Patent ID: 12255048

DETAILED DESCRIPTION

An exemplary embodiment of a plasma processing system is shown generally inFIG.1. As depicted, a plasma power supply102is coupled to a plasma processing chamber104and a switch-mode power supply106is coupled to a support108upon which a substrate110rests within the chamber104. Also shown is a controller112that is coupled to the switch-mode power supply106.

In this exemplary embodiment, the plasma processing chamber104may be realized by chambers of substantially conventional construction (e.g., including a vacuum enclosure which is evacuated by a pump or pumps (not shown)). And, as one of ordinary skill in the art will appreciate, the plasma excitation in the chamber104may 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 plasma114in the reactor, and a gas inlet may be provided for introduction of a gas into the chamber104.

As depicted, the exemplary plasma chamber104is arranged and configured to carry out plasma-assisted etching of materials utilizing energetic ion bombardment of the substrate110, and other plasma processing (e.g., plasma deposition and plasma assisted ion implantation). The plasma power supply102in 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 chamber104so as to ignite and sustain the plasma114. It should be understood that the present invention is not limited to any particular type of plasma power supply102or source to couple power to the chamber104, and that a variety of frequencies and power levels may be may be capacitively or inductively coupled to the plasma114.

As depicted, a dielectric substrate110to be treated (e.g., a semiconductor wafer), is supported at least in part by a support108that may include a portion of a conventional wafer chuck (e.g., for semiconductor wafer processing). The support108may be formed to have an insulating layer between the support108and the substrate110with the substrate110being capacitively coupled to the platforms but may float at a different voltage than the support108.

As discussed above, if the substrate110and support108are conductors, it is possible to apply a non-varying voltage to the support108, and as a consequence of electric conduction through the substrate110, the voltage that is applied to the support108is also applied to the surface of the substrate110.

When the substrate110is a dielectric, however, the application of a non-varying voltage to the support108is ineffective to place a voltage across the treated surface of the substrate110. As a consequence, the exemplary switch-mode power supply106is configured to be controlled so as to effectuate a voltage on the surface of the substrate110that is capable of attracting ions in the plasma114to collide with the substrate110so as to carry out a controlled etching and/or deposition of the substrate110, and/or other plasma-assisted processes.

Moreover, as discussed further herein, embodiments of the switch-mode power supply106are configured to operate so that there is an insubstantial interaction between the power applied (to the plasma114) by the plasma power supply102and the power that is applied to the substrate110by the switch-mode power supply106. The power applied by the switch-mode power supply106, for example, is controllable so as to enable control of ion energy without substantially affecting the density of the plasma114.

Furthermore, many embodiments of the exemplary switch-mode supply106depicted inFIG.1are 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 supply106are 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, however, has not been adopted by commercial entities because it has not proven to be cost effective nor sufficiently manageable. In particular, the linear amplifier that is utilized is typically large, very expensive, inefficient, and difficult to control. Furthermore, 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, however, has been found to adversely affect the plasma density because the high frequency power that is applied to the substrate affects the plasma density.

In some embodiments, the switch-mode power supply106depicted inFIG.1may be realized by buck, boost, and/or buck-boost type power technologies. In these embodiments, the switch-mode power supply106may be controlled to apply varying levels of pulsed power to induce a potential on the surface of the substrate110.

In other embodiments, the switch-mode power supply106is realized by other more sophisticated switch mode power and control technologies. Referring next toFIG.2, for example, the switch-mode power supply described with reference toFIG.1is realized by a switch-mode bias supply206that is utilized to apply power to the substrate110to effectuate one or more desired energies of the ions that bombard the substrate110. Also shown are an ion energy control component220, an arc detection component222, and a controller212that is coupled to both the switch-mode bias supply206and a waveform memory224.

The illustrated arrangement of these components is logical; thus the components can be combined or further separated in an actual implementation, and the components can be connected in a variety of ways without changing the basic operation of the system. In some embodiments for example, the controller212, which may be realized by hardware, software, firmware, or a combination thereof, may be utilized to control both the power supply202and switch-mode bias supply206. In alternative embodiments, however, the power supply202and the switch-mode bias supply206are realized by completely separated functional units. By way of further example, the controller212, waveform memory224, ion energy control portion220and the switch-mode bias supply206may be integrated into a single component (e.g., residing in a common housing) or may be distributed among discrete components.

The switch-mode bias supply206in this embodiment is generally configured to apply a voltage to the support208in 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 supply206is 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 portion220, the switch-mode bias supply206applies 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 memory224. 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).

As depicted, the switch-mode power supply206includes switch components226′,226″ (e.g., high power field effect transistors) that are adapted to switch power to the support208of the substrate210responsive to drive signals from corresponding drive components228′,228″. And the drive signals230′,230″ that are generated by the drive components228′,228″ are controlled by the controller212based upon timing that is defined by the content of the waveform memory224. For example, the controller212in many embodiments is adapted to interpret the content of the waveform memory and generate drive-control signals232′,232″, which are utilized by the drive components228′,228″ to control the drive signals230′,230″ to the switching components226′,226″. Although two switch components226′,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).

In many modes of operation, the controller212(e.g., using the waveform data) modulates the timing of the drive-control signals232′,232″ to effectuate a desired waveform at the support208of the substrate210. In addition, the switch mode bias supply206is adapted to supply power to the substrate210based upon an ion-energy control signal234, which may be a DC signal or a time-varying waveform. Thus, the present embodiment enables control of ion distribution energies by controlling timing signals to the switching components and controlling the power (controlled by the ion energy control component220) that is applied by the switching components226′,226″.

In addition, the controller212in this embodiment is configured, responsive to an arc in the plasma chamber204being detected by the arc detection component222, to carry out arc management functions. In some embodiments, when an arc is detected the controller212alters the drive-control signals232′,232″ so that the waveform applied at the output236of the switch mode bias supply206extinguishes arcs in the plasma214. In other embodiments, the controller212extinguishes arcs by simply interrupting the application of drive-control signals232′,232″ so that the application of power at the output236of the switch-mode bias supply206is interrupted.

Referring next toFIG.3, it is a schematic representation of components that may be utilized to realize the switch-mode bias supply206described with reference toFIG.2. As shown, the switching components T1and T2in this embodiment are arranged in a half-bridge (also referred to as or totem pole) type topology. Collectively, R2, R3, C1, and C2represent a plasma load, C10is an effective capacitance (also referred to herein as a series capacitance or a chuck capacitance), and C3is 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. C10is 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. As depicted, L1is stray inductance (e.g., the natural inductance of the conductor that feeds the power to the load). And in this embodiment, there are three inputs: Vbus, V2, and V4.

V2and V4represent drive signals (e.g., the drive signals230′,230″ output by the drive components228′,228″ described with reference toFIG.2), and in this embodiment, V2and V4can be timed (e.g., the length of the pulses and/or the mutual delay) so that the closure of T1and T2may be modulated to control the shape of the voltage output Vout, which is applied to the substrate support. In many implementations, the transistors used to realize the switching components T1and T2are 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 V2and V4enables a desired waveform to be applied at Vout.

For example, the switches T1, T2may be operated so that the voltage at the surface of the substrate110,210is 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 substrate110,210is what defines the energy of the ions, which may be characterized in terms of an ion energy distribution function (IEDF). To effectuate desired voltage(s) at the surface of the substrate110,210, 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 substrate110,210so as to attract enough electrons to the surface of the substrate110,210in 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 T1, 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. Referring briefly again toFIG.2, 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, V4may 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. In other words, the voltage Vbus may affect the pulse width, pulse shape and/or the relative phase of the signals V2, V4. Referring briefly toFIG.4, for example, shown is a timing diagram depicting two drive signal waveforms that may be applied to T1and T2(as V2and V4) so as to generate the period voltage function at Vout as depicted inFIG.4. To modulate the shape of the pulses at Vout (e.g. to achieve the smallest time for the pulse at Vout, yet reach a peak value of the pulses) the timing of the two gate drive signals V2, V4may be controlled.

For example, the two gate drive signals V2, V4may be applied to the switching components T1, T2so 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 substrate110,210to attract electrons to the surface of the substrate110,210. Moreover, it has been found that by changing 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). In some modes of operation, the repetition rate of the gate pulses is about 400 kHz, but this rate may certainly vary from application to application.

Although not required, in practice, based upon modeling and refining upon actual implementation, 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 toFIG.1as a sequence of voltage levels). In addition, in many implementations, 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).

Referring again toFIG.3, Vbus can be modulated to control the energy of the ions, and the stored waveforms may be used to control the gate drive signals V2, V4to achieve a desired pulse amplitude at Vout while minimizing the pulse width. Again, this is done in accordance with the particular characteristics of the transistors, which may be modeled or implemented and empirically established. Referring toFIG.5, for example, shown are graphs depicting Vbus versus time, voltage at the surface of the substrate110,210versus time, and the corresponding ion energy distribution.

The graphs inFIG.5depict a single mode of operating the switch mode bias supply106,206, which effectuates an ion energy distribution that is concentrated at a particular ion energy. As depicted, to effectuate the single concentration of ion energies in this example, the voltage applied at Vbus is maintained constant while the voltages applied to V2and V4are controlled (e.g., using the drive signals depicted inFIG.3) so as to generate pulses at the output of the switch-mode bias supply106,206, which effectuates the corresponding ion energy distribution shown inFIG.5.

