I|||||||||||l||||||||||||||||||||||||||||||||||||||||||||||l|||||||||||||||
`
`USUU63U6265l31
`
`(13) United States Patent
`l*‘u ct al.
`
`(in Patent N6:
`(45) Date of Patent:
`
`US 6,306,265 B1
`Oct. 23, 2001
`
`(54) HIGH-l)l'1NSl"l'Y PLASMA FOR IONIZEU
`METAL DEPOSITION CAPABLE OF
`EXCITING A PLASMA WAVE
`
`(GB)
`".-"'1'"-"J1
`2 241 710 ‘
`(J 1’)
`-
`4E1‘-*3?
`52-39914
`‘*3-l822'=—’~ W933 U P1 -
`l1—f.I?4225
`3il‘3‘»“-|
`[JP].
`
`204333.19
`
`(75)
`
`invenlursi Jismming F‘l.l. San loss; Prahuram
`Gnpalraja. Sunnyvale; Fusen Chen.
`Sm-amga; Jmm [rm-star, gm 5:‘,-3n,_-.'5,m_
`an of CA (US)
`
`(73) Amignec: Applied Materials, Inc., Santa Clam,
`CA (US)
`
`( ' ) Nolicc:
`
`Subjucl to any disclain1e:r,Ih:: lt:lTl‘l uflllis
`palunl is cxlcndcd or adjusted under 35
`U.S.C. 15401) by D days.
`
`(31) AWL N“; QQI545,-ygg
`
`(22
`
`Fil-rd:
`
`Aim 11. 2000
`
`0'I'”ER IJUBLICAHONS
`_
`I
`_
`:1]. “Charged particle liuxcs Lrom planar
`B. Wlndow cl
`rnagnclron sourcn:s", J . Vac. Sci. Tcchnol. A 4(3), Marjflpr.
`1986. pp.
`l9(1‘2{12.*
`J. Musil, cl al. "Unbalanced magnclrons and new spiitlcring
`.-syslcms wilh enhanced plasma ionization". J. Vac. Sci
`‘lbchnol. A 9(3). Mayflun. 1991, pp. 117]-ll';'7.*
`W. Mun: “'l"i‘u: unhalzlnccd magnetron: currcnl slalus of
`Llcvclopnw-nl“. Surface and Coaiings'l‘cchnology.-18(1991).
`pp. 81-94.‘
`Mal?-uoka ct al.. "Dense plasma production and film depo-
`51' lion by new high-—ratc spullcxing using an cleclriu rnirror.”
`Jcmrnrri of Vacmirri ..\‘cie*r.Ic-cl imd Iieciirinlogyd. vol. 7. No. 4.
`.illi..*'/\Llg. 1989, pp. 3632-2657.
`
`Related U.S. Application Data
`
`' *’-5i1*'—"-1 5}’ ‘-'«’?‘3"“i11*—'1'
`
`P'f'_"f'_""-"' ["‘”""’."'9r_—N."m Nglf-W"
`_
`Anrsinrir E.‘l'(i'J'l'H!Ir:‘} —(m:g§ Canlclnm
`(74) M0rm‘='_\'» =1:-?-i’»'"- 0" Fm’?-'—C’11=fl’1¢5 3- G1l=U?~’I- Esq
`(57)
`ABSTRACT
`
`"_‘W'PT°5**}”*'
`3d\{=mw1-:*.wU_S for
`A mflgnclwn ~_='-i>'='~'1"=11|>*
`plasma .-spulic-ring, or sustained s.c1i—spnItcr1ng having
`reduced are-3 bul
`lull
`large! CL\VIJf3gC.
`I110 rnagrlclron
`includes an outer pole fan: surrouncling an inner pole fact
`with a gap lhcrcl\clwucn.'l'l1c outer pole of the magnetron of
`the invention L: smaller than mm of a circular magnetron
`similarly extending from lht: center to Lhu pcriphury of mu
`largcl. A on-:1}-:rrs:cI
`lrianglilar shape having a blTlHii apex
`angli: of EU in 30° rnay ht: lorrncd from oulcr bar niagncls of
`DDI:
`IT1i1g,l'1|:l1I.I pfliiiflly enclosing iiI.1JI]t'li.‘-I'1”I1figl'lE-lIJi[i'lE.' Olllcl’
`rnalgnelic polarity. The magnetron allows the gencralion of
`plasma wawss
`in lhc ncighhorhootl of 22 MHZ which
`inluracl with [he 1
`lo 20 cV E-leclmns of the plasma to
`Ilaurchy increase thc plasma density.
`
`22 Claims. 11 Drawing Sheets
`
`(63) Cunlinualion—in-part ofapplicalion N6. Ia9,.«373,n-J7. Iilcd on
`Aug .1 2! 1990’ now PHL Nu “T 133?“ I 4’ which is a mminw
`alien-in-parl ofapplicnlioli N0. l}0;'24U,4bS, filcdon Feb, 12.
`W09"
`Int. Cl.’
`(51)
`(52) u.s. Cl.
`(58) Field of Seflmh
`
`C23C 14/34
`20-$192.12; 2U4.’2*JS.2
`304,-39319‘ 398,21
`204*.-3g3_22’ 193,12
`
`(_.-,6)
`
`Refumnces Cited
`
`U-5- PATENT DOCUMENTS
`__:’__H;1‘643 , #1084 Gurrell
`5!3_53:_-553
`10;1gg_:, Dcnlmay N “L
`5__ji7(|__n;5
`M1993 Kjyma _________ __
`5_SlJ7_.‘!53 ‘
`'-ii"1W‘J
`llong et a1.
`5,9nrj_.rirJ7 '
`lU_«"1-U00
`(‘hue :1 Hi.
`FOREIGN PATENT l)O[."UMEl'\TTS
`
`
`
`Zmagfiu
`_ _:gg4,3g3_3
`1|}_L,r2f;3 _)_
`, 2ri4;29s,2
`438.-’31'_I5
`
`(KHJEEIESSA
`Fl I591 —'H‘3 Al
`
`ll}! 1 994 05,1’) .
`la’1'.J‘Jr':
`(Ii?)
`
`‘
`
`2n4r29s.lu
`
`40
`
`ZTCJIZZTT
`
`
`
`
`
`
`oI
`
`
`
`0 4
`on
`S1
`i
`
`Eg
`
`If
`AL\x\\§
`
`7
`
`46
`
`GILLETTE 1216
`
`GILLETTE 1216
`
`

