U.S. patent application number 15/162528 was filed with the patent office on 2016-09-15 for methods and apparatus for synchronizing rf pulses in a plasma processing system.
The applicant listed for this patent is Lam Research Corporation. Invention is credited to Bradford J. Lyndaker, Harmeet Singh, John C. Valcore, JR..
Application Number | 20160268100 15/162528 |
Document ID | / |
Family ID | 48981797 |
Filed Date | 2016-09-15 |
United States Patent
Application |
20160268100 |
Kind Code |
A1 |
Valcore, JR.; John C. ; et
al. |
September 15, 2016 |
METHODS AND APPARATUS FOR SYNCHRONIZING RF PULSES IN A PLASMA
PROCESSING SYSTEM
Abstract
A synchronized pulsing arrangement for providing at least two
synchronized pulsing RF signals to a plasma processing chamber of a
plasma processing system is provided. The arrangement includes a
first RF generator for providing a first RF signal. The first RF
signal is provided to the plasma processing chamber to energize
plasma therein, the first RF signal representing a pulsing RF
signal. The arrangement also includes a second RF generator for
providing a second RF signal to the plasma processing chamber. The
second RF generator has a sensor subsystem for detecting values of
at least one parameter associated with the plasma processing
chamber that reflects whether the first RF signal is pulsed high or
pulsed low and a pulse controlling subsystem for pulsing the second
RF signal responsive to the detecting the values of at least one
parameter.
Inventors: |
Valcore, JR.; John C.;
(Fremont, CA) ; Lyndaker; Bradford J.; (San Ramon,
CA) ; Singh; Harmeet; (Fremont, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Lam Research Corporation |
Fremont |
CA |
US |
|
|
Family ID: |
48981797 |
Appl. No.: |
15/162528 |
Filed: |
May 23, 2016 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
13550719 |
Jul 17, 2012 |
9368329 |
|
|
15162528 |
|
|
|
|
61602041 |
Feb 22, 2012 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01J 37/32183 20130101;
H01J 37/32146 20130101; H01J 37/32174 20130101 |
International
Class: |
H01J 37/32 20060101
H01J037/32 |
Claims
1. A method comprising: generating a first radio frequency (RF)
signal, wherein the first RF signal is a pulse signal; sending the
first RF signal to an impedance match network, wherein the
impedance match network is coupled to a plasma chamber; generating
a second RF signal; sending the second RF signal to the impedance
match network; sensing a parameter indicating a change in an
impedance of plasma within the plasma chamber, wherein the change
in the impedance occurs when a state of the first RF signal changes
from one state to another; and pulsing the second RF signal from
one state to another upon sensing the parameter indicating the
change in the impedance.
2. The method of claim 1, wherein the parameter is sensed at an
output of an RF generator that generates the second RF signal.
3. The method of claim 1, wherein the first RF signal is a
low-frequency RF signal and the second RF signal is a
high-frequency RF signal, wherein the high-frequency is greater
than the low-frequency, wherein the parameter is associated with
forward power and reflected power.
4. The method of claim 1, wherein the one state of the first RF
signal is an on state and the other state of the first RF signal is
an off state, wherein the one state of the second RF signal is an
on state and the other state of the second RF signal is an off
state, wherein the change in the plasma impedance occurs as a
consequence of a transition of the first RF signal from the one
state to the other state, wherein the pulse of the first RF signal
is generated upon receiving a control signal from a computer,
wherein the pulsing of the second RF signal is performed to
synchronize the pulsing of the second RF signal with pulsing of the
first RF signal.
5. The method of claim 1, wherein the second RF signal is pulsed
from the one state to the other state when a predetermined power
set point is applied to the second RF signal, wherein the second RF
signal is pulsed from the other state to the one state when another
predetermined power set point is applied to the second RF
signal.
6. The method of claim 1, wherein the parameter is gamma, or
forward power, or reflected power, or a voltage and current probe
measurement, or a complex impedance, wherein the parameter is
sensed at an output of an RF generator.
7. A method comprising: generating a first RF signal; sending the
first RF signal to an impedance match network that is coupled to a
plasma chamber; sensing a parameter indicating a change in an
impedance of plasma within the plasma chamber, wherein the change
in the impedance occurs when a state of a second RF signal changes
from one state to another; and pulsing the first RF signal from one
state to another in response to sensing the parameter indicating
the change in the impedance.