As depicted inFIG.5, the potential at the surface of the substrate110,210is generally negative to attract the ions that bombard and etch the surface of the substrate110,210. The periodic short pulses that are applied to the substrate110,210(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 substrate110,210(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 substrate110,210. As depicted inFIG.5, 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. In other modes of operation, two or more separate concentrations of ion energies may be created (e.g., seeFIG.49).

One of skill in the art will recognize that 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. As such, 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, VPS.

Referring next toFIG.6, for example, shown are graphs depicting a bi-modal mode of operation in which two separate peaks in ion energy distribution are generated. As shown, in this mode of operation, the substrate experiences two distinct levels of voltages and periodic pulses, and as a consequence, two separate concentrations of ion energies are created. As depicted, to effectuate the two distinct ion energy concentrations, the voltage that is applied at Vbus alternates between two levels, and each level defines the energy level of the two ion energy concentrations.

AlthoughFIG.6depicts the two voltages at the substrate110,210as alternating after every pulse (e.g.,FIG.48), this is certainly not required. In other modes of operation for example, the voltages applied to V2and V4are switched (e.g., using the drive signals depicted inFIG.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).

In prior art techniques, attempts have been made to apply the combination of two waveforms (generated by waveform generators) to a linear amplifier and apply the amplified combination of the two waveforms to the substrate in order to effectuate multiple ion energies. This approach, however, is much more complex then the approach described with reference toFIG.6, and requires an expensive linear amplifier, and waveform generators.

Referring next toFIGS.7A and7B, 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. As depicted inFIG.7A, the ion energy distribution is concentrated around 80 eV responsive to a non-varying application of a voltage to Vbus (e.g., as depicted inFIG.5). And inFIG.7B, 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 inFIG.6).

Referring next toFIG.8, shown is a block diagram depicting another embodiment of the present invention. As depicted, a switch-mode power supply806is coupled to a controller812, an ion-energy control component820, and a substrate support808via an arc detection component822. The controller812, switch-mode supply806, and ion energy control component820collectively operate to apply power to the substrate support808so as to effectuate, on a time-averaged basis, a desired (or defined) ion energy distribution at the surface of the substrate810.

Referring briefly toFIG.9Afor example, 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.9Bis an exploded view of the portion of the periodic voltage function that is circled inFIG.9A, andFIG.9Cdepicts the resulting distribution of ion energies, on a time-averaged basis, that results from the sinusoidal modulation of the periodic voltage function. AndFIG.9Ddepicts 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. As discussed further herein, 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.

Referring toFIGS.10A and10Bas another example, 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 inFIG.10Con a time-averaged basis. As depicted, the periodic voltage function utilized in connection withFIG.10is the same as inFIG.9, except that the periodic voltage function inFIG.10is modulated by a sawtooth function instead of a sinusoidal function.

It should be recognized that the ion energy distribution functions depicted inFIGS.9C and10Cdo not represent an instantaneous distribution of ion energies at the surface of the substrate810, but instead represent the time average of the ion energies. With reference toFIG.9C, for example, at a particular instant in time, 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.

It should also be recognized that 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. For example, if a particular distribution of ion energies is needed to etch a particular geometric construct or to etch through a particular material, 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.

Similarly, the periodic voltage function (e.g., the 400 kHz components inFIGS.9A,9B,10A, and10Band Vout inFIG.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 substrate810.

Referring back toFIG.8, the controller812provides drive-control signals832′,832″ to the switch-mode supply806so that the switch-mode supply806generates a periodic voltage function. The switch mode supply806may be realized by the components depicted inFIG.3(e.g., to create a periodic voltage function depicted inFIG.4), but it is certainly contemplated that other switching architectures may be utilized.

In general, the ion energy control component820functions to apply a modulating function to the periodic voltage function (that is generated by the controller812in connection with the switch mode power supply806). As shown inFIG.8, the ion energy control component820includes a modulation controller840that is in communication with a custom IEDF portion850, an IEDF function memory848, a user interface846, and a power component844. 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 modulation controller840in this embodiment generally controls the power component844(and hence its output834) based upon data that defines a modulation function, and the power component844generates the modulation function (based upon a control signal842from the modulation controller840) that is applied to the periodic voltage function that is generated by the switch-mode supply806. The user interface846in this embodiment is configured to enable a user to select a predefined IEDF function that is stored in the IEDF function memory848, or in connection with the custom IEDF component850, define a custom IEDF

In many implementations, the power component844includes 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 inFIG.3). In these implementations, the modulation controller840controls the voltage level that is output by the power component844so that the power component844applies a voltage that conforms to the modulating function.

In some implementations, the IEDF function memory848includes a plurality of data sets that correspond to each of a plurality of IEDF distribution functions, and the user interface846enables a user to select a desired (or defined) IEDF function. Referring toFIG.11for example, shown in the right column are exemplary IEDF functions that may be available for a user to select. And the left column depicts the associated modulating function that the modulation controller840in connection with the power component844would apply to the periodic voltage function to effectuate the corresponding IEDF function. It should be recognized that the IEDF functions depicted inFIG.11are only exemplary and that other IEDF functions may be available for selection.

The custom IEDF component850generally functions to enable a user, via the user interface846, to define a desired (or defined) ion energy distribution function. In some implementations for example, the custom IEDF component850enables a user to establish values for particular parameters that define a distribution of ion energies.

For example, the custom IEDF component850may 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. In many instances, only IF-high, IF-low, and the IEDF function between these levels is sufficient to define an IEDF function. As a specific example, 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.

It is also contemplated that the custom IEDF portion850may 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. And in yet alternative embodiments, it is contemplated that the custom IEDF component850in connection with the user interface846enables 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.

In addition, it is also contemplated that the IEDF function memory848and the custom IEDF component850may interoperate to enable a user to select a predefined IEDF function and then alter the predefined IEDF function so as to produce a custom IEDF function that is derived from the predefined IEDF function.

Once an IEDF function is defined, the modulation controller840translates data that defines the desired (or defined) IEDF function into a control signal842, which controls the power component844so that the power component844effectuates the modulation function that corresponds to the desired (or defined) IEDF. For example, the control signal842controls the power component844so that the power component844outputs a voltage that is defined by the modulating function.

Referring next toFIG.12, it is a block diagram depicting an embodiment in which an ion current compensation component1260compensates for ion current in the plasma chamber1204. Applicants have found that, at higher energy levels, higher levels of ion current within the chamber affect the voltage at the surface of the substrate, and as a consequence, the ion energy distribution is also affected. Referring briefly toFIGS.15A-15Cfor example, shown are voltage waveforms as they appear at the surface of the substrate1210or wafer and their relationship to IEDF.

More specifically,FIG.15Adepicts a periodic voltage function at the surface of the substrate1210when ion current IIis equal to compensation current Ic;FIG.15Bdepicts the voltage waveform at the surface of the substrate1210when ion current IIis greater than the compensation current Ic; andFIG.15Cdepicts the voltage waveform at the surface of the substrate when ion current is less than the compensation current Ic.

As depicted inFIG.15A, when II=Ic a spread of ion energies1470is relatively narrow as compared to a uniform spread1472of ion energies when II>Ic as depicted inFIG.15Bor a uniform spread1474of ion energies when II<Ic as depicted inFIG.15C. Thus, the ion current compensation component1260enables 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 spread1572,1574of uniform ion energy to be controlled (e.g., when it is desirable to have a spread of ion energies).

As depicted inFIG.15B, without ion current compensation (when II>Ic) the voltage at the surface of the substrate, between the positive portions of the periodic voltage function, becomes less negative in a ramp-like manner, which produces a broader spread1572of ion energies. Similarly, when ion current compensation is utilized to increase a level of compensation current to a level that exceeds the ion current (II<Ic) as depicted inFIG.15C, the voltage at the surface of the substrate becomes more negative in a ramp-like manner between the positive portions of the periodic voltage function, and a broader spread1574of uniform ion energies is produced.

Referring back toFIG.12, the ion current compensation component1260may be realized as a separate accessory that may optionally be added to the switch mode power supply1206and controller1212. In other embodiments, (e.g., as depicted inFIG.13) the ion current compensation component1260may share a common housing1366with other components described herein (e.g., the switch-mode power supply106,206,806,1206and ion energy control220,820components). In this embodiment, the periodic voltage function provided to the plasma chamber1204can be referred to as a modified periodic voltage function since it comprises the periodic voltage function modified by the ion current compensation from ion current compensation component1260. The controller1212can sample a voltage at different times at an electrical node where outputs of the switch mode power supply1206and the ion current compensation1260combine.

As depicted inFIG.13, shown is an exemplary ion current compensation component1360that includes a current source1364coupled to an output1336of a switch mode supply and a current controller1362that is coupled to both the current source1364and the output1336. Also depicted inFIG.13is a plasma chamber1304, and within the plasma chamber are capacitive elements C1, C2, and ion current II. As depicted, C1represents the inherent capacitance (also referred to herein as effective capacitance) of components associated with the chamber1304, which may include, but is not limited to, insulation, the substrate, substrate support, and an e-chuck, and C2represents sheath capacitance and stray capacitances. In this embodiment, the periodic voltage function provided to the plasma chamber1304, and measurable at V0, can be referred to as a modified periodic voltage function since it comprises the periodic voltage function modified by the ion current compensation, Ic.

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, λsheath, is a function of plasma characteristics such as plasma density and plasma temperature.

