-averaged ion energy distribution, and then modulate the periodic voltage function with one or more cycles of another modulating function to effectuate another, time-averaged ion energy distribution. Such changes to the modulating function (which modulates the periodic voltage function) may be beneficial in many instances.
• a first modulating function may be used, and then another modulating function may subsequently be used to effectuate a different etch geometry or to etch through another material.
• the periodic voltage function (e.g., the 400 kHz components in FIGS. 9A, 9B, 10A, and 10B and Vout in FIG. 4) need not be rigidly fixed (e.g., the shape and frequency of the periodic voltage function may vary), but generally its frequency is established by the transit time of ions within the chamber so that ions in the chamber are affected by the voltage that is applied to the substrate 810.
• the controller 812 provides drive-control signals 832', 832" to the switch-mode supply 806 so that the switch-mode supply 806 generates a periodic voltage function.
• the switch mode supply 806 may be realized by the components depicted in FIG. 3 (e.g., to create a periodic voltage function depicted in FIG. 4), but it is certainly contemplated that other switching architectures may be utilized.
• the ion energy control component 820 functions to apply a modulating function to the periodic voltage function (that is generated by the controller 812 in connection with the switch mode power supply 806).
• the ion energy control component 820 includes a modulation controller 840 that is in communication with a custom IEDF portion 850, an IEDF function memory 848, a user interface 846, and a power component 844. It should be recognized that the depiction of these components is intended to convey functional components, which in reality, may be effectuated by common or disparate components.
• the power component 844 includes a DC power supply (e.g., a DC switch mode power supply or a linear amplifier), which applies the modulating function (e.g. a varying DC voltage) to the switch mode power supply (e.g., to Vbus of the switch mode power supply depicted in FIG. 3).
• the modulation controller 840 controls the voltage level that is output by the power component 844 so that the power component 844 applies a voltage that conforms to the modulating function.
• the custom IEDF component 850 may enable IEDF functions to be defined in terms of a relative level of flux (e.g., in terms of a percentage of flux) at a high-level (IF-high), a mid- level (IF-mid), and a low level (IF-low) in connection with a function(s) that defines the IEDF between these energy levels.
• IF-high high-level
• IF-mid mid- level
• IF-low low level
• IEDF function between these levels is sufficient to define an IEDF function.
• a user may request 1200 eV at a 20% contribution level (contribution to the overall IEDF), 700 eV at a 30 % contribution level with a sinusoid IEDF between these two levels.
• the custom IEDF portion 850 may enable a user to populate a table with a listing of one or more (e.g., multiple) energy levels and the corresponding percentage contribution of each energy level to the IEDF.
• the custom IEDF component 850 in connection with the user interface 846 enables a user to graphically generate a desired (or defined) IEDF by presenting the user with a graphical tool that enables a user to draw a desired (or defined) IEDF.
• the ion current compensation component 1260 enables a narrow spread of ion energies when the ion current is high (e.g., by compensating for effects of ion current), and it also enables a width of the spread 1572, 1574 of uniform ion energy to be controlled (e.g., when it is desirable to have a spread of ion energies).
• the controller 1212 can sample a voltage at different times at an electrical node where outputs of the switch mode power supply 1206 and the ion current compensation 1260 combine.
• an exemplary ion current compensation component 1360 that includes a current source 1364 coupled to an output 1336 of a switch mode supply and a current controller 1362 that is coupled to both the current source 1364 and the output 1336. Also depicted in FIG.
• the sheath (also herein referred to as a plasma sheath) is a layer in a plasma near the substrate surface and possibly walls of the plasma processing chamber with a high density of positive ions and thus an overall excess of positive charge.
• the surface with which the sheath is in contact with typically has a preponderance of negative charge.
• the sheath arises by virtue of the faster velocity of electrons than positive ions thus causing a greater proportion of electrons to reach the substrate surface or walls, thus leaving the sheath depleted of electrons.
