US 6,896,773 B2
`(10) Patent N0.:
`(12) United States Patent
`
`Chistyakov
`(45) Date of Patent:
`*May 24, 2005
`
`U5006896773B2
`
`(54) HIGH DEPOSITION RATE SPUTTERING
`
`(75)
`
`Inventor: Roman Chistyakov, Andover, MA
`(US)
`
`(73) Assignee: Zond, Inc. Mansfield MA (US)
`
`6,398,929 B1 *
`6,413,382 B1
`6,413,383 B1
`6,436,251 B2
`2002/0033480 A1
`
`......... 204/298.11
`6/2002 Chiang et al.
`........... 204/192.12
`7/2002 Wang et al.
`......... 204/192.13
`7/2002 Chiang et al.
`8/2002 Gopalraja et al.
`..... 204/298.12
`3/2002 Kawamata et al.
`
`.............. 427/569
`8/2002 Sumiya et al.
`2002/0114897 A1
`FOREIGN PATENT DOCUMENTS
`
`( * ) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`.
`.
`.
`.
`.
`This patent is subject to a terminal d1s-
`claimer.
`
`DE
`EP
`GB
`JP
`W0
`W0
`
`3210351 A1
`0 788 139 A1
`1339910
`57194254
`WO 98/40532
`WO 01/98553 A1
`
`9/1983
`8/1997
`12/1973
`11/1982
`9/1998
`12/2001
`
`OTHER PUBLICATIONS
`US 5,863,392, 1/1999, Drummond et al. (Withdrawn)
`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.
`(Continued)
`Primary Examiner—Rodney G McDonald
`(74) Attorney, Agent,
`or Firm—Kurt Rauschenbach;
`Rauschenback Patent Law Group, LLC
`
`(57)
`ABSTRACT
`Methods and apparatus for high-deposition sputtering are
`described. A sputtering source includes an anode and a
`cathode assembly that is positioned adjacent to the anode.
`The cathode assembly includes a sputtering target. An
`ionization source generates a weakly-ionized plasma proxi-
`mate to the anode and the cathode assembly. Apower supply
`produces an electric field between the anode and the cathode
`assembly that creates a strongly-ionized plasma from the
`weakly-ionized plasma. The strongly-ionized plasma
`includes a first plurality of ions that impact the sputtering
`target to generate sufficient thermal energy in the sputtering
`target to cause a sputtering yield of the sputtering target to
`be non-linearly related to a temperature of the sputtering
`target.
`
`40 Claims, 13 Drawing Sheets
`
`504
`
`To
`
`T
`
`GILLETTE 1101
`
`(65)
`
`(21) Appl. No.: 10/065,739
`(22) Filed'
`NOV 14 2002
`.
`I
`’
`Prior Publication Data
`US 2004/0094411 A1 May 20, 2004
`Int. Cl.7 ................................................ C23C 14/35
`(51)
`(52) U.S. Cl.
`..................... 204/192.12, 204/192.13,
`204/298.03, 204/298.06, 204/298.07, 204/298.08,
`204/29814; 204/298’19
`(58) Field of Search ....................... 204/192.12, 192.13,
`204/298.03, 298.06, 298.07, 298.08, 298.14,
`29819
`
`(56)
`
`References Cited
`US. PATENT DOCUMENTS
`
`..... 204/298
`5/1986 Cuomo et al.
`5/1991 Gruen ......................... 427/38
`1/1992 Koshiishi et al.
`....... 315/111.81
`2/1994 Szczyrbowski
`et al.
`..................... 204/298.08
`2/1998 Drummond et al.
`204/192.12
`3/1998 Okamura et al.
`...... 204/298.11
`3/1998 Hershcovitch et al.
`. 204/192.11
`5/2000 Hausmann et al.
`......... 438/706
`7/2000 Kobayashi et 81.
`5/2001 Kahn et al.
`............ 204/598.04
`10/2001 Kouznetsov ........... 204/192.12
`3/2002 Kobayashi et al.
`204/298.11
`
`4,588,490 A
`5,015,493 A
`5,083,061 A
`5,286,360 A
`
`5,718,813 A
`5,728,278 A
`5,733,418 A
`6,057,244 A
`6,083,361 A
`6,238,537 B1
`6,296,742 B1
`6,361,667 B1
`
`500
`\
`
`502
`
`10
`
`e 6
`
`4
`
`2 0
`
`Y
`
`GILLETTE 1101
`
`