It should be noted that because C1in this embodiment is an inherent (also referred to herein as effective) capacitance of components associated with the chamber1304, it is not an accessible capacitance that is added to gain control of processing. For example, some prior art approaches that utilize a linear amplifier couple bias power to the substrate with a blocking capacitor, and then utilize a monitored voltage across the blocking capacitor as feedback to control their linear amplifier. Although a capacitor could couple a switch mode power supply to a substrate support in many of the embodiments disclosed herein, it is unnecessary to do so because feedback control using a blocking capacitor is not required in several embodiments of the present invention.

While referring toFIG.13, simultaneous reference is made toFIG.14, which is a graph depicting an exemplary voltage (e.g., the modified periodic voltage function) at Vo depicted inFIG.13. In operation, the current controller1362monitors the voltage at Vo, and ion current is calculated over an interval t (depicted inFIG.14) as:

II=C1⁢dVodt(Equation⁢1)

Ion current, II, and inherent capacitance (also referred to as effective capacitance), C1, can either or both be time varying. Because C1is substantially constant for a given tool and is measureable, only Vo needs to be monitored to enable ongoing control of compensation current. As discussed above, to obtain a more mono-energetic distribution of ion energy (e.g., as depicted inFIG.15A) the current controller controls the current source1364so 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. And in addition, if desired, the spread of the ion energy may be controlled as depicted inFIGS.15B and15Cso that additional ion energies are realized at the surface of the substrate.

Also depicted inFIG.13is a feedback line1370, which may be utilized in connection with controlling an ion energy distribution. For example, the value of ΔV (also referred to herein as a voltage step or the third portion1406) depicted inFIG.14, is indicative of instantaneous ion energy and may be used in many embodiments as part of a feedback control loop. In one embodiment, the voltage step, ΔV, is related to ion energy according to Equation 4. In other embodiments, the peak-to-peak voltage, VPPcan be related to the instantaneous ion energy. Alternatively, the difference between the peak-to-peak voltage, VPP, and the product of the slope, dV0/dt, of the fourth portion1408times time, t, can be correlated to the instantaneous ion energy (e.g., VPP−dV0/dt·t).

Referring next toFIG.16, shown is an exemplary embodiment of a current source1664, which may be implemented to realize the current source1364described with reference toFIG.13. In this embodiment, a controllable negative DC voltage source, in connection with a series inductor L2, function as a current source, but one of ordinary skill in the art will appreciate, in light of this specification, that a current source may be realized by other components and/or configurations.

FIG.43illustrates one embodiment of a method of controlling an ion energy distribution of ions impacting a surface of a substrate. The method4300starts by applying a modified periodic voltage function4302(see the modified periodic voltage function4402inFIG.44) to a substrate support supporting a substrate within a plasma processing chamber. The modified periodic voltage function can be controlled via at least two ‘knobs’ such as an ion current compensation, IC, (see IC4404inFIG.44) and a power supply voltage, VPS, (see power supply voltage4406inFIG.44). An exemplary component for generating the power supply voltage is the switch mode power supply106inFIG.1. 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, IC,4304. At least two samples of a voltage of the modified periodic voltage function are taken for each value of the ion current compensation, IC. The sampling4304is performed in order to enable calculations4306(or determinations) of the ion current, II, and a sheath capacitance, Csheath,4306. Such determination may involve finding an ion current compensation, IC, 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 calculations4306can also optionally include determining a voltage step, ΔV, (also known as a third portion1406of the modified periodic voltage function1400) based on the sampling4304of the waveform of the modified periodic voltage function. The voltage step, ΔV, can be related to the ion energy of ions reaching the substrate's surface. When finding the ion current, II, for the first time, the voltage step, ΔV, can be ignored. Details of the sampling4304and the calculations4306will be provided in discussions ofFIG.30to follow.

Once the ion current, II, and sheath capacitance, Csheath, are known, the method4300may move to the method3100ofFIG.31involving setting and monitoring an ion energy and a shape (e.g., width) of the IEDF. For instance,FIG.46illustrates how a change in the power supply voltage can effect a change in the ion energy. In particular, a magnitude of the illustrated power supply voltage is decreased resulting in a decreased magnitude of the ion energy. Additionally,FIG.47illustrates that given a narrow IEDF4714, the IEDF can be widened by adjusting the ion current compensation, IC. Alternatively or in parallel, the method4300can perform various metrics as described with reference toFIGS.32-41that make use of the ion current, II, the sheath capacitance, Csheath, and other aspects of the waveform of the modified periodic voltage function.

In addition to setting the ion energy and/or the IEDF width, the method4300may adjust the modified periodic voltage function4308in order to maintain the ion energy and the IEDF width. In particular, adjustment of the ion current compensation, IC, provided by an ion current compensation component, and adjustment of the power supply voltage may be performed4308. In some embodiments, the power supply voltage can be controlled by a bus voltage, Vbus, of the power supply (e.g., the bus voltage VbusofFIG.3). The ion current compensation, IC, controls the IEDF width, and the power supply voltage controls the ion energy.

After these adjustments4308, the modified periodic voltage function can again be sampled4304and calculations of ion current, II, sheath capacitance, Csheath, and the voltage step, ΔV, can again be performed4306. If the ion current, II, or the voltage step, ΔV, are other than defined values (or in the alternative, desired values), then the ion current compensation, IC, and/or the power supply voltage can be adjusted4308. Looping of the sampling4304, calculating,4306, and adjusting4308may occur in order to maintain the ion energy, eV, and/or the IEDF width.

FIG.30illustrates another embodiment of a method of controlling an ion energy distribution of ions impacting a surface of a substrate. In some embodiments, as discussed above, it may be desirable to achieve a narrow IEDF width (e.g., a minimum IEDF width or in the alternative, ˜6% full-width half maximum). As such, the method3000can provide a modified periodic voltage function to the chamber and to the substrate support such that a constant substrate voltage, and hence sheath voltage, exists at the surface of the substrate. This in turn accelerates ions across the sheath at a substantially constant voltage thus enabling ions to impact the substrate with substantially the same ion energy, which in turn provides a narrow IEDF width. For instance, inFIG.45it can be seen that adjusting the ion current compensation, IC, can cause the substrate voltage, Vsub, between pulses to have a constant, or substantially constant voltage thus causing the IEDF to narrow.

Such a modified periodic voltage function is achieved when the ion current compensation, IC, equals the ion current, II, assuming no stray capacitances (see the last five cycles of the periodic voltage function (V0) inFIG.45). In the alternative, where stray capacitance, Cstray, is considered, the ion current compensation, IC, is related to the ion current, II, according to Equation 2:

II=IC⁢C1C1+Cstray(Equation⁢2)where, C1, is an effective capacitance (e.g., the inherent capacitance described with reference toFIGS.3and13). The effective capacitance, C1, can vary in time or be constant. For the purposes of this disclosure, the narrow IEDF width can exist when either II=ICor, in the alternative, when Equation 2 is met.FIGS.45-50use the nomenclature, II=IC, but it should be understood that these equalities are merely simplifications of Equation 2, and thus Equation 2 could substitute for the equalities used inFIGS.45-50. The stray capacitance, Cstray, is a cumulative capacitance of the plasma chamber as seen by the power supply. There are eight cycles illustrated inFIG.45.

The method3000can begin with an application of a modified periodic voltage function (e.g., the modified periodic voltage function depicted inFIG.14or the modified periodic voltage function4402inFIG.44) to the substrate support3002(e.g., substrate support108inFIG.1). A voltage of the modified periodic voltage function can be sampled3004at two or more times, and from this sampling, a slope dV0/dt for at least a portion of a cycle of the modified periodic voltage function can be calculated3006(e.g., a slope of the portion between the pulses or the fourth portion1408). At some point before a decision3010, a previously-determined value of an effective capacitance C1(e.g., inherent capacitance C1inFIG.13, and an inherent capacitance C10inFIG.3) can be accessed3008(e.g., from a memory or from a user input). Based on the slope, dV0/dt, the effective capacitance, C1, and the ion current compensation, IC, a function ƒ (Equation 3), can be evaluated for each value of the ion current compensation, IC, as follows:

f⁡(IC)=dV0dt-ICC1=0(Equation⁢3)

If the function ƒ is true, then the ion current compensation, IC, equals the ion current, II, or in the alternative, makes Equation 2 true, and a narrow IEDF width has been achieved3010(e.g., seeFIG.45). If the function ƒ is not true, then the ion current compensation, IC, can be adjusted3012further until the function ƒ is true. Another way to look at this is that the ion current compensation, IC, can be adjusted until it matches the ion current, II, (or in the alternative, meets the relationship of Equation 2), at which point a narrow IEDF width will exist. Such an adjustment to the ion current compensation, Ic, and resulting narrowing of the IEDF, can be seen inFIG.45. The ion current, II, and the corresponding ion current compensation, Ic, can be stored (e.g., in a memory) in store operation3014. The ion current, IC, can vary in time, as can the effective capacitance, C1.

When Equation 3 is met, ion current, II, is known (either because IC=II, or because Equation 2 is true). Thus, the method3000enables remote and non-invasive measurements of ion current, II, in real time without affecting the plasma. This leads to a number of novel metrics such as those that will be described with reference toFIGS.32-41(e.g., remote monitoring of plasma density and remote fault detection of the plasma source).

