U.S. patent application number 14/803815 was filed with the patent office on 2016-01-21 for ion energy bias control apparatus.
The applicant listed for this patent is Advanced Energy Industries, Inc.. Invention is credited to Victor Brouk, Daniel Carter, Daniel J. Hoffman, Dmitri Kovalevskii.
Application Number | 20160020072 14/803815 |
Document ID | / |
Family ID | 50184247 |
Filed Date | 2016-01-21 |
United States Patent
Application |
20160020072 |
Kind Code |
A1 |
Brouk; Victor ; et
al. |
January 21, 2016 |
ION ENERGY BIAS CONTROL APPARATUS
Abstract
This disclosure describes systems, methods, and apparatus for
operating a plasma processing chamber. In particular, a periodic
voltage function combined with an ion current compensation can be
provided as a bias to a substrate support as a modified periodic
voltage function. This in turn effects a DC bias on the surface of
the substrate that controls an ion energy of ions incident on a
surface of the substrate. A peak-to-peak voltage of the periodic
voltage function can control the ion energy, while the ion current
compensation can control a width of an ion energy distribution
function of the ions. Measuring the modified periodic voltage
function can provide a means to calculate an ion current in the
plasma and a sheath capacitance of the plasma sheath. The ion
energy distribution function can be tailored and multiple ion
energy peaks can be generated, both via control of the modified
periodic voltage function.
Inventors: |
Brouk; Victor; (Fort
Collins, CO) ; Hoffman; Daniel J.; (Fort Collins,
CO) ; Carter; Daniel; (Fort Collins, CO) ;
Kovalevskii; Dmitri; (Fort Collins, CO) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Advanced Energy Industries, Inc. |
Fort Collins |
CO |
US |
|
|
Family ID: |
50184247 |
Appl. No.: |
14/803815 |
Filed: |
July 20, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14011305 |
Aug 27, 2013 |
9105447 |
|
|
14803815 |
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Current U.S.
Class: |
156/345.28 ;
118/663 |
Current CPC
Class: |
H01J 37/241 20130101;
H01J 37/32146 20130101; H01J 37/32091 20130101 |
International
Class: |
H01J 37/32 20060101
H01J037/32; H01J 37/24 20060101 H01J037/24 |
Claims
1. A plasma processing apparatus comprising: a substrate support
bias supply providing a periodic voltage function; an ion current
compensation component providing an ion current compensation that
is combined with the periodic voltage function to form a modified
periodic voltage function that is provided to the substrate support
and thereby effects a DC voltage on a surface of the substrate
opposite to the substrate support, which in turn controls an ion
energy of ions incident on the surface of the substrate opposite to
the substrate support, the modified periodic voltage function
having: a first portion comprising a rapidly increasing voltage; a
second portion comprising a substantially constant voltage; and a
third portion comprising: a sloped voltage having a starting
voltage that is a voltage step, .DELTA.V, below the substantially
constant voltage, the voltage step, .DELTA.V, corresponding to the
ion energy, and a slope, dV.sub.0/dt, controlled by the ion current
compensation; and a controller to control ion current, I.sub.I, as
a function of the effective capacitance, C.sub.1, and the slope,
dV.sub.0/dt.
Description
CLAIM OF PRIORITY UNDER 35 USC .sctn.120
[0001] The present Application for Patent is a Continuation of
patent application Ser. No. 14/011,305 entitled "WIDE DYNAMIC RANGE
ION ENERGY BIAS CONTROL; FAST ION ENERGY SWITCHING; ION ENERGY
CONTROL AND A PULSED BIAS SUPPLY; AND A VIRTUAL FRONT PANEL" filed
Aug. 27, 2013, pending, and assigned to the assignee hereof and
hereby expressly incorporated by reference herein.
BACKGROUND
[0002] Plasma processing can benefit from precise control over ion
energy and further from an ability to control an ion energy
distribution function (IEDF) of ions incident on a substrate during
processing. However, precise control is hampered by a lack of
non-invasive and real-time means for monitoring ion energy and
IEDF.
[0003] Additionally there are various metrics that can be monitored
via a knowledge of ion current, I.sub.I, and sheath capacitance,
C.sub.2 (or C.sub.sheath). However, there is also a lack of systems
and methods that can non-invasively and in real-time monitor these
values.
FIELD OF THE DISCLOSURE
[0004] The present disclosure relates generally to plasma
processing and in particular to controlling ion energy.
SUMMARY OF THE DISCLOSURE
[0005] Exemplary embodiments of the present invention that are
shown in the drawings are summarized below. These and other
embodiments are more fully described in the Detailed Description
section. It is to be understood, however, that there is no
intention to limit the invention to the forms described in this
Summary of the Invention or in the Detailed Description. One
skilled in the art can recognize that there are numerous
modifications, equivalents and alternative constructions that fall
within the spirit and scope of the invention as expressed in the
claims.
[0006] There are five primary aspects of this disclosure: circuit
`memory` as a cause of inaccuracies in ion energy, wide dynamic
range, fast ion energy switching, pulsed ion energy control, and a
virtual front panel. Wide dynamic range involves a bias supply of a
plasma processing chamber, where the bias supply can effectuate two
or more ion energies within a plasma of the plasma processing
chamber. The two or more ion energies can be effectuated with
accuracy, stability, and a wide dynamic range (ion energies that
have a large ion energy separation). Fast ion energy switching
involves the bias supply effectuating the two or more ion energies
in a short period of time for instance from one bias supply pulse
or cycle to the next (pulses or cycles are also known as periods of
a modified periodic voltage function). Fast ion energy switching
also includes the bias supply's ability to compensate for
disturbances in ion energy within a single cycle. Pulsed ion energy
control involves the timing of a pulsed envelope of bias supply
cycles relative to a pulsed envelope of the plasma source supply.
The virtual front panel involves a user interface enabling control
of the systems, methods, and apparatus discussed in these first
three aspects.
[0007] In one aspect of the disclosure, a method of operating a
plasma processing chamber is described. The method can include
sustaining a plasma in contact with a substrate on a substrate
support within the plasma processing chamber. The method can
further include accessing an effective capacitance, C.sub.1, of the
substrate support. The method can yet further include providing a
modified periodic voltage function to the substrate support in
order to effect a potential on a surface of the substrate, the
modified period voltage function formed from a combination of a
periodic voltage function and an ion current compensation, I.sub.C.
Lastly, the method can include calculating ion current, I.sub.I, in
the plasma as a function of measurements of the modified periodic
voltage function.
[0008] In another aspect of the disclosure, a plasma processing
system is disclosed. The system can include a substrate support in
a plasma processing chamber. The substrate support can support a
substrate. The system can also include a substrate support bias
supply that provides a periodic voltage function. The system can
further include an ion current compensation component that provides
an ion current compensation. The ion current compensation can be
combined with the periodic voltage function to form a modified
periodic voltage function, which can be provided to the substrate
support. In turn, effects a direct current voltage on a surface of
the substrate opposite to the substrate support. This in turn
controls an ion energy of ions incident on the surface of the
substrate opposite to the substrate support. The modified periodic
voltage function can have a first portion, a second portion, and a
third portion. The first portion can include a rapidly increasing
voltage while the second portion can include a substantially
constant voltage. The third portion can include a sloped voltage
having a starting voltage that is a voltage step, .DELTA.V, below
the substantially constant voltage. The voltage step, .DELTA.V, can
correspond to the ion energy, and a slope, dV.sub.0/dt, can be
controlled by the ion current compensation. The system can further
include a controller having a non-transitory, tangible computer
readable storage medium encoded with processor readable instruction
to: access an effective capacitance of the substrate support,
C.sub.1; measure the slope, dV.sub.0/dt, for at least two ion
current compensation values; and calculate ion current, I.sub.I, as
a function of the effective capacitance, C.sub.1, and the slope,
dV.sub.0/dt.
[0009] In yet another aspect of the disclosure, a non-transitory
tangible computer readable storage medium is disclosed. The storage
medium can be encoded with processing readable instructions to
perform a method for controlling characteristics of an ion energy
distribution function of ions from a plasma that are incident on a
substrate within a plasma processing chamber. The method can
include accessing an effective capacitance, C.sub.1, of a substrate
support supporting the substrate. The method can also include
controlling a periodic voltage function provided by a substrate
bias supply and an ion current compensation provided by an ion
current compensation component. A combination of the periodic
voltage function and the ion current compensation can be referred
to as a modified periodic voltage function. The modified periodic
voltage function can be provided to the substrate support in order
to effect a potential on a surface of the substrate opposite to the
substrate support and thereby control an ion energy, eV, of ions
incident on the substrate from the plasma. The method can further
include taking measurements of the modified periodic voltage
function and repeatedly calculating an ion current, I.sub.I, in the
plasma based on the measurements.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] Various objects and advantages and a more complete
understanding of the present invention are apparent and more
readily appreciated by referring to the following detailed
description and to the appended claims when taken in conjunction
with the accompanying drawings:
[0011] FIG. 1 is an embodiment of a plasma processing system;
[0012] FIG. 2 is a schematic representation of components that may
be utilized to realize a switch-mode bias supply;
[0013] FIG. 3 is a timing diagram depicting two drive signal
waveforms that may be applied to T.sub.1 and T.sub.2 (as V2 and V4)
so as to generate the periodic voltage function at V.sub.out;
[0014] FIG. 4 is a graphs depicting V.sub.bus versus time, voltage
at the surface of the substrate versus time, and the corresponding
ion energy distribution;
[0015] FIG. 5 is a single mode of operating the switch mode bias
supply, which effectuates an ion energy distribution (or ion energy
distribution function (IEDF)) that is concentrated at a particular
ion energy;
[0016] FIG. 6 is a block diagram depicting an embodiment in which
an ion current compensation component compensates for ion current
in the plasma chamber;
[0017] FIG. 7 is an exemplary ion current compensation
component;
[0018] FIG. 8 is graph depicting an exemplary voltage (e.g., the
modified periodic voltage function) at V.sub.0;
[0019] FIG. 9 is illustrates an inductance L1 between switch
components T.sub.1 and T.sub.2 and the series capacitance,
C.sub.series;
[0020] FIG. 10 is a bias supply with a particular embodiment of the
energy evacuation component;
[0021] FIG. 11 illustrates graphs of various IEDF shapes;
[0022] FIG. 12 is a modified periodic voltage function where a
disturbance can be seen in a first cycle, which influences the
.DELTA.V of a next cycle;
[0023] FIG. 13 is shows a similar modified periodic voltage
function, but in this case a disturbance causes the falling voltage
to follow the path rather than the path;
[0024] FIG. 14 is a waveform where the systems and methods herein
disclosed are used to achieve a desired ion energy despite
different disturbances in a previous cycle;
[0025] FIG. 15 is a waveform where the systems and methods herein
disclosed are used to achieve a desired ion energy despite
different disturbances in a previous cycle;
[0026] FIG. 16 is an exemplary embodiment of a current source,
which may be implemented to realize the current source described
with reference to FIG. 7;
[0027] FIG. 17 is one embodiment of a method of controlling an ion
energy distribution of ions impacting a surface of a substrate;
[0028] FIG. 18 is another embodiment of a method of controlling an
ion energy distribution of ions impacting a surface of a
substrate;
[0029] FIG. 19 shows methods for setting the IEDF width and the ion
energy;
[0030] FIG. 20 illustrates three relationships between a power
supply voltage, V.sub.PS, and an ion energy distribution
function;
[0031] FIG. 21 is an embodiment of charts showing relations between
power supply switch timing, periodic voltage function, ion current
compensation, modified periodic voltage function, substrate surface
voltage, and ion energy distribution function;
[0032] FIG. 22 is a further embodiment of charts showing relations
between power supply switch timing, periodic voltage function, ion
current compensation, modified periodic voltage function, substrate
surface voltage, and ion energy distribution function;
[0033] FIG. 23 is yet a embodiment of charts showing relations
between power supply switch timing, periodic voltage function, ion
current compensation, modified periodic voltage function, substrate
surface voltage, and ion energy distribution function;
[0034] FIG. 24 is yet a embodiment of charts showing relations
between power supply switch timing, periodic voltage function, ion
current compensation, modified periodic voltage function, substrate
surface voltage, and ion energy distribution function;
[0035] FIG. 25 is another embodiment of charts showing relations
between power supply switch timing, periodic voltage function, ion
current compensation, modified periodic voltage function, substrate
surface voltage, and ion energy distribution function;
[0036] FIG. 26 is yet another embodiment of charts showing
relations between power supply switch timing, periodic voltage
function, ion current compensation, modified periodic voltage
function, substrate surface voltage, and ion energy distribution
function;
[0037] FIG. 27 is a further embodiment of charts showing relations
between power supply switch timing, periodic voltage function, ion
current compensation, modified periodic voltage function, substrate
surface voltage, and ion energy distribution function;
[0038] FIG. 28 is a source supply being pulsed within a pulse
envelope indicated by dashed lines;
[0039] FIG. 29 is a modified periodic voltage for a bias supply
being pulsed within a pulse envelope indicated by dashed lines;
[0040] FIG. 30 shows measured waveforms for plasma density and bias
supply;
[0041] FIG. 31 is an embodiment of a virtual front panel;
[0042] FIG. 32 is an embodiment of a virtual front panel;
[0043] FIG. 33 is an embodiment of a virtual front panel;
[0044] FIG. 34 is an embodiment of a virtual front panel;
[0045] FIG. 35 is an embodiment of a virtual front panel;
[0046] FIG. 36 is an embodiment of a virtual front panel;
[0047] FIG. 37 is an embodiment of a virtual front panel;
[0048] FIG. 38 is an embodiment of a virtual front panel;
[0049] FIG. 39 is an embodiment of a virtual front panel;
[0050] FIG. 40 is an embodiment of a virtual front panel;
[0051] FIG. 41 is an embodiment of a virtual front panel;
[0052] FIG. 42 is an embodiment of a virtual front panel;
[0053] FIG. 43 is an embodiment of a virtual front panel;
[0054] FIG. 44 is an embodiment of a virtual front panel;
[0055] FIG. 45 is an embodiment of a virtual front panel;
[0056] FIG. 46 is an embodiment of a virtual front panel;
[0057] FIG. 47 is an embodiment of a virtual front panel;
[0058] FIG. 48 is an embodiment of a virtual front panel;
[0059] FIG. 49 is an embodiment of a virtual front panel;
[0060] FIG. 50 is an embodiment of a virtual front panel;
[0061] FIG. 51 is an embodiment of a virtual front panel;
[0062] FIG. 52 is an embodiment of a virtual front panel; and
[0063] FIG. 53 shows a diagrammatic representation of one
embodiment of a control system within which a set of instructions
can execute for causing a device to perform or execute any one or
more of the aspects and/or methodologies of the present
disclosure.
