United States Patent [19]
`Mavretic et al.
`
`11111111111111111111111111111t116III1111111111111111111111111111
`
`5,654,679
`Aug. 5, 1997
`
`[11] Patent Number:
`[45] Date of Patent:
`
`APPARATUS FOR MATCHING A VARIABLE
`LOAD IMPEDANCE WITH AN RF POWER
`GENERATOR IMPEDANCE
`
`Primary Examiner—Paul Gensler
`Attorney, Agent, or Firm—Blakely, Sokoloff, Taylor &
`Zafman LLP
`
`[54]
`
`[75]
`
`Inventors: Anton Mavretic, Marlton; Andrew
`Ciszek, Maple Shade; Joseph Stach,
`Medford, all of N.J.
`
`[73]
`
`Assignee: RF Power Products, Inc., Voorhees,
`N.J.
`
`[21]
`
`Appl. No.: 662,886
`
`[22]
`
`Filed:
`
`Jun. 13, 1996
`
`[51]
`[52]
`[58]
`
`hit. C1.6
`U.S. Cl.
`Field of Search
`
` HO3H 7/40
` 333/17.3; 333/32
` 333/17.3, 99 PL,
`333/32; 343/861; 315/111.21
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`[57]
`
`ABSTRACT
`
`An apparatus for matching the variable impedance of a load
`with the fixed impedance of a radio frequency (RF) power
`generator to provide maximum power transfer. The imped-
`ance matching network further allows an RF power genera-
`tor to vary the frequency of the voltage applied to a load,
`e.g., a plasma chamber as may be utilized in semiconductor
`or fiat panel plasma display manufacturing processes. The
`impedance matching network further utili7es fixed solid
`state components to adjust the impedance of the attached
`load to provide maximum power transfer between the gen-
`erator and the load. A parallel switched capacitor network is
`controlled by an electrical switching means such as PIN
`diodes to turn fixed capacitors on or off. A means for varying
`the frequency of the applied voltage is used to match the
`impedance of the load with the impedance of the RF power
`generator within milliseconds.
`
`2,981,902
`5,424,691
`
`4/1961 Familier
`6/1995 Sadinsky
`
` 333/17.3 X
` 333/17.3
`
`17 Claims, 6 Drawing Sheets
`
`RF Gen.
`210
`
`603
`
`605
`
`Frequency
`Synthesizer
`606
`
`306
`
`Phase
`Det.
`601
`
`Mag.
`Det.
`602
`
`Direct
`Coupler
`607
`
`•••=1=111111.1111=
`
`I—
`
`C1
`
`307
`
`308
`F____•• Load
`230
`
`• • • CN I
`
`604
`609
`
`610
`
`V
`
`Controller
`608
`
`612
`
`613
`
`PIN Diodes
`Driver
`611
`
`620
`
`Power
`Supply - 500v
`614
`
`Page 1 of 12
`
`ADVANCED ENERGY INDUSTRIES INC.
`Exhibit 1004
`
`

`

`jualud 'S*11
`
`9 JO I paqs
`
`Servo Motor
`
`107
`
`110
`Board
`Control
`
`
` v
` 0
`
`104
`
` x
`
`25-1000pF
`
`Load
`
`102
`
`RF Output
`
`130
`
`106
`
`25-1000pF
`
`Tune
`
`S
`105
`
`Servo Motor
`
`103
`
`I
`I
`I
`I
`r -
`
`111
`
`109
`MAG
`
`101
`PH
`
`112
`
`v
`
`0
`
`108
`
`RF Input
`
`120
`
`FIG. 1 (Prior Art)
`
`Page 2 of 12
`
`ADVANCED ENERGY INDUSTRIES INC.
`Exhibit 1004
`
`

`

`U.S. Patent
`
`Aug. 5, 1997
`
`Sheet 2 of 6
`
`5,654,679
`
`RF Power
`Generator
`210
`
`FIG. 2
`
`Impedance
`Matching Network
`220
`
`FIG. 3
`
`Plasma
`Process Chamber
`230
`
`215
`
`220
`
`230
`
`307
`
`308
`
`306
`
`± 1309
`r
`312 313
`
`310
`—J
`
`311
`
`304
`
`I I
`
`I I
`J L
`
`210
`
`r-
`
`301
`
`302
`
`303
`
`)
`
`)
`
`305
`
`L
`
`L
`
`300
`
`Page 3 of 12
`
`ADVANCED ENERGY INDUSTRIES INC.
`Exhibit 1004
`
`

