TSMC-1223
`TSMC v. Zond, Inc.
`Page 1 of 24
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`

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`U.S. Patent
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`Oct. 23,2001
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`Sheet 1 ofll
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`US 6,306,265 B1
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`TSMC-1223 I Page 2 of 24
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`U.S. Patent
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`06:. 23, 2001
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`Sheet 2 of 11
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`US 6,306,265 B1
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`FIG. 3
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`TSMC-1223 I Page 3 of 24
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`U.S. Patent
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`Oct. 23,2001
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`Sheet 3 ofll
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`US 6,306,265 B1
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`72
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`TSMC-1223 I Page 4 of 24
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`TSMC-1223 / Page 4 of 24
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`

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`U.S. Patent
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`TSMC-1223 I Page 5 of 24
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`U.S. Patent
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`06:. 23, 2001
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`Sheet 5 of 11
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`US 6,306,265 B1
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`TSMC-1223 I Page 6 of 24
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`U.S. Patent
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`Oct. 23,2001
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`Sheet 6 ofll
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`US 6,306,265 B1
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`
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`78
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`FIG. 12
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`U.S. Patent
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`061. 23, 2001
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`Sheet 7 6111
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`US 6,306,265 B1
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`TSMC-1223 I Page 8 of 24
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`U.S. Patent
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`Oct. 23,2001
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`Sheet 8 ofll
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`US 6,306,265 B1
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`190
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`TSMC-1223 I Page 9 of 24
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`U.S. Patent
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`Oct. 23,2001
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`Sheet 9 ofll
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`US 6,306,265 B1
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`200
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`206 202
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`TSMC-1223 I Page 10 of 24
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`U.S. Patent
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`061. 23, 2001
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`Sheet 10 6111
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`US 6,306,265 B1
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`
`
`80
`
`60
`
`BOTTOM
`
`COVERAGE
`(*9
`40
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`
`ASPECT RATIO
`
`TSMC-1223 I Page 11 of 24
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`U.S. Patent
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`Oct. 23,2001
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`Sheet 11 of 11
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`US 6,306,265 B1
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`
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`1
`
`20
`
`40
`
`60
`
`80
`
`100
`
`PRESSURE
`(NWT)
`
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`
`40
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`30
`STEP
`COVERAGE
`(%)
`20
`
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`
`ASPECT RATIO
`
`TSMC-1223 I Page 12 of 24
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`US 6,306,265 Bl
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`1
`HIGH-l)ICNSI'I‘Y PLASMA FOR !0NI'I.l£l}
`METAL I)I£I’()SITI(]N CAPAIILIC OF
`EXCITING A PLASNIA VVAVE
`
`Rl:iLAl'l:LD A1’l’Ll(.'Al‘lUN
`
`This application is a continuation in part oli Ser. No.
`fl‘),-'37‘3,tl97, filed Aug. 12, 1999, now us. Pat. No. 5,133,
`614 Iicb. 6, 2001 which is a continuation in part of Ser. No.
`095249.463. filed Feb. 13, 1999.
`
`FIEID OF THE INVENTION
`
`The invention relates generally to sputtering of materials.
`In particular, the invention relates to the magnetron creating
`a magnetic field to enhance sputtering.
`
`BACKGROUND ART
`
`Sputtering, alternatively called physical vapor deposition
`(PVD), is the most prevalent method of depositing layers of
`metals and related materials in the fabrication of semicon-
`ductor integrated circuits.Aconventional PVI) reactor 10 is
`illustratetl schematically in cross section in FIG. 1, and the
`illustration is based upon the Iindura PVD Reactor available
`from Applied Materials, Inc. of Santa Clara, California. The
`reactor 10 includes a vacuum chamber 12 sealed to a PVD
`target 14 composed of the material, usually a metal, to be
`sputter deposited on a wafer 16 Iield on a heater pedestal 18.
`A shield 20 held within the chamber protects the chamber
`wall '12 from the sputtered material and provides the anode
`grounding plane. A selectable DC power supply 22 nega-
`tively biases the target 14 to about —6[I[lVD(.‘ with respect to
`the shield 2|]. Conventionally, the pedestal I8 and hence the
`wafer 16 are left electrically floating.