DETAILED DESCRIPTION
[0064] An exemplary embodiment of a plasma processing system is
shown generally in FIG. 1. As depicted, a plasma power supply 102
is coupled to a plasma processing chamber 104 and a switch-mode
power supply 106 is coupled to a support 108 upon which a substrate
110 rests within the chamber 104. Also shown is a controller 112
that is coupled to the switch-mode power supply 106.
[0065] In this exemplary embodiment, the plasma processing chamber
104 may be realized by chambers of substantially conventional
construction (e.g., including a vacuum enclosure which is evacuated
by a pump or pumps (not shown)). And, as one of ordinary skill in
the art will appreciate, the plasma excitation in the chamber 104
may be by any one of a variety of sources including, for example, a
helicon type plasma source, which includes magnetic coil and
antenna to ignite and sustain a plasma 114 in the reactor, and a
gas inlet may be provided for introduction of a gas into the
chamber 104.
[0066] As depicted, the exemplary plasma chamber 104 is arranged
and configured to carry out plasma-assisted etching of materials
utilizing energetic ion bombardment of the substrate 110, and other
plasma processing (e.g., plasma deposition and plasma assisted ion
implantation). The plasma power supply 102 in this embodiment is
configured to apply power (e.g., RF power) via a matching network
(not shown)) at one or more frequencies (e.g., 13.56 MHz) to the
chamber 104 so as to ignite and sustain the plasma 114. It should
be understood that the present invention is not limited to any
particular type of plasma power supply 102 or source to couple
power to the chamber 104, and that a variety of frequencies and
power levels may be may be capacitively or inductively coupled to
the plasma 114.
[0067] As depicted, a dielectric substrate 110 to be treated (e.g.,
a semiconductor wafer), is supported at least in part by a support
108 that may include a portion of a conventional wafer chuck (e.g.,
for semiconductor wafer processing). The support 108 may be formed
to have an insulating layer between the support 108 and the
substrate 110 with the substrate 110 being capacitively coupled to
the platforms but may float at a different voltage than the support
108.
[0068] As discussed above, if the substrate 110 and support 108 are
conductors, it is possible to apply a non-varying voltage to the
support 108, and as a consequence of electric conduction through
the substrate 110, the voltage that is applied to the support 108
is also applied to the surface of the substrate 110.
[0069] When the substrate 110 is a dielectric, however, the
application of a non-varying voltage to the support 108 is
ineffective to place a voltage across the treated surface of the
substrate 110. As a consequence, the exemplary switch-mode power
supply 106 is configured to be controlled so as to effectuate a
voltage on the surface of the substrate 110 that is capable of
attracting ions in the plasma 114 to collide with the substrate 110
so as to carry out a controlled etching and/or deposition of the
substrate 110, and/or other plasma-assisted processes.
[0070] Moreover, as discussed further herein, embodiments of the
switch-mode power supply 106 are configured to operate so that
there is an insubstantial interaction between the power applied (to
the plasma 114) by the plasma power supply 102 and the power that
is applied to the substrate 110 by the switch-mode power supply
106. The power applied by the switch-mode power supply 106, for
example, is controllable so as to enable control of ion energy
without substantially affecting the density of the plasma 114.
[0071] Furthermore, many embodiments of the exemplary switch-mode
supply 106 depicted in FIG. 1 are realized by relatively
inexpensive components that may be controlled by relatively simple
control algorithms. And as compared to prior art approaches, many
embodiments of the switch mode power supply 106 are much more
efficient; thus reducing energy costs and expensive materials that
are associated with removing excess thermal energy.
[0072] 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.
[0073] 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.
[0074] In some embodiments, the switch-mode power supply 106
depicted in FIG. 1 may be realized by buck, boost, and/or
buck-boost type power technologies. In these embodiments, the
switch-mode power supply 106 may be controlled to apply varying
levels of pulsed power to induce a potential on the surface of the
substrate 110.
[0075] Referring next to FIG. 2, it is a schematic representation
of components that may be utilized to realize a switch-mode bias
supply. As shown, the switching components T.sub.1 and T.sub.2 in
this embodiment are arranged in a half-bridge (also referred to as
or totem pole) type topology. Collectively, R2, R3, C1, and C2
represent a plasma load, C10 is an effective capacitance (also
referred to herein as a series capacitance or a chuck capacitance),
and C3 is an optional physical capacitor to prevent DC current from
the voltage induced on the surface of the substrate or from the
voltage of an electrostatic chuck (not shown) from flowing through
the circuit. C10 is referred to as the effective capacitance
because it includes the series capacitance (or also referred to as
a chuck capacitance) of the substrate support and the electrostatic
chuck (or e-chuck) as well as other capacitances inherent to the
application of a bias such as the insulation and substrate. As
depicted, L1 is 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: V.sub.bus, V2, and V4.
[0076] V2 and V4 represent drive signals, and in this embodiment,
V2 and V4 can be timed (e.g., the length of the pulses and/or the
mutual delay) so that the closure of T.sub.1 and T.sub.2 may be
modulated to control the shape of the voltage output V.sub.out,
which is applied to the substrate support. In many implementations,
the transistors used to realize the switching components T.sub.1
and T.sub.2 are not ideal switches, so to arrive at a desired
waveform, the transistor-specific characteristics are taken into
consideration. In many modes of operation, simply changing the
timing of V2 and V4 enables a desired waveform to be applied at
V.sub.out.
[0077] For example, the switches T.sub.1, T.sub.2 may be operated
so that the voltage at the surface of the substrate 110 is
generally negative with periodic voltage pulses approaching and/or
slightly exceeding a positive voltage reference. The value of the
voltage at the surface of the substrate 110 is 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 substrate 110, the pulses at
V.sub.out may be generally rectangular and have a width that is
long enough to induce a brief positive voltage at the surface of
the substrate 110 so as to attract enough electrons to the surface
of the substrate 110 in order to achieve the desired voltage(s) and
corresponding ion energies.
[0078] 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 T.sub.1,
T.sub.2. 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.
[0079] V.sub.bus in this embodiment defines the amplitude of the
pulses measured at V.sub.out, which defines the voltage at the
surface of the substrate, and as a consequence, the ion energy.
[0080] The pulse width, pulse shape, and/or mutual delay of the two
signals V2, V4 may be modulated to arrive at a desired waveform at
V.sub.out (also referred to herein as a modified periodic voltage
function), and the voltage applied to V.sub.bus may affect the
characteristics of the pulses. In other words, the voltage
V.sub.bus may affect the pulse width, pulse shape and/or the
relative phase of the signals V2, V4. Referring briefly to FIG. 3,
for example, shown is a timing diagram depicting two drive signal
waveforms that may be applied to T.sub.1 and T.sub.2 (as V2 and V4)
so as to generate the periodic voltage function at V.sub.out. To
modulate the shape of the pulses at V.sub.out (e.g. to achieve the
smallest time for the pulse at V.sub.out, yet reach a peak value of
the pulses) the timing of the two gate drive signals V2, V4 may be
controlled.
[0081] For example, the two gate drive signals V2, V4 may be
applied to the switching components T.sub.1, T.sub.2 so the time
that each of the pulses is applied at V.sub.out may be short
compared to the time t between pulses, but long enough to induce a
positive voltage at the surface of the substrate 110 to attract
electrons to the surface of the substrate 110. 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 V.sub.out 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.
[0082] 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 to FIG. 1 as a sequence of
voltage levels). In addition, in many implementations, the
waveforms can be generated directly (e.g., without feedback from
V.sub.out); thus avoiding the undesirable aspects of a feedback
control system (e.g., settling time).
[0083] Referring again to FIG. 2, V.sub.bus can be modulated to
control the energy of the ions, and the stored waveforms may be
used to control the gate drive signals V2, V4 to achieve a desired
pulse amplitude at V.sub.out 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 to FIG. 4, for
example, shown are graphs depicting V.sub.bus versus time, voltage
at the surface of the substrate 110 versus time, and the
corresponding ion energy distribution.
[0084] The graphs in FIG. 4 depict a single mode of operating the
switch mode bias supply 106, which effectuates an ion energy
distribution (or ion energy distribution function (IEDF)) 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 V.sub.bus is maintained constant while the
voltages applied to V2 and V4 are controlled (e.g., using the drive
signals depicted in FIG. 3) so as to generate pulses at the output
of the switch-mode bias supply 106, which effectuates the
corresponding ion energy distribution shown in FIG. 4.
