`Fu et al.
`
`USOO6306265B1
`(10) Patent No.:
`US 6,306,265 B1
`(45) Date of Patent:
`Oct. 23, 2001
`
`(54) HIGH-DENSITY PLASMA FOR IONIZED
`METAL DEPOSITION CAPABLE OF
`EXCITING A PLASMA WAVE
`
`(75) Inventors: Jianming Fu, San Jose; Praburam
`Gopalraja, Sunnyvale; Fusen Chen,
`Saratoga; John Forster, San Francisco,
`all of CA (US)
`(73) Assignee: Applied Materials, Inc., Santa Clara,
`CA (US)
`
`(*) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(21) Appl. No.: 09/546,798
`(22) Filed:
`Apr. 11, 2000
`Related U.S. Application Data
`
`63) Continuation-in-part of application No. 09/373.097, filed on
`(63) Aug. 12, 1999, E. Pat. RE 6,183,614, CE a continu-
`ation-in-part of application No. 09/249,468, filed on Feb. 12,
`1999.
`(51) Int. Cl." ..................................................... C23C 14/34
`(52) U.S. Cl. .................................... 204/192.12; 204/298.2
`(58) Field of Search ............................ 204298.19, 298.2,
`204/298.22, 192.12
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`4/1984 Garrett .............................. 20429s
`4,444,643
`10/1993 Demaray et al. .
`... 204/298.2
`5,252,758
`6/1998 Kiyota ............................... 204/298.2
`5,770,025
`5,897,752 * 4/1999 Hong et al. ...
`204/298.2
`5,966,607
`10/1999 Chee et al. ........................... 438/305
`FOREIGN PATENT DOCUMENTS
`06-620583A
`10/1994 (EP).
`0 691 419 A1 * 1/1996 (EP) ................................ 204/298.19
`
`2241 710 * 9/1991 (GB) ............................... 204/298.19
`62-89864
`4/1987 (JP).
`63-282263
`11/1988 (JP).
`11-074225
`3/1999 (JP).
`OTHER PUBLICATIONS
`B. Window et al. “Charged particle fluxes from planar
`magnetron Sources”, J. Vac. Sci. Technol. A 4(2), Mar/Apr.
`1986, pp. 196-202.*
`J. Musil, et al. "Unbalanced magnetrons and new Sputtering
`Systems with enhanced plasma ionization, J. Vac. Sci.
`Technol. A 9(3), May/Jun. 1991, pp. 1171–1177.*
`W. Munz. “The unbalanced magnetron: current status of
`development”, Surface and Coatings Technology, 48 (1991),
`pp. 81-94.*
`Matsuoka et al., “Dense plasma production and film depo
`Sition by new high-rate Sputtering using an electric mirror,”
`Journal of Vacuum Science and Technology A, vol. 7, No. 4,
`Jul/Aug. 1989, pp. 2652–2657.
`* cited by examiner
`Primary Examiner Nam Nguyen
`ASSistant Examiner-Gregg Cantelmo
`(74) Attorney, Agent, or Firm-Charles S. Guenzer, Esq.
`(57)
`ABSTRACT
`A magnetron especially advantageous for low-pressure
`plasma, Sputtering or Sustained self-sputering having
`reduced area but full target coverage. The magnetron
`includes an outer pole face Surrounding an inner pole face
`with a gap therebetween. The outer pole of the magnetron of
`the invention is Smaller than that of a circular magnetron
`Similarly extending from the center to the periphery of the
`target. A preferred triangular shape having a Small apex
`angle of 20 to 30 may be formed from outer bar magnets of
`one magnetic polarity enclosing an inner magnet of the other
`magnetic polarity. The magnetron allows the generation of
`plasma waves in the neighborhood of 22 MHz which
`interact with the 1 to 20 eV electrons of the plasma to
`thereby increase the plasma density.
`
`22 Claims, 11 Drawing Sheets
`
`
`
`
`
`4O
`
`5O
`
`S N
`
`N
`CZ
`
`N
`
`46
`
`Demaray Ex. 2006-p. 1
`Applied Materials v Demaray
`IPR2021-00106
`
`
`
`U.S. Patent
`
`Oct. 23, 2001
`
`Sheet 1 of 11
`
`US 6,306,265 B1
`
`1 O
`
`34
`
`32
`1.