`A gas source 2.4 supplies a sputtering working gas,
`typically the chemically inactive gas argon, to the chamber
`12 through a mass fiow controller 26. In reactive metallic
`nitride sputtering, for example, of titanium nitride, nitrogen
`is supplied from another gas source 27 through its own mass
`flow controller 26. Oxygen can also be supplied to produce
`oxides such as A1203. The gases can be admitted to the top
`of the chamber, as illustrated, or at its bottom, either with
`one or more inlet pipes penetrating the bottom of the shield
`or through the gap between the shield 20 and the pedestal 18.
`A vacuum system 28 maintains the chamber at
`a
`low
`pressure. Although the base pressure can be held to about
`10‘? Torr or even lower, the pressure of the working gas is
`typically maintained at between about 1 and 1000 mTorr. A
`computer-based controller 30 controls the reactor including
`the DC power supply 22 and the mass flow controllers 26.
`When the argoti
`is admitted into the chantber, the DC
`voltage between the target 14 and the shield 21] ignites the
`argon into a plasma, and the positively charged argon ions
`are attracted to the negatively charged target 14. The ions
`strike the target 14 at a substantial energy and cause target
`atoms or atomic clusters to be sputtered from the target 14.
`Some of the target particles strike the wafer 16 and are
`thereby deposited on it, thereby forming a film of the target
`material. In reactive sputtering of a metallic nitride, nitrogen
`is additionally admitted into the chamber 12, and it reacts
`with the sputtered metallic atoms to form a metallic nitride
`on the wafer '16.
`
`To provide efficient sputtering, a magnetron 32 is posi-
`tioned in back of the target I4. It has opposed magnets 34,
`36 creating a magnetic held within the chamber in the
`neighborhood of the magnets 34, 36. The magnetic field
`traps electrons and, for charge neutrality, the ion density also
`
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`
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`
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`
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`
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`
`60
`
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`increases to form a high-density plasma region 38 within the
`chamber adjacent to the magnetron 32. The magnetron 32 is
`usually rotated about the center of the target 14 to achieve
`full coverage in sputtering of the target 14. The form of the
`magnetron is a subject of this patent applieatioti, arid the
`illustrated form is intended to be only suggestive.
`The advancing level of integration in semiconductor
`integrated circuits has placed increasing demands upon
`sputtering equipment and processes. Matty of the problems
`are associated with contact and via holes. As illustrated in
`the cross—sectional view of FIG. 2, via or contact holes 40
`are etched through an interlevel dielectric layer 42 to reach
`a conductive feature 44 in the underlying layer or substrate
`46. Sputtering is then used to till metal into the hole 40 to
`provide inter—leve| electrical connections. If the underlying
`layer 46 is the semiconductor substrate, the filled hole 40 is
`called a contact; if the underlying layer is a lower-level
`metallization level, the filled hole 40 is called a via. For
`simplicity, we will refer hereafter only to vias. The widths of
`intcr—lcvcl vias have (IGCl'CaSC(l to the neighborliood of (L25
`pm and below while the thickness of the inter-level dielectric
`has remained nearly constant at around 0.7 pm. As a result,
`the via holes in advanced integrated circuits have increased
`aspect ratios of three and greater. For some technologies
`under developrrient, aspect ratios of six and even greater are
`required.
`Such high aspect ratios present a problem for sputtering
`because most
`forms of sputtering are not strongly
`anisotropic, a cosine dependence off the vertical being
`typical, so that the initially sputtered material preferentially
`deposits at
`the top of the hole and may bridge it,
`thus
`preventing the filling of the bottom of the hole and creating
`a void in the via metal.
