Ulllted States Patent [19]
`Dible et al.
`
`USOO5824606A
`[11] Patent Number:
`[45] Date of Patent:
`
`5,824,606
`Oct. 20, 1998
`
`[54] METHODS AND APPARATUSES FOR
`
`5,436,424
`
`7/1995 Nakayama et al. .............. .. 219/121.43
`
`CONTROLLING PHASE DIFFERENCE IN
`
`5,573,595 11/1996 Dible . . . . . . . . . . . . . .
`
`. . . .. 118/723
`
`PLASMA PROCESSING SYSTEMS
`
`118/723 I
`7/1997 Zhao et al.
`5,643,364
`5,698,062 12/1997 Sakamoto et al. .................... .. 156/345
`
`[75] Inventors: Robert D. Dible; Stephen G. Bradley;
`Seyed J afar J afarian-Tehrani, all of
`Fremont, Calif.
`
`[73] Assignee: Lam Research Corporation, Fremont,
`Calif.
`
`[21] Appl. No.: 642,172
`[22] Filed:
`Mar. 29, 1996
`
`FOREIGN PATENT DOCUMENTS
`WO 95/15672 6/1995 European Pat. Off. .
`WO 95/32315 11/1995 European Pat. Off. .
`0685873A1 12/1995 European Pat. Off. .
`
`Primary Examiner—William Powell
`Attorney, Agent, or Firm—Beyer & Weaver, LLP
`[57]
`ABSTRACT
`
`[51] Int. Cl.6 ............................. .. H01L 21/00; B44C 1/22
`[52] US. Cl. .......................... .. 438/729; 156/345; 216/60;
`216/67; 438/9; 438/14
`[58] Field of Search ................................ .. 216/67, 59, 60;
`156/345 P, 345 C, 345 MT; 118/723 E,
`723 ER, 723 I, 723 IR; 204/29808, 29834;
`438/9, 14, 729
`
`[56]
`
`References Cited
`
`U'S' PATENT DOCUMENTS
`9/1985 Takagi et a1. ......................... .. 156/614
`4,539,068
`5,057,185 10/1991 Thomas, 111 et a1,
`_____ __ 156/643
`5,116,482
`5/1992 Setoyama et al. ..... ..
`.. 204/298.08
`156/345
`5,147,493
`9/1992 Nishimura et al- -
`572287939
`7/1993 Ch“ ~~~~~~~~~~~~ ~~
`156/345
`572737616 12/1993 Bozler et a1‘
`156/603
`5,332,880
`7/1994 Kubota et al.
`219/121.52
`5,401,350
`3/1995 Patrick et al.
`..... .. 156/345
`5,414,324
`5/1995 Roth et al.
`315/11121
`5,433,813
`7/1995 Kuwabara ............................. .. 156/345
`
`A method in a plasma processing system for modifying a
`phase difference between a ?rst radio frequency (RF) signal
`and a second RF signal. The ?rst RF signal is supplied by a
`?rst RF power source to a ?rst electrode and the second RF
`signal is supplied by a second RF power source to a second
`electrode of a plasma processing system. The second RF
`power source is coupled to the ?rst RF power source as a
`slave RF power source in a master-and-slave con?guration.
`The method includes the step of ascertaining a phase dif
`ference between a phase of the ?rst RF signal and a phase
`of the second RF signal. The method further includes the
`step of Comparing the Phase difference With a Phase Control
`set point signal to output a control signal to the second RF
`power source, whereby the second RF power source, respon
`sive to the control signal, modi?es the phase of the second
`RF signal to cause the phase difference to approximate a
`phase difference value represented by the phase control set
`Oint Si nal
`p
`g '
`
`16 Claims, 11 Drawing Sheets
`
`PHASE
`
`BIAS
`
`SELECT
`
`404
`
`410
`
`MATCH
`
`414
`I
`
`con.
`
`412
`
`SENSOR @
`
`u
`
`PHASE CONTROL POINT
`
`420
`
`/422
`
`\
`406
`
`\
`418
`
`MATCH
`l
`
`403
`
`SENSOR
`
`I \
`
`416
`
`AC / DC BIAS
`MEASUREMENT
`
`440)
`
`V
`
`BIAS
`SET
`POINT
`
`442
`
`PEAK BIAS
`CONTROL
`
`‘
`
`444
`
`Exhibit 2002
`IPR2017-0391
`
`

`

`U.S. Patent
`
`Oct. 20, 1998
`
`Sheet 1 of 11
`
`5,824,606
`
`108
`
`140
`
`FIG. 1
`
`Exhibit 2002
`|PR201 7-0391
`
`Exhibit 2002
`IPR2017-0391
`
`