`

`U.S. Patent
`
`Aug. 5, 1997
`
`Sheet 3 of 6
`
`5,654,679
`
`Input
`Impedance
`
`y 401
`
`400 —
`
`300 —
`
`200 —
`
`100 —
`
`50
`
`FIG. 4
`
`RLOAD =1 0
`311
`
`311 = 10 0
`
`311 = 50 S2
`
`311 =100 SI
`
`403 I
`
`11
`
`12
`
`13
`
`13.56 14
`
`15
`
`Frequency (MHz)
`
`-
`
`c
`402
`
`Page 4 of 12
`
`ADVANCED ENERGY INDUSTRIES INC.
`Exhibit 1004
`
`

`

`U.S. Patent
`
`Aug. 5, 1997
`
`Sheet 4 of 6
`
`5,654,679
`
`FIG. 5
`
`IME2
`
`Variation of
`311 in FIG. 3
`
`100 S2
`
`50 E2
`
`1052
`
`X 501
`
`400 —
`
`300
`
`Load
`Potential
`
`200 —
`
`100 —
`
`11
`
`12
`
`13
`
`13.56
`
`14
`
`15
`
`502
`
`Frequency (MHz)
`
`Page 5 of 12
`
`ADVANCED ENERGY INDUSTRIES INC.
`Exhibit 1004
`
`

`

`lualud *S'fl
`
`9 JO s laaqs
`
`308
`
`307
`
`• • •
`
` ••• CN1
`I
`
`C2
`
`
`
`C1
`
`Coupler
`Direct
`
`607
`
`306
`
`FIG. 6
`
`L604
`
`602
`Det.
`Mag.
`
`605 ,----
`
`601
`Det.
`Phase
`
`6?3
`
`RF Gen.
`
`210
`
`Supply - 500v
`
`Power
`
`614
`
`4a
`
`PIN Diodes
`
`611
`Driver
`
`613
`
`612-
`
`620
`S
`
`Controller
`
`608
`
`"V
`
`Synthesizer
`Frequency
`
`606
`
`V
`
`304
`
`1-
`
`L
`
`610
`
`609 —
`
`Page 6 of 12
`
`ADVANCED ENERGY INDUSTRIES INC.
`Exhibit 1004
`
`

`

`U.S. Patent
`
`Aug. 5, 1997
`
`Sheet 6 of 6
`
`5,654,679
`
`FIG. 7
`
`
`
`624
`
`625
`__.,.
`.
`
`-II--
`
`623
`
`612 622
`
`621
`+5v •-- ‘44,
`
`
`
`v
`•
`From m
`620
`608
`
`X626
`-500v
`614
`
`-II--
`
`PL-- 611
`
`Page 7 of 12
`
`ADVANCED ENERGY INDUSTRIES INC.
`Exhibit 1004
`
`

