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`Samsung Electronics Co., Ltd. v. Demaray LLC
`Samsung Electronic's Exhibit 1012
`Exhibit 1012, Page 1
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`

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`U.S. Patent
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`Mar.5, 2002
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`US 6,352,629 B1
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`4“Os
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`15
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`50G
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`100G
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`ION
`CURRENT
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`5
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`0
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`fhIG. C
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`1
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`CURRENT (A)
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`2
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`Ex. 1012, Page 2
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`Ex. 1012, Page 2
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`

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`US 6,352,629 B1
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`10
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`25
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`1
`COAXIAL ELECTROMAGNETIN A
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`MAGNETRON SPUTTERING REACTOR
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`FIELD OF THE INVENTION
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`The invention relates generally to plasma sputtering. In
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`particular,
`the invention relates to auxiliary sources of
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`magnetic field in magnetron sputtering.
`BACKGROUND ART
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`Magnetronsputtering is a principal method of depositing
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`metal onto a semiconductor integrated circuit during its
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`fabrication in order to form electrically connections and
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`other structures in the integrated circuit. A target is com-
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`posed of the metal to be deposited, and ions in a plasmaare
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`attracted to the target at sufficient energy that target atoms
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`are dislodged from the target, that is, sputtered. The sput-
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`tered atomstravel generally ballistically toward the wafer
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`being sputter coated, and the metal atoms are deposited on
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`the wafer in metallic form. Alternatively, the metal atoms
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`react with another gas in the plasma, for example, nitrogen,
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`to reactively deposit a metal compound on the wafer. Reac-
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`tive sputtering is often used to form thin barrier and nucle-
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`ation layers of titantum nitride or tantalum nitride on the
`sides of narrow holes.
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`DC magnetron sputtering is the most usually practiced
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`commercial form of sputtering. The metallic target is biased
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`to a negative DC bias in the range of about -400 to
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`-600VDC to attract positive ions of the argon working gas
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`toward the target to sputter the metal atoms. Usually, the
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`sides of the sputter reactor are covered with a shield to
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`protect
`the chamber walls from sputter deposition. The
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`shield is usually electrically grounded and thus provides an
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`anode in opposition to the target cathode to capacitively
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`couple the DC target power into the chamberandits plasma.
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`A magnetron having at least a pair of opposed magnetic
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`poles is disposed in back ofthe target to generate a magnetic
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`field close to and parallel to the front face of the target. The
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`magnetic field traps electrons, and, for charge neutrality in
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`the plasma, additional argon ions are attracted into the
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`region adjacent to the magnetron to form there a high-
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`density plasma. Thereby, the sputtering rate is increased.
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`However, conventional sputtering presents challenges in
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`the formation of advanced integrated circuits. As mentioned
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`above, sputtering is fundamentally a ballistic process having
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`an approximate isotropic sputtering pattern that
`is well
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`suited for coating planar surfaces butill suited for depositing
`metal into the narrow features characteristic of advanced
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`integrated circuits. For example, advanced integrated cir-
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`cuits include many inter-level vias having aspect ratios of
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`5:1 and higher, which need to be coated and filled with
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`metal. However, techniques have been developed for draw-
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`ing the sputtered atoms deep within the narrow, deep holes
`to coat the bottom and sides and then to fill the hole with
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`metal without bridging the hole and thereby forming an
`included void.
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`A general technique for sputtering into deep holesis to
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`cause the sputtered atoms to be ionized and to additionally
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`negatively bias the wafer to cause the positively charged
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`sputtered metal atoms to accelerate toward the wafer.
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`Thereby,
`the sputtering pattern becomes anisotropic and
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`directed toward the bottom of the holes. A negative self-bias
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`naturally develops on an electrically floating pedestal.
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`However, for more control, a voltage may be impressed on
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`the pedestal. Typically, an RF power supply is coupled to a
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`pedestal electrode through a coupling capacitor, and a nega-
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`tive DC self-bias voltage develops on the pedestal adjacent
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`to the plasma.
