(12) Unlted States Patent
`(10) Patent N0.:
`US 6,413,382 B1
`
`Wang et al.
`(45) Date of Patent:
`Jul. 2, 2002
`
`USOO6413382B1
`
`(54) PULSED SPUTTERING WITH A SMALL
`ROTATING MAGNETRON
`
`11/1999 Tanaka .................. 204/192.15
`5,976,327 A
`FOREIGN PATENT DOCUMENTS
`
`(75)
`
`IHVentorSI Wei Wang Santa Clara; Praburam
`Gopalraja, Sunnyvale; Jianming Fu,
`San Jose; Zheng Xu, Foster City, all of
`CA (US)
`
`(73) Assignee: Applied Materials, Inc., Santa Clara,
`CA (us)
`
`W0
`
`W0 00/48226 A1
`
`8/2000
`
`............ H01J/37/34
`
`OTHER PUBLICATIONS
`
`Kouznetsov et al., “A novel pulsed magnetron sputter tech-
`nique utilizing 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
`Filed:
`(22)
`Int. Cl.7 ................................................ C23C 14/35
`(51)
`(52) US. Cl.
`............................ 204/192.12; 204/298.08;
`204/298.17; 204/298.2; 204/298.22
`(58) Field Of Search ....................... 204/192.12 298.08
`204/298.17 298.2 298.22
`’
`’
`
`(56)
`
`References Cited
`
`US. PATENT DOCUMENTS
`5,789,071 A
`8/1998 Sproul et a1.
`............... 428/216
`5,810,982 A
`9/1998 Sellers .................. 204/29808
`
`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% 0f the target area rotating about
`the target center,
`whereby? very high plasma density is produced during the
`pulse adjacent to the area of the magnetron. The power
`@115ng 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.
`
`27 Claims, 4 Drawing Sheets
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`92
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`CONTROLLER
`
`SYNC.
`CONTROL
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`80
`
`
`
`
`
`J
`
`
`L
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`PULSED DC
`SUPPLY
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`GILLETTE 1002
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`GILLETTE 1002
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`

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`US. Patent
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`Jul. 2, 2002
`
`Sheet 1 0f 4
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`US 6,413,382 B1
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`58
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`CONTROLLER
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`
`"Illa”...
`
`IX,
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`92
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`
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`PULSED DC
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`SYNC.
`CONTROL
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`SUPPLY
`
`FIG.
`
`1
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`

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`US. Patent
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`Jul. 2, 2002
`
`Sheet 2 0f 4
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`US 6,413,382 B1
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`60
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`600
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`DEPOSITION 400
`RATE
`(um/min)
`
`200
`
`0
`
`FIG. 3
`
`74
`
`76
`
`Cu°
`
`Cu+
`
`12
`
`16
`
`20
`
`DC TARGET POWER (kW)
`
`

`

`US. Patent
`
`Jul. 2, 2002
`
`Sheet 3 0f 4
`
`US 6,413,382 B1
`
`TARGET
`
`DC
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`POWER
`
`FIG. 4
`
`ROTATION
`
`360°
`
`ANGLE
`
`TARGET
`
`POWER
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`82
`
`82
`
`FIG. 5
`
`

`

`US. Patent
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`Jul. 2, 2002
`
`Sheet 4 0f 4
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`US 6,413,382 B1
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`
`
`TIME
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`

`

`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.
`
`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 difficult 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 flux.
`if a large
`that
`It has been long recognized, however,
`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 films 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 modified but to nonetheless achieve efficient filling
`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, filed 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, filed 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 modifications
`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.
`
`5
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`10
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`15
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`20
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`25
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`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
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`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
`flux integrated over the area of the outer pole is at least 150%
`of that of the inner pole. The magnetic field lines emanating
`from the stronger pole may be decomposed into not only a
`conventional horizontal magnetic field adjacent the target
`face but also a vertical magnetic field extending toward the
`wafer. The vertical field 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, filed 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 field is mostly confined 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 sufficient 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 flux does not easily enter high-aspect
`ratio holes. Furthermore, the neutral flux 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 flux 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 as 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
`
`

`

`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 filling 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 sufficient
`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 first 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
`
`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
`
`10
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`4
`anode for the cathode of the negatively biased target 14. A
`floating 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 flow
`controller 34 to a region in back of the grounded shield 24.
`The gas flows 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
`sufficient 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
`field 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 flux 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 field
`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 flow 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
`figure 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.
`
`

`

`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 "up, 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 significant
`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
`significantly 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 as 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 specified rather than the
`current or voltage pulse widths.
`The ratio of the pulse width to repetition period "cw/1P 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.
`
`5
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`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, filed Mar. 2, 2000
`now US. Pat. No. 6,277,249 discloses a two-step sputtering
`process in which the first step sputters metal with higher
`energy and higher ionization fraction in the first 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 fM 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 ”UM, 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 ”CM and TP 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 ”UM/”UP. The
`condition will be the same for the frequencies fM and fP.
`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.
`
`

`

`US 6,413,382 B1
`
`7
`The on-and-off pulsing represented in the waveforms of
`FIG. 4 can be further improved to benefit 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 PP corresponding to that contemplated
`in FIG. 4. The background level P3 is chosen to exceed the
`minimum power necessary to support a plasma in the
`chamber at the operational pressure. Preferably, the peak
`power PP 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 P3 of 1 kW will typically be sufficient to
`support a plasma with the torpedo magnetron and a 200 mm
`wafer although with little if any actual sputter deposition. As
`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 significant 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
`simplified 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 filter 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 filter 104.
`The time constant of the high-pass filter is preferably chosen
`to fall between the pulse width ”cw and the pulse repetition
`period "up. The time constant of the low-pass filter 102 is
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`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 filter
`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, filed 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 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 with a duty cycle of less than 10%;
`wherein said power supply delivers said pulses braving a
`peak power level rising from a background power
`level, whereby power delivered from said power supply
`does not fill below a finite level between said pulses,
`whereby a plasma is continuously maintained in said
`reactor between said pulses.
`7. The reactor of claim 6, wherein a ratio of said peak
`power level to said finite level is at least 10.
`8. The reactor of claim 7, wherein said ratio is at least 100.
`9. A pulsed magnetron sputter reactor, comprising:
`
`

`

`US 6,413,382 B1
`
`9
`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 positioned at a back of said target;
`an adjustable DC power supply connected to said target
`delivering a selected negative DC voltage;
`a pulsed power supply connected in parallel with said
`adjustable DC power supply and delivering pulses of
`negative voltage with a duty cycle of less than 10%;
`and
`
`a motor for rotating said