• the sheath thickness, s eath is a function of plasma characteristics such as plasma density and plasma temperature.
• FIG. 14 is a graph depicting an exemplary voltage (e.g., the modified periodic voltage function) at Vo depicted in FIG. 13.
• the current controller 1362 monitors the voltage at Vo, and ion current is calculated over an interval t (depicted in FIG. 14) as: dt (Equation 1)
• Ion current, 3 ⁇ 4, and inherent capacitance can either or both be time varying. Because Ci is substantially constant for a given tool and is measureable, only Vo needs to be monitored to enable ongoing control of compensation current.
• the current controller controls the current source 1364 so that Ic is substantially the same as Ii (or in the alternative, related according to Equation 2). In this way, a narrow spread of ion energies may be maintained even when the ion current reaches a level that affects the voltage at the surface of the substrate.
• the spread of the ion energy may be controlled as depicted in FIGS. 15B and 15C so that additional ion energies are realized at the surface of the substrate.
• a feedback line 1370 which may be utilized in connection with controlling an ion energy distribution.
• the value of AY also referred to herein as a voltage step or the third portion 1406) depicted in FIG. 14, is indicative of instantaneous ion energy and may be used in many embodiments as part of a feedback control loop.
• the voltage step, AY is related to ion energy according to Equation 4.
• the peak-to-peak voltage, Vpp can be related to the instantaneous ion energy.
• FIG. 16 shown is an exemplary embodiment of a current source 1664, which may be implemented to realize the current source 1364 described with reference to FIG. 13.
• a controllable negative DC voltage source in connection with a series inductor L2
• a current source may be realized by other components and/or configurations.
• Vps In order to help explain the power supply voltage, Vps, it is illustrated herein as if measured without coupling to the ion current and ion current compensation.
• the modified periodic voltage function is then sampled at a first and second value of an ion current compensation, I c , 4304. At least two samples of a voltage of the modified periodic voltage function are taken for each value of the ion current compensation, I c .
• the sampling 4304 is performed in order to enable calculations 4306 (or determinations) of the ion current, 3 ⁇ 4, and a sheath capacitance, C sheath , 4306.
• Such determination may involve finding an ion current compensation, I c , that if applied to the substrate support (or as applied to the substrate support) would generate a narrow (e.g., minimum) ion energy distribution function (IEDF) width.
• the calculations 4306 can also optionally include determining a voltage step, AV, (also known as a third portion of the modified periodic voltage function 1406) based on the sampling 4304 of the waveform of the modified periodic voltage function.
• the voltage step, AV can be related to the ion energy of ions reaching the substrate's surface.
• the voltage step, AV can be ignored. Details of the sampling 4304 and the calculations 4306 will be provided in discussions of FIG. 30 to follow.
• the method 4300 may move to the method 3100 of FIG. 31 involving setting and monitoring an ion energy and a shape (e.g., width) of the IEDF.
• FIG. 46 illustrates how a change in the power supply voltage can effect a change in the ion energy.
• a magnitude of the illustrated power supply voltage is decreased resulting in a decreased magnitude of the ion energy.
• FIG. 47 illustrates that given a narrow IEDF 4714, the IEDF can be widened by adjusting the ion current compensation, I c .
• the method 4300 can perform various metrics as described with reference to FIGS. 32-41 that make use of the ion current, 3 ⁇ 4, the sheath capacitance, Qheath, and other aspects of the waveform of the modified periodic voltage function.
• Such a modified periodic voltage function is achieved when the ion current compensation, I c , equals the ion current, 3 ⁇ 4, assuming no stray capacitances (see the last five cycles of the periodic voltage function (Vo) in FIG. 45).