[0085] As depicted in FIG. 4, the potential at the surface of the
substrate 110 is generally negative to attract the ions that
bombard and etch the surface of the substrate 110. The periodic
short pulses that are applied to the substrate 110 (by applying
pulses to V.sub.out) have a magnitude defined by the potential that
is applied to V.sub.bus, and these pulses cause a brief change in
the potential of the substrate 110 (e.g., close to positive or
slightly positive potential), which attracts electrons to the
surface of the substrate to achieve the generally negative
potential along the surface of the substrate 110. As depicted in
FIG. 4, the constant voltage applied to V.sub.bus effectuates a
single concentration of ion flux at particular ion energy; thus a
particular ion bombardment energy may be selected by simply setting
V.sub.bus to a particular potential. In other modes of operation,
two or more separate concentrations of ion energies may be created
(e.g., see FIGS. 5, 20, 23, 25, 26, 27).
[0086] 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, V.sub.PS.
[0087] Referring next to FIG. 5, 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 V.sub.bus alternates between two levels, and
each level defines the energy level of the two ion energy
concentrations.
[0088] Although FIG. 5 depicts the two voltages at the substrate
110 as alternating after every pulse (e.g., FIGS. 25 and 27), this
is certainly not required. In other modes of operation for example,
the voltages applied to V2 and V4 are switched (e.g., using the
drive signals depicted in FIG. 3) relative to the voltage applied
to V.sub.out so that the induced voltage at the surface of the
substrate alternates from a first voltage to a second voltage (and
vice versa) after two or more pulses (e.g., FIG. 26).
[0089] 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 to FIG. 5, and requires an
expensive linear amplifier, and waveform generators.
[0090] Referring next to FIG. 6, it is a block diagram depicting an
embodiment in which an ion current compensation component 660
compensates for ion current in the plasma chamber 604. 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.
[0091] The ion current compensation component 660 may be realized
as a separate accessory that may optionally be added to the switch
mode power supply 606 and controller 612. In other embodiments,
(e.g., as depicted in FIG. 7) the ion current compensation
component 660 may share a common housing 766 (see FIG. 7) with
other components described herein (e.g., the switch-mode power
supply 106, 606 and ion current compensation 660). In this
embodiment, the periodic voltage function provided to the plasma
chamber 604 can 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
component 660. The controller 612 can sample a voltage, V.sub.0, at
different times at an electrical node where outputs of the switch
mode power supply 606 and the ion current compensation 660
combine.
[0092] As depicted in FIG. 7, shown is an exemplary ion current
compensation component 760 that includes a current source 764
coupled to an output 736 of a switch mode supply and a current
controller 762 that is coupled to both the current source 764 and
the output 736. Also depicted in FIG. 7 is a plasma chamber 704,
and within the plasma chamber are capacitive elements C.sub.1,
C.sub.2, and ion current I.sub.I. As depicted, C.sub.1 represents
the inherent capacitance (also referred to herein as effective
capacitance) of components associated with the chamber 704, which
may include, but is not limited to, insulation, the substrate,
substrate support, and an e-chuck, and C.sub.2 represents sheath
capacitance and stray capacitances. In this embodiment, the
periodic voltage function provided to the plasma chamber 704, and
measurable as V.sub.0, can be referred to as a modified periodic
voltage function since it comprises the periodic voltage function
modified by the ion current compensation, I.sub.C.
[0093] 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, .lamda..sub.sheath, is a function of plasma
characteristics such as plasma density and plasma temperature.
[0094] It should be noted that because C.sub.1 in this embodiment
is an inherent (also referred to herein as effective) capacitance
of components associated with the chamber 704, it is not a
capacitance that can be controlled during 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.
[0095] While referring to FIG. 7, simultaneous reference is made to
FIG. 8, which is a graph depicting an exemplary voltage (e.g., the
modified periodic voltage function) at V.sub.0 depicted in FIG. 7.
In operation, the current controller 762 monitors the voltage (the
modified periodic voltage function) at V.sub.0. Ion current is
calculated over an interval t or some sub portion thereof (depicted
in FIG. 8) as:
I I = C 1 V 0 t ( Equation 1 ) ##EQU00001##
[0096] Ion current, I.sub.I, and inherent capacitance (also
referred to as effective capacitance), C.sub.1, can either or both
be time varying. Because C.sub.1 is substantially constant for a
given tool and is measureable, only V.sub.o needs to be monitored
to enable ongoing control of compensation current. As discussed
above, to obtain a more mono-energetic distribution of ion energy
the current controller controls the current source 764 so that
I.sub.C is substantially the same as I.sub.I (or in the
alternative, related according to Equation 3). 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.
[0097] Also depicted in FIG. 7 is a feedback line 770, which may be
utilized in connection with controlling an ion energy distribution.
For example, the value of .DELTA.V (also referred to herein as a
voltage step or the third portion 806) depicted in FIG. 8, 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, .DELTA.V, is related to ion energy according to
Equation 6. In other embodiments, the peak-to-peak voltage,
V.sub.PP can be related to the instantaneous ion energy.
Alternatively, the difference between the peak-to-peak voltage,
V.sub.PP, and the product of the slope, dV.sub.0/dt, of the fourth
portion 808 times time, t, can be correlated to the instantaneous
ion energy (e.g., V.sub.PP-dV.sub.0/dtt).
[0098] Referring next to FIG. 16, shown is an exemplary embodiment
of a current source 1664, which may be implemented to realize the
current source 764 described with reference to FIG. 7. 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.
[0099] FIG. 17 illustrates one embodiment of a method of
controlling an ion energy distribution of ions impacting a surface
of a substrate. The method 1700 starts by applying a modified
periodic voltage function 1702 (see the modified periodic voltage
function 802 in FIG. 8) 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, I.sub.C, (see I.sub.C 2104 in FIG. 21)
and a power supply voltage, V.sub.PS, (see power supply voltage
2106 in FIG. 21). An exemplary component for generating the power
supply voltage is the switch mode power supply 106 in FIG. 1. In
order to help explain the power supply voltage, V.sub.PS, it is
illustrated herein as if measured without coupling to the ion
current and ion current compensation. The modified periodic voltage
function is then sampled at a first and second value of an ion
current compensation, I.sub.C, 1704. At least two samples of a
voltage of the modified periodic voltage function are taken for
each value of the ion current compensation, I.sub.C. The sampling
1704 is performed in order to enable calculations 1706 (or
determinations) of the ion current, I.sub.I, and a sheath
capacitance, C.sub.2, 1706 (e.g., C2 in FIG. 2). Ion current,
I.sub.I, for instance, can be determined using Equation 1. Such
determinations may involve finding an ion current compensation,
I.sub.C, that if applied to the substrate support (or as applied to
the substrate support) would generate a narrow (e.g., minimum) ion
energy distribution function (IEDF) width. The calculations 1706
can also optionally include determining a voltage step, .DELTA.V,
(also known as a third portion of the modified periodic voltage
function 1406) based on the sampling 1704 of the waveform of the
modified periodic voltage function. The voltage step, .DELTA.V, can
be related to an ion energy of ions reaching the substrate's
surface. When finding the ion current, I.sub.I, for the first time,
the voltage step, .DELTA.V, can be ignored. Details of the sampling
1704 and the calculations 1706 will be provided in discussions of
FIG. 18 to follow. Sheath capacitance, C.sub.2, can be calculated
via the following equation:
C 2 = C 1 ( I I + I C ) I C - C 1 V 0 t ( Equation 2 )
##EQU00002##
[0100] Once the ion current, I.sub.I, and sheath capacitance,
C.sub.2, are known, the method 1700 may move to the method 1900 of
FIG. 19 involving setting and monitoring an ion energy and a shape
(e.g., width) of the IEDF. For instance, FIG. 23 illustrates 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. 24 illustrates that given a narrow IEDF
2414, the IEDF can be widened by adjusting the ion current
compensation, I.sub.C. Alternatively or in parallel, the method
1700 can perform various metrics that make use of the ion current,
I.sub.I, the sheath capacitance, C.sub.2, and other aspects of the
waveform of the modified periodic voltage function.
[0101] In addition to setting the ion energy and/or the IEDF width,
the method 1700 may adjust the modified periodic voltage function
1708 in order to maintain the ion energy and the IEDF width. In
particular, adjustment of the ion current compensation, I.sub.C,
provided by an ion current compensation component, and adjustment
of the power supply voltage may be performed 1708. In some
embodiments, the power supply voltage can be controlled by a bus
voltage, V.sub.bus, of the power supply (e.g., the bus voltage
V.sub.bus of FIG. 2). The ion current compensation, I.sub.C,
controls the IEDF width, and the power supply voltage controls the
ion energy.
[0102] After these adjustments 1708, the modified periodic voltage
function can again be sampled 1704 and calculations of ion current,
I.sub.I, sheath capacitance, C.sub.2, and the voltage step,
.DELTA.V, can again be performed 1706. If the ion current, I.sub.I,
or the voltage step, .DELTA.V, are other than defined values (or in
the alternative, desired values), then the ion current
compensation, I.sub.C, and/or the power supply voltage can be
adjusted 1708. Looping of the sampling 1704, calculating, 1706, and
adjusting 1708 may occur in order to maintain the ion energy, eV,
and/or the IEDF width.
[0103] FIG. 18 illustrates 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, .about.6% full-width half maximum). As
such, the method 1800 can 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 using a substantially constant voltage thus enabling ions to
impact the substrate with substantially the same ion energy (in
other words, a narrow IEDF width). For instance, in FIG. 22 it can
be seen that adjusting the ion current compensation, I.sub.C, can
cause the substrate voltage, V.sub.sub, between pulses to have a
constant, or substantially constant voltage thus causing the IEDF
to narrow.
[0104] Such a modified periodic voltage function is achieved when
the ion current compensation, I.sub.C, equals the ion current,
I.sub.I, assuming no stray capacitances (see the last five cycles
of the periodic voltage function (V.sub.0) in FIG. 22). In the
alternative, where stray capacitance, C.sub.stray, is considered,
the ion current compensation, I.sub.C, is related to the ion
current, I.sub.I, according to Equation 3:
I I = I C C 1 C 1 + C stray ( Equation 3 ) ##EQU00003##
[0105] where, C.sub.1, is an effective capacitance (e.g., the
inherent capacitance described with reference to FIGS. 2 and 9-10).
The effective capacitance, C.sub.1, can vary in time or be
constant. For the purposes of this disclosure, the narrow IEDF
width can exist when either I.sub.I=I.sub.C or, in the alternative,
when Equation 3 is met (the equivalence of I.sub.I and I.sub.C
taking into account stray capacitance). FIGS. 21-27 use the
nomenclature, I.sub.I=I.sub.C, but it should be understood that
this relationship assumes negligible stray capacitance. The more
rigorous relationship is shown via Equation 3, and thus Equation 3
could substitute for the equalities used in FIGS. 21-27. The stray
capacitance, C.sub.stray, is a cumulative capacitance of the plasma
chamber as seen by the power supply. There are eight cycles
illustrated in FIG. 22.
