(12)
`
`United States Patent
`Chistyakov
`
`(10) Patent N0.:
`(45) Date of Patent:
`
`US 7,147,759 B2
`*Dec. 12, 2006
`
`US007147759B2
`
`(54) HIGH-POWER PULSED MAGNETRON
`SPUTTERING
`
`(75) Inventor: Roman Chistyakov, Andover, MA
`(Us)
`
`(73) Assigneez Zond, Inc" Mans?eld’ MA (Us)
`
`6,398,929 B1* 6/2002 Chiang etal. ....... .. 204/298.11
`6,413,382 B1
`7/2002 Wang et al. ......... .. 204/192.12
`6,436,251 B1
`8/2002 Gopalraja et al.
`204/298.12
`6,440,280 B1
`8/2002 BPITOH et al'
`6,456,642 B1
`9/2002 Hilliard
`2002/0033480 A1
`3/2002 Kawamata et al.
`2005/0252763 A1* 11/2005 Chistyakov .......... .. 204/192.12
`
`FOREIGN PATENT DOCUMENTS
`
`DE
`
`3210351 A1
`
`9/1983
`
`_
`
`( * ) Not1ce:
`
`_
`
`_
`
`_
`
`_
`
`Subject to any d1scla1mer, the term of this
`patent is extended or adjusted under 35
`
`This patent is subject to a terminal dis-
`
`OTHER PUBLICATIONS
`
`Booth, et al., The Transition From Symmetric To Asymmetric
`Discharges In Pulsed 13.56 MHZ Capacity Coupled Plasmas, J.
`Appl. Phys, Jul. 15, 1997, pp. 552-560, vol. 82 (2), American
`Institute °fPhYSi°S'
`
`(Continued)
`Primary ExamineriRodney G. McDonald
`(74) Attorney, Agent, or FirmiKurt Rauschenbach;
`Rauschenbach Patent LaW Group, LLC
`
`(57)
`
`ABSTRACT
`
`Magnetically enhanced sputtering methods and apparatus
`are described. A magnetically enhanced sputtering source
`according to the present invention includes an anode and a
`cathode assembly having a target that is positioned adjacent
`to the anode. An ionization source generates a Weakly
`ionized plasma proximate to the anode and the cathode
`assembly. A magnet is positioned to generate a magnetic
`?eld proximate to the Weakly-ionized plasma. The magnetic
`?eld substantially traps electrons in the Weakly-ionized
`plasma proximate to the sputtering target. A poWer supply
`produces an electric ?eld in a gap between the anode and the
`cathode assembly. The electric ?eld generates excited atoms
`in the Weakly ionized plasma and generates secondary
`electrons from the sputtering target. The secondary electrons
`ionize the excited atoms, thereby creating a strongly-ionized
`plasma having ions that impact a surface of the sputtering
`target to generate sputtering ?ux.
`
`50 Claims, 18 Drawing Sheets
`
`l '
`
`.
`
`C almer
`
`.
`(21) Appl' NO" 10/065’277
`(22) Filed:
`Sep. 30, 2002
`
`(65)
`
`Prior Publication Data
`
`Us 2004/0060813 A1
`(51) I t Cl
`
`n .
`
`.
`
`Apr' 1’ 2004
`
`(2006.01)
`C23C 14/35
`(52) US. Cl. ......................... .. 204/192.12; 204/192.13;
`204/298-03; 20409806; 204/298-08; 204/298-14;
`204/29819
`(58) Field of Classi?cation Search ......... .. 204/ 192.12,
`204/192.13, 298.03, 298.06, 298.08, 298.14,
`204/29819, 298.26
`See application ?le for complete search history.
`References Cited
`
`(56)
`
`U.S. PATENT DOCUMENTS
`
`6/1970 Muly, Jr. et a1.
`3,516,920 A
`8/1990 Eldridge et a1. ............ .. 372/87
`4,953,174 A
`4,965,248 A 10/1990 Poppe et a1.
`505/1
`5,015,493 A
`5/1991 Gruen ....................... .. 427/38
`5,616,224 A
`4/1997 Boling
`5,875,207 A
`2/1999 Osmanow .................. .. 372/86
`5,942,089 A
`8/1999 Sproul et al.
`6,083,361 A
`7/2000 Kobayashi et a1.
`6,296,742 B1
`10/2001 Kouznetsov ......... .. 204/192.12
`6,342,132 B1
`1/2002 Rossnagel
`
`2"“
`
`21o
`
`200
`\
`
`VACUUM
`SYSTEM 204
`
`GILLETTE 1106
`
`

