(12) United States Patent
`Wang
`
`US006352629B1
`(io) Patent No.: US 6,352,629 Bl
`(45) Date of Patent:
`Mar. 5,2002
`
`(54) COAXIAL ELECTROMAGNET IN A
`MAGNETRON SPUTTERING REACTOR
`
`(75)
`
`Inventor: Wei Wang, Santa Clara, CA (US)
`
`(73) Assignee: Applied Materials, Inc., Santa Clara,
`CA (US)
`
`( * ) Notice: Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(21) Appl. No.: 09/612,861
`Jul. 10, 2000
`(22) Filed:
`Int. Cl.7.................................................. C23C 14/34
`(51)
`(52) U.S. Cl.................................... 204/298.2; 204/298.16
`(58) Field of Search ....................... 204/192.12, 298.08,
`204/298.16, 298.17, 298.18, 298.19, 298.2
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`2/1977 Welch ................... ....... 204/298
`4,006,073 A
`4,853,102 A *
`8/1989 Tateishi et al.......... .. 204/298.16
`4,880,515 A * 11/1989 Yoshikawa et al. .. .. 204/192.12
`5,069,770 A
`12/1991 Glocker ................. .. 204/192.12
`2/1992 Setoyama et al. ... .. 204/298.16
`5,085,755 A
`5,455,197 A * 10/1995 Ghanbari et al....... .... 204/298.2
`5,556,519 A *
`9/1996 Teer ....................... .. 204/192.12
`5,744,011 A
`4/1998 Okubo et al............ .. 204/192.12
`5,795,451 A *
`8/1998 Tan et al................. .... 204/298.2
`5,851,365 A * 12/1998 Scobey .................. .. 204/192.12
`
`EP
`IP
`IP
`
`5,897,752 A * 4/1999 Hong et al................ 204/192.12
`6,179,973 Bl 1/2001 Lai et al.................... 204/192.12
`FOREIGN PATENT DOCUMENTS
`0 691 419 Al 1/1996
`............ C23C/14/35
`.............. 204/298.19
`* 3/1979
`54-37076
`* 12/1982 ............... 204/298.19
`57-207173
`OTHER PUBLICATIONS
`Anders, “Approaches to rid cathodic arc plasma of mac-
`ro-and nanoparticles: a review,” Surface and Coatings Tech­
`nology, vols. 120-121, 1999, pp. 319-330.
`* cited by examiner
`Primary Examiner—Rodney G. McDonald
`(74) Attorney, Agent, or Firm—Charles S. Guenzer
`ABSTRACT
`(57)
`A magnetron sputter reactor capable of ionizing 15% or
`more of the metal atoms sputtered from the target. A small
`magnetron having closed bands of opposed magnetic polar­
`ity is rotated about the center of the target, and a large
`amount of power is applied to the target. Thereby the
`effective power density determined by the magnetron area is
`increased. A DC coil is wrapped around the space between
`the target and the substrate being sputter coated to generate
`an axial magnetic field to guide the metal ions towards the
`substrate. The pedestal electrode supporting the substrate
`may be negatively biased to accelerate the metal ions to deep
`within high aspect-ratio holes.
`
`7 Claims, 1 Drawing Sheet
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`36
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`APPLIED MATERIALS EXHIBIT 1012
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`U.S. Patent
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`Mar. 5, 2002
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`US 6,352,629 Bl
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`FIG. 2
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`CURRENT (A)
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`1
`COAXIAL ELECTROMAGNET IN A
`MAGNETRON SPUTTERING REACTOR
`FIELD OF THE INVENTION
`The invention relates generally to plasma sputtering. In
`particular, the invention relates to auxiliary sources of
`magnetic field in magnetron sputtering.
`BACKGROUND ART
`Magnetron sputtering is a principal method of depositing
`metal onto a semiconductor integrated circuit during its
`fabrication in order to form electrically connections and
`other structures in the integrated circuit. A target is com­
`posed of the metal to be deposited, and ions in a plasma are
`attracted to the target at sufficient energy that target atoms
`are dislodged from the target, that is, sputtered. The sput­
`tered atoms travel generally ballistically toward the wafer
`being sputter coated, and the metal atoms are deposited on
`the wafer in metallic form. Alternatively, the metal atoms
`react with another gas in the plasma, for example, nitrogen,
`to reactively deposit a metal compound on the wafer. Reac­
`tive sputtering is often used to form thin barrier and nucle­
`ation layers of titanium nitride or tantalum nitride on the
`sides of narrow holes.
