United States Patent [19J
`Hanawa
`
`[54] AUTOMATIC FREQUENCY TUNING OF AN
`RF POWER SOURCE OF AN INDUCTIVELY
`COUPLED PLASMA REACTOR
`
`[75]
`
`Inventor: Hiroji Hanawa, Sunnyvale, Calif.
`
`[73] Assignee: Applied Ma~erials, Inc., Santa Clara,
`Calif.
`
`[21] Appl. No.: 389,888
`
`Feb. 15, 1995
`
`[22] Filed:
`Int. Cl.6
`........................................................ C23F 1/02
`[51]
`[52] U.S. CI •......................................... 1561345; 156/643.1
`[58] Field of Search ............................ 118/723 I, 723 IR,
`118/723 E, 723 ER, 723 MP, 671; 156/345,
`643.1, 626.1, 627.1; 216/68; 204/298.08,
`298.32, 298.03
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`3,573,840
`4,795,529
`4,842,683
`4,844,775
`4,872,947
`4,948,458
`4,954,212
`4,992,665
`5,122,251
`5,234,529
`5,277,751
`5,280,154
`5,346,578
`5,368,710
`5,401,350
`5,474,648
`
`4/1971 Gouillou et al. ••.•.............•.•••.. 343/895
`1/1989 Kawasaki et al .••••..•.............•• 1561643
`6/1989 Cheng et al. .....••••••.•..........•.•• 1561345
`7/1989 Keeble .................................... 1561643
`10/1989 Wang et al ............................. 1561643
`8/1990 Ogle ........................................ 1561643
`9/1990 Gabriel et al. •.......••••.•••••........ 1561627
`2/1991 Mohl ................................... 250/423 R
`6/1992 Campbell et al. ················· 204/298.06
`8/1993 Jolmson ....•.•.•......•..•....•••.......• 1561345
`1/1994 Ogle ........................................ 1561643
`1/1994 Cuomo et al ............•..•.•.... 219/121.52
`9/1994 Benzing et al. •.••...............•.... 1561345
`11/1994 Chen et al .•.••..............•.•.•• 264/192.32
`3/1995 Patrick et al.
`.......................... 1561345
`12/1995 Patrick et al .•.•••................•. 1561627.1
`
`11111111111111111111111 Hll 111111111111111~11111111111 1111111 Ill
`
`US005688357A
`[111 Patent Number:
`[451 Date of Patent:
`
`5,688,357
`Nov. 18, 1997
`
`5,540,824
`5,558,722
`
`7/1996 Yin et al ............................ 204/298.34
`9/1996 Okumura et al ...................... 118n23 I
`
`FOREIGN PATENT DOCUMENTS
`
`0 058 820
`0 379 828 A2
`0 379 828 A3
`0 489 407
`0 520 519Al
`0 552 491 Al
`0 593 924
`0 596 551 Al
`0 602 764
`2 231 197
`WO 92/20833
`
`1/1982
`8/1990
`8/1990
`611992
`12/1992
`7/1993
`4/1994
`5/1994
`611994
`11/1990
`11/1992
`
`European Pat. Off ..
`European Pat. Off ..
`European Pat. Off ..
`European Pat. Off ..
`European Pat. Off ..
`European Pat. Off ..
`European Pat. Off ..
`European Pat. Off ..
`European Pat. Off ..
`United Kingdom .
`WIPO.
`
`Primary Examiner-John Niebling
`Assistant Examiner-Joni Y. Chang
`Attome~ Agent, or Firm-Michaelson & Wallace
`
`[57]
`
`ABSTRACT
`
`A plasma reactor has a reactor chamber for containing a
`semiconductor wafer to be processed and gas inlet apparatus
`for introducing an ionizable gas into the chamber, a variable
`frequency RF power source, an RF antenna near the
`chamber, the antenna connected to the RF power source for
`coupling RF power to the ionizable gas to produce a plasma
`therefrom, a power sensor connected to the antenna for
`sensing either (or both) transmitted power to the plasma or
`reflected power to said source, and a control circuit con(cid:173)
`nected to a control input of the variable frequency RF power
`source and responsive to the power sensor for changing the
`frequency of the variable frequency RF power source so as
`to either increase the transmitted power or decrease the
`reflected power, so as to provide an accurate RF match
`instantly responsive to changes in plasma impedance.
`
`30 Claims, 13 Drawing Sheets
`
`48
`
`46
`
`10
`
`/
`
`28
`
`rR°F SoURcE -
`I
`
`-
`s1
`
`-
`
`- -;2- --,
`I
`ss
`REFLECTED
`GEN~TOR I
`POWER
`I
`SENSOR
`54
`I
`I so
`!----s~ ______ _J
`
`COMPUTER
`
`26
`30
`I RF MATCH -(
`r------,
`I CIRCUIT
`I 32
`36
`34
`I
`I
`GENERATOR I
`RF
`I
`....-.--1---.-<AMP
`L _____ _J
`I
`
`Page 1 of 20
`
`Samsung Exhibit 1010
`
`