`

`US 6,896,773 132
`
`Page 2
`
`OTHER PUBLICATIONS
`
`Booth, et al., The Transition From Symmetric To Asymmet-
`ric Discharges In Pulsed 13.56 MHZ Capacity Coupled
`Plasmas, J. Appl. Phys., Jul. 15, 1997, pp. 552—560, vol. 82
`(2), American Institute of Physics.
`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—Bea-
`m—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
`Dioxide With A Dual Frequency 27/2 MHZ Capacitive RF
`Discharge.
`Macak, Reactive Sputter Deposition Process of A1203 and
`Characterization 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 Dis-
`charge,
`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 —Sta-
`tionary Discharge In A Magnetic Field: Experimental
`Research, Plasma Physics 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
`ASputtering 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 Sputter-
`ing Yields, Applied Physics A., 1985, pp. 37—42, vol. 36,
`Springer—Verlag.
`
`Chistyakov, Roman, High—Power Pulsed Magnetron Sput-
`tering, U.S. Appl. No. 10/065,277, filed Sep. 30, 2002.
`
`Chistyakov, Roman, High—Power Pulsed Magnetically
`Enhanced Plasma Processing, U.S. Appl. No. 10/065,551,
`filed Oct. 30, 2002.
`
`Chistyakov, Roman, Methods and Apparatus for Generating
`High—Density Plasma, U.S. Appl. No. 10/065,629, filed
`Nov. 04, 2002.
`
`Encyclopedia Of Low Temperature Plasma, p. 119, vol. 3.
`
`Encyclopedia Of Low Temperature Plasma, p. 123, vol. 3.
`
`* cited by examiner
`
`

`

`US. Patent
`
`May 24, 2005
`
`Sheet 1 0f 13
`
`US 6,896,773 B2
`
`100
`
`102
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`

`

`US. Patent
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`May 24, 2005
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`Sheet 2 0f 13
`
`US 6,896,773 B2
`
`
`
`FIG. 2
`
`PRIOR ART
`
`
`
`FIG. 3
`
`PRIOR ART
`
`

`

`US. Patent
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`May 24, 2005
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`Sheet 3 0f 13
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`US 6,896,773 B2
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`US. Patent
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`May 24, 2005
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`Sheet 4 0f 13
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`US 6,896,773 B2
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`US. Patent
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`May 24, 2005
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`Sheet 5 0f 13
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`US 6,896,773 B2
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`US. Patent
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`US. Patent
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`May 24, 2005
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`US. Patent
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`May 24, 2005
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`Sheet 12 0f 13
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`US 6,896,773 B2
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`650
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`START
`
`602
`
`PUMP DOWN CHAMBER
`
`604
`
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` CHAMBER
`
`PRESSURE
`
`CORRECT?
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`PASS FEED GAS INTO CHAMBER
`
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`PROXIMATE TO A CATHODE (TARGET) ASSEMBLY
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`CHAMBER
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`FIELD PROXIMATE TO FEED GAS
`
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`FIG. 11A
`
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`IONIZE FEED GAS TO GENERATE
`WEAKLY-IONIZED PLASMA
`
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`
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` FIG. 118
`GAS
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`
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`
`

`

`US. Patent
`
`May 24, 2005
`
`Sheet 13 0f 13
`
`US 6,896,773 B2
`
`6
`
`GENERATE STRONGLY-IONIZED
`PLASMA FROM WEAKLY~IONIZED PLASMA
`
`EXCHANGE STRONGLY—IONIZED
`PLASMA WITH FEED GAS
`
`622
`
`
`
`
`PLASMA
`STRONGLY-
`
`IONIZED?
`
`
`Y
`
`MONITOR SPUTTER YIELD
`
`628
`
`
`
`
`
`INCREASE
`HIGH—POWER PULSE
` SPUTI'ER
`
`
`YIELD
`Y
`TO CATHODE (TARGET)
`
`
`SUFFICENT
`ASSEMBLY TO
`
`
`
`INCREASE SPUTTER
`? 634
`
`
`YIELD
`
`
`CONTINUE
`SPUTTERING
`
`
` SPUTTER
`
`636
`
`DEPOSITION
`
`COMPLETE
`
`
`
`FIG. 11B
`
` m
`
`

