`Us 6,679,981 B1
`(10) Patent N0.:
`
`Pan et al.
`*Jan. 20, 2004
`(45) Date of Patent:
`
`US006679981B1
`
`(54)
`
`INDUCTIVE PLASMA LOOP ENHANCING
`MAGNETRON SPUTTERING
`
`(75)
`
`Inventors: Shaoher X. Pan, San Jose, CA (US);
`-
`--
`.
`giglCHilgi‘s‘iii‘85:11:11yFX‘IrZEéigg (15:),
`.
`'
`’
`’
`(US)> Fuse“ Chem saratogeb CA (Us)
`_
`_
`.
`(73) ASSlgHeei APPIIEd Materlalss 1116-, 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.
`
`This patent is subject to a terminal dis-
`claimer.
`
`(21) Appl. N0.: 09/569,736
`
`(22)
`
`Filed:
`
`May 11,2000
`
`(51)
`
`Int. Cl.7 ......................... C23C 14/34, C23C 16/00,
`H01L 21/00
`............................ 204/298.06; 204/298.16;
`(52) US. Cl.
`204/298.31; 204/298.34; 156/345.35; 156/345.48;
`156/345.49; 118/723 IR
`(58) Field Of Search ....................... 204/298.06, 298.07,
`204/298~16> 298~19> 298~31> 298~33> 29834;
`156/345-35> 345-48> 345-49; 118/723 R,
`723 ME 723 MR 723 E 723 BR 723 I,
`723 IR 723 MP
`
`(56)
`
`_
`References Cited
`U.S. PATENT DOCUMENTS
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`3/1944 Drummond ................. 427/251
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`10/1963 Papp .................... 250/556
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`3,291,715 A * 12/1966 Anderson .............. 204/298.06
`4,431,898 A
`2/1984 Reinberg et al.
`....... 219/121.43
`4,778,561 A
`10/1988 Ghanbari
`..................... 216/70
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`9/1989 Harada et al.
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`4/1992 Borden et al.
`.............. 505/480
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`3/1994 Zarowin et al.
`....... 156/345.35
`5,290,382 A
`111/133:
`SDIililVie 6t al~ ~~~~~~~~ 1191787721341]:
`3922:9333 2
`an ..................
`,
`,
`6/1998 Moore .................. 333/32
`5,770,982 A
`
`..... 204/192.12
`4/1999 Hong et al.
`5,897,752 A *
`
`...... 118/723 R
`9/1999 Shan et al.
`5,948,168 A
`
`12/1999 Shun’Ko ............... 315/111.51
`5,998,933 A
`3/2000 Murzin et al.
`............ 118/723 1
`6,041,735 A
`11/2000 Smith et al.
`........... 219/121.54
`6,150,628 A
`2/2002 Hanawa et al.
`........... 118/723l
`6,348,126 B1 *
`5/2002 Shun’ko ................ 315/111.51
`6,392,351 B1 *
`9/2002 Hanawa et al.
`........... 118/723 I
`6,453,842 B1 *
`FOREIGN PATENT DOCUMENTS
`
`EP
`EP
`WO
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`W0
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`0 546 852
`0 836 218
`99/00823
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`0141650
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`6/1993
`4/1998
`1/1999
`
`Mom
`
`* cited by examiner
`
`Primary Examiner—Rodney G McDonald
`(74) Attorney, Agent, or Firm—Roberts, Abokhair &
`Mardula LLC
`
`ABSTRACT
`(57)
`A plasma reaction chamber, particularly a DC magnetron
`sputter reactor, in which the plasma density and the ioniza-
`tion fraction of the plasma is increased by a plasma inductive
`loop passing through the processing space.Atube has its two
`ends connected to the vacuum chamber on confronting sides
`of the processing space. An RF coil powered by an RF power
`supply is positioned adjacent to the tube outside of the
`chamber and aligned to produce an RF magnetic field
`around the toroidal circumference of the tube such that an
`
`electric field is induced along the tube axis. Thereby, a
`plasma is generated in the tube in a loop circling through the
`processing space.