`

`-...I
`Ol
`"' w
`~
`~
`"' ~
`tit
`
`..... w
`~
`.....
`ll.
`~ ('D
`
`~
`~ .....
`.....
`~
`z
`
`~
`
`~ t"'l'-a
`
`00 •
`~
`
`In_
`I
`AMP
`I CIRCUIT
`I 32 I 36
`r RF MATCH 1 r -
`r---~~------_J
`I
`I so
`.
`I
`SENSOR
`I
`--POWER
`I
`---,
`
`COMPUTER
`
`28--I
`
`54
`
`GENERATOR
`
`RF
`
`2
`
`--;
`
`ss
`
`-
`
`-
`
`s1
`
`-
`
`I
`rRFsoURcE -
`
`REFLECTED
`
`10
`
`/
`
`46
`
`48
`
`FIG. 4
`
`~-
`
`~100 28
`
`I
`
`?A.
`
`FIG. 1
`
`--
`
`L _____ _J
`GENERATOR I
`I
`34RF
`...,
`
`-
`
`-
`
`-
`
`-
`
`42
`
`30
`
`' 26
`
`I
`
`Page 2 of 20
`
`

`

`QO
`QO
`~
`-..
`Ul
`
`Ul "
`tu
`
`""""
`l..H
`~
`N
`~
`
`r::n =(cid:173)~
`
`"""" ~
`"""" 00
`~
`
`~
`
`'4
`
`~ !
`
`00 •
`~
`
`FIG. 3
`
`FIG. 2
`
`NO
`
`74
`
`YES
`
`NO
`
`64
`
`YES
`
`SAMPLE TRANSMITTED POWER
`DECREMENT FREQUENCY AND
`
`SAMPLE REFLECTED POWER
`DECREMENT FREQUENCY AND
`
`,....._ ____ ......,.NO
`
`NO
`
`YES
`
`YES
`
`70
`
`60
`
`SAMPLE TRANSMITTED POWER
`INCREMENT FREQUENCY AND
`
`SAMPLE REFLECTED POWER
`INCREMENT FREQUENCY AND
`
`START
`
`START
`
`Page 3 of 20
`
`

`

`U.S. Patent
`
`Nov. 18, 1997
`
`Sheet 3of13
`
`5,688,357
`
`v
`N
`
`I '
`
`C'I
`C'I
`
`0
`N
`
`~I
`
`0
`t")
`
`::i::
`01-
`~=>
`~() a::: -
`l&.. (.)
`a::
`
`-11
`
`11
`
`Page 4 of 20
`
`

`

`U.S. Patent
`
`Nov. 18, 1997
`
`Sheet 4of13
`
`5,688,357
`
`48
`
`48
`
`20
`
`22
`
`18
`
`26
`
`RF
`SOURCE
`
`100
`
`\
`
`28
`
`p
`
`RF MATCH
`c1Rcurr
`
`30
`
`FIG. 6
`
`/10
`100a 2Ba
`
`20
`
`22
`
`2Bb
`
`26a
`
`RF
`SOURCE
`
`RF
`SOURCE
`
`26b
`
`RF MATCH
`CIRCUIT
`
`30
`
`FIG. 9
`
`Page 5 of 20
`
`

`

`U.S. Patent
`
`Nov. 18, 1997
`
`Sheet 5of13
`
`5,688,357
`
`48
`
`48
`
`20
`
`22
`
`~
`
`26
`
`RF
`SOURCE
`
`100
`
`\
`
`28
`
`p
`
`RF MATCH
`CIRCUIT
`
`30
`
`FIG. 7
`
`/10
`
`100a
`
`2Ba
`
`100b
`
`2Bb
`
`26a
`
`RF
`SOURCE
`
`RF
`SOURCE
`
`26b
`
`ooOOOO
`00
`00
`0
`0
`
`8
`
`0
`
`20
`
`22
`
`RF MATCH
`CIRCUIT
`
`30
`
`FIG.
`
`10
`
`Page 6 of 20
`
`

`

`U.S. Patent
`
`Nov. 18, 1997
`
`Sheet 6of13
`
`5,688,357
`
`48
`
`20
`
`22
`
`100
`
`26
`
`RF
`SOURCE
`
`10
`
`~
`
`48
`
`RF MATCH
`CIRCUIT
`
`30
`
`100a
`
`FIG. B
`
`2Ba
`
`2Bb
`
`26a
`
`RF
`SOURCE
`
`RF
`SOURCE
`
`26b
`
`RF MATCH
`CIRCUIT
`
`30
`
`FIG. 11
`
`Page 7 of 20
`
`

