I|||||||||||l||||||||||||||||||||||||||||||||||||||||||||||l|||||||||||||||
`
`USUU63U6265l31
`
`(6) United States Patent
`l*‘u ct al.
`
`(16, Patent No;
`(45) Date of Patent:
`
`US 6,306,265 B1
`Oct. 23, 2001
`
`(54) HIGH-l)l‘1NSl"l'Y PLASMA FUR IONIZEII
`METAL DEPOSITION CAPABLE OF
`EXCITING A PLASMA WAVE
`
`2 241 710 ‘
`02-393'“
`‘*3-l822'=—’~
`l1—f.I?4225
`
`(GB)
`".-"I"-"J1
`(J 1’)
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`“W933 U P1 -
`3fl‘3‘»“-|
`(JP).
`
`20-“£93.19
`
`(75)
`
`Inventors: Jianniing F‘l.l. Sun .1055; Pl'dhlll‘al]l
`Gnpalraga. Sunnyvale; Fusen Chen.
`gm-amga;Ju|m Fm-star, San Fl-3!-,,_-.'5,m_
`an of cf‘ (U3)
`
`(73) Assignccr Applied Materials, lnc., Santa Clara,
`CA(Us)
`
`( ' ) Nolicc:
`
`Subjucl to any disclaimer, Iht: lcn'n uflhjs
`palunl is cxlcndcd or adjusted under 35
`U.S.C. 15401) by D days.
`
`(31) AWL N“; 093545393
`1_
`Irll-rd:
`
`Aim 11. 2000
`
`(22)
`
`0'I'”ER IJUBLICAHONS
`_
`_
`I
`_
`[luxcs Lrom planar
`ill.‘ “Charged Pilfllclf
`B. Window cl
`magnetron suurcn:s' , J. Vac. Sci. lcchnol. A 4(3), Mar.H\pr.
`1986. pp. 19(1-2{12.*
`J. Musil, cl 3|. "Un|.'!:Ilanccd Inagnclrons and new s.putlcrIt1_g
`.-syslcms with enhanced plasma ionization". J. Vac. Sci
`‘lbchncul. A 9(3). Mayflun. 1991, pp. 117]-ll'z'7.*
`W. Mun: “'l"l1t: unhalzlnccd inagnctronz current status of
`dcvclopnw-nl“. Surface and Coalings'l‘cchno]ogy.-18(1991).
`pp. 81-94.‘
`Mulsuoka ct 3].. "Dense plasma production and film depo-
`5:’ lion by new high-—ratc sputtering using an electric rnirror.”
`Journal of Vacnztrri ..\‘cfe*r.Ic-cl and Ié*c.’mnlogyA. vol. 7. No. 4.
`.lul.x'Aug. 1989, pp. 3632-2657.
`
`Related U.S. Application Data
`
`' ‘-5i1*'—"-1 5}’ ‘-'«’?‘3"“i11*—'1'
`
`(63) Cnnlinualion—in-part ofapplicalion N6.:a<)..+373,n-J7. Iilcd on
`Aug .12! 1900’ now PHL Nu ',‘Tm3?l.‘I 4’ which is a mminw
`J’.
`alien-in-parl ofapplicalioni No. I-.«[":"24U,"l-68, filudon Feb. 12.
`‘W 5"
`Int. Cl.’
`(51)
`(52) u.s.C1.
`(53) Field of Search
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`C23C l-‘U34
`20-$192.12; 2r14s2tJs.2
`3u4;'393_1o, 393,3‘
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`Refumnces Cited
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`P'f"_"f'_""-"i [""i""m.'€';_—Nf'I" Nglf-W"
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`(74) Mflrm-:\'. -4:-?CW- 0*’ Fm?-'—U1=fl’1c5 5- €I1l=U?~‘I- Esq
`(57)
`ABSTRACT
`
`_
`"_‘W'PT'35**}”*'
`3d\{=m|a1-:*.°0U_S F0!
`A mflgnclwn ‘~’_5P'3°'“1“>’
`131355‘-'1
`-'5P“”'~""1"£. _0T 51'5131'3'-id 5'°”'5l“':'”‘3|‘1“B '-"3"1“E»
`reduced area but
`lull
`largct
`I:Lwu:.r::gc.
`I110 rnagnclron
`includes an outer pole f}1C\.‘. surrouncling an inner pole fact:
`with a gap lhcrcl\clwucn.'l'l1c outer pole ol the magnetron ol
`the invention L: smaller than that of .1 circular magnetron
`similarly extending from the center to lhu pcriphcry of this
`largct. Arrrr-:1":-:rr;:cl
`lriangtllar shape having a small apex
`Elflglt.‘ of
`1U
`may ht? lUI'ITl¢d rr(!ITI UUICF bar fl13gUU15C\r
`DDI: magnetic pflliifily cnclosing an inner magnet ufiht: Olllct’
`rnalgnelic polarity. The magnetron allows the generation of
`plasma wavos in lh-is nciglihorhootl of 22 MHz which
`illlcracl with [he 1
`lo 20 cV electrons of the plasma to
`Ilaurchy incrcasc thc plasma density.
`
`‘
`
`2t'J4I293.lu
`
`22 Claims, 11 Drawing Sheets
`
`U-3- PATENT DOCUMENTS
`__H4__L643 , #1084 Gurrell
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`Page 1 of 24
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`U.S. Patent
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`01-1. 23, 2001
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`sheet 1 of 11
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`US 6,306,265 B1
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`TSMC-1117 I Page 2 of
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`TSMC-1117 / Page 2 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 2 of 11
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`US 6,306,265 B1
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`TSMC-1117 I Page 3 of
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`TSMC-1117 / Page 3 of 24
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`