8. The method of claim 7, wherein the parameter is sensed at an
output of an RF generator that generates the second RF signal.
9. The method of claim 7, wherein the second RF signal is a
low-frequency RF signal and the first RF signal is a high-frequency
RF signal, wherein the high-frequency is greater than the
low-frequency.
10. The method of claim 7, wherein the one state of the first RF
signal is an on state and the other state of the first RF signal is
an off state, wherein the one state of the second RF signal is an
on state and the other state of the second RF signal is an off
state, wherein the pulse of the second RF signal is generated upon
receiving a control signal from a computer.
11. The method of claim 7, wherein the first RF signal is pulsed
from the one state to the other state when a predetermined power
set point is applied to the first RF signal, wherein the first RF
signal is pulsed from the other state to the one state when another
predetermined power set point is applied to the first RF signal,
wherein the parameter is sensed at an output of an RF
generator.
12. A method for providing a plurality of synchronized pulsing RF
signals to a plasma processing chamber of a plasma processing
system, comprising: pulsing a first RF signal, using a first RF
generator, said first RF signal provided to said plasma processing
chamber to energize plasma therein; detecting values of at least
one parameter associated with said plasma processing chamber that
reflects whether said first RF signal is pulsed high or pulsed low;
and pulsing a second RF signal, using a second RF generator,
responsive to said detecting said values of said at least one
parameter.
13. The method of claim 12, wherein said at least one parameter
that reflects whether said first RF signal is pulsed high or pulsed
low represents at least one of forward RF power and reflected RF
power.
14. The method of claim 12, wherein said at least one parameter
that reflects whether said first RF signal is pulsed high or pulsed
low represents gamma, said gamma representing a numerical index
indicating a degree of mismatch between reflected power and forward
power of said second RF generator.
15. The method of claim 12, further comprising receiving a trigger
threshold value from a tool host computer, said trigger threshold
value to enable circuitry in a sensor subsystem of said second RF
generator to ascertain whether said first RF signal is pulsed high
or pulsed low.
16. The method of claim 12, wherein said second RF signal comprises
at least a high level and a low level when pulsed, said high level
and said low level governed by at least one value provided a tool
host computer.
17. The method of claim 12, wherein said second RF signal, when
pulsed, comprises at least a high pulse value and a low pulse
value, wherein said low pulse value is non-zero.
18. The method of claim 12, wherein said at least one parameter
that reflects whether said first RF signal is pulsed high or pulsed
low represents values obtained from a VI probe or represents an
output impedance of said second RF generator.
19. The method of claim 12, further comprising a match subsystem
coupled to outputs of said first RF generator and said second RF
generator, wherein said at least one parameter that reflects
whether said first RF signal is pulsed high or pulsed low
represents an impedance of an input of said match subsystem.
20. The method of claim 12, wherein said second RF signal, when
pulsed, pulses between a predefined high pulse value and a
predefined low pulse value.
Description
PRIORITY CLAIM
[0001] This application is a divisional of and claims the benefit
of and priority under 35 U.S.C. .sctn.120, to U.S. patent
application Ser. No. 13/550,719, filed on Jul. 17, 2012, and titled
"METHODS AND APPARATUS FOR SYNCHRONIZING RF PULSES IN A PLASMA
PROCESSING SYSTEM", which claims priority under 35 USC.
.sctn.119(e) to a provisional Patent Application No. 61/602,041,
filed on Feb. 22, 2012, and titled "METHODS AND APPARATUS FOR
SYNCHRONIZING RF PULSES IN A PLASMA PROCESSING SYSTEM", all of
which are incorporated herein by reference in their entirety.
BACKGROUND OF THE INVENTION
[0002] Plasma processing has long been employed to process
substrates (e.g., wafer or flat panels or other substrates) to
create electronic devices (e.g., integrated circuits or flat panel
displays). In plasma processing, a substrate is disposed in a
plasma processing chamber, which employs one or more electrodes to
excite a source gas (which may be an etchant source gas or a
deposition source gas) into a plasma for processing the substrate.
The electrodes may be excited by an RF signal, which is furnished
by a RF generator, for example.
[0003] In some plasma processing systems, multiple RF signals, some
of which may have the same or different RF frequencies, may be
provided to one or more electrodes to generate plasma. In a
capacitively-coupled plasma processing system, for example, one or
more RF signals may be provided to the top electrode, the bottom
electrode, or both in order to generate the desired plasma.