`

`U.S. Patent
`
`Nov. 18, 1997
`
`Sheet 7of13
`
`5,688,357
`
`1210
`
`)
`
`28
`
`26
`
`RF
`SOURCE
`
`10
`
`~
`
`14
`
`FIG. 12
`
`RF MATCH
`CIRCUIT
`
`30
`
`2Ba
`
`10
`
`~
`
`14
`
`FIG. 13
`
`RF MATCH
`CIRCUIT
`
`30
`
`26
`
`RF
`SOURCE
`
`2Bb
`
`Page 8 of 20
`
`

`

`U.S. Patent
`
`Nov. 18, 1997
`
`Sheet 8of13
`
`5,688,357
`
`lO I
`
`10 I
`
`26
`
`RF
`SOURCE
`p
`
`26
`
`RF
`SOURCE
`
`FIG. 14
`
`RF MATCH
`CIRCUIT
`
`30
`
`--
`
`12
`
`20
`I i 111 14
`
`FIG. 15
`
`RF MATCH
`CIRCUIT
`
`30
`
`Page 9 of 20
`
`

`

`U.S. Patent
`
`Nov. 18, 1997
`
`Sheet 9of13
`
`5,688,357
`
`~1310
`
`26
`
`RF
`SOURCE
`
`~1320
`
`FIG. 16
`
`Page 10 of 20
`
`

`

`U.S. Patent
`
`Nov. 18, 1997
`
`Sheet 10 of 13
`
`5,688,357
`
`1740
`
`1710
`
`1720
`
`1730
`
`1750
`
`26
`
`RF
`SOURCE
`
`1760
`
`1770
`
`FIG. 17
`
`Page 11 of 20
`
`

`

`U.S. Patent
`US. Patent
`
`Nov. 18, 1997
`Nov. 18, 1997
`
`Sheet 11 of 13
`Sheet 11 of 13
`
`5,688,357
`5,688,357
`
`0
`30
`I"')
`
`co
`18
`
`~
`
`>-
`(I) ..J
`<(a..
`(!) D...
`:J
`(/)
`
`J:
`:5.—
`UI--
`!;( :::>
`"5
`<0
`::EU
`a::::
`2a:
`1.1.5
`LLU
`er;
`
`•
`c.J
`t--1
`~
`
`.0
`UJ
`N
`
`... w
`CJ
`LL 0::::
`0:: :::>
`0
`Ul
`
`.0
`0
`0
`
`11
`
`Page 12 0f 20
`
`CK
`
`f'.~
`,....
`
`0
`('\I
`
`,.....
`
`~I
`
`, ,
`
`Page 12 of 20
`
`

`

`QC w
`Ol "' QC
`
`.....:a
`Ol
`
`~ w
`~
`N
`~
`
`~ ('D a
`
`""-I
`~
`
`~
`
`00
`~
`~
`0
`'.Z
`
`~
`
`FIG. 20
`
`FIG. 19
`
`SOURCE
`
`RF
`
`26b
`
`CIRCUIT
`RF MATCH
`
`30
`
`SOURCE
`
`RF
`
`26b
`
`CIRCUIT
`RF MATCH
`
`30
`
`SOURCE
`
`RF
`
`26c
`
`SOURCE
`
`RF
`
`26c
`
`100c
`
`. ~
`
`100c
`
`2020 ~
`.......
`~
`00 •
`~
`
`I ~
`
`-
`
`2010
`26a
`
`SOURCE
`
`RF
`
`100a
`
`I
`
`26a
`
`SOURCE
`
`RF
`
`Page 13 of 20
`
`

`

`U.S. Patent
`
`Nov. 18, 1997
`
`Sheet 13 of 13
`
`5,688,357
`
`..0
`<D
`N
`
`LLJ
`(.)
`LL. 0::
`a::: :::>
`0
`(/')
`
`0
`N
`0
`
`N I
`
`0 ...-
`N~
`
`11
`
`,..-f
`C\1
`
`•
`~
`t--f
`~
`
`lLJ
`(.)
`LL. a:::
`a:: :::>.
`0
`Vl
`
`0
`0
`
`0 -
`
`UJ
`CJ
`LL. a::
`0:: ;:::)
`0
`Vl
`
`Page 14 of 20
`
`