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`11 Claims, 4 Drawing Sheets
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`TSMC et al. v. Zond, Inc.
`GILLETTE-1013
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`Page 1 of 8
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`TSMC et al. v. Zond, Inc.
`GILLETTE-1013
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`Jan. 20, 2004
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`US 6,679,981 B1
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`Jan. 20, 2004
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`Sheet 3 0f4
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`GILLETTE-1013 / Page 4 of 8
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`Sheet 4 0f4
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`GILLETTE-1013 / Page 5 of 8
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`US 6,679,981 B1
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`1
`INDUCTIVE PLASMA LOOP ENHANCING
`MAGNETRON SPUTTERING
`
`FIELD OF THE INVENTION
`
`The invention relates generally to plasma processing of
`substrates. In particular, the invention relates to a enhancing
`the plasma for processing a substrate, most particularly for
`plasma sputtering a metallic layer on a substrate.
`BACKGROUND ART
`
`The continuing miniaturization of integrated circuits has
`been accomplished in large part by the decreasing sizes of
`the elements of the integrated circuit. At the present time, the
`minimum lateral feature sizes of integrated circuits for
`advanced applications is about 0.25 pm and is being pushed
`rapidly downward to 0.13 pm and even 0.11 pm. At the same
`time, the thickness of inter-level dielectric layers is being
`maintained in the region of about 1 pm. As a result of this
`interaction between shrinking lateral dimension and nearly
`constant vertical dimension, the aspect ratio of the via or
`contact holes interconnecting two levels of the integrated
`circuit is rapidly increasing from 4:1 to 10:1. Filling metal
`into such a high aspect-ratio hole is a major technological
`problem.
`Sputtering or physical vapor deposition (PVD) is the
`favored technology for metal hole filling because of its rapid
`deposition rate and relatively low cost of equipment.
`However, PVD is not inherently suited to filling of deep,
`narrow holes because of its generally ballistic nature and
`nearly isotropic pattern of deposition, which do not foster
`effective filling of the bottom of such high aspect-ratio holes.
`Nonetheless, it has been recognized that deep hole filling by
`PVD can be achieved by ionizing the sputtered atoms and,
`one way or the other, electrically biasing the wafer being
`sputter coated so that the ionized sputtered ions are accel-
`erated towards the wafer in a very anisotropic pattern that
`reaches deeply into the hole.
`At least two methods have been recognized for deep hole
`filling of metals by increasing the ionization fraction of the
`metallic sputtered atoms. One method uses various tech-
`niques to increase the plasma density adjacent to the sput-
`tering target in a diode sputtering reactor and to extend the
`plasma further away from the target. These methods often
`involve either small magnetrons which need to be scanned
`over the target or complexly shaped targets. Furthermore,
`the high ionization fractions are achieved only at lower
`chamber pressures which produces electron temperatures
`typically smaller than that needed to produce a very high
`ionization fraction of sputtered atoms.
`Another method involves inductively coupling RF energy
`into a plasma source region at least somewhat remote from
`the wafer being sputter deposited in a reactor otherwise
`generally configured as a diode reactor. For sputtering, this
`usually involves an inductive coil wrapped around the
`periphery of the processing space between the target and the
`wafer. Such inductive coupling allows a large amount of RF
`power to be coupled into an extended plasma source region.
`The combination of a high-density plasma extending over a
`significant distance and moderate pressures thermalizes the
`sputtered metal atoms and then ionizes them.
`However, inductively coupling RF power into a sputtering
`reactor for depositing a metal presents some fundamental
`problems. If the RF induction coil is located outside the
`chamber, the chamber wall must be dielectric so that it does
`not short out the RF power. Dielectric chamber walls are
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`2
`available, such as of quartz, but such ceramic walls are
`generally poorly suited to the extreme vacuum requirements
`of sputtering, in the neighborhood of 10'8 Torr. Chamber
`walls for sputtering reactors are preferably composed of
`stainless steel, but stainless steel is moderately conductive
`electrically and would tend to short out RF field induced
`across it. Furthermore, sputtering metals such as aluminum
`and copper invariably coats some of the metal onto the
`chamber walls so that even a dielectric wall becomes
`conductive after extended use.
