`
`United States Patent
`Wang et al.
`
`(10) Patent N0.:
`(45) Date 0f Patent:
`
`US 6,413,382 B1
`Jul. 2, 2002
`
`US006413382B1
`
`(54) PULSED SPUTTERING WITHA SMALL
`ROTATING MAGNETRON
`
`(75) Inventors Wei Wang Santa Clara; Praburam
`Gopalraja, Sunnyvale; J ianming Fu,
`San Jose; Zheng Xu, Foster City, all of
`CA (US)
`
`(73) Assignee: Applied Materials, Inc., Santa Clara,
`CA (Us)
`
`5,976,327 A 11/1999 Tanaka ................ .. 204/192.15
`
`FOREIGN PATENT DOCUMENTS
`
`W0
`
`WO 00/48226 A1
`
`8/2000
`
`.......... .. HO1J/37/34
`
`OTHER PUBLICATIONS
`
`KouZnetsov et al., “A novel pulsed magnetron sputter tech
`niqlle ut?iZing Very high target Power densities”, Surface
`and Coatings Technology, vol. 122, 1999, pp. 290—293.
`
`( * ) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`Primary Examiner—Steven H. VerSteeg
`(74) Attorney, Agent, or Firm—Charles S. GuenZer
`(57)
`ABSTRACT
`
`(21) Appl. No.: 09/705,324
`.
`_
`NOV‘ 3’ 2000
`(22) Flled'
`(51) Int. c1.7 .............................................. .. c230 14/35
`(52) US. Cl. .......................... .. 204/192.12; 204/298.08;
`20409817; 204/2982; 20409822
`204/192 12 298 08
`17 29's 2’ 298' 22’
`’
`'
`’
`'
`
`""""""
`
`'
`
`(58) Field of Search
`
`(56)
`
`References Cited
`
`US. PATENT DOCUMENTS
`
`A magnetron sputter reactor having a target that is pulsed
`With a duty cycle of less than 10% and preferably less than
`1% and further having a small magnetron of area less than
`20% of the target area rotating about the target center,
`whereby a Very high Plasma density is Produced during the
`pulse adjacent to the area of the magnetron. The poWer
`pulsing frequency needs to be desynchroniZed from the
`rotation frequency so that the magnetron does not overlie the
`same area of the magnetron during different pulses.
`Advantageously, the poWer pulses are delivered above a DC
`background level sufficient to continue to excite the plasma
`so that no ignition is required for each pulse.
`
`5,789,071 A
`5,810,982 A
`
`8/1998 Sproul et a1. ............. .. 428/216
`9/1998 Sellers ................ .. 204/298.08
`
`27 Claims, 4 Drawing Sheets
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`PULSED DC
`SUPPLY
`
`mm
`
`TSMC-1104
`TSMC v. Zond, Inc.
`Page 1 of 11
`
`
`
`U.S. Patent
`
`Jul. 2, 2002
`
`Sheet 1 0f 4
`
`US 6,413,382 B1
`
`><56
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`SUPPLY
`
`FIG. 1
`
`TSMC-1104 / Page 2 of 11
`
`
`
`U.S. Patent
`
`Jul. 2, 2002
`
`Sheet 2 0f 4
`
`US 6,413,382 B1
`
`62
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`64
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`66
`
`FIG 2
`
`A
`
`600 -
`
`"
`
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`
`DEPOSITION 400 "
`
`RATE
`
`(nm/min)
`
`__
`
`200 -
`
`Cu+
`
`74
`
`76
`
`0
`
`FIG. 3
`
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`
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`:
`:
`20
`16
`12
`DC TARGET POWER (kW)
`
`:
`
`>
`
`TSMC-1104 / Page 3 of 11
`
`
`
`U.S. Patent
`
`Jul. 2, 2002
`
`Sheet 3 0f 4
`
`US 6,413,382 B1
`
`A
`
`—> Tp <—
`
`DC
`TARGET
`POWER
`
`TW
`
`(
`82
`
`(
`82
`
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`
`TIME>
`
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`
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`ANGLE
`
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`
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`POWER
`
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`
`leTm »‘
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`
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`82
`
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`82
`
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`
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`
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`
`>
`
`>
`
`TSMC-1104 / Page 4 of 11
`
`
`
`U.S. Patent
`
`Jul. 2, 2002
`
`Sheet 4 0f 4
`
`US 6,413,382 B1
`
`4,1 'TP [4*
`
`96
`
`‘'‘w
`
`A
`
`Pp
`
`PB
`
`FIG. 6
`
`P
`TIME
`
`14
`
`Z
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`
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`
`104
`
`8
`
`PULSED DC
`SUPPLY
`
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`
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`HPF
`
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`
`L406
`
`FIG. '7
`
`TSMC-1104 / Page 5 of 11
`
`
`
`US 6,413,382 B1
`
`1
`PULSED SPUTTERING WITH A SMALL
`ROTATING MAGNETRON
`FIELD OF THE INVENTION
`The invention relates generally to sputtering of materials.