`

`5,688,357
`
`1
`AUTOMATIC FREQUENCY TUNING OF AN
`RF POWER SOURCE OF AN INDUCTIVELY
`COUPLED PLASMA REACTOR
`
`BACKGROUND OF THE INVENTION
`
`2
`therefrom, a power sensor connected to the antenna for
`sensing either (or both) transmitted power to the plasma or
`reflected power to said source, and a control circuit con(cid:173)
`nected to a control input of the variable frequency RF power
`5 source and responsive to the power sensor for changing the
`frequency of the variable frequency RF power source so as
`to either increase the transmitted power or decrease the
`reflected power, so as to provide an accurate RF match
`instantly responsive to changes in plasma impedance.
`
`BRIEF DESCRIPITON OF THE DRAWINGS
`
`FIG. 1 is a schematic diagram of an RF plasma reactor
`system including the present invention.
`FIG. 2 is a block flow diagram illustrating a frequency
`control process carried out by logic in the system of FIG. 1.
`FIG. 3 is a block flow diagram illustrating a frequency
`control process carried out by logic in an alternative embodi(cid:173)
`ment of the system of FIG. 1.
`FIG. 4 illustrates a translatable RF connector employed in
`the embodiment of FIG. 1.
`FIGS. 5-11 are simplified diagrams of embodiments of
`the invention in which the antenna coil has a top section
`overlying the chamber and a side section surrounding a
`portion of the chamber.
`FIGS. 12-17 are simplified diagrams of embodiments of
`the invention in which the antenna coil consists of plural
`oppositely wound sections joined at common points of
`connection.
`FIGS. 18-21 are simplified diagrams of embodiments of
`the invention in which the antenna coil consists of plural
`concentric windings.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`35
`
`1. Technical Field
`The present invention is related to inductively coupled RF
`plasma reactors used in semiconductor processing, of the
`type employing a coiled antenna to couple RF power to the 10
`plasma reactor chamber, and in particular to methods for
`tuning the RF power circuit (including the coil antenna) in
`response to impedance changes in the plasma.
`2. Background Art
`An inductively coupled plasma reactor typically has a 15
`coiled antenna adjacent the plasma reactor chamber and an
`RF generator connected through an impedance match circuit
`and a 50 Ohm cable to the coiled antenna. As disclosed in
`U.S. patent application Ser. No. 08/277,531 filed Jul. 18,
`1994 by Gerald Ym et al. entitled PLASMA REACTOR 20
`WITH MULTI-SECTION RF COIL AND ISOLATED
`CONDUCTING LID and assigned to the assignee of the
`present application, such an inductively coupled plasma
`reactor may have a ceiling over which the coiled antenna is
`wound. In carrying out semiconductor processes such as 25
`metal etching, as one example, the amount of power applied
`to the plasma in the chamber is a critical parameter and is
`selected with great care. Any significant deviation from the
`selected power level may so change the process as to reduce
`product yield, as is well-known to those skilled in the art. 30
`For example, the plasma density, which affects etch rate, is
`a function of the power coupled to the plasma.
`The RF impedance presented by the plasma fluctuates
`during processing. Unless the RF match circuit is able to
`compensate for such fluctuations, an RF mis-match arises
`between the RF source and the plasma, so that some of the
`RF power is reflected back to the source rather than being
`coupled to the plasma. Plasma impedance fluctuations dur(cid:173)
`ing RF plasma processing on the order of 5% are typical. In
`order to enable the RF match circuit to compensate or follow
`such fluctuations and maintain an RF match condition, the
`RF match circuit includes variable capacitors controlled by
`electric motor servos governed by an RF detector circuit.
`The RF detector circuit responds to changes in reflected
`power by changing the variable capacitors to maintain RF
`match between the RF source and the plasma.
`One problem with this approach is that the electric motor
`servos and variable capacitors are expensive and heavy. A
`related problem is that it is difficult to compensate for large 50
`fluctuations in plasma impedance using electric motor ser(cid:173)
`vos and variable capacitors. A further problem is that the
`electric motor servos are relatively slow and unreliable
`(being subject to mechanical breakdown). What is needed is
`a device for instantly responding to wide fluctuations in 55
`plasma impedance to maintain RF match without employing
`heavy or expensive mechanical devices or variable capaci(cid:173)
`tors.
`
`40
`
`45
`
`Referring now to FIG. 1, an inductively coupled RF
`plasma reactor 10 includes a sealed reactor chamber 12
`bounded by a generally cylindrical conductive (metal) side
`wall 14 and a dielectric (quartz) dome-shaped ceiling 16.
`Gas inlet apparatus 17 coupled to a gas supply provides an
`ionizable processing gas into the interior of the chamber 12.
`A wafer pedestal 18 in the middle of the chamber supports
`a semiconductor wafer 20 on an isolated conductive top 22.
`RF power is coupled to the plasma in the chamber 10 by a
`coiled antenna 24 wound around the exterior of the dome-
`shaped ceiling 16. The coil 24 is connected to a matched RF
`source 26 via a 50-0hm cable 28. In order to control plasma
`ion energy, the wafer pedestal base 22 is connected through
`an RF match circuit 30 and a 50-0hm cable 32 to an RF
`generator 34 and amplifier 36. In one implementation, the
`RF match circuit 30 includes a series 100-picoFarad capaci(cid:173)
`tor 40, a series variable inductor 42 (nominally 3
`microHenries) and a variable shunt capacitor 44 (nominally
`1200 picoFarads). However, it should be understood that
`these values will vary depending upon specific plasma
`reactor design choices, and are readily determined by the
`skilled worker for a particular reactor design. A conventional
`vacuum pump (not shown) maintains the interior of the
`60 chamber 12 at a desired pressure (e.g., between 0 and 100
`millITorr.
`In accordance with one aspect of the invention, no sepa(cid:173)
`rate RF match circuit (such as the RF match circuit 30) is
`required to match the RF source 26 to the load. Instead, a
`match is achieved by employing the coil antenna 24 itself as
`a fixed RF match reactance. For this purpose, the power
`cable from the RF source 26 is connected through a slidable
`
`SUMMARY OF THE INVENTION
`
`The invention is embodied in an RF plasma reactor
`having a reactor chamber for containing a semiconductor
`substrate to be processed and gas inlet apparatus for intro(cid:173)
`ducing an ionizable gas into the chamber, a variable fre(cid:173)
`quency RF power source, an RF antenna near the chamber, 65
`the antenna connected to the RF power source for coupling
`RF power to the ionizable gas to produce a plasma
`
`Page 15 of 20
`
`