`
`It has become known, however, that deep hole filling can
`be facilitated by causing a significant fraction of the sput-
`tered particles to be ioni7ed in the plasma between the target
`I4 and the pedestal 18. The pedestal 18 of FIG. 1, even if it
`is lelt electrically lloating, develops a DC sell"-bias, which
`attracts ionized sputtered particles from the plasma across
`the plasma sheath adjacent to the pedestal 18 and deep into
`the hole 40 in the dielectric layer 42. The effect can be
`accentuated with additional DC or Rli biasing of the pedestal
`electrode 18 to additionally accelerate the ionized particles
`extracted across the plasma sheath towards the wafer 16,
`thereby controlling the directionality of sputter deposition.
`The process of sputtering with a significant
`fraction of
`ionized sputtered atoms is called ionized metal deposition or
`ionized metal plating (IMP). Two related quantitative mea-
`sures of the ellectiveness of hole filling are bottom coverage
`and side coverage. As illustrated schematically in FIG. 2, the
`initial phase of sputtering deposits a layer 50, which has a
`surface or blanket thickness of sl, a bottom thickness of s_,,
`and a sidewall thickness of s3. The bottom coverage is equal
`to S381, and the sidewall coverage is equal to s3.t's1. The
`model
`is overly simplified but
`in many situations is
`adequate.
`One method of increasing the ionization fraction is to
`create a high-density plasma [IIDP), such as by adding an
`RF coil around the sides of the chamber 12 of FIG. 1. An
`HIJP reactor not only creates a high—density argon plasma
`but also increases the ioniration fraction of the sputtered
`atoms. However, Hl)l’ PVI) reactors are new and relatively
`expensive, and the quality of the deposited films is not
`always the best. It is desired to continue using the principally
`DC sputtering of the PVD reactor of FIG. 1.
`Another method for increasing the ionization ratio is to
`use a hollow-cathode magnetron in which the target has the
`
`TSMC-1223 I Page 13 of 24
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`US 6,306,265 Bl
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`3
`shape of atop hat. This type of reactor, though, runs very hot
`and the complexly shaped targets are very expensive.
`It has been observed that copper sputtered with either an
`inductively coupled IIDP sputter
`reactor or a hollow-
`cathode reactor tends to form an undulatory copper film on
`the via sidewall, and further the deposited metal tends to
`dewet. The variable thickness is particularly serious when
`the sputtered copper layer is being used as a seed layer of a
`predetermined minimum thickness for a subsequent depo-
`sition process such as electroplating to complete the copper
`hole filling.
`the sidewall
`is that
`A further problem in the prior art
`coverage tends to be asymmetric with the side facing the
`center of the target being more heavily coated than the more
`shielded side facing a larger solid angle outside the target.
`Not only does the asymmetry require excessive deposition to
`achieve a seed layer of predetermined minimum thickness,
`it causes cross-shaped trenches used as alignment indicia in
`the photolithography to appear to move as the trenches are
`asymmetrically narrowed.
`that promotes deep hole
`Another operational control
`is generally believed that
`iilling is chamber pressure.
`It
`lower chamber pressures promote hole filling. At higher
`pressures,
`there is a higher probability that sputtered
`particles, whether neutral or ionized, will collide with atoms
`of the argon carrier gas. Collisions tend to neutralize ions
`and to randomize velocities, both effects degrading hole
`filling. However, as described before, the sputtering relies
`upon the existence of a plasma at least adjacent to the target.
`lf the pressure is reduced too much,
`the plasma collapses,
`although the minimum pressure is dependent upon several
`factors.
`
`"Jr
`
`10
`
`lb
`
`20
`
`[Jon
`
`30
`
`4
`sputtered. Furthermore, the material redeposited on uIrsput-
`tered areas may build up to such a thickness that it is prone
`to flake oil‘, producing severe particle problems. While radial
`scanning can potentially avoid these problems, the required
`scanning mechanisms are complex and generally considered
`infeasible in a production environment.