[0106] The method 1800 can begin with an application of a modified
periodic voltage function (e.g., the modified periodic voltage
function depicted in FIG. 8 or the modified periodic voltage
function 2102 in FIG. 21) to the substrate support 1802 (e.g.,
substrate support 108 in FIG. 1). A voltage of the modified
periodic voltage function can be sampled 1804 at two or more times,
and from this sampling, a slope dV.sub.0/dt for at least a portion
of a cycle of the modified periodic voltage function can be
calculated 1806 (e.g., a slope of the portion between the pulses or
the fourth portion 808). At some point before a decision 1810, a
previously-determined value of an effective capacitance C.sub.1
(e.g., inherent capacitance C.sub.1 in FIG. 13, and an inherent
capacitance C10 in FIG. 2) can be accessed 1808 (e.g., a
previously-measured value retrieved from a memory, a value entered
by a user, or a value measured in real-time). Based on the slope,
dV.sub.0/dt, the effective capacitance, C.sub.1, and the ion
current compensation, I.sub.C, a function f (Equation 4), can be
evaluated for each value of the ion current compensation, I.sub.C,
as follows:
f ( I C ) = V 0 t - I C C 1 = 0 ( Equation 4 ) ##EQU00004##
[0107] If the function f is true, then the ion current
compensation, I.sub.C, equals the ion current, I.sub.I, or in the
alternative, makes Equation 3 true, and a narrow IEDF width has
been achieved 1810 (e.g., see FIG. 22). If the function f is not
true, then the ion current compensation, I.sub.C, can be adjusted
1812 further until the function f is true. Another way to look at
this is that the ion current compensation, I.sub.C, can be adjusted
until it matches the ion current, I.sub.I, (or in the alternative,
meets the relationship of Equation 3), at which point a narrow IEDF
width will exist. Such an adjustment to the ion current
compensation, I.sub.C, and resulting narrowing of the IEDF, can be
seen in FIG. 22. The ion current, I.sub.I, and the corresponding
ion current compensation, I.sub.C, can be stored (e.g., in a
memory) in store operation 1814. The ion current, I.sub.C, can vary
in time, as can the effective capacitance, C.sub.1.
[0108] When Equation 4 is met, ion current, I.sub.I, is known
(either because I.sub.C=I.sub.I, or because Equation 3 is true).
Thus, the method 1800 enables remote and non-invasive measurements
of ion current, I.sub.I, in real time without affecting the plasma.
This leads to a number of novel metrics such as remote monitoring
of plasma density and remote fault detection of the plasma
source.
[0109] While adjusting 1812 the compensation current, I.sub.C, the
ion energy will likely be broader than a delta function and the ion
energy will resemble that of FIG. 21. However, once the
compensation current, I.sub.C, is found that meets Equation 3, the
IEDF will appear as the right portion of FIG. 22--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 I.sub.C=I.sub.I (or alternatively when
Equation 3 is true). In FIG. 23 the substrate voltage, 2308,
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 voltage 2308 is referred to as
being substantially constant.
[0110] The following provides further details about each of the
method steps illustrated in FIG. 18. In one embodiment, the
modified periodic voltage function can have a waveform like that
illustrated in FIG. 8 and can include a first portion (e.g., first
portion 802), a second portion (e.g., 804), a third portion (e.g.,
third portion 806), and a fourth portion (e.g., fourth portion
808), where the third portion can have a voltage step, .DELTA.V,
and the fourth portion can have a slope, dV.sub.0/dt. The slope,
dV.sub.0/dt, can be positive, negative, or zero. The modified
periodic voltage function 800 can also be described as having
pulses comprising the first portion 802, the second portion 804,
and the third portion 806, and a portion between the pulses, a
fourth portion 808, which is often sloped.
[0111] The modified periodic voltage function can be measured as
V.sub.0 in FIG. 2 and can appear as the modified periodic voltage
function 2102 in FIG. 21. The modified period voltage function 2102
is produced by combining the power supply voltage 2106 (also known
as the periodic voltage function) with the ion current compensation
2104. The power supply voltage 2106 is largely responsible for
generating and shaping the pulses of the modified periodic voltage
function 2102 and the ion current compensation 2104 is 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 in FIG. 22.
Decreasing a magnitude of the power supply voltage 2306 causes a
decrease in a magnitude of the amplitude of the pulses and the
peak-to-peak voltage of the modified periodic voltage function 2302
as seen in FIG. 23.
[0112] In cases where the power supply is a switch-mode power
supply, the switching diagram 2110 of a first switch T.sub.1 and a
second switch T.sub.2 can apply. For instance, the first switch
T.sub.1 can be implemented as the switch T.sub.1 in FIG. 2 and the
second switch T.sub.2 can be implemented as the second switch
T.sub.2 in FIG. 2. The two switches are illustrated as having
identical switching times, but being 180.degree. out of phase. In
other embodiments, the switches may have a slight phase offset such
as that illustrated in FIG. 3. When the first switch T.sub.1 is on
(up to a first time .tau..sub.1), the power supply voltage
(V.sub.PS) is drawn to a maximum magnitude (a negative voltage
since the power supply has a negative bus voltage). The second
switch T.sub.2 is turned off during this period so that the power
supply voltage 2106 is isolated from ground. When the switches
reverse (at the first time .tau..sub.1), the power supply voltage
2106 ramps and slightly passes ground and then settles at this
positive voltage. This ramping and settling occurs between the
first time .tau..sub.1 and a second time .tau..sub.2. The first
switch T.sub.1 is then turned on again and the second switch
T.sub.2 is turned off until a third time .tau..sub.3. Turning the
first switch T.sub.1 on causes the voltage to drop by a voltage
step .DELTA.V, which is then followed by a sloped region having a
slope dV.sub.0/dt until the switches again reverse at the third
time .tau..sub.3. The third time .tau..sub.3 is also a first time
of a subsequent cycle or period of the modified periodic voltage
function.
[0113] 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.
[0114] The modified periodic voltage function can be applied to the
substrate support 1802, and sampled 1804 as V.sub.0 at a last
accessible point before the modified periodic voltage function
reaches the substrate support (e.g., between the switch mode power
supply and the effective capacitance). The unmodified periodic
voltage function (or power supply voltage 2106 in FIG. 21) can be
sourced from a power supply such as the switch mode power supply
1206 in FIG. 12. The ion current compensation 2104 in FIG. 21 can
be sourced from a current source such as the ion current
compensation component 1260 in FIG. 12 or 1360 in FIG. 13.
[0115] A portion of or the whole modified periodic voltage function
can be sampled 1804. For instance, the fourth portion (e.g., fourth
portion 808) can be sampled. The sampling 1804 can be performed
between the power supply and the substrate support. For instance,
in FIG. 1, the sampling 1804 can be performed between the switch
mode power supply 106 and the support 108. In FIG. 2, the sampling
1804 can be performed between the inductor L1 and the inherent
capacitance C10. In one embodiment, the sampling 1804 can be
performed at V.sub.0 between the capacitance C3 and the inherent
capacitance C10. Since the inherent capacitance C10 and the
elements representing the plasma (R2, R3, C1, and C2) are not
accessible for real time measurement, the sampling 1804 is
typically performed to the left of the inherent capacitance C10 in
FIG. 2. Although the inherent capacitance C10 typically 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 C10 can vary with time.
[0116] 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
portions 802, 804, 806, 808 of the periodic voltage function
illustrated in FIG. 8 can be distinguished, which may not be
possible at traditional sampling rates. In some embodiments, the
higher sampling rates enable resolving of the voltage step,
.DELTA.V, and the slope, dV.sub.0/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.
[0117] The calculation 1806 of the slope, dV.sub.0/dt, can be based
on a plurality of V.sub.0 measurements taken during the time t
(e.g., the fourth portion 808). For instance, a linear fit can be
performed to fit a line to the V.sub.0 values where the slope of
the line gives the slope, dV.sub.o/dt. In another instance, the
V.sub.0 values at the beginning and end of time t (e.g., the fourth
portion 808) in FIG. 8 can be ascertained and a line can be fit
between these two points with the slope of the line given as
dV.sub.o/dt. These are just two of numerous ways that the slope,
dV.sub.o/dt, of the portion between the pulses can be
calculated.
[0118] The decision 1810 can be part of an iterative loop used to
tune the IEDF to a narrow width (e.g., a minimum width, or in the
alternative, 6% full-width half maximum). Equation 4 only holds
true where the ion current compensation, Ic, is equal to the ion
current, I.sub.I (or in the alternative, is related to I.sub.I
according to Equation 3), which only occurs where there is a
constant substrate voltage and thus a constant and substantially
singular ion energy (a narrow IEDF width). A constant substrate
voltage 2308 (V.sub.sub) can be seen in FIG. 23. Thus, either ion
current, I.sub.I, or alternatively ion current compensation, Ic,
can be used in Equation 4.
[0119] Alternatively, two values along the fourth portion 808 (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 4 true for a third, but not-yet-measured, slope.
Thus, an ion current, I.sub.I, can be estimated that is predicted
to correspond to a narrow IEDF width. These are just two of the
many ways that a narrow IEDF width can be determined, and a
corresponding ion current compensation, Ic, and/or a corresponding
ion current, I.sub.I, can be found.
[0120] The adjustment to the ion current compensation, Ic, 1812 can
involve either an increase or a decrease in the ion current
compensation, Ic, and there is no limitation on the step size for
each adjustment. In some embodiments, a sign of the function f in
Equation 4 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.
[0121] Once an ion current compensation, Ic, has been identified
that equals the ion current, I.sub.I (or in the alternative, is
related thereto according to Equation 3), the method 1800 can
advance to further set point operations (see FIG. 19) or remote
chamber and source monitoring operations. The further set point
operations can include setting the ion energy (see also FIG. 23)
and the distribution of ion energy or IEDF width (see also FIG.
24). The source and chamber monitoring can include monitoring
plasma density, source supply anomalies, plasma arcing, and
others.
[0122] Furthermore, the method 1800 can optionally loop back to the
sampling 1804 in order to continuously (or in the alternative,
periodically) update the ion current compensation, Ic. For
instance, the sampling 1804, calculation 1806, the decision 1810,
and the adjusting 1812 can periodically be performed given a
current ion current compensation, Ic, in order to ensure that
Equation 4 continues to be met. At the same time, if the ion
current compensation, Ic, that meets Equation 4 is updated, then
the ion current, I.sub.I, can also be updated and the updated value
can be stored 1814.
[0123] While the method 1800 can find and set the ion current
compensation, Ic, so as to equal the ion current, I.sub.I, or in
the alternative, to meet Equation 3, a value for the ion current
compensation, Ic, needed to achieve a narrow IEDF width can be
determined without (or in the alternative, before) setting the ion
current, I.sub.C, to that value. For instance, by applying a first
ion current compensation, Ic.sub.1, for a first cycle and measuring
a first slope, dV.sub.01/dt, of the voltage between the pulses, and
by applying a second ion current compensation, Ic.sub.2, for a
second cycle and measuring a second slope, dV.sub.02/dt, of the
voltage between the pulses, a third slope, dV.sub.03/dt, associated
with a third ion current compensation, Ic.sub.3, can be determined
at which Equation 4 is expected to be true. The third ion current
compensation, Ic.sub.3, can be one that if applied would result in
a narrow IEDF width. Hence, the ion current compensation, Ic, that
meets Equation 4 and thus corresponds to ion current, I.sub.I, can
be determined with only a single adjustment of the ion current
compensation. The method 1800 can then move on to the methods
described in FIG. 19 without ever setting the ion current, I.sub.C,
to a value needed to achieve the narrow IEDF width. Such an
embodiment may be carried out in order to increase tuning
speeds.
