`
`US007l47759B2
`
`(12)
`
`United States Patent
`Chistyakov
`
`(10) Patent N0.:
`(45) Date of Patent:
`
`US 7,147,759 B2
`*Dec. 12, 2006
`
`(54) HIGH-POWER PULSE1) IVLAGNETRON
`SPUTTERING
`
`6,398,929 131*
`6.413.332 Bl
`6.436.251 Bl
`
`6/2002 (Ihiang et £11.
`
`7/2002 Wang et al.
`8/2002 Gopalrzijaetal.
`
`204/298.11
`204/192.12
`204298 12
`
`(75)
`
`Inventor: Roman Chistyakov. Andover. MA
`(US)
`
`9440-3813 B1
`6.45664. B1
`2‘
`L00:/0033480 A1
`
`E‘/£003 B‘}”_"“ 9‘ ‘ll
`~)/-00..
`llllllard
`_»/2002
`lxawamata etal.
`
`(73) Assigneei
`
`loud’ Inc’, Mallsfieldi MA (US)
`
`11/2005 Lhtstyakov
`2005/0252/63 A1*
`FOREIGN I’/\'I‘ENT DOCUMENTS
`
`204/192.12
`
`( * ) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U'S'L' 154(1)) by 0 days’
`
`DE
`
`This patent is subject to a temiinal dis-
`l
`'
`.
`C mmer
`
`(51)
`
`‘.
`‘
`‘
`2
`( 1) App] No 10/065377
`(22)
`Filed:
`Sep_ 30, 2002
`(65)
`Prior Publication Data
`‘
`U5 2004/0060813 A1
`AP“ 1= 2004
`Int. CL
`(2006.01)
`C23C 14/35
`(52) U.S.Cl.
`......................... .. 204/l92.I2:204/192.13;
`204/293-03;Z04/298.06;204/298.08;204/298.14;
`204/298-19
`Field of Classification Search ......... .. 204/192.12.
`204/192.13, 298.03, 298.06. 298.08, 298.14.
`204/298.19.298.26
`See application file for complete search history.
`References Cited
`U.S. PATENT DOCUI\/IENTS
`
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`
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`3210321 A‘
`(Continued)
`
`OTHER PUBLICATIONS
`
`211.. The Transition From Symmetric To Asymmetric
`Booth, et
`Discharges In Pulsed 13.56 MIIZ Capacity Coupled Plasmas,
`.1.
`Appl. 1’hys., Jul. 15, 1997. pp. 552-560. vol. 32 (2), Amei'ica.u
`Institute ofI’hysics.
`
`—-L1)
`(Co 1'
`H mm
`Primary E.\‘ami)7er«R0dney G. McDonald
`(74) Attorney, Agent, or
`I<‘1‘rm—Kurt Rauschenbach:
`R‘l’bz1P
`'
`G
`.LLC
`al1bC1t.l1 iei
`atent Law roup
`(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
`z::= 1')1’./
`2 J':
`=d
`*>'>z
`2
`V
`isseni
`3
`\ mignct is pmitionc
`to generate 1 mignctic
`lield proximate to the WCél1\’1y~it)l11'[.&3(.1 plasma. The niag'netic
`field substantially traps electrons in the weal(ly—ioni'/.ed
`plasma proximate to the sputtering target. A power supply
`produces an electric field in a gap between the anode and the
`cathode assembly. The electric field 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 flux.
`
`50 Claims, 18 Drawing Sheets
`
`
`
`VACUUM
`sramm
`
`20.
`
`211
`
`EX 1211
`
`EX 1211
`
`
`
`US 7,147,759 B2
`Page 2
`
`FOREIGN PA1'l:'N'1' DOC U M1:'N'l‘S
`
`EP
`GB
`IP
`JP
`W0
`W0
`W0
`
`0 788 139 Al
`1339910
`57194254
`10204633
`WO9504368
`WO 98/40532
`WO 01/98553 A1
`
`*
`
`8/1997
`12/"1973
`ll/"1982
`S/1998
`2/1995
`9/1998
`12/2001
`
`OTHER P1 1131 .l(‘ATlONS
`
`Biinshah, ct 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—loni'Aeil
`Discharges. Applied Science Letters. May 15. 1976. vol. 28. No. 10.
`American Institute of Physics.
`Goto. ct :11. Dual Excitation Reactive lon T.tchcr for 1 ow linergy
`Plasma Processing.
`.1. Vac. Sci. Technol. A. Sep.-’(.)ct. 1992, pp.
`3048-3054. vol. 10. No. 5. American Vacuum Society.
`Koiiznetsov. 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 MIIZ Capacitive RF Discharge.