`

`5,688,357
`
`10
`
`3
`conductor attachment A (FIG. 4) to an intermediate point P
`(FIG. 1) on the coil antenna 24. The point P divides the coil
`antenna 24 into two windings, a top winding 24a and a
`bottom winding 24b. The end of the top winding 24a is
`grounded through a high voltage capacitor 46 to an RF 5
`shield 48 surrounding the coil antenna 24. In the illustrated
`implementation, the high voltage capacitor 46 was 500
`picoFarads. The end of the bottom winding 24b is grounded
`directly to the RF shield 48. A perfect RF match is achieved
`by sliding the slidable attachment A to vary the location of
`the attachment point P along the conductor of the coil
`antenna 24 while continuously measuring RF power
`reflected back to the RF source until the reflected RF power
`is minimized. For this purpose, the skilled worker may
`connect a conventional power meter such as the reflected
`power sensor 50 at the output of the RF source 26. Such a 15
`conventional power meter typically provides continuous
`measurements of both reflected power and transmitted
`power. As is well-known to those skilled in the art, such a
`power meter is readily implemented with a conventional RF
`dual direction coupler circuit. It should be noted that the 20
`worker may have to try sliding the attachment A in both
`directions to determine which direction is the correct one in
`which to move the slidable attachment A.
`Of course, once a plasma is ignited within the chamber 12,
`the RF match condition may be lost as the plasma impedance
`fluctuates. Therefore, it is necessary to compensate for such
`fluctuations to maintain RF match between the RF source 26
`and the load or chamber 12. For this purpose, the RF source
`26 employs a conventional variable-frequency RF generator
`52 having a frequency control input 54 and power output 56 30
`with an amplifier 57 and a computer 58. The computer 58
`monitors the reflected power level measured by the reflected
`power sensor 50 and applies a control signal to the frequency
`control input 54 of the variable-frequency RF generator 52.
`In one implementation the RF generator is a voltage- 35
`controlled oscillator and the computer 58 changes the output
`frequency of the generator 52 by varying the voltage applied
`to the control input 54. In other implementations of the
`invention, any device capable of performing the above(cid:173)
`described control tasks of the computer 58, such as a 40
`programmed logic array or an analog control circnit, may be
`employed in lieu thereof.
`The computer 58 (which is preferably a conventional
`microprocessor with a programmable read-only memory) is
`programmed to vary the frequency of the RF generator 52 so 45
`as to continuously minimize the amount of reflected power
`measured by the reflected power sensor 50. One algorithm
`with which the computer 58 may be programmed to accom(cid:173)
`plish this purpose is illustrated in FIG. 2. The successive
`steps of the algorithm of FIG. 2 are performed serially 50
`during successive execution cycles of the computer 58. First,
`the frequency of the RF generator 52 is incremented
`(increased by a predetermined amount) and the reflected RF
`power is then sampled (block 60 of FIG. 2). The computer
`58 then makes a decision (block 62 of FIG. 2): If the current 55
`sampled reflected RF power is less than the previous sample
`(YES branch of block 62), then the incrementing and
`sampling step of block 60 is repeated. Otherwise (NO
`branch of block 60), the next step (block 64) is to decrement
`the frequency and again sample the reflected RF power. 60
`Again, the computer makes a decision (block 66): If the
`reflected RF power has decreased (YES branch of block 66),
`then the decrementing and sampling step of block 64 is
`repeated. Otherwise, (NO branch of block 66), the algorithm
`returns to the incrementing and sampling step of block 60. 65
`The result is that in response to any large fluctuation in
`plasma impedance, either the frequency incrementing step
`
`4
`of block 60 will be repeated many times until RF match is
`reached or else the frequency decrementing step of block 64
`will be repeated many times until RF match is reached. At
`RF match, the algorithm dithers between alternating fre(cid:173)
`quency decrementing and frequency incrementing steps.
`In the illustrated implementation, the nominal frequency
`of the RF source 26 was 2.0 MHz. Typical plasma imped(cid:173)
`ance fluctuations require a 5% increase or decrease in that
`frequency to maintain RF match. Such a fractional change in
`frequency does not appreciably affect the processing char(cid:173)
`acteristics of the plasma reactor. The computer 58 incre-
`ments or decrements the output frequency of the RF gen(cid:173)
`erator 52 preferably in 0.01 MHz steps, so that the entire
`range of frequency variations is covered in 100 execution
`cycles of the computer. Since the computer 58 may be
`expected to operate at MegaHertz rates, the response to any
`plasma impedance fluctuations is virtually instantaneous,
`compared with the slow response of prior art variable
`capacitors and electric motor servos.
`The invention thus eliminates not only the need for
`variable capacitors and electric motor servos in the RF
`match circuit, but also eliminates the entire RF match circuit
`itself, exploiting the coil antenna 24 to obtain the needed
`reactance for an RF match between the chamber 10 and the
`25 RF source 26.
`In operation, a nominal or initial RF match is obtained
`prior to plasma ignition by moving the connection point P
`until reflected RF power measured by the sensor 50 is
`minimized. Then, after the plasma is ignited in the chamber
`10, the computer 58 controls the frequency of the RF
`generator 52 to compensate for the plasma impedance and
`any changes in plasma impedance. Preferably, if it is
`determined, for example, that an RF match is expected to
`obtain at a nominal output frequency of the RF source 26 of
`2.0 MHZ, then frequency of the RF source 26 is set at
`slightly below the expected match frequency of 2.0 MHz
`(e.g., 1.7 MHz) when the plasma if ignited, so that the
`computer 58 increases the frequency until RF match
`(minimum reflected RF power) is obtained.
`In the illustrated embodiment, the coil antenna 24 had an
`inductance of 10 microHenries and the attachment point P
`was located such that the ratio of the number of windings in
`the top winding 24a and the bottom winding 24b was
`approximately 8:2.
`While the invention has been described with reference to
`an embodiment in which the computer 58 samples the
`reflected power measured by the sensor 50 and strives to
`minimize that power in the algorithm of FIG. 2, in an
`alternative embodiment the computer samples transmitted
`power measured by the sensor 50 and strives to maximize
`that measurement. In this alternative embodiment, the algo(cid:173)
`rithm of FIG. 2 is modified to change the "decrease?"
`inquiries of steps 62 and 66 to "increase?" inquiries, as
`illustrated in FIG. 3. Thus, in FIG. 3, the frequency is
`incremented and the transmitted power is sampled (block 70
`of FIG. 3). If this results in an increase in transmitted power
`(YES branch of block 72) then the step is repeated. Other(cid:173)
`wise (NO branch of block 72), the frequency is decremented
`and the transmitted power sampled thereafter (block 74). If
`this results in an increase in transmitted power (YES branch
`of block 76, then this step is repeated. Otherwise (NO branch
`of block 76), the process returns to the initial step of block
`70.
`While the invention has been described with reference to
`an embodiment in which the RF match circuit is eliminated,
`a separate RF match circuit may be connected at the output
`
`Page 16 of 20
`
`