While adjusting3012the compensation current, IC, the ion energy will likely be broader than a delta function and the ion energy will resemble that of eitherFIGS.15B,15C, or44. However, once the compensation current, IC, is found that meets Equation 2, the IEDF will appear as illustrated inFIG.15Aor the right portion ofFIG.45—as having a narrow IEDF width (e.g., a minimum IEDF width). This is because the voltage between pulses of the modified periodic voltage function causes a substantially constant sheath or substrate voltage, and hence ion energy, when IC=II(or alternatively when Equation 2 is true). InFIG.46the substrate voltage,4608, includes pulses between the constant voltage portions. These pulses have such a short duration that their effect on ion energy and IEDF is negligible and thus the substrate voltage4608is referred to as being substantially constant.

The following provides further details about each of the method steps illustrated inFIG.30. In one embodiment, the modified periodic voltage function can have a waveform like that illustrated inFIG.14and can include a first portion (e.g., first portion1402), a second portion (e.g.,1404), a third portion (e.g., third portion1406), and a fourth portion (e.g., fourth portion1408), where the third portion can have a voltage step, ΔV, and the fourth portion can have a slope, dV0/dt. The slope, dV0/dt, can be positive, negative, or zero. The modified periodic voltage function1400can also be described as having pulses comprising the first portion1402, the second portion1404, and the third portion1406, and a portion between the pulses (fourth portion1408).

The modified periodic voltage function can be measured as V0inFIG.3and can appear as the modified periodic voltage function4402inFIG.44. The modified period voltage function4402is produced by combining the power supply voltage4406(also known as the periodic voltage function) with the ion current compensation4404. The power supply voltage4406is largely responsible for generating and shaping the pulses of the modified periodic voltage function4402and the ion current compensation4404is largely responsible for generating and shaping the portion between the pulses, which is often a straight sloped voltage. Increasing the ion current compensation, Ic, causes a decrease in a magnitude of the slope of the portion between the pulses as seen inFIG.45. Decreasing a magnitude of the power supply voltage4606causes a decrease in a magnitude of the amplitude of the pulses and the peak-to-peak voltage of the modified periodic voltage function4602as seen inFIG.46.

In cases where the power supply is a switch-mode power supply, the switching diagram4410of a first switch T1and a second switch T2can apply. For instance, the first switch T1can be implemented as the switch T1inFIG.3and the second switch T2can be implemented as the second switch T2inFIG.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 inFIG.4. When the first switch T1is on, the power supply voltage is drawn to a maximum magnitude, which is a negative value inFIG.44since the power supply has a negative bus voltage. The second switch T2is turned off during this period so that the power supply voltage4406is isolated from ground. When the switches reverse, the power supply voltage4406approaches and slightly passes ground. In the illustrated embodiment, there are two pulse widths, but this is not required. In other embodiments, 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 support3002, and sampled3004as V0at 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 voltage4406inFIG.44) can be sourced from a power supply such as the switch mode power supply1206inFIG.12. The ion current compensation4404inFIG.44can be sourced from a current source such as the ion current compensation component1260inFIG.12or1360inFIG.13.

A portion of or the whole modified periodic voltage function can be sampled3004. For instance, the fourth portion (e.g., fourth portion1408) can be sampled. The sampling3004can be performed between the power supply and the substrate support. For instance, inFIG.1, the sampling3004can be performed between the switch mode power supply106and the support108. InFIG.3, the sampling3004can be performed between the inductor L1and the inherent capacitance C10. In one embodiment, the sampling3004can be performed at V0between the capacitance C3and the inherent capacitance C10. Since the inherent capacitance C10and the elements representing the plasma (R2, R3, C1, and C2) are not accessible for real time measurement, the sampling3004is typically performed to the left of the inherent capacitance C10inFIG.3. Although the inherent capacitance C10typically is not measured during processing, it is typically a known constant, and can therefore be set during manufacturing. At the same time, in some cases the inherent capacitance C10can vary with time.

While only two samples of the modified periodic voltage function are needed in some embodiments, in others, hundreds, thousands, or tens of thousands of samples can be taken for each cycle of the modified periodic voltage function. For instance, 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 portions1402,1404,1406,1408of the periodic voltage function illustrated inFIG.14can be distinguished, which may not be possible at traditional sampling rates. In some embodiments, the higher sampling rates enable resolving of the voltage step, ΔV, and the slope, dV0/dt, which are not possible in the art. In some embodiments, a portion of the modified periodic voltage function can be sampled while other portions are not sampled.

The calculation3006of the slope, dV0/dt, can be based on a plurality of V0measurements taken during the time t (e.g., the fourth portion1408). For instance, a linear fit can be performed to fit a line to the V0values where the slope of the line gives the slope, dVo/dt. In another instance, the V0values at the beginning and end of time t (e.g., the fourth portion1408) inFIG.14can be ascertained and a line can be fit between these two points with the slope of the line given as dVo/dt. These are just two of numerous ways that the slope, dVo/dt, of the portion between the pulses can be calculated.

The decision3010can 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, II(or in the alternative, is related to IIaccording 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 voltage4608(Vsub) can be seen inFIG.46. Thus, either ion current, II, or alternatively ion current compensation, Ic, can be used in Equation 3.

Alternatively, two values along the fourth portion1408(also referred to as the portion between the pulses) 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, II, 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, II, can be found.

The adjustment to the ion current compensation, Ic,3012can 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. In some embodiments, a sign of the function ƒ 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.

Once an ion current compensation, Ic, has been identified that equals the ion current, II(or in the alternative, is related thereto according to Equation 2), the method3000can advance to further set point operations (seeFIG.31) or remote chamber and source monitoring operations (seeFIGS.32-41). The further set point operations can include setting the ion energy (see alsoFIG.46) and the distribution of ion energy or IEDF width (see alsoFIG.47). The source and chamber monitoring can include monitoring plasma density, source supply anomalies, plasma arcing, and others.

Furthermore, the method3000can optionally loop back to the sampling3004in order to continuously (or in the alternative, periodically) update the ion current compensation, Ic. For instance, the sampling3004, calculation3006, the decision3010, and the adjusting3012can periodically be performed given a current ion current compensation, Ic, in order to ensure that Equation 3 continues to be met. At the same time, if the ion current compensation, Ic, that meets Equation 3 is updated, then the ion current, II, can also be updated and the updated value can be stored3014.

While the method3000can find and set the ion current compensation, Ic, so as to equal the ion current, II, 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, IC, to that value. For instance, by applying a first ion current compensation, Ic1, for a first cycle and measuring a first slope, dV01/dt, of the voltage between the pulses, and by applying a second ion current compensation, Ic2, for a second cycle and measuring a second slope, dV02/dt, of the voltage between the pulses, a third slope, dV03/dt, associated with a third ion current compensation, Ic3, can be determined at which Equation 3 is expected to be true. The third ion current compensation, Ic3, can be one that if applied would result in a narrow IEDF width. Hence, the ion current compensation, Ic, that meets Equation 3 and thus corresponds to ion current, II, can be determined with only a single adjustment of the ion current compensation. The method3000can then move on to the methods described inFIG.31and/orFIGS.32-41without ever setting the ion current, IC, to a value needed to achieve the narrow IEDF width. Such an embodiment may be carried out in order to increase tuning speeds.

FIG.31illustrates methods for setting the IEDF width and the ion energy. The method originates from the method3000illustrated inFIG.30, and can take either of the left path3100(also referred to as an IEDF branch) or the right path3101(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, ΔV, or the third portion1406of the modified periodic voltage function1400ofFIG.14. The relationship between ion energy, eV, and the voltage step, ΔV, can be written as Equation 4:

eV=ΔV⁢C1C2+C1(Equation⁢4)where C1is the effective capacitance (e.g., chuck capacitance; inherent capacitance, C10, inFIG.3; or inherent capacitance, C1, inFIG.13), and C2is a sheath capacitance (e.g., the sheath capacitance C4inFIG.3or the sheath capacitance C2inFIG.13). The sheath capacitance, C2, may include stray capacitances and depends on the ion current, II. The voltage step, ΔV, can be measured as a change in voltage between the second portion1404and the fourth portion1408of the modified periodic voltage function1400. By controlling and monitoring the voltage step, ΔV, (which is a function of a power supply voltage or a bus voltage such as bus voltage, VbusinFIG.3), ion energy, eV, can be controlled and known.

At the same time, the IEDF width can be approximated according to Equation 5:

IEDF⁢width=VPP-ΔV-ItC(Equation⁢5)where I is IIwhere C is Cseries, or I is ICwhere C is Ceffective. Time, t, is the time between pulses, VPP, is the peak-to-peak voltage, and ΔV is the voltage step.

Additionally, sheath capacitance, C2, can be used in a variety of calculations and monitoring operations. For instance, the Debye sheath distance, λsheath, can be estimated as follows:

λsheath=ϵ⁢AC2(Equation⁢6)where ϵ is vacuum permittivity and A is an area of the substrate (or in an alternative, a surface area of the substrate support). In some high voltage applications, Equation 6 is written as equation 7:

λsheath=Te.ϵ0ne⁢q·(V2⁢Te).75(Equation⁢7)

Additionally, an e-field in the sheath can be estimated as a function of the sheath capacitance, C2, the sheath distance, λsheath, and the ion energy, eV. Sheath capacitance, C2, along with the ion current, II, can also be used to determine plasma density, ne, from Equation 8 where saturation current, Isat, is linearly related to the compensation current, IC, for singly ionized plasma.