`
`US 7,147,759 B2
`Page 2
`
`FOREIGN PATENT DOCUMENTS
`
`EP
`GB
`JP
`JP
`WO
`W0
`W0
`
`0 788 139 A1
`1339910
`57194254
`10204633
`WO9504368
`WO 98/40532
`WO 01/98553 A1
`
`8/1997
`12/1973
`11/1982
`8/1998
`* 2/1995
`9/1998
`12/2001
`
`OTHER PUBLICATIONS
`
`Bunshah, et al., Deposition Technologies For Films And Coatings,
`Materials Science Series, pp. 176-183, Noyes Publications, Park
`Ridge, New Jersey.
`Daugherty, et al., Attachment-Dominated Electron-Beam-IoniZed
`Discharges, Applied Science Letters, May 15, 1976, vol. 28, No. 10,
`American Institute of Physics.
`Goto, et al., Dual Excitation Reactive Ion Etcher for Low Energy
`Plasma Processing, J. Vac. Sci. Technol. A, Sep./Oct. 1992, pp.
`3048-3054, vol. 10, No. 5, American Vacuum Society.
`KouZnetsov, et al., A Novel Pulsed Magnetron Sputter Technique
`Utilizing Very High Target Power Densities, Surface & Coatings
`Technology, pp. 290-293, Elsevier Sciences S.A.
`Lindquist, et al., High Selectivity Plasma Etching Of Silicon Diox
`ide With A Dual Frequency 27/2 MHZ Capacitive RF Discharge.
`Macak, Reactive Sputter Deposition Process of A1203 and Charac
`teriZation Of A Novel High Plasma Density Pulsed Magnetron
`Discharge, Linkoping Studies in Science And Technology, 1999, pp.
`1-2, Sweden.
`Macak, et al., Ionized Sputter Deposition Using An Extremely High
`Plasma Density Pulsed Magnetron Discharge, J. Vac. Sci. Technol.
`A., Jul/Aug. 2000, pp. 1533-1537, vol. 18, No. 4, American
`Vacuum Society.
`
`MoZgrin, et al., High-Current Low-Pressure Quasi -Stationary Dis
`charge In A Magnetic Field: Experimental Research, Plasma Phys
`ics Reports, 1995, pp. 400-409, vol. 21, No. 5, MoZgrin, Feitsov,
`Khodachenko.
`Rossnagel, et al., Induced Drift Currents In Circular Planar
`Magnetrons, J. Vac. Sci. Technol. A., Jan/Feb. 1987, pp. 88-91, vol.
`5, No. 1, American Vacuum Society.
`Sheridan, et al., Electron Velocity Distribution Functions In A
`Sputtering Magnetron Discharge For The EXB Direction, J. Vac.
`Sci. Technol. A., Jul/Aug. 1998, pp. 2173-2176, vol. 16, No. 4,
`American Vacuum Society.
`Steinbruchel, A Simple Formula For Low-Energy Sputtering Yields,
`Applied Physics A., 1985, pp. 37-42, vol. 36, Springer-Verlag.
`Turenko, et al., Magnetron Discharge In The Vapor Of The Cathode
`Material, Soviet Technical Physics Letters, Jul. 1989, pp. 519-520;
`vol. 15, No. 7, New York, US.
`Encyclopedia Of Low Temperature Plasma, p. 119, vol. 3.
`Encyclopedia Of Low Temperature Plasma, p. 123, vol. 3.
`Sugimoto, et al; Magnetic Condensation Of A Photoexcited Plasma
`During Fluoropolymer Sputtering; J. Appl. Phys.; Feb. 15, 1990; pp.
`2093-2099; vol. 67, No. 4; American Institute of Physics; New
`York, US.
`Yamaya, et al; Use Of A Helicon-Wave Excited Plasma For Alu
`minum-Doped ZnO Thin-Film Sputtering; Appl. Phys. Lett.; Jan.
`12, 1998; pp. 235-237; vol. 72; No. 2; American Institute ofPhysics:
`New York US.
`
`* cited by examiner
`
`

`
`U.S. Patent
`
`Dec. 12, 2006
`
`Sheet 1 0f 18
`
`US 7,147,759 B2
`
`100
`\
`
`104
`/
`
`102
`f
`PULSED
`POWER
`SUPPLY
`
`118
`
`120
`122
`
`132
`
`__
`
`_
`
`i
`2
`5
`§
`g
`Z
`124i
`
`126
`r
`
`N
`
`s
`
`127
`I’
`
`s
`
`5
`2
`5
`128 ?
`\
`N
`
`/
`
`114
`
`__
`—
`_.___
`
`-——--_
`
`2
`j;
`f
`i 116
`’
`@4130
`;
`M/Il'I/I/?/??/JMM'II/I/Z/I/IV
`;
`,
`I \\\\\\ \\\\\\\\ a
`’
`/ III'IIIIIA
`'IIIIIII'I
`
`142
`
`134
`
`142
`
`F108
`
`VACUUM 106
`PUMP
`
`PRIOR ART
`FIG. 1
`
`110-1:
`
`112
`
`109
`
`