`
`U.S. Patent
`
`Oct. 23, 2001
`
`Sheet 3 of 11
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`Us 6,306,265 B1
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`72
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`TSMC-1117 I Page 4 of
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`TSMC-1117 / Page 4 of 24
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`TSMC-1117 I Page 5 of
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`TSMC-1117 / Page 5 of 24
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`U.S. Patent
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`Oct. 23, 2001
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`Sheet 5 of 11
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`TSMC-1117 I Page 6 of
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`TSMC-1117 / Page 6 of 24
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`TSMC-1117 I Page 7 of
`
`TSMC-1117 / Page 7 of 24
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`

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`U.S. Patent
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`US 6,306,265 B1
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`TSMC-1117 I Page 8 of
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`TSMC-1117 / Page 8 of 24
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`

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

`
`U.S. Patent
`
`Oct. 23, 2001
`
`sheet 9 of 11
`
`US 6,306,265 B1
`
`200
`
`206
`
`202
`
`TSMC-1117 I Page 10 of
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`TSMC-1117 / Page 10 of 24
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`

`
`U.S. Patent
`
`out. 23, 2001
`
`sheet 10 :1!’ 11
`
`US 6,306,265 B1
`
`
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`80
`
`60
`
`BOTTOM
`
`COVERAGE
`W 40
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`---r3--- 250w BIAS
`
`20 —-{y~—10ow Bms
`
`ASPECT RAND
`
`TSMC-1117 I Page 11 of
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`TSMC-1117 / Page 11 of 24
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`

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`U.S. Patent
`
`01-1. 23. 2001
`
`sheet 11 of 11
`
`US 6,306,265 B1
`
`PRESSURE
`
`(MT)
`
`1
`
`20
`
`40
`
`60
`
`80
`
`100
`
`N2 FLOW (scam)
`
`50
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`40
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`STEP 30
`COVERAGE
`(z)
`20
`
`10
`
`ASPECT RATIO
`
`TSMC-1117 I Page 12 of
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`TSMC-1117 / Page 12 of 24
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`