`In particular, the invention relates to sputtering apparatus
`and a method capable of producing a high fraction of ioniZed
`sputter particles.
`
`2
`In one type of SIP sputtering, the magnetron has unbal
`anced poles, usually a strong outer pole of one magnetic
`polarity surrounding a Weaker inner pole. The total magnetic
`?ux integrated over the area of the outer pole is at least 150%
`of that of the inner pole. The magnetic ?eld lines emanating
`from the stronger pole may be decomposed into not only a
`conventional horiZontal magnetic ?eld adjacent the target
`face but also a vertical magnetic ?eld extending toWard the
`Wafer. The vertical ?eld lines extend the plasma closer
`toWard the Wafer and also guide the metal ions toWard the
`Wafer. Furthermore, the vertical magnetic lines close to the
`chamber Walls act to block the diffusion of electrons from
`the plasma to the grounded shields. The reduced electron
`loss is particularly effective at increasing the plasma density
`and extending the plasma across the processing space.
`Gopalraja et al. disclose another type of SIP sputtering,
`called SIP+ sputtering, in US. patent application Ser. No.
`09/518,180, ?led Mar. 2, 2000noW US. Pat. No. 6,277,249,
`also incorporated herein by reference in its entirety. SIP+
`sputtering relies upon a target having a shape With an
`annular vault facing the Wafer. Magnets of opposed polari
`ties disposed behind the facing sideWalls of the vault pro
`duce a high-density plasma in the vault. The magnets usually
`have a small circumferential extent along the vault sideWalls
`and are rotated about the target center to provide uniform
`sputtering. Although some of the designs use asymmetri
`cally siZed magnets, the magnetic ?eld is mostly con?ned to
`the volume of the vault.
`SIP sputtering may be accomplished Without the use of
`RF inductive coils. The small HDP region produced by a
`small-area SIP magnetron is suf?cient to ioniZe a substantial
`fraction of metal ions, estimated to be betWeen 10 and 25%,
`Which is sufficient to reach into deep holes. Particularly at
`the high ioniZation fraction, the ioniZed sputtered metal
`atoms are attracted back to the targets and sputter yet further
`metal atoms. As a result, the argon Working pressure may be
`reduced Without the plasma collapsing. Therefore, argon
`heating of the Wafer is less of a problem, and there is reduced
`likelihood of the metal ions colliding With argon atoms,
`Which Would both reduce the ion density and randomiZe the
`metal ion sputtering pattern.
`HoWever, SIP sputtering could still be improved. The
`ioniZation fraction is only moderately high. The remaining
`75 to 90% of the sputtered metal atoms are neutral and not
`subject to acceleration toWard the biased Wafer. This gen
`erally isotropic neutral ?ux does not easily enter high-aspect
`ratio holes. Furthermore, the neutral ?ux produces a non
`uniform thickness betWeen the center and the edge of the
`Wafer since the center is subjected to deposition from a
`larger area of the target than does the edge When accounting
`for the Wider neutral ?ux pattern. Further increases in target
`poWer Would increase the ioniZation levels. HoWever, large
`poWer supplies become increasingly costly, and this problem
`Will be exacerbated for 300 mm Wafers. Also, increases in
`poWer applied to the target requires increased target cooling
`if the target is not to melt. For these reasons, it is desired to
`limit the average poWer applied to sputtering targets.