`
`U.S. Patent
`
`Dec. 12,2006
`
`Sheet 2 of 18
`
`US 7,147,759 B2
`
`209
`L
`
`\\\‘
`
`V _—h
`M
`/4. §
`
`\\\\\§
`%.\S\\X\\\
`
`7¢¢¢¢¢ 6¢V
`
`/J’
`17/
`_________-7,....._-_2_4§::_--
`=3 ______
`245 254 220 245
`254 233
`.§\‘\'.\\\\
`;
`////77/W//Z? 7///1'7/.7/1'/WJWJV//0&4’AV/AM/J1/flJVIl./W///A’l¢
`
`//5
`
`7/
`
`7'
`
`
`
`r,.
`
`“.:'a.=\=.'.:-.':.-.;*....\.-‘*.*..==::-‘-.':.-.".!..
`
`.
`
`-.
`
`212 §L
`
`

`
`U.S. Patent
`
`Dec. 12, 2006
`
`Sheet 3 0f 18
`
`US 7,147,759 B2
`
`mmw
`
`EN
`
`

`
`U.S. Patent
`
`Dec. 12, 2006
`
`Sheet 4 0f 18
`
`US 7,147,759 B2
`
`ME:
`
`00m
`
`I I I I I l I I I I I l l I I I I 1|
`
`mom
`
`:5
`
`......................................... E232 .ET
`
`in
`----___----------------.---_...--------l--------__
`ad
`
`w .OE
`
`l l l I I l I U I I I I l I i I l I l I I l ll.
`
`l l l l I l I II
`
`. . . . . . . . . . . . . . . -- -2652 - 3.?
`
`

`
`S.
`
`Dec. 12, 2006
`
`Sheet 5 of 18
`
`US 7,147,759 B2
`
`VVvIAAWmmmmmmPWWt.VW...41OnWmmA.4mm4ommwa.4_..umPmo~
`
`InIuIII|IIlIIIIIIIIII|I:|IIIIIII
`
`FIG. 5
`
`

`
`U.S. Patent
`
`Dec. 12, 2006
`
`Sheet 6 0f 18
`
`US 7,147,759 B2
`
`mmm
`
`\\
`
`wvwk
`
`W»
`
`$5,
`h!//////
`
`(w .OE
`wow v
`
`llu
`
`I.‘ ///4
`
`

`
`U.S. Patent
`
`Dec. 12, 2006
`
`Sheet 7 0f 18
`
`US 7,147,759 B2
`
`QM
`
`\ 8v
`
`9
`
`m;
`
`N; NE
`
`
`
`ms“ 1 3w 3J3.
`
`
`
`Q51 7/, §\\\\\ ‘E4 \\
`
`, \\\\|||\\\..\l),UZ/2 \\\\\\\\\|llllly// ;_ \
`
`mm .OE
`
`

`
`U.S. Patent
`
`Dec. 12, 2006
`
`Sheet 8 0f 18
`
`US 7,147,759 B2
`
`mmw
`
`\
`
`

`
`U.S. Patent
`
`Dec. 12, 2006
`
`Sheet 9 0f 18
`
`US 7,147,759 B2
`
`mmw
`
`mwmk
`
`

`
`U.S. Patent
`
`Dec. 12,2006
`
`Sheet 10 of 18
`
`US 7,147,759 B2
`
`450
`
`ll PK;
`
`§ &
`7
`I
`
`v..
`E41
`
`&\\§
`7\\\\\z
`j.V//A .57/////J//I A
`
`//
`
`\
`
`N
`S
`
`fl
`
`III
`
` .
`
`'//////A%//////////4N7 I521
` ! iE
`
`E C)
`
`218
`
`S
`N
`
`\\\\\\\\\\\\\\\
`
`¢¢? Z\
`
`\L\\\\\\\\\\\\.\\\\\\§.\\\\\.\\.§
`/
`
`R\\' k
`
`///A//C
`
` '
`
`3
`
`whiny
`\n!!nv
`_a
`_______________,,___.__,,__,_/;___,________________-v
`233 &\\\\§\
`254
`254
`\
`//////017/J4 W////////I/I/I.%/////J]//Illlfl/Fifi//Iflfiffli
`
`

`
`U.S. Patent
`
`Dec. 12, 2006
`
`Sheet 11 0f 18
`
`US 7,147,759 B2
`
`w .OE
`
`I l I I I I l l l I I l l I l l I l I I I I l I l | | I | l I | in
`
`| l l I l l l I l l I I I U I I I I l l l J I f I I I a i.
`
`wow.
`
`wow
`
`03
`
`com
`
`Ema/Om
`
`New
`
`I 2202 - 5.01
`
`

`
`U.S. Patent
`
`Dec. 12,2006
`
`Sheet 12 of 18
`
`US 7,147,759 B2
`
`on
`("D
`
`218"
`
`FIG.9C
`238
`
`9 L
`
`L
`
`

`
`U.S. Patent
`
`Dec. 12, 2006
`
`Sheet 13 0f 18
`
`US 7,147,759 B2
`
`450'
`
`MATCHING
`UNIT
`
`GAS
`SOURCE
`
`202
`
`456
`
`VACUUM
`SOURCE
`
`FIG. 10
`
`

