US007604716B2
`
`(12) Unlted States Patent
`(10) Patent No.:
`US 7,604,716 B2
`
`Chistyakov
`(45) Date of Patent:
`*Oct. 20, 2009
`
`(54) METHODS AND APPARATUS FOR
`GENERATING HIGH-DENSITY PLASMA
`
`(75)
`
`Inventor: Roman Chistyakov, Andover, MA (US)
`.
`(73) Ass1gnee: Zond, Inc., Mansfield, MA (US)
`
`*
`
`Notice:
`
`J
`y
`Sub'ect to an disclaimer, the term of this
`patent is extended or adjusted under 35
`U‘S‘C‘ 154(1)) by 748 days‘
`
`....... 204/298.11
`3/1998 Okamura et a1.
`5,728,278 A
`3/1998 Hershcovitch et a1.
`. 204/192.11
`5,733,418 A
`8/1998 Kinoshita et a1.
`...... 204/298.37
`5,795,452 A
`6/1999 Kumagai
`5,916,455 A
`5,993,761 A * 11/1999 Czernichowski et a1.
`
`423/210
`
`(Continued)
`FOREIGN PATENT DOCUMENTS
`
`This patent is subject to a terminal d1s-
`cla1mer.
`
`EP
`
`0 650 183 A1
`
`4/1995
`
`(21) Appl.No.: 10/897,257
`
`(22)
`
`Filed:
`
`Jul. 22, 2004
`
`(65)
`
`Prior Publication Data
`
`US 2005/0006220 A1
`
`Jan. 13, 2005
`
`(51)
`
`Int. C1.
`(2006.01)
`C23C 14/35
`(2006.01)
`C23C 16/00
`(52) US. Cl.
`............................ 204/192.12; 204/298.08;
`204/298.06; 204/298.19; 315/111.21; 315/111.41;
`118/723 R; 118/723 E
`(58) Field of Classification Search ............ 204/ 192.12,
`204/29808, 298.06, 298.19; 118/723 R,
`118/723 E; 315/111.21, 111.41
`See application file for complete search history.
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`4,588,490 A
`4,953,174 A
`5,015,493 A
`5’041’760 A *
`5 ’083’061 A
`5’247’531 A
`5’286’360 A
`5,433,258 A
`5,696,428 A
`5,718,813 A
`
`5/1986 Cuomo et 31.
`............... 204/298
`8/ 1990 Eldridge et 31~
`-
`------- 372/87
`
`5/1991 Gruen ...................... 427/38
`
`8/1991 K0100”
`315/111'41
`
`1/ 1992 KOShllShl et al' ““““ 315/111'81
`9/1993 Muller—HorShe """"""" 372/38
`2/1994 szcyrbOWSki et al' " 204/298'08
`7/1995 Barnes et a1.
`12/1997 Pasch
`2/1998 Drummond et a1.
`
`204/192.12
`
`(Continued)
`OTHER PUBLICATIONS
`
`_
`_
`_
`_
`_
`Booth, et al., The Trans1t10n From Symmetrlc T0 Asymmetrlc D1s-
`charges In Pulsed 13 .56 MHZ Capacitively Coupled Plasmas, J. Appl.
`Phys, Jul. 15, 1997, pp. 552-560, V01. 82, N0. 2, American Institute
`of Physics.
`
`d
`.
`(Commue )
`Primary ExamineriRodney G McDonald
`(74) Attorney, Agent, or FirmiKurt Rauschenbach;
`Rauschenbach Patent Law Group, LLC
`
`(57)
`
`ABSTRACT
`
`Methods and apparatus for generating a strongly-ionized
`plasma are described. An apparatus for generating a strongly-
`ionized plasma according to the present invention includes an
`anode and a cathode that is positioned adjacent to the anode to
`form a gap there between. An ionization source generates a
`weakly-ionized plasma proximate to the cathode. A power
`supply produces an electric field in the gap between the anode
`and the cathode. The electric field generates excited atoms in
`the weakly-ionized plasma and generates secondary electrons
`from the cathode. The secondary electrons ionize the excited
`atoms thereby creating the strongly-ionized plasma
`’
`'
`
`33 Claims, 13 Drawing Sheets
`
`202
`
`PULSED 210
`208
`POWER
`MATCHING
`SUPPLY
`U MT
`206
`
`
`
`
`
`iV/////////////////////////////\?
`
`
`
`>\\\\\\\\\\\\\\\\\‘\V\‘/\\\</\<</”////‘i
`
`
` INTEL 1101
`
`INTEL 1101
`
`