[0004] In some applications, the RF signals may be pulsed. For any
given RF signal, RF pulsing involves turning the RF signal on and
off, typically within the same RF signal period but may span
multiple RF signal periods. Furthermore, the RF pulsing may be
synchronized among signals. For example, if two signals RF1 and RF2
are synchronized, there is an active pulse of signal RF1 for every
active pulse of signal RF2. The pulses of the two RF signals may be
in phase, or the leading edge of one RF pulse may lag behind the
leading edge of the other RF pulse, or the trailing edge of one RF
pulse may lag behind the trailing edge of the other RF pulse, or
the RF pulses may be out of phase.
[0005] In the prior art, pulsing synchronization of multiple RF
signals typically involves a communication network to facilitate
control communication among the various RF generators. To
facilitate discussion, FIG. 1 is a high level drawing of a generic
prior art implementation of a typical pulsed RF plasma processing
system 102. Pulsed RF plasma processing system 102 includes two RF
generators 104 and 106. In the example of FIG. 1, RF generator 104
represents a 2 MHz generator while RF generator 106 represents a 60
MHz generator.
[0006] A host computer 110 implements tool control and receives a
feedback signal 112 from an impedance matching network 114 to
provide (via a digital or analog communications interface 116)
power set point data to RF generator 104 and RF generator 106 via
paths 118 and 120 respectively. The feedback signal 112 pertains to
the impedance mismatch between the source and the load, and is
employed to control either the delivered power or the forward power
levels of RF generators 104 and 106 to maximize power delivery and
minimize the reflected power.
[0007] Host computer 110 also provides Pulse_Enable signal 160 to a
pulse synchronizer and controller 130. Responsive to the
Pulse_Enable signal 160, the pulse synchronizer and controller 130
provides the synchronized control signals 170 and 172 to RF
generator 104 and RF generator 106 (via External Synchronization
Interfaces 140 and 142) to instruct RF generators 104 and 106 to
pulse its RF signals using power controllers 150 and 152
respectively to produce pulsed RF signals 162 and 164. The pulsed
RF signals 162 and 164 are then delivered to the load in plasma
chamber 161 via impedance matching network 114.
[0008] Although the pulsed RF synchronization scheme of FIG. 1 can
provide the synchronized pulsing function for the RF generators,
there are drawbacks. For example, synchronizing the pulsing
function of the various RF generators in FIG. 1 requires the use of
a network to communicate among host computer 110, pulse
synchronizer/controller 130, and external synchronization
interfaces 140 and 142 in RF generators 104 and 106. Further,
synchronizing the pulsing function of the various RF generators in
FIG. 1 requires the implementation of the external synchronization
interfaces (such as 140 and 142) in the various generators.
Implementing these external synchronization interfaces adds an
extra layer of complexity to RF generator designs, and render
existing RF generators incapable of being used for RF synchronized
pulsing.
[0009] In view of the foregoing, there are desired improved
techniques and systems for implementing synchronized RF pulsing in
a plasma processing system.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The present invention is illustrated by way of example, and
not by way of limitation, in the figures of the accompanying
drawings and in which like reference numerals refer to similar
elements and in which:
[0011] FIG. 1 is a high level drawing of a generic prior art
implementation of a typical pulsed RF plasma processing system.
[0012] FIG. 2 shows a timing diagram of the pulsing of a 2 MHz RF
signal to illustrate the change in gamma value for one RF generator
when another RF generator pulses its RF signal.
[0013] FIG. 3 shows a simplified circuit block diagram of an
implementation of the synchronized pulsing RF, in accordance with
an embodiment of the invention.
[0014] FIG. 4 is an example implementation of a DP RF generator for
providing the synchronized RF pulsing capability, in accordance
with an embodiment of the invention.
DETAILED DESCRIPTION OF EMBODIMENTS
[0015] The present invention will now be described in detail with
reference to a few embodiments thereof as illustrated in the
accompanying drawings. In the following description, numerous
specific details are set forth in order to provide a thorough
understanding of the present invention. It will be apparent,
however, to one skilled in the art, that the present invention may
be practiced without some or all of these specific details. In
other instances, well known process steps and/or structures have
not been described in detail in order to not unnecessarily obscure
the present invention.
[0016] Various embodiments are described herein below, including
methods and techniques. It should be kept in mind that the
invention might also cover articles of manufacture that includes a
computer readable medium on which computer-readable instructions
for carrying out embodiments of the inventive technique are stored.