`DC magnetron sputtering is the most usually practiced
`commercial form of sputtering. The metallic target is biased
`to a negative DC bias in the range of about -400 to
`-600VDC to attract positive ions of the argon working gas
`toward the target to sputter the metal atoms. Usually, the
`sides of the sputter reactor are covered with a shield to
`protect the chamber walls from sputter deposition. The
`shield is usually electrically grounded and thus provides an
`anode in opposition to the target cathode to capacitively
`couple the DC target power into the chamber and its plasma.
`A magnetron having at least a pair of opposed magnetic
`poles is disposed in back of the target to generate a magnetic
`field close to and parallel to the front face of the target. The
`magnetic field traps electrons, and, for charge neutrality in
`the plasma, additional argon ions are attracted into the
`region adjacent to the magnetron to form there a high-
`density plasma. Thereby, the sputtering rate is increased.
`However, conventional sputtering presents challenges in
`the formation of advanced integrated circuits. As mentioned
`above, sputtering is fundamentally a ballistic process having
`an approximate isotropic sputtering pattern that is well
`suited for coating planar surfaces but ill suited for depositing
`metal into the narrow features characteristic of advanced
`integrated circuits. For example, advanced integrated cir­
`cuits include many inter-level vias having aspect ratios of
`5:1 and higher, which need to be coated and filled with
`metal. However, techniques have been developed for draw­
`ing the sputtered atoms deep within the narrow, deep holes
`to coat the bottom and sides and then to fill the hole with
`metal without bridging the hole and thereby forming an
`included void.
`A general technique for sputtering into deep holes is to
`cause the sputtered atoms to be ionized and to additionally
`negatively bias the wafer to cause the positively charged
`sputtered metal atoms to accelerate toward the wafer.
`Thereby, the sputtering pattern becomes anisotropic and
`directed toward the bottom of the holes. A negative self-bias
`naturally develops on an electrically floating pedestal.
`However, for more control, a voltage may be impressed on
`the pedestal. Typically, an RF power supply is coupled to a
`pedestal electrode through a coupling capacitor, and a nega­
`tive DC self-bias voltage develops on the pedestal adjacent
`to the plasma.
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`At least two techniques are available which increase the
`plasma density in the sputtering chamber and thereby
`increase the fraction of ionized sputtered atoms.
`One method, called ionized metal plating (IMP), uses an
`RF inductive coil wrapped around the processing space
`between the target and the wafer to couple RF energy in the
`megahertz frequency range into the processing space. The
`coil generates an axial RF magnetic field in the plasma
`which in turn generates a circumferential electric field at the
`edges of the plasma, thereby coupling energy into the
`plasma in a region remote from the wafer and increasing its
`density and thereby increasing the metal ionization rate. IMP
`sputtering is typically performed at a relatively high argon
`pressure of 50 to 100 milliTorr.
`IMP is very effective at deep hole filing. Its ionization
`fraction can be well above 50%. However, IM Pequipment
`is relatively expensive. Even more importantly,IMP tends to
`be a hot energetic, high pressure process in which a large
`number of argon ions are also accelerated toward the wafer.
`Film quality resulting from IMP is not optimal for all
`applications.
`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 U.S. patent application Ser. No.
`09/546,798, filed Apr. 11, 2000, and by Chiang et al. in U.S.
`patent application Ser. No. 09/414,614, filed Oct. 8, 1999,
`both incorporated herein by reference in their entireties.
`The SIP sputter reactor described in the above cited
`patents is modified from a conventional magnetron sputter
`reactor configured for single-wafer processing. SIP sputter­
`ing uses 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 arc 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 disposed to a side of a center of the
`target and is rotated about the center to provide more
`uniform sputtering and deposition.
`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 magnetic field
`lines emanating from the stronger pole may be decomposed
`into not only a conventional horizontal magnetic field adja­
`cent the target face but also a vertical magnetic field extend­
`ing 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 U.S. patent application Ser. No.
`09/518,180, filed Mar. 2, 2000, 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 polarities disposed behind the facing
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`US 6,352,629 Bl
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`sidewalls of the vault produce 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 asymmetrically sized magnets, the mag­
`netic 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 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 col­
`lapsing. 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 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.