Isat=∑ni⁢qi⁢kTemi⁢A≈ne⁢q⁢kTe〈m〉⁢A(Equation⁢8)

An effective mass of ions at the substrate surface can be calculated using the sheath capacitance, C2and the saturation current, Isat. Plasma density, ne, electric field in the sheath, ion energy, eV, effective mass of ions, and a DC potential of the substrate, VDC, 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.

As seen in Equation 4, the sheath capacitance, C2, can also be used to monitor and control the ion energy, eV, as illustrated in the ion energy branch3101of FIG.31. The ion energy branch3101starts by receiving a user selection of ion energy3102. The ion energy branch3101can then set an initial power supply voltage for the switch-mode power supply that supplies the periodic voltage function3104. At some point before a sample periodic voltage operation3108, the ion current can also be accessed3106(e.g., accessed from a memory). The periodic voltage can be sampled3108and a measurement of the third portion of the modified periodic voltage function can be measured3110. Ion energy, II, can be calculated from the voltage step, ΔV, (also referred to as the third portion (e.g., third portion1406)) of the modified periodic voltage function3112. The ion energy branch3101can then determine whether the ion energy equals the defined ion energy3114, and if so, the ion energy is at the desired set point and the ion energy branch3101can come to an end. If the ion energy is not equal to the defined ion energy, then the ion energy branch3101can adjust the power supply voltage3116, and again sample the periodic voltage3108. The ion energy branch3101can then loop through the sampling3108, measuring3110, calculating3112, decision3114, and the setting3116until the ion energy equals the defined ion energy.

The method for monitoring and controlling the IEDF width is illustrated in the IEDF branch3100ofFIG.31. The IEDF branch3100includes receiving a user selection of an IEDF width3150and sampling a current IEDF width3152. A decision3154then determines whether the defined IEDF width equals the current IEDF width, and if the decision3152is met, then the IEDF width is as desired (or defined), and the IEDF branch3100can 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 adjusted3156. This determination3154and the adjustment3156can continue in a looping manner until the current IEDF width equals the defined IEDF width.

In some embodiments, the IEDF branch3100can also be implemented to secure a desired IEDF shape. Various IEDF shapes can be generated and each can be associated with a different ion energy and IEDF width. For instance, a first IEDF shape may be a delta function while a second IEDF shape may be a square function. Other IEDF shapes may be cupped. Examples of various IEDF shapes can be seen inFIG.11.

With knowledge of the ion current, II, and the voltage step, ΔV, Equation 4 can be solved for ion energy, eV. The voltage step, ΔV, can be controlled by changing the power supply voltage which in turn causes the voltage step, ΔV, to change. A larger power supply voltage causes an increase in the voltage step, ΔV, and a decrease in the power supply voltage causes a decrease in the voltage step, ΔV. In other words, increasing the power supply voltage results in a larger ion energy, eV.

Furthermore, since the above systems and methods operate on a continuously varying feedback loop, 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.

AlthoughFIGS.30-41have been described in terms of a single ion energy, one of skill in the art will recognize that these methods of generating and monitoring a desired (or defined) IEDF width (or IEDF shape) and ion energy can be further utilized to produce and monitor two or more ion energies, each having its own IEDF width (or IEDF shape). For instance, by providing a first power supply voltage, VPS, in a first, third, and fifth cycles, and a second power supply voltage in a second, fourth, and sixth cycles, two distinct and narrow ion energies can be achieved for ions reaching the surface of the substrate (e.g.,FIG.42A). Using three different power supply voltages results in three different ion energies (e.g.,FIG.42B). By varying a time during which each of multiple power supply voltages is applied, or the number of cycles during which each power supply voltage level is applied, the ion flux of different ion energies can be controlled (e.g.,FIG.42C).

The above discussion has shown how combining a periodic voltage function provided by a power supply with an ion current compensation provided by an ion current compensation component, can be used to control an ion energy and IEDF width and/or IEDF shape of ions reaching a surface of a substrate during plasma processing.

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 portions1406and1408illustrated inFIG.14); and (3) a high sampling rate (e.g., 125 MHz) that enables accurate monitoring of the distinct features of the waveform. For instance, where the prior art, such as linear amplifiers, sends a waveform to the substrate that is similar to the modified periodic voltage function, undesired variations between cycles make it difficult to use those prior art waveforms to characterize the ion energy or IEDF width (or IEDF shape).

Where linear amplifiers have been used to bias a substrate support, the need to sample at a high rate has not been seen since the waveform is not consistent from cycle to cycle and thus resolving features of the waveform (e.g., a slope of a portion between pulses) typically would not provide useful information. Such useful information does arise when a fixed waveform is used, as seen in this and related disclosures.

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. A number of examples follow to illustrate just some of the multitude of ways that the heretofore mentioned systems and methods can be used for non-invasive monitoring and fault detection of the source and chamber.

As an example of monitoring, and with reference toFIG.14, the DC offset of the periodic voltage function1400can represent a health of the plasma source (hereinafter referred to as the “source”). In another, a slope of a top portion1404(the second portion) of a pulse of the modified periodic voltage function can be correlated to damping effects within the source. The standard deviation of the slope of the top portion1404from horizontal (illustrated as having a slope equal to 0) is another way to monitor source health based on an aspect of the periodic voltage function1400. Another aspect involves measuring a standard deviation of sampled V0points along the fourth portion1408of the modified periodic voltage function and correlating the standard deviation to chamber ringing. For instance, where 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.32illustrates two modified periodic voltage functions delivered to the substrate support according to one embodiment of this disclosure. When compared, the two modified periodic voltage functions can be used for chamber matching or in situ anomaly or fault detection. For instance, 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. Alternatively, 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 portion3202of the modified periodic voltage functions).

FIG.33illustrates an ion current waveform that can indicate plasma source instability and changes in the plasma density. Fluctuations in ion current, II, such as that illustrated inFIG.33, can be analyzed to identify faults and anomalies in the system. For instance, the periodic fluctuations inFIG.33may indicate a low-frequency instability in the plasma source (e.g., plasma power supply102). Such fluctuations in ion current, II, 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, II, can be used to particular advantage.

FIG.34illustrates an ion current, II, of a modified periodic voltage function having a non-cyclical shape. This embodiment of an ion current, II, can indicate non-cyclical fluctuations such as plasma instability and changes in plasma density. Such a fluctuation may also indicate various plasma instabilities such as arcing, formation of parasitic plasma, or drift in plasma density.

FIG.35illustrates 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 supply1206inFIG.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.36illustrates 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. In each of the three illustrated cycles a nonlinearity in the fourth portion3602of 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.37illustrates 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 dV0/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.38illustrates 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.39illustrates a sampling of ion current for different process parameters. In this illustration 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. For instance 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. For instance, 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.40illustrates 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. In an embodiment 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.

FIG.41illustrates two modified periodic voltage functions that can be used to validate a plasma process. The first modified periodic voltage function can be a reference waveform while the second modified periodic voltage function can be a currently monitored waveform. The currently monitored waveform can be compared to the reference waveform and any differences can indicate parasitic and/or non-capacitive impedance issues that are otherwise not detectable using traditional monitoring methods. For instance, the ringing seen on the waveform ofFIG.35may be detected and could represent ringing in the power supply.

Any of the metrics illustrated inFIGS.32-41can be monitored while the method3000loops in order to update the ion current compensation, Ic, ion current, II, and/or the sheath capacitance, Csheath. For instance, after each ion current, II, sample is taken inFIG.38, the method3000can loop back to the sampling3004in order to determine an updated ion current, II. In another example, as a result of a monitoring operation, a correction to the ion current, II, ion energy, eV, or the IEDF width may be desired. A corresponding correction can be made and the method3000can loop back to the sampling3004to find a new ion current compensation, Ic, that meets Equation 3.

One of skill in the art will recognize that the methods illustrated inFIGS.30,31, and43do not require any particular or described order of operation, nor are they limited to any order illustrated by or implied in the figures. For instance, metrics (FIGS.32-41) can be monitored before, during, or after setting and monitoring the IEDF width and/or the ion energy, eV.

FIG.44illustrates various waveforms at different points in the systems herein disclosed. Given the illustrated switching pattern4410for switching components of a switch mode power supply, power supply voltage, VPS,4406(also referred to herein as a periodic voltage function), ion current compensation, Ic,4404, modified periodic voltage function4402, and substrate voltage, Vsub,4412, the IEDF has the illustrated width4414(which may not be drawn to scale) or IEDF shape4414. This width is wider than what this disclosure has referred to as a “narrow width.” As seen, when the ion current compensation, Ic,4404is greater than the ion current, II, the substrate voltage, Vsub,4412is not constant. The IEDF width4414is proportional to a voltage difference of the sloped portion between pulses of the substrate voltage, Vsub,4412.

Given this non-narrow IEDF width4414, the methods herein disclosed call for the ion current compensation, Ic, to be adjusted until IC=II(or in the alternative are related according to Equation 2).FIG.45illustrates the effects of making a final incremental change in ion current compensation, Ic, in order to match it to ion current II. When IC=IIthe substrate voltage, Vsub,4512becomes substantially constant, and the IEDF width4514goes from non-narrow to narrow.