`

`Oct.20,1998
`0099
`m.,
`
`1as.
`
`momzmm
`
`U.S. Patent
`
`.Evma.W.:OONwvcS.o_.v
`
`tJII._oEzoo%08..
`mmBmzmm,m<_mPOmomzmm1022Emw<:n_
`
`4<zo_m
`
`mKvmv
`
`
`mowK._.Z_On_405200mm<:¢
`
`\.
`
`M2teehS
`Sheet 2 0f 11
`
`5,824,606
`5,824,606
`
`Hm<_mon.\o<m<_mx<mn_
`
`<N.0_..._
`
`»zm__2mm3m<ms_
`
`oi.
`
`40m._.ZOO
`
`m<_m
`
`Em
`
`kZ_On_
`
`Exhibit 2002
`|PR201 7-0391
`
`Exhibit 2002
`IPR2017-0391
`
`
`
`

`

`U.S. Patent
`
`Oct.20,1998
`
`Sheet 3 0f 11
`
`5,824,606
`
`/ 410
`
`=
`
`> X
`cp
`
`k},
`c:S
`
`:
`
`LP
`
`7
`
`LS
`
`V
`COIL&
`iPLASMA LOAD
`
`?t
`
`-
`
`FIG. 2B
`
`/ 408
`
`0;,
`i‘ .L
`
`OS
`Ls‘
`m5 : .L
`
`1.
`
`:
`
`>
`
`LP / l-s
`
`>
`
`J7
`
`FIG. 2C
`
`Exhibit 2002
`IPR2017-0391
`
`

`

`U.S. Patent
`U.S. Patent
`
`Oct. 20, 1998
`Oct. 20, 1998
`
`Sheet 4 of 11
`Sheet 4 0f 11
`
`5,824,606
`5,824,606
`
`460
`460
`
`470
`
`472
`
`476
`
`474
`
`V
`
`FIG. 20
`FIG. 2D
`
`Exhibit 2002
`|PR201 7-0391
`
`Exhibit 2002
`IPR2017-0391
`
`

`

`U.S. Patent
`
`Oct. 20, 1998
`
`Sheet 5 0f 11
`
`5,824,606
`
`OPTTCAL AMPLITUDE VS. PHASE SHIFT
`
`
`
`
`
`261 nm AMPLITUDE (COUNTS)
`
`18100 #
`
`17900 -
`
`17700 ~
`
`17500 —
`
`I
`
`17300 —
`
`17100 -
`
`16900 -
`
`16700 -—
`
`16500
`410
`
`1
`
`4
`
`-6O
`
`-30
`
`4'
`
`0
`
`L
`
`30
`
`|
`
`L
`
`|
`
`l
`
`1
`
`60
`
`90
`
`120 150 180
`
`GENERATOR PHASE SHIFT (DEGREES)
`
`FIG. 3
`
`ELECTRODE P-P VOLTAGE VS. PHASE SHIFT
`
`
`
`
`
`P-P VOLTS (C1-C6)
`
`42 ~
`
`41 ~
`
`40 ~~
`
`39 -
`
`38 a
`
`37 ——
`
`33 -
`
`32
`
`l
`
`l
`
`—60
`
`—30
`
`l
`
`O
`
`l
`
`l
`
`l
`
`1
`
`l
`
`L
`
`30
`
`60
`
`90
`
`120 150 180
`
`GENERATOR PHASE SHIFT (DEGREES)
`
`FIG. 4
`
`Exhibit 2002
`IPR2017-0391
`
`

`

`U.S. Patent
`
`Oct. 20, 1998
`
`Sheet 6 0f 11
`
`5,824,606
`
`DC BIAS VS. PHASE SHIFT
`
`
`
`
`
`BIAS (-v) C1-C6
`
`40
`
`as
`
`as
`
`32
`
`3O
`28
`26
`
`24
`
`22
`2O
`-90
`
`L
`1
`
`—60
`
`L
`|
`
`-30
`
`1
`l
`f I
`
`0
`
`30
`
`4
`I
`
`6O
`
`1
`‘I
`
`L
`l
`
`|
`T
`
`\
`I
`
`9D 12D ‘ISU 180
`
`GENERATOR PHASE SHIFT (DEGREES)
`
`FIG. 5
`
`REMAINING OXIDE VS PHASE SHIFT
`
`
`
`
`
`REMAINING OXIDE (ANG)
`
`1440 I
`
`1420 -
`
`1400 ~
`
`1380 a
`
`1360
`
`1340 T
`
`1320 -
`
`1300 I
`
`1280
`
`1
`
`l
`
`I; l
`
`l
`
`l
`
`1
`
`AL
`
`-60
`
`-30
`
`O
`
`30
`
`6O
`
`90
`
`120 150 180
`
`GENERATOR PHASE SHIFT (DEGREES)
`
`FIG. 6B
`
`Exhibit 2002
`IPR2017-0391
`
`