The computer readable medium may include, for example,
semiconductor, magnetic, opto-magnetic, optical, or other forms of
computer readable medium for storing computer readable code.
Further, the invention may also cover apparatuses for practicing
embodiments of the invention. Such apparatus may include circuits,
dedicated and/or programmable, to carry out tasks pertaining to
embodiments of the invention. Examples of such apparatus include a
general-purpose computer and/or a dedicated computing device when
appropriately programmed and may include a combination of a
computer/computing device and dedicated/programmable circuits
adapted for the various tasks pertaining to embodiments of the
invention.
[0017] Embodiments of the invention relate to methods and apparatus
for implementing synchronized pulsing of RF signals in a plasma
processing system having a plurality of RF generators. In one or
more embodiments, one of the RF generators is designated the
independent pulsing (IP) RF generator, and other RF generators are
designated dependent pulsing (DP) generators.
[0018] The IP RF generator represents the RF generator that pulses
independently from the DP RF generators. The IP RF generator
(independent pulsing generator) generates its RF pulses responsive
to a signal from the tool host or another controller. The DP RF
generators (dependent pulsing generators) monitor the change in
plasma impedance that is characteristic of pulsing by the IP RF
generator and trigger their individual RF pulses responsive to the
detected change in plasma impedance. In one or more embodiments,
the change in the plasma impedance is detected by the power sensor
in each of the DP RF generators, which may measure, for example,
the forward and reflected RF powers.
[0019] The inventors herein recognize that existing RF generators
are already provided with sensors (such as power sensors) which can
monitor parameters related to the plasma impedance. When the values
of these parameters change in a certain manner, a change in the
plasma impedance may be detected.
[0020] To further elaborate, the efficiency with which an RF
generator delivers RF power to a load depends on how well the load
impedance matches with the source impedance. The more closely the
load impedance matches the source impedance, the more efficient the
RF power is delivered by an RF generator. Since this matching issue
is well-known, many or most prior art RF generators have been
provided with the ability to sense the mismatch between the source
impedance and the load impedance, and to adjust the delivered or
forward power in order to reduce the mismatch. The parameter gamma
is typically employed to measure the load-source impedance
mismatch. A gamma value of zero indicates perfect matching while a
gamma value of 1 indicates a high degree of mismatch. In some RF
generators, this gamma value is calculated from values provided by
the power sensor, which detects the source and reflected RF
powers.
[0021] The inventors herein further realize that the plasma
impedance is a function of power delivered to the plasma. When a
given RF generator (referred to herein as the independent pulsing
or IP RF generator) pulses, the delivered RF power changes, and the
plasma impedance changes accordingly. Other RF generators (referred
to herein as dependent pulsing or DP RF generators) react to this
change in the plasma impedance by varying their power output to
match their source impedance with the plasma (or load)
impedance.
[0022] The detection of changes in the plasma impedance typically
relies on the measurement of one or more parameters whose values
can be analyzed to directly or indirectly ascertain changes in the
plasma impedance. If the plasma impedance change caused by RF
pulsing of the IP RF generator can be detected by other RF
generators, and more importantly, if this detection can be used to
trigger RF pulsing by these other RF generators, synchronized
pulsing can be achieved without the need to explicitly link the RF
generators via a control network as is done in the prior art.
[0023] To illustrate the change in gamma value for one RF generator
when another RF generator pulses its RF signal, FIG. 2 shows a
timing diagram of the pulsing of a 2 MHz RF signal 202, which is
pulsed at 159 Hz, with a 50% duty cycle. In the example of FIG. 2,
two RF generators are involved: a 2 MHz RF generator outputting
6000 Watts RF signal and a 60 MHz RF generator outputting a 900
Watts RF signal. The 2 MHz RF signal is pulsed between 6000 Watts
and 0 Watts, as discussed, while the 60 MHz RF signal (204) is not
pulsed.
[0024] When the 2 MHz RF signal 202 is active (from reference
number 210 to 212), the RF power sensor of the 60 MHz RF generator
reacts to the plasma impedance value caused by the high 2 MHz RF
signal 202. In this case, the real value of the impedance at the
match input (generator output) of the 60 MHz RF generator is 52.9
ohms. The gamma value, which describes the source-load impedance
mismatch, is 0.039.