[0124] Alternatively, given a first slope, dV.sub.01/dt, and a
corresponding first ion current compensation, I.sub.C1, a second
slope, dV.sub.02/dt, and a corresponding second ion current
compensation, I.sub.C2, and the effective capacitance C.sub.1, the
ion current, I.sub.I, can be estimated using the following equation
without adjusting the ion compensation current I.sub.C to equal the
ion current, I.sub.I, or adjusting it to meet Equation 3:
I I = C 1 ( I C 1 V 02 t - I C 2 V 01 t ) I C 1 - I C 2 + C 1 ( V
02 t - V 01 t ) ( Equation 5 ) ##EQU00005##
[0125] FIG. 19 illustrates methods for setting the IEDF width and
the ion energy. The method originates from the method 1800
illustrated in FIG. 18, and can take either of the left path 1900
(also referred to as an IEDF branch) or the right path 1901 (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, .DELTA.V, or the third portion 806
of the modified periodic voltage function 800 of FIG. 8. The
relationship between ion energy, eV, and the voltage step,
.DELTA.V, can be written as Equation 6:
eV = .DELTA. V C 1 C 2 + C 1 ( Equation 6 ) ##EQU00006##
[0126] where C.sub.1 is the effective capacitance (e.g., chuck
capacitance; inherent capacitance, C10, in FIG. 2; or inherent
capacitance, C1, in FIG. 13), and C.sub.2 is a sheath capacitance
(e.g., the sheath capacitance C2 in FIG. 2 or the sheath
capacitance C2 in FIG. 13). The sheath capacitance, C.sub.2, may
include stray capacitances and depends on the ion current, I.sub.I.
The voltage step, .DELTA.V, can be measured as a change in voltage
between the second portion 804 and the fourth portion 808 of the
modified periodic voltage function 800. By controlling and
monitoring the voltage step, .DELTA.V, (which is a function of a
power supply voltage or a bus voltage such as bus voltage,
V.sub.bus in FIG. 2), ion energy, eV, can be controlled and
known.
[0127] Throughout this disclosure ion energy, eV, is referred to as
if it is a singular value. However, the meaning of ion energy, eV,
has slightly different meanings depending on the IEDF width. Where
the IEDF width is minimized, the ion energy, eV, is an average ion
energy of the IEDF. When the IEDF width is not minimized, the ion
energy, eV, marks either a minimum or maximum of the IEDF,
depending on whether I.sub.I<I.sub.C or I.sub.I>I.sub.C.
Where I.sub.I<I.sub.C, the ion energy, eV, corresponds to a
minimum ion energy, eV, of the IEDF. Where I.sub.I>I.sub.C, the
ion energy, eV, corresponds to a maximum ion energy, eV, of the
IEDF. Where the IEDF width is small, this technicality is not too
important, and thus ion energy, eV, will be treated as if
representing an average ion energy for an IEDF. But, for the sake
of rigor, one should bear in mind the above description.
[0128] At the same time, the IEDF width can be approximated
according to Equation 7:
IEDF width = V PP - .DELTA. V - It C ( Equation 7 )
##EQU00007##
[0129] where I is I.sub.I where C is C.sub.series, or I is I.sub.C
where C is C.sub.effective. Time, t, is the time between pulses,
V.sub.PP, is the peak-to-peak voltage, and .DELTA.V is the voltage
step.
[0130] Additionally, sheath capacitance, C.sub.2, can be used in a
variety of calculations and monitoring operations. For instance,
the Debye sheath distance, .lamda..sub.sheath, can be estimated as
follows:
.lamda. sheath = .epsilon. A C 2 ( Equation 8 ) ##EQU00008##
[0131] where .di-elect cons. 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 8
is written as Equation 9:
.lamda. sheath = T e .epsilon. 0 n e q ( V 2 T e ) .75 ( Equation 9
) ##EQU00009##
[0132] Additionally, an e-field in the sheath can be estimated as a
function of the sheath capacitance, C.sub.2, the sheath distance
.lamda..sub.sheath, and the ion energy, eV. Sheath capacitance,
C.sub.2, along with the ion current, I.sub.I, can also be used to
determine plasma density, n.sub.e, from Equation 10 where
saturation current, I.sub.sat, is linearly related to the
compensation current, I.sub.C, for singly ionized plasma.
I sat = .SIGMA. n i q i kT e m i A .apprxeq. n e q kT e m A (
Equation 10 ) ##EQU00010##
[0133] An effective mass of ions at the substrate surface can be
calculated using the sheath capacitance, C.sub.2 and the saturation
current, I.sub.sat. Plasma density, n.sub.e, electric field in the
sheath, ion energy, eV, effective mass of ions, and a DC potential
of the substrate, V.sub.DC, are fundamental plasma parameters that
are typically only monitored via indirect means in the art. This
disclosure enables direct measurements of these parameters thus
enabling more accurate monitoring of plasma characteristics in real
time.
[0134] As seen in Equation 6, the sheath capacitance, C.sub.2, can
also be used to monitor and control the ion energy, eV, as
illustrated in the ion energy branch 1901 of FIG. 19. The ion
energy branch 1901 starts by receiving a user selection of ion
energy 1902. The ion energy branch 1901 can then set an initial
power supply voltage for the switch-mode power supply that supplies
the periodic voltage function 1904. At some point before a sample
periodic voltage operation 1908, the ion current can also be
accessed 1906 (e.g., accessed from a memory). The periodic voltage
can be sampled 1908 and a measurement of the third portion of the
modified periodic voltage function can be measured 1910. Ion
energy, I.sub.I, can be calculated from the voltage step, .DELTA.V,
(also referred to as the third portion (e.g., third portion 806))
of the modified periodic voltage function 1912. The ion energy
branch 1901 can then determine whether the ion energy equals the
defined ion energy 1914, and if so, the ion energy is at the
desired set point and the ion energy branch 1901 can come to an
end. If the ion energy is not equal to the defined ion energy, then
the ion energy branch 1901 can adjust the power supply voltage
1916, and again sample the periodic voltage 1908. The ion energy
branch 1901 can then loop through the sampling 1908, measuring
1910, calculating 1912, decision 1914, and the setting 1916 until
the ion energy equals the defined ion energy.
[0135] The method for monitoring and controlling the IEDF width is
illustrated in the IEDF branch 1900 of FIG. 19. The IEDF branch
1900 includes receiving a user selection of an IEDF width 1950 and
sampling a current IEDF width 1952. A decision 1954 then determines
whether the defined IEDF width equals the current IEDF width, and
if the decision 1952 is met, then the IEDF width is as desired (or
defined), and the IEDF branch 1900 can come to an end. However, if
the current IEDF width does not equal the defined IEDF width, then
the ion current compensation, Ic, can be adjusted 1956. This
determination 1954 and the adjustment 1956 can continue in a
looping manner until the current IEDF width equals the defined IEDF
width.
[0136] In some embodiments, the IEDF branch 1900 can 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 in FIG. 11.
[0137] With knowledge of the ion current, I.sub.I, and the voltage
step, .DELTA.V, Equation 6 can be solved for ion energy, eV. The
voltage step, .DELTA.V, can be controlled by changing the power
supply voltage which in turn causes the voltage step, .DELTA.V, to
change. A larger power supply voltage causes an increase in the
voltage step, .DELTA.V, and a decrease in the power supply voltage
causes a decrease in the voltage step, .DELTA.V. In other words,
increasing the power supply voltage results in a larger ion energy,
eV.
[0138] 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.
[0139] Although FIGS. 17-19 have 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, V.sub.PS, 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., top two
figures in FIG. 20). Using three different power supply voltages
results in three different ion energies (e.g., middle two figures
in FIG. 20). 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., bottom two figures
in FIG. 20).
[0140] 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.
[0141] Some of the heretofore mentioned controls are enabled by
using some combination of the following: (1) a fixed waveform
(consecutive cycles of the waveform are the same); (2) a waveform
having at least two portions that are proportional to an ion energy
and an IEDF (e.g., the third and fourth portions 806 and 808
illustrated in FIG. 8); 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).
[0142] 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.
[0143] 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.
[0144] As an example of monitoring, and with reference to FIG. 8,
the DC offset of the waveform 800 can represent a health of the
plasma source (hereinafter referred to as the "source"). In
another, a slope of a top portion 804 (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 portion 804 from horizontal (illustrated as having
a slope equal to 0) is another way to monitor source health based
on an aspect of the waveform 800. Another aspect involves measuring
a standard deviation of sampled V.sub.0 points along the fourth
portion 808 of 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.
[0145] One of skill in the art will recognize that the methods
illustrated in FIGS. 17, 18, and 19 do 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 can
be monitored before, during, or after setting and monitoring the
IEDF width and/or the ion energy, eV.
[0146] FIG. 21 illustrates various waveforms at different points in
the systems herein disclosed. Given the illustrated switching
pattern 2110 for switching components of a switch mode power
supply, power supply voltage, V.sub.PS, 2106 (also referred to
herein as a periodic voltage function), ion current compensation,
Ic, 2104, modified periodic voltage function 2102, and substrate
voltage, V.sub.sub, 2112, the IEDF has the illustrated width 2114
(which may not be drawn to scale) or IEDF shape 2114. This width is
wider than what this disclosure has referred to as a "narrow
width." As seen, when the ion current compensation, Ic, 2104 is
greater than the ion current, I.sub.I, the substrate voltage,
V.sub.sub, 2112 is not constant. The IEDF width 2114 is
proportional to a voltage difference of the sloped portion between
pulses of the substrate voltage, V.sub.sub, 2112.
[0147] Given this non-narrow IEDF width 2114, the methods herein
disclosed call for the ion current compensation, Ic, to be adjusted
until I.sub.C=I.sub.I (or in the alternative are related according
to Equation 3). FIG. 22 illustrates the effects of making a final
incremental change in ion current compensation, Ic, in order to
match it to ion current I.sub.I. When I.sub.C=I.sub.I the substrate
voltage, V.sub.sub, 2212 becomes substantially constant, and the
IEDF width 2214 goes from non-narrow to narrow.
[0148] Once the narrow IEDF has been achieved, one can adjust the
ion energy to a desired or defined value as illustrated in FIG. 23.
Here, a magnitude of the power supply voltage (or in the
alternative a bus voltage, V.sub.bus, of a switch-mode power
supply) is decreased (e.g., a maximum negative amplitude of the
power supply voltage 2306 pulses is reduced). As a result,
.DELTA.V.sub.1 decreases to .DELTA.V.sub.2 as does the peak-to-peak
voltage, from V.sub.PP1 to V.sub.PP2. A magnitude of the
substantially constant substrate voltage, V.sub.sub, 2308
consequently decreases, thus decreasing a magnitude of the ion
energy from 2315 to 2314 while maintaining the narrow IEDF
width.
[0149] Whether the ion energy is adjusted or not, the IEDF width
can be widened after the narrow IEDF width is achieved as shown in
FIG. 24. Here, given I.sub.I=I.sub.C (or in the alternative,
Equation 3 giving the relation between I.sub.I and I.sub.C),
I.sub.C can be adjusted thus changing a slope of the portion
between pulses of the modified periodic voltage function 2402. As a
result of ion current compensation, Ic, and ion current, I.sub.I,
being not equal, the substrate voltage moves from substantially
constant to non-constant. A further result is that the IEDF width
2414 expands from the narrow IEDF 2414 to a non-narrow IEDF 2402.
The more that I.sub.C is adjusted away from I.sub.I, the greater
the IEDF 2414 width.
[0150] FIG. 25 illustrates 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 IEDF 2514 width. A magnitude of
the power supply voltage 2506 alternates each cycle. This results
in an alternating .DELTA.V and peak-to-peak voltage for each cycle
of the modified periodic voltage function 2502. The substrate
voltage 2512 in 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 IEDF 2514
width.
[0151] FIG. 26 illustrates another pattern of the power supply
voltage that can be used to achieve more than one ion energy level
where each ion energy level has a narrow IEDF 2614 width. Here, the
power supply voltage 2606 alternates 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 V.sub.PS 2606
were alternated every cycle. This shows just one example of how
various other patterns of the V.sub.PS 2606 can be used to achieve
the same ion energies.