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`2
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`Atleast two techniques are available which increase the
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`plasma density in the sputtering chamber and thereby
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`increase the fraction of ionized sputtered atoms.
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`One method, called ionized metal plating (IMP), uses an
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`RF inductive coil wrapped around the processing space
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`between the target and the wafer to couple RF energy in the
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`megahertz frequency range into the processing space. The
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`coil generates an axial RF magnetic field in the plasma
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`which in turn generates a circumferential electric field at the
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`edges of the plasma,
`thereby coupling energy into the
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`plasma in a region remote from the wafer and increasing its
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`density and thereby increasing the metal ionization rate. IMP
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`sputtering is typically performed at a relatively high argon
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`pressure of 50 to 100 milliTorr.
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`IMPis very effective at deep hole filing. Its ionization
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`fraction can be well above 50%. However, IM Pequipment
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`is relatively expensive. Even more importantly,IMPtends to
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`be a hot energetic, high pressure process in which a large
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`numberof argon ionsare also accelerated toward the wafer.
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`Film quality resulting from IMP is not optimal for all
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`applications.
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`A recently developed technology of self-tonized plasma
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`(SIP) sputtering allows plasma sputtering reactors to be only
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`slightly modified but to nonetheless achieveefficientfilling
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`of metals into high aspect-ratio holes in a low-pressure,
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`low-temperature process. This technology has been
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`described by Fu et al. in U.S. patent application Ser. No.
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`09/546,798,filed Apr. 11, 2000, and by Chianget al. in U.S.
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`patent application Ser. No. 09/414,614, filed Oct. 8, 1999,
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`both incorporated herein by reference in their entireties.
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`The SIP sputter reactor described in the above cited
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`patents is modified from a conventional magnetron sputter
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`reactor configured for single-wafer processing. SIP sputter-
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`ing uses a variety of modifications to a fairly conventional
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`capacitively coupled magnetron sputter reactor to generate a
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`high-density plasma adjacent to the target and to extend the
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`plasma and guide the metal ions toward the wafer. Relatively
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`high amounts of DC power are applied to the target, for
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`example, 20 to 40 kW for a chamber designed for 200 mm
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`wafers. Furthermore, the magnetron has a relatively small
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`area so that the target power is concentrated in the smaller
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`area of the magnetron, thus increasing the power density
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`supplied to the HDP region adjacent the magnetron. The
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`small-area magnetronis disposed to a side of a center of the
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`target and is rotated about
`the center to provide more
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`uniform sputtering and deposition.
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`In one type of SIP sputtering, the magnetron has unbal-
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`anced poles, usually a strong outer pole of one magnetic
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`polarity surrounding a weakerinner pole. The magneticfield
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`lines emanating from the stronger pole may be decomposed
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`into not only a conventional horizontal magnetic field adja-
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`cent the target face but also a vertical magnetic field extend-
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`ing toward the wafer. The vertical field lines extend the
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`plasma closer toward the wafer and also guide the metal ions
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`toward the wafer. Furthermore, the vertical magnetic lines
`close to the chamber walls act to block the diffusion of
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`electrons from the plasma to the grounded shields. The
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`reduced electron loss is particularly effective at increasing
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`the plasma density and extending the plasma across the
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`processing space.
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`Gopalraja et al. disclose another type of SIP sputtering,
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`called SIP* sputtering, in U.S. patent application Ser. No.
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`09/518,180, filed Mar. 2, 2000, also incorporated herein by
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`reference in its entirety. SIP* sputtering relies upon a target
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`having a shape with an annular vault facing the wafer.
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`Magnets of opposed polarities disposed behind the facing
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`Ex. 1012, Page 3
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`Ex. 1012, Page 3
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`

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`SUMMARYOF THE INVENTION
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`In a magnetron sputter reactor, a coil is wrapped around
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`the processing space between the target and pedestal sup-
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`65
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`US 6,352,629 B1
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`3
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`sidewalls of the vault produce a high-density plasmain the
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`vault. The magnets usually have a small circumferential
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`extent along the vault sidewalls and are rotated about the
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`target center to provide uniform sputtering. Although some
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`of the designs use asymmetrically sized magnets, the mag-
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`netic field is mostly confined to the volume of the vault.