`Short-pulse sputtering is an alternative approach to pro
`ducing a high metal ioniZation fraction in a loW-pressure
`chamber, as described by KouZnetsov et al. in “A novel
`pulsed magnetron sputter technique utiliZing very high tar
`get poWer densities,” Surface and Coating Technology, vol.
`122, 1999, pp. 290—293. This techniques apparently uses a
`stationary magnetron With 50 to 100 ps pulses of DC poWer
`applied to the target With a repetition rate of about 50 HZ,
`that is, a target poWer duty cycle of less than 1%. As a result,
`a relatively modestly siZed pulsed DC poWer supply having
`
`BACKGROUND ART
`Sputtering, alternatively called physical vapor deposition
`(PVD), is the most prevalent method of depositing layers of
`metals and related materials in the fabrication of semicon
`ductor integrated circuits. In particular, the sputtered metals
`are used in forming the many layers of electrical intercon
`nects required in advanced integrated circuits. HoWever,
`advanced integrated circuit structures have via holes con
`necting tWo layers of metalliZation and formed through an
`intermediate dielectric layer. These via holes tend to be
`narroW and deep With aspect ratios of 5:1 and greater in
`advanced circuits. Coating the bottom and sides of these
`holes by sputtering is dif?cult because sputtering is funda
`mentally a ballistic and generally isotropic process in Which
`the bottom of a via hole is shielded from most of an isotropic
`sputtering ?ux.
`It has been long recogniZed, hoWever, that if a large
`fraction of the sputtered particles are ioniZed, the positively
`charged sputtered ions can be accelerated toWards a nega
`tively charged Wafer and reach deep into high aspect-ratio
`holes.
`This approach has long been exploited in high-density
`plasma sputter reactors in Which the ioniZation density of the
`sputtering Working gas, typically argon, is increased to a
`high level by, for example, using inductive RF coils to create
`a remote plasma source. As a result of the high-density
`plasma, a large fraction of the sputtered metal atoms passing
`through the argon plasma are ioniZed and thus can be
`electrically attracted to the biased Wafer support. HoWever,
`the argon pressure needs to be maintained relatively high,
`and the argon ions are also attracted to the Wafer, resulting
`in a hot process. The sputtered ?lms produced by this
`method are not alWays of the best quality.
`A recently developed technology of self-ioniZed plasma
`(SIP) sputtering alloWs plasma sputtering reactors to be only
`slightly modi?ed but to nonetheless achieve efficient ?lling
`of metals into high aspect-ratio holes in a loW-pressure,
`loW-temperature process. This technology has been
`described by Fu et al. in US. patent application Ser. No.
`09/546,798, ?led Apr. 11, 2000, noW issued as US. Pat. No.
`6,306,265, and by Chiang et al. in US. patent application
`Ser. No. 09/414,614, ?led Oct. 8, 1999, both incorporated
`herein by reference in their entireties. An earlier form of the
`former reference has been published as PCT publication WO
`00/48226 on Aug. 17, 2000.
`The SIP sputter reactor employs a variety of modi?cations
`to a fairly conventional capacitively coupled magnetron
`sputter reactor to generate a high-density plasma adjacent to
`the target and to extend the plasma and guide the metal ions
`toWard the Wafer. Relatively high amounts of DC poWer are
`applied to the target, for example, 20 to 40 kW for a chamber
`designed for 200 mm Wafers. Furthermore, the magnetron
`has a relatively small area so that the target poWer is
`concentrated in the smaller area of the magnetron, thus
`increasing the poWer density supplied to the HDP region
`adjacent the magnetron. The small-area magnetron is dis
`posed to a side of a center of the target and is rotated about
`the center to provide more uniform sputtering and deposi
`tion.
`
`10
`
`15
`
`20
`
`25
`
`30
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`35
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`40
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`45
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`50
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`55
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`60
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`65
`
`TSMC-1104 / Page 6 of 11
`
`
`
`US 6,413,382 B1
`
`3
`an average power capability of the order of tens of kilowatts
`can deliver peak poWer of up to 2.4 MW. KouZnetsov et al.
