USOO7811421B2
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`(12)
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`United States Patent
`Chistyakov
`
`(10) Patent N0.:
`
`(45) Date of Patent:
`
`US 7,811,421 B2
`*Oct. 12, 2010
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`(54)
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`(75)
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`(73)
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`HIGH DEPOSITION RATE SPUTTERING
`
`Inventor: Roman Chistyakov, Andover. MA (US)
`
`Assignee: Zond, Inc., Mansfield, MA (US)
`
`5.733.418 A
`6.024.844 A
`6.057.244 A
`6.083.361 A
`6,086,730 A
`6.217.717 B1
`
`3/1998 Hershcoviteh et a1.
`2/2000 Drummond ct al.
`5/2000 Hausmann et a1.
`7/2000 Kobayashi et a1.
`7/2000 1 iu ct al.
`4/2001 Dnumnond et a1.
`
`( *>
`
`Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 896 days.
`
`This patent is subject to a terminal dis—
`claimer.
`
`(21)
`
`Appl. No: 11/183,463
`
`(Continued)
`FOREIGN PATENT DOCUMENTS
`
`DE
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`3210351 Al
`
`9/1983
`
`(Continued)
`OTHER PUBLICATIONS
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`(22)
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`(65)
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`(63)
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`(51)
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`(52)
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`(58)
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`(56)
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`Filed:
`
`Jul. 18, 2005
`
`Prior Publication Data
`
`US 2005/0252763 Al
`
`Nov. 17. 2005
`
`Booth, et 211.. The Transition From Symmetric To Asymmetric Dis»
`charges In Pulsed 13 56 MHZ (‘ripacitively Coupled Plasmas. .lAppl.
`Phys. Jul. 15. 1997. pp. 552-560. vol. 82(2). American Institute 01'
`Physics.
`
`(Continued)
`
`Related U.S. Application Data
`
`Continuation of application No.
`Mar. 28, 2005, now abandoned.
`
`1 1/09l,814. filed on
`
`Primary EmmineriRodney G McDonald
`(74)
`.fl/Iomqv. Age/71. or Firm Kurt Rausehenbach:
`Rauschenbach Patent Law Group. Ll.l’
`
`Int. Cl.
`(236‘ 14/35
`US. Cl.
`
`.
`
`(2006.01)
`. 204/192.12: 204/29808;
`204/29806
`Field of Classification Search ............ 204/192.12.
`204/298.06. 298.08
`
`See application file for complete search history.
`References Cited
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`ABSTRACT
`
`Methods and apparatus for high—deposition sputtering are
`described. A sputtering source includes an anode and a cath—
`ode assembly that is positioned adjacent to the anode. The
`cathode assembly includes a sputtering target. An ionization
`source generates a weakly-ionized plasma proximate to the
`anode and the cathode assembly. A power supply produces an
`electric field between the anode and the cathode assembly
`that creates a strongly—ionized plasma from the weakly—ion—
`ized 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 01' the sputtering target to be non-linearly
`related to a temperature ol‘the sputtering target.
`
`48 Claims. 13 Drawing Sheets
`
`200
`\
`
`no
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`207-
`
`.:
`
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`1_J.—-—?--w—--
`.
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`INTEL 1001
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`US 7,811,421 32
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`US. Patent
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`Oct. 12, 2010
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`Sheet 1 0113
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`US 7,811,421 B7.
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`US. Patent
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`Oct. 12, 2010
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`Sheet 2 of 13
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`US 7,811,421 B2
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`FIG. 2
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`PRIOR ART
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`FIG. 3
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`PRIOR ART
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`U.S. Patent
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`Oct. 12, 2010
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`US. Patent
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`Oct. 12, 2010
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`Sheet 4 0113
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`U.S. Patent
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`Oct. 12, 2010
`
`Sheet 5 of 13
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`US 7,811,421 B2
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`U.S. Patent
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`Oct. 12, 2010
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`Oct. 12, 2010
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`US. Patent
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`Oct. 12, 2010
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`US 7,811,421 B2
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`Oct. 12, 2010
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`U.S. Patent
`
`Oct. 12, 2010
`
`Sheet 11 0113
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`US 7,811,421 B2
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`US Patent
`
`Oct. 12, 2010
`
`Sheet 12 0113
`
`US 7,811,421 B2
`
`650
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`PUMP DOWN CHAMBER
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`PRESSURE
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`PROXIMATE TO A CATHODE (TARGET) ASSEMBLY
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`WEAKLY-IONIZED PLASMA
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`
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`
`FIG. 11 B
`
`FIG. 11
`
`

`

`U.S. Patent
`
`Oct. 12, 2010
`
`Sheet 13 0f13
`
`US 7,811,421 32
`
`0
`
`622
`
`GENERATE STRONGLY-IONIZED
`PLASMA FROM WEAKLY-IONIZED PLASMA
`
`EXCHANGE STRONGLY—IONIZED
`PLASMA WITH FEED GAS
`
`
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`STRONGLY—
`IONIZE D?
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`MONITOR SPUTTER YIELD
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`HIGH-POWER PULSE
`
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`YIELD
`TO CATHODE (TARGET)
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`DEPOSITION
`COMPLETE
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`
`FIG. 11B
`
`