`

`US 6,896,773 B2
`
`1
`HIGH DEPOSITION RATE 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 10'1 and 10'2 Torr. A plasma
`discharge 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 then 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
`electromagnets) in planar magnetron sputtering systems are
`placed behind the cathode. The magnetic field lines gener-
`ated 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 dissipated by electrons arriving at the substrate.
`Conventional magnetron sputtering systems deposit films
`that have relatively low uniformity. The film uniformity can
`be increased by mechanically moving the substrate and/or
`the magnetron. However, such systems are relatively com-
`plex and expensive to implement. Conventional magnetron
`sputtering systems also have relatively poor target utiliza-
`tion. The term “target utilization” is defined herein to be a
`metric of how uniform the target material erodes during
`sputtering. For example, high target utilization would indi-
`cate that the target material erodes in a highly uniform
`manner.
`
`In addition, conventional magnetron sputtering systems
`have a relatively low deposition rate. The term “deposition
`rate” is defined herein to mean the amount of material
`deposited on the substrate per unit of time. In general, the
`deposition rate is proportional to the sputtering yield. The
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`2
`term “sputtering yield” is defined herein to mean the number
`of target atoms ejected from the target per incident particle.
`Thus, increasing the sputtering yield will increase the depo-
`sition rate.
`
`BRIEF DESCRIPTION OF DRAWINGS
`
`This invention is described with particularity in the
`detailed description. The above and further advantages of
`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 a prior art
`cathode assembly having a cathode cooling system.
`FIG. 3 illustrates a known process for sputtering material
`from a target.
`FIG. 4 illustrates a cross-sectional view of an embodiment
`of a magnetron sputtering apparatus according to the present
`invention.
`
`FIG. 5A through FIG. 5D illustrate cross-sectional views
`of the magnetron sputtering apparatus of FIG. 4.
`FIG. 6 illustrates graphical representations of the applied
`voltage, current, and power as a function of time for periodic
`pulses applied to the plasma in the magnetron sputtering
`apparatus of FIG. 4.
`FIG. 7A through FIG. 7D illustrate various simulated
`magnetic field distributions proximate to the cathode assem-
`bly for various electron ExB drift currents in a magnetically
`enhanced plasma sputtering apparatus according to the
`invention.
`
`FIG. 8 illustrates a graphical representation of sputtering
`yield as a function of temperature of the sputtering target.
`FIG. 9 illustrates a process for sputtering material from a
`target according one embodiment of the present invention.
`FIG. 10 illustrates a cross-sectional view of a cathode
`assembly according to one embodiment of the invention.
`FIG. 11 is a flowchart of an illustrative process of enhanc-
`ing a sputtering yield of a sputtering target according to the
`present invention.
`DETAILED DESCRIPTION
`
`The sputtering process can be quantified in terms of the
`sputtering yield. The term “sputtering yield” is defined
`herein to mean the number of target atoms ejected from the
`target per incident particle. The sputtering yield depends on
`several factors, such as the target species, bombarding
`species, energy of the bombarding ions, and the angle of
`incidence of the bombarding ions. In typical known sput-
`tering processes, the sputtering yield is generally insensitive
`to target temperature.
`The deposition rate of a sputtering process is generally
`proportional to the sputtering yield. Thus, increasing the
`sputtering yield typically will increase the deposition rate.
`One way to increase the sputtering yield is to increase the
`ion density of the plasma so that a larger ion flux impacts the
`surface of the target. The density of the plasma is generally
`proportional to the number of ionizing collisions in the
`plasma.
`Magnetic fields can be used to confine electrons in the
`plasma to increase the number of ionizing collisions
`between electrons and neutral atoms in the plasma. The
`magnetic and electric fields in magnetron sputtering systems
`
`