`
`US 6,306,265 B1
`
`1
`HIGH-l)ICNSlTY PLASMA It‘OR ION [ZED
`METAI. l)I‘lPOSITI()N CAl’AB[.F. OI‘
`EXCITINII A PLASMA WAVE
`
`RELATED APPLICATION
`
`'lhis application is a continuation in pan of Scr. No.
`lI9l373,tl‘)'?, tiled Aug. 12, 1999, now US. Pat. No. 6,183,
`61-1 Feb. t’), 2001 which is a continuation in part of Ser. No.
`(l9r'2-'19,-168. 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 held to entrance sputtering.
`
`BACKG ROUND ART
`
`Sputtering. alternatively culled physical vapor deposition
`(PVD). is the ntost prevalent method of depositing layers of
`metals and related materials in the fabrication of semicot'I-
`ductor integrated circuits. A conventional PVD reactor III 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 charnlrier 12 sealed to a PVD
`target 14 com posed ol‘ 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)(lVlJ(‘ with respect to
`the shield 20. Crinventionally, the pedestal 18 and hence the
`wafer 16 are left electrically tloating.
`A gas source 24 supplies a sputtering working gas,
`typically the chemically inactive gas argon. to the chamber
`12 through a mass llow controller 26. In reactive metallic
`nitride sputtering, for example, oi‘ 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 A1303. 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
`l(l'7 'l'otT or even lower. the pressure of the working gas is
`typically maintained at between about 1 and 1000 tn’ hrr. A
`com puter-based controller 30 controls the reactor including
`the DC power supply 22 and the mass llow 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 :1 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 fortning 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 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 held within the chamber in the
`neighborhood of the magnebs 34, 36. The magnetic lield
`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
`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
`inteyated circuits has placed increasing demands upon
`sputtering equipment and processes. Many of the pnobierns
`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 [ill metal into the hole 40 to
`provide intcr—level electrical connections. If the underlying
`layer 46 is the semiconductor substrate, the tilted hole 40 is
`called a contact;
`if the underlying layer is a lower-level
`ntetallixatiott level, the Illled hole 4-0 is called a via. For
`simplicity, we will refer liercafteronly to vias. The widths of
`inter-level vias have decreased to the neighborhood of 0.25
`pm and below while the thickness ofthc irtter— level die lcctric
`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 it problem for sputtering
`because most
`forms of sputtering are not strongly
`anisotropic,
`a cosine dependence ol1'
`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 lilting 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 lloatirtg, develops at 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 ellect 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.
`Tlie process of sputtering with a significant
`fraction of
`ionized sputtered atoms is called ionized metal deposition or
`ioniared metal plating (IMP). Two related quantitative mea-
`sures ol‘ the ellicctiveuests ofhole lilting are bottom coverage
`and side cove rage. As illustrated se|1cn1at'ical|y in FIG. 2.. the
`initial phase of sputtering deposits :1 layer 50, which has it
`surface or blanket thickness of s, , a bottom thickness of s,
`and it sidewall thickness ofs3. The bottom coverage is equal
`to 5:;’Sl, and the sidewall coverage is equal to s_,ls,. The
`model
`is overly simplified but
`in many situations is
`adequate.
`One method of increasing the ionization lrttction is to
`create a high-density plasma (IIDP), such as by adding an
`RF ooil around the sides of the chamber 12 of FIG. 1. An
`HDI’ reactor not only creates a high—density argon plasma
`but also increases the ionization traction of the sputtered
`atoms. Ilowevcr, IIDP PVIJ 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 [or increasing the ionization ratio is to
`use a hollow-cathode magnetron in which the target has the
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`TSMC-1117 I Page 13 of
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`TSMC-1117 / Page 13 of 24
`
`