`

`US 7,604,716 B2
`
`Page 2
`
`U.S. PATENT DOCUMENTS
`
`.......... 438/706
`5/2000 Hausmann et al.
`6,057,244 A
`5/2001 Kahnet al.
`............ 204/598.04
`6,238,537 B1
`10/2001 Kouznetsov ......
`.. 204/192.12
`6,296,742 B1
`
`3/2002 Kobayashiet al.
`.. 204/298.11
`6,361,667 B1
`............ 204/192.12
`7/2002 Wang et a1.
`6,413,382 B1
`7/2002 Chiang et al.
`.......... 204/192.13
`6,413,383 B1
`8/2002 Mahoney et al.
`6,432,260 B1
`...... 204/298.12
`8/2002 Gopalraja et al.
`6,436,251 B2
`9/2002 Liu et al.
`.................... 438/710
`6,451,703 B1
`.. 204/192.37
`10/2002 Kumaret a1.
`6,471,833 B2
`
`. 204/298.06
`6,488,825 B1* 12/2002 Hilliard ......
`
`438/714
`2002/0019139 A1
`2/2002 Zhang et al.
`........... 427/569
`2002/0114897 A1
`8/2002 Sumiya et al.
`
`1/2003 Horioka et al.
`........ 156/345.46
`2003/0006008 A1
`
`FOREIGN PATENT DOCUMENTS
`
`W0
`W0
`W0
`
`WO 98/40532
`WO 01/98553
`WO 01/98553 A1
`
`9/1998
`12/2001
`12/2001
`
`OTHER PUBLICATIONS
`
`Bunshah, et al., Deposition Technologies For Films And Coatings,
`pp. 178-183, Noyes Publications, Park Ridge, New Jersey.
`Daugherty, et al., Attachment-Dominated Electron-Beam-Ionized
`Discharges, Applied Physics Letters, May 15, 1976, pp. 581-583, 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 and Coatings
`Technology, 1999, pp. 290-293, vol. 122, Elsevier Science SA.
`Lindquist, et al., High Selectivity Plasma Etching Of Silicone 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 Dis-
`charge, Linkoping Studies In Science And Technology, pp. 1-2.
`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., AmericanVacuum
`Society.
`Mozgrin, et al., High-Current Low-Pressure Quasi-Stationary Dis-
`charge In A Magnetic Field: Experimental Research, Plasma Physics
`Reports, 1995, pp. 400-409, vol. 21, No. 5.
`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 Sput-
`tering 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.
`Encyclopedia Of Low Temperature Plasma p. 119, vol. 3.
`Encyclopedia Of Low Temperature Plasma p. 123, vol. 3.
`Chistyakov, Roman, High Power Pulsed Magnetron Sputtering, 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. 29, 2002.
`
`Booth, et al., The Transition From Symmetric To Asymmetric Dis-
`charges 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-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 Dioxide
`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 Dis-
`charge, Linkoping Studies In ScienceAnd 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, AmericanVacuum
`Society.
`Mozgrin, et al., High-Current Low-Pressure Quasi-Stationary Dis-
`charge In A Magnetic Field: Experimental Research, Plasma Physics
`Reports, 1995, pp. 400-409, vol. 21, No. 5, Mozgrin, Feitsov,
`Khodachenko.
`Chistyakov, Roman, High-Power Pulsed Magnetron Sputtering, 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, High-Power Pulsed Magnetron Sputtering, U.S. Appl.
`No. 10/065,277, filed Sep. 30, 2002.
`Chistyakov, High-Power Pulsed Magnetically Enhanced Plasma Pro-
`cessing, U.S. Appl. No. 10/065,551, filed Oct. 29, 2002.
`Chistyakov, Roman, Method And Apparatus For Generating High-
`Density Plasma, U.S. Appl. No. 10/065,629, filed Nov. 4, 2002.
`Chistyakov, Roman, High Deposition Rate Sputtering, U.S. Appl.
`No. 10/065,739, filed Nov. 14, 2002.
`Chistyakov, Roman, Plasma Generation Using Multi-Step Ioniza-
`tion, U.S. Appl. No. 10/249,202, filed Mar. 21, 2003.
`Chistyakov, Roman, High-Density Plasma Source, US. Appl. No.
`10/249,595, filed Apr. 22, 2003.
`Chistyakov, Roman, Generation Of Uniformly Distributed Plasma,
`U.S. Appl. No. 10/249,773, filed May 6,2003.
`Chistyakov, Roman, High-Density Plasma Source Using Excited
`Atoms, U.S. Appl. No. 10/249,844, filed May 12, 2003.
`Chistyakov, Roman, Plasma Source With Segmented Cathode, U.S.
`Appl. No. 60/481,671, filed Nov. 19,2003.
`Chistyakov, Roman, Methods And Apparatus For Generating
`Strongly-Ionized Plasmas With Ionizational Instabilities, U.S. Appl.
`No. 10/708,281, filed Feb. 22, 2004.
`Chistyakov, Roman, Plasma Source With Segmented Cathode, U.S.
`Appl. No. 10/710,946, filed Aug. 13,2004.
`“Notification Of Transmittal Of The International Search Report Or
`The Declaration” For PCT/USO3/34483, Apr. 8, 2004, 5 pages, The
`International Searching Authority/EPO, Rij swijk, The Netherlands.
`US 5,863,392, 01/1999, Drummond et al. (withdrawn)
`
`* cited by examiner
`
`