`

`5,654,679
`
`1
`APPARATUS FOR MATCHING A VARIABLE
`LOAD IMPEDANCE WITH AN RF POWER
`GENERATOR IMPEDANCE
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`The present invention relates to the field of impedance
`matching networks. More specifically, the present invention
`relates to a method and apparatus for matching the imped-
`ance of a load with the internal impedance of a radio
`frequency (RF) power generator to provide maximum power
`transfer, where the frequency of the applied voltage gener-
`ated by the RF power generator and the impedance of the
`load may independently vary.
`2. Description of the Related Art
`The Federal Communications Commission (FCC) has
`designated Industrial, Scientific and Medical (ISM) frequen-
`cies at 13.56 MHz, 27.12 MHz and 40.68 MHz, respectively.
`ISM frequencies may be radiated by equipment into the
`atmosphere without concern for causing radio frequency
`disturbances to other equipment. Plasma etch and deposition
`equipment manufacturers have traditionally used the 13.56
`MHz frequency to operate a plasma chamber for manufac-
`turing integrated circuits and plasma displays. However,
`ISM frequencies do not always provide an optimum fre-
`quency at which to operate a plasma chamber to achieve
`critical process steps, especially in view of decreasing
`integrated circuit dimensions. As a result, equipment manu-
`facturers have developed plasma chambers that are capable
`of operating over a range of frequencies.
`ISM-based RF power generators, however, are commonly
`designed to assure minimum deviation from a set ISM
`frequency, e.g., 13.56 MHz. In contrast, a variable frequency
`RF power generator ("generator") may be coupled to a load,
`e.g., a plasma chamber, to manipulate the frequency of the
`voltage applied to the load so that the load may be operated
`over a range of voltage frequencies. However, in an alter-
`nating current (AC) circuit, impedance is affected by the
`frequency of the applied voltage, which impedance, in turn,
`affects the transfer of power between the generator and the
`load. Moreover, the impedance of a plasma chamber may
`vary independent of the frequency of the applied voltage
`depending on such variables as chamber pressure, gas
`composition, and plasma ignition. What is needed, therefore,
`is an impedance matching network that allows the frequency
`of the applied voltage to vary while maintaining the imped-
`ance of the load with respect to the generator, i.e., the input
`impedance to the generator.
`As is well known to those of ordinary skill in the related
`art, impedance for a given circuit may be comprised of both
`a resistive component and a reactive component, the latter of
`which may be either inductive or capacitive. Maximum
`power transfer between a generator and an attached load is
`achieved when the resistance of the load is equal to the
`internal resistance of the generator and the net reactance
`between the load and generator is zero. Thus, it is advanta-
`geous to counterbalance the reactance between the generator
`and the load to achieve a net reactance of zero. A net
`reactance of zero between the generator and load occurs
`when the impedance of the load is the conjugate of the
`internal impedance of the generator. Thus, if the generator
`has an inductive reactance, then a load that has a capacitive
`reactance of equal magnitude and opposite phase will result
`in a net reactance of zero to the circuit comprising the
`generator and the load, and vice versa. An impedance
`matching network may be utilized to maintain an input
`
`2
`impedance that is the conjugate of the internal impedance of
`the generator as the frequency of the voltage applied by the