`
`US 6,306,265 B1
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`3
`shape ol :1 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-
`calhode reactor tends to form an undulatory copper film on
`the via sidewall, and further the deposited rnctal tends to
`dewet. The variable thickness is particularly serious when
`the sputtered copper layer is being used as it 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 preclelermirtocl 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
`titling is chamber pressure.
`It
`lower charnhcr pressures promote hole filling. At higher
`pressures.
`there is a higher probability that sputtered
`particles, whether neutral or ionized. will collide with atonts
`of the argon carrier gas. Collisions tend to neutralize ions
`and to randomize velocities, both effects degrading hole
`lllling. 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
`liactors.
`
`The extreme of low~pressure plasma sputtering is sus-
`tained self-sputtering (SSS), as disclosed by Fu ct al. in US.
`patent application, Scr. No. tIBr'854.U(IB, filed May 8, 1997.
`In SSS. the density of positively ionized sputtered atoms is
`so high that a suflicient number are attracted hack to the
`negatively biased target to rcsputter more ionized atoms.
`Under the right conditions for a limited number of target
`metals. the sell‘-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 lield. 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, a lull-coverage. high-licld
`magnetron needs to be developed.
`Increased power applied to the target allows reduced
`pressure, perhaps to the point ot" sustained sell‘-sputtering.
`The incrcasctl 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 ellective sputtering. Hence.
`a small. high-Iield 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 unifonnity. 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 etliciently used, but more importantly the uniformity of
`sputter deposition is degraded, and sortie of the sputtered
`material redeposits on the target in areas that are not hcirtg
`
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`sputtered. Furthemiore, 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
`nning can potentially avoid these problems, the required
`scanning ntechanisms are complex and generally considers.-cl
`infeasible in a production environment.
`One type ttfcommcrciaily available magnetron is kidney-
`shaped, as excrnplilicd by Tepmart 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 llices 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. Thu.-.
`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 held and for uniform
`sputtering hut 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 snnall.
`high-field magnetron providing full coverage so as to pro-
`mote deep hole filling and sustained copper sell’-sputte-ri.ng.
`
`SUMMARY 017 THE Il'*«lVENTlON
`
`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 extcnd along the target
`radius with respect to the typical rotation axis of the mag-
`netron. The shapes include rttcetracks, ellipses. egg shapes.
`triangles, and arced triangles asymmetrically pofitiont.-d
`about the target center.
`The magnetron is rotated on the backside of the target
`about it point preferably near the rr1ttgrteI.ron‘s thin e-nd, and
`the thicker end is positioned more closely to the target
`periphery. Prefcralily,
`the total magnetic flux is greater
`outside than inside the hall" radius of the target.
`The magnetic intensity away l'rot't't
`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 Wlcm‘? to be applied from an 18 kW power supply
`to a fully covered sputtering target used to sputter deposit at
`200 mm wafer.
`
`The high power density and the rrtttgnctic field extending
`far away from the target are two means possible to produce
`a plasma wave which can further drive the plasma to it
`higher density and ionization. Advantageously, a primary
`plastna wave is generated at a higher frequency in the range-
`ofhunrlreds of megahertz, which is para.melricnl.ly converted
`to another wave at :1 much lower l'requr:nt:y.l'orett:1mple, 5
`to 75 Mllz. corresponding to the thermal velocity of elec-
`trons in the plasma produced hy eapacitively coupling DC
`power to the target.
`The magnetron is configured to produce less magnetic
`llux in its inner pole than in its surrounding outer pole.
`Thereby, the magnetic field reaches further into the sputter-
`ing cl'ta.n1ber 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
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`