`

`US 6,896,773 B2
`
`3
`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 ionization regions
`causes 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 production of ionized gas and,
`therefore, increase the target utilization and the sputtering
`yield. However, increasing the applied power can lead to
`undesirable target heating and target damage. Furthermore,
`increasing the voltage applied between the target and the
`anode increases the probability of establishing an undesir-
`able electrical discharge (an electrical arc) in the process
`chamber. An undesirable electrical discharge can corrupt the
`sputtering process.
`Pulsing the power applied to the plasma can be advanta-
`geous since the average discharge power can remain low
`while relatively large power pulses are 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 undesir-
`able 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 coupled to the vacuum chamber 104 by a gas
`inlet 110. Avalve 112 controls the gas flow from the feed gas
`source 109.
`
`The magnetron sputtering apparatus 100 also includes a
`cathode assembly 114 having a target 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 posi-
`tioned behind the cathode assembly 114 to protect a magnet
`126 from bombarding ions. The magnet 126 shown in FIG.
`1 is generally shaped in the form of a ring that has 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 from the target 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.
`In operation,
`the pulsed power supply 102 applies a
`voltage pulse between the cathode assembly 114 and the
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`anode 130 that has a sufficient amplitude to ionize the argon
`feed gas in the vacuum chamber 104. The 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 sufficient acceleration so that
`the ions sputter the target material from the target 116. A
`portion of the sputtered target material 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.
`Consequently, the target 116 is eroded more 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 116 and, thus
`relatively poor target utilization.
`Dramatically increasing the power applied to the plasma
`can result in more uniform erosion of the target 116 and
`higher sputtering yield. However,
`the amount of applied
`power necessary to achieve this increased uniformity can
`increase the probability of generating an electrical break-
`down condition that leads to an undesirable electrical dis-
`charge between the cathode assembly 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 overheat the target
`and cause target damage.
`Sputtering yields are generally determined experimen-
`tally. The yield dependence on the bombarding ion energy
`approximately exhibits a threshold that is between about
`10—30 eV, followed by a nearly linear range that extends to
`several hundred eV. At higher energies, the dependence is
`less than linear. Sputtering processes are generally most
`energy efficient when the ion energies are within the linear
`range.
`Sputtering systems are generally calibrated to determine
`the deposition rate under certain operating conditions. The
`erosion rate of the target 116 can be expressed by the
`following equation:
`
`JYM
`R = kTA/min
`
`where k is a constant, J is the ion current density in
`mA/cm2, Y is the sputtering yield in atoms/ion, and M is the
`atomic weight in grams, and p is the density in gm/cm3 of
`the target material. The deposition rate is generally propor-
`tional to the sputtering yield Y.
`FIG. 2 illustrates a cross-sectional view of a prior art
`cathode assembly 114' having a cathode cooling system. The
`cathode assembly 114'
`includes target 116'. The cathode
`cooling system also includes a conduit 150 that contains a
`fluid 152 for conducting heat away from the cathode assem-
`bly 114'. The fluid 152 can be a liquid coolant or a gas, for
`example.
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`US 6,896,773 B2
`
`5
`In operation, ions 154 in a plasma impact a surface 156 of
`the target 116'. The impact of the ions 154 generates heat 158
`at the surface 156. Additionally, the impact of the ions 154
`eventually dislodges atoms 160 from the surface 156 of the
`target 116' causing sputtering. The heat 158 that is generated
`by the ion impact radiates through the cathode assembly
`114'. The cathode assembly 114' is in thermal communica-
`tion with the conduit 150. The fluid 152 absorbs the heat 158
`and transfers it away from the cathode assembly 114'.
`FIG. 3 illustrates a known process for sputtering material
`from a target 116'. An ion 154 having a mass M,- and a
`velocity vi impacts a target particle 162 having a mass Mt
`which is initially at rest on the surface 156 of the target 116'.
`The ion 154 impacts the surface 156 at normal incidence.
`The momentum from the ion 154 transfers to the target
`particle 162 driving the target particle 162 into the target
`116'.
`Thus, the ejection of a sputtered particle 164 from the
`target 114' generally requires a sequence of collisions for a