`
`U.S. Patent
`
`US 7,147,759 B2
`
`6m\..2WWM.§y)2,#4I“IMuoJI“I.a//“IWa4J/‘ID/WH.“\_\W.
`u7.V.\W\.
`
`u
`
`\\.
`
`40¢.
` fi
`
`..
`
`W“m.\00\“\A..n\\...n,10\\mflaom4|MM”WWum.\\\\\\\&_...lWF
`
`\
`
`472
`
`A
`
`
`
`
`
`W//IIIWW4.IWW.3/.£2.r/I.
`
`V g
`
`
`
`
`
`

`
`U.S. Patent
`
`Dec. 12, 2006
`
`Sheet 15 0f 18
`
`US 7,147,759 B2
`
`600
`
`START 602
`
`PUMP DOWN CHAMBER 4
`
`606
`CHAMBER
`PRESSURE
`CORRECT?
`
`PASS FEED GAS INTO CHAMBER
`PROXIMATE TO A CATHODE (TARGET) ASSEMBLY i
`
`/ 608
`
`CHAMBER
`PRESSURE
`CORRECT?
`
`610
`
`GAS
`PRESSURE
`CORRECT?
`
`/B14
`APPLY APPROPRIATE MAGNETIC
`FIELD PROXIMATE TO FEED GAS
`
`FIG. 12A
`
`FIG. 12B
`
`FIG. 12
`
`IONIZE SPUTTERING GAS TO
`GENERATE WEAKLfY-IONIZED PLASMA
`
`/s1s
`
`620
`
`GAS
`WEAKLY
`iONlZED'?
`
`FIG. 12A
`
`

`
`U.S. Patent
`
`Dec. 12, 2006
`
`Sheet 16 0f 18
`
`US 7,147,759 B2
`
`/622
`GENERATE STRONGLY-IONIZED SUBSTANTIALLY
`UNIFORM PLASMA FROM WEAKLY-IONIZED PLASMA
`
`‘
`
`STRONGLY
`ONIZED?
`
`MONITOR SPU'ITER DEPOSITION
`
`628
`
`/ 532
`END
`
`630
`
`SPUTI'ER
`DEPOSITION
`COMPLETE
`
`FIG. 12B
`
`

`
`U.S. Patent
`
`Dec. 12, 2006
`
`Sheet 17 0f 18
`
`US 7,147,759 B2
`
`650
`
`\
`
`START / 602
`
`I
`
`/604
`
`: PUMP DOWN CHAMBER <
`
`606
`CHAMB ER
`PRESSURE
`CORRECT?
`
`/ 608
`J
`PASS FEED GAS INTO CHAMBER
`PROXIMATE TO A CATHODE (TARGET) ASSEMBLY T
`
`CHAMBER
`PRESSURE
`CORRECT?
`
`610
`
`GAS
`PRESSURE
`CORRECT?
`
`/a14
`APPLY APPROPRIATE MAGNETIC
`FIELD PROXIMATE TO FEED GAS
`
`4
`
`FIELD
`ROPER?
`
`IONIZE SPUTI'ERING GAS TO
`GENERATE WEAKLY-IONIZED PLASMA II
`
`FIG. 13A
`
`FIG. 13B
`
`FIG. 13
`
`Y
`
`FIG. 13A
`
`

`
`U.S. Patent
`
`Dec. 12, 2006
`
`Sheet 18 0f 18
`
`US 7,147,759 B2
`
`/ 622
`GENERATE STRONGLY-IONIZED SUBSTANTIALLY
`UNIFORM PLASMA FROM WEAKLY-IONiZED PLASMA '
`
`624
`
`STRONGLY-
`ONIzEO?
`
`N
`
`MONITOR SPUTTER RATE
`
`1652
`_
`
`/656
`INCREASE HIGH-POWER
`PULSE TO CATHODE
`(TARGET) ASSEMBLY
`TO INCREASE
`SPUTTER RATE
`
`CONTINUE
`' SPUTTERING
`
`‘
`
`660
`
`SPUTTER
`DEPOSITION
`COMPLETE
`
`END
`
`FIG. 13B
`
`