`have shoWn effective hole ?lling With a peak poWer density
`of 2.8 kW/cm2. HoWever, the favorable results shoWn by
`KouZnetsov et al. have apparently been accomplished With
`a target having a diameter of 150 mm. Such a target siZe is
`adequate for 100 mm Wafers, but considerably smaller than
`the siZe required for 200 mm or 300 mm Wafers. When the
`poWer supplies are scaled up for the larger area targets
`required for the larger Wafers noW of commercial interest,
`again the siZe of the poWer supply becomes an issue.
`SWitching of large amounts of poWer is both costly and
`operationally disadvantageous.
`
`SUMMARY OF THE INVENTION
`
`A pulsed magnetron sputter reactor in Which a small
`magnetron is rotated about the back of a target and DC
`poWer is delivered to the target in short pulses having duty
`cycles of less than 10%, preferably less than 1%. Thereby,
`a high plasma density is achieved adjacent to the magnetron
`during the pulse. The rotation Waveform and the pulse
`Waveform should be desynchroniZed.
`In one variation, the pulses rise from a DC level suf?cient
`to maintain the plasma in the reactor betWeen pulses. The
`pulses preferably have a poWer level at least 10 times the DC
`level, more preferably 100 times, and most preferably 1000
`times for the greatest effect of the invention.
`The level of metal ioniZation can be controlled by varying
`the peak pulse poWer. In the case that pulsed poWer supply
`is limited by the total pulse energy, the peak pulse poWer can
`be controlled by varying the peak pulse Width. In a multi
`step sputtering process, the pulse Width is changed betWeen
`the steps.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a schematic cross-sectional vieW of a magnetron
`sputter reactor of one embodiment of the invention.
`FIG. 2 is a schematic plan vieW of one magnetron usable
`in the reactor of FIG. 1.
`FIG. 3 is a graph illustrating the dependence of the
`deposition rates of neutral and ioniZed copper upon the
`target poWer.
`FIG. 4 is a timing diagram of a ?rst inventive method of
`pulsing the target of the reactor of FIG. 1.
`FIG. 5 is a timing diagram illustrating the relationship
`betWeen magnetron rotation and target pulsing.
`FIG. 6 is a timing diagram of a second inventive method
`of pulsing the target of the reactor of FIG. 1.
`FIG. 7 is an electrical diagram of an embodiment of the
`poWer supplies usable With the timing method of FIG. 6.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`
`10
`
`15
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`The invention applies pulsed DC poWer to a DC plasma
`sputter reactor With a small rotatable magnetron such as the
`SIP (self-ioniZed plasma) reactor 10 illustrated in FIG. 1.
`Most parts of this reactor have already been described by
`Chiang et al. in the previously cited patent application. It
`includes a grounded chamber 12, Which supports a planar
`sputtering target 14 through a dielectric isolator 16. A
`pedestal electrode 18 supports a Wafer 20 to be sputter
`coated in planar opposition to the target 14 across a pro
`cessing region 22. A grounded shield 24 protects the cham
`ber Walls from sputter deposition and also acts as a grounded
`
`60
`
`65
`
`4
`anode for the cathode of the negatively biased target 14. A
`?oating shield 26 supported on a second dielectric isolator
`28 becomes negatively charged in the presence of a high
`density plasma and acts to focus sputtered metal ions
`toWards the Wafer 20. A sputter Working gas such as argon
`is supplied from a gas source 32 through a mass ?oW
`controller 34 to a region in back of the grounded shield 24.
`The gas ?oWs into the processing region 22 through a gap
`formed betWeen the pedestal 18, the grounded shield 24, and
`a clamp ring or plasma focus ring 36 surrounding the
`periphery of the Wafer 20. A vacuum system 38 pumps the
`chamber through a pumping port 40.