`generator to the load varies, and/or as the impedance of the
`load varies, so that maximum power transfer occurs between
`5 the generator and the load.
`With reference to FIG. 1, a prior art impedance matching
`network 100 is illustrated. An RF power generator can be
`coupled to RF input 120. A load such as a plasma chamber
`can be coupled to RF output 130. The impedance matching
`10 network 100 ("network") comprises a phase detector 101
`that samples the transmission line 108 at a fixed impedance,
`e.g., 50 ohms, and generates a signal over line 112 to control
`board 110. Control board 110 then causes servo motor 107
`to turn variable capacitor 106, depending on the polarity of
`15 the phase shift between the input RF voltage and current
`caused by a non-linear impedance in the load, e.g., as occurs
`under ignited plasma conditions in a plasma chamber.
`Magnitude detector 109 also samples the deviation from
`an impedance of, e.g., 50 ohms, on transmission line 108,
`20 and generates a signal over line 111 to control board 110
`based thereon. Control board 110 then causes servo motor
`103 to turn variable capacitor 102. The capacitance provided
`by capacitor 102 is also dependent, to a lesser extent, on the
`polarity of the phase shift between the RF voltage and
`25 current. The magnitude detector 109 detects the deviation
`from a characteristic impedance of, for example, 50 ohms.
`If the impedance in line 108 is greater than 50 ohms, the
`signal transmitted over line 111 is positive, and if the
`impedance in line 108 is less than 50 ohms, the signal
`30 transmitted over line 111 is negative. As can be seen, the
`prior art impedance matching network 100 is relatively slow
`because of the time needed for servo motors 103 and 107 to
`turn capacitors 102 and 106, respectively, to match the
`impedance of the generator with the impedance of the load.
`35 Moreover, the network 100 does not allow the generator to
`change the frequency of the applied voltage as may be
`desired depending on the load.
`Today, semiconductor and flat panel plasma display
`equipment manufacturing process times are decreasing, such
`that the amount of time required to establish matching
`impedance between an RF power generator and a plasma
`chamber (whose operating frequency and impedance varies)
`is a limiting factor affecting throughput on the manufactur-
`45 ing line. What is needed is an impedance matching network
`coupling a generator to a load, e.g., a plasma chamber, that
`allows the generator to vary the frequency of the voltage
`applied to the load and utilises fixed solid state components
`to rapidly and accurately adjust the input impedance of the
`50 attached load to maintain maximum power transfer to the
`load.
`
`40
`
`SUMMARY OF THE DISCLOSURE
`
`The present invention is related to the field of impedance
`55 matching networks. More specifically, the present invention
`relates to a method and apparatus for matching the variable
`impedance of a load with the fixed internal impedance of a
`radio frequency (RF) power generator ("generator") to pro-
`vide maximum power transfer to the load, where the fre-
`60 quency of the applied voltage generated by the RF power
`generator and the impedance of the load may independently
`vary. The impedance matching network allows a generator
`to vary the frequency of the voltage applied to a load, for
`example, a plasma chamber, as may be utilized in semicon-
`65 ductor or flat panel plasma display manufacturing processes.
`The impedance matching network further utilizes fixed solid
`state components to adjust, within milliseconds, the input
`
`Page 8 of 12
`
`ADVANCED ENERGY INDUSTRIES INC.
`Exhibit 1004
`
`