`
`US 7,147,759 B2
`
`1
`HIGH-POWER PULSED MAGNETRON
`SPUTTERING
`
`BACKGROUND OF INVENTION
`
`Sputtering is a well-known technique for depositing films
`on substrates. Sputtering is the physical ejection of atoms
`from a target surface and is sometimes referred to as
`physical vapor deposition (PVD). Ions, such as argon ions,
`are generated and then directed to a target surface where the
`ions physically sputter target material atoms. The target
`material atoms ballistically flow to a substrate where they
`deposit as a film of target material.
`Diode sputtering systems include a target and an anode.
`Sputtering is achieved in a diode sputtering system by
`establishing an electrical discharge in a gas between two
`parallel-plate electrodes inside a chamber. A potential of
`several kilovolts is typically applied between planar elec-
`trodes in an inert gas atmosphere (e.g., argon) at pressures
`that are between about 10” and l0‘2 Torr. A plasma dis-
`charge is then formed. The plasma discharge is separated
`from each electrode by what is referred to as the dark space.
`The plasma discharge has a relatively constant positive
`potential with respect to the target. Ions are drawn out of the
`plasma, and are accelerated across the cathode dark space.
`The target has a lower potential than the region in which the
`plasma is formed. Therefore, the target attracts positive ions.
`Positive ions move towards the target with a high velocity.
`Positive ions impact the target and cause atoms to physically
`dislodge or sputter from the target. The sputtered atoms then
`propagate to a substrate where they deposit a film of
`sputtered target material. The plasma is replenished by
`electron-ion pairs formed by the collision of neutral mol-
`ecules with secondary electrons generated at
`the target
`surface.
`
`Magnetron sputtering systems use magnetic fields that are
`shaped to trap and to concentrate secondary electrons, which
`are produced by ion bombardment of the target surface. The
`plasma discharge generated by a magnetron sputtering sys-
`tem is located proximate to the surface of the target and has
`a high density of electrons. The high density of electrons
`causes ionization of the sputtering gas in a region that is
`close to the target surface.
`One type of magnetron sputtering system is a planar
`magnetron sputtering system. Planar magnetron sputtering
`systems are similar in configuration to diode sputtering
`systems. However, the magnets (permanent or electromag-
`nets) in planar magnetron sputtering systems are placed
`behind the cathode. The magnetic field lines generated by
`the magnets enter and leave the target cathode substantially
`normal to the cathode surface. Electrons are trapped in the
`electric and magnetic fields. The trapped electrons enhance
`the efficiency of the discharge and reduce the energy dissi-
`pated by electrons arriving at the substrate.
`Conventional magnetron sputtering systems deposit films
`that have relatively low uniformity. However,
`the film
`uniformity can be increased by mechanically moving the
`substrate and/or the magnetron, but such systems are rela-
`tively complex and expensive to implement. Conventional
`magnetron sputtering systems also have relatively poor
`target utilization. By poor target utilization, we mean that the
`target material erodes in a non-uniform manner.
`
`BRIEF DESCRIPTION OF DRAWINGS
`
`This invention is described with particularity in the
`detailed description. The above and further advantages of
`
`2
`
`this invention may be better understood by referring to the
`following description in conjunction with the accompanying
`drawings,
`in which like numerals indicate like structural
`elements and features in various figures. The drawings are
`not necessarily to scale, emphasis instead being placed upon
`illustrating the principles of the invention.
`FIG. 1 illustrates a cross-sectional view of a known
`
`magnetron sputtering apparatus having a pulsed power
`source.
`FIG. 2 illustrates a cross-sectional view of an embodiment
`
`10
`
`of a magnetron sputtering apparatus according to the present
`invention.
`FIG. 3 illustrates a cross-sectional view of the anode and
`
`15
`
`the cathode assembly of the magnetron sputtering apparatus
`of FIG. 2.
`
`FIG. 4 illustrates a graphical representation of the applied
`power of a pulse as a function of time for periodic pulses
`applied to the plasma in the magnetron sputtering system of
`FIG. 2.
`
`FIG. 5 illustrates graphical representations of the absolute
`value of applied voltage, current, and power as a function of
`time for periodic pulses applied to the plasma in the mag-
`netron sputtering system of FIG. 2.
`FIG. 6A through FIG. 6D illustrate various simulated
`magnetic field distributions proximate to the cathode assem-
`bly for various electron E><B drift currents according to the
`present invention.
`FIG. 7 illustrates a cross-sectional view of another
`
`embodiment of a magnetron sputtering apparatus according
`to the present invention.
`FIG. 8 illustrates a graphical representation of pulse
`power as a function of time for periodic pulses applied to the
`plasma in the magnetron sputtering system of FIG. 7.
`FIG. 9A through FIG. 9C are cross-sectional views of
`various embodiments of cathode assemblies according to the
`present invention.
`FIG. 10 illustrates a cross-sectional view of another
`
`20
`
`25
`
`30
`
`35
`
`40
`
`illustrative embodiment of a magnetron sputtering apparatus
`according to the present invention.
`FIG. 11 is a cross-sectional view of another illustrative
`
`embodiment of a magnetron sputtering apparatus according
`to the present invention.
`FIG. 12 is a flowchart of an illustrative process of sputter
`deposition according to the present invention.
`FIG. 13 includes FIGS.13 A and 13 B which is a flowchart
`
`of an illustrative process of controlling sputtering rate
`according to the present invention.
`
`DETAILED DESCRIPTION
`
`The magnetic and electric fields in magnetron sputtering
`systems are concentrated in narrow regions close to the
`surface of the target. These narrow regions are located
`between the poles of the magnets used for producing the
`magnetic field. Most of the ionization of the sputtering gas
`occurs in these localized regions. The location of the ion-
`ization regions causes a non-uniform erosion or wear of the
`target that results in poor target utilization.
`Increasing the power applied between the target and the
`anode can increase the amount of ionized gas and, therefore,
`increase the target utilization. However, undesirable target
`heating and target damage can occur. Furthermore, increas-
`ing the voltage applied between the target and the anode
`increases the probability of establishing an undesirable
`electrical discharge (an electrical arc) in the process cham-
`ber.
`
`45
`
`50
`
`55
`
`60
`
`65
`
`