`A DC magnetron sputter reactor conventionally biases the
`target 14 to betWeen about —300 to —700VDC to support a
`plasma of the argon Working gas. The negatively biased
`target 14 attracts the positively charged argon ions With
`suf?cient acceleration that they sputter particles from the
`target, and some of them strike the Wafer 20 depositing a
`layer of the material of the target 14. In reactive sputtering,
`for example, of TiN using a titanium target, a reactive gas,
`for example, nitrogen is supplied to the processing space 22
`to react With the sputtered titanium to form TiN on the
`surface of the Wafer 20. A small rotatable magnetron 40 is
`disposed in the back of the target 14 to create a magnetic
`?eld near the face of the target 14 Which traps electrons from
`the plasma to increase the electron density. For charge
`neutrality, the ion density also increases, thus creating a
`region 42 of a high-density plasma (HDP), Which not only
`increases the sputtering rate but also at sufficiently high
`density ioniZes a substantial fraction of the sputtered par
`ticles into positively charged metal ions. To control the
`energy and direction of the metal ions, an RF bias poWer
`supply is connected to the pedestal electrode 18 to create a
`negative DC self-bias on the Wafer 20.
`For SIP sputtering, the magnetron 40 is small and unbal
`anced With a outer magnet 46 of one magnetic polarity
`surrounding an inner magnet 48 of the other polarity. A
`magnetic yoke 50 magnetically couples the tWo backs of the
`tWo magnets 46, 48 as Well as mechanically supports them.
`The total magnetic ?ux of the outer magnet 46 is substan
`tially larger than that of the inner magnet 48, preferably at
`least 50% greater, so that the unbalanced magnetic ?eld
`loops far into the processing space 22, thus enlarging the
`HDP region 42 and guiding the metal ions toWard the Wafer
`20. The magnetron 40 is rotated about a central axis 52 by
`a motor shaft 54 and attached motor 56. The rotation
`frequency fM of the motor 56 and attached magnetron 40 is
`often though not necessarily in the range of 50 to 200rpm.
`The rotation scans the HDP region 42 about the face of the
`target 14 to more evenly erode the target 14 and to produce
`a more uniform sputter coating on the Wafer 20. A comput
`eriZed controller 58 controls the bias poWer supply 44 and
`mass ?oW controller 34, as illustrated, and additionally
`controls the motor 56 and target poWer supply, as Will be
`explained beloW.
`An advantageous magnetron 60 illustrated in the plan
`vieW of FIG. 2 forms the general shape of a torpedo. The
`?gure illustrates the loWer pole faces and the respective
`magnetic polarities of the magnets placed in back of the pole
`faces. The outer magnet assembly of one magnetic polarity
`include a semi-circular band 62 positioned near the target
`periphery, tWo parallel side bands 64, 66 extending parallel
`to a radius of the target, and tWo inclined bands 68, 70
`meeting near but slightly outside of the target center 52,
`about Which the magnetron 60 rotates. The outer magnet
`assembly surrounds a band 72 of the opposite magnetic
`polarity extending along the target radius.
`
`TSMC-1104 / Page 7 of 11
`
`
`
`US 6,413,382 B1
`
`5
`The magnetron 60 is relatively small compared to the
`target, having a total area less than 20% and preferably less
`than 10% of the target. Because the sputtering is concen
`trated the area of the target below the magnetron, the effect
`is to increase the power density on the target by a factor of
`5 or 10 Without using a larger poWer supply.
`It is knoWn that both the sputter deposition rate and the
`ioniZation fraction increase With target poWer. As illustrated
`in the graph of FIG. 3, the deposition rate With the torpedo
`magnetron 60 varies as a function of DC target poWer for
`both copper neutrals, as shoWn by line 74, and for copper
`ions, as shoWn by line 76. Importantly, the ratio of ions to
`neutrals increases from about 25% at 12 kW to 30% at 20
`kW. The linear increase of the ioniZation ratio is expected to
`continue to someWhat higher poWers, but as previously
`mentioned the poWer supply becomes increasingly costly
`and target cooling becomes a problem.