`

`U.S. Patent
`
`Oct.20,1998
`
`Sheet 7 0f 11
`
`5,824,606
`
`OXIDE ETCH RATE VS. PHASE SHIFT
`
`0
`
`1800 -~
`
`A 1700 -—
`
`z
`E
`g 1600 !!
`<
`0
`
`LL]
`‘E75
`
`1500 --
`
`I
`
`2 LL‘ 1400 ~-
`
`.
`
`0
`
`1300
`-9O
`
`+
`—6O
`
`I—
`-3O
`
`I
`0
`
`:
`3O
`
`.L
`6O
`
`I
`90
`
`:
`'r
`1
`120 156 180
`
`GENERATOR PHASE SHIFT (DEGREES)
`
`ALUMINUM/OXIDE SELECTIVITY vs. PHASE SHIFT
`
`6.50“
`
`6.00 ~~
`
`0
`5.50 o
`
`5.00 -~
`
`0
`
`4050 -—
`
`>-
`t
`E
`O
`LLI
`_.l
`H
`
`I
`
`'
`
`—
`
`4.00
`—90
`
`I
`—6O
`
`I
`-3O
`
`I
`0
`
`I
`3O
`
`I
`6O
`
`I
`90
`
`I
`I
`I
`120 150 ‘I80
`
`GENERATOR PHASE SHIFT (DEGREES)
`
`FIG. 7
`
`Exhibit 2002
`IPR2017-0391
`
`

`

`U.S. Patent
`
`Oct.20,1998
`
`Sheet 8 0f 11
`
`5,824,606
`
`RESIST ETCH RATE VS. PHASE SHIFT
`
`3100
`
`3000
`
`2900
`
`2800
`
`2700
`
`2600
`
`
`
`ETCH RATE
`
`'
`
`2500
`—90
`
`I
`-6
`
`I
`-30
`
`I
`0
`
`I
`30
`
`I
`60
`
`I
`90
`
`I
`I
`I
`120 150 180
`
`GENERATOR PHASE SHIFT (DEGREES)
`
`FIG. 8
`
`AL/RESIST SELECTIVITY VS. PHASE SHIFT
`
`SELECTIVITY
`
`3.3 1 l
`
`3.2
`
`3.1
`
`3.0 -~
`
`2.9 —-
`
`I
`I
`2.8
`—90 -60 -30
`
`0
`
`I
`0
`
`I
`30
`
`‘r
`60
`
`I
`90
`
`I
`I
`I
`120 150 180
`
`GENERATOR PHASE SHIFI' (DEGREES)
`
`FIG. 9
`
`Exhibit 2002
`IPR2017-0391
`
`

`

`U.S. Patent
`
`Oct. 20, 1998
`
`Sheet 9 0f 11
`
`5,824,606
`
`REMAINING PHOTORESIST (CENTER) VS. PHASE SHIFT
`
`
`
`
`
`RESIST THICKNESS (uM)
`
`
`
`
`
`RESIST THICKNESS (uM)
`
`0.75 ~
`
`0.71 '
`
`O.69 -
`
`0.67 4h
`
`0.65
`
`I
`—60
`
`I
`-3O
`
`0
`
`I
`0
`
`0
`
`I
`
`I
`
`I
`90
`
`I
`I
`I
`120 150 ‘I80
`
`GENERATOR PHASE SHIFT (DEGREES)
`
`FIG. 1 0
`
`REMAINING PHOTORESIST (EDGEI) VS. PHASE SHIFT
`
`0.78 I
`
`0.73 -
`
`0.58
`
`I
`
`I
`-30
`
`I
`0
`
`I
`3O
`
`I
`6O
`
`I
`90
`
`I
`I
`I
`‘I20 150 180
`
`GENERATOR PHASE SHIFI' (DEGREES)
`
`FIG. 11
`
`Exhibit 2002
`IPR2017-0391
`
`

`

`U.S. Patent
`
`Oct.20,1998
`
`Sheet 10 0f 11
`
`5,824,606
`
`CD (CENTER) VS. PHASE SHIFT
`
`0.85 -
`
`0
`
`0.8 0
`
`3
`EL
`C]
`O
`
`D
`
`o
`
`u
`
`0.75
`-90
`
`i
`-60
`
`I
`-3O
`
`i
`0
`
`T
`30
`
`i
`60
`
`‘I
`90
`
`T
`‘I
`i
`120 150 180
`
`GENERATOR PHASE SHIFT (DEGREES)
`
`CD (EDGE) VS. PHASE SHIFT
`
`0.85 -—
`
`0
`
`0
`
`g
`3
`O
`O
`
`0.8 -
`
`u
`0
`
`G
`
`0.7 ——
`
`0.65
`-90
`
`%
`-6O
`
`l
`-30
`
`l
`0
`
`i
`3O
`
`%
`6O
`
`i
`90
`
`I‘
`l
`i
`120 150 180
`
`o
`
`GENERATOR PHASE SHIFT (DEGREES)
`
`FIG. 13
`
`Exhibit 2002
`IPR2017-0391
`
`