`
`US 7,147,759 B2
`
`3
`Pulsing the power applied to the plasma can be advanta-
`geous since the average discharge power can remain low
`while relatively large power pulses can be periodically
`applied. Additionally, the duration of these large voltage
`pulses can be preset so as to reduce the probability of
`establishing an electrical breakdown condition leading to an
`undesirable electrical discharge. However, very large power
`pulses can still result in undesirable electrical discharges and
`undesirable target heating regardless of their duration.
`FIG. 1 illustrates a cross-sectional view of a known
`
`magnetron sputtering apparatus 100 having a pulsed power
`source 102. The known magnetron sputtering apparatus 100
`includes a vacuum chamber 104 where the sputtering pro-
`cess is performed. The vacuum chamber 104 is positioned in
`fluid communication with a vacuum pump 106 via a conduit
`108. The vacuum pump 106 is adapted to evacuate the
`vacuum chamber 104 to high vacuum. The pressure inside
`the vacuum chamber 104 is generally less than 100 Pa
`during operation. A feed gas source 109, such as an argon
`gas source,
`is introduced into the vacuum chamber 104
`through a gas inlet 110. The gas flow is controlled by a valve
`112.
`
`The magnetron sputtering apparatus 100 also includes a
`cathode assembly 114 having a target material 116. The
`cathode assembly 114 is generally in the shape of a circular
`disk. The cathode assembly 114 is electrically connected to
`a first output 118 of the pulsed power supply 102 with an
`electrical transmission line 120. The cathode assembly 114
`is typically coupled to the negative potential of the pulsed
`power supply 102. In order to isolate the cathode assembly
`114 from the vacuum chamber 104, an insulator 122 can be
`used to pass the electrical transmission line 120 through a
`wall of the vacuum chamber 104. A grounded shield 124 can
`be positioned behind the cathode assembly 114 to protect a
`magnet 126 from bombarding ions. The magnet 126 shown
`in FIG. 1 is generally ring-shaped having its south pole 127
`on the inside of the ring and its north pole 128 on the outside
`of the ring. Many other magnet configurations can also be
`used.
`
`An anode 130 is positioned in the vacuum chamber 104
`proximate to the cathode assembly 114. The anode 130 is
`typically coupled to ground. A second output 132 of the
`pulsed power supply 102 is also typically coupled to ground.
`A substrate 134 is positioned in the vacuum chamber 104 on
`a substrate support 135 to receive the sputtered target
`material 116. The substrate 134 can be electrically connected
`to a bias voltage power supply 136 with a transmission line
`138. In order to isolate the bias voltage power supply 136
`from the vacuum chamber 104, an insulator 140 can be used
`to pass the electrical transmission line 138 through a wall of
`the vacuum chamber 104.
`
`the pulsed power supply 102 applies a
`In operation,
`voltage pulse between the cathode assembly 114 and the
`anode 130 that has a suflicient amplitude to ionize the argon
`feed gas in the vacuum chamber 104. This typical ionization
`process is referred to as direct ionization or atomic ioniza-
`tion by electron impact and can be described as follows:
`Ar+e’—>—>Ar*+2e’
`
`where Ar represents a neutral argon atom in the feed gas
`and e‘ represents an ionizing electron generated in response
`to the voltage pulse applied between the cathode assembly
`114 and the anode 130. The collision between the neutral
`
`argon atom and the ionizing electron results in an argon ion
`(Ar’') and two electrons.
`The negatively biased cathode assembly 114 attracts
`positively charged ions with suflicient acceleration so that
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`4
`
`the ions sputter the target material 116. A portion of the
`sputtered target material 116 is deposited on the substrate
`134.
`
`The electrons, which cause the ionization, are generally
`confined by the magnetic fields produced by the magnet 126.
`The magnetic confinement is strongest in a confinement
`region 142 where there is relatively low magnetic field
`intensity. The confinement region 142 is substantially in the
`shape of a ring that
`is located proximate to the target
`material. Generally, a higher concentration of positively
`charged ions in the plasma is present in the confinement
`region 142 than elsewhere in the chamber 104. Conse-
`quently, the target material 116 is eroded rapidly in areas
`directly adjacent to the higher concentration of positively
`charged ions. The rapid erosion in these areas results in
`undesirable non-uniform erosion of the target material 116
`and, thus relatively poor target utilization.
`Dramatically increasing the power applied to the plasma
`can result in more uniform erosion of the target material 116.
`However, the amount of applied power necessary to achieve
`this increased uniformity can increase the probability of
`generating an electrical breakdown condition that leads to an
`undesirable electrical discharge between the cathode assem-
`bly 114 and the anode 130 regardless of the duration of the
`pulses. An undesirable electrical discharge will corrupt the
`sputtering process and cause contamination in the vacuum
`chamber 104. Additionally, the increased power can over-
`heat the target and cause target damage.
`FIG. 2 illustrates a cross-sectional view of an embodiment
`
`of a magnetron sputtering apparatus 200 according to the
`present invention. The magnetron sputtering apparatus 200
`includes a chamber 202, such as a vacuum chamber. The
`chamber 202 is coupled in fluid communication to a vacuum
`system 204 through a vacuum control system 206. In one
`embodiment,
`the chamber 202 is electrically coupled to
`ground potential. The chamber 202 is coupled by one or
`more gas lines 207 to a feed gas source 208. In one
`embodiment, the gas lines 207 are isolated from the chamber
`and other components by insulators 209. Additionally, the
`gas lines 207 can be isolated from the feed gas source using
`in-line insulating couplers (not shown). A gas flow control
`system 210 controls the gas flow to the chamber 202. The
`gas source 208 can contain any feed gas, such as argon. In
`some embodiments, the feed gas includes a mixture of gases.
`In some embodiments, the feed gas includes a reactive gas.
`A substrate 211 to be sputter coated is supported in the
`chamber 202 by a substrate support 212. The substrate 211
`can be any type of work piece such as a semiconductor
`wafer. In one embodiment,
`the substrate support 212 is
`electrically coupled to an output 213 of a bias voltage source
`214. An insulator 215 isolates the bias voltage source 214
`from a wall of the chamber 202. In one embodiment, the bias
`voltage source 214 is an alternating current (AC) power
`source, such as a radio frequency (RF) power source. In
`other embodiments (not shown), the substrate support 212 is
`coupled to ground potential or is electrically floating.
`The magnetron sputtering apparatus 200 also includes a
`cathode assembly 216. In one embodiment,
`the cathode
`assembly 216 includes a cathode 218 and a sputtering target
`220 composed of target material. The sputtering target 220
`is in contact with the cathode 218. In one embodiment, the
`sputtering target 220 is positioned inside the cathode 218.
`The distance from the sputtering target 220 to the substrate
`211 can vary from a few centimeters to about one hundred
`centimeters.
`
`The target material can be any material suitable for
`sputtering. For example, the target material can be a metallic
`
`