Once the narrow IEDF has been achieved, one can adjust the ion energy to a desired or defined value as illustrated inFIG.46. Here, a magnitude of the power supply voltage (or in the alternative a bus voltage, Vbus, of a switch-mode power supply) is decreased (e.g., a maximum negative amplitude of the power supply voltage4606pulses is reduced). As a result, ΔV1decreases to ΔV2as does the peak-to-peak voltage, from VPP1to VPP2. A magnitude of the substantially constant substrate voltage, Vsub,4608consequently decreases, thus decreasing a magnitude of the ion energy from4615to4614while maintaining the narrow IEDF width.

Whether the ion energy is adjusted or not, the IEDF width can be widened after the narrow IEDF width is achieved as shown inFIG.47. Here, given II=IC(or in the alternative, Equation 2 giving the relation between IIand IC), ICcan be adjusted thus changing a slope of the portion between pulses of the modified periodic voltage function4702. As a result of ion current compensation, Ic, and ion current, II, being not equal, the substrate voltage moves from substantially constant to non-constant. A further result is that the IEDF width4714expands from the narrow IEDF4714to a non-narrow IEDF4702. The more that ICis adjusted away from II, the greater the IEDF4714width.

FIG.48illustrates one 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 IEDF4814width. A magnitude of the power supply voltage4806alternates each cycle. This results in an alternating ΔV and peak-to-peak voltage for each cycle of the modified periodic voltage function4802. The substrate voltage4812in turn has two substantially constant voltages that alternate between pulses of the substrate voltage. This results in two different ion energies each having a narrow IEDF4814width.

FIG.49illustrates 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 IEDF4914width. Here, the power supply voltage4906alternates between two different magnitudes but does so for two cycles at a time before alternating. As seen, the average ion energies are the same as if VPS4906were alternated every cycle. This shows just one example of how various other patterns of the VPS4906can be used to achieve the same ion energies.

FIG.50illustrates one combination of power supply voltages, VPS,5006and ion current compensation, Ic,5004that can be used to create a defined IEDF5014. Here, alternating power supply voltages5006result in two different ion energies. Additionally, by adjusting the ion current compensation5004away from the ion current, II, the IEDF5014width for each ion energy can be expanded. If the ion energies are close enough, as they are in the illustrated embodiment, then the IEDF5014for both ion energies will overlap resulting in one large IEDF5014. Other variations are also possible, but this example is meant to show how combinations of adjustments to the VPS5006and the IC5004can be used to achieve defined ion energies and defined IEDFs5014.

Referring next toFIGS.17A and17B, shown are block diagrams depicting other embodiments of the present invention. As shown, the substrate support1708in these embodiments includes an electrostatic chuck1782, and an electrostatic chuck supply1780is utilized to apply power to the electrostatic chuck1782. In some variations, as depicted inFIG.17A, the electrostatic chuck supply1780is positioned to apply power directly to the substrate support1708, and in other variations, the electrostatic chuck supply1780is positioned to apply power in connection with the switch mode power supply. It should be noted that serial chucking can be carried by either a separate supply or by use of the controller to effect a net DC chucking function. In this DC-coupled (e.g., no blocking capacitor), series chucking function, the undesired interference with other RF sources can be minimized.

Shown inFIG.18is a block diagram depicting yet another embodiment of the present invention in which a plasma power supply1884that generally functions to generate plasma density is also configured to drive the substrate support1808alongside the switch mode power supply1806and electrostatic chuck supply1880. In this implementation, each of the plasma power supply1884, the electrostatic chuck supply1880, and the switch mode power supply1806may reside in separate assemblies, or two or more of the supplies1806,1880,1884may be architected to reside in the same physical assembly. Beneficially, the embodiment depicted inFIG.18enables a top electrode1886(e.g., shower head) to be electrically grounded so as to obtain electrical symmetry and reduced level of damage due to fewer arcing events.

Referring toFIG.19, shown is a block diagram depicting still another embodiment of the present invention. As depicted, the switch mode power supply1906in this embodiment is configured to apply power to the substrate support and the chamber1904so as to both bias the substrate and ignite (and sustain) the plasma without the need for an additional plasma power supply (e.g., without the plasma power supply102,202,1202,1702,1884). For example, the switch-mode power supply1806may be operated at a duty cycle that is sufficient to ignite and sustain the plasma while providing a bias to the substrate support.

Referring next toFIG.20, it is a block diagram depicting input parameters and control outputs of a control portion that may be utilized in connection with the embodiments described with reference toFIGS.1-19. The depiction of the control portion is intended to provide a simplified depiction of exemplary control inputs and outputs that may be utilized in connection with the embodiments discussed herein—it is not intended to a be hardware diagram. In actual implementation, the depicted control portion may be distributed among several discrete components that may be realized by hardware, software, firmware, or a combination thereof.

With reference to the embodiments previously discussed herein, the controller depicted inFIG.20may provide the functionality of one or more of the controller112described with reference toFIG.1; the controller212and ion energy control220components described with reference toFIG.2; the controller812and ion energy control portion820described with reference toFIG.8; the ion current compensation component1260described with reference toFIG.12; the current controller1362described with reference toFIG.13; the Icc control depicted inFIG.16, controllers1712A,1712B depicted inFIGS.17A and17B, respectively; and controllers1812,1912depicted inFIGS.18and19, respectively.

As shown, the parameters that may be utilized as inputs to the control portion include dVo/dt and ΔV, which are described in more detail with reference toFIGS.13and14. As discussed, dVo/dt may be utilized to in connection with an ion-energy-distribution-spread input ΔE to provide a control signal Icc, which controls a width of the ion energy distribution spread as described with reference toFIGS.12,13,14,15A-C, andFIG.16. In addition, an ion energy control input (Ei) in connection with optional feedback ΔV may be utilized to generate an ion energy control signal (e.g., that affects Vbus depicted inFIG.3) to effectuate a desired (or defined) ion energy distribution as described in more detail with reference toFIGS.1-11. And another parameter that may be utilized in connection with many e-chucking embodiments is a DC offset input, which provides electrostatic force to hold the wafer to the chuck for efficient thermal control.

FIG.21illustrates a plasma processing system2100according to an embodiment of this disclosure. The system2100includes a plasma processing chamber2102enclosing a plasma2104for etching a top surface2118of a substrate2106(and other plasma processes). The plasma is generated by a plasma source2112(e.g., in-situ or remote or projected) powered by a plasma power supply2122. A plasma sheath voltage Vsheathmeasured between the plasma2104and the top surface2118of the substrate2106accelerates ions from the plasma2104across a plasma sheath2115, causing the accelerated ions to impact a top surface2118of a substrate2106and etch the substrate2106(or portions of the substrate2106not protected by photoresist). The plasma2104is at a plasma potential V3relative to ground (e.g., the plasma processing chamber2102walls). The substrate2106has a bottom surface2120that is electrostatically held to a support2108via an electrostatic chuck2111and a chucking potential Vchuckbetween a top surface2121of the electrostatic chuck2111and the substrate2106. The substrate2106is dielectric and therefore can have a first potential V1at the top surface2118and a second potential V2at the bottom surface2120. The top surface of the electrostatic chuck2121is in contact with the bottom surface2120of the substrate, and thus these two surfaces2120,2121are at the same potential, V2. The first potential V1, the chucking potential Vchuck, and the second potential V2, are controlled via an AC waveform with a DC bias or offset generated by a switch mode power supply2130and provided to the electrostatic chuck2111via a first conductor2124. Optionally, the AC waveform is provided via the first conductor2124, and the DC waveform is provided via an optional second conductor2125. The AC and DC output of the switch mode power supply2130can be controlled via a controller2132, which is also configured to control various aspects of the switch mode power supply2130.

Ion energy and ion energy distribution are a function of the first potential V1. The switch mode power supply2130provides an AC waveform tailored to effect a desired first potential V1known 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 inFIGS.5,6,11,14,15a,15b, and15c. The first potential V1can be proportional to the change in voltage ΔV illustrated inFIG.14. The first potential V1is also equal to the plasma voltage V3minus the plasma sheath voltage Vsheath. But since the plasma voltage V3is often small (e.g., less than 20 V) compared to the plasma sheath voltage Vsheath(e.g., 50 V-2000 V), the first potential V1and the plasma sheath voltage Vsheathare approximately equal and for purposes of implementation can be treated as being equal. Thus, since the plasma sheath voltage Vsheathdictates ion energies, the first potential V1is proportional to ion energy distribution. By maintaining a constant first potential V1, the plasma sheath voltage Vsheathis constant, and thus substantially all ions are accelerated via the same energy, and hence a narrow ion energy distribution is achieved. The plasma voltage V3results from energy imparted to the plasma2104via the plasma source2112.

The first potential V1at the top surface2118of the substrate2106is formed via a combination of capacitive charging from the electrostatic chuck2111and charge buildup from electrons and ions passing through the sheath2115. The AC waveform from the switch mode power supply2130is tailored to offset the effects of ion and electron transfer through the sheath2115and the resulting charge buildup at the top surface2118of the substrate2106such that the first potential V1remains substantially constant.

The chucking force that holds the substrate2106to the electrostatic chuck2111is a function of the chucking potential Vchuck. The switch mode power supply2130provides a DC bias, or DC offset, to the AC waveform, so that the second potential V2is at a different potential than the first potential V1. This potential difference causes the chucking voltage Vchuck. The chucking voltage Vchuckcan be measured from the top surface2221of the electrostatic chuck2111to a reference layer inside the substrate2106, where the reference layer includes any elevation inside the substrate except a bottom surface2120of the substrate2106(the exact location within the substrate2106of the reference layer can vary). Thus, chucking is controlled by and is proportional to the second potential V2.