`

`5,654,679
`
`3
`impedance of the attached load to accomplish maximum
`power transfer to the load. A means for varying the fre-
`quency of the applied voltage and a parallel switched
`capacitor network for very quickly matching the input
`impedance of the load with the impedance of the generator
`is used.
`It is an object of the impedance matching network as may
`be utilized by the present invention to improve the perfor-
`mance of prior art impedance matching networks by reduc-
`ing impedance matching convergence times, decrease
`impedance matching network circuit size for easier chamber
`mounting, and provide impedance load independence.
`It is a further object of the present invention to increase
`the reliability of an impedance matching network by elimi-
`nating mechanical moving parts such as variable, vacuum-
`type capacitors and servo motors in favor of an electroni-
`cally controlled impedance matching network having solid
`state components, thereby eliminating the maintenance and
`calibration requirements associated with prior art impedance
`matching networks.
`
`20
`
`BRIEF DESCRIP'T'ION OF THE DRAWINGS
`
`The present invention is illustrated by way of example
`and not limitation in the following figures. Like references
`indicate similar elements, in which:
`FIG. 1 illustrates an embodiment of a prior art impedance
`matching network as may be utilized by an RF power
`generator to match the impedance of the generator and an
`attached load;
`FIG. 2 is a block diagram of an embodiment of the present
`invention;
`FIG. 3 is a schematic diagram providing an electrical
`representation of an embodiment of the present invention;
`FIG. 4 provides a graphical analysis of the simulation of
`input impedance versus varying load impedance for the
`circuit in FIG. 3;
`FIG. 5 graphically illustrates varying the frequency of
`voltage applied to a load; and
`FIG. 6 illustrates a preferred embodiment of the present
`invention.
`FIG. 7 is a circuit diagram of the PIN diodes driver in FIG.
`6.
`
`DETAILED DESCRIPTION OF THE
`EMBODIMENTS OF THE INVENTION
`
`Described herein is a method and apparatus for matching
`the variable impedance of a load with the fixed impedance
`of a radio frequency (RF) power generator ("generator") to
`provide maximum power transfer from the generator to the
`load, where the generator varies the frequency of the voltage
`applied to the load. In the following description, numerous
`specific details and examples are set forth in order to provide
`a thorough understanding of the present invention. It will be
`apparent, however, to one of ordinary skill in the art that the
`present invention may be practiced in this or related fields
`without this specific information. In other instances, well-
`known circuits, components, and techniques have not been
`shown in order not to unnecessarily obscure the present
`invention.
`
`OVERVIEW OF AN EMBODIMENT OF THE
`PRESENT INVENTION
`
`The increasing complexity of present and future genera-
`tion plasma processing requirements significantly impacts
`
`4
`the performance requirements of radio frequency (RF)
`power generators and related impedance matching networks
`used in this field. Plasma processing equipment manufac-
`turers continue to reduce process times, modify plasma
`5 chamber pressures and gas compositions, and decrease
`plasma chamber cleaning cycle times in order to increase
`throughput, provide consistent production and reliable per-
`formance. To that end, prior art motor driven impedance
`matching networks are being replaced by faster, electroni-
`to cally controlled impedance matching networks. As the block
`diagram in FIG. 2 illustrates, an embodiment of the present
`invention provides a solid state impedance matching net-
`work 220 ("network 220") that employs no moving electri-
`cal or mechanical parts to maintain an input impedance of,
`15 for example, 50 ohms, and allow an RF power generator 210
`("generator 210") to vary the frequency of the applied
`voltage around a base frequency to achieve, among other
`things, plasma ignition in the plasma process chamber 230
`("plasma chamber").
`FIG. 3 is an electrical schematic representing the RF
`power generator 210, impedance matching network 220,
`connector 215 connecting generator 210 to network 220, and
`plasma processing chamber 230 coupled to network 220.
`The generator 210 is comprised of an alternating current
`25 power supply 301 and an internal impedance 302. The
`power provided by the generator 210 may be variable from
`0 watts to 5 kilowatts. The generator base frequency is
`arbitrary. However, it is common practice in the semicon-
`ductor industry to use the ISM frequency of 13.56 MHz. The
`30 generator's internal impedance 302 is generally 50 ohms,
`but the impedance could be any value, as long as the cable
`303 delivering power to the network 220 has the same
`characteristic impedance.
`Within the impedance matching network 220, RF trans-
`former 305 may or may not be utilized. The purpose of
`transformer 305 is to further transform the input impedance
`from 50 ohms to some lower value, e.g., 12.5 ohms, so that
`the portion of the impedance matching network to the right
`of the transformer 305 will operate at a lower impedance
`level.
`A capacitance 306 is comprised of at least one fixed-value
`capacitor 312. In one embodiment, an additional number of
`capacitors may be coupled in parallel to capacitor 312, as is
`45 illustrated by capacitor 313. Sufficient capacitors may be
`coupled in parallel to capacitor 312 to provide, for example,
`8, 16, or more discrete values. The capacitors are electrically
`and individually switched by respective switches in switch
`circuit 304. In one embodiment, diodes with a large intrinsic
`50 region between p- and n-doped semiconducting regions,
`hereafter referred to as PIN diodes, may be utilized to
`provide the switching function. In a second embodiment,
`switch circuit 304 is comprised of RF relays.
`Inductance 307 is a fixed value as well. The value of
`55 resistance 309 is selected to maintain the capacitance 306
`discharged under no plasma ignition conditions. The portion
`of network 220 comprised of capacitance 306, induction
`307, and capacitance 308 is a typical L-type impedance
`matching network configuration. With respect to the plasma
`60 chamber 230, capacitive component 310 and resistive com-
`ponent 311 are the equivalent capacitance and resistance
`representing a plasma chamber when ignited.
`FIG. 4 provides a graphical analysis of a simulation of
`input impedance versus varying load impedance for the
`circuit in FIG. 3, in which it is demonstrated that a constant
`input impedance, i.e., the impedance seen by the generator
`210 from the load, is maintained by network 220 over a load
`
`35
`
`40
`
`65
`
`Page 9 of 12
`
`ADVANCED ENERGY INDUSTRIES INC.
`Exhibit 1004
`
`