`component of the initial momentum vector to change by
`more than ninety degrees. Typically, an incident ion 154
`experiences a cascade of collisions and its energy is parti-
`tioned over a region of the target surface 156. However, the
`sputtering momentum exchange occurs primarily within a
`region extending only about ten angstroms below the surface
`156. The incident ion 154 generally strikes two lattice atoms
`166, 168 almost simultaneously. This low energy knock-on
`receives a side component of momentum and initiates sput-
`tering of one or more of its neighbors. The primary knock-on
`is driven into the target 114', where it can be reflected and
`sometimes returned to the surface 156 to produce sputtering
`by impacting the rear of a surface atom 170.
`A fraction of the kinetic energy of the incident ion 154 is
`transferred to the target particle 162. This kinetic energy
`transfer function can be expressed as follows:
`
`4MiM,
`a = —
`(M; + Mr)2
`
`The sputtering yield Y can be expressed as follows,
`assuming perpendicular ion incidence onto a substantially
`planar surface 156:
`
`E
`
`Y=k><s><U><a(M,/M;)
`
`where k is a constant, e is the energy transfer function, (X
`is a near-linear function of the ratio of the mass of the target
`atom 162 to the mass of the incident ion 154, E is the kinetic
`energy of the incident ion 154, and U is the surface binding
`energy for the target material. For most sputtering materials,
`the mass dependence of e (X does not vary greatly from one
`material to another. The primary material-sensitive factor is
`the surface binding energy, and this has only a first power
`dependence.
`At energies above 20—30 eV, heavy particles can sputter
`atoms from a surface of a target. The sputtering yield
`increases rapidly with energy up to a few hundred eV, with
`500—1000 eV argon ions being typically used for physical
`sputtering. Above a few hundred eV, there is a possibility
`that ions 154 will be implanted in the target 116'. This can
`especially occur at energies over 1 keV.
`FIG. 4 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 valve 206.
`In one
`embodiment,
`the chamber 202 is electrically coupled to
`ground potential.
`
`6
`The chamber 202 is coupled to a feed gas source 208 by
`one or more gas lines 207. 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 iso-
`lated from the feed gas source using in-line insulating
`couplers (not shown). A gas flow control system 210 con-
`trols the gas flow to the chamber 202. The gas source 208
`can contain any feed gas. For example, the feed gas can be
`a noble gas or a mixture of noble gases. The feed gas can
`also be a reactive gas, a non-reactive gas, or a mixture of
`both reactive and non-reactive gases.
`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. In one embodiment, the
`cathode 218 is formed of a metal. In one embodiment, the
`cathode 218 is formed of a chemically inert material, such
`as stainless steel. The sputtering target 220 is in physical
`contact with the cathode 218.
`In one embodiment,
`the
`sputtering target 220 is positioned inside the cathode 218 as
`shown in FIG. 4. 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
`material, polymer material, superconductive material, mag-
`netic material
`including ferromagnetic material, non-
`magnetic material, conductive material, non-conductive
`material, composite material, reactive material, or a refrac-
`tory 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 (not shown), the first output 232 of the
`pulsed power supply 234 is directly coupled to the cathode
`assembly 216. In one embodiment (not shown), the second
`output 236 of the pulsed power supply 234 and the anode
`238 are both coupled to ground. 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 second output
`236 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 between about 5 kV and about 30
`kV. In one embodiment, operating voltages are generally
`between about 50V and 1 kV. In one embodiment, the pulsed
`power supply 234 sustains discharge current levels that are
`on order of about 1 A to 5,000 A depending on the volume
`of the plasma. Typical operating currents varying from less
`than about one hundred amperes to more than a few thou-
`sand amperes depending on the volume of the plasma. In one
`embodiment, the power pulses have a repetition rate that is
`below 1 kHz. In one embodiment, the pulse width of the
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`US 6,896,773 B2
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`7
`pulses generated by the pulsed power supply 234 is sub-
`stantially between about one microsecond and several sec-
`onds.
`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 cm
`and 10 cm. The surface area of the cathode assembly 216
`determines the volume of the region 245. The gap 244 and
`the total volume of the region 245 are parameters in the
`ionization process as described herein.
`An anode shield 248 is positioned adjacent to the anode
`238 and functions 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 magnetro