`14
`s
`36
`26 by
`2
`2 22
`N,
`w
`1.
`
`
`
`5'
`Ar
`
`,
`,
`,
`Hill % NP
`
`N2 H(X) / N
`
`!y 7777777.77
`
`N
`
`2O N-
`
`NN
`&zzzz-27 N 2O
`
`28-D-
`
`234
`() 252
`
`3O
`
`CONTROLLER
`
`-
`
`(PRIOR ART)
`FIG 1
`
`Demaray Ex. 2006-p. 2
`Applied Materials v Demaray
`IPR2021-00106
`
`
`
`U.S. Patent
`
`Oct. 23, 2001
`
`Sheet 2 of 11
`
`US 6,306,265 B1
`
`5O
`
`S. S.
`N
`
`33 24. 27
`
`
`
`
`
`
`
`N
`
`
`
`
`
`
`
`46
`
`FIG 2
`
`56 57
`
`14
`
`s -52
`
`(PRIOR ART)
`
`FIG 3
`
`D
`
`Demaray Ex. 2006-p. 3
`Applied Materials v Demaray
`IPR2021-00106
`
`
`
`U.S. Patent
`
`Oct. 23, 2001
`
`Sheet 3 of 11
`
`US 6,306,265 B1
`
`72 68 7O
`
`so-1
`
`FIG 4
`
`goo,
`OGOOOO
`PoGGGGGGG
`v
`FIG 5
`
`/
`
`\
`
`
`
`Demaray Ex. 2006-p. 4
`Applied Materials v Demaray
`IPR2021-00106
`
`
`
`U.S. Patent
`
`Oct. 23, 2001
`
`Sheet 4 of 11
`
`US 6,306,265 B1
`
`
`
`11 O
`
`1 O8
`
`122
`
`1 O6
`
`114
`
`78
`
`112
`
`FIG 8
`
`Demaray Ex. 2006-p. 5
`Applied Materials v Demaray
`IPR2021-00106
`
`
`
`U.S. Patent
`
`Oct. 23, 2001
`
`Sheet S of 11
`
`US 6,306,265 B1
`
`-
`
`126
`
`136
`
`
`
`152
`
`1 4-8
`
`FIG 10
`
`152
`
`-
`
`14O
`
`13 O
`
`15O
`
`1 4-4
`
`Demaray Ex. 2006-p. 6
`Applied Materials v Demaray
`IPR2021-00106
`
`
`
`U.S. Patent
`
`Oct. 23, 2001
`
`Sheet 6 of 11
`
`US 6,306,265 B1
`
`164
`
`97
`
`(o) (O)
`(O)
`
`(O)
`Soo
`6
`ice
`(ê
`(252 5
`66
`(O)N 16O YO)
`96.
`-162
`©GG)
`FIG 11
`
`Demaray Ex. 2006-p. 7
`Applied Materials v Demaray
`IPR2021-00106
`
`
`
`U.S. Patent
`
`Oct. 23, 2001
`
`Sheet 7 of 11
`
`US 6,306,265 B1
`
`TT Y2
`%:
`T
`
`TT Y4.
`
`174
`
`176
`
`FIG 13
`
`0
`
`900
`
`18O
`
`P 7,
`
`TT-2
`
`T
`
`2
`
`178
`
`18O
`
`9 OO
`
`0
`
`18O
`
`Demaray Ex. 2006-p. 8
`Applied Materials v Demaray
`IPR2021-00106
`
`
`
`U.S. Patent
`
`Oct. 23, 2001
`
`Sheet 8 of 11
`
`US 6,306,265 B1
`
`
`
`Demaray Ex. 2006-p. 9
`Applied Materials v Demaray
`IPR2021-00106
`
`
`
`U.S. Patent
`
`Oct. 23, 2001
`
`Sheet 9 of 11
`
`US 6,306,265 B1
`
`
`
`2OO
`
`2O6 202
`
`Demaray Ex. 2006-p. 10
`Applied Materials v Demaray
`IPR2021-00106
`
`
`
`U.S. Patent
`
`Oct. 23, 2001
`
`Sheet 10 of 11
`
`US 6,306,265 B1
`
`
`
`
`
`6O
`BOTTOM
`COVERAGE
`(%)
`40
`
`FIG. 20
`
`-0- NO BAS
`20T --O-- 10OW BIAS
`- - - A - - - 25OW BAS
`
`ASPECT RATIO
`
`Demaray Ex. 2006-p. 11
`Applied Materials v Demaray
`IPR2021-00106
`
`
`
`U.S. Patent
`
`Oct. 23, 2001
`
`Sheet 11 of 11
`
`US 6,306,265 B1
`
`
`
`PRESSURE
`(mT)
`
`4O
`6O
`N2 FLOW (scom)
`
`8O
`
`1 OO
`
`1
`
`2O
`
`FIG 22
`
`
`
`STEP 50
`COVERAGE
`(%) 20
`
`1 O
`
`FIG 23
`
`ASPECT RATIO
`
`Demaray Ex. 2006-p. 12
`Applied Materials v Demaray
`IPR2021-00106
`
`
`
`US 6,306,265 B1
`
`1
`HIGH-DENSITY PLASMA FOR ONIZED
`METAL DEPOSITION CAPABLE OF
`EXCITING A PLASMA WAVE
`
`RELATED APPLICATION
`This application is a continuation in part of Ser. No.