`
`the preferred conventional configuration
`As a result,
`places the RF coil within the vacuum chamber adjacent to
`the source plasma it is generating. For sputtering, the coil is
`usually wrapped around the cylindrical space between the
`target and the wafer being sputter coated. But, such a
`configuration presents inherent problems. The RF coil must
`penetrate the vacuum chamber. More importantly, the RF
`coil dissipates a large amount of RF power and absorbs
`energy from the plasma and must therefore be cooled if its
`temperature is to be maintained below 1000° C. Cooling
`within a high-vacuum chamber is always difficult particu-
`larly when it involves parts that are highly biased electri-
`cally.
`is desired to generate a high density
`it
`Accordingly,
`plasma without placing an inductive coil inside the chamber.
`
`SUMMARY OF THE INVENTION
`
`The invention can be summarized as a plasma reactor,
`more particularly a DC magnetron sputter reactor having a
`negatively biased target, in which one or more tubes external
`to the reactor are connected to pairs of ports disposed across
`the processing space of the reactor. When a plasma is excited
`in the reactor, the plasma extends into the tubes. Each tube
`defines a plasma current loop through the tube and across the
`processing space of the reactor. An RF power source powers
`an inductive coil that is magnetically coupled to the current
`loop within the tube. That is, the inductive coil is a primary
`coil and the tube is a secondary coil of an electrical trans-
`former.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a schematic cross-sectional view of a one
`
`embodiment of a sputter reactor of the invention.
`FIG. 2 is a plan view of the reactor of FIG. 1.
`FIG. 3 is a schematic cross-sectional side view of the
`
`reactor of FIGS. 1 and 2 taken along view line 3—3 of FIG.
`2.
`
`FIG. 4 is an orthographic view of a two-tube embodiment
`of the invention.
`
`FIG. 5 is a schematic representation, generally in plan
`view, of a three-tube embodiment of the invention.
`FIG. 6 is a schematic representation, generally in plan
`view, of a six-tube embodiment of the invention.
`FIG. 7 is a schematic cross-sectional view of an alterna-
`
`tive embodiment of a sputter reactor of the invention using
`a bottom connection.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`
`The invention is based on a conventional DC magnetron
`sputter reactor. As illustrated in the schematic cross-
`sectional view of FIG. 1, the reactor includes a stainless steel
`vacuum chamber 12 that is electrically grounded. Awafer 14
`to be sputter coated is supported on a pedestal 16 which may
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`GILLETTE-1013 / Page 6 of 8
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`US 6,679,981 B1
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`3
`include heating and cooling elements and an electrostatic
`chuck for holding the wafer 14. Advantageously, the ped-
`estal 16 acts as an electrode and is electrically biased by an
`RF electrical source 18 through a matching network 20. A
`target 22 of the material to be sputtered, for example copper,
`is supported on and seal to the chamber 12 through an
`electrical isolator 24. The target 22 is negatively biased by
`a DC power source 26 to a voltage of about —600 VDC. A
`magnetron 28 is positioned in back of the target and pro-
`duces a magnetic field inside the chamber to intensify the
`plasma adjacent
`to the target 22. The magnetron 28 is
`typically rotated about the central axis of the chamber to
`produce more uniform sputtering. A gas source 29 supplies
`a working gas such as argon into chamber, and unillustrated
`vacuum ports and vacuum pump maintain the interior of the
`chamber at a low pressure.
`In conventional operation, the DC voltage applied to the
`target 22 is sufficient to excite the argon into a plasma such
`that
`the positively charged argon ions are energetically
`attracted to the target 22. The energetic argon ions sputter
`target atoms, e.g. copper, from the target 22, and the sput-
`tered atoms traverse the processing space and coat the wafer
`14. If the plasma is intense enough and extends over a
`significant portion of the trajectory of the sputtered atoms, a
`sizable fraction of the atoms become ionized. The illustra-
`tion is simplified and omits certain features such as chamber
`wall shields and means for inserting the wafer 14 into the
`chamber. The features described to this point are all con-
`ventional and well known.