`

`US 7,811,421 B2
`
`1
`HIGH DEPOSITION RATE SPUTTERING
`
`
`R ELATED APPLICATION SECTION
`
`This application claims priority to US. patent application
`Ser. No. 11/091814, filed Mar. 28. 2005, and entitled “High
`Deposition Rate Sputtering”, which is a continuation ol'US.
`patent application. Ser. No. 10/065.739. filed Nov. 14. 2002.
`and entitled “High Deposition Rate Sputtering“, which is now
`US. Pat. No. 6.896.773. the entire application and patent of
`which are incorporated herein by reference
`
`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 gener-
`ated 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 estab—
`lishing an electncal discharge in a gas between two parallel-
`plate electrodes inside a chamber. A potential of several kilo—
`volts is typically applied between planar electrodes 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 physi—
`cally 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 elec—
`tron-ion pairs formed by the collision of neutral molecules
`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 ofelectrons. The hi gh density ofelectrons 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 mag—
`netron sputtering system. Planar magnetron sputtering sys—
`tems are similar in configuration to diode sputtering systems.
`However. the magnets (permanent or electromagnets) in pla—
`nar magnetron sputtering systems are placed behind the cath—
`ode. The magnetic field lines generated by the magnets enter
`and leave the target cathode substantially nortnal to the cath—
`ode 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 arriv—
`ing 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 complex
`and expensive to implement. Conventional magnetron sput—
`
`'Jl
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`
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`
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`tering systems also have relatively poor target utilization. 'l"hc
`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 indicate 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 depos—
`ited on the substrate per unit oftime. In general. the deposi—
`tion rate is proportional
`to the sputtering yield. The 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 ofthis
`invention may be better understood by referring to the fol—
`lowing description in conjunction with the accompanying
`drawings. in which like numerals indicate like structural ele-
`ments and features in various figures. 'lhc 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 mag—
`netron sputtering apparatus having a pulsed power source.
`FIG. 2 illustrates a cross—sectional view of a prior art cath—
`ode 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 ol‘an embodiment
`ofa magnetron sputtering apparatus according to the present
`invention.
`FIGS. 5A. AB. AC. 5D illustrate cross-sectional views of
`the magnetron sputtering apparatus of FIG. 4.
`FIG. 6 illustrates graphical representatiot'ts of the applied
`voltage. current. and power as a function ol‘time for periodic
`pulses applied to the plasma in the magnetron sputtering
`apparatus of FIG. 4.
`FIGS. 7A. 713. 7C, 7D illustrate various sit'nulated mag—
`netic field distributions proximate to the cathode assembly for
`various electron 13x13 drift currents
`in a magnetically
`enhanced plasma sputtering apparatus according to the inven-
`tion.
`
`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 ofthe invention.
`FIGS. 11. 11A, 1 IB is a flowchart ofan illustrative process
`ofcnhancing a sputtering yield ol‘a sputtering target accord—
`ing to the present invention.
`
`DFXI‘AIIFD DFSCRIP'I‘ION
`
`()0
`
`65
`
`The sputtering process can be quantified in terms of the
`sputtering yield. The term “sputtering yield” is defined herein
`to mean the number oftarget atoms ejected from the target per
`incident particle. The sputtering yield depends on several
`factors. such as the target species. bombarding species.
`energy ofthe bombarding ions. and the angle of incidence of
`the bombarding ions. In typical known sputtering processes.
`the sputtering yield is generally insensitive to target tempera—
`ture.
`
`

`

`US 7,811,421 B2
`
`3
`The deposition rate of a sputtering process is generally
`proportional to the sputtering yield. Thus, increasing the sput-
`tering 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 he used to confine electrons in the
`plasma to increase the number ol‘ionizing collisions between
`electrons and neutral atoms in the plasma. The magnetic and
`electric fields in magnetron sputtering systems are concen—
`trated in narrow regions close to the surface of the target.
`These narrow regions are located between the poles 01‘ 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 ol. the target that results in poor target
`utilization.
`
`Increasing the power applied between the target and the
`anode can increase the production 01‘ ionized gas and. there—
`fore. increase the target utilization and the sputtering yield
`I-Iowever, increasing the applied power can lead to undesir—
`able target heating and target damage. Furthermore. increas-
`ing the voltage applied between the target and the anode
`increases the probability ol‘ establishing an undesirable elec—
`trical 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 ofthese large voltage pulses can be
`preset so as to reduce the probability ol‘establishing an elec—
`trical breakdown condition leading to an undesirable electri—
`cal discharge. Howevcr. 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 mag-
`netron sputtering apparatus 100 having a pulsed power source
`102. The known magnetron sputtering apparatus 100 includes
`a vacuum chamber 104 where the sputtering process is per—
`formed. The vacuum chamber 104 is positioned in fluid cor-.1-
`munication with a vacuum pump 106 via a conduit 108. '1 he
`vacuum pump 106 is adapted to evacuate the vacuum cham—
`ber 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 1'10. A valve 112
`controls the gas flow from the feed gas source 109.
`'lhe magnetron sputtering apparatus 100 also includes a
`cathode assembly 114 having a target 116. The cathode
`assembly 114 is generally in the shape ofa circular disk. The
`cathode assembly 114 is electrically connected to a first out-
`put 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 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.
`
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`An anode 130 is positioned in the vacuum chamber 104
`proximate to the cathode assembly 114.
`'l'hevanode 130 is
`typically coupled to ground. A second output 132 01‘ 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
`lroi'n the target 116. The substrate 134 can be electrically
`connected to a bias voltage power supply 136 with a trans—
`mission 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 anode 130
`that has a sufficient amplitude to ionize the argon feed gas 11]
`the vacuum chamber 104. The typical ionization process is
`referred to as direct ionization or atomic ionization by elec—
`tron impact and can be described as tolltwvs:
`Arte HA! ‘ Me
`
`Where Ar represents a neutral argon atom in the iced 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‘L) and two electrons.
`The negatively biased cathode assembly 114 attracts posi—
`tively charged ions with sufficient acceleration so that the ions
`sputter the target material from the target 1 16. A portion ofthe
`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 coniinemcnt
`region 142 where there is relatively low magnetic field inten—
`sity. The confinement region 142 is substantially in the shape
`01' 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 1114. Consequently. t