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`
`USt'ltIlt3306265131
`
`(12) United States Patent
`US 6,306,265 Bl
`(10) Patent No;
`
` Fu ct al. (45) Date of Patent: Oct. 23, 2001
`
`
`(54] HIGH-IJI‘INSITY PLASMA FOR IONIZEII
`METAL DEPOSITION CAPABLE OF
`EXCITING A PLASMA WAVE
`
`(75)
`
`Inventors: Jianming Fit. San Jose; Prahuranl
`analrnja. Sunnyvale; Fusen Chen.
`Saratoga; John Forster, San Francisco.
`all 01‘ 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. 15401) by D days.
`
`(21) App]. No.: 09f54fi,793
`
`(22
`
`Filed:
`
`Apr. 11, 2000
`
`2 24] 710 “
`“2‘89“”
`03-28226}
`ll—ii'MZZS
`
`(GB)
`".-"l"-")l
`431937 (JP) -
`llt'l'S'BS (J P) .
`Jil‘l‘l‘l
`(JP) .
`Ci’I'llER PUBLICAI‘IONS
`
`204329319
`
`:1]. “Charged particle fluxes [rom planar
`B. Window et
`magnetron sources", .l . Vac. Sci. 'l'eehnol. A 4(3), MarJApr.
`1986. pp. 1964202.‘
`J. Musil, el al. "Unbalanced magnetrons and new sputtering
`systems with enhanced plasma ionization". J. Vac. Sci
`‘l'eehnol. A 9(3). Maytlun. 1991, pp. 117]—-ll77.*
`W. Munz ”The unbalanced magnetron: current status of
`development“. Surface and Coatings 'l‘eehnology. 48 (1991).
`pp. 81'94}
`Malsuoka et 3].. "Dense plasma production and tllm depo-
`sition by new high—rate sputtering using an electric mirror.”
`Journal of Vacuum Science and léchnnlogy/l. vol. 7. No. 4.
`.lul.t'Aug. 1989, pp. 3632—2657.
`
`Related U.S. Application Data
`
`‘ cited by examiner
`
`(63) Continuation—impart of app] icalion No. ”9,673,097. Iiled on
`Aug. ll, 1900, now Pal. No. h.t£3_.hl4, which is: a continu—
`ation-[It‘pttrl of application No. IWEZLI‘L-lbs, filed on Feb, 12.
`1999.
`
`Int. Cl.7
`[51 )
`(53) U.5. Cl.
`(58) Field of Search
`
`C23C 14134
`..
`204i192 12; 204298”‘
`.. 2(I4r298. 19, 298.2,
`Zth‘Z‘JS. 23. 192.12
`
`(5(1)
`
`References Cited
`U .S. PATENT DOCUMENTS
`
`Primary l;'.t‘:ttttirt€J‘—Nitrn Nguyen
`Assistant Exmtrirrt‘r—Gregg Cantelmo
`(74) Attorney, Agent. or Firm—Charles S. Guenzer. Esq
`
`(57)
`
`ABSTRACT
`
`low—pressure
`A magnetron especially advantageous [or
`plasma sputtering or sustained self—sputtering having
`reduced are-a but
`111"
`target coverage. The magnetron
`includes an outer pole face surrounding an inner pole face
`with a gap therebetwuen. 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 31] to 30° may he [owned 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 23 MHz which
`interact with the l
`to 20 eV electrons of the plasma to
`thereby increase the plasma density.
`
`22 Claims, 11 Drawing Sheets
`
`4,444,643 = #1084 Garrett
`5.252.758
`tllt'le Dentnray et al.
`S,7?tl_.o.25
`6:19th Kiyota ............
`5.397.753 ‘
`4:199le
`lloug et at.
`iii-Hoyt}? '
`[@1090 Cher: elal.
`
`204mm
`204.9298.)
`
`2th293.2
`438L305
`
`.. 104.32.03.31.
`
`FOREIGN PATENT DOCUMENTS
`
`(Kt-EJZIISSEIA
`o nut-41": A!
`
`llltt‘J‘J-l 0:11)).
`‘ Hume (1-1?)
`
`molest»
`
`40
`
`TSMC-1117
`
`TSMC v. Zond, Inc.
`
`Page 1 of 24
`
`mtiutIIlr
`
`mm
`
`AL\\\\“
`
`TSMC-1117
`TSMC v. Zond, Inc.
`Page 1 of 24
`
`