`
`US 7,147,759 B2
`
`5
`material, polymer material, superconductive material, mag-
`netic material including ferromagnetic material, non-mag-
`netic material, conductive material, non-conductive mate-
`rial, composite material, reactive material, or a refractory
`material.
`
`The cathode assembly 216 is coupled to an output 222 of
`a matching unit 224. An insulator 226 isolates the cathode
`assembly 216 from a grounded wall of the chamber 202. An
`input 230 of the matching unit 224 is coupled to a first output
`232 of a pulsed power supply 234. A second output 236 of
`the pulsed power supply 234 is coupled to an anode 238. An
`insulator 240 isolates the anode 238 from a grounded wall of
`the chamber 202. Another insulator 242 isolates the anode
`
`238 from the cathode assembly 216.
`In one embodiment, the first output 232 of the pulsed
`power supply 234 is directly coupled to the cathode assem-
`bly 216 (not shown). In one embodiment, the second output
`236 of the pulsed power supply 234 is coupled to ground
`(not shown). In this embodiment,
`the anode 238 is also
`coupled to ground (not shown).
`In one embodiment (not shown), the first output 232 of the
`pulsed power supply 234 couples a negative voltage impulse
`to the cathode assembly 216. In another embodiment (not
`shown), the first output 232 of the pulsed power supply 234
`couples a positive voltage impulse to the anode 238.
`In one embodiment, the pulsed power supply 234 gener-
`ates peak voltage levels of up to about 30,000V. Typical
`operating voltages are generally between about 100V and 30
`kV.
`In one embodiment,
`the pulsed power supply 234
`generates peak current levels of less than one ampere to
`about 5,000 A or more depending on the size of the mag-
`netron sputtering system. Typical operating currents varying
`from less than a few amperes to more than a few thousand
`amperes depending on the size of the magnetron sputtering
`system. In one embodiment, the power pulses have a rep-
`etition rate that is below 1 kHz. In one embodiment, the
`pulse width of the pulses generated by the pulsed power
`supply 234 is substantially between about one microsecond
`and several seconds.
`
`The anode 238 is positioned so as to form a gap 244
`between the anode 238 and the cathode assembly 216 that is
`sufficient to allow current to flow through a region 245
`between the anode 238 and the cathode assembly 216. In one
`embodiment,
`the gap 244 is between approximately 0.3
`centimeters (0.3 cm) and ten centimeters (10 cm). The
`volume of region 245 is determined by the area of the
`sputtering target 220. The gap 244 and the total volume of
`region 245 are parameters in the ionization process as will
`be discussed with reference to FIG. 3.
`
`An anode shield 248 is positioned adjacent to the anode
`238 so as to protect the interior wall ofthe chamber 202 from
`being exposed to sputtered target material. Additionally, the
`anode shield 248 can function as an electric shield to
`
`electrically isolate the anode 238 from the plasma. In one
`embodiment, the anode shield 248 is coupled to ground
`potential. An insulator 250 is positioned to isolate the anode
`shield 248 from the anode 238.
`
`The magnetron sputtering apparatus 200 also includes a
`magnet assembly 252. In one embodiment,
`the magnet
`assembly 252 is adapted to create a magnetic field 254
`proximate to the cathode assembly 216. The magnet assem-
`bly 252 can include permanent magnets 256, or alterna-
`tively, electro-magnets (not shown). The configuration of the
`magnet assembly 252 can be varied depending on the
`desired shape and strength of the magnetic field 254. In
`alternate embodiments, the magnet assembly can have either
`a balanced or unbalanced configuration.
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`6
`In one embodiment, the magnet assembly 252 includes