`

`U.S. Patent
`
`Oct.20,1998
`
`Sheet 11 0f 11
`
`5,824,606
`
`500 -/
`
`PRE-ETCH PROCESSING
`
`_/
`502
`
`CONTROLLING PHASE
`DIFFERENCE BETWEEN PHASES
`OF RF SIGNALS PRovIDED BY
`RF POWER SUPPLIES
`
`v
`
`504 / ETCH AT LEAST A PORTION
`OF LAYER STACK
`
`\
`
`506 -/
`
`POST-ETCH PROCESSING
`
`FIG. 14
`
`Exhibit 2002
`IPR2017-0391
`
`

`

`1
`METHODS AND APPARATUSES FOR
`CONTROLLING PHASE DIFFERENCE IN
`PLASMA PROCESSING SYSTEMS
`
`BACKGROUND OF THE INVENTION
`
`10
`
`15
`
`25
`
`35
`
`45
`
`55
`
`The present invention relates to methods and apparatuses
`for inducing plasma in plasma enhanced processing systems,
`Which are typically used in semiconductor fabrication. More
`speci?cally, the invention relates to methods and appara
`tuses for controlling the phase shift betWeen generators in
`plasma processing systems to achieve desired process
`results.
`Plasma-enhanced semiconductor processes for etching,
`oxidation, anodiZation, chemical vapor deposition (CVD),
`or the like are knoWn. For illustration purposes, FIG. 1
`shoWs a chemical etch reactor 100, representing a plasma
`generating system Which utiliZes an inductive coil for
`plasma generation. Reactor 100 includes coil system 102
`and chamber 124. Coil system 102 includes a coil element
`106, Which is excited by a radio frequency generator 110.
`Coil element 106 is coupled to a matching circuit 108 for
`matching the impedance of coil element 106 to that of radio
`frequency generator 110. The matching of the impedances
`permits radio frequency generator 110 to ef?ciently deliver
`poWer to coil element 106. To provide a path to ground, the
`chamber Wall of chamber 124 is typically grounded.
`Alternatively, the ground path may be provided through the
`loWer electrode, e.g., a chuck 128 of FIG. 1, When the
`plasma is con?ned.
`Within chamber 124, there typically exists a shoWer head
`126. ShoWer head 126 is shoWn disposed above a chuck 128
`and Wafer 134, Which is supported by chuck 128. Chuck 128
`acts as a second electrode and is preferably biased by its
`independent radio frequency circuit 120 via a matching
`netWork 122. It should be borne in mind that the components
`of FIG. 1, as Well as of other ?gures herein, are shoWn only
`representatively for ease of illustration and to facilitate
`discussion. In actuality, coil element 106 and match 108 are
`typically disposed proximate to chamber 124 While RF
`generator 110 may be placed in any reasonable location.
`ShoWer head 126 represents the apparatus for dispensing
`etchant or deposition materials onto Wafer 134. ShoWer head
`126 preferably includes a plurality of holes for releasing
`gaseous source materials (typically around the periphery
`edge of shoWer head 126) into the RF-induced plasma
`region betWeen itself and Wafer 134 during operation. In one
`embodiment, shoWer head 126 is made of quartZ although it
`may also be made of other suitable materials and may be left
`either electrically ?oating or grounded.
`To provide poWer to the plasma etch system 100, gen
`erators 110 and 120 are typically driven at a given RF
`frequency. To ensure that both generators deliver poWer at
`the same frequency, they may be frequency-locked in a
`master-and-slave con?guration. For example, loWer (bias)
`generator 120 may be designated the master, and the fre
`quency of the upper (coil) generator 110 may slaved to that
`of master generator 120 (or vice versa). Frequency locking
`may be achieved by any conventional technique, including,
`e.g., disabling the frequency-generating crystal in the slave
`generator and employing the frequency-generating crystal in
`the master generator to drive both the master and slave
`generators.
`While the con?guration of the tWo generators in a master
`and-slave con?guration enables both generators to deliver
`poWer at the same RF frequency, such a con?guration does
`not guarantee that poWer Will be delivered by the two
`
`5,824,606
`
`2
`generators at the same phase. Aphase difference may arise
`due to factors internal to the generators themselves or due to
`system parameters such as the difference in the lengths of the
`cables that couple the generators to their respective elec
`trodes. It is discovered that the phase difference may give
`rise to undesirable or unexpected process and electrical
`characteristics, Which may lead to uncertain consequences
`on the process results.
`In vieW of the foregoing, What is desired is methods and
`apparatuses for controlling the phase difference betWeen
`master-and-slave con?gured RF generators that are
`employed to deliver poWer to plasma processing systems.
`
`SUMMARY OF THE INVENTION
`
`The invention relates, in one embodiment, to a plasma
`processing system for generating plasma for use in semi
`conductor fabrication. The plasma processing chamber has a
`?rst radio frequency (RF) poWer source for outputting a ?rst
`RF signal to a ?rst electrode and a second RF poWer source
`for outputting a second RF signal to a second electrode. The
`second RF poWer source is coupled to the ?rst RF poWer
`source as a slave RF poWer source in a master-and-slave
`con?guration. The plasma processing system includes a
`control circuit, Which includes a ?rst sensor circuit coupled
`to the ?rst electrode for detecting a phase of the ?rst RF
`signal and a second sensor circuit coupled to the second
`electrode for detecting a phase of the second RF signal.
`The plasma processing system further includes a mixer
`circuit coupled to the ?rst sensor circuit and the second
`sensor circuit for detecting a phase difference betWeen the
`?rst RF signal and the second RF signal and for outputting
`a ?rst signal representing the phase difference. There is
`further included a phase servo circuit coupled to the second
`RF poWer source and the mixer circuit. The phase servo
`circuit outputs, responsive to the ?rst signal and a phase
`control set point signal, a control signal to the second RF
`poWer source for modifying a phase of the second RF signal,
`thereby causing the phase difference to approximate a phase
`difference value represented by the phase control set point
`signal.
`In another embodiment, the invention relates to a method
`in a plasma processing system for modifying a phase dif
`ference betWeen a ?rst radio frequency (RF) signal and a
`second RF signal. The ?rst RF signal is supplied by a ?rst
`RF poWer source to a ?rst electrode and the second RF
`signal is supplied by a second RF poWer source to a second
`electrode of a plasma processing system. The second RF
`poWer source is coupled to the ?rst RF poWer source as a
`slave RF poWer source in a master-and-slave con?guration.
`The method includes the step of ascertaining a phase dif
`ference betWeen a phase of the ?rst RF signal and a phase
`of the second RF signal. The method further includes the
`step of comparing the phase difference With a phase control
`set point signal to output a control signal to the second RF
`poWer source, Whereby the second RF poWer source, respon
`sive to the control signal, modi?es the phase of the second
`RF signal to cause the phase difference to approximate a
`phase difference value represented by the phase control set
`point signal.
`These and other advantages of the present invention Will
`become apparent upon reading the folloWing detailed
`descriptions and studying the various ?gures of the draW
`1ngs.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 shoWs a typical plasma generating system.
`
`Exhibit 2002
`IPR2017-0391
`
`