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`SIP sputtering may be accomplished without the use of
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`RF inductive coils. The small HDPregion is sufficient to
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`ionize a substantial fraction of metal ions, estimated to be
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`between 10 and 25%, which is sufficient to reach into deep
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`holes. Particularly at the high ionization fraction, the ionized
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`sputtered metal atoms are attracted back to the targets and
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`sputter yet further metal atoms. As a result,
`the argon
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`working pressure may be reduced without the plasma col-
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`lapsing. Therefore, argon heating of the wafer is less of a
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`problem, and there is reduced likelihood of the metal ions
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`colliding with argon atoms, which would both reduce the ion
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`density and randomize the metal ion sputtering pattern.
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`However, SIP sputtering could still be improved. The
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`ionization fraction is only moderately high. The remaining
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`75 to 90% of the sputtered metal atoms are neutral and not
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`subject to acceleration toward the biased wafer. This gen-
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`erally isotropic neutral flux does not easily enter high-aspect
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`ratio holes. Furthermore, the neutral flux produces a non-
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`uniform thickness between the center and the edge of wafer
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`since the center is subjected to deposition from a larger area
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`of the target than does the edge when accounting for the
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`wider neutral flux pattern.
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`One method of decreasing the neutral flux relative to the
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`ionized flux is to increase the throw of the sputter reactor,
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`thatis, the spacing between the target and pedestal. For a 200
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`mm wafer, a conventional throw may be 190 mm while a
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`long throw may be 290 mm. Long throw maybe defined as
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`a throw that is greater than 125% of the wafer diameter. In
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`long throw, the more isotropic neutral flux preferentially
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`deposits on the shields while the anisotropic ionized flux is
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`not substantially reduced. That is, the neutrals are filtered
`out.
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`However,
`long-throw sputtering has drawbacks when
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`combined with SIP sputtering relying upon an unbalanced
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`magnetron to project the magnetic field toward the wafer.
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`The vertical magnetic component is relatively weak and
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`rapidly attenuates away from the target since it necessarily
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`returns to the magnetron. It is estimated that for a typical
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`unbalanced magnetron producing a 1 kilogauss horizontal
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`magneticfield at the target produces only a 10 gaussvertical
`45
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`magnetic field 100 mm from the target, and it rapidly
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`decreases yet further away. Therefore, an unbalanced mag-
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`netron in a long-throw sputter reactor does not provide the
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`magnetic plasma support and magnetic guidancecloseto the
`wafer that is needed to obtain the beneficial results of SIP
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`sputtering.
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`Another problem arises in SIP sputtering using a strongly
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`unbalanced magnetron because the vertical components of
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`the magnetic field close to the wafer are invariably non-
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`uniform as they are being attracted back toward the mag-
`55
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`netron. Such non-uniformity in the magnetic field is bound
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`to degrade the uniformity of sputtering across the wafer.
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`Also, in SIP* sputtering with the vaulted target, there is
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`relatively little magnetic field extending out of the vault to
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`support the plasma and guide the metal ions toward the
`wafer.
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`Accordingly, it is desired to provide a better alternative
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`for magnetic confinement and guidance of ionized sputtered
`atoms.
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`4
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`is
`porting the substrate being sputter coated. The coil
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`powered, preferably by a DC power supply, to generate an
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`axial field in the sputter reactor. The axial magnetic field is
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`preferably in the range of 15 to 100 gauss.
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`The magnetron preferably is unbalanced with a stronger
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`pole surrounding a weaker inner pole of the opposed mag-
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`netic polarity. The stronger pole preferably generates a
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`magnetic flux parallel to the magnetic flux generated by the
`coaxial DC coil.
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`BRIEF DESCRIPTION OF THE DRAWINGS
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`FIG. 1 is a schematic cross-sectional view of a sputter
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`reactor including a magnetic coil of the invention.