`One method of decreasing the neutral flux relative to the
`ionized flux is to increase the throw of the sputter reactor,
`that is, the spacing between the target and pedestal. For a 200
`mm wafer, a conventional throw may be 190 mm while a
`long throw may be 290 mm. Long throw may be defined as
`a throw that is greater than 125% of the wafer diameter. In
`long throw, the more isotropic neutral flux preferentially
`deposits on the shields while the anisotropic ionized flux is
`not substantially reduced. That is, the neutrals are filtered
`out.
`However, long-throw sputtering has drawbacks when
`combined with SIP sputtering relying upon an unbalanced
`magnetron to project the magnetic field toward the wafer.
`The vertical magnetic component is relatively weak and
`rapidly attenuates away from the target since it necessarily
`returns to the magnetron. It is estimated that for a typical
`unbalanced magnetron producing a 1 kilogauss horizontal
`magnetic field at the target produces only a 10 gauss vertical
`magnetic field 100 mm from the target, and it rapidly
`decreases yet further away. Therefore, an unbalanced mag­
`netron in a long-throw sputter reactor does not provide the
`magnetic plasma support and magnetic guidance close to the
`wafer that is needed to obtain the beneficial results of SIP
`sputtering.
`Another problem arises in SIP sputtering using a strongly
`unbalanced magnetron because the vertical components of
`the magnetic field close to the wafer are invariably non­
`uniform as they are being attracted back toward the mag­
`netron. Such non-uniformity in the magnetic field is bound
`to degrade the uniformity of sputtering across the wafer.
`Also, in SIP+ sputtering with the vaulted target, there is
`relatively little magnetic field extending out of the vault to
`support the plasma and guide the metal ions toward the
`wafer.
`Accordingly, it is desired to provide a better alternative
`for magnetic confinement and guidance of ionized sputtered
`atoms.
`
`SUMMARY OF THE INVENTION
`In a magnetron sputter reactor, a coil is wrapped around
`the processing space between the target and pedestal sup­
`
`4
`porting the substrate being sputter coated. The coil is
`powered, preferably by a DC power supply, to generate an
`axial field in the sputter reactor. The axial magnetic field is
`preferably in the range of 15 to 100 gauss.
`The magnetron preferably is unbalanced with a stronger
`pole surrounding a weaker inner pole of the opposed mag­
`netic polarity. The stronger pole preferably generates a
`magnetic flux parallel to the magnetic flux generated by the
`coaxial DC coil.
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is a schematic cross-sectional view of a sputter
`reactor including a magnetic coil of the invention.
`FIG. 2 is a graph illustrating the dependence of ion flux
`upon applied magnetic field.
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`A first embodiment of a plasma sputtering reactor 10 of
`the invention is illustrated in the schematic cross-section
`view of FIG. 1. A vacuum chamber 12 includes generally
`cylindrical sidewalls 14, which are electrically grounded.
`Typically, unillustrated grounded replaceable shields are
`located inside the sidewalls 14 to protect them from being
`sputter coated, but they act as chamber sidewalls except for
`holding a vacuum. A sputtering target 16 composed of the
`metal to be sputtered is sealed to the chamber 12 through an
`insulator 18. A pedestal electrode 22 supports a wafer 24 to
`be sputter coated in parallel opposition to the target 16.
`A sputtering working gas, preferably argon, is metered
`into the chamber from a gas supply 26 through a mass flow
`controller 28. A vacuum pumping system 30 maintains the
`interior of the chamber 12 at a very low base pressure of
`typically 10-8 Torr or less. During plasma ignition, the argon
`pressure is supplied in an amount producing a chamber
`pressure of approximately 5 milliTorr, but as will be
`explained later the pressure is thereafter decreased. A DC
`power supply 34 negatively biases the target 16 to approxi­
`mately -60 VDC causing the argon working gas to be
`excited into a plasma containing electrons and positive
`argon ions. The positive argon ions arc attracted to the
`negatively biased target 16 and sputter metal atoms from the
`target.