`
`U.S. Patent
`
`01-1. 23, 2001
`
`sheet 1 of 11
`
`US 6,306,265 B1
`
`10
`
`\ _ ’/F
`
`34
`
`36
`
`32
`
`14
`
`h.) -l‘-‘-
`
`IN) 0'‘!
`
`Ar -—
`
`--
`
`20
`
`30
`
`22
`
`1
`,7'___:
`:,...i4
`
`
`
`
`
`\ E
`
`H i._,,_
`
`E
`
`5....,,.5
`
`..
`
`1. 20
`
`234
`
`232
`
`h
`
`1.
`
`‘
`
`28 *1‘
`
`G T
`
`(PRIOR ART)
`
`FIG.
`
`1
`
`

`
`U.S. Patent
`
`Oct. 23, 2001
`
`Sheet 2 of 11
`
`US 6,306,265 B1
`
`4-O
`
`
`
`50 A
`»\\\\\\\\‘
`
`W%
`
`
`
`.\\\\\‘
`- \\=
`
`
`
`
`
`Q:
`
`46
`
`(PRIOR ART)
`
`FIG. 3
`
`

`
`U.S. Patent
`
`Oct. 23, 2001
`
`Sheet 3 of 11
`
`Us 6,306,265 B1
`
`72
`
`68
`
`70
`
`
`
`W6/1
`
`Fm.4
`
`%
`
`(?@@%@@©©@%)
`© @@@@@© @
`@@@@@@@@@@
`
`w
`
`Fm.5
`
`K/“m”
`
`Fm.6
`
`% M
`
`96
`
`