• the ion current compensation, Ic is related to the ion current, 3 ⁇ 4, according to Equation 2:
• an inherent capacitance CIO in FIG. 3 can be accessed 3008 (e.g., from a memory or from a user input). Based on the slope, dVo/dt, the effective capacitance, C l5 and the ion current compensation, I c , a function /(Equation 3), can be evaluated for each value of the ion current compensation, I c , as follows: d t Cl (Equation 3)
• the ion current compensation, Ic equals the ion current, 3 ⁇ 4, or in the alternative, makes Equation 2 true, and a narrow IEDF width has been achieved 3010 (e.g., see FIG. 45). If the function / is not true, then the ion current compensation, Ic, can be adjusted 3012 further until the function /is true. Another way to look at this is that the ion current compensation, Ic, can be adjusted until it matches the ion current, 3 ⁇ 4, (or in the alternative, meets the relationship of Equation 2), at which point a narrow IEDF width will exist.
• the slope, dVo/dt can be positive, negative, or zero.
• the modified periodic voltage function 1400 can also be described as having pulses comprising the first portion 1402, the second portion 1404, and the third portion 1406, and a portion between the pulses (fourth portion 1408).
• the switching diagram 4410 of a first switch Tl and a second switch T2 can apply.
• the first switch Tl can be implemented as the switch Tl in FIG. 3 and the second switch T2 can be implemented as the second switch T2 in FIG. 3.
• the two switches are illustrated as having identical switching times, but being 180° out of phase. In other embodiments, the switches may have a slight phase offset such as that illustrated in FIG. 4.
• the first switch Tl is on, the power supply voltage is drawn to a maximum magnitude, which is a negative value in FIG. 44 since the power supply has a negative bus voltage.
• the second switch T2 is turned off during this period so that the power supply voltage 4406 is isolated from ground.
• the power supply voltage 4406 approaches and slightly passes ground.
• the pulse width can be identical for all cycles. In other embodiments, the pulse width can be varied or modulated in time.
• the modified periodic voltage function can be applied to the substrate support 3002, and sampled 3004 as Vo at a last accessible point before the modified periodic voltage function reaches the substrate support (e.g., between the switch mode power supply and the effective capacitance).
• the unmodified periodic voltage function (or power supply voltage 4406 in FIG. 44) can be sourced from a power supply such as the switch mode power supply 1206 in FIG. 12.
• the ion current compensation 4404 in FIG. 44 can be sourced from a current source such as the ion current compensation component 1260 in FIG. 12 or 1360 in FIG. 13.
• a portion of or the whole modified periodic voltage function can be sampled 3004.
• the fourth portion e.g., fourth portion 1408
• the sampling 3004 can be performed between the power supply and the substrate support.
• the sampling 3004 can be performed between the switch mode power supply 106 and the support 108.
• the sampling 3004 can be performed between the inductor LI and the inherent capacitance CIO.
• the sampling 3004 can be performed at Vo between the capacitance C3 and the inherent capacitance CIO.
• the sampling rate can be greater than 400 kHz. These sampling rates enable more accurate and detailed monitoring of the modified periodic voltage function and its shape. In this same vein, more detailed monitoring of the periodic voltage function allows more accurate comparisons of the waveform: between cycles, between different process conditions, between different processes, between different chambers, between different sources, etc. For instance, at these sampling rates, the first, second, third, and fourth portions 1402, 1404, 1406, 1408 of the periodic voltage function illustrated in FIG. 14 can be distinguished, which may not be possible at traditional sampling rates.
• the higher sampling rates enable resolving of the voltage step, AV, and the slope, dVo/dt, which are not possible in the art.
• a portion of the modified periodic voltage function can be sampled while other portions are not sampled.
• the calculation 3006 of the slope, dVo/dt can be based on a plurality of Vo measurements taken during the time t (e.g., the fourth portion 1408). For instance, a linear fit can be performed to fit a line to the Vo values where the slope of the line gives the slope, dV 0 /dt. In another instance, the Vo values at the beginning and end of time t (e.g., the fourth portion 1408) in FIG.