`One type of commercially available magnetron is kidney-
`shaped, as exemplified by Tepman in US. Pat. No. 5,320,
`728. Parker discloses more exaggerated forms of this shape
`in U.S. Pat. No. 5,242,566. As illustrated in plan view in
`FIG. 3, the Tepman magnetron 52 is based on a kidney shape
`for the magnetically opposed pole faces 54, 56 separated by
`a circuitous gap 57 of nearly constant width. The pole faces
`54, 56 are magnetically coupled by unillustrated horseshoe
`magnets hridging the gap 57. The magnetron rotates about a
`rotational axis 58 at the center of the target 14 and near the
`ooncave edge of the kidney-shaped inner pole face 54. The
`convexly curved outer periphery of the outer pole face 56,
`which is generally parallel to the gap 57 in that area, is close
`to the outer periphery of the usable portion if the target 14.
`This shape has been optimized for high field and for uniform
`sputtering but has an area that is nearly half that of the target.
`It is noted that the magnetic lield is relatively weak in areas
`separated from the pole gap 57.
`For these reasons,
`it
`is desirable to develop a small,
`high-field magnetron providing full coverage so as to pro-
`mote deep hole filling and sustained copper self-sputtering.
`
`SUMMARY OF THE INVENTION
`
`The invention includes a sputtering magnetron having an
`oval or related shape of smaller area than a circle of equal
`diameter where the two diameters extend along the target
`radius with respect to the typical rotation axis of the mag-
`netron. The shapes include racetracks, ellipses, egg shapes,
`triangles, and arced triangles asymmetrically positioned
`about the target center.
`The magnetron is rotated on the backside of the target
`about a point preferably near the magnetron’s thin end, and
`the thicker end is positioned more closely to the target
`periphery. Preferably,
`the total magnetic flux is greater
`outside than inside the half radius of the target.
`The magnetic intensity away from the target can be
`increased for a triangular magnetron having a relatively
`small apex angle by using bar magnets.
`The small area allows an electrical power density of at
`least 600 Wfcrn: to be applied from an 18 kW power supply
`to a fully covered sputtering target used to sputter deposit a
`200 mm wafer.
`
`The high power density and the magnetic field extending
`far away from the target are two means possible to produce
`a plasma wave which can further drive the plasma to a
`higher density and ionization. Advantageously, a primary
`plasma wave is generated at a higher frequency in the range
`of hu ndreds ot‘ megahertz, which is parametrieally converted
`to another wave at a much lower frequency, for example, 5
`to 75 MHZ, corresponding to the thermal velocity of elec-
`trons in the plasma produced by capaeitively coupling DC
`power to the target.
`The magnetron is configured to produce less magnetic
`flux in its inner pole than in its surrounding outer pole.
`Thereby, the magnetic lield reaches further into the sputter-
`ing chamber to promote low—prcssure sputtering and sus-
`tained self—sput1ering.
`The invention also includes sputtering methods achiev-
`able with such a magnetron. The high magnetic field extend-
`
`TSMC-1223 I Page 14 of 24
`
`=10
`
`45
`
`50
`
`The extreme of low-pressure plasma sputtering is sus-
`tained self-sputtering (SSS), as disclosed by Fu et al. in US.
`patent application, Ser. No. 08,t854,(t08, filed May 8, 1997.
`ln SSS, the density of positively ion ized sputtered atoms is
`so high that a sullicient number are attracted back to the
`negatively biased target
`to resputter more ionined atoms.
`Under the right conditions for a limited number of target
`metals, the self—sputtering sustains the plasma, and no argon
`working gas is required. (Topper is the metal most prone to
`SSS, but only under conditions of high power and high
`ma gnelie field. Copper sputtering is being seriously devel-
`oped because of copper's low resistivity and low suscepti-
`bility to eloctromigration. However, for copper SSS to
`become commercially feasible, a full—mverage, high—field
`magnetron needs to be developed.
`Increased power applied to the target allows reduced
`pressure, perhaps to the point of sustained self—sputtering.
`The increased power also increases the ionization density.
`However, excessive power requires expensive power sup-
`plies and increased cooling. Power levels in excess of 30 kW
`are expensive and should be avoided if possible. In fact, the
`.non
`pertinent factor is not power but the power density in the .