`

`5,654,679
`
`5
`impedance range of 1 to 100 ohms (typical resistive loads for
`ignited plasma conditions in a plasma chamber are from 1 to
`100 ohms). The vertical axis 401 represents the input
`impedance while the horizontal axis represents the fre-
`quency of the applied voltage. In the simulation, both the
`frequency of the applied voltage and the resistive load
`component 311 are varied. The capacitive load component
`310 is maintained as a constant.
`Regardless of the value of the resistive load, all the curves
`in FIG. 4 go through point 403 where input impedance is 50
`ohms and the frequency of the applied voltage is 13.56 MHz.
`In the case where the load is a plasma chamber, it is
`advantageous to select values of capacitance 306, induc-
`tance 307, and capacitance 308 in the impedance matching
`network 220 such that those impedance and frequency
`conditions are satisfied. However, it is well understood by
`those of ordinary skill in the related art that other values of
`inductance and capacitance may be chosen, depending on
`the type of load coupled to the impedance matching network
`220.
`FIG. 5 graphically illustrates a simulation of plasma
`ignition in a plasma chamber coupled to the impedance
`matching network 220 of FIG. 3, where the frequency of the
`applied voltage increases to slightly above 13.56 MHz, then
`returns to 13.56 MHz during the processing cycle within a
`period of milliseconds. The vertical axis 501 represents the
`applied voltage on capacitive and resistive load components
`310 and 311 in FIG. 3, while the horizontal axis 502
`represents the frequency of the applied voltage.
`The analysis illustrates that the applied voltage peaks
`slightly above 13.56MHz at levels high enough to strike the
`plasma, as desired. As can be seen, the frequency of the
`applied voltage is swept above 13.56 MHz to the voltage
`peak. at which point the plasma is struck before the fre-
`quency of the applied voltage automatically returns to 13.56
`MHz.
`This graph illustrates a series of curves for various plasma
`chamber impedances. The resistive load component 311 in
`FIG. 3 is the characteristic impedance of the plasma cham-
`ber chemistry. While it is not necessary for purposes of
`understanding the present invention to fully describe the
`various plasma chambers, in general, this method of varying
`the frequency of the applied voltage is valid for all plasma
`chambers. It should be noted that the impedance matching
`network 220 develops a high voltage at the beginning of the
`plasma processing cycle. The high voltage is needed to start
`ionization and, hence, plasma ignition, as the voltage peak-
`ing in FIG. 5 illustrates. The plasma processing cycle is the
`elapsed time that the plasma is ignited. A typical time is a
`few seconds, however, in some cases, it may be longer. As
`will be discussed in greater detail, the impedance matching
`capability of the network 220 in FIG. 3 is accomplished by
`changing the frequency of the applied voltage and changing,
`via solid state components, the capacitance of the impedance
`matching network 220 in response thereto.
`
`DETAILED DESCRIPTION OF AN
`EMBODIMENT OF THE PRESENT INVENTION
`An impedance matching network as may be embodied by
`the present invention provides maximum power transfer
`between an RF power generator and a load, e.g., a plasma
`chamber. The impedance matching network provides an
`input impedance that matches the internal impedance of the
`RF power generator, typically 50 ohms, while providing an
`impedance to the plasma chamber that matches the varying
`impedance of the plasma chamber.
`
`6
`The impedance of the plasma chamber varies according to
`the stage at which it is operating. For example, before