`The invention is particularly useful with SIP sputtering in
`which a small magnetron is supported on an unillustrated
`back plate behind the target 36. An unillustrated motor and
`drive shaft aligned to a central axis 38 rotates the back plate
`and the target about the central axis 38. The chamber 12 and
`target 16 are generally circularly symmetric about the cen­
`tral axis 38. The SIP magnetron 36 includes an inner magnet
`pole 40 of one magnetic polarity and a surrounding outer
`magnet pole 42 of the other magnetic polarity, both sup­
`ported by and magnetically coupled through a magnetic
`yoke 44. In an unbalanced magnetron, the outer pole 42 has
`a total magnetic flux integrated over its area that is larger
`than that produced by the inner pole 40. The opposed
`magnetic poles create a magnetic filed BM inside the cham­
`ber 12 with strong components parallel and close to the face
`of the target 16 to create a high-density plasma there to
`thereby increase the sputtering rate and increase the ioniza­
`tion fraction of the sputtered metal atoms. An RF power
`supply 50, for example, having a frequency of 13.56 MHz
`is connected to the pedestal electrode 22 to create a negative
`self-bias on the wafer 24. The bias attracts the positively
`charged metal atoms across the sheath of the adjacent
`plasma, thereby coating the sides and bottoms of high
`aspect-ratio holes.
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`In SIP sputtering, the magnetron is small and has a high
`magnetic strength and a high amount of DC power is applied
`to the target so that the plasma density rises to above IO10
`cm-3 near the target 16. In the presence of this plasma
`density, a large number of sputtered atoms are ionized into
`positively charged metal ions. The metal ion density is high
`enough that a large number of them are attracted back to the
`target to sputter yet further metal ions. As a result, the metal
`ions can at least partially replace the argon ions as the
`effective working species in the sputtering process. That is,
`the argon pressure can be reduced. The reduced pressure has
`the advantage of reducing scattering and deionization of the
`metal ions. For copper sputtering, under some conditions it
`is possible in a process called sustained self-sputtering (SSS)
`to completely eliminate the argon working gas once the
`plasma has been ignited. For aluminum or tungsten
`sputtering, SSS is not possible, but the argon pressure can be
`substantially reduced from the pressures used in conven­
`tional sputtering, for example, to less than 1 milliTorr.
`According to the invention, an electromagnet 40 is posi­
`tioned around the chamber sidewalls 14 to produce a mag­
`netic field Bc extending generally parallel to the chamber
`axis 38 between the target 16 and the wafer 24. The
`electromagnet 40 is most typically a coil wrapped around the
`sidewalls 14 and supplied with DC power from a power
`source 42. The coil is generally centered about the central
`axis 38 and thus coaxial with the chamber 12 and the target
`16.
`Since the magnetic field of the unbalanced magnetron 36
`is still helpful for confining electrons near the top portion of
`the chamber sidewall, it is preferable that the direction of the
`coil field Bc be generally parallel with the magnetic field
`produced by the outer magnetron pole 42.
`The coil magnetic field Bc. is strong enough to trap
`plasma electrons to produce two beneficial effects. Electron
`loss to the unillustrated grounded shield (or equivalently to
`the grounded chamber sidewall 14) is reduced, thus increas­
`ing the plasma density. Furthermore, the magnetic field lines
`extend toward the wafer 24, and plasma electrons gyrate
`around them in a spiral pattern and travel toward the wafer
`24. The metal ions, even if not trapped by the magnetic field
`lines, follow the plasma electrons toward the wafer 24. The
`effect is to increases the sputtered metal ion flux incident on
`the wafer. The ionized flux is effective at filling deep, narrow
`holes or coating their sides.
`The previously described SIP sputtering relies upon a
`strongly unbalanced magnetron, that is, one having magnetic
`poles of significantly different total strengths, to project the
`magnetic field toward the wafer. The unbalanced approach
`has the disadvantage that the projected magnetic field is
`distinctly non-uniform in the vicinity of the wafer. In
`contrast, the sputter reactor of FIG. 1 does not require a
`strongly unbalanced magnetron to project the magnetic field.
`Instead, the electromagnet 40 projects a substantially
`uniform, axial magnetic field Bc from the target to the wafer
`24.
`Another difficulty with the use of an unbalanced magne­
`tron for projecting the magnetic field is that only the
`unbalanced portion is projected, and this portion must return
`to the back of the magnetron. Such a field rapidly attenuates
`with distance, typically with a dependence of the fourth
`power of distance. Exemplary attenuation is that a 1000
`gauss field is reduced to 10 gauss over 100 mm.
`Furthermore, SIP ionization rates are limited to about 25%.