`

`3
`FIG. 2A is a schematic illustrating, in one embodiment of
`the present invention, the overall control circuit for control
`ling the phase difference betWeen tWo frequency-locked RF
`generators of a plasma processing system.
`FIG. 2B shoWs an implementation of the upper TCP
`match circuit of the control circuit of FIG. 2A.
`FIG. 2C illustrates an implementation of the loWer TCP
`match circuit of the control circuit of FIG. 2A.
`FIG. 2D illustrates an implementation of the dc. bias
`measurement circuit of the control circuit of FIG. 2A.
`FIG. 3 is a graph illustrating, in accordance With one
`aspect of the present invention, the effect of the phase shift
`on the optical amplitude of the 261 nm plasma emission,
`Which is employed to determine the endpoint for the alu
`minum etch.
`FIG. 4 is a graph illustrating, in accordance With one
`aspect of the present invention, the effect of the phase shift
`on the loWer (bias) electrode RF peak-to-peak voltage.
`FIG. 5 is a graph illustrating, in accordance With one
`aspect of the present invention, the effect of the phase shift
`on the Wafer dc. bias voltage.
`FIG. 6A is a graph illustrating, in accordance With one
`aspect of the present invention, the effect of the phase shift
`on the oXide etch rate.
`FIG. 6B is a graph illustrating, in accordance With one
`aspect of the present invention, the effect of the phase shift
`on the remaining oXide thickness.
`FIG. 7 is a graph illustrating, in accordance With one
`aspect of the present invention, the effect of the phase shift
`on the aluminum-to-oXide selectivity.
`FIG. 8 is a graph illustrating, in accordance With one
`aspect of the present invention, the effect of the phase shift
`on the photoresist etch rate.
`FIG. 9 is a graph illustrating, in accordance With one
`aspect of the present invention, the effect of the phase shift
`on the aluminum-to-photoresist selectivity.
`FIGS. 10 and 11 are graphs illustrating, in accordance
`With one aspect of the present invention, the effect of the
`phase shift on the remaining photoresist thickness at the
`center of the Wafer (FIG. 10), and at the edge of the Wafer
`(FIG. 11).
`FIGS. 12 and 13 are graphs illustrating, in accordance
`With one aspect of the present invention, the effect of the
`phase shift on the critical dimension (CD) at the center of the
`Wafer and the edge of the Wafer respectively.
`FIG. 14 shoWs, in accordance With one aspect of the
`present invention, the steps involved in the inventive etch
`process in Which the phase difference betWeen the RF poWer
`supplies are controlled, either actively or passively, to
`achieve the desired process results.
`
`10
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`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`
`55
`
`An invention is described for improving process results
`by controlling the phase difference of the phases of the RF
`signals supplied by the RF poWer supplies of a plasma
`processing system. In the folloWing description, numerous
`speci?c details are set forth in order to provide a thorough
`understanding of the present invention. It Will be obvious,
`hoWever, to one skilled in the art, that the present invention
`may be practiced Without some or- all of these speci?c
`details. In other instances, Well knoWn process steps have
`not been described in detail in order not to unnecessarily
`obscure the present invention.
`
`65
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`5,824,606
`
`4
`FIG. 2A is a schematic illustrating, in one embodiment of
`the present invention, the overall control circuit for control
`ling the phase difference betWeen tWo frequency-locked
`generators of a plasma processing system. In FIG. 2A, RF
`generators 402 and 404 are arranged in a master-and-slave
`con?guration With RF generator 402 acting as the reference
`generator. PoWer to the plasma in a plasma processing
`chamber 406 are delivered by these tWo RF generators 402
`and 404 through match circuits 408 and 410, respectively. It
`should be noted that although the chuck RF generator, e.g.,
`RF generator 402, is designated the master generator in FIG.
`2A, the invention applies equally Well When the RF genera
`tor associated With the upper electrode, e.g., RF generator
`404, is designated the master. Further, although the upper
`electrode 412 is shoWn having an Archimedes spiral coil in
`FIG. 2A, other suitable electrodes may Well be employed to
`generate plasma Within the plasma processing chamber. One
`end of the coil may be isolated from ground, e.g., through a
`transformer, or grounded.
`To ascertain the phase of the RF signal supplied to coil
`412, a sensor 414 is coupled to one end of coil 412. Sensor
`414 is preferably disposed betWeen coil 412 and match
`netWork 410 to avoid the effects of the tuning netWorks that
`are used for impedance matching. LikeWise, a sensor 416 is
`preferably coupled betWeen chuck electrode 418 and match
`circuit 408 to ascertain the phase of the RF signal supplied
`to chuck electrode 418.
`The outputs of sensors 414 and 416 are input into a miXer
`circuit 420, Which may be implemented by any one of the
`conventional miXer circuit designs. The output of miXer
`circuit 420, representing the feedback signal that is propor
`tional to the phase difference betWeen the phases of the RF
`signals detected by sensors 414 and 416, is then input into
`a phase servo circuit 422. When the Phase/Bias select
`control signal 423 is set to phase control, phase servo circuit
`422, Which may be implemented by an error ampli?er or any
`number of knoWn phase servo circuit designs, compares the
`feedback signal from miXer circuit 420 With a phase control
`set point signal 424 to output a control signal 430 to the slave
`generator, e.g., RF generator 404 in FIG. 2A. Responsive to
`control signal 430, the slave generator then modi?es its
`phase, thereby causing the phase difference betWeen the
`phases of the RF signals detected by sensors 414 and 416 to
`substantially match the value speci?ed by phase control set
`point signal 424.
`In one embodiment, phase control set point value 424 may
`represent a prede?ned value to facilitate system matching,
`i.e., to ensure that the difference betWeen the phases of the
`RF signals supplied to the upper electrode and loWer elec
`trode is substantially the same from machine to machine.
`The inventive technique of feedback control to ensure that
`the phase difference conforms to a prede?ned value is
`referred to herein as passive control of the phase difference.
`When the phase difference is passively controlled, it is
`possible to ensure that the phase difference betWeen the
`phases of the RF signals Will stay substantially constant
`across different systems irrespective of system parameters,
`e.g., the placement of the RF generators relative to the
`plasma processing chamber.
`In another embodiment, phase control set point value 424
`may represent a user-variable value for actively controlling
`the phase difference betWeen the phases of the RF signals to
`achieve desired process results. The inventive technique of
`actively modifying the phase difference to achieve speci?c
`desired process results is referred to herein as active control
`of the phase difference. By Way of eXample, a user may
`specify that the RF signal supplied to the upper electrode
`
`Exhibit 2002
`IPR2017-0391
`
`