`09/373,097, filed Aug. 12, 1999, now U.S. Pat. No. 6,183,
`614 Feb. 6, 2001 which is a continuation in part of Ser. No.
`09/249,468, filed Feb. 12, 1999.
`
`FIELD 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.
`
`15
`
`2
`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 application, and 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. Many 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 fill metal into the hole 40 to
`provide inter-level 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
`inter-level vias have decreased to the neighborhood of 0.25
`lum and below while the thickness of the inter-level dielectric
`has remained nearly constant at around 0.7 um. As a result,
`the via holes in advanced integrated circuits have increased
`aspect ratioS of three and greater. For Some technologies
`under development, 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 ionized in the plasma between the target
`14 and the pedestal 18. The pedestal 18 of FIG. 1, even if it
`is left electrically floating, develops a DC self-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 RF 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 effectiveness 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 S, a bottom thickness of S,
`and a Sidewall thickness of S. The bottom coverage is equal
`to S/S, and the Sidewall coverage is equal to S/S. 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 (HDP), Such as by adding an
`RF coil around the sides of the chamber 12 of FIG. 1. An
`HDP reactor not only creates a high-density argon plasma
`but also increases the ionization fraction of the Sputtered
`atoms. However, HDPPVD 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
`
`25
`
`35
`
`40
`
`45
`
`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. A conventional PVD reactor 10 is
`illustrated Schematically in croSS Section in FIG. 1, and the
`illustration is based upon the Endura 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 held 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 -600VDC with respect to
`the shield 20. Conventionally, the pedestal 18 and hence the
`wafer 16 are left electrically floating.
`A gas Source 24 Supplies a Sputtering working gas,
`typically the chemically inactive gas argon, to the chamber
`12 through a mass flow 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 Al-O. 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
`107 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.
`50
`When the argon is admitted into the chamber, the DC
`voltage between the target 14 and the shield 20 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 14. It has opposed magnets 34,
`36 creating a magnetic field within the chamber in the
`neighborhood of the magnets 34, 36. The magnetic field
`traps electrons and, for charge neutrality, the ion density also
`
`55
`
`60
`
`65
`
`Demaray Ex. 2006-p. 13
`Applied Materials v Demaray
`IPR2021-00106
`
`
`
`3
`shape of a top 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 HDP 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.
`A further problem in the prior art is that the sidewall
`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.
`Another operational control that promotes deep hole
`filling is chamber pressure. It is generally believed that
`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.
`If the pressure is reduced too much, the plasma collapses,
`although the minimum pressure is dependent upon Several
`factors.
`The extreme of low-pressure plasma Sputtering is SuS
`tained self-sputtering (SSS), as disclosed by Fu et al. in U.S.
`patent application, Ser. No. 08/854,008, filed May 8, 1997.