`area below the magnetron since that
`is the area of thc
`high-density plasma promoting effective sputtering. llence,
`a small, high—field magnet would most easily produce a high
`ionization density. For this reason, some prior art discloses
`a small circularly shaped magnet. However, such a magne-
`tron requires not only rotation about the center of the target
`to provide uniformity, but it also requires radial scanning to
`assure full and fairly uniform coverage of the target. If full
`magnetron coverage is not achieved, not only is the target
`not efliciently used, but more importantly the uniformity of
`sputter deposition is degraded, and some of the sputtered
`material redeposits on the target in areas that are not being
`
`60
`
`TSMC-1223 / Page 14 of 24
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`

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`US 6,306,265 Bl
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`5
`a small closed area facilitates sustained sell-
`ing over
`sputtering. Many metals not subject
`to sustained sell‘-
`sputlering can be sputtered at chamber pressures of less than
`0.5 1nilliTorr, often less than 0.2 n1illiTorr, and even at 0.]
`milliTorr. The bottom coverage can be further improved by
`applying an RF bias of less than 250 W to a pedestal
`electrode sized to support a 200 mm wafer. Copper can be
`sputtered with 18 kW of DC power for a 330 mm target and
`200 mm wafer either in a fully self—sustained mode or with
`a minimal chamber pressure of (1.3 milliTorr or less.
`The invention provides for high—power density sputtering
`with power supplies of reduced capacity.
`The invention also includes sputtering with oondition,
`such as a sufliciently target power and high magnetic field
`away from the target, that a non-linear wave-beam interac-
`tion occurs that pumps energy into plasma electrons, thereby
`increasing the plasma density.
`BRIILI-' l)l:lS(7RIP'l‘[(]l\I 01-‘ '['lIl_-' DRAWINGS
`
`FIG. 1 is a schematic diagram of a l)(_‘ plasma sputtering
`reactor.
`FIG. 2 is a cross—sectional view of a inter—level via in a
`semiconductor integrated circuit.
`FIG. 3 is a plan view of a conventional magnetron.
`FIG. 4 is a plan view of the pole pieces of an embodiment
`of the magnetron of the invention taken along the view line
`4—4 of FIG. 7.
`
`"II
`
`‘I0
`
`15
`
`20
`
`to"J:
`
`FIG. 5 is a plan view of the magnets used in the magne-
`tron of FIG. 4.
`
`30
`
`FIG. 6 is a cross—sectional view of one of the magnets
`used in conjunction with the embodiments of the invention.
`FIG. 7 is a cross—sectional view of the magnetron of FIG.
`
`4.
`
`FIG. 8 is a plan view of an egg-shaped magnetron.
`FIG. 9 is a plan view of a triangularly shaped magnetron.
`FIG. 10 is a plan view ofa modification olithe triangularly
`shaped magnetron of FIG. 9, referred to as an arced trian-
`gular magnetron.
`FIG. 11 is a plan view ol‘ the magnets used in the arced
`triangular magnetron of FIG. 10.
`FIG. 12 is a plan view of two model magnetrons used to
`calculate areas and peripheral lengths.
`FIG. 13 is a graph ofthe angular dependenees ofthe areas
`of a triangular and of a circular magnetron.
`FIG. 14 is a graph of the angular dependences of the
`peripheral lengths of the two types of rnagnetrons of FIG.
`12.
`
`=10
`
`45
`
`50
`
`FIG. 15 is a bottom plan view of a magnetron of the
`invention using bar magnets.
`FIG.
`'16 is a bottom plan view of an alternative to the
`magnetron of FIG. 15.
`.n-'2:
`FIG. 17 is a side view of an idealization of the magnetic ‘
`field produced with the described embodiments ofthe inven-
`tion.
`
`FIGS. 18 and 19 are a top plan view and a schematic side
`view of a chamber and magnetron arranged for measuring
`plasma wave generated by a magnetron of the invention.
`FIG. 20 is a graph of a typical energy distribution of
`plasma electrons.
`FIG. 21 is a graph showing the effect of RF wafer bias in
`bottom coverage in titanium sputtering.
`FIG. 22 is a graph of the dependence ofchamber pressure
`upon nitrogen fiow illustrating the two modes of deposition
`
`60
`
`obtained in reactive sputtering of titanium nitride with a
`magnetron of the invention.