`
`US 6.306.265 B1
`
`5
`tag over a small closed area facilitates sustained sell‘-
`sputtering. Many metals not subject
`to sustained self-
`spultering can be spulterecl at chamber pressttres of less than
`[LS milliTorr. often less than 0.3 milljTorr, and even at 0.1
`rnilliTorr. 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 titlly .-self-sustahted 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 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
`ittcmasing the plasma density.
`BRII.*.l" IJESCRIPTION O1’ TI-IE IJRAWINGS
`
`FIG. 1 is a schenttttic diagram of a DC‘ plasma sputtering
`I'€3ClC|I'.
`FIG. 2 is a cross-sectional view of at
`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.
`
`inter—level via in a
`
`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 olthc magnetron ol‘ FIG.
`
`4.
`
`FIG. 8 is a plan view of an egg—sha ped magnetron.
`FIG. 9 is :1 pl an view of a triangularly shaped magnetron.
`FIG. [0 is a plan view of 3 morlilication of the triartgularly
`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. 10.
`FIG. 12 is a plan view of two model magnetron.-5 used to
`calculate areas and peripheral lengths.
`FIG. 13 is a graph of the angular dcpenrlcnces ofthe areas
`ot‘ 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 ltottorn 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. 1’? is a side view ot‘ an idealization of the magnetic
`[leld produced with the described embodiments of the inven-
`tion.
`
`FIGS. 18 and 19 are atop 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 n
`magnetron ol‘ the invention.
`FIG. 23 is a graph of the step coverage obtained in the two
`sputtering modes for reactive sputtering of titanium nitride
`with it magnetron of the invention.
`
`.DE'l'AlI.ED DESCRlP'I‘lON OF THE
`PRl3[-‘ERRED IEMBOIJIMENTS
`
`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, 63. The outer pole face 68 of the
`other magnetic polarity includes opposed parallel middle
`straight sections 72 connected by two rounded e-rtds 74 in
`general central symmetry with the inner pole face 62. The
`middle sections '.-'2 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 boll: as
`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 gene ral mag-
`netic ellects as far as the invention is concerned. The
`
`illustrated assembly produces a generally semi-toroidal
`magnetic ticld having parallel arcs extending perpendicu-
`larly to it closed path with a minimal lie-ld—t’ree region in the
`center. There results :1 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 ofuniform composition.
`The rotation axis 78 is located at or near one prc-late 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 ccnter provides it small
`magnetron nonetheless achieving full target coverage. The
`outer usable periphery oi‘ the target is not easily defined
`because ditlerent magnetron designs use ditfcrent portions
`of the same target. However. it is bourlded by the tint area of
`the target and almost always extends to significantly beyond
`the diameter of the water 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 Inagrtetrons 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
`prefe-rahl_v within 2t]""»tE- 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
`
`.10
`
`EU
`
`40
`
`St]
`
`55
`
`Eli!
`
`O5
`
`TSMC-1117 I Page 15 of
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`

`
`US 6,306,265 B1
`
`7
`the pole faces 62, 68. the magnets 9t], 92, and possibly at
`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. It" they are
`of rtillerent, magnetic composition, diameter, or length. the
`lime produced by dilferent magnets may be dille-re-nt. A
`eross—section:tl 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 mate rial. 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 fonn an air-tight canister. The caps 96 are
`composed of a soft magnetic material, preferably S5410
`stainless steel, and the tubttlar sidewall 96 is composed of a
`non-magnetic material, preferably S8304 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 at magnetic yoke to he 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 of
`FIG. 7, so that the magnets 90 of the inner pole 62 are
`aligned to have their magnetic tield 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.
`'I'l1at 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 anti in the yoke 98 lit the magnets 90. 92, and
`unillustrated ha rdw-are tix l.l'It‘.: pole faces 62. 68 to the yoke
`98.
`
`The inner magnets 90 and inner pole fact: 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. 'lhe magnetic yoke 98
`magnetically coup lcs the inner and outer poles and substan-
`tially confines the magnetic lield on the back or top side of
`the rnagnetron to the yoke 98. Ascrni-toroidal magnetic ticld
`III!) is thereby produced. which extends through the non-
`magnetic targct 14 into the vacuum chamber 12 to define the
`high-density plasma region 38. The field 100 extends
`through the non—rnagnctic target 14 into the vacuum cham-
`ber 12 to deline the extent of the high-density plasma region
`38. The magnets 90, 92 may he of different magnetic
`strength. I-Iowever, 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 1'aces 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 extcncling along the rotation axis 78 and
`
`10
`
`35
`
`40
`
`-
`
`SU
`
`55
`
`so
`
`65
`
`8
`rotated by a motor 106. As illustrated, the rllagrtetrort 60
`extends htirimntally from approximately the center of the
`target 14 to the right hand side ofthe usable area of the target
`14. Demartty 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
`ll]-1. 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 at slightly different position, but one preferably
`not deviating more than 2(t‘.Pc.-, more preferably 10%. from
`the inner prolate and St] 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 conliguration of FIG. 4 has the advantage
`of sirnplitzity and a very small area while still providing full
`target coverage. As will be discussed later. the asymmetric
`magnetic llux 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 extend