`
`U.S. Patent
`
`3Lk(
`
`U
`
`M
`
`__I_B
`
`2_F
`G0T.l._.|W.1|
`
`47M...8COh.|5O
`H2am1.
`
`2
`
`a4%2.,.|
`
`«J,4.61S1
`
`8_..I
`
`2
`
`FIG. 8
`
`
`

`
`U.S. Patent
`
`Oct. 23, 2001
`
`Sheet 5 of 11
`
`US 6,306,265 B1
`
`/126
`
`136
`
`148
`
`‘/,..——14o
`
`130
`
`150
`
`144
`
`152
`
`

`
`U.S. Patent
`
`Oct. 23, 2001
`
`Sheet 6 of 11
`
`US 6,306,265 B1
`
`©
`@
`
`9é@
`
`@@ ©@
`@ @
`©@@@ @
`@@ 16O@@ @
`@1152
`@@>@
`L666
`
`/”*‘5O
`
`FIG.
`
`11
`
`

`
`U.S. Patent
`
`um. 23, 2001
`
`sheet 7 of 11
`
`US 6.306.265 B1
`
`A
`/R12‘
`
`"/2
`
`“/4
`
`P/R
`
`T
`
`7T+2
`
`7T
`
`2
`
`174
`
`175
`
`90°
`
`6
`
`180°
`
`178
`
`‘I80
`
`90°
`
`9
`
`180°
`
`

`
`U.S. Patent
`
`Oct. 23, 2001
`
`Sheet 3 0f 11
`
`US 6,306,265 B1
`
`190
`
`
`
`190'
`
`

`
`U.S. Patent
`
`01-1. 23, 2001
`
`Sl1c.et9af1l
`
`US 6,306,265 B1
`
`200
`
`206
`
`202
`
`

`
`U.S. Patent
`
`um. 23, 2001
`
`sheet 10 of 11
`
`US 6,306,265 B1
`
`
`
`BO
`
`60
`
`BOTTOM
`
`COVERAGE
`W 40
`
`20 —-{»»—1oow Bms
`
`———a—-- 250w BIAS
`
`ASPECT RAND
`
`

`
`U.S. Patent
`
`out. 23. 2001
`
`sheet 11 of 11
`
`US 6,306,265 B1
`
`PRESSURE
`
`(NWT)
`
`1
`
`20
`
`40
`
`60
`
`80
`
`100
`
`N2 FLOW (sccm)
`
`50
`
`40
`
`STEP 30
`COVERAGE
`<7’)
`20
`
`10
`
`ASPECT RATIO
`
`

`
`US 6,306,265 B1
`
`1
`HIGH-DI-INSITY PLASMA It‘OR ION IZED
`METAL l)l‘lPOSITI()N CAPABLE. 0|"
`I'L\'CITlNG A PLASMA WAVE
`
`RELATED APPUCATION
`
`'lhis application is a continuation in pan of Ser. No.
`tI9l373,tl‘)'?, tiled Aug. 12, 1999, now US. Pat. No. 6,183,
`61-1 Feb. t’), 3001 which is a continuation in part of Ser. No.
`(l9f2-19,-165. 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 enhance sputtering.
`
`BACKG ROUND ART
`
`Sputtering. alternatively culled 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 charnbt.-r 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 —fit)(lVlJ(‘ with respect to
`the shield 20. Conventionally, 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 flow 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 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’ brr. 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 :1 substantial energy and cause target
`atoms or atomic clusters to be sputteretl 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. to 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 it magnetic held within the chamber in the
`neighborhood of the magneLs 34, 36. The magnetic lleld
`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 he only suggestive.
`The advancing level of integration in semiconductor
`inteyated 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 [ill metal into the hole 40 to
`provide inter—level electrical connections. ll the underlying
`layer 46 is the semiconductor substrate, the tilted hole 40 is
`called a contact;
`if the underlying layer is a lower-level
`metallixatiott level, the Illled hole 4-0 is called a via. For
`simplicity, we will refer hereafteronly to vias. The widths of
`inter-level vias have decreased to the neighborhood of 0.25
`pm and below while the thickness ofthc inter—level dielectric
`has remained nearly constant at around 0.7;rm. 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 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 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 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 ellect can be
`accentuated with additional DC or RF biasing of the pedestal
`electrode 18 to additionally accelerate the iottined 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 ellieetiveness ofhole lilting are bottom coverage
`and side coverage. As illustrated sc|1en1at'ical|y in FIG. 2.. the
`initial phase of sputtering deposits rt layer 50, which has it
`surface or bla nltct thickness of 51, a bottom tltickness of s,
`and it sidewall thickness ofs3. The bottom coverage is equal
`to 5:;’Sl. and the sidewall coverage is equal to s_,t’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 (IIDP). such as by adding an
`RF coil 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 fraction of the sputtered
`atoms. Ilowever, 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
`
`or
`
`ll!
`
`.10
`
`35
`
`40
`
`St]
`
`55
`
`of]
`
`55
`
`