`FIG. 23 is a graph of the step coverage obtained in the two
`sputtering modes for reactive sputtering of titanium nitride
`with a magnetron of the invention.
`
`DI.-l'I‘AILI_-'.D DI.-JSCRIP'l'ION 01-" Till:
`l’RI:lFl:'RRI:'.D I:'.MBODIMI:'l\I'l"S
`
`One entbodirnent of the invention is a racetrack magne-
`tron 60, illustrated in plan view in FIG. 4. The racetrack
`magnetron 60 has a central bar—shaped pole face 62 of one
`magnetic polarity having opposed parallel middle straight
`sides 64 connected by two rounded ends 66. The central,
`bar—shaped pole face 62 is surrounded by an outer elongated
`ring—shaped pole face 68 of the other polarity with a gap 70
`of nearly constant width separating the bar-shaped and
`ring-shaped pole faces 62, 68. the outer pole face 68 of the
`other magnetic polarity includes opposed parallel middle
`straight sections 72 connected by two rounded ends 74 in
`general central symmetry with the inner pole face 62. The
`middle sections 72 and rounded ends 74 are bands having
`nearly equal widths. Magnets, to be described shortly, cause
`the pole faces 62, 68 to have opposed magnetic polarities. A
`backing plate, also to be described shortly, provides both a
`magnetic yoke between the magnetically opposed pole faces
`62, 63 and support for the magnetron structure.
`Although the two pole faces 62, 68 are illustrated with
`specific magnetic polarities producing magnetic fields
`extending generally perpendicularly to the plane of
`illustration, it is of course appreciated that the opposite set
`of magnetic polarities will produce the same general mag-
`netic effects as far as the invention is concerned. The
`
`illustrated assembly produces a generally semi-toroidal
`magnetic field having parallel arcs extending perpendicu-
`larly to a closed path with a minimal field-free region in the
`center. There results a closed tunnel of magnetic field
`forming struts of the tunnel.
`The pole assembly of FIG. 4 is intended to be continu-
`ously rotated during sputter deposition at a fairly high
`rotation rate about a rotation axis 78 approximately coinci-
`dent with the center of the target 14 of uniform composition.
`The rotation axis 78 is located at or near one prolate end 80
`of the outer pole face 68 and with its other prolate end 82
`located approximately at the outer radial usable extent of the
`target 14. The asymmetric placement of the rotating mag-
`netron 60 with respect to the target eenter provides a small
`magnetron nonetheless achieving full target coverage. The
`outer usable periphery of the target
`is not easily defined
`because dillierent magnetron designs use different portions
`of the same target. However, it is bounded by the [lat area of
`the target and almost always extends to significantly beyond
`the diameter of the wafer being sputter deposited and is
`somewhat less than the area of the target face. For 200 mm
`wafers, target faces of 325 mm are typical. A 15% unused
`target radius may be considered as an upper practical limit.
`Racetrack magnetrons are well known in the prior art, but
`they are generally positioned symmetrically about the center
`of the target. In the described invention, the racetrack is
`asymmetrically positioned with its inner end either overly-
`ing the target center or terminating at a radial position
`preferably within 20% and more preferably within IIJGE; of
`the target radius from the target center. The illustrated
`racetrack extends along a diameter of the target.
`As illustrated in the plan view of FIG. 5, two sets ol‘
`magnets 90, 92 are disposed in back of the pole faces 62, 68
`to produce the two magnetic polarities. The combination of
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`US 6,306,265 Bi
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`the pole faces 62, 68, the magnets 90, 92, and possibly a
`back magnetic yoke produces two opposite magnetic poles
`having areas defined by the pole faces 62, 68. Other means
`may be used to aehie-ved such poles.
`The two types of magnets 90, 92 may be of similar
`construction and composition producing an axially extend-
`ing magnetic fltlx on each vertically facing end. If they are
`of different, magnetic composition, diameter, or length, the
`flux produced by different magnets may be different. A
`cross-sectional view of a magnet 90, 92 is shown in FIG. 6.