`Macak, Reactive Splitter 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 ln A Magnetic Field: l‘iXpC1'lIT]€11l11l Research. Plasma Phys-
`ics Reports. 1995. pp. 400-409, vol. 21, No. 5. Mo’/.grin. Fcitsov.
`Khodachenko.
`
`ln (‘ircular Planar
`lndiiced Drift Currents
`a1..
`et
`Rossnagcl.
`Magnetrons. J. Vac. Sci.'1‘ec1ino1. A.. Jan./1"eb. 1987. pp. 88-91. vol.
`5. No. 1. American Vacuum Society.
`Sheridan. et
`21].. Electron Velocity Distribution Functions In A
`Sputtering Magnetron Discharge I501‘ The IJIXB Direction. J. Vac.
`Sci. Technol. A., Jiil.:’./\ug. 1998. pp. 2173-2176. vol. 16. No 4.
`American Vacuum Society.
`Steinbi1ichcl.A Simple Formula For l.ow—Fincrgy Sputtcri ng Yields.
`Applied Physics A.. 1985. pp, 37-42. vol 36. Springer-Verlag.
`’l'uren1<o. ct éll.. Magnetron Discharge In The Vapor ()t"1'hc ('athoitc
`Material. Soviet Technical Physics letters. Jul. 1939. pp. 5 19-520:
`vol. 15, No. 7. New York. US.
`
`l-Lncyclopedia ()t' l.ow licmperatiirc Plasma. p. 119. vol. 3.
`Encyclopedia 01 Low Temperature Plasma. p. 123. vol. 3.
`Sugimoto. et al; Magnetic Condensation (,)fA 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-
`miniun—Doped ZnO Thin—Film Sputtering; Appl. Phys.
`l..ett.; Jan.
`12, 1998; pp. 235-237; vol. 72; No. 2; American Institute of Physics:
`New York US.
`
`* cited by examiner
`
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`U.S. Patent
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`Dec. 12,2006
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`US 7,147,759 B2
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`Dec. 12,2006
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`Sheet 15 of 18
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`US 7,147,759 B2
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`600
`PUMP DOWN CHAMBER I
`
`
`604
`
` CHAMBER
`PRESSURE
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`
`608
` PASS FEED GAS INTO CHAMBER
`PROXIMATE TO A CATHODE (TARGET) ASSEMBLY
`
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`
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`FIG. 12B
`
`FIG. 12
`
`
`
`U.S. Patent
`
`Dec. 12,2006
`
`Sheet 16 of 18
`
`US 7,147,759 B2
`
`
`
`STRONGLY-
`ONIZED?
`
`
`
`
`MONITOR SPUTTER DEPOSITION
`
`
`
`
`
`DEPOSITION
`COMPLETE
`?
`
`FIG. 12B
`
`
`
`GENERATE STRONGLY-IONIZED SUBSTANTIALLY '
`UNIFORM PLASMA FROM WEAKLY-IONIZED PLASMA
`
`
`
`
`
`U.S. Patent
`
`Dec. 12,2006
`
`Sheet 17 of 18
`
`Us 7,147,759 B2
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`604
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`
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`
`
`
`FIG. 13A
`
`FIG. 13A
`
`FIG. 13B
`
`FIG/13
`
`
`
`U.S. Patent
`
`Dec. 12,2006
`
`Sheet 18 of 18
`
`US 7,147,759 B2
`
`
`
`GENERATE STRONGLY—lONlZED SUBSTANTIALLY I
`UNIFORM PLASMA FROM WEAKLY—|ONiZED PLASMA
`
`
`
`STRONGLY-
`
`MONITOR SPUTTER RATE
`
`
` SPUTTER
`
`INCREASE HIGH-POWER
`PULSE TO CATHODE
`
`(TARGET) ASSEMBLY
`TO INCREASE
`SPUTTER RATE
`
`
`
`
`
`
`
`
`
`
`
`SPUTTER
`DEPOSITION
`
`COMPLETE
`
`
`
`FIG. 13B
`
`
`
`US 7,147,759 B2
`
`2
`this invention may be better understood by referring to the
`following description in conjuiiction 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 ofan embodiment
`ofa magnetron sputtering apparatus according to the present
`invention.
`FIG. 3 illustrates a cross-sectional view of the anode and
`the cathode assembly ofthe magnetron sputtering apparatus
`of FIG. 2.
`
`'.II
`
`10
`
`15
`
`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.
`
`25
`
`30
`
`..: at
`
`FIG. 5 illustrates graphical representations ofthe 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. 6]")
`illustrate various simulated
`magnetic field distributions proximate to the cathode assem-
`bly for various electron E><B drifi 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 oftime for periodic pulses applied to the
`plasma in the magnetron sputtering system of FIG. 7.