[0152] FIG. 27 illustrates one combination of power supply
voltages, V.sub.PS, 2706 and ion current compensation, Ic, 2704
that can be used to create a defined IEDF 2714. Here, alternating
power supply voltages 2706 result in two different ion energies.
Additionally, by adjusting the ion current compensation 2704 away
from the ion current, I.sub.I, the IEDF 2714 width for each ion
energy can be expanded. If the ion energies are close enough, as
they are in the illustrated embodiment, then the IEDF 2714 for both
ion energies will overlap resulting in one large IEDF 2714. Other
variations are also possible, but this example is meant to show how
combinations of adjustments to the V.sub.PS 2706 and the I.sub.C
2704 can be used to achieve defined ion energies and defined IEDFs
2714.
Circuit Memory as a Cause of Inaccurate Ion Energies
[0153] Referring to FIGS. 2 and 8, a modified periodic voltage
function 800 can be seen as generated at an output of the
switch-mode power supply 206. The modified period voltage function
800 begins with an upswing in voltage, V.sub.0, as the first switch
component 226' closes and charges a series capacitance,
C.sub.series, that includes the substrate support 208. When
C.sub.series is charged, the first switch component 226' is opened.
The first and second switch components 226' and 226'' can both be
open for a short time (tc-t) causing the voltage across
C.sub.series to remain constant. The second switch component 226''
is then closed causing V.sub.0 to drop a voltage .DELTA.V, after
which point the modified periodic voltage function 800 begins to
slope downward with a slope dV.sub.0/dt as ion current compensation
from the ion energy control 220 is provided to the substrate
support 208. The voltage step .DELTA.V is related to ion energy for
ions striking a substrate surface in the plasma processing chamber
204. The modified periodic voltage function 800 is illustrated and
described without disturbances.
[0154] However, in practice disturbances can affect .DELTA.V and
thus ion energy. For instance, where a narrow ion energy
distribution function IEDF is desired, .DELTA.V, should be constant
from cycle to cycle. If a disturbance causes .DELTA.V to differ in
some cycles, then the IEDF will have a smear or jitter.
[0155] This problem is illustrated in FIGS. 12 and 13. FIG. 12
illustrates a modified periodic voltage function 1200 where a
disturbance 1212 can be seen in a first cycle, which influences the
.DELTA.V of a next cycle. FIG. 12 also shows a more accurate
presentation of the voltage rise at the start of each cycle--this
shape is more sinusoidal than the vertical shape illustrated in
FIG. 8. The sinusoidal shape is a result of the recharging of
C.sub.series through L.sub.1 that is occurring during this voltage
rise.
[0156] A disturbance 1212 is seen during the downward sloping
portion of the first cycle (other types of disturbances are also
possible and such disturbances can occur anywhere in a cycle, not
just during the sloped portion). Without the disturbance 1212, the
voltage would continue to fall with substantially the same slope
along line 1214. However, the disturbance 1212 causes the voltage
to continue to fall with the same slope, but along a line 1208
having a higher voltage. As a result, when the first switch
component 226' is again closed and V.sub.0 begins to rise, instead
of following the path 1214 followed in the previous cycle, V.sub.0
follows the path 1208 leading to a .DELTA.V' which is lower than
the .DELTA.V of the previous cycle and lower than desired. This
affect can be referred to as `memory` since each cycle remembers
the voltage at which the previous cycle ended (e.g., when the first
switch component 226' closes).
[0157] FIG. 13 shows a similar modified periodic voltage function
1300, but in this case a disturbance 1312 causes the falling
voltage to follow the path 1308 rather than the path 1314. As a
result, V.sub.0 is lower when the first switch component 226' is
closed and C.sub.series begins to charge. Consequently, V.sub.0
follows the path 1308 rather than 1314 when the first switch
component 226' opens. The result is a .DELTA.V' that is larger than
desired and larger than the .DELTA.V of the previous cycle.
[0158] Thus, this `memory` causes inaccuracies, and potentially
instability, in the ion energy. There is therefore a need in the
art to eliminate this memory and achieve accurate and stable ion
energy while still using energy efficient resonant switching.
[0159] The memory is partially the result of excess energy stored
in a series capacitance C.sub.series that would normally be
completely removed from C.sub.series by the time the first switch
component 226' closes. However, where there is a disturbance (e.g.,
1312), energy remains in C.sub.series when the first switch
component 226' closes. One way to remove this energy is to couple
C.sub.series to a resistor such that the energy dissipates into the
resister. This is a fast method of removing the memory from
C.sub.series, but has the downside of wasting energy as the energy
is merely converted to heat rather than put to work.
[0160] A preferred operating regime is known as resonant since
energy is passed back and forth between a capacitor and an inductor
and thus reused rather than being wasted in a resistor (some
dissipation in inherent resistances is unavoidable, but at least is
smaller than in a resistive regime). However, inductors are not
charged quickly, and thus an inductor in a resonant system is not
effective to remove excess capacitance from the capacitor at the
end of each cycle.
[0161] Thus, there is a need in the art for systems, methods, and
apparatus operating in the more efficient resonant regime, while
also being able to quickly remove excess charge from a capacitor of
the system in order to avoid inaccuracies and instability caused by
so-called memory.
[0162] FIGS. 14 and 15 illustrate waveforms where the systems and
methods herein disclosed are used to achieve a desired ion energy
despite different disturbances in a previous cycle. In FIG. 14 the
disturbance 1408 would have caused .DELTA.V to be higher than
desired (recall FIG. 13), but instead, as V.sub.0 rises at the
start of a cycle (with a first switch component closed), the bias
supply monitors the rising voltage and cuts off the increasing
voltage when V.sub.0 reaches a voltage 1408 that corresponds to a
desired ion energy. In other words, the bias supply cuts off the
voltage increase before the default period for the voltage rise--or
before C.sub.series is fully charged. In FIG. 15 the disturbance
1508 would have caused .DELTA.V to be lower than desired (recall
FIG. 12), but instead, as V.sub.0 rises at the start of the cycle,
the bias supply monitors the rising voltage and cuts off the
increasing voltage when V.sub.0 reaches a level that corresponds to
the desired ion energy 1508. In this case, the voltage is allowed
to rise for longer than a default period for the voltage rise--but
still is cutoff before C.sub.series is fully charged.
[0163] In FIG. 14, the key is to cut off the voltage rise before a
default period. However, in FIG. 15, there are two keys to the
method: first the bus voltage, V.sub.bus is set such that V.sub.0
can theoretically be allowed to rise far higher than would ever be
required (e.g., level 1514). In other words, V.sub.bus is set such
that C.sub.series typically will not be fully charged in order to
achieve any desired ion energies. In this way, V.sub.0 can be
cutoff later than the default period, and thus can rise above where
it would otherwise reach due to the disturbance 1512.
[0164] Unfortunately, when V.sub.0 is cutoff before the voltage is
allowed to rise to a Max V.sub.0, energy remains stored in an
inductor of the bias supply, and/or in inherent inductance of the
bias supply. Were the bias supply allowed to fully charge
C.sub.series, the inductor's energy would have been fully
discharged into or exchanged with C.sub.series. Thus, while the
switching algorithm herein described enables resonant operation and
the ability to wipe out `memory` from the previous cycle, thus
removing inaccuracy and instability, a new problem is created in
that the inductor and/or inductance of the bias supply is never
fully depleted. This stored energy can cause further `memory`
problems for the subsequent cycle, and thus there is a further need
to quickly and efficiently remove the remaining stored energy in
the inductor and/or inductance of the bias supply. Solutions to
this problem are described with reference to the system illustrated
in FIG. 9.
[0165] FIG. 9 illustrates an inductance L.sub.1 between switch
components T.sub.1 and T.sub.2 and the series capacitance,
C.sub.series (the use of C.sub.series assumes that there is no
stray capacitance; where stray capacitance is considered,
C.sub.effective can be used, where C.sub.series can be a part of
C.sub.effective). The inductance L.sub.1 can represent a discrete
inductor or a combination of a discrete inductor and inherent
inductances. There is also an inherent resistance R.sub.1 in the
switch component T.sub.1 as well as an inherent resistance R.sub.2
in switch component T.sub.2. The series combination of R.sub.1 and
C.sub.series acts as a RC circuit leading to an exponential decay
or discharge of C.sub.series whenever the switch component T.sub.1
is open and switch component T.sub.2 is closed. The series
combination of inherent inductance L.sub.1 and series capacitance
C.sub.series operates as an LC circuit having a resonant nature
leading to the exchange of energy between C.sub.series and L.sub.1
in a periodic fashion. Were R.sub.1 to dominate over L.sub.1 this
RLC circuit would operate resistively and energy discharged from
C.sub.series would be wasted as heat dissipated in R.sub.1. This
would be an inefficient and undesirable situation.
[0166] One alternative is for this RLC circuit to operate in a
resonant regime in which L.sub.1 dominates over R.sub.1, and energy
primarily is exchanged between C.sub.series and L.sub.1 with only a
small fraction of energy being lost to R.sub.1. The downside of
operating in a resonant fashion is that energy stored in the
inductor L.sub.1 and C.sub.series leads to what will be referred to
as a `memory,` wherein disturbances in one cycle affect the
waveform of a subsequent cycle. Because of this memory, the voltage
provided to the right-hand side of C.sub.series, which is
representative of a substrate surface within a plasma, may see
inaccuracies or instability.
[0167] For instance in FIG. 12 a disturbance 1212 in the modified
periodic voltage function measured at V.sub.o in FIG. 9 causes an
inaccuracy in that .DELTA.V' is smaller than it would have been
without the disturbance and smaller than .DELTA.V in the previous
cycle. This leads to some ions being accelerated with .DELTA.V and
some being accelerated at .DELTA.V', leading to a
broader-than-desired, or smeared, IEDF. In FIG. 13 a disturbance
1308 causes an inaccuracy in that .DELTA.V' is larger than it would
have been without the disturbance and larger than .DELTA.V of the
previous cycle. In both cases, since .DELTA.V' is other than
expected and desired, there is an inaccuracy in ion energy.
[0168] Furthermore, since an inaccuracy in one cycle causes a
further inaccuracy in the subsequent cycle, a single disturbance
can cause instability--an increasing error in .DELTA.V each
cycle.
[0169] In order to have the bias supply 902 operate in an efficient
resonant regime, the discrete inductor L.sub.1 is used that renders
the resistive effects of R.sub.1 negligible. While L.sub.1
represents at least an inductance of a discrete inductor, in some
embodiments it can also represent inherent inductances as well,
although these should be small relative to the inductance of the
discrete inductor. For purposes of this disclosure, L.sub.1 in FIG.
9 can refer to an inductance of a discrete inductor or to an
inductance of a discrete inductor and inherent inductances. Either
way, L.sub.1 dominates over R.sub.1, so that the bias supply 902
operates resonantly. But as described above, this along with the
novel switching algorithm leads to unwanted stored energy in
L.sub.1 at the end of each cycle.
[0170] To solve the problems associated with excess energy being
stored in L.sub.1 when switch component T.sub.1 opens, an energy
evacuation component 908 can be used to remove this stored energy
and to do so in a fraction of a cycle length. The energy evacuation
component 908 can remove energy from L.sub.1 at any point or any
period during what is labeled T.sub.evac in FIGS. 14 and 15. In
other words, the energy evacuation component 1408 can be activated
at any time during T.sub.evac. The particular time at which the
energy evacuation component 908 begins to remove energy from the
inductor L.sub.1 is governed by controller 910 and the eV setpoint,
which is provided to the controller 910. In particular, the switch
component T.sub.1 closes to begin a cycle and charge C.sub.series.