`The remaining 75% of sputtered metal atoms arc neutral,
`and the wafer biasing is ineffective at directing the neutral
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`component to deep within high-aspect ratio holes. It is
`desirable to filter out the neutral component by extending the
`throw of the sputter reactor, for example, to 290 mm for a
`200 mm wafer. The long throw has the further advantage of
`increasing the center-to-edge uniformity. However, unbal­
`anced magnetrons cannot easily project the magnetic field
`over these increased distances.
`The invention thus reduces the need for an unbalanced
`magnetron. In particular, many of the advantages of SIP
`sputtering using the magnetic coil of the invention can be
`achieved with a small rotatable magnetron having inner and
`outer closed magnetic bands of the same or substantially the
`same magnetic strengths of opposed magnetic polarities.
`Closed magnetrons with a parallel band structure are well
`known and are easily achieved with horseshoe magnets
`arranged in a close shape and providing a strong magnetic
`field between the poles of the horseshoe magnets, as has
`been disclosed by Parker in U.S. Pat. No. 5,242,566 and by
`Tepman in U.S. Pat. No. 5,320,728. However, these mag­
`netrons are large magnetrons, not conforming to the require­
`ment that a SIP magnetron have an encompassing area
`smaller than a circle extending from the target center to the
`periphery of its usable area or, alternatively, that the target
`be divided into two half-spaces separated by a plane passing
`through the central axis and that the magnetron be princi­
`pally disposed in one half-space and not extend into the
`other half-space by more than 15% of the target radius.
`In contrast, the magnetic coil of the invention produces a
`magnetic field that is substantially axially uniform over the
`length of the coil, and even outside the coil the magnetic
`field strength does not diminish precipitously. Accordingly,
`the throw of the sputter reactor can be increased without
`unnecessarily reducing the metal ion flux.
`Okubo et al. in U.S. Pat. No. 5,744,011 have disclosed a
`DC coil wrapped around a large magnetron. However, their
`configuration is predicated on a large stationary magnetron
`so that the combination of magnetron and coil field produces
`a horizontal magnetic field near the substrate being coated.
`In contrast, the coil of the invention produces a vertical
`magnetic field at the wafer, and the field of the magnetron is
`substantially limited to near the target. In quantifiable terms,
`the combined magnetron and coil magnetic field is incident
`at all parts of the wafer at no more than 20° from the normal,
`preferably no more than 10°. Another distinguishing factor
`associated with the normal incident magnetic is that the coil
`of the present invention extends towards the wafer in an area
`at least as close to the pedestal as to the target and preferably
`past the 75% distance of the path from the target to the
`pedestal. Thereby, the coil magnetic field has less opportu­
`nity to deflect as it returns to the outside of the coil. In
`contrast, Okubo et al. place their coil close to the target so
`that the coil field is largely horizontal near the wafer.
`The invention has been tested by wrapping 300 to 400
`turns of electrical wire around the chamber sidewall 14. A
`coil current of 2 A produces an axial magnetic field Bc of
`about 100 gauss.
`A sputter reactor having a copper target and a racetrack
`magnetron of the sort described by Fu et al. was tested with
`such an electromagnet. The target was powered with 35 kW
`of DC power, and the pedestal was biased with 300 W of
`13.56 MHz power with a flow of 5 seem of argon into the
`chamber. The ion current to the pedestal electrode was
`measured as a function of coil current. The results are shown
`in the graph of FIG. 2. A coil current of 1A producing a coil
`field of 50 gauss increases the ion current to the pedestal by
`more than a factor of two. The quoted magnetic fields are
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`measured in the bore of the coil near its center. The central
`axial field may be approximated for a very thin coil as
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`where I is the coil current, N is the number of turns, a is the
`radius of the coil, and z is the axial distance from the coil.
`In the context of sputtering into deep holes, a high ion
`current is preferred. However, a further increase to 2 A and
`100 gauss causes the observed ion current to decrease. It is
`believed the decrease is caused by the axial coil field
`interfering with the electron trapping of the horizontal
`magnetron field. From these results, it becomes apparent that
`for typical SIP magnetrons, the coil field should be greater
`than 15 gauss and less than 100 gauss.
`The DC magnetic coil of the invention advantageously
`differs from the RF coil of an IMP reactor in that it may be
`placed outside of the chamber as long as the chamber and
`shields are composed of non-magnetic materials. In contrast,
`an RF coil such as that used in an inductively coupled IMP
`reactor needs to be placed inside of the chamber and even
`inside of the shield (unless the shield is turned into a Faraday
`shield). Otherwise, the conductive chamber and shield will
`short the RF fields.