`plasma ignition, the impedance of the plasma chamber is as
`high as 10 megaohms, while after ignition the impedance is
`5 approximately 2 ohms. When the plasma is not yet ignited,
`the plasma chamber is essentially a vacuum chamber and
`high voltages are required to ignite the plasma, hence, the
`high impedance. The impedance may further vary during
`operation, depending on a number of factors, including the
`10 size of the plasma chamber, gas chemistry, and gas pressure.
`At some point in the process cycle, a chemical mixture of
`gases is pushed into the plasma chamber. The gases may be
`used for etching, deposition, or cleaning target material in
`the plasma chamber. The ionized gases inside the plasma
`15 chamber present low impedance to the impedance matching
`network 220 that is supplying RF power to the plasma
`chamber. To maximize power transfer between the generator
`and the plasma chamber, the impedance matching network
`needs to respond to impedance changes in the plasma
`20 chamber in the shortest time reasonably possible, e.g.,
`within 100 milliseconds or less.
`The output of the impedance matching network 220 is a
`series resonant circuit that presents the conjugate impedance
`to the load for impedance matching. The present invention
`25 utilizes an L-type impedance matching network in a low
`pass configuration. With reference to FIG. 6, the network
`comprises a shunt capacitance 306 and a series inductance
`307. The capacitance 306 reduces any inductive impedance
`in the load 230, while the inductance 307 resonates with, i.e.,
`30 cancels, any capacitive reactive component present in the
`Load. In one embodiment, the capacitance 306 (also referred
`to as load capacitance) is electronically variable by way of
`PIN diode-controlled switch circuit 304 whenever the mag-
`nitude of the input impedance deviates from the internal
`35 impedance of the power generator 210, e.g., 50 ohms. In a
`second embodiment, switch circuit 304 may be controlled
`by RF relays (not shown).
`A magnitude detector 602 samples impedance on the
`transmission line 603 at e.g., 50 ohms, and generates a signal
`40 604 that switches on a bank of one or more shunt capacitors
`comprising capacitance 306 via their respective PIN diodes,
`depending on the magnitude of the input impedance which
`varies according to the load. The polarity of the signal
`governs whether there is an increase or decrease in shunt
`45 capacitance 306. In either case, the inductance provided by
`series inductance 307 remains unchanged.
`While capacitance 306 is illustrated as having two fixed
`shunt capacitors Cl and C2, any number of capacitors in
`parallel may be utilized. The greater the number of
`50 capacitors, the more accurate the adjustment possible in
`matching the input impedance to the load impedance.
`However, from a practical point of view, there is no reason
`to increase the number of capacitors beyond a certain
`number, e.g., 8 or 16, to obtain a full range of discrete
`55 values. The capacitors being switched, e.g., C1 and C2, each
`have a value that is one half the value of the previous
`capacitor. For example, if C1=400 pF, then C2=200 pF, and
`capacitor C(n) is one half the capacitance of capacitor
`C(n-1), etc.
`The phase and magnitude detectors are coupled to a
`directional coupler 607. The directional coupler 607 outputs
`two signals, 609 and 610, which represent both incident and
`reflective power. These signals are coupled to a controller
`608. The controller 608 contains well known devices such as
`65 a multiplier/divider chip, a comparator, an analog to digital
`converter, and a buffer. The controller 608 evaluates the
`signals thus input, compares them with a reference signal,
`
`60
`
`Page 10 of 12
`
`ADVANCED ENERGY INDUSTRIES INC.
`Exhibit 1004
`
`