`switching electro-magnets, which generate a pulsed mag-
`netic field proximate to the cathode assembly 216. In some
`embodiments, additional magnet assemblies (not shown)
`can be placed at various locations throughout the chamber
`202 to direct different types of sputtered target materials to
`the substrate 212.
`
`In one embodiment, the magnetron sputtering apparatus
`200 is operated by generating the magnetic field 254 proxi-
`mate to the cathode assembly 216. In the embodiment shown
`in FIG. 2, the permanent magnets 256 continuously generate
`the magnetic field 254. In other embodiments, the magnetic
`field 254 is generated by energizing a current source (not
`shown) that is coupled to electro-magnets. In one embodi-
`ment, the strength of the magnetic field 254 is between about
`one hundred and two thousand gauss. After the magnetic
`field 254 is generated, the feed gas from the gas source 208
`is supplied to the chamber 202 by the gas flow control
`system 210. In one embodiment, the feed gas is supplied to
`the chamber 202 directly between the cathode assembly 216
`and the anode 238.
`
`In one embodiment, the pulsed power supply 234 is a
`component
`in an ionization source that generates the
`weakly-ionized plasma. The pulsed power supply applies a
`voltage pulse between the cathode assembly 216 and the
`anode 238. In one embodiment, the pulsed power supply 234
`applies a negative voltage pulse to the cathode assembly
`216. The amplitude and shape of the voltage pulse are such
`that a weakly-ionized plasma is generated in the region 246
`between the anode 238 and the cathode assembly 216. The
`weakly-ionized plasma is also referred to as a pre-ionized
`plasma. In one embodiment, the peak plasma density of the
`pre-ionized plasma is between about 106 and 1012 cm‘3 for
`argon feed gas. The pressure in the chamber can vary from
`about
`l0‘3 to 10 Torr. The peak plasma density of the
`pre-ionized plasma depends on the properties of the specific
`magnetron sputtering system and is a function of the loca-
`tion of the measurement in the pre-ionized plasma.
`In one embodiment, the pulsed power supply 234 gener-
`ates a low power pulse having an initial voltage of between
`about one hundred volts and five kilovolts with a discharge
`current of between about 0.1 amperes and one hundred
`amperes in order to generate the weakly-ionized plasma. In
`some embodiments the width of the pulse can be in on the
`order of 0.1 microseconds up to one hundred seconds.
`Specific parameters of the pulse are discussed herein in more
`detail in connection with FIG. 4 and FIG. 5.
`
`In one embodiment, prior to the generating of the weakly-
`ionized plasma, the pulsed power supply 234 generates a
`potential difference between the cathode assembly 216 and
`the anode 238 before the feed gas is supplied between the
`cathode assembly 216 and the anode 238.
`In another embodiment, a direct current (DC) power
`supply (not shown) is used to generate and maintain the
`weakly-ionized or pre-ionized plasma. In this embodiment,
`the DC power supply is adapted to generate a voltage that is
`large enough to ignite the pre-ionized plasma.
`In one
`embodiment,
`the DC power supply generates an initial
`voltage of several kilovolts with a discharge current of
`several hundred milliarnps between the cathode assembly
`216 and the anode 238 in order to generate and maintain the
`pre-ionized plasma. The value of the current depends on the
`power level generated by the power supply and is a function
`of the size of the magnetron. Additionally, the presence of a
`magnetic field in the region 245 can have a dramatic effect
`on the value of the applied voltage and current required to
`generate the weakly-ionized plasma.
`
`

`
`US 7,147,759 B2
`
`7
`In some embodiments, the DC power supply generates a
`current that is between about 1 mA and 100 A depending on
`the size of the magnetron