`According to the invention, the target 14 is poWered by
`narroW pulses of negative DC poWer supplied from a pulsed
`DC poWer supply 80, as illustrated in FIG. 1. The pulse form
`is generically represented in the timing diagram of FIG. 4
`and includes a periodic sequence of poWer pulses 82 having
`a pulse Width "cw and a pulse repetition period '51,, Which is
`the inverse of the pulse repetition frequency fP,. The illus
`trated pulse form is idealiZed. Its exact shape depends on the
`design of the pulsed DC poWer supply 80, and signi?cant
`rise times and fall times are expected. A long fall time may
`produce a long tail, but the poWer levels in the tail Will be
`signi?cantly loWer than the peak. Also, in this embodiment,
`each pulse 82 needs to ignite the plasma and maintain it. The
`effective chamber impedance dramatically changes betWeen
`these tWo phases. A typical pulsed poWer supply Will output
`relatively high voltage and almost no current in the ignition
`phase and a loWer voltage and substantial current in the
`maintenance phase. As mentioned by KouZnetsov et al.,
`ignition may require over 50 us.
`The sputtering of the invention increases the achievable
`target peak poWer density over that available in either the
`DC SIP reactor of Fu or the pulsed unrotated reactor of
`KouZnetsov. As a result, the sputtering of the invention
`alloWs for an increase in ioniZation fractions over What is
`otherWise available using realistically siZed poWer supplies.
`The choice of pulse Widths "cw is dictated by consider
`ations of both poWer supply design, radio interference, and
`sputtering process conditions. Typically, it should be at least
`50 us in this embodiment. Its upper limit is dictated mostly
`by the pulse repetition period "up, but it is anticipated that for
`most applications it Will be less than 1 ms, and typically less
`than 200 us is for achieving the greatest effect. The illus
`trated rectangular pulse Widths are idealiZed. Numerical
`values of pulse Widths should be measured as the full Width
`at half maximum. Where chamber impedance is changing,
`the poWer pulse Width is preferably speci?ed rather than the
`current or voltage pulse Widths.
`The ratio of the pulse Width to repetition period "cw/"5P is
`preferably less than 10% and more preferably less than 1%
`to achieve the greatest effect of the invention. This ratio is
`also referred to as the duty cycle. Because most pulsed
`poWer supplies are limited by the average poWer rather than
`peak poWer, a duty cycle of 1% often provides an increase
`of peak pulsed poWer by a factor of 100. That is, peak poWer
`may be over 1 MW using a 10 kW pulsed poWer supply. It
`is anticipated that the copper ioniZation fraction using the
`Torpedo magnetron Will be Well over 80% at these high peak
`poWers.
`It is anticipated that the pulse repetition frequency is best
`maintained around 50 to 500 HZ.
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`6
`HoWever, it has been recogniZed that for some complex
`structures the metal ioniZation fraction should be reduced
`from its maximum possible level so that a controlled fraction
`of sputtered atoms are neutrals. Sometimes, a sputtering
`process may involve multiple steps in the same sputter
`reactor With the ion/neutral fraction and Wafer bias changed
`betWeen the steps. For example, Golparaja et al. in US.
`patent application Ser. No. 09/518,180, ?led Mar. 2, 2000
`now US. Pat. No. 6,277,249 discloses a tWo-step sputtering
`process in Which the ?rst step sputters metal With higher
`energy and higher ioniZation fraction in the ?rst step than in
`the second step. Although the greatest effects of pulsed
`poWer are achieved With duty cycles of less than 10% or 1%,
`for multi-step sputtering, one of the steps may have a higher
`duty cycle to achieve a more conventional level of plasma
`density.
`The control of the ion/neutral fraction can be effected in
`the present invention Without substantial reduction of depo
`sition rate by varying the duty cycle of the target poWer
`While possibly maintaining constant the average target
`poWer. Because a typical pulsed poWer supply is limited by
`the energy delivered by the pulse, an increase of pulse Width
`is usually accompanied by a reduction of peak poWer. The
`selection of pulse Width is another control over the sputter
`ing process.