`

`US. Patent
`
`()c1.23,2001
`
`Sheet 1 of 11
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`US 6,306,265 BI
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`10
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`28 L
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`a 232
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`T
`
`(PRIOR ART)
`
`FIG.
`
`1
`
`TSMC-1117 / Page 2 of 24
`
`TSMC-1117 / Page 2 of 24
`
`

`

`US. Patent
`
`Oct. 23, 2001
`
`Sheet 2 of 11
`
`US 6,306,265 Bl
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`WE5
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`(PRIOR ART)
`
`FIG. 3
`
`TSMC-1117 / Page 3 of 24
`
`TSMC-1117 / Page 3 of 24
`
`

`

`US. Patent
`
`Oct. 23, 2001
`
`Sheet 3 of 11
`
`US 6,306,265 BI
`
`72
`
`68
`
`7O
`
`
`
`mJ/i
`
`PM 4
`
`OE9696969@@@@G§>@O
`@ @@@©@© @
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`\_—V____/
`
`FIG. 5
`
`FIG. 6
`
`/—90,92
`
`TSMC-1117 / Page 4 of 24
`
`TSMC-1117 / Page 4 of 24
`
`

`

`US. Patent
`
`Oct. 23, 2001
`
`Sheet 4 of 11
`
`US 6,306,265 Bl
`
`FIG.
`
`’7
`
`110
`
`108
`
`122
`
`106'
`
`114
`
`78
`
`112
`
`FIG. 8
`
`TSMC-1117 / Page 5 of 24
`
`TSMC-1117 / Page 5 of 24
`
`
`

`

`US. Patent
`
`Oct. 23, 2001
`
`Sheet 5 of 11
`
`US 6,306,265 B]
`
`A//#H#§F
`
`126
`
`152
`
`4//—
`
`140
`
`136
`144 FIG 10
`
`148
`
`130
`
`150
`
`152
`
`TSMC-1117 / Page 6 of 24
`
`TSMC-1117 / Page 6 of 24
`
`

`

`US. Patent
`
`Oct. 23, 2001
`
`Sheet 6 of 11
`
`US 6,306,265 Bl
`
`97
`@969
`@@
`
`150
`
`164
`
`©
`
`@®©© 95
`©
`@@ ®
`@@@ @
`© 160 ©
`@©@
`($2462
`@6969
`\_—fi/____/
`
`FIG.
`
`11
`
`r“ \ 14
`
`‘170
`’172
`
`R?“
`
`78
`
`FIG. 12
`
`TSMC-1117 / Page 7 of 24
`
`TSMC-1117 / Page 7 of 24
`
`

`

`US. Patent
`
`um. 23. 2001
`
`Sheet 7 0f 11
`
`US 6,306,265 Bl
`
`éfiz
`T
`
`7T
`/2
`
`,n
`/4
`
`174
`
`176
`
`FIG 13
`
`9
`
`90°
`
`180°
`
`178
`
`180
`
`90°
`
`1800
`
`e
`
`fl+2
`
`1 2
`
`P/RT
`
`TSMC-1117 / Page 8 of 24
`
`TSMC-1117 / Page 8 of 24
`
`

`

`US. Patent
`
`Oct. 23, 2001
`
`Sheet 8 of 11
`
`US 6,306,265 B1
`
`190
`
`
`
`TSMC-1117 / Page 9 of 24
`
`TSMC-1117 / Page 9 of 24
`
`

`

`US. Patent
`
`Oct. 23, 2001
`
`Sheet 9 uf 11
`
`US 6,306,265 Bl
`
`200
`
`206
`
`202
`
`
`
`TSMC-1117 / Page 10 of 24
`
`TSMC-1117 / Page 10 of 24
`
`

`

`US. Patent
`
`Oct. 23, 2001
`
`Sheet 10 0f 11
`
`US 6,306,265 B1
`
`
`
`80
`
`60
`
`BOTTOM
`
`COVERAGE
`W 40
`
`
`
`20 —-{}J—1oow Bms
`---fl--- 250w BIAS
`
`ASPECT RAND
`
`TSMC-1117 / Page 11 of 24
`
`TSMC-1117 / Page 11 of 24
`
`

`

`US. Patent
`
`0a. 23. 2001
`
`Sheet 11 0f 11
`
`US 6,306,265 B1
`
`PRESSURE
`
`OfiT)
`
`1
`
`2O
`
`4O
`
`60
`
`80
`
`100
`
`FIG 22
`
`N2 FLOW (scam)
`
`50
`
`STEP 30
`COVERAGE
`(%)
`20
`
`40
`
`1O
`
`FIG 23
`
`ASPECT RATIO
`
`TSMC-1117 / Page 12 of 24
`
`TSMC-1117 / Page 12 of 24
`
`