`

`5,688,357
`
`5
`
`10
`
`5
`of the RF source 26, although no variable reactive compo(cid:173)
`nents (e.g., variable capacitors) would be required.
`FIG. 4 illustrates an implementation of the movable
`attachment point A, which is a conductive ring 100 around
`the conductor of the coil antenna 24, the ring 100 maintain(cid:173)
`ing electrical contact with the antenna 24 but being suffi(cid:173)
`ciently loose to permit translation in either direction along
`the length of the coil antenna 24.
`Referring to FIG. 5, the coil antenna 24 may have a
`multi-radius dome shape, the slide connection conductive
`ring 100 being on or near the bottom winding of the coil
`antenna 24. Referring to FIG. 6, the coil antenna 24 may
`comprise a fiat or disk-shaped top portion 610 overlying the
`chamber and a cylindrical side portion 620 surrounding a
`portion of the chamber. Referring to FIG. 7, the coil antenna
`24 may comprise a lower cylindrical portion 710, an inter(cid:173)
`mediate dome-shaped corner 720 and a fiat or discoid top
`portion 730. Referring to FIG. 8, the coil antenna 24 may
`comprise a lower truncated conical portion 810 and a fiat
`discoid top 820. Referring to FIG. 9, the coil antenna of FIG.
`6 may be divided so that the discoid top winding 610 and the
`cylindrical winding 620 are separately connected to the R.F.
`source 26. In the implementation of FIG. 9, the top winding
`610 is connected to the R.F. source 26 by a first slide
`connection ring lOOa on or near the outermost winding
`thereof, while the cylindrical winding is connected to the
`R.F. source 26 by a second slide connection ring lOOb on or
`near the top winding thereof. Referring to FIG. 10, the coil
`antenna of FIG. 7 may be divided so that the cylindrical
`portion 710 is connected at the top winding thereof by the
`first slide connector ring lOOa to the R.F. source 26 while the
`dome and discoid portions 720, 730 are connected to the R.F.
`source 26 at the outermost winding thereof by the second
`slide connector ring lOOb. Referring to FIG. 11, the embodi(cid:173)
`ment of FIG. 8 may be divided so that the conical winding
`810 is connected on or near its top winding to the R.F. source
`26 by the first slide connector ring lOOa while the discoid
`winding 820 is connected at or near its outermost winding to
`the R.F. source 26 by the second slide connector ring lOOb.
`The embodiments of FIGS. 5-11 incorporate inventions 40
`disclosed in U.S. application Ser. No. 08/389,899 filed on
`Feb. 15, 1995 by Hiroji Hanawa et al. and entitled "RF
`Plasma Reactor with Hybrid Coil Inductor and Multi-Radius
`Dome Ceiling" and assigned to the present assignee, the
`disclosure of which is incorporated herein by reference.
`Referring to FIG. 12, the coil antenna 24 may be divided
`into two oppositely wound sections 1210, 1220 connected at
`a common point A to the RF source 26 by the slidable
`connector ring 100, while the top and bottom ends of the coil
`antenna 24 are grounded. The two sections 1210, 1220 are 50
`oppositely wound so that the magnetic flux from each
`section reinforces that of the other. Referring to FIG. 13, the
`common connection point of two sections 1310, 1320 is
`fixed while the connections near the top and bottom ends of
`the coil antenna 24 comprise the two slidable connection 55
`rings lOOa, lOOb, respectively. While the embodiments of
`FIGS. 12 and 13 are dome-shaped windings, FIGS. 14 and
`15 illustrate cylindrical-shaped windings corresponding to
`variations of the embodiments of the embodiments of FIGS.
`12 and 13, respectively. FIG. 16 is a perspective view of the 60
`embodiment of FIG. 15. While each of the embodiments of
`FIGS. 12-16 is illustrated as having two coil sections with
`a single common connection point, the perspective view of