`The invention requires both the rotation of the magnetron
`at a rotation rate f M and repetitive pulsing of the target at the
`repetition rate fP. In vieW of the small magnetron area and
`the narroW pulse Width, the effect is for a single pulse to
`sputter a single restricted area of the target. Both rates may
`be the same general range. Heretofore, the exact frequency
`for either Was not important. HoWever, for the invention, it
`is important that the motor rotation be desynchroniZed from
`the pulse repetition. In the Worst case, if the tWo rates are the
`exactly the same, for example, synchroniZed to the poWer
`line frequency of 50 or 60 HZ, then all pulses Will sputter the
`same small area of the target. Obviously, this Would produce
`non-uniform target erosion and non-uniform sputter depo
`sition on the Wafer. The same or nearly the same inferior
`result Would occur if either frequency Were exactly a small
`integer multiple of the other.
`Therefore, as illustrated in the timing diagram of FIG. 5,
`the motor rotation angle Waveform 90, characteriZed by a
`rotation period "5M, needs to be desynchroniZed from the
`Waveform of the target pulses 82 characteriZed by a repeti
`tion period "up. This relationship is mathematically expressed
`as "5M and IF being incommensurate, at least for small
`integers. They Will be incommensurate if no integers M and
`P can be found having a ratio M/P equal to ‘CM/‘UP. The
`condition Will be the same for the frequencies fM and fl).
`HoWever, a more practical though approximate Way of
`expressing the condition is that the motor rotation rate fM
`and the pulse repetition rate fP are chosen so that the target
`is pulsed at at least tWenty different angular positions of the
`magnetron as it is rotated about the target center. Therefore,
`the target Will be sputtered about its entire circumference
`With little if any discernible angular erosion pattern devel
`oping.
`Accordingly as shoWn in FIG. 1, a synchroniZation con
`troller 92 controlled by the controller 58 controls the fre
`quencies of the pulsed DC poWer supply 80 and of the motor
`56 so that the tWo remain desynchroniZed. The synchroni
`Zation controller 92 may be implemented as softWare in the
`controller 58. In the case, Where the motor 56 is a stepper
`motor and the pulsed DC supply is pulsed on pulsed com
`mand from the controller 58, the desynchroniZation is
`accomplished by assuring that the tWo pulses do not occur
`on the same repetitive cycle of the controller 58.
`
`TSMC-1104 / Page 8 of 11
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`US 6,413,382 B1
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`20
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`30
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`7
`The on-and-off pulsing represented in the Waveforms of
`FIG. 4 can be further improved to bene?t semiconductor
`processing. Plasma ignition, particularly in plasma sputter
`reactors, has a tendency to generate particles during the
`initial arcing, Which may dislodge large particles from the
`target or chamber. Any die on the Wafer on Which any large
`particle falls is likely to fail, thereby reducing the Wafer
`yield. Also, plasma ignition is an electronically noisy
`process, and it is best not to generate such noise hundreds of
`times a second. Each of the previously described short
`pulses need to ignite the plasma since the target is unpoW
`ered betWeen the pulses.
`Accordingly, it is advantageous to use a target poWer
`Waveform illustrated in FIG. 6 in Which the target is main
`tained at a background poWer level PB betWeen pulses 96
`rising to a peak level P P corresponding to that contemplated
`in FIG. 4. The background level PE is chosen to eXceed the
`minimum poWer necessary to support a plasma in the
`chamber at the operational pressure. Preferably, the peak
`poWer P P is at least 10 times the background poWer PB, more
`preferably at least 100 times, and most preferably 1000
`times to achieve the greatest effect of the invention. A
`background poWer PB of 1 kW Will typically be suf?cient to
`support a plasma With the torpedo magnetron and a 200 mm
`Wafer although With little if any actual sputter deposition. As
`25
`a result, once the plasma has been ignited at the beginning
`of sputtering prior to the illustrated Waveform, no more
`plasma ignition occurs. Instead, the application of the high
`peak poWer PP instead quickly causes the already existing
`plasma to spread and increases the density of the plasma.
`In one mode of operating the reactor, during the back
`ground period, little or no target sputtering is eXpected. The
`SIP reactor is advantageous for a loW-poWer, loW-pressure
`background period since the small rotating SIP magnetron
`can maintain a plasma at loWer poWer and loWer pressure
`than can a larger stationary magnetron. HoWever, it is
`possible to combine highly ioniZed sputtering during the
`pulses With signi?cant neutral sputtering during the back
`ground period.