`Some of the advantages of the invention can be employed
`by replacing the coil with an annular magnet magnetized
`along its axis or equivalent by a series of axially polarized
`magnets arranged circumferentially about the chamber side­
`walls. However, the coil is more effective at producing a
`uniform magnetic field and can be controlled for different
`values of magnet field.
`It is possible to enjoy many of the advantages of the
`invention with a sub-kilohertz AC powering of the coil,
`specifically a frequency of less than 1 kHz. However, DC
`coil power is best because it is always producing its maxi­
`mum effect with no nulls.
`The magnetic coil of the invention may also be advanta­
`geously applied to a sputter reactor with a vaulted target
`such as that described by Gopalraja et al. for SIP+ sputtering.
`The coil is particularly advantageous for vaulted targets
`since the restrained geometry involved in placing magnets
`on opposed lateral sides of the vault makes strongly unbal­
`anced magnetrons difficult to achieve.
`Although the invention has been described as a substitute
`for an inductively coupled IMP sputter reactor, a coaxial
`magnetic coil of the invention may be combined with such
`an IMP sputter reactor. Unlike the RF magnetic field pro­
`duced by an RF coil, a DC or low-AC magnetic field of the
`invention can deeply penetrate the high density plasma of
`the IMP sputter reactor.
`The invention thus provides additional controls for mag­
`netron sputtering with the addition of a standard and eco­
`nomical coil. The invention has been shown to be effective
`at generating a high ionization fraction of sputtered metal
`atoms useful for deep hole filling.
`What is claimed is:
`1. A sputter reactor, comprising:
`a vacuum chamber having sidewalls;
`a sputtering target sealed to but electrically isolated from
`said sidewalls of said vacuum chamber and configured
`to be electrically biased;
`
`8
`a magnetron principally disposed on one side of a central
`axis of said chamber at a backside of said target,
`rotatable about said axis, and comprising an inner pole
`of a first magnetic polarity and having a first total
`magnetic flux and an outer pole of a second magnetic
`polarity opposite said first magnetic polarity and hav­
`ing a second total magnetic flux larger than said first
`total magnetic flux, said magnetron having an area
`smaller than that of said target and being rotatable
`about a central axis thereof;
`a pedestal for supporting a substrate to be sputter coated
`with material of said target while disposed in opposi­
`tion to said target along said sidewalls; and
`magnetic field means including a coil wrapped around
`said sidewalls and configured to be electrically pow­
`ered to produce a magnetic field extending along said
`central axis in a region between said target and said
`pedestal, having said second magnetic polarity in said
`region, and being incident upon said substrate sup­
`ported by said pedestal at an angle deviating by no
`more than 20° from said central axis.
`2. The sputter reactor of claim 1, further comprising a DC
`power supply connectable to said coil.
`3. The sputter reactor of claim 1, further comprising an
`AC power supply having a frequency of less than 1 kHz
`connectable to said coil.
`4. The sputter reactor of claim 1, wherein said angle is no
`more than 10°.
`5. The sputter reactor of claim 1, wherein said substrate is
`substantially circular and a spacing between said target and
`said pedestal is larger than 125% of a diameter of said
`substrate.
`6. The sputter reactor of claim 1, wherein said inner pole
`is disposed away from said central axis.
`7. A sputter reactor, comprising:
`a vacuum chamber having sidewalls;
`a sputtering target sealed to said sidewalls;
`a magnetron disposed at a back of said target and rotatable
`about a central axis and comprising an inner pole
`producing a magnetic field of a first polarity adjacent to
`a face of said target and an outer pole surrounding said
`inner pole and producing a magnetic field of a second
`polarity adjacent to a face of said target, wherein said
`inner pole is disposed away from said central axis,
`wherein said inner pole produces a first total magnetic
`flux and said outer pole produces a second total mag­
`netic flux larger than said first total magnetic flux;
`a pedestal for supporting a substrate to be sputter coated
`with material of said target while in opposition to said
`target along said sidewalls;
`a coil wrapped about said central axis and extending from
`said target to a distance of at least 75% along a path
`from said target to said pedestal; and
`a DC power supply connectable to said coil;
`wherein said coil and DC power supply create a magnetic
`field of said first polarity in an interior of said coil.
`
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