`

`US 6,306,265 I31
`
`1
`HIGH-DENSITY PIASMA 1"OR ION [ZED
`METAL DISPOSITION CAPABLE OF
`EXCITING A PLASMA WAVE
`
`RELATED APPLICATION
`
`'lhis application is a continuation in pan of Ser. No.
`09,673,097, tiled Aug. 12, 1999, now US. Pat. No. 6,183,
`61-1Feb. (t, 2001 which is a continuation in part at Ser. No.
`(BEE-19.468. filed Feb. 12, 199‘).
`
`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 entrance sputtering.
`
`BACKG ROUND 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. I. and the
`illustration is based upon the Bndura 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 ot‘ 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 —fit)(lVDC with respect to
`the shield 20. Conventionally, the pedestal 18 and hence the
`wafer 16 are left electrically ttoaling.
`A gas source 24 supplies a sputtering working gas,
`typically the chemically inactive gas argon. to the chamber
`12 through a mass [low controller 26. In reactive metallic
`nitride sputtering, for example, ol‘ 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,0,. 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
`10'7 TDIT or even lower. the pressure of the working gas is
`typically maintained at between about 1 and 1000 m'l‘orr. A
`corn puter-based controller 30 controls the reactor including
`the DC power supply 22 and the mass [low controllers 26.
`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 ofa 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 water 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
`
`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
`filll 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 amociated 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 [ill 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-lcvel
`metallizalion level, the tilled hole 4-0 is called a via. For
`simplicity, we will refer hereaftcronly to vias. The widths of
`inter-level vias have decreased to the neighborhood of 0.25
`rim and below while the thickness ofthc inter—level dielectric
`has remained nearly constant at around 0.7,ttm. 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 oll'
`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 tilting of the bottom of the hole and creating
`a Void in the via metal.
`
`It has become known, however, that deep hole tilting 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. I. 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 ot‘ the pedestal
`electrode 18 to additionally accelerate the ionincd 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 ol‘ the ell‘ectiveness of hole lilting are bottom coverage
`and side cove rage. As illustrated schematically in FIG. 2.. the
`initial phase of sputtering deposits :1 layer 50, which has a
`surface or blanket thickness of 51 , a bottom thickness of 53,
`and a sidewall thickness ofsj. The bottom coverage is equal
`to Sal’Sl. and the sidewall coverage is equal to sjt’sl. The
`model
`is overly simplified but
`in many situations is
`adequate.
`One method ot’ increasing the ionization fraction is to
`create a high-density plasma ([1119). such as by adding an
`RF coil around the sides of the chamber 12 of FIG. I. An
`HDP reactor not only creates a high—density argon plasma
`but also increases the ionization traction of the sputtered
`atoms. However, IIDP 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
`
`f."
`
`it!
`
`3.5
`
`40
`
`St]
`
`_
`
`on
`
`65
`
`TSMC-1117 I Page 13 of 24
`
`TSMC-1117 / Page 13 of 24
`
`

`

`US 6,306,265 131
`
`3
`shape 01' a top hat. This type ol‘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.
`the sidewall
`is that
`A further problem in the prior art
`coverage tends to he 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 photolilhography to appear to move as the trenches are
`asymmetrically narrowed.
`that promotes deep hole
`Another operational control
`is generally believed that
`filling 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 lend to neutralize ions
`and to randomize velocities, both effects degrading hole
`lilling. 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
`l‘actors.
`
`The extreme of low~pressurc plasma sputtering is sus—
`tained self-sputtering (SSS). as disclosed by Fu c1 at. in US.
`patent application, Ser. No. ler'854.U(l8, filed May 8. 1997.
`In SSS. the density of positively ionized sputtered atoms is
`so high that a suflicient number are attracted back to the
`negatively biased target to rcsputter 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 clectromigration. However,
`for copper SSS to
`become commercially feasible.
`:1 full-coverage. high-lield
`magnetron needs to be developed.
`Increased power applied to the target allows reduced
`pressure, perhaps to the point or" 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 elIectivc 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 l'ull
`magnetron coverage is not achieved, not only is the target
`not efl’tcieutly used, but more importantly the uniformity of
`sputter deposition is degraded, and some of the sputtered
`material redcposits on the target in areas that are not being
`
`f."
`
`.10
`
`10
`
`3-0
`
`3.5
`
`40
`
`5t]
`
`55
`
`6t]
`
`65
`
`4
`sputtered. Funhen'nore. the ma terial redeposited on unsput-
`tered areas may build up to such a thickness that it is prone
`to flake oil". producing severe particle problems. While radial
`sea nning can potentially avoid these problems, the required
`scanning mechanisms are complex and generally considered
`infeasible in a production environment.
`One type ofcomrncrcially available magnetron is kidney-
`shapcd, as exemplified by 'l‘epmart
`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 Teprnan 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.
`[I 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 cove-rage so as to pro—
`mote deep bole 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 pom‘tioned
`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 Wr’cm‘2 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-
`ofhundrcds ol" megahertz. which is parametricnlly 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 hy capacitive ly 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.
`'l'hcrcby, 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-
`
`TSMC-1117 I Page 14 of 24
`
`TSMC-1117 / Page 14 of 24
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`