`

`5,824,606
`
`5
`lead the RF signal supplied to the lower electrode by 180°
`to maximize aluminum-to-photoresist selectivity during an
`aluminum etch step (the effect of the phase difference on the
`aluminum-to-photoresist selectivity is illustrated in a sub
`sequent FIG. 9 herein). As a further example, the user may
`specify that the RF poWer supplies deliver their poWer in
`phase to maximiZe the etch rate during an oxide etch step
`(FIG. 6A). Other examples are readily apparent to those
`skilled in the art upon revieWing the ?gures and the disclo
`sure herein.
`In another embodiment, either the chuck’s RF peak-to
`peak ac. voltage or the Wafer’s dc. voltage may be used as
`a feedback signal to facilitate control of either of those tWo
`values by changing the phase difference. With reference to
`FIG. 2A, an a.c./d.c. bias measurement circuit 440
`represents, for ease of illustration, the circuit for measuring
`either the chuck’s RF peak-to-peak ac. voltage or the
`Wafer’s dc. voltage (depending on the embodiment). By
`Way of example, if the chuck employs mechanical clamping,
`a.c./d.c. bias measurement circuit 440 may represent a dc.
`bias measurement circuit. On the other hand, if the chuck is
`an electrostatic chuck, a.c./d.c. bias measurement circuit 440
`may represent either a dc. bias measurement circuit or one
`that measures the chuck’s RF peak-to-peak ac. voltage.
`The chuck’s RF peak-to-peak ac. voltage may be mea
`sured using a voltage probe or any other conventional
`technique. The Wafer’s dc. voltage may be sensed by, for
`example, employing a probe inside chamber 406 to sense the
`state of the plasma Within chamber 406, or by inferring it
`from the chuck’s RF peak-to-peak ac. voltage itself. For
`further information regarding a method of inferring the
`Wafer’s dc. bias from the chuck’s RF peak-to-peak ac.
`voltage, reference may be made to the commonly-assigned,
`co-pending patent applications entitled “Dynamic Feedback
`Electrostatic Chuck,” (Attorney’s Docket No. P169/
`LAM1P006) and “Voltage Controller for Electrostatic
`Chuck of Vacuum Plasma Processors” by Neil Benjamin,
`Seyed Jafar Jafarian-Tehrani, and Max Artussi (Attorney’s
`Docket No. 2328-016), both ?led on even date, and incor
`porated herein by reference.
`The signal output by a.c./d.c. bias measurement circuit
`440 is then input into a peak bias control circuit 442. Peak
`bias control circuit 442 represents the circuit for comparing
`the signal output by a.c./d.c. bias measurement circuit 440
`With a user-input bias set point signal 444 and for outputting
`an error signal 446. Responsive to this error signal, phase
`servo circuit 422 then modi?es control signal 430, thereby
`modifying the phase difference betWeen the RF signals
`supplied by the tWo RF generators and indirectly modifying
`either chuck’s RF peak-to-peak ac. voltage or the Wafer’s
`dc. bias voltage (depending on the implementation of ac/dc
`bias measurement circuit 440) until it matches the bias set
`point signal 444.
`It is contemplated that the signal output by a.c./d.c. bias
`measurement circuit 440 may be monitored by an appropri
`ate logic circuit to alloW the user to, for example, determine
`the phase difference that results in a speci?c value of chuck’s
`RF peak-to-peak ac. voltage (or Wafer’s dc. bias voltage).
`By Way of example, the phase of the slave generator may be
`modi?ed While monitoring the value output by a.c./d.c. bias
`measurement circuit 440 to ascertain the phase difference
`value that results in, e.g., the highest or loWest chuck’s RF
`peak-to-peak ac. voltage (or Wafer’s dc. bias voltage).
`Since these speci?c values of the chuck’s RF peak-to-peak
`ac. voltage (or the Wafer’s dc. bias voltage) are directly
`related to speci?c process characteristics, the user may then
`employ the ascertained phase difference as an input into