In an embodiment, the second potential V2is equal to the DC offset of the switch mode power supply2130modified by the AC waveform (in other words an AC waveform with a DC offset where the DC offset is greater than a peak-to-peak voltage of the AC waveform). The DC offset may be substantially larger than the AC waveform, such that the DC component of the switch mode power supply2130output dominates the second potential V2and the AC component can be neglected or ignored.

The potential within the substrate2106varies between the first and second potentials V1, V2. The chucking potential Vchuckcan be positive or negative (e.g., V1>V2or V1<V2) since the coulombic attractive force between the substrate2106and the electrostatic chuck2111exists regardless of the chucking potential Vchuckpolarity.

The switch mode power supply2130in conjunction with the controller2132can monitor various voltages deterministically and without sensors. In particular, the ion energy (e.g., mean energy and ion energy distribution) is deterministically monitored based on parameters of the AC waveform (e.g., slope and step). For instance, the plasma voltage V3, ion energy, and ion energy distribution are proportional to parameters of the AC waveform produced by the switch mode power supply2130. In particular the ΔV of the falling edge of the AC waveform (see for exampleFIG.14), is proportional to the first potential V1, and thus to the ion energy. By keeping the first potential V1constant, the ion energy distribution can be kept narrow.

Although the first potential V1cannot be directly measured and the correlation between the switch mode power supply output and the first voltage V1may vary based on the capacitance of the substrate2106and processing parameters, a constant of proportionality between ΔV and the first potential V1can be empirically determined after a short processing time has elapsed. For instance, where the falling edge ΔV of the AC waveform is 50 V, and the constant of proportionality is empirically found to be 2 for the given substrate and process, the first potential V1can be expected to be 100 V. A proportionality between the step voltage, ΔV, and the first potential V1(and thus also ion energy, eV) is described by Equation 4. Thus, the first potential V1, along with ion energy, and ion energy distribution can be determined based on knowledge of the AC waveform of the switch mode power supply without any sensors inside the plasma processing chamber2102. Additionally, the switch mode power supply2130in conjunction with the controller2132can monitor when and if chucking is taking place (e.g., whether the substrate2106is being held to the electrostatic chuck2111via the chucking potential Vchuck).

Dechucking is performed by eliminating or decreasing the chucking potential Vchuck. This can be done by setting the second potential V2equal to the first potential V1. In other words, the DC offset and the AC waveform can be adjusted in order to cause the chucking voltage Vchuckto approach 0 V. Compared to conventional dechucking methods, the system2100achieves faster dechucking and thus greater throughput since both the DC offset and the AC waveform can be adjusted to achieve dechucking. Also, when the DC and AC power supplies are in the switch mode power supply2130, their circuitry is more unified, closer together, can be controlled via a single controller2132(as compared to typical parallel arrangements of DC and AC power supplies), and change output faster. The speed of dechucking enabled by the embodiments herein disclosed also enables dechucking after the plasma2104is extinguished, or at least after power from the plasma source2112has been turned off.

The plasma source2112can take a variety of forms. For instance, in an embodiment, the plasma source2112includes an electrode inside the plasma processing chamber2102that establishes an RF field within the chamber2102that both ignites and sustains the plasma2104. In another embodiment, the plasma source2112includes a remote projected plasma source that remotely generates an ionizing electromagnetic field, projects or extends the ionizing electromagnetic field into the processing chamber2102, and both ignites and sustains the plasma2104within the plasma processing chamber using the ionizing electromagnetic field. Yet, the remote projected plasma source also includes a field transfer portion (e.g., a conductive tube) that the ionizing electromagnetic field passes through en route to the plasma processing chamber2102, during which time the ionizing electromagnetic field is attenuated such that the field strength within the plasma processing chamber2102is only a tenth or a hundred or a thousandth or an even smaller portion of the field strength when the field is first generated in the remote projected plasma source. The plasma source2112is not drawn to scale.

The switch mode power supply2130can float and thus can be biased at any DC offset by a DC power source (not illustrated) connected in series between ground and the switch mode power supply2130. The switch mode power supply2130can provide an AC waveform with a DC offset either via AC and DC power sources internal to the switch mode power supply2130(see for exampleFIGS.22,23,26), or via an AC power source internal to the switch mode power supply2130and a DC power supply external to the switch mode power supply2130(see for exampleFIGS.24,27). In an embodiment, the switch mode power supply2130can be grounded and be series coupled to a floating DC power source coupled in series between the switch mode power supply2130and the electrostatic chuck2111.

The controller2132can control an AC and DC output of the switch mode power supply when the switch mode power supply2130includes both an AC and DC power source. When the switch mode power supply2130is connected in series with a DC power source, the controller2132may only control the AC output of the switch mode power supply2130. In an alternative embodiment, the controller2132can control both a DC power supply coupled to the switch mode power supply2130, and the switch mode power supply2130. One skilled in the art will recognize that while a single controller2132is illustrated, other controllers can also be implemented to control the AC waveform and DC offset provided to the electrostatic chuck2111.

The electrostatic chuck2111can be a dielectric (e.g., ceramic) and thus substantially block passage of DC voltages, or it can be a semiconductive material such as a doped ceramic. In either case, the electrostatic chuck2111can have a second voltage V2on a top surface2121of the electrostatic chuck2111that capacitively couples voltage to a top surface2118of the substrate2106(usually a dielectric) to form the first voltage V1.

The plasma2104shape and size are not necessarily drawn to scale. For instance, an edge of the plasma2104can be defined by a certain plasma density in which case the illustrated plasma2104is not drawn with any particular plasma density in mind. Similarly, at least some plasma density fills the entire plasma processing chamber2102despite the illustrated plasma2104shape. The illustrated plasma2104shape is intended primarily to show the sheath2115, which does have a substantially smaller plasma density than the plasma2104.

FIG.22illustrates another embodiment of a plasma processing system2200. In the illustrated embodiment, the switch mode power supply2230includes a DC power source2234and an AC power source2236connected in series. Controller2232is configured to control an AC waveform with a DC offset output of the switch mode power supply2230by controlling both the AC power source2236waveform and the DC power source2234bias or offset. This embodiment also includes an electrostatic chuck2211having a grid or mesh electrode2210embedded in the chuck2211. The switch mode power supply2230provides both an AC and DC bias to the grid electrode2210. The DC bias along with the AC component, which is substantially smaller than the DC bias and can thus be neglected, establishes a third potential V4on the grid electrode2210. When the third potential V4is different than a potential at a reference layer anywhere within the substrate2206(excluding the bottom surface2220of the substrate2206), a chucking potential Vchuckand a coulombic chucking force are established which hold the substrate2206to the electrostatic chuck2211. The reference layer is an imaginary plane parallel to the grid electrode2210. The AC waveform capacitively couples from the grid electrode2210through a portion of the electrostatic chuck2211, and through the substrate2206to control the first potential V1on a top surface2218of the substrate2206. Since a plasma potential V3is negligible relative to a plasma sheath voltage Vsheath, the first potential V1and the plasma sheath voltage Vsheathare approximately equal, and for practical purposes are considered equal. Therefore, the first potential V1equals the potential used to accelerate ions through the sheath2215.

In an embodiment, the electrostatic chuck2211can be doped so as to be conductive enough that any potential difference through the body of the chuck2211is negligible, and thus the grid or mesh electrode2210can be at substantially the same voltage as the second potential V2.

The grid electrode2210can be any conductive planar device embedded in the electrostatic chuck2211, parallel to the substrate2206, and configured to be biased by the switch mode power supply2230and to establish a chucking potential Vchuck. Although the grid electrode2210is illustrated as being embedded in a lower portion of the electrostatic chuck2211, the grid electrode2210can be located closer or further from the substrate2206. The grid electrode2210also does not have to have a grid pattern. In an embodiment, the grid electrode2210can be a solid electrode or have a non-solid structure with a non-grid shape (e.g., a checkerboard pattern). In an embodiment, the electrostatic chuck2211is a ceramic or other dielectric and thus the third potential V4on the grid electrode2210is not equal to the first potential V1on a top surface2221of the electrostatic chuck2211. In another embodiment, the electrostatic chuck2211is a doped ceramic that is slightly conductive and thus the third potential V4on the grid electrode2210can be equal to the second potential V2on the top surface2221of the electrostatic chuck2211.

The switch mode power supply2230generates an AC output that can be non-sinusoidal. The switch mode power supply2230is able to operate the DC and AC sources2234,2236in series because the DC power source2234is AC-conductive and the AC power source2236is DC-conductive. Exemplary AC power sources that are not DC-conductive are certain linear amplifiers which can be damaged when provided with DC voltage or current. The use of AC-conductive and DC-conductive power sources reduces the number of components used in the switch mode power supply2230. For instance, if the DC power source2234is AC-blocking, then an AC-bypass or DC-blocking component (e.g., a capacitor) may have to be arranged in parallel with the DC power source2234. If the AC power source2236is DC-blocking, then a DC-bypass or AC-blocking component (e.g., an inductor) may have to be arranged in parallel with the AC power source2236.