`

`US 6,306,265 131
`
`5
`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
`[LS milliTorr. often less Ihan 0.3 milleorr, 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 (L3 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 su fliciently target powur and high magnetic field
`away from the target, that a non-linear wave~beam interac-
`tion occurs that pumps energy into plasma electrons, thereby
`mcmasing the plasma density.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a schematic diagram of a DC plasma sputtering
`[fillCICIC
`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»
`Iron 01' 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 ofthe magnetron of FIG.
`
`4.
`
`FIG. 8 is a plan view of an egg—she pod magnetron.
`FIG. 9 is a plan view of a triangularly shaped magnetron.
`FIG. [0 is a plan view of a modification of the tt-iartgulnrly
`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 areed
`triangular magnetron of FIG. til.
`FIG. 12 is a plan view of two model magnetron-s used to
`calculate areas and peripheral lengths.
`FIG. 13 is a graph of the angular dcpendences 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 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 idealizetion ot‘ the magnetic
`[lcld 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 ohtaioed in the two
`sputtering modes [or 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 he 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 ofunil’orm composition.
`The rotation axis 78 is located at or near one pro-late end 80
`of the outer pole face 68 and with its other prolale end 82
`located approximately at the outer radial usable extent of the
`target .14. The asymmetric placement of the rotating msg—
`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 ditferent magnetron designs use ditTerent portions
`of the same target. However. it is bounded by the tint 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 magnetrous 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
`
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`TSMC-1117 I Page 15 of 24
`
`TSMC-1117 / Page 15 of 24
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`US 6,306,265 131
`
`7
`the pole faces 62, 158. the magnets 91], 92, and possibly a
`back magnetic yoke produces two opposite magnetic poles
`having areas defined by the pole faces 621 68. Other means
`may he 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. 11' they are
`of different, magnetic composition, diameter, or length. the
`flux produced by dilIerent magnets may be dillerc-nt. A
`cross-sectional view ol‘ a magnet 90, 92 is shown in FIG. 6.
`A cylindrical magnetic core 93 extending along an axis is
`composed of a strongly magnetic mate rial. such as neody-
`mium boron iron (NdBIr‘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 $3411]
`stainless. steel, and the tubular sidewall 96 is composed of a
`non-magnetic material, preferably 58304 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 El magnetic yoke to be shortly described.
`"thereby. the magnets 90, 92 are fixed in the magnetron. The
`magnetic core 93 is magnetized alongits axial direction. but
`the two different types of magnets. 90. 92 are oriented in the
`magnetron 60. as illustrated in the cross-sectional view ol‘
`FIG. 7, so that the magnets 90 of the inner pole 62 are
`aligned to have their magnetic lield extending vertically in
`one direction, and the magnets 92 of the outer pole 63 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 l4.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 lit: the magnets 90. 92, and
`unillustrated ha rdware [is 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. 'll‘re 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. Asemi-toroidal magnetic field
`tilt} 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 deline 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
`55416 stainless steel.
`
`The inner prolate end 80 of the magnetron 60 is connected
`to a shaft 104 extending along the rotation axis 78 and
`
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`rotated by a motor 106. As illustrated, the magnetron 60
`extends horimntally from approximately the center of the
`target 14 to the right hand side ot'thc usable area of the target
`14. Demaray et at.
`in U.S. Pat. No. 5.252.194 disclose
`exemplary details of the connections between the motor .106.
`the magnetron 611. 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
`optimizer] to a slightly different position, but one preferably
`not deviating more than 20%, more preferably 10%. from
`the inner prolale end 81] 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 tater. 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.
`continuously curved shapes of continuously 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.
`'I'abuchi illustrates a symmetric oval magnetron in Laid-
`open Japanese Patent Application fiB-l‘tflfift. This shape
`however has the disadvantage of a complex shape. espe—
`cially for packing the magnets in the in her pole.
`Another oval shape is r