`FIG. 17 illustrates how the same structure may be repeated
`to provide three (or more) sections 1710, 1720, 1730, each 65
`pair of adjacent sections being oppositely wound and having
`a common connection point (1740, 1750, 1760, 1770)
`
`6
`therebetween, alternate common connection points 1750,
`1770) being connected to the RF source 26 and remaining
`common connection points (1740, 1760) being connected to
`ground. The embodiments of FIGS. 12-17 incorporate
`inventions disclosed in U.S. application Ser. No. 08/277 ,531
`filed Jul. 18, 1994 by Gerald Z Ym et al. and entitled
`"Plasma Reactor with Multi-Section RF Coil and Isolated
`Conducting Lid" and assigned to the present assignee, the
`disclosure of which is incorporated herein by reference.
`Referring to FIG. 18, the coil antenna 24 may comprise
`plural (e.g., three) concentrically wound conductors 1810,
`1820, 1830 having a common apex point 1840 connected to
`ground and three ends 1810a, 1820a, 1830a symmetrically
`disposed around the outer circumference of the coil antenna.
`15 In the implementation of FIG. 18, the three ends 1810a,
`1820a, 1830a are connected to the RF source 26 by three
`slide connector rings lOOa, lOOb, lOOc, respectively. While
`the embodiment of FIG. 18 is a fiat discoid coil, FIG. 19
`illustrates how the plural concentric windings may have a
`20 cylindrical shape. FIG. 20 illustrates how the embodiments
`of FIGS. 18 and 19 may be combined to provide a fiat top
`discoid winding 2010 and a cylindrical side winding 2020.
`The embodiment of FIG. 21 comprises a dome-shaped top
`2110 consisting of plural concentric windings. As illustrated
`25 in FIG. 21, the dome-shaped top 2110 may be combined
`with the cylindrical side winding 2020 of FIG. 20. The
`embodiments of FIGS. 18-21 incorporate inventions dis(cid:173)
`closed in U.S. application Ser. No. 08/332,569 filed Oct. 31,
`1994 by Xue-Yu Qian et al. entitled "Inductively Coupled
`30 Plasma Reactor with Symmetrical Parallel Multiple Coils
`Having a Common RF Terminal" and assigned to the present
`assignee, the disclosure of which is incorporated herein by
`reference.
`While the invention has been described in detail by
`35 specific reference to preferred embodiments, it is understood
`that variations and modifications thereof may be made
`without departing from the true spirit and scope of the
`invention.
`What is claimed is:
`1. A plasma reactor, comprising:
`a reactor chamber for containing a substrate to be pro(cid:173)
`cessed and a gas inlet to permit introduction of an
`ionizable gas into said chamber;
`a variable frequency RF power source;
`an RF antenna near said chamber, said antenna connected
`to said RF power source for coupling RF power to said
`ionizable gas to produce a plasma therefrom;
`a power sensor connected to said antenna for sensing at
`least one of: (a) transmitted power to said plasma and
`(b) reflected power to said source; and
`a control circuit connected to a control input of the
`variable frequency RF power source and responsive to
`said power sensor for regulating the frequency of said
`variable frequency RF power source so as to effect at
`least one of: (a) an increase in said transmitted power
`and (b) a decrease in said reflected power.
`2. The reactor of claim 1 further comprising a fixed RF
`match circuit comprising at least one reactive component
`connected to said RF antenna
`3. The reactor of claim 1 further comprising a movable RF
`connector on said RF antenna, said movable RF connector
`being translatable along the length of said RF antenna, said
`variable frequency RF power source being connected to said
`RF antenna at said movable RF connector.
`4. The reactor of claim 3 wherein the location of said
`movable RF connector and a reactance of said reactive
`
`45
`
`Page 17 of 20
`
`