`Once again, the actual Waveforms Will differ from the
`idealiZed illustrated ones. In particular, a long fall time for
`the pulses Will present a inter-pulse poWer that is much
`loWer than the peak poWer, but may not ever settle to a
`substantial DC level. HoWever, the minimum poWer in the
`inter-pulse period Will not fall beloW a selected DC level.
`The initial plasma ignition needs be performed only once
`and at much loWer poWer levels so that particulates pro
`duced by arcing are much reduced. Further, the chamber
`impedance changes relatively little betWeen the tWo poWer
`levels PB, PP since a plasma alWays eXist in the chamber.
`Therefore, the design of the pulsed DC poWer supply is
`simpli?ed since it does not need to adjust to vastly different
`chamber impedances While handling large amounts of
`poWer.
`The background and pulsed poWer may be generated by
`distinctly different circuitry, as illustrated in FIG. 7. A
`variable DC poWer supply 100 is connected to the target 14
`through a loW-pass ?lter 102 and supplies an essentially
`constant negative voltage to the target 14 corresponding to
`the background poWer PB. The pulsed DC poWer supply 80
`produces a train of negative voltage pulses With an essen
`tially Zero baseline. It is connected to the target 14 in parallel
`to the DC poWer supply 100 through a high-pass ?lter 104.
`The time constant of the high-pass ?lter is preferably chosen
`to fall betWeen the pulse Width "cw and the pulse repetition
`period "up. The time constant of the loW-pass ?lter 102 is
`
`50
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`60
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`8
`chosen to be longer than the pulse repetition period "up.
`Advantageously, the plasma may be ignited by the DC
`poWer supply 100 before the pulsed poWer supply 80 is even
`turned on, thus simplifying the design of the pulsed DC
`poWer supply 80. HoWever, it may then be necessary to
`provide a selectable bypass 106 around the loW-pass ?lter
`102 so that the DC poWer supply 100 can quickly transition
`its output from plasma ignition to plasma maintenance. An
`alternative arrangement uses that output of the DC poWer
`supply 100 as the reference potential for the pulsed poWer
`supply 80, but this arrangement requires careful grounding
`design and complicates the ignition.
`The invention may be applied to other sputter reactors,
`such as one of the SIP+ reactors described by Golparaja et
`al. in Us. patent application Ser. No. 09/518,180, ?led Mar.
`2, 2000 now US. Pat. No. 6,277,249. This reactor includes
`a target having an annular vault formed its surface facing the
`Wafer. In most of the reactors, the magnetron includes
`magnets placed in back of both of the sideWalls of the vault,
`and some portion of the magnetron is scanned around the
`closed path of the vault to create a localiZed region of
`high-density plasma. Accordingly, in the effective area of the
`magnetron is substantially less than the target area.
`The invention thus provides controllable and high plasma
`densities Without the need for excessively large poWer
`supplies. The invention also alloWs controllable metal ion
`iZation fractions While maintaining a high deposition rate.
`What is claimed is:
`1. A pulsed magnetron sputter reactor, comprising:
`a plasma sputter reactor having a target and a pedestal for
`supporting a substrate to be sputter deposited in oppo
`sition to said target;
`a magnetron having an area of less than 20% of the area
`of the target and being rotatable about a back of said
`target; and
`a poWer supply connected to said target and delivering
`pulses of poWer of negative voltage With a duty cycle
`of less than 10%.
`2. The reactor of claim 1, Wherein said duty cycle is less
`than 1%.
`3. The reactor of claim 1, Wherein said pulses have a
`poWer pulse Width of no more than 1ms.
`4. The reactor of claim 3, Wherein said pulse Width is no
`more than 200 us.
`5. The reactor of claim 1, Wherein said magnetron com
`prises a closed outer pole of one magnetic polarity surround
`ing an inner pole of a second magnetic polarity.
`6. A pulsed magnetron sputter reactor, comprising:
`a plasma