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`phase servo circuit 422 to ensure that the desired process
`results can be obtained more reliably and consistently.
`It Will be apparent to those skilled in the art that the
`inventive control circuit does not have to include all the
`components shoWn in FIG. 2A and may include essentially
`of sensors 414 and 416, mixer circuit 420, and phase servo
`circuit 422. With these circuit blocks, the detection of the
`phase difference betWeen the RF signals supplied by the RF
`poWer supplies and the modi?cation of that phase difference
`are facilitated. If it is desired to also modify the phase
`difference to achieve a speci?c RF peak-to-peak ac. voltage
`set point or a speci?c Wafer dc. voltage set point, the control
`circuit may include a.c./d.c. bias measurement circuit 440
`and peak bias control circuit 442 of FIG. 2A.
`It should be noted that sensor 414 may, in one
`embodiment, be disposed betWeen match circuit 410 and RF
`generator 404. Analogously, sensor 416 may be disposed
`betWeen match circuit 408 and RF generator 402 in one
`embodiment. Match circuits 408 and 410 may be imple
`mented by any number of conventional match circuits. FIG.
`2B shoWs an implementation of upper TCP match circuit
`410 that has been found to be suitable. In FIG. 2B, capacitor
`Cs resonates the inductance of the TCP coil. Capacitor CP
`transforms the load impedance to match the source imped
`ance of the RF poWer source, Which is typically about 50 Q.
`Inductors LP and Ls are primary and secondary inductances
`of the match transformer. The values of these inductances LP
`and Ls depend on the coil siZe and the coupling factor
`betWeen the coil and the plasma. One version of match
`circuit 410, knoWn by its part number 853-031685-001, is
`available from the aforementioned Lam Research Corp.
`FIG. 2C illustrates an implementation of loWer TCP
`match circuit 408. In FIG. 2C, variable inductor Ls’ is
`employed to resonate the load. Variable coupling factor K
`transforms the load to the proper impedance to maximiZe
`poWer delivery by the RF generator. One version of match
`circuit 408, knoWn by its part number 853-015130-002, is
`available from the aforementioned Lam Research Corp.
`FIG. 2D illustrates a dc. bias measurement circuit that is
`suitable for implementing a.c./d.c. bias measurement circuit
`440. In FIG. 2D, the chuck’s RF signal is sensed through a
`plurality of resistors 460, Which provides a high impedance
`to ground to limit amount of RF current draWn. In one
`embodiment, there are ?ve resistors 460 in series to reduce
`the capacitive division effect of the dc. bias measurement
`circuit. Resistors 470 and 472 form a resistor netWork for
`scaling doWn the signal received through the plurality of
`resistors 460. Capacitor 474 is coupled in parallel With
`resistors 470 and 472 to supply a dc. signal on conductor
`476, Which is coupled to the peak bias control circuit, e.g.,
`peak bias control circuit 442 of FIG. 2. One version of the
`dc. bias measurement circuit, knoWn by its part number
`810-017029-001, is available from the aforementioned Lam
`Research Corp.
`In accordance With one aspect of the present invention,
`the effects of the phase shift on process characteristics are
`investigated to determine Whether changes to the phase shift
`impact certain critical process parameters such as the RF
`peak-to-peak voltage on the loWer electrode, the Wafer dc.
`bias, etch rates, aluminum-to-photoresist selectivity, and
`others. As shoWn in the graphs of FIGS. 3 to 13 beloW, it is
`determined that changes in the phase shift betWeen the RF
`signals supplied by the RF generators do indeed impact
`certain critical process parameters. These discoveries but
`tress the conclusion that the ability to achieve reliable,
`consistent process results can be enhanced When the phase
`shift is controlled either passively or actively.
`
`Exhibit 2002
`IPR2017-0391
`
`