`
`US 6,306,265 B1
`
`3
`shape of :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-
`catbnde reactor tends tn form an undulatory copper film on
`Ihe via sidewall, and further the deposited metal tends to
`dewet. The variable thiclutess is particularly serious when
`Ibc sputtered copper layer is being used as a seed layer of a
`predetermined minimum thickness for a subsequent depo-
`sition process such as electroplating to complete the copper
`hole filling.
`the sidewall
`is that
`A further problem in the prior art
`coverage tends to be asymmetric with the side facing the
`center of the target being more heavily coated than the more
`shielded side facing a larger solid angle outside the target.
`Not only does the asymmetry require excessive deposition to
`achieve a seed layer of predelerrniried minimum thickness,
`it causes cross-shaped trenches used as alignment indicia in
`the photnlilhograpliy to appear to move as the trenches are
`asymmetrically narrowed.
`that promotes deep hole
`Another operational control
`is generally believed that
`filling is charnber pressure.
`It
`lower chamber pressures promote hole filling. At higher
`pressures,
`there is a higher probability that sputtered
`particles, whether neutral or ionized. will collide with atoms
`of the argon carrier gas. Collisions tend to neutralize ions
`and to randomize velocities, both effects degrading hole
`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
`factors.
`
`The extreme of low~pressurc plasma sputtering is sus-
`tained self-spunering (SSS), as disclosed by Fu ct al. in US.
`patent application, Scr. No. (IBr'854.U(IB, filed May 8, 1997.
`In SSS. the density of positively ionized sputtered atoms is
`so high that a sullicient 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 tield. 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-lield
`magnetron needs to be developed.
`Increased power applied to the target allows reduced
`pressure, perhaps to the point of sustained sell‘-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 el1'ective 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 efficiently used, but more importantly the uniformity of
`sputter deposition is degraded, and sorne of the sputtered
`material redcposits on the target in areas that are not being
`
`or
`
`.10
`
`10
`
`4-0
`
`51]
`
`55
`
`Elli
`
`55
`
`4
`sputtered. Funhenriore, the material redeposited on unspoi-
`tered areas may build up to such a thickness that it is prone
`to flake off. 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 ttfcommercinlly available magnetron is kidney-
`shaped, as exernplilied by Tepmari in US. Pat. No. 5,320,
`728. Parker discloses more exaggerated forms of this shape
`in U.S. Pat. No. 5,242 566. As illustrated in plan view in
`FIG. 3, the Tepman magnetron 52 is based on a kidney shape
`for the magnetically opposed pole faces 54, 56 separated by
`a circuitous gap 57 of nearly constant width. The pole faces
`54, 56 are magnetically coupled by unillustraterl 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 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 snaall.
`high-field magnetron providing full coverage so as to pro-
`mote deep hole filling and sustained copper sel.l'-sputte-rirtg.
`
`SUMMARY OF 'I'lll3. 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 asynametrically positioned
`about the target center.
`The magnetron is rotated on the backside of the target
`about ta point preferably near the rnttgneI.ron‘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 hall" radius of the target.
`The magnetic intensity away l'rot't'l
`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 magnetic 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
`plasma wave is generated at a higher frequency in the range-
`of hundreds of megahertz, which is paramctrically converted
`to another wave at a much lower frequency, for example, 5
`to 75 Mllz. corresponding to the thermal velocity of elec-
`trons in the plasma produced by eapacitively coupling DC
`power to the target.
`The magnetron is configured to produce less magnetic
`llux in its inner pole than in its surrounding noter 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 6.3tJ6_.265 B1
`
`5
`ittg over a small closed area facilitates sustained sell‘-
`sputtcring. Many metals not subject