`
`According to the invention, a plasma is inductively gen-
`erated remote from the processing space and the plasma
`forms a current loop passing through the processing space.
`Atube 30 has the bores of its two ends connected into the
`
`interior of the vacuum chamber through ports 32, 34 in the
`chamber wall 12. The illustration shows the tube 30 are
`
`being disposed above the chamber, but as more accurately
`illustrated in the plan view of FIG. 2 and the perpendicularly
`arranged cross-sectioned side view of FIG. 3, the tube length
`can be shortened by placing it fairly close to the outside of
`the cylindrical chamber wall 12. The tube 30 may be
`composed of non-magnetic stainless steel so that it is both a
`good vacuum wall and does not shunt the magnetic field.
`Vacuum-sealing RF isolators 36, 38 are placed between the
`tube 30 and the chamber 12 so as to electrically isolate the
`tube 30 from the chamber wall 12. Alternatively, a single
`isolator in the middle of the tube 30 will interrupt the current
`path in the tube wall.
`An RF coil 40 driven by a second RF source 42 is placed
`closely adjacent to the tube with its winding axis placed
`perpendicularly to the axis of the tube 30 in that vicinity
`such that the magnetic field B generated by the RF coil
`encircles the tube 30 with the result that an electric field
`
`proportional to aB/at (alternatively expressed as 00B, where
`u) is the RF frequency) is generated along the axis of the tube
`30. The frequency of the RF source 42 should be above 10
`kHz, preferably above 1 MHZ, and most preferably is 13.56
`MHZ. When the tube 30 contains a plasma,
`it is highly
`conductive electrically and the tube defines a current path.
`When the interior of the chamber 12 also contains a plasma,
`the current path extends through it
`to complete a low
`impedance loop. This loop acts as the secondary winding of
`a transformer in which the RF coil 40 is the primary
`winding. Thereby, the RF power from the second RF source
`42 is inductively coupled into the plasma at a position well
`exterior of the chamber interior. Amatching network includ-
`ing a variable capacitor 46 and a coupling coil 48 wound
`about the magnetic field B may be used to stabilize the
`plasma within the chamber and tube.
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`Note that this configuration differs from the usual one of
`an inductively coupled plasma in which the RF magnetic
`field is aligned with chamber or tube axis so that a circum-
`ferential electric field is induced inside the chamber. Instead,
`in the apparatus of FIGS. 1—3,
`the RF magnetic field
`circumferentially surrounds the tube to thereby induce an
`axial electric field in the tube. Also, this configuration is
`distinctly different from a remote plasma source (RPS) in
`which a plasma is generated remotely, for example, by
`microwaves or electron cyclotron resonance (ECR) and the
`plasma diffuses from the point of generation to the process-
`ing space. In such lengthy diffusion, it is typical for the
`ionized particles in the plasma to recombine although radi-
`cals usually survive the diffusion time.
`Instead,
`in the
`apparatus of FIGS. 1—3, the RF energy is applied remotely,
`but it electrically drives a ionized plasma loop that circulates
`through the processing space.
`The plasma within the tube is primarily composed of the
`argon working gas, but within the main processing chamber
`it interacts with the metal atoms sputtered from the target to
`create metal ions. It is advantageous to supply the argon
`working gas through the middle portions of the plasma tube
`so that metal atoms and ions are flushed away from the tube
`and do not plate its interior.
`The principle of operation of the apparatus of FIGS. 1—3
`has been demonstrated with a sputter reactor in which the
`target is replaced with a grounded plate connected to the two
`ends of the plasma tube 30, which had an internal diameter
`of 2% inches (7 cm). The chamber is pressurized with 10
`milliTorr of argon. When 1000 W of RF power at 13.56 MHz
`is applied to a two-turn tube coil 40, a bright plasma forms
`in the main processing chamber. Furthermore, the plasma is
`stable and extends over a large portion of the chamber
`between the grounded target plate and the wafer surface. In
`this power range, ambient air cooling of the metal tubing is
`sufficient.