In this embodiment, the AC power source2238is generally configured to apply a voltage bias to the electrostatic chuck2211in a controllable manner so as to effectuate a desired (or defined) ion energy distribution for the ions bombarding the top surface2218of the substrate2206. More specifically, the AC power source2236is configured to effectuate the desired (or defined) ion energy distribution by applying one or more particular waveforms at particular power levels to the grid electrode2210. And more particularly, the AC power source2236applies particular power levels to effectuate particular ion energies, and applies the particular power levels using one or more voltage waveforms defined by waveform data stored in a waveform memory (not illustrated). As a consequence, one or more particular ion bombardment energies may be selected to carry out controlled etching of the substrate2206(or other plasma-assisted processes). In one embodiment, the AC power source2236can make use of a switched mode configuration (see for exampleFIGS.25-27). The switch mode power supply2230, and particularly the AC power source2236, can produce an AC waveform as described in various embodiments of this disclosure.

One skilled in the art will recognize that the grid electrode2210may not be necessary and that other embodiments can be implemented without the grid electrode2210. One skilled in the art will also recognize that the grid electrode2210is just one example of numerous devices that can be used to establish chucking potential Vchuck.

FIG.23illustrates another embodiment, of a plasma processing system2300. The illustrated embodiment includes a switch mode power supply2330for providing an AC waveform and a DC bias to an electrostatic chuck2311. The switch mode power supply2330includes a DC power source2334and an AC power source2336, both of which can be grounded. The AC power source2336generates an AC waveform that is provided to a first grid or mesh electrode2310embedded in the electrostatic chuck2311via a first conductor2324. The AC power source2336establishes a potential V4on the first grid or mesh electrode2310. The DC power source2334generates a DC bias that is provided to a second grid or mesh electrode2312embedded in the electrostatic chuck2311via a second conductor2325. The DC power source2334establishes a potential V5on the second grid or mesh electrode2312. The potentials V4and V5can be independently controlled via the AC and DC power sources2336,2334, respectively. However, the first and second grid or mesh electrodes2310,2312can also be capacitively coupled and/or there can be DC coupling between the grid or mesh electrodes2310,2312via a portion of the electrostatic chuck2311. If either AC or DC coupling exists, then the potentials V4and V5may be coupled. One skilled in the art will recognize that the first and second grid electrodes2310,2312can be arranged in various locations throughout the electrostatic chuck2311including arranging the first grid electrode2310closer to the substrate2306than the second grid electrode2312.

FIG.24illustrates another embodiment of a plasma processing system2400. In this embodiment, a switch mode power supply2430provides an AC waveform to an electrostatic chuck2411, where the switch mode power supply2430output is offset by a DC bias provided by a DC power supply2434. The AC waveform of the switch mode power supply2430has a waveform selected by controller2435to bombard a substrate2406with ions from a plasma2404having a narrow ion energy distribution. The AC waveform can be non-sinusoidal (e.g., square wave or pulsed) and can be generated via an AC power source2436of the switch mode power supply2430. Chucking is controlled via the DC offset from the DC power supply2434, which is controlled by controller2433. The DC power supply2434can be coupled in series between ground and the switch mode power supply2430. The switch mode power supply2430is floating such that its DC bias can be set by the DC power supply2434.

One skilled in the art will recognize that while the illustrated embodiment shows two independent controllers2433,2435, these could be combined into a single functional unit, device, or system such as optional controller2432. Additionally, controllers2433and2435can be coupled so as to communicate with each other and share processing resources.

FIG.25illustrates a further embodiment of a plasma processing system2500. The illustrated embodiment includes a switch mode power supply2530that produces an AC waveform that can have a DC offset provided by a DC power supply (not illustrated). The switch mode power supply can be controlled via optional controller2535, which encompasses a voltage and current controller2537,2539. The switch mode power supply2530can include a controllable voltage source2538having a voltage output controlled by the voltage controller2537, and a controllable current source2540having a current output controlled by the current controller2539. The controllable voltage and current sources2538,2540can be in a parallel arrangement. The controllable current source2540is configured to compensate for an ion current between a plasma2504and a substrate2506.

The voltage and current controllers2537,2539can be coupled and in communication with each other. The voltage controller2537can also control a switched output of the controllable voltage source2538. The switched output can include two switches in parallel as illustrated, or can include any circuitry that converts an output of the controllable voltage source2538into a desired AC waveform (e.g., non-sinusoidal). Via the two switches, a controlled voltage or AC waveform from the controllable voltage source2538can be combined with a controlled current output of the controllable current source2540to generate an AC waveform output of the switch mode power supply2530.

The controllable voltage source2538is illustrated as having a given polarity, but one skilled in the art will recognize that the opposite polarity is an equivalent to that illustrated. Optionally, the controllable voltage and current sources2538,2540along with the switched output2539can be part of an AC power source2536and the AC power source2536can be arranged in series with a DC power source (not illustrated) that is inside or outside of the switch mode power supply2530.

FIG.26illustrates yet another embodiment of a plasma processing system2600. In the illustrated embodiment, a switch mode power supply2630provides an AC waveform having a DC offset to an electrostatic chuck2611. The AC component of the waveform is generated via a parallel combination of a controllable voltage source2638and a controllable current source2640connected to each other through a switched output2639. The DC offset is generated by a DC power source2634coupled in series between ground and the controllable voltage source2638. In an embodiment, the DC power source2634can be floating rather than grounded. Similarly, the switch mode power supply2630can be floating or grounded.

The system2600can include one or more controllers for controlling an output of the switch mode power supply2630. A first controller2632can control the output of the switch mode power supply2630, for instance via a second controller2633and a third controller2635. The second controller2633can control a DC offset of the switch mode power supply2630as generated by the DC power source2634. The third controller2635can control the AC waveform of the switch mode power supply2630by controlling the controllable voltage source2638and the controllable current source2640. In an embodiment, a voltage controller2637controls the voltage output of the controllable voltage source2638and a current controller2639controls a current of the controllable current source2640. The voltage and current controllers2637,2639can be in communication with each other and can be a part of the third controller2635.

One skilled in the art will recognize that the embodiments above, describing various configurations of controllers relative to the power sources2634,2638,2640, are not limiting, and that various other configurations can also be implemented without departing from this disclosure. For instance, the third controller2635or the voltage controller2637can control a switched output2639between the controllable voltage source2638and the controllable current source2640. As another example, the second and third controllers2633,2635can be in communication with each other (even though not illustrated as such). It should also be understood that the polarities of the controllable voltage and current sources2638,2640are illustrative only and not meant to be limiting.

The switched output2639can operate by alternately switching two parallel switches in order to shape an AC waveform. The switched output2639can include any variety of switches including, but not limited to, MOSFET and BJT. In one variation, the DC power source2634can be arranged between the controllable current source2640and the electrostatic chuck2611(in other words, the DC power source2634can float), and the switch mode power supply2630can be grounded.

FIG.27illustrates another embodiment of a plasma processing system2700. In this variation, the switch mode power supply2730again is grounded, but instead of being incorporated into the switch mode power supply2730, here the DC power source2734is a separate component and provides a DC offset to the entire switch mode power supply2730rather than just components within the switch mode power supply2730.

FIG.28illustrates a method2800according to an embodiment of this disclosure. The method2800includes a place a substrate in a plasma chamber operation2802. The method2800further includes a form a plasma in the plasma chamber operation2804. Such a plasma can be formed in situ or via a remote projected source. The method2800also includes a switch power operation2806. The switch power operation2806involves controllably switching power to the substrate so as to apply a period voltage function to the substrate. The periodic voltage function can be considered a pulsed waveform (e.g., square wave) or an AC waveform and includes a DC offset generated by a DC power source in series with a switch mode power supply. In an embodiment, the DC power source can be incorporated into the switch mode power supply and thus be in series with an AC power source of the switch mode power supply. The DC offset generates a potential difference between a top surface of an electrostatic chuck and a reference layer within the substrate and this potential difference is referred to as the chucking potential. The chucking potential between the electrostatic chuck and the substrate holds the substrate to the electrostatic chuck thus preventing the substrate from moving during processing. The method2800further includes a modulate operation2808in which the periodic voltage function is modulated over multiple cycles. The modulation is responsive to a desired (or defined) ion energy distribution at the surface of the substrate so as to effectuate the desired (or defined) ion energy distribution on a time-averaged basis.

FIG.29illustrates another method2900according to an embodiment of this disclosure. The method2900includes a place a substrate in a plasma chamber operation2902. The method2900further includes a form a plasma in the plasma chamber operation2904. Such a plasma can be formed in situ or via a remote projected source. The method2900also includes a receive at least one ion-energy distribution setting operation2906. The setting received in the receive operation2906can be indicative of one or more ion energies at a surface of the substrate. The method2900further includes a switch power operation2908in which power to the substrate is controllably switched so as to effectuate the following: (1) a desired (or defined) distribution of ion energies on a time-averaged basis; and (2) a desired chucking potential on a time-averaged basis. The power can have an AC waveform and a DC offset.

In conclusion, the present invention provides, among other things, a method and apparatus for selectively generating desired (or defined) ion energies using a switch-mode power supply. Those skilled in the art can readily recognize that numerous variations and substitutions may be made in the invention, its use, and its configuration to achieve substantially the same results as achieved by the embodiments described herein. Accordingly, there is no intention to limit the invention to the disclosed exemplary forms. Many variations, modifications, and alternative constructions fall within the scope and spirit of the disclosed invention.