[0025] When the 2 MHz RF signal 202 is inactive (from reference
number 212 to 214), the RF power sensor of the 60 MHz RF generator
reacts to the plasma impedance caused by the low 2 MHz RF signal
202. In this case, the real value of the impedance at the match
input (generator output) of the 60 MHz RF generator is only 27.44
ohms. The gamma value, which describes the source-load impedance
mismatch, is 0.856.
[0026] As can be seen in the example of FIG. 2, either the
impedance at the match input or the gamma value may be monitored
and if a change occurs from the value reflective of the "on" state
of the 2 MHz RF signal 202 to the value reflective of the "off"
state of the 2 MHz RF signal 202 (or vice versa), the detection of
such change may be employed as a trigger signal to a circuit to
generate an RF pulse for the 60 MHz signal of the 60 MHz DP RF
generator. If there are other DP RF generators, each DP RF
generator may monitor the plasma impedance (e.g., a parameter that
is directly or indirectly reflective of this plasma impedance) and
use the detection of plasma impedance change to trigger pulse
generation. In this manner, no explicit control network between a
master control circuit/device (such as from host computer 110 or
pulse synchronization controller circuit 130) and the various RF
generators is needed. Further, the RF generators do not require any
additional circuitry to interface with the control network (such as
external synchronization interface circuits 140 and 142 of FIG.
1).
[0027] Instead, only one RF generator (the IP RF generator such as
the 2 MHz IP RF generator in the example) needs to be explicitly
controlled for RF pulsing. Other RF generators (the DP RF
generators) leverage on existing detection circuitry (which is
traditionally used to monitor the forward and reflected RF power
for adjusting the power set point for RF delivery to match the
source impedance to the load impedance) in order to indirectly
detect when the IP generator RF signal has pulsed. This detection
provides a triggering signal to the DP RF generators to allow the
DP RF generators to generate their own RF pulses in response to the
detection of RF pulsing by the IP RF generator. In this manner,
vastly more simplified synchronized pulsing is accomplished.
[0028] The features and advantages of embodiments of the invention
may be better understood with reference to the figures and
discussions that follow. FIG. 3 shows a simplified circuit block
diagram of an implementation of the synchronized pulsing RF 300, in
accordance with an embodiment of the invention. In FIG. 3, RF
generator 302 represents the IP RF generator and receives its
pulsing control signal from tool host computer 304 (via
digital/analog communications interface 306). IP RF generator 302
then generates, using power controller 308, an RF pulse using a
power setpoint provided by tool host computer 304. The pulse is
furnished to impedance matching network 314 to energize the
RF-driven plasma chamber 316. The plasma impedance in RF-driven
plasma chamber 316 changes as a result of the on-state of the 2 MHz
pulse from IP RF generator 302.
[0029] This plasma impedance change is then detected by RF sensor
320 of DP RF generator 322. By way of example, the forward and
reflected power of the DP 60 MHZ RF generator 322 may be monitored.
Generally an IP_RF_Pulse_High threshold value may be employed to
determine when the 2 MHz pulse from the IP RF generator 302 is
deemed to be high. In an embodiment, the gamma value obtained from
measurements taken by RF sensor 320 is employed and compared
against the aforementioned IP_RF_Pulse_High value. Once the 2 MHz
pulse from the IP RF generator 302 is deemed to be on, pulse
generation circuit associated with DP RF generator 322 may be
employed to generate a pulse for the 60 MHz signal from DP RF
generator 322.
[0030] The pulse from DP RF generator 322 may be set to stay on for
a predefined duration (e.g., in accordance with some duty cycle
specification) or may be synchronized to turn off when the 2 MHz
pulse from IP RF generator 302 transitions from a high state to a
low state (by monitoring the plasma impedance state in the manner
discussed earlier).
[0031] FIG. 4 is an example implementation of a DP RF generator 400
for providing the synchronized RF pulsing capability. In FIG. 4, a
signal 402 is provided from the tool host, which signal may include
two additional values: a trigger threshold and a gain value. The
trigger threshold represents the predefined value for triggering
the RF pulse for the DP generator (which keys off the plasma
impedance change caused by the independent pulsing generator). By
way of example, if the gamma value is monitored by the DP RF
generator for detecting the plasma impedance change due to the
pulsing of the IP RF generator, the threshold value may represent
the gamma value which, when traversed, represents the triggering
signal for triggering the RF pulse by the DP RF generator. The gain
value represents a value for scaling the signal to provide the high
level and the low level of the RF pulse by the DP RF generator
(since it is possible that different power levels may be desired
for high and low instead of full-on or full-off).