`A cylindrical magnetic core 93 extending along an axis is
`composed of a strongly magnetic material, such as neody-
`mium boron iron [NdBI-‘e]. Because such a material is easily
`oxidized, the core 93 is encapsulated in a case made of a
`tubular sidewall 94 and two generally circular caps 96
`welded together to form an air-tight canister. The caps 96 are
`composed of a soft magnetic material, preferably S8410
`stainless steel, and the tubular sidewall 96 is composed of a
`non—magnetic material, preferably S3304 stainless steel.
`Each cap 96 includes an axially extending pin 97, which
`engages a corresponding capture hole in one of the pole
`faces 62, 68 or in a magnetic yoke to be shortly described,
`Thereby, the magnets 90, 92 are fixed in the magnetron. The
`magnetic core 93 is magnetized along its axial direction, but
`the two different types of magnets 90, 92 are oriented in the
`magnetron 60,
`illustrated in the cross—sectional view of
`FIG. 7, so that
`the magnets 90 of the inner pole 62 are
`aligned to have their magnetic field extending vertically in
`one direction, and the magnets 92 of the outer pole 68 are
`aligned to have their magnetic field extending vertically in
`the other direction. that is,
`they have opposed magnetic
`polarities.
`'7, the
`As illustrated in the cross-sectional view of FIG.
`magnets 90, 92 are arranged closely above (using the
`orientation of FIG. 1)
`the pole faces 62, 68 located just
`above the back of the target 14. Amagnetie yoke 98 having
`a generally closed shape generally conforming to the outer
`periphery of the outer pole face 68 is closely positioned in
`back of the magnets 90, 92 to magnetically couple the two
`poles 62, 68. As mentioned previously, holes in the pole
`faces 62, 68 and in the yoke 98 fix the magnets 90, 92, and
`unilluslrated hardware fix the pole faces 62, 68 to the yoke
`98.
`
`"Jr
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`10
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`15
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`20
`
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`30
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`45
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`50
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`The inner magnets 90 and inner pole face 62 constitute an
`inner pole of one magnetic polarity while the outer magnets
`92 and the outer pole face 68 constitute a surrounding outer
`pole of the other magnetic polarity. The magnetic yoke 98
`magnetically couples the inner and outer poles and substan-
`tially conlines the magnetic field on the back or top side of
`the magnetron to the yoke 98. Asemi—toroidal magnetic field
`100 is thereby produced, which extends through the non-
`magnetic target 14 into the vacuum chamber 12 to (feline the
`high-density plasma region 38. The field 100 extends
`through the non—magnetic target 14 into the vacuum cham-
`.n-'2:
`ber 12 to define the extent ofthe high—dcnsity plasma region ,
`38. The magnets 90, 92 may be of different magnetic
`strength. However, it is desired for reasons to be explained
`later that
`the total magnetic flux produced by the outer
`magnets 92 be substantially greater than that produced by
`the inner magnets 90. As illustrated,
`the magnetron 60
`extends horizontally from approximately the center of the
`target 14 to the edge of the usable area of the target 14. 'lhc
`magnetic yoke 90 and the two pole faces 62, 68 are
`preferably plates formed of a soft magnetic material such as
`S8416 stainless steel.
`
`60
`
`The inner prolate end 80 of the magnetron 60 is connected
`to a shaft 104 extending along the rotation axis 78 and
`
`8
`rotated by a motor 106. As illustrated, the magnetron 60
`extends horiyiontally from approximately the center of the
`target 14 to the right hand side ofthe usable area of the target
`14. Demaray el al.
`in US. Pat. No. 5,252,194 disclose
`exemplary details of the connect ions between the tnotor 106,
`the magnetron 60, and the vacuum chamber 12. The mag-
`netron assembly 60 should include counter-weighting to
`avoid flexing of the shaft 104. Although the center of
`rotation 78 is preferably disposed within the inner prolate
`enrt 74 of the outer pole face 72.