• the decision 3010 can be part of an iterative loop used to tune the IEDF to a narrow width (e.g., a minimum width, or in the alternative, 6% full- width half maximum). Equation 3 only holds true where the ion current compensation, Ic, is equal to the ion current, 3 ⁇ 4 (or in the alternative, is related to 3 ⁇ 4 according to Equation 2), which only occurs where there is a constant substrate voltage and thus a constant and substantially singular ion energy (a narrow IEDF width).
• a constant substrate voltage 4608 (V su b) can be seen in FIG. 46.
• ion current, 3 ⁇ 4, or alternatively ion current compensation, Ic can be used in Equation 3.
• two values along the fourth portion 1408 can be sampled for a first cycle and a second cycle and a first and second slope can be determined for each cycle, respectively. From these two slopes, an ion current compensation, Ic, can be determined which is expected to make Equation 3 true for a third, but not-yet-measured, slope. Thus, an ion current, I can be estimated that is predicted to correspond to a narrow IEDF width. These are just two of the many ways that a narrow IEDF width can be determined, and a corresponding ion current compensation, Ic, and/or a corresponding ion current, I can be found.
• the adjustment to the ion current compensation, Ic, 3012 can involve either an increase or a decrease in the ion current compensation, Ic, and there is no limitation on the step size for each adjustment.
• a sign of the function / in Equation 3 can be used to determine whether to increase or decrease the ion current compensation. If the sign is negative, then the ion current compensation, Ic, can be decreased, while a positive sign can indicate the need to increase the ion current compensation, Ic.
• the method 3000 can advance to further set point operations (see FIG. 31) or remote chamber and source monitoring operations (see FIGS. 32-41).
• the further set point operations can include setting the ion energy (see also FIG. 46) and the distribution of ion energy or IEDF width (see also FIG. 47).
• the source and chamber monitoring can include monitoring plasma density, source supply anomalies, plasma arcing, and others.
• the method 3000 can optionally loop back to the sampling 3004 in order to continuously (or in the alternative, periodically) update the ion current compensation, Ic.
• the sampling 3004, calculation 3006, the decision 3010, and the adjusting 3012 can periodically be performed given a current ion current compensation, Ic, in order to ensure that Equation 3 continues to be met.
• the ion current compensation, Ic that meets Equation 3 is updated, then the ion current, I can also be updated and the updated value can be stored 3014.
• the method 3000 can find and set the ion current compensation, Ic, so as to equal the ion current, I or in the alternative, to meet Equation 2, a value for the ion current compensation, Ic, needed to achieve a narrow IEDF width can be determined without (or in the alternative, before) setting the ion current, I c , to that value.
• the ion current compensation, Ic that meets Equation 3 and thus corresponds to ion current, I can be determined with only a single adjustment of the ion current compensation.
• the method 3000 can then move on to the methods described in FIG. 31 and/or FIGS. 32-41 without ever setting the ion current, I c , to a value needed to achieve the narrow IEDF width. Such an embodiment may be carried out in order to increase tuning speeds.
• FIG. 31 illustrates methods for setting the IEDF width and the ion energy.
• the method originates from the method 3000 illustrated in FIG. 30, and can take either of the left path 3100 (also referred to as an IEDF branch) or the right path 3101 (also referred to as an ion energy branch), which entail setting of the IEDF width and the ion energy, respectively.
• Ion energy, eV is proportional to a voltage step, AV, or the third portion 1406 of the modified periodic voltage function 1400 of FIG. 14.
• Ci is the effective capacitance (e.g., chuck capacitance; inherent capacitance, CIO, in FIG. 3; or inherent capacitance, CI, in FIG. 13)
• C 2 is a sheath capacitance (e.g., the sheath capacitance C4 in FIG. 3 or the sheath capacitance C2 in FIG. 13).
• the sheath capacitance, C 2 may include stray capacitances and depends on the ion current, 3 ⁇ 4.
• the voltage step, AV can be measured as a change in voltage between the second portion 1404 and the fourth portion 1408 of the modified periodic voltage function 1400.
• ion energy, eV can be controlled and known.