`to sustained self-
`spultering can be sputtered at chamber presstires of less than
`[L5 milliTorr. often less than 0.3 milljTorr, and even at 0.1
`roilliTorr. 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 t-1W of DC‘ power for a 330 mm target and
`200 mm wafer either in a thlly .-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 |]ici:.-ntly target power and high magnetic liuld
`away from the target, that a non-linear wave-beam interac-
`tion occurs that pumps energy into plasma electrons, thereby
`i.ncrt:asing the plasma density.
`BRII.*.l" IJESCRIPTION 01’ THE IJRAWINGS
`
`FIG. 1 is a schematic diagram of a DC‘ plasma sputtering
`I'€.'.lli.'lC|l'.
`FIG. 2 is a cross-sectional view of it
`semiconductor integrated circuit.
`I-'|(j. 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—lcvel 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 ofthe magnetron ol‘ 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. [0 is a plan view of 3 morlilication 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 magnetron.-5 used to
`t:alr.'ulttte areas and peripheral lengths.
`FIG. 13 is a graph of the angular dcpendcnces otthe 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 rnagnctron of the
`invention using bar rnague-ts.
`FIG. 16 is a bottom plan view of an alternative to the
`magnetron of FIG. 15.
`FIG. 1’? is a side view of an idealizatiort 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 generate-d by a magnetron of the invention.
`FIG. 20 is a graph ot' 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'Al1.ED DESCRlP'I‘lON OF THE
`PRl3[-‘ERRED [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,
`har—shaped pole face 62 is surrounded by an outer elongated
`ring-shaped pole face 68 til’ the other polarity with a gap 70
`of nearly constant width separating the bar-shaped and
`ting-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 ends 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 both 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 illusmatcd with
`specitic magnetic polarities producing magnetic fields
`extending generally perpendicularly to the plane of
`illustration, it is of course appreciaterl that the opposite set
`of magnetic polarities will produce the same gene rat mag-
`netic cllects as far as the invention is concerned. Thu:
`illustrated assembly produces a generally semi-toroidal
`magnetic tield 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 amembly of FIG. 4 is intended to he continu-
`ously rotated during sputter deposition at
`it
`fairly high
`rotation rate about it 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 prolate end 80
`of the outer pole face 68 and with its other prolate end 82
`located approxirnately 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 it small
`magnetron nonetheless achieving full target coverage. The
`outer usable periphery oi.‘ the target is not easily defined
`because ditferent magnetron designs use ditfcrent 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 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 rnagrtetrons 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
`it
`radial position
`preferalaly 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
`
`30
`
`4-0
`
`St]
`
`55
`
`Eli!
`
`O5
`
`

`
`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 extending along the radius of the target and with the
`minor axis preferably parallel to a rotational circumference.
`Tahuehi illustrates a symmetric oval magnetron in I.aicl-
`opcn Japanese Patent Application 63-112763. This shape
`however has the disadvantage of a complex shape, espe-
`cially for packing the magnets in the inner pole.
`Another oval shape is represented by an egg-shape-(I
`magnetron 106, illustrated in plan view in FIG. 8. It has an
`outer pole face 108 ofone magnetic polarity surrounding an
`inner pole face 110 of the other polarity with it nearly
`constant gap 122 lnetwecn them. Both pole face.-5108, 110 are
`shaped like the outline of an eg with at mttjor tocis extending
`along the radius of the target. However. an inner end 112 of
`the outer pole face 108 near the rotation axis 78 is sharper
`than an outer end 114 near the periphery of the target. The
`egg shape is related to an elliptical shape but is asymmetric
`with respect to the target rad