`its position may be
`optimized to a slightly different position, but one preferably
`not deviating more than $96, more preferably 10%, from
`the inner prolate end 80 as normalized to the prolate length
`of the magnetron 60. Most preferably, the inner end of the
`outer pole face 68 near the prolate end 80 overlies the
`rotation center 78.
`
`The racetrack configuration of l~'l(J‘. 4 has the advantage
`of simplicity and a very small area while still providing full
`target oovcragc. As will be discussed later, the asymmetric
`magnetic flux of the two poles is advantageous for low-
`pressure sputtering and sustained self-sputtering.
`The racetrack configuration of FIG. 4 can be alternatively
`characterized as an extremely flattened oval. Other oval
`shapes are also included within the invention, for example,
`oontinuously curved shapes ofcontinuously changing diam-
`eter such as elliptical shapes with the major axis of the
`ellipse extending along the radius of the target and with the
`minor axis preferably parallel to a rotational circumference.
`Tabuchi
`illustrates a symmetric oval magnetron in Laid-
`open Japanese Patent Application 63482263. This shape
`however has the disadvantage of a complex shape, espe-
`cially for packing the magnets in the inner pole.
`Another oval shape is represented by an egg-shaped
`magnetron 106, illustrated in plan view in FIG. 8. It has an
`outer pole face 108 of one magnetic polarity surrounding an
`inner pole face 110 of the other polarity with a nearly
`constant gap 122 between them. Both pole faces I08. 110 are
`shaped like the outline of an egg with a major axis extending
`along the radius of the target. llowever, an inner end 112 of
`the outer pole face 108 near the rotation axis 78 is sharper
`than an outer end 114 near the periphery of the target. The
`egg shape is related to an elliptical shape but is asymmetric
`with respect to the target radius. Specifically, the minor axis
`is pushed closer to the target periphery than its center. The
`inner pole face 110 and the gap "122 are similarly shaped.
`Such an egg shape places more of the magnetic flux closer
`to the target periphery so as to improve sputtering unifor-
`mity. Such a preferred flux distribution may be characterixed
`with respect to the half radius of the target extending from
`its center to its outer usable radius. l-‘or improved uniformity,
`the total magnetic flux located outside the half radius is
`greater than that located inside the half radius, for example,
`by at least a 3:2 ratio, and preferably between 1.8 and 2.3.
`The ratio of magnetic flux outside to inside the target half
`radius in this configuration is about 2:1.
`A related shape is represented by a triangular magnetron
`"[26, illustrated in plan view in FIG. 9. It has a triangular
`outer pole face 128 of one magnetic polarity surrounding a
`substantially solid inner pole face 130 of the other magnetic
`polarity with a gap 132 between them. The triangular shape
`of the inner pole face 130 with rounded corners allows
`hexagonal close packing of the button magnets 90, 92 of
`1-‘IC-. 6. The outer pole face 128 has three straight sections
`134 are preferably offset by 60° with respect to each other
`and are connected by rounded corners 136. Preferably, the
`rounded corners 136 have smaller lengths than the straight
`sections 134. One rounded corner 136 is located near the
`
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`rotation center 78 and target center, preferably within 20%,
`more preferably within lit‘?/o of the target radius, and most
`preferably with the apex portion of the outer pole face 128
`overlying the rotation center 78. The triangularly shaped
`inner pole piece 130 may include a central aperture, but it is
`preferred that the size of such an aperture be kept small to
`minimize the size of the central magnetic cusp.
`A modified triangular shape is represented by an arced
`triangular magnetron 140 of I~'IG. 10. It includes the trian-
`gular inner pole face 130 surrounded by an arced triangular
`outer pole face 142 with a gap 144 between them and
`between the magnets of the respective poles and with the
`magnetic yoke in back of the gap 144. The outer pole face
`142 includes two straight sections 146 connected to each
`other by a rounded apex corner 148 and connected to an arc
`section 150 by rounded circumferential corners 152. The
`apex corner 148 is placed near the rotational center 78 and
`the target center, preferably within 20% and more preferably
`within 10% of the target radius. The are section 150 is
`located generally near the circumferential periphery of the
`target. It curvature may be equal t