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`FIG. 2 is a graph illustrating the dependence of ion flux
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`upon applied magnetic field.
`DETAILED DESCRIPTION OF THE
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`PREFERRED EMBODIMENTS
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`A first embodiment of a plasma sputtering reactor 10 of
`the invention is illustrated in the schematic cross-section
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`view of FIG. 1. A vacuum chamber 12 includes generally
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`cylindrical sidewalls 14, which are electrically grounded.
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`Typically, unillustrated grounded replaceable shields are
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`located inside the sidewalls 14 to protect them from being
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`sputter coated, but they act as chambersidewalls except for
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`holding a vacuum. A sputtering target 16 composed of the
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`metal to be sputtered is sealed to the chamber 12 through an
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`insulator 18. A pedestal electrode 22 supports a wafer 24 to
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`be sputter coated in parallel opposition to the target 16.
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`A sputtering working gas, preferably argon, is metered
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`into the chamber from a gas supply 26 through a mass flow
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`controller 28. A vacuum pumping system 30 maintains the
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`interior of the chamber 12 at a very low base pressure of
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`typically 10-° Torr or less. During plasmaignition, the argon
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`pressure is supplied in an amount producing a chamber
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`pressure of approximately 5 milliTorr, but as will be
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`explained later the pressure is thereafter decreased. A DC
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`powersupply 34 negatively biases the target 16 to approxi-
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`mately -60 VDC causing the argon working gas to be
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`excited into a plasma containing electrons and positive
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`argon ions. The positive argon ions arc attracted to the
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`negatively biased target 16 and sputter metal atoms from the
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`target.
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`The invention is particularly useful with SIP sputtering in
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`which a small magnetron is supported on an unillustrated
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`back plate behind the target 36. An unillustrated motor and
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`drive shaft aligned to a central axis 38 rotates the back plate
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`and the target about the central axis 38. The chamber 12 and
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`target 16 are generally circularly symmetric about the cen-
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`tral axis 38. The SIP magnetron 36 includes an inner magnet
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`pole 40 of one magnetic polarity and a surrounding outer
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`magnet pole 42 of the other magnetic polarity, both sup-
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`ported by and magnetically coupled through a magnetic
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`yoke 44. In an unbalanced magnetron, the outer pole 42 has
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`a total magnetic flux integrated over its area that is larger
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`than that produced by the inner pole 40. The opposed
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`magnetic poles create a magnetic filed B,, inside the cham-
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`ber 12 with strong components parallel and close to the face
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`of the target 16 to create a high-density plasma there to
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`thereby increase the sputtering rate and increase the ioniza-
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`tion fraction of the sputtered metal atoms. An RF power
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`supply 50, for example, having a frequency of 13.56 MHz
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`is connected to the pedestal electrode 22 to create a negative
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`self-bias on the wafer 24. The bias attracts the positively
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`charged metal atoms across the sheath of the adjacent
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`thereby coating the sides and bottoms of high
`plasma,
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`aspect-ratio holes.
`
`Ex. 1012, Page 4
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`Ex. 1012, Page 4
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`

`

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`US 6,352,629 B1
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`10
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`25
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`6
`5
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`is
`component
`to deep within high-aspect ratio holes. It
`In SIP sputtering, the magnetron is small and has a high
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`desirable to filter out the neutral componentby extending the
`magnetic strength and a high amount of DC poweris applied
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`to the target so that the plasma density rises to above 107°
`throw of the sputter reactor, for example, to 290 mm for a
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`cm? near the target 16. In the presence of this plasma
`200 mm wafer. The long throw hasthe further advantage of
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`increasing the center-to-edge uniformity. However, unbal-
`density, a large number of sputtered atoms are ionized into
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`anced magnetrons cannoteasily project the magnetic field
`positively charged metal ions. The metal ion density is high
`over these increased distances.