• the IEDF width can be approximated according to
• IEDF width V PP - AV - ⁇ (Equation 5)
• I is 3 ⁇ 4 where C is C ser ies, or I is Ic where C is C e ff ec tive- Time, t, is the time between pulses, Vpp, is the peak-to-peak voltage, and AV is the voltage step.
• sheath capacitance, C 2 can be used in a variety of calculations and monitoring operations.
• Equation 6 is written as equation 7:
• an e-field in the sheath can be estimated as a function of the sheath capacitance, C 2 , the sheath distance, s eath , and the ion energy, eV.
• Sheath capacitance, C 2 along with the ion current, 3 ⁇ 4, can also be used to determine plasma density, n e , from Equation 8 where saturation current, I sat , is linearly related to the compensation current, I c , for singly ionized plasma.
• hat ⁇ niqi _ _4 * n e q ⁇ - ⁇ A (Equation 8)
• An effective mass of ions at the substrate surface can be calculated using the sheath capacitance, C 2 and the saturation current, I sat .
• Plasma density, n e , electric field in the sheath, ion energy, eV, effective mass of ions, and a DC potential of the substrate, V DC are fundamental plasma parameters that are typically only monitored via indirect means in the art. This disclosure enables direct measurements of these parameters thus enabling more accurate monitoring of plasma characteristics in real time.
• the sheath capacitance, C 2 can also be used to monitor and control the ion energy, eV, as illustrated in the ion energy branch 3101 of FIG. 31.
• the ion energy branch 3101 starts by receiving a user selection of ion energy 3102.
• the ion energy branch 3101 can then set an initial power supply voltage for the switch-mode power supply that supplies the periodic voltage function 3104.
• the ion current can also be accessed 3106 (e.g., accessed from a memory).
• the periodic voltage can be sampled 3108 and a measurement of the third portion of the modified periodic voltage function can be measured 3110.
• Ion energy, 3 ⁇ 4 can be calculated from the voltage step, AV, (also referred to as the third portion (e.g., third portion 1406)) of the modified periodic voltage function 3112.
• the ion energy branch 3101 can then determine whether the ion energy equals the defined ion energy 3114, and if so, the ion energy is at the desired set point and the ion energy branch 3101 can come to an end. If the ion energy is not equal to the defined ion energy, then the ion energy branch 3101 can adjust the power supply voltage 3116, and again sample the periodic voltage 3108.
• the ion energy branch 3101 can then loop through the sampling 3108, measuring 3110, calculating 3112, decision 3114, and the setting 3116 until the ion energy equals the defined ion energy.
• the method for monitoring and controlling the IEDF width is illustrated in the IEDF branch 3100 of FIG. 31.
• the IEDF branch 3100 includes receiving a user selection of an IEDF width 3150 and sampling a current IEDF width 3152.
• a decision 3154 determines whether the defined IEDF width equals the current IEDF width, and if the decision 3152 is met, then the IEDF width is as desired (or defined), and the IEDF branch 3100 can come to an end. However, if the current IEDF width does not equal the defined IEDF width, then the ion current compensation, Ic, can be adjusted 3156. This determination 3154 and the adjustment 3156 can continue in a looping manner until the current IEDF width equals the defined IEDF width.
• the desired (or defined) ion energy and IEDF width can be maintained despite changes in the plasma due to variations or intentional adjustments to the plasma source or chamber conditions.
• Using three different power supply voltages results in three different ion energies (e.g., FIG. 42B).
• the ion flux of different ion energies can be controlled (e.g., FIG. 42C).
• Some of the heretofore mentioned controls are enabled by using some combination of the following: (1) a fixed waveform (consecutive cycles of the waveform are the same); (2) a waveform having at least two portions that are proportional to an ion energy and an IEDF (e.g., the third and fourth portions 1406 and 1408 illustrated in FIG. 14); and (3) a high sampling rate (e.g., 125 MHz) that enables accurate monitoring of the distinct features of the waveform.