`FIG. 9A through FIG. 9(" are cross-sectional views of
`various embodiments o fcathode assemblies according to the
`present invention.
`FIG. 10 illustrates a cross-sectional view of another
`illustrative embodiment ofa 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 llowchart ofan illustrative process ofsputter
`.- deposition according to the present invention.
`FIG. 13 includes FIGS.l3 A and 13 B which is a flowchart
`of an illustrative process of controlling sputtering rate
`according to the present invention.
`
`1
`HIGH-POWER P-ULSEI) MAGNETROl\'
`SPU'l"l‘ERlNG
`
`BACKGROIIND OF lNVF.NTI()N
`
`Sputtering is a well—l<nown technique for depositing films
`on substrates. Sputtering is the physical ejection of atoms
`from a target surface and is sotnetimes 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 How 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 frotn 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 molv
`ecules with secondary electrons generated at
`the target
`surface.
`
`40
`
`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. Hlectroiis are trapped in the
`electric and magietie fields. The trapped electrons enhance
`the efficiency of the discharge and reduce the energy dissi-
`pated by electrons arriving at the substrate.
`./I ‘Jr
`Conventional magnetron sputtering systems deposit films .
`that have relatively low uniformity. However.
`the lilm
`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-uniforin manner.
`
`DETAILED DESCRIl"I'ION
`
`The magnetic and electric lields in rnagrietron 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 ofthe
`target that results in poor target utili7ation.
`Increasing the power applied between the target and the
`anode can increase the amount of ionized gas and. there fore.
`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.
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`BRIEF l)ESCRlP'l'l()N OI“ DRAWINGS
`
`This invention is described with particularity in the
`detailed description. The above and further advantages of
`
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`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 perfonned. 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.
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`the ions sputter the target material 116. A portion of the
`sputtered target material 116 is deposited on the substrate
`I34.
`The electrons. which cause the ioni"/.ation. 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 lield
`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 ol‘ 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 ofthe 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 ofthe
`pulses. An undesirable electrical discharge will corrupt the
`sputtering process and cause contamination in the vacuum
`chamber 104. Additionally. the increased power can over-
`h ‘at the target and cause target damage.
`FIG. 2 illustrates a cross—sectional view ofan 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
`water. In one embodiment.
`the substrate support 212 is
`electrically coupled to an output 213 ofa 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 lloating.
`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 mat.crial can be any material suitable for
`sputtering. For example. the target material can be a metallic
`
`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 ofa 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 ofthe 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.
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`3t’)
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`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 sullicient 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 sullicient acceleration so that
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`material. polymer material, superconductive material, mag-
`netic niaterial including ferromagnetic material, non—niag—
`netic material, conductive material. noii-conductive mate-
`rial, composite material, reactive material, or a refractory
`material.
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`5
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`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 cotipled to the cathode asseni-
`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 IOOV 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
`aiiiperes 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
`suflicient
`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
`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.
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`J. 'J\
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`In one embodiment. the magnet assembly 252 includes
`switching electro—inagnets. which generate a pulsed niag—
`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 coiitiiniously 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 einbodi—
`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 llow 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.
`the pulsed power supply 234 is a
`In one embodiment.
`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—ioni7/ed plasma is also referred to as a pre—ioni7.ed
`plasma. In one embodiment, the peak plasma density of the
`pre-ionized plasma is between about 10° and 1013 cm'3 for
`argon feed gas. The pressure in the chamber can vary from
`about
`l0‘3 to I0 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 em initial voltage of between
`about one hundred volts and five kilovolts with a discharge
`current of between about 0.1 amperes and one hundred
`aniperes in order to generate the wealdy—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 o lithe weakly-
`ionizcd plasma. the pulsed power supply 234 generates a
`potential dilference 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—ioni7.ed or pre-ionized plasma. In this enibodinieiit
`the l)(‘ 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 ol‘
`several hundred inillianips 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 Iiave a dramatic eflect
`on the value of the applied voltage and current required to
`generate the weakly-ionized plasma.
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`US 7,l47,759 B2
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`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 and the strength of a magnetic field
`in the region 245. In one embodiment, before generating the
`weakly—ioniZed plasma, the DC power supply is adapted to
`generate and maintain an initial voltage between the cathode
`assembly 216 and the anode 238 before the introduction of
`the feed gas.
`The pre—ionized or weakly«ioni7.ed plasma can be gener-
`ated by numerous other techniques including UV radiation
`techniques. X-ray techniques. electron beam techniques. ion
`beam techniques, or
`ionizing filament
`techniques.
`for
`example. In one em