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`enough that a large numberof them are attracted back to the
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`The invention thus reduces the need for an unbalanced
`target to sputter yet further metal ions. As a result, the metal
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`ions can at least partially replace the argon ions as the
`magnetron. In particular, many of the advantages of SIP
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`effective working species in the sputtering process. That is,
`sputtering using the magnetic coil of the invention can be
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`the argon pressure can be reduced. The reduced pressure has
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`achieved with a small rotatable magnetron having inner and
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`the advantage of reducing scattering and deionization of the
`outer closed magnetic bands of the same or substantially the
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`metal ions. For copper sputtering, under some conditionsit
`same magnetic strengths of opposed magnetic polarities.
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`is possible in a process called sustained self-sputtering (SSS)
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`Closed magnetrons with a parallel band structure are well
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`to completely eliminate the argon working gas once the
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`known and are easily achieved with horseshoe magnets
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`plasma has been ignited. For aluminum or
`tungsten
`arranged in a close shape and providing a strong magnetic
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`sputtering, SSSis not possible, but the argon pressure can be
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`field between the poles of the horseshoe magnets, as has
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`substantially reduced from the pressures used in conven-
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`been disclosed by Parker in U.S. Pat. No. 5,242,566 and by
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`tional sputtering, for example, to less than 1 milliTorr.
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`Tepman in U.S. Pat. No. 5,320,728. However, these mag-
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`netronsare large magnetrons, not conforming to the require-
`According to the invention, an electromagnet40 is posi-
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`that a SIP magnetron have an encompassing area
`tioned around the chambersidewalls 14 to produce a mag-
`ment
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`netic field B, extending generally parallel to the chamber
`smaller than a circle extending from the target center to the
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`periphery of its usable area or, alternatively, that the target
`axis 38 between the target 16 and the wafer 24. The
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`be divided into two half-spaces separated by a plane passing
`electromagnet 40 is most typically a coil wrapped around the
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`through the central axis and that the magnetron be princi-
`sidewalls 14 and supplied with DC power from a power
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`pally disposed in one half-space and not extend into the
`source 42. The coil is generally centered about the central
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`other half-space by more than 15% of the target radius.
`axis 38 and thus coaxial with the chamber 12 andthe target
`16.
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`In contrast, the magnetic coil of the invention produces a
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`magnetic field that is substantially axially uniform over the
`Since the magnetic field of the unbalanced magnetron 36
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`length of the coil, and even outside the coil the magnetic
`is still helpful for confining electrons near the top portion of
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`field strength does not diminish precipitously. Accordingly,
`the chamber sidewall, it is preferable that the direction of the
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`coil field By be generally parallel with the magnetic field
`the throw of the sputter reactor can be increased without
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`unnecessarily reducing the metal ion flux.
`produced by the outer magnetron pole 42.
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`Okuboet al. in U.S. Pat. No. 5,744,011 have disclosed a
`The coil magnetic field By.
`is strong enough to trap
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`DC coil wrapped around a large magnetron. However, their
`plasma electrons to produce two beneficial effects. Electron
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`loss to the unillustrated grounded shield (or equivalently to
`configuration is predicated on a large stationary magnetron
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`the grounded chambersidewall 14) is reduced, thus increas-
`so that the combination of magnetron and coil field produces
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`a horizontal magnetic field near the substrate being coated.
`ing the plasmadensity. Furthermore, the magnetic field lines
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`In contrast, the coil of the invention produces a vertical
`extend toward the wafer 24, and plasma electrons gyrate
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`magnetic field at the wafer, and the field of the magnetron is
`around them in a spiral pattern and travel toward the wafer
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`substantially limited to near the target. In quantifiable terms,
`24. The metal ions, even if not trapped by the magnetic field
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`the combined magnetron and coil magnetic field is incident
`lines, follow the plasma electrons toward the wafer 24. The
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`at all parts of the wafer at no more than 20° from the normal,
`effect is to increases the sputtered metal ion flux incident on
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`preferably no more than 10°. Another distinguishing factor
`the wafer. The ionized fluxis effective atfilling deep, narrow
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`associated with the normal incident magnetic is that the coil
`holes or coating their sides.