• a fixed waveform consistecutive cycles of the waveform are the same
• a waveform having at least two portions that are proportional to an ion energy and an IEDF e.g., the third and fourth portions 1406 and 1408 illustrated in FIG. 14
• a high sampling rate e.g., 125 MHz
• the herein disclosed fixed waveform and the high sampling rate further lead to more accurate statistical observations being possible. Because of this increased accuracy, operating and processing characteristics of the plasma source and the plasma in the chamber can be monitored via monitoring various characteristics of the modified periodic voltage function. For instance, measurements of the modified periodic voltage function enable remote monitoring of sheath capacitance and ion current, and can be monitored without knowledge of the chamber process or other chamber details.
• measurements of the modified periodic voltage function enable remote monitoring of sheath capacitance and ion current, and can be monitored without knowledge of the chamber process or other chamber details.
• this standard deviation is monitored among consecutive pulses, and the standard deviation increases over time, this may indicate that there is ringing in the chamber, for instance in the e-chuck. Ringing can be a sign of poor electrical connections to, or in, the chamber or of additional unwanted inductance or capacitance.
• FIG. 32 illustrates two modified periodic voltage functions delivered to the substrate support according to one embodiment of this disclosure.
• the two modified periodic voltage functions can be used for chamber matching or in situ anomaly or fault detection.
• one of the two modified periodic voltage functions can be a reference waveform and the second can be taken from a plasma processing chamber during calibration. Differences between the two modified periodic voltage functions (e.g., differences in peak-to-peak voltage, Vpp) can be used to calibrate the plasma processing chamber.
• the second modified periodic voltage function can be compared to the reference waveform during processing and any difference (e.g., shifts) in waveform characteristics can be indicative of a fault (e.g., a difference in the slope of a fourth portion 3202 of the modified periodic voltage functions).
• FIG. 33 illustrates an ion current waveform that can indicate plasma source instability and changes in the plasma density.
• Fluctuations in ion current, 3 ⁇ 4, such as that illustrated in FIG. 33 can be analyzed to identify faults and anomalies in the system.
• the periodic fluctuations in FIG. 33 may indicate a low-frequency instability in the plasma source (e.g., plasma power supply 102).
• Such fluctuations in ion current, I can also indicate cyclical changes in plasma density.
• This indicator and the possible faults or anomalies that it may indicate are just one of many ways that remote monitoring of the ion current, I can be used to particular advantage.
• FIG. 35 illustrates a modified periodic voltage function that can indicate faults within the bias supply.
• a top portion (also referred to herein as a second portion) of the third illustrated cycle shows anomalous behavior that may be indicative of ringing in the bias supply (e.g., power supply 1206 in FIG. 12).
• This ringing may be an indication of a fault within the bias supply. Further analysis of the ringing may identify characteristics that help to identify the fault within the power system.
• FIG. 36 illustrates a modified periodic voltage function that can be indicative of a dynamic (or nonlinear) change in a capacitance of the system. For instance, a stray capacitance that nonlinearly depends on voltage could result in such a modified periodic voltage function. In another example, plasma breakdown or a fault in the chuck could also result in such a modified periodic voltage function.
• a nonlinearity in the fourth portion 3602 of each cycle can be indicative of a dynamic change in the system capacitance. For instance, the nonlinearities can indicate a change in the sheath capacitance since other components of system capacitance are largely fixed.
• FIG. 37 illustrates a modified periodic voltage function that may be indicative of changes in plasma density.
• the illustrated modified periodic voltage function shows monotonic shifts in the slope dVo/dt, which can indicate a change in plasma density. These monotonic shifts can provide a direct indication of an anticipated event, such as a process etch end point. In other embodiments, these monotonic shifts can indicate a fault in the process where no anticipated event exists.
• FIG. 38 illustrates a sampling of ion current for different process runs, where drift in the ion current can indicate system drift.
• Each data point can represent an ion current for a given run, where the acceptable limit is a user-defined or automated limit which defines an acceptable ion current.