`
`In this experimental arrangement, the magnetic coupling
`between the tube coil 40 and the tube 36 relies only on air
`coupling. The efficiency of coupling could be improved by
`inserting a loop-shaped magnetic transformer core through
`the interior of the tube coil 40 and around the tube 30. Either
`
`the core or the tube could be wrapped around the other
`member for added magnetic coupling.
`The uniformity of the high-density plasma in the process-
`ing chamber can be increased by increasing the number of
`tubes entering the chamber at different azimuthal points. For
`example, as illustrated in the orthographic view of FIG. 4,
`two tubes 50, 52 have their ends connected to four ports
`arranged at 90° about the chamber 12. Each tube 50, 52
`extends around 180° so the two tubes 50, 52 overlap for
`about 90° and are slightly offset vertically to avoid interfer-
`ing with each other. The current paths set by the tubes 50, 52
`within the chamber are thus offset by 90°.
`One advantage of the overlapping portions of the two
`tubes 50,52 is that a single RF coil and source can be
`positioned adjacent to the overlapping portions of the tubes
`50, 52 and simultaneously drive both tubes 50, 52. However,
`the two plasma loops will then be synchronized, and care
`must be taken that an undesired fixed phase difference
`between the two loops may cause the loops to constructively
`or destructively interfere and produce maxima and minima
`of the plasma density in the processing region. If instead
`independent RF power supplies of nominally the same
`frequency drive the two tubes 50, 52, the two current loops
`are uncorrelated on the time scale of the wafer processing,
`thus assuring no interference.
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`GILLETTE-1013 / Page 7 of 8
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`GILLETTE-1013 / Page 7 of 8
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`US 6,679,981 B1
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`5
`Other and more complex plasma circuits are possible. The
`two tubes 50, 52 of FIG. 4 can be connected between
`neighboring ones of the four ports rather than opposed ones.
`Six tubes 54, schematically in FIG. 5, can be connected
`across opposed ones of six ports arranged at 60° intervals
`around the chamber 12. The internal conduction paths 58 are
`overly simplified because they are diffuse and rely strongly
`upon the relative phases of the three plasma loops.
`Alternatively, the tubes 54 can connect neighboring ports 56
`or even next neighboring ports 56. Yet again, six tubes 60,
`illustrated schematically in FIG. 6, can be connected across
`neighboring ones of twelve ports 62 arranged at 300 inter-
`vals around the chamber 12 to produce internal conduction
`paths 64 generally running along the walls of the chamber
`12.
`
`The previous examples have passed the plasma loops
`through the sidewalls of the chamber. Alternatively,
`the
`tubes can enter other walls of the chamber. For example, as
`illustrated in the schematic cross-sectional view of FIG. 7, a
`U-shaped tube 70 may be connected between two ports 72,
`74 on a bottom wall 72 of the chamber beneath the pedestal
`16 and on opposite lateral sides of the pedestal 16. The tube
`coil 40 powered by the RF supply 42 is positioned closely
`adjacent to the bottom portion of the U and induces a plasma
`loop passing through the interior of the chamber 12. With
`proper electrical conditions on the pedestal 16, an internal
`plasma path 78 will extend above the wafer 14, thereby
`forming a large volume of a high-density plasma between
`the wafer 14 and the target 22. As before, this configuration
`may be generalized to multiple tubes.
`The invention is not restricted to sputtering reactors.
`Plasma reactors have been developed for both chemical
`vapor deposition (CVD) and etching that use means such as
`RF inductive coils to increase the plasma density. These
`chambers usually have one or more electrodes configured to
`capacitively couple power, usually RF power, into the cham-
`ber for creating a plasma of the processing gas. This con-
`figuration is referred to generally as a diode reactor. Ceramic
`dielectric windows can be used in these higher-pressure
`operations to pass the RF inductive power (assuming a metal
`is not being deposited), but they still present problems. By
`means of the plasma tubes and loops of the invention, the
`plasma density within the processing area can be increased
`without the need for ceramic walls or domes, and the CVD
`deposition of metal presents much less problem.