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`of the present invention extends towards the wafer in an area
`The previously described SIP sputtering relies upon a
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`at least as close to the pedestal as to the target and preferably
`strongly unbalanced magnetron,that is, one having magnetic
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`past the 75% distance of the path from the target to the
`poles of significantly different total strengths, to project the
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`pedestal. Thereby, the coil magnetic field has less opportu-
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`magnetic field toward the wafer. The unbalanced approach
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`nity to deflect as it returns to the outside of the coil. In
`has the disadvantage that the projected magnetic field is
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`contrast, Okuboet al. place their coil close to the target so
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`distinctly non-uniform in the vicinity of the wafer.
`In
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`that the coil field is largely horizontal near the wafer.
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`contrast, the sputter reactor of FIG. 1 does not require a
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`The invention has been tested by wrapping 300 to 400
`strongly unbalanced magnetronto project the magneticfield.
`turns of electrical wire around the chamber sidewall 14. A
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`the electromagnet 40 projects a substantially
`Instead,
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`coil current of 2 A produces an axial magnetic field B. of
`uniform, axial magnetic field B. from the target to the wafer
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`about 100 gauss.
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`A sputter reactor having a copper target and a racetrack
`Another difficulty with the use of an unbalanced magne-
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`magnetron of the sort described by Fu et al. was tested with
`tron for projecting the magnetic field is that only the
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`such an electromagnet. The target was powered with 35 kW
`unbalanced portion is projected, and this portion must return
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`to the back of the magnetron. Suchafield rapidly attenuates of DC power, and the pedestal was biased with 300 W of
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`with distance, typically with a dependence of the fourth
`13.56 MHz powerwith a flow of 5 seem of argon into the
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`power of distance. Exemplary attenuation is that a 1000
`chamber. The ion current
`to the pedestal electrode was
`measured as a function of coil current. The results are shown
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`gauss field is reduced to 10 gauss over 100 mm.
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`Furthermore, SIP ionization rates are limited to about 25%.
`in the graph of FIG. 2. Acoil current of 1 A producing a coil
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`The remaining 75% of sputtered metal atoms arc neutral,
`field of 50 gauss increases the ion current to the pedestal by
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`and the wafer biasing is ineffective at directing the neutral
`more than a factor of two. The quoted magnetic fields are
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`Ex. 1012, Page 5
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`Ex. 1012, Page 5
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`7
`measured in the bore of the coil near its center. The central
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`axial field may be approximated for a very thin coil as
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`US 6,352,629 B1
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`a
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`Pe a
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`10
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`15
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`25
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`whereI is the coil current, N is the numberofturns, a is the
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`radius of the coil, and z is the axial distance from the coil.
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`In the context of sputtering into deep holes, a high ion
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`current is preferred. However, a further increase to 2 A and
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`100 gauss causes the observed ion current to decrease. It is
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`believed the decrease is caused by the axial coil field
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`interfering with the electron trapping of the horizontal
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`magnetron field. From these results, it becomes apparent that
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`for typical SIP magnetrons, the coil field should be greater
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`than 15 gauss and less than 100 gauss.
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`The DC magnetic coil of the invention advantageously
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`differs from the RF coil of an IMPreactor in that it may be
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`placed outside of the chamber as long as the chamber and
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`shields are composed of non-magnetic materials. In contrast,
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`an RF coil such as that used in an inductively coupled IMP
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`reactor needs to be placed inside of the chamber and even
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`insideof the shield (unlessthe shield is turned into a Faraday
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`shield). Otherwise, the conductive chamber and shield will
`short the RFfields.
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`Someof the advantages of the invention can be employed
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`by replacing the coil with an annular magnet magnetized
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`along its axis or equivalent by a series of axially polarized
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`magnets arranged circumferentially about the chamberside-
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`walls. However, the coil is more effective at producing a
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`uniform magnetic field and can be controlled for different
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`values of magnetfield.
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`It is possible to enjoy many of the advantages of the
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`invention with a sub-kilohertz AC powering of the coil,
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`specifically a frequency of less than 1 kHz. However, DC
`35
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`coil power is best because it is always producing its maxi-
`mum effect wi