• Drift in the ion current which gradually pushes the ion current above the acceptable limit can indicate that substrate damage is possible.
• This type of monitoring can also be combined with any number of other traditional monitors, such as optical omission, thickness measurement, etc. These traditional types of monitors in addition to monitoring ion current drift can enhance existing monitoring and statistical control.
• FIG. 39 illustrates a sampling of ion current for different process parameters.
• ion current can be used as a figure of merit to differentiate different processes and different process characteristics.
• Such data can be used in the development of plasma recipes and processes.
• eleven process conditions could be tested resulting in the eleven illustrated ion current data points, and the process resulting in a preferred ion current can be selected as an ideal process, or in the alternative as a preferred process.
• the lowest ion current may be selected as the ideal process, and thereafter the ion current associated with the preferred process can be used as a metric to judge whether a process is being carried out with the preferred process condition(s).
• This figure of merit can be used in addition to or as an alternative to similar traditional merit characteristics such as rate, selectivity, and profile angle, to name a few non-limiting examples.
• FIG. 40 illustrates two modified periodic voltage functions monitored without a plasma in the chamber. These two modified periodic voltage functions can be compared and used to characterize the plasma chamber.
• the first modified periodic voltage function can be a reference waveform while the second modified periodic voltage function can be a currently-monitored waveform. These waveforms can be taken without a plasma in the processing chamber, for instance after a chamber clean or preventative maintenance, and therefore the second waveform can be used to provide validation of an electrical state of the chamber prior to release of the chamber into (or back into) production.
• the method 3000 can loop back to the sampling 3004 in order to determine an updated ion current, 3 ⁇ 4.
• a correction to the ion current, 3 ⁇ 4, ion energy, eV, or the IEDF width may be desired.
• a corresponding correction can be made and the method 3000 can loop back to the sampling 3004 to find a new ion current compensation, Ic, that meets Equation 3.
• metrics can be monitored before, during, or after setting and monitoring the IEDF width and/or the ion energy, eV.
• FIG. 49 illustrates another pattern of the power supply voltage that can be used to achieve more than one ion energy level where each ion energy level has a narrow IEDF 4914 width.
• the power supply voltage 4906 alternates between two different magnitudes but does so for two cycles at a time before alternating.
• the average ion energies are the same as if Vps 4906 were alternated every cycle. This shows just one example of how various other patterns of the Vps 4906 can be used to achieve the same ion energies.
• FIG. 50 illustrates one combination of power supply voltages, Vps, 5006 and ion current compensation, Ic, 5004 that can be used to create a defined IEDF 5014.
• alternating power supply voltages 5006 result in two different ion energies.
• the IEDF 5014 width for each ion energy can be expanded. If the ion energies are close enough, as they are in the illustrated embodiment, then the IEDF 5014 for both ion energies will overlap resulting in one large IEDF 5014.
• Other variations are also possible, but this example is meant to show how combinations of adjustments to the Vps 5006 and the I c 5004 can be used to achieve defined ion energies and defined IEDFs 5014.
• a DC offset input which provides electrostatic force to hold the wafer to the chuck for efficient thermal control.
• FIG. 21 illustrates a plasma processing system 2100 according to an embodiment of this disclosure.
• the system 2100 includes a plasma processing chamber 2102 enclosing a plasma 2104 for etching a top surface 2118 of a substrate 2106 (and other plasma processes).
• the plasma is generated by a plasma source 2112 (e.g., in-situ or remote or projected) powered by a plasma power supply 2122.
• a plasma source 2112 e.g., in-situ or remote or projected
• the substrate 2106 is dielectric and therefore can have a first potential Vi at the top surface 2118 and a second potential V 2 at the bottom surface 2120.
• the top surface of the electrostatic chuck 2121 is in contact with the bottom surface 2120 of the substrate, and thus these two surfaces 2120, 2121 are at the same potential, V 2 .