`In SSS, the density of positively ionized sputtered atoms is
`So high that a Sufficient number are attracted back to the
`negatively biased target to resputter more ionized 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. Copper is the metal most prone to
`SSS, but only under conditions of high power and high
`magnetic field. Copper Sputtering is being Seriously devel
`oped because of copper's low resistivity and low Suscepti
`bility to electromigration. However, for copper SSS to
`become commercially feasible, a full-coverage, 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
`pertinent factor is not power but the power density in the
`area below the magnetron Since that is the area of the
`high-density plasma promoting effective Sputtering. Hence,
`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 efficiently 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
`
`4
`Sputtered. Furthermore, the material redeposited on unsput
`tered areas may build up to Such a thickness that it is prone
`to flake off, 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 U.S. 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 bridging the gap 57. The magnetron rotates about a
`rotational axis 58 at the center of the target 14 and near the
`concave 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 field 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 W/cm 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 hundreds of megahertz, which is parametrically 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 capacitively 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 field reaches further into the Sputter
`ing chamber to promote low-pressure Sputtering and Sus
`tained Self-Sputtering.
`The invention also includes Sputtering methods achiev
`able with Such a magnetron. The high magnetic field extend
`
`US 6,306,265 B1
`
`15
`
`25
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`Demaray Ex. 2006-p. 14
`Applied Materials v Demaray
`IPR2021-00106
`
`
`
`US 6,306,265 B1
`
`S
`ing over a Small closed area facilitates Sustained Self
`Sputtering. Many metals not Subject to Sustained Self
`Sputtering can be Sputtered at chamber preSSures of less than
`0.5 milliTorr, often less than 0.2 milliTorr, and even at 0.1
`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 0.3 milliTorr or less.
`The invention provides for high-power density Sputtering
`with power Supplies of reduced capacity.
`The invention also includes Sputtering with condition,
`Such as a Sufficiently 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.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is a Schematic diagram of a DC 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.
`FIG. 5 is a plan view of the magnets used in the magne
`tron of FIG. 4.
`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 of a modification of the triangularly
`shaped magnetron of FIG. 9, referred to as an arced trian
`gular magnetron.
`FIG. 11 is a plan view of 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 of the angular dependences of the 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 magnetrons of FIG.
`12.
`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.
`FIG. 17 is a side view of an idealization of the magnetic
`field produced with the described embodiments of the 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 of chamber pressure
`upon nitrogen flow illustrating the two modes of deposition
`
`6
`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.
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`One embodiment 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, 68 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 center provides a Small
`magnetron nonetheless achieving full target coverage. The
`outer usable periphery of the target is not easily defined
`because different magnetron designs use different portions
`of the same target. However, it is bounded by the flat 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 10% 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 of
`magnets 90, 92 are disposed in back of the pole faces 62, 68
`to produce the two magnetic polarities. The combination of
`
`15
`
`25
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`Demaray Ex. 2006-p. 15
`Applied Materials v Demaray
`IPR2021-00106
`
`
`
`US 6,306,265 B1
`
`15
`
`25
`
`35
`
`40
`
`7
`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 achieved Such poles.
`The two types of magnets 90, 92 may be of similar
`construction and composition producing an axially extend
`ing magnetic flux 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 (NdBFe). 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 SS410
`stainless steel, and the tubular sidewall 96 is composed of a
`non-magnetic material, preferably SS304 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, as 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.
`As illustrated in the cross-sectional view of FIG. 7, the
`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. A magnetic 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
`unillustrated hardware fix the pole faces 62, 68 to the yoke
`98.
`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 confines the magnetic field on the back or top side of
`the magnetron to the yoke 98. A semi-toroidal magnetic field
`100 is thereby produced, which extends through the non
`magnetic target 14 into the vacuum chamber 12 to define the
`high-density plasma region 38. The field 100 extends
`through the non-magnetic target 14 into the vacuum cham
`ber 12 to define the extent of the high-density 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. The
`magnetic yoke 90 and the two pole faces 62, 68 are
`preferably plates formed of a Soft magnetic material Such as
`SS416 stainless steel.
`The inner prolate end 80 of the magnetron 60 is connected
`to a shaft 104 extending along the rotation axis 78 and
`
`45
`
`50
`
`55
`
`60
`
`65
`
`8
`rotated by a motor 106. As illustrated, the magnetron 60
`extends horizontally from approximately the center of the
`target 14 to the right hand Side of the uSable area of the target
`14. Demaray et al. in U.S. Pat. No. 5,252,194 disclose
`exemplary details of the connections between the motor 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
`end 74 of the outer pole face 72, its position may be
`optimized to a slightly different position, but one preferably
`not deviating more than 20%, 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 FIG. 4 has the advantage
`of Simplicity and a very Small area while Still providing full
`target coverage. AS will be discussed later, the asymmetric
`magnetic flux of the two poles is a