V.sub.0 rises and would reach a maximum voltage (Max V.sub.0) if
the switch component T.sub.1 were not opened at some point. In
other words, if C.sub.series were charged indefinitely, V.sub.0
would reach and settle at the Max V.sub.0. V.sub.bus can be set
such that C.sub.series can be charged beyond a level corresponding
to a desired ion energy. In this way, if there is a disturbance in
a previous cycle, the switch component T.sub.1 can close and then
open before C.sub.series is fully charged, thus achieving a desired
V.sub.0 regardless of disturbances. As V.sub.0 rises, the
controller 910 can receive voltage measurements from V.sub.o and
compare these to the eV set point. When V.sub.o matches the eV set
point, the controller 910 can instruct the switch component T.sub.1
to open, thus cutting off the increase in V.sub.o. At this time, or
any time during T.sub.evac, the controller 910 can instruct the
energy evacuation component 908 to activate or begin removing
energy from L.sub.1.
[0171] The energy evacuation component 908 can include any variety
of circuitry, such as batteries, capacitors, resistors, switches,
and/or electrical connections to other portions of the bias supply
902 or any component that can benefit from the energy removed from
L.sub.1. For instance, the energy evacuation component 908 can
include a battery or capacitive element that stores the energy
evacuated from L.sub.1 for later use (e.g., providing the energy
back to V.sub.bus to supplement the rail voltage).
[0172] FIG. 10 illustrates a bias supply with a particular
embodiment of the energy evacuation component. Here, a switch 1014
of the energy evacuation component 1008 closes at a point during
T.sub.evac and any energy in L.sub.1 is evacuated into the energy
evacuation component 1008 and dissipated in a resistor 1012.
[0173] The controllers 910 and 1010, in some embodiments, can
include an analog comparator or an A-to-D converter feeding a
digital comparator.
Wide Dynamic Range
[0174] At low energies, the inaccuracies and instability discussed
above, become more problematic. This makes it difficult to achieve
a wide dynamic range for ion energies since a wide dynamic range of
ion energies typically require at least one ion energy having a low
value. The systems and methods discussed above can therefore be
implemented to remove inaccuracies and instabilities at high
energies, and especially at low energies, thus enabling a bias
supply to achieve a wide dynamic range of ion energies in a
plasma.
Fast Ion Energy Control
[0175] Certain applications call for a `fast` change in ion energy,
where `fast` can include changes in ion energy within a few cycles
of the modified periodic voltage function, or even from cycle to
cycle. One way to change ion energy is to adjust V.sub.bus, but
this is difficult to do fast enough for `fast` applications.
However, using the switching algorithm discussed above and the
energy evacuation component to remove excess energy stored in an
inductor of a bias supply, ion energy can be adjusted from cycle to
cycle (i.e., where a first cycle produces a first ion energy and a
next cycle produces a second ion energy).
[0176] The systems and methods herein disclosed can adjust the ion
energy without a change in V.sub.bus. For instance, in FIGS. 12-15
it can be seen that various ion energies (different .DELTA.V) can
be achieved for a given V.sub.bus. Ion energy switching is so
`fast` that the ion energy for a cycle can even be selected while
V.sub.0 is rising. In other words, .DELTA.V, or the ion energy, can
be decided upon at any time prior to the switching component
T.sub.1 being opened.
[0177] While `fast` ion energy control can be advantageous when
switching between different ion energies, it is also advantageous
when a plasma is ignited, since the ability to stop charging
C.sub.series at an exact eV set point greatly reduces if not
eliminates transients in plasma ion energy that are sometimes seen
when a plasma is ignited.
Pulsed Ion Energy Control
[0178] Many plasma processing recipes call for a pulsing envelope
for RF power provided by a plasma source. FIG. 28 illustrates a
pulsed source supply as a function of time. As seen, the RF sine
wave is pulsed according to a pulse envelope indicated with dashed
lines. Pulsing enables, for instance, the ratio of ions to free
radicals to be controlled. In particular, free radicals typically
have a longer lifetime than ions, and therefore, when the RF is
turned off, the ratio of free radicals to ions increases with time.
An increased ratio of radicals can affect, for instance, the
relative etch rates of various materials on the surface of a work
piece, which is advantageous in some recipes. However, to maintain
a desired level of free radicals and ions, the RF power is turned
back on, hence pulsing of the source supply is carried out. In some
cases the source supply can be pulsed between two different RF
amplitudes rather than between an RF amplitude and 0 for the
purpose of maintaining a more consistent level of ions and radicals
within the processing chamber.
[0179] When pulsed RF source supplies are used, bias supplies are
typically synchronized in some manner to the source supply pulses
(see FIG. 29). Where bilevel source supply voltages are used, the
bias supply can also be pulsed between two different bias supply
voltages. However, systems and methods in the art of pulsing
multiple supplies suffer from various disadvantages. For instance,
pulsed bias supplies can see transients in the ion density and ion
energy every time that the bias supply is turned on. One example
can be seen in FIG. 30, where the bias supply illustrates a slow
turn-on transient in addition to an overshoot of the desired
voltage target shortly after being turned on prior to settling into
a desired voltage regime. Similarly, the intra-pulse turn-on
transient seen on the source pulse envelope is affected by the
turn-on of the bias supply. These transients can result in part
from the fact that traditional bias supplies and plasma density are
non-orthogonal--a change in bias supply voltage has a substantial
effect on the plasma density. These transients not only make
accurate processing recipes difficult to design, but when
monitoring bias supply voltages, many methods in the art do not use
data points from the transient regimes, thus injecting potential
measurement and regulation errors while potentially increasing
processing time. Some recipes may also call for rapid changes in
ion energy within a given source supply pulse. Traditional systems
and methods have difficulty controlling the ion energy with
accuracy and stability and have difficulty making such changes at
all within a period of time as short as a few cycles of the bias
supply.
[0180] The systems and methods herein disclosed solve a number of
these issues. FIG. 29 illustrates a modified periodic voltage for a
bias supply, such as the bias supply 902 of FIG. 9, being pulsed
within a pulse envelope indicated by dashed lines. The pulses of
the bias supply are synchronized with those of the source supply in
FIG. 28. Transients, such as that seen in FIG. 30, can be reduced
and possibly eliminated since the maximum voltage of the modified
periodic voltage function produced by the herein disclosed bias
supply can be accurately controlled via opening a switch component
T.sub.1 at the exact moment needed to achieve a desired ion energy.
These systems and methods also enable orthogonality between the ion
energy control and the plasma density control. Thus, the same
systems and methods that previously were described as reducing
inaccuracy and instability in ion energy have the additional
benefit of avoiding transients during pulsed bias supply operation
and enabling orthogonality between the ion energy and plasma
density controls.
[0181] Transients are also avoided since the systems and methods
herein disclosed achieve a nearly orthogonal relationship between
ion energy and plasma density--thus pulsing of the bias supply
(e.g., 902) has a negligible effect on plasma density.
[0182] Further, because the herein disclosed systems and methods
can be used to achieve `fast` ion energy changes (e.g., changing
ion energy from cycle-to-cycle), ion energy can be altered one or
more times within a single source supply or bias supply pulse.
[0183] The systems and methods discussed relative to the wide
dynamic range can also be used in pulsed bias supply embodiments to
achieve wide dynamic ranges of multiple ion energies within a
single pulse of the bias supply.
[0184] Along with changes to ion energy as discussed above, in
other embodiments the ion energy distribution function (IEDF) can
be adjusted from cycle-to-cycle. In other words, within a given
pulse of the bias supply, the IEDF and/or ion energy can be
adjusted one or more times.
[0185] Pulsed bias supply embodiments can further benefit from the
ability to set presets for I.sub.C. Thus, at the start of a bias
supply pulse, I.sub.c can be `guessed` so that a desired ion energy
can be achieved in less time. For instance, as previously
discussed, some iterations may be required to determine a minimum
IEDF after which time the desired ion energy can be set. By
starting such iterations with an I.sub.c based on prior IEDF
settings, the minimum IEDF may be found quicker and thus the
desired ion energy can be established sooner. In other embodiments,
the I.sub.C used in a previous pulse can be used as an initial
condition at the start of a subsequent pulse to again decrease the
time used to set ion energy for the pulse. Further, if multiple ion
energies are to be set in a given pulse, than the I.sub.C used in
the previous pulse or previous pulses can be used as initial
conditions for setting the various ion energies in subsequent
pulses. Similarly, C.sub.2 or its more accurate derivative,
C.sub.series/(C.sub.2+C.sub.series) can be used as initial
conditions in combination with or alternatively to I.sub.C.
[0186] Pulsing embodiments can also benefit from the ability to
measure plasma density via ion current and C.sub.2 as discussed
earlier, but here applied to pulsed bias supply situations. This
leads to further embodiments, in which the bias supply can be
controlled based upon measurements of plasma density during pulse
operation. For instance, bias supply pulses can be triggered, or
regulated in amplitude, duty factor, etc., based on a plasma
density threshold (e.g., the bias supply can turn on when the
plasma density falls below a threshold). In another example,
changes to ion energy or the eV set point can be triggered by the
plasma density falling below or rising above a plasma density
threshold. The ion energy and IEDF within a bias supply pulse can
also be controlled as a function of plasma density.
[0187] In other embodiments, the source supply can be controlled as
a function of plasma density. For instance, pulses of the source
supply can be triggered, or amplitude, duty factor, etc. of the
pulse envelope, can be regulated based on the plasma density
crossing a plasma density threshold or for the purpose of
maintaining plasma density near to a desired level.
Virtual Front Panel
[0188] FIGS. 31 to 52 illustrate various `virtual front panel`
(VFP) displays associated with a bias supply as disclosed earlier.
The VFPs can have a variety of controls (e.g., buttons, sliders,
radio buttons), indicators (e.g., color indicators, bar indicators,
numerical indicators), and graphs or charts (e.g., voltage versus
time). The VFPs can include controls and monitoring charts and
indicators for controlling a bias supply and or a source supply.
For instance, the VFPs can enable control of eV setpoints and IEDF
shapes and widths and monitoring of achieved ion energies and IEDF
shapes and widths. The VFPs can also be used to monitor ion
current, I.sub.I, as well as calibration of a bias supply and/or
plasma processing chamber. These are just a few of the many
embodiments in which a VFP can be used.
[0189] The VFPs can be embodied in a single display (e.g., LCD flat
panel display embedded in a bias supply or coupled to a bias
supply) or multiple displays. The VFP can include touch-sensitive
control.
[0190] FIG. 31 illustrates a VFP charting a modified periodic
voltage function. The VFP further includes a power output control
to toggle a bias supply output on and off. A number of warning
indicators are arranged down the left side of the VFP. There are
also bars and numerical indicators for showing a ion energy (eV),
an ion current compensation, I.sub.C (Icompensation), and a
peak-to-peak voltage (V.sub.pp).
[0191] FIG. 33 illustrates a VFP shows two controls of a bias
supply, one for an ion energy set point (eV setpoint) and another
for an ion current compensation (Current Offset). The VFP also has
a bar indicator for the measured ion energy (eV).
[0192] FIG. 35 illustrates a VFP having a chart for three ion
energies. The chart can either be a readout or an input screen. For
instance, the chart can be used to indicate the achieved ion
energies and the concentrations of ions at each of the three ion
energies, or the chart can be used to show ion energies and
concentrations that the system is to try and achieve.
[0193] FIG. 36 illustrates a VFP having a chart for an ion energy
distribution function having a trapezoidal shape. The IEDF
stretches from just below 500 to just above 1000 eV where the
concentration of ions increases with ion energy. The VFP also
includes controls on the left for controlling the low and high ends
of the IEDF as well as a concentration of ions at both ends.