`

`5,688,357
`
`15
`
`7
`component provide an initial RF match of said variable
`frequency RF power source.
`5. The reactor of claim 1 further comprising an RF bias
`source, a wafer pedestal within said chamber and a bias RF
`match circuit connected between said RF bias source and
`said wafer pedestal.
`6. The reactor of claim 5 wherein said RF bias source has
`a fixed RF frequency and said bias RF match circuit provides
`an RF match of said RF bias source to said wafer pedestal
`at said fixed RF frequency of said RF bias source.
`7. The reactor of claim 3 wherein:
`said reactive component comprises a capacitor connected
`between .one end of said RF antenna and ground;
`an opposite end of said RF antenna is connected directly
`to ground; and
`said movable connector is located between said ends of
`said antenna.
`8. The reactor of claim 1 wherein said control circuit
`comprises a computer programmed monitor coupled to said
`power sensor and to change said frequency of said variable
`frequency RF power source so as to effect one of: (a) 20
`minimizing said reflected power and (b) maximizing said
`transmitted power.
`9. The reactor of claim 8 wherein said computer is
`programmed to determine which one of an increase or
`decrease in frequency minimizes reflected power and to 25
`change the frequency of said variable frequency RF power
`source until said reflected power is minimized.
`10. The reactor of claim 7 wherein said antenna comprises
`an inductive coil antenna and wherein said reactor is an
`inductively coupled plasma reactor.
`11. The plasma reactor of claim 1 wherein said RF
`antenna comprises a top coil section overlying said chamber
`and a side coil section surrounding a portion of said cham(cid:173)
`ber.
`12. The plasma reactor of claim 11 wherein said top and
`side coil sections comprise a single winding.
`13. The plasma reactor of claim 11 wherein said top and
`side coil sections are separately connected to said RF power
`source.
`14. The plasma reactor of claim 1 wherein said RF
`antenna comprises plural coil sections, adjacent ones of said
`plural coil sections being oppositely wound and having a
`common connection therebetween.
`15. The plasma reactor of claim 14 wherein said common
`connection is connected to said RF power source.
`16. The plasma reactor of claim 14 wherein there are
`plural pairs of adjacent coil sections with plural common
`connections therebetween, alternate ones of said common
`connections being connected to said RF power source and
`remaining ones of said common connections being con(cid:173)
`nected to ground.
`17. The plasma reactor of claim 1 wherein said RF
`antenna comprises plural concentric windings having a
`common apex connection and respective ends.
`18. The plasma reactor of claim 17 wherein said common
`apex connection is connected to one of (a) said RF power 55
`source and