`

`5,654,679
`
`7
`and generates control voltages to drive a PIN diode driver
`circuit 611. The PIN diode driver circuit 611 enables the
`switching devices, i.e., PIN diodes, in switch circuit 304 via
`lines 612 and 613. The PIN diodes are switched on accord-
`ing to the signals received from the PIN diode driver circuit
`611, which in turn is controlled by controller 608. If the PIN
`diodes receive no signal, they are biased into a cutoff state,
`i.e., no conduction. The combination of capacitors switched
`on is selected for the best impedance match between the RF
`generator 210 and the load 230.
`In FIG. 7, the PIN diodes driver is illustrated, where, for
`example, PIN diode 623 is turned on and capacitor 624 is
`thus connected to ground via a low resistance PIN diode. To
`turn on PIN diode 623, a control line 620 driven by
`controller 608, transmits zero volts, or a logical zero, turning
`transistor 621 on and forward biasing PIN diode 623 with
`current (0.5 amps of direct current in the preferred
`embodiment). Resistor 622 controls the DC bias current. At
`that high DC current in the forward direction, PIN diode 623
`exhibits very low dynamic resistance (about 0.1 ohm in the
`preferred embodiment), thereby shorting capacitor 624 to
`ground. When control line 20 is driven high, e.g., 5 volts, by
`controller 608, the transistor 621 is in an off state—no DC
`current flows in the forward direction. At the same time,
`negative voltages (-500 volts in the preferred embodiment)
`appear on the p- side of the PIN diode 623, forcing the PIN
`diode to an off state. The LC networks 625 and 626 operate
`as filters resonating at the RF frequency, e.g., 13.56 MHz
`and not allowing RF signals to reach the power supply 614.
`FIG. 6 futher illustrates phase detector 601. Whereas in
`the prior art illustrated in FIG. 1, the phase detector was used
`to control capacitance, the preferred embodiment of the
`present invention utilises the phase detector only to control
`the frequency of the applied voltage. The phase detector 601
`samples the impedance on the transmission line 603 at 50
`ohms and generates a signal 605 that controls a frequency
`synthesizer circuit 606. To match the impedance of the load,
`the frequency synthesizer circuit 606 adjusts, via line 630,
`the frequency of the applied voltage provided by the RF
`generator 210 according to the phase detector signal 605.
`Frequency changes in the applied voltage during normal
`plasma chamber operation are typically less than 1 MHz.
`Thus, the frequency changes of the RF power generator can
`be limited to a commensurate upper and lower limit. It is
`desirable to so limit the frequency because filters and other
`circuits in the impedance matching network are optimized
`for this particular frequency range. Moreover, it is possible
`to stay within the 1 MHz limit and have a full range of
`acceptable impedance load variations.
`There are, of course, alternatives to the described embodi-
`ment which are within the understanding of one of ordinary
`skill in the relevant art. The present invention is intended to
`be limited only by the claims presented below.
`What is claimed is:
`1. An impedance matching network coupling a radio
`frequency power generator (RFPG) to a load, comprising:
`a phase detector coupled to said RFPG, said phase detec-
`tor detecting a phase shift in a voltage and a current
`provided by said RFPG;
`a magnitude detector coupled to said RFPG, said magni-
`tude detector detecting a magnitude of an impedance of
`said load;
`a first capacitance coupled in parallel to said load;
`an inductance coupled in series with said load;
`a second capacitance coupled in series with said load;
`a switching circuit coupled to said magnitude detector for
`coupling and decoupling said first capacitance to
`
`8
`ground depending on said magnitude of said impedance
`of said load detected by said magnitude detector.
`2. The impedance matching network of claim 1 wherein
`said first capacitance is further comprised of a plurality of
`5 capacitors coupled in parallel to said load.
`3. The impedance matching network of claim 2 wherein
`said plurality of capacitors equals at least 8 capacitors.
`4. The impedance matching network of claim 2 wherein
`10 said plurality of capacitors equals at least 16 capacitors.
`5. The impedance matching network of claim 2 wherein
`each one of said plurality of capacitors has a fixed value of
`capacitance.
`6. The impedance matching network of claim 5 wherein
`15 each one of said plurality of capacitors has a value of
`capacitance generally one-half the value of capacitance as a
`previous capacitor in said plurality of capacitors.
`7. The impedance matching network of claim 2 wherein
`said switching circuit is comprised of a plurality of diodes
`20 each coupled to one of said plurality of capacitors for
`coupling and decoupling said one of said plurality of capaci-
`tors to ground.
`8. The impedance matching network of claim 7 wherein
`each one of said plurality of diodes has a large intrinsic
`region between a p-doped semiconducting region and an
`n-doped semiconducting region.
`9. The impedance matching network of claim 2 wherein
`said switching circuit is comprised of a plurality of radio
`30 frequency relays, each coupled to one of said plurality of
`capacitors for coupling and decoupling one of said plurality
`of capacitors to ground.
`10. An impedance matching network coupled to a trans-
`mission line, said transmission line coupling a radio fire-
`35 quency power generator to a load, said impedance matching
`network comprising:
`a phase detector coupled to said transmission line, said
`phase detector detecting a phase shift in a voltage and
`a current on said transmission line;
`a frequency synthesizer circuit coupled to said phase
`detector, said frequency synthesizer circuit changing
`the frequency of said voltage depending on said phase
`shift in said voltage and said current on said transmis-
`sion line detected by said phase detector;
`a magnitude detector coupled to said transmission line,
`said magnitude detector detecting an impedance on said
`transmission line;
`a plurality of capacitors coupled to said transmission line
`parallel to said load;
`an inductance coupled to said transmission line in series
`with said load;
`a capacitance coupled to said transmission line in series
`with said load, said capacitance, said plurality of
`capacitors, and said inductance forming an L-type
`impedance matching network;
`a plurality of switches, each coupled to one of said
`plurality of capacitors, said plurality of switches cou-
`pling and decoupling said plurality of capacitors to a
`ground depending on said impedance of said transmis-
`sion line detected by said magnitu