`

`7
`In the disclosure that follows, it should be borne in mind
`that the disclosed invention may be practiced in any plasma
`etch systems to etch, among others, the metalliZation layer,
`the oxide layer, or the polysilicon layer. The invention may
`also be practiced, as can be appreciated by those skilled in
`the art, in plasma CVD systems to control ?lm characteris
`tics such as density and/or stress, or in any plasma process
`ing systems, which may be employed for annodiZation,
`oxidation, or the like. To better illustrate the invention and
`to provide one speci?c example, however, details pertaining
`to speci?c systems and materials are disclosed. To achieve
`the results illustrated in subsequent FIGS. 3—13, two
`frequency-locked Advanced Energy 1,250 Watt 13.56 MHZ
`RF generators are con?gured in a master-and-slave con?gu
`ration to provide power to a TCP 9600TM etching system,
`which is available from Lam Research Corporation of
`Fremont, Calif. In this con?guration, the lower (bias) gen
`erator is employed as the master to the upper (TCP) slave
`generator (although the invention applies equally well when
`the upper generator serves as the master).
`To generate the requisite phase shift for the experiments
`pertaining to FIGS. 3—13, an ENI VL400 phase shift con
`troller by ENI, which is a division of Astec America Inc. of
`Rochester, NY, was coupled to both generators to keep the
`lower (bias) generator ?xed and to phase shift the upper
`(TCP) generator relative to the lower generator. To deter
`mine etch rates and selectivities, a patterned wafer from
`SEMATECH of Austin, Tex., was exposed to a partial etch.
`This SEMATECH wafer comprises the following layers:
`photoresist layer, TiN arc (anti-re?ective) layer, metalliZa
`tion layer comprising aluminum-silicon-copper, barrier
`layer comprising titanium, and oxide layer. To determine the
`oxide etch rates, a wafer having thereon patterned thermal
`oxide is employed.
`In the TCP 9600TM plasma processing system, the process
`settings for the experiments related to FIGS. 3—13 are
`approximately as follows:
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`TABLE 1
`
`Power to top electrode (watts)
`Power to bottom electrode (watts)
`Reactor chamber pressure (mTorr)
`C12 ?ow rate (sccm)
`BCl3 ?ow rate (sccm)
`Wafer Temperature (°C.)
`Helium cooling gas (Torr)
`
`400
`100
`5
`62
`18
`50
`12
`
`To determine the impact of the phase shift between the RF
`signals supplied by the master-and-slave con?gured RF
`generators, four different phase shift settings were
`employed: —90° (i.e., the top generator lags the bottom
`generator by 90°), 0° (i.e.