[0194] FIG. 37 illustrates a VFP for controlling a spread of ion
energies (Spread.sub.1) around an ion energy V.sub.1. In the
illustrated embodiments, the concentration of ions at each energy
drops off towards 0 for energies moving away from V.sub.1.
[0195] FIG. 38 illustrates a VFP for controlling two narrow IEDF
and one IEDF having a defined spread. As seen, two narrow IEDFs can
exist at h.sub.1 and h.sub.2, and have ion concentrations equal to
v.sub.1 and v.sub.2. The IEDF2 Parameters control the center ion
energy of the wide IEDF (V.sub.1) and the IEDF spread
(Spread.sub.1).
[0196] FIG. 39 illustrates a VFP for controlling an IEDF comprising
four ion energies each having particular concentrations where a
spread between any two adjacent ion energies has a concentration
that linearly connects the two adjacent ion energies.
[0197] FIG. 40 illustrates a VFP charting ion energy, I.sub.ion, as
a function of time or position.
[0198] FIG. 43 illustrates a VFP charting plasma density, n.sub.e,
as a function of time or position.
[0199] FIG. 44 illustrates a VFP charting a substrate potential,
V.sub.DC, as a function of time or position.
Pulsed Heater
[0200] In a typical chuck there is an electrical heating system
that may be powered from the AC distribution system of the premises
where the processing chamber is housed. It is known that RF power
can potentially propagate to the AC distribution system. To prevent
this undesirable current path, an RF filter may be placed in the
heating system so that it passes the 60 Hz or 50 Hz distribution
power, but acts as a trap for the RF frequencies (e.g., 13.56 MHz
or 60 MHz). But in some instances, there is not enough physical
space for a filter (or two filters) because the filter must handle
a substantial amount of power, and when a bias substrate supply is
utilized, there are several frequencies that are applied (e.g.,
from 0.4 to 5 MHz), so a filter is difficult to design.
[0201] As a consequence, instead of utilizing a typical filter, a
pulse may be generated with a heater power supply that is applied
to a primary side of a transformer that has low inter-winding
capacitance. The power is passed to a secondary of the transformer,
then rectified and applied to the heater. The low capacitance
barrier of the transformer does not allow a broad range of
frequencies to pass from the secondary back to the primary of the
transformer; thus preventing unwanted frequencies from propagating
to the AC distribution system of the premises.
[0202] The systems and methods described herein can be implemented
in connection with a control and processing components in addition
to the specific physical devices previously described herein. FIG.
53 shows a diagrammatic representation of one embodiment of a
control system 5300 within which a set of instructions can execute
for causing a device to perform or execute any one or more of the
aspects and/or methodologies of the present disclosure. For
example, the control system 5300 may be utilized to realize the
control component 112, 612, 762, 910, 1010. But the components in
FIG. 53 are examples only and do not limit the scope of use or
functionality of any hardware, software, firmware, embedded logic
component, or a combination of two or more such components
implementing particular embodiments of this disclosure. Some or all
of the illustrated components can be part of the control system
5300. For instance, the control system 5300 can include a general
purpose computer or an embedded logic device (e.g., an FPGA), to
name just two non-limiting examples.
[0203] Control system 5300 in this embodiment includes at least a
processor 5301 such as a central processing unit (CPU) or an FPGA
to name two non-limiting examples. The control system 5300 may also
comprise a memory 5303 and storage 5308, both communicating with
each other, and with other components, via a bus 5340. The bus 5340
may also link a display 5332, one or more input devices 5333 (which
may, for example, include a keypad, a keyboard, a mouse, a stylus,
etc.), one or more output devices 5334, one or more storage devices
5335, and various non-transitory, tangible processor-readable
storage media 5336 with each other and with one or more of the
processor 5301, the memory 5303, and the storage 5308. All of these
elements may interface directly or via one or more interfaces or
adaptors to the bus 5340. For instance, the various non-transitory,
tangible processor-readable storage media 5336 can interface with
the bus 5340 via storage medium interface 5326. Control system 5300
may have any suitable physical form, including but not limited to
one or more integrated circuits (ICs), printed circuit boards
(PCBs), mobile handheld devices, laptop or notebook computers,
distributed computer systems, computing grids, or servers.
[0204] Processor(s) 5301 (or central processing unit(s) (CPU(s)))
optionally contains a cache memory unit 5302 for temporary local
storage of instructions, data, or processor addresses. Processor(s)
5301 are configured to assist in execution of non-transitory
processor-readable instructions stored on at least one
non-transitory, tangible processor-readable storage medium. Control
system 5300 may provide functionality as a result of the
processor(s) 5301 executing instructions embodied in one or more
non-transitory, tangible processor-readable storage media, such as
memory 5303, storage 5308, storage devices 5335, and/or storage
medium 5336 (e.g., read only memory (ROM)). For instance,
instructions to effectuate one or more steps of the methods
described with reference to FIGS. 17-19 may be embodied in one or
more non-transitory, tangible processor-readable storage media and
processor(s) 5301 may execute the instructions. Memory 5303 may
read the instructions from one or more other non-transitory,
tangible processor-readable storage media (such as mass storage
device(s) 5335, 5336) or from one or more other sources through a
suitable interface, such as network interface 5320. Carrying out
such processes or steps may include defining data structures stored
in memory 5303 and modifying the data structures as directed by the
software.
[0205] The signal input component 5350 generally operates to
receive signals (e.g., digital and/or analog signals) that provide
information about one or more aspects of the switch mode power
supply 106, switch mode power supply 606, ion current compensation
660, plasma processing chamber 604, and current source 764. In some
implementations, controller 112 and 612 may provide an output
signal (e.g., a binary bit) to inform the switch mode power supply
106 and 506 to adjust a duty cycle of pulses or power supply
voltage. In other implementations, the control system 5300 may be
utilized in part to realize the ion current compensation 660,
current control 762, controller 910, controller 1010.
[0206] The signal output component 5360 may include
digital-to-analog components known to those of ordinary skill in
the art to generate switch control signals to control switches
T.sub.1 and T.sub.2. When switches T.sub.1 and T.sub.2 are
implemented as field effect transistors (FETs), for example, the
signal output component 5360 may generate gate drive signals to
control the switches T.sub.1 and T.sub.2.
[0207] The memory 5303 may include various components (e.g.,
non-transitory, tangible processor-readable storage media)
including, but not limited to, a random access memory component
(e.g., RAM 5304) (e.g., a static RAM "SRAM", a dynamic RAM "DRAM",
etc.), a read-only component (e.g., ROM 5305), and any combinations
thereof. ROM 5305 may act to communicate data and instructions
unidirectionally to processor(s) 5301, and RAM 5304 may act to
communicate data and instructions bidirectionally with processor(s)
5301. ROM 5305 and RAM 5304 may include any suitable
non-transitory, tangible processor-readable storage media described
below. In some instances, ROM 5305 and RAM 5304 include
non-transitory, tangible processor-readable storage media for
carrying out the methods described herein.
[0208] Fixed storage 5308 is connected bidirectionally to
processor(s) 5301, optionally through storage control unit 5307.
Fixed storage 5308 provides additional data storage capacity and
may also include any suitable non-transitory, tangible
processor-readable media described herein. Storage 5308 may be used
to store operating system 5309, EXECs 5310 (executables), data
5311, API applications 5312 (application programs), and the like.
Often, although not always, storage 5308 is a secondary storage
medium (such as a hard disk) that is slower than primary storage
(e.g., memory 5303). Storage 5308 can also include an optical disk
drive, a solid-state memory device (e.g., flash-based systems), or
a combination of any of the above. Information in storage 5308 may,
in appropriate cases, be incorporated as virtual memory in memory
5303.
[0209] In one example, storage device(s) 5335 may be removably
interfaced with control system 5300 (e.g., via an external port
connector (not shown)) via a storage device interface 5325.
Particularly, storage device(s) 5335 and an associated
machine-readable medium may provide nonvolatile and/or volatile
storage of machine-readable instructions, data structures, program
modules, and/or other data for the control system 5300. In one
example, software may reside, completely or partially, within a
machine-readable medium on storage device(s) 5335. In another
example, software may reside, completely or partially, within
processor(s) 5301.
[0210] Bus 5340 connects a wide variety of subsystems. Herein,
reference to a bus may encompass one or more digital signal lines
serving a common function, where appropriate. Bus 5340 may be any
of several types of bus structures including, but not limited to, a
memory bus, a memory controller, a peripheral bus, a local bus, and
any combinations thereof, using any of a variety of bus
architectures. As an example and not by way of limitation, such
architectures include an Industry Standard Architecture (ISA) bus,
an Enhanced ISA (EISA) bus, a Micro Channel Architecture (MCA) bus,
a Video Electronics Standards Association local bus (VLB), a
Peripheral Component Interconnect (PCI) bus, a PCI-Express (PCI-X)
bus, an Accelerated Graphics Port (AGP) bus, HyperTransport (HTX)
bus, serial advanced technology attachment (SATA) bus, and any
combinations thereof.
[0211] Control system 5300 may also include an input device 5333.
In one example, a user of control system 5300 may enter commands
and/or other information into control system 5300 via input
device(s) 5333. Examples of an input device(s) 5333 include, but
are not limited to, a touch screen, an alpha-numeric input device
(e.g., a keyboard), a pointing device (e.g., a mouse or touchpad),
a touchpad, a joystick, a gamepad, an audio input device (e.g., a
microphone, a voice response system, etc.), an optical scanner, a
video or still image capture device (e.g., a camera), and any
combinations thereof. Input device(s) 5333 may be interfaced to bus
5340 via any of a variety of input interfaces 5323 (e.g., input
interface 5323) including, but not limited to, serial, parallel,
game port, USB, FIREWIRE, THUNDERBOLT, or any combination of the
above.
[0212] Information and data can be displayed through a display
5332. Examples of a display 5332 include, but are not limited to, a
liquid crystal display (LCD), an organic liquid crystal display
(OLED), a cathode ray tube (CRT), a plasma display, and any
combinations thereof. The display 5332 can interface to the
processor(s) 5301, memory 5303, and fixed storage 5308, as well as
other devices, such as input device(s) 5333, via the bus 5340. The
display 5332 is linked to the bus 5340 via a video interface 5322,
and transport of data between the display 5332 and the bus 5340 can
be controlled via the graphics control 5321.
[0213] In addition or as an alternative, control system 5300 may
provide functionality as a result of logic hardwired or otherwise
embodied in a circuit, which may operate in place of or together
with software to execute one or more processes or one or more steps
of one or more processes described or illustrated herein. Moreover,
reference to a non-transitory, tangible processor-readable medium
may encompass a circuit (such as an IC) storing instructions for
execution, a circuit embodying logic for execution, or both, where
appropriate. The present disclosure encompasses any suitable
combination of hardware in connection with software.
[0214] The various illustrative logical blocks, modules, and
circuits described in connection with the embodiments disclosed
herein may be implemented or performed with a general purpose
processor, a digital signal processor (DSP), an application
specific integrated circuit (ASIC), a field programmable gate array
(FPGA) or other programmable logic device, discrete gate or
transistor logic, discrete hardware components, or any combination
thereof designed to perform the functions described herein. A
general purpose processor may be a microprocessor, but in the
alternative, the processor may be any conventional processor,
controller, microcontroller, or state machine. A processor may also
be implemented as a combination of computing devices, e.g., a
combination of a DSP and a microprocessor, a plurality of
microprocessors, one or more microprocessors in conjunction with a
DSP core, or any other such configuration.
[0215] In conclusion, the present invention provides, among other
things, a system and method for arc-handling during plasma
processing. 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 as expressed in the claims.
* * * * *