• the first potential V l5 the chucking potential V chuck , and the second potential V 2 are controlled via an AC waveform with a DC bias or offset generated by a switch mode power supply 2130 and provided to the electrostatic chuck 2111 via a first conductor 2124.
• the AC waveform is provided via the first conductor 2124
• the DC waveform is provided via an optional second conductor 2125.
• the AC and DC output of the switch mode power supply 2130 can be controlled via a controller 2132, which is also configured to control various aspects of the switch mode power supply 2130.
• Ion energy and ion energy distribution are a function of the first potential
• the switch mode power supply 2130 provides an AC waveform tailored to effect a desired first potential Vi known to generate a desired (or defined) ion energy and ion energy distribution.
• the AC waveform can be RF and have a non- sinusoidal waveform such as that illustrated in FIGS. 5, 6, 11, 14, 15a, 15b, and 15c.
• the first potential Vi can be proportional to the change in voltage AY illustrated in FIG. 14.
• the first potential Vi is also equal to the plasma voltage V 3 minus the plasma sheath voltage V sheath - But since the plasma voltage V 3 is often small (e.g., less than 20 V) compared to the plasma sheath voltage V s heath (e.g., 50 V - 2000 V), the first potential Vi and the plasma sheath voltage sheath are approximately equal and for purposes of implementation can be treated as being equal. Thus, since the plasma sheath voltage V s h ea th dictates ion energies, the first potential Vi is proportional to ion energy distribution.
• the first potential Vi at the top surface 2118 of the substrate 2106 is formed via a combination of capacitive charging from the electrostatic chuck 2111 and charge buildup from electrons and ions passing through the sheath 2115.
• the AC waveform from the switch mode power supply 2130 is tailored to offset the effects of ion and electron transfer through the sheath 2115 and the resulting charge buildup at the top surface 2118 of the substrate 2106 such that the first potential Vi remains substantially constant.
• FIG. 22 illustrates another embodiment of a plasma processing system
• the grid electrode 2210 can be any conductive planar device embedded in the electrostatic chuck 2211, parallel to the substrate 2206, and configured to be biased by the switch mode power supply 2230 and to establish a chucking potential V chuck - Although the grid electrode 2210 is illustrated as being embedded in a lower portion of the electrostatic chuck 2211, the grid electrode 2210 can be located closer or further from the substrate 2206. The grid electrode 2210 also does not have to have a grid pattern. In an embodiment, the grid electrode 2210 can be a solid electrode or have a non- solid structure with a non-grid shape (e.g., a checkerboard pattern).
• the AC power source 2236 can make use of a switched mode configuration (see for example FIGS. 25-27).
• the switch mode power supply 2230, and particularly the AC power source 2236, can produce an AC waveform as described in various embodiments of this disclosure.
• FIG. 23 illustrates another embodiment, of a plasma processing system
• FIG. 24 illustrates another embodiment of a plasma processing system
• FIG. 26 illustrates yet another embodiment of a plasma processing system
• the system 2600 can include one or more controllers for controlling an output of the switch mode power supply 2630.
• a first controller 2632 can control the output of the switch mode power supply 2630, for instance via a second controller 2633 and a third controller 2635.
• the second controller 2633 can control a DC offset of the switch mode power supply 2630 as generated by the DC power source 2634.
• the third controller 2635 can control the AC waveform of the switch mode power supply 2630 by controlling the controllable voltage source 2638 and the controllable current source 2640.
• a voltage controller 2637 controls the voltage output of the controllable voltage source 2638 and a current controller 2639 controls a current of the controllable current source 2640.
• FIG. 29 illustrates another method 2900 according to an embodiment of this disclosure.
• the method 2900 includes a place a substrate in a plasma chamber operation 2902.
• the method 2900 further includes a form a plasma in the plasma chamber operation 2904.
• Such a plasma can be formed in situ or via a remote projected source.
• the method 2900 also includes a receive at least one ion-energy distribution setting operation 2906.
• the setting received in the receive operation 2906 can be indicative of one or more ion energies at a surface of the substrate.

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