`The description above has assumed that semiconductor
`wafers of size 200 to 300 mm are being processed in
`single-wafer chambers. The invention is not so limited. For
`example, flat panel displays are being fabricated with semi-
`conductor fabrication techniques on glass substrates have
`dimensions approach a meter. Very large plasma processing
`chambers are required. Achieving high plasma densities
`throughout large chambers has been a problem. The inven-
`tion allows the use of nearly arbitrarily many plasma tubes
`and RF sources with associated plasma loops distributed
`through the chamber to supplement the plasma density and
`particularly the ionization density.
`The invention advantageously allows standard plasma
`processing chambers to be slightly redesigned with the
`addition of ports for the plasma tubes, and thus permit low
`plasma-density chambers to be readily adapted to high
`plasma-density use.
`What is claimed is:
`
`1. A plasma reaction chamber, comprising:
`a vacuum chamber adapted to accommodate a substrate to
`be processed and having at least one pair of opposed
`ports formed through side walls of the chamber;
`a respective tube connecting each of the pairs of the ports;
`and
`
`6
`a coil adapted for connection to an RF electrical power
`supply and disposed adjacent to the tube to encircle a
`circumference of the tube with an RF magnetic field.
`2. The plasma reaction chamber of claim 1, further
`comprising a diode circuit adapted to induce a plasma in the
`vacuum chamber.
`3. The plasma reaction chamber of claim 1, wherein said
`ports are disposed on sidewalls of said vacuum chamber in
`an area adjacent a surface of a substrate being processed.
`4. The plasma reaction chamber of claim I configured as
`a plasma sputtering reactor.
`5. The plasma reaction chamber of claim I configured as
`a plasma etch reactor.
`6. The plasma reaction chamber of claim I configured as
`a chamber for plasma enhanced chemical vapor deposition.
`7. A plasma reaction chamber comprising:
`a vacuum chamber adapted to accommodate a substrate to
`be processed and having at least one pair of ports
`formed through walls of the chamber;
`a respective tube connecting each of the pairs of the ports;
`an RF electrical power supply;
`a coil adapted for connection to the RF electrical power
`supply and disposed adjacent to the tube to encircle a
`circumference of the tube with an RF magnetic field;
`and
`
`a pedestal having an upper side adapted to support a
`substrate to be processed and wherein the ports are
`disposed on a wall of the vacuum chamber facing a
`bottom side of the pedestal.
`8. A DC magnetron sputtering reactor, comprising:
`a vacuum chamber;
`a pedestal within the chamber for supporting a substrate
`to be sputter coated;
`a target sealed to the chamber comprising a material to be
`sputter coated;
`a magnetron positioned in back of the target;
`a DC power supply connected to the target;
`a tube having two ends connected to the vacuum chamber;
`an inductive coil positioned adjacent
`to the tube and
`disposed to produce a magnetic field encircling the
`tube; and
`an RF power supply connected to the coil;
`wherein the tube has its two ends connected to a side wall
`of the vacuum chamber between the target and the
`pedestal.
`9. The reactor of claim 8, wherein the target is metallic.
`10. The reactor of claim 9, wherein the target principally
`comprises copper.
`11. A DC magnetron sputtering reactor, comprising:
`a vacuum chamber;
`a pedestal within the chamber for supporting a substrate
`to be sputter coated;
`a target sealed to the chamber comprising a material to be
`sputter coated;
`a magnetron positioned in back of the target;
`a DC power supply connected to the target;
`a tube having two ends connected to the vacuum chamber;
`an inductive coil positioned adjacent
`to the tube and
`disposed to produce a magnetic field encircling the
`tube; and
`an RF power supply connected to the coil;
`wherein the tube has its two ends connected to a wall of
`the vacuum chamber on an opposite side of the pedestal
`from the target.
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