[0032] Returning now to FIG. 4, if the IDPC input is zero (block
404, signifying that the chamber is not operating in the RF pulsing
mode), the RF pulsing functionality is bypassed in the example of
FIG. 4. In this case, the default power set point (normally
furnished by the tool host computer to govern the power output by
the RF generator) is sent to the power amplifier (block 406) and
amplified via the RF power amplifier 408, which is then output to
the plasma chamber 450 via path 410.
[0033] The RF sensors 412 monitors the forward and reflected powers
in the example of FIG. 4, and provides these values to logic
circuit 414 in order to permit default scaling circuit 416 to scale
the power set point to optimize power delivery. For example, if the
gamma value is too high (indicating a large mismatch between the
forward and reflected power), the power set point provided by the
tool host may be increased or decreased as necessary to optimize
power delivery to the plasma load.
[0034] However, if the IDPC input is not equal to zero (block 404,
signifying that the chamber is operating in the RF pulsing mode),
the RF pulsing functionality is enabled in the example of FIG. 4
(via pulse power scaling circuit 420). In this case, the power set
point (furnished by the tool host computer to govern the power
output by the RF generator and is part of the IDPC input in this
case) is sent to the pulse power scaling circuit 420. The scaling
may toggle between two values, high and low, depending on the
detection of the plasma impedance by RF sensor 412 and logic
circuit 414.
[0035] Suppose RF sensor 412 and logic circuit 414 detect that the
gamma value has traversed the trigger threshold value provided with
signal 402, this information is provided to pulse power scaling
circuit 420, which then scales the default power set point scaling
to reflect the high RF pulse state. Once pulse scaling is complete
(block 420), the newly scaled power setpoint is then sent to block
408 for RF amplification (via block 406) and the high RF pulse
level is sent to the plasma chamber. To implement a low pulse,
another scaling value may be employed by block 420 (e.g., upon
detection of the low pulse of the IP RF generator or after a
predefined duration of time has past since the DP RF pulse went
high) to generate a low RF pulse level to be sent to the plasma
chamber.
[0036] In an embodiment, a generalized method for synchronizing RF
pulsing may involve independent pulsing at least one RF power
supply (the IP RF power supply). Each of the other RF supplies may
then monitor for indicia of plasma impedance change (such as gamma
value, forward power, reflected power, VI probe measurement, real
and/or complex values of the generator output impedance, etc.). In
other words, detection that the plasma impedance has changed in a
manner that is characteristic of pulsing by the independent pulsing
RF generator is not limited to gamma monitoring.
[0037] In an advantageous example, the DP RF generators may analyze
VI probe measurements and/or phase information received from the
chamber in order to detect plasma impedance change that is
characteristic of pulsing by the independent pulsing RF generator.
Upon detection that the plasma impedance has changed in a manner
that is characteristic of pulsing by the independent pulsing RF
generator (e.g., from low to high or high to low), the dependent RF
power supply may use that detection as a trigger to generate its
pulse. The high RF pulse of the dependent RF generator may persist
for a predefined period of time, or the RF pulse of the dependent
RF generator may transition to a low value upon detecting that the
independent pulsing RF signal has transitioned to a low state.
[0038] As can be appreciated from the foregoing, embodiments of the
invention detects plasma impedance change that is characteristic of
pulsing events by the independent pulsing RF generator and employs
the detection as a trigger signal to pulse the dependent pulsing RF
generator. In this manner, complicated networks and interfaces are
no longer necessary to synchronize pulsing among a plurality of RF
generators.
[0039] While this invention has been described in terms of several
preferred embodiments, there are alterations, permutations, and
equivalents, which fall within the scope of this invention.
Although various examples are provided herein, it is intended that
these examples be illustrative and not limiting with respect to the
invention.
[0040] Also, the title and summary are provided herein for
convenience and should not be used to construe the scope of the
claims herein. Further, the abstract is written in a highly
abbreviated form and is provided herein for convenience and thus
should not be employed to construe or limit the overall invention,
which is expressed in the claims. If the term "set" is employed
herein, such term is intended to have its commonly understood
mathematical meaning to cover zero, one, or more than one member.
It should also be noted that there are many alternative ways of
implementing the methods and apparatuses of the present invention.
It is therefore intended that the following appended claims be
interpreted as including all such alterations, permutations, and
equivalents as fall within the true spirit and scope of the present
invention.
* * * * *