`

`US. Patent
`
`Oct. 20, 2009
`
`Sheet 1 0f 13
`
`US 7,604,716 B2
`
`“i”
`
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`
`FIG. 1
`
`PRIOR ART
`
`

`

`US. Patent
`
`Oct. 20, 2009
`
`Sheet 2 0f 13
`
`US 7,604,716 B2
`
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`US. Patent
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`Oct. 20, 2009
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`Sheet 3 0f 13
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`US 7,604,716 B2
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`

`U.S. Patent
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`US 7,604,716 B2
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`US. Patent
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`Oct. 20, 2009
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`Sheet 10 0f 13
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`US 7,604,716 B2
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`Oct. 20, 2009
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`Oct. 20, 2009
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`
`

`

`US 7,604,716 B2
`
`1
`METHODS AND APPARATUS FOR
`GENERATING HIGH-DENSITY PLASMA
`
`BACKGROUND OF INVENTION
`
`Plasma is considered the fourth state of matter. A plasma is
`a collection of charged particles moving in random direc-
`tions. A plasma is, on average, electrically neutral. One
`method of generating a plasma is to drive a current through a
`low-pressure gas between two parallel conducting electrodes.
`Once certain parameters are met, the gas “breaks down” to
`form the plasma. For example, a plasma can be generated by
`applying a potential of several kilovolts between two parallel
`conducting electrodes in an inert gas atmosphere (e.g., argon)
`at a pressure that is between about 10'1 and 10'2 Torr.
`Plasma processes are widely used in many industries, such
`as the semiconductor manufacturing industry. For example,
`plasma etching is commonly used to etch substrate material
`and films deposited on substrates in the electronics industry.
`There are four basic types of plasma etching processes that
`are used to remove material from surfaces: sputter etching,
`pure chemical etching, ion energy driven etching, and ion
`inhibitor etching.
`Plasma sputtering is a technique that is widely used for
`depositing films on substrates. Sputtering is the physical ej ec-
`tion 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 are drawn out of the plasma, and
`are accelerated across a 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 mate-
`rial. The plasma is replenished by electron-ion pairs formed
`by the collision ofneutral 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 high density ofelectrons causes
`ionization of the sputtering gas in a region that is close to the
`target surface.
`
`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. 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 plasma
`generating apparatus having a radio-frequency (RF) power
`supply.
`FIG. 2A through FIG. 2D illustrate cross-sectional views
`of a plasma generating apparatus having a pulsed power sup-
`ply according to one embodiment of the invention.
`FIG. 3 illustrates a graphical representation of the pulse
`power as a function of time for periodic pulses applied to the
`plasma in the plasma generating apparatus of FIG. 2A.
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`FIG. 4 illustrates graphical representations of the applied
`voltage, current, and power as a function of time for periodic
`pulses applied to the plasma in the plasma generating appa-
`ratus of FIG. 2A.
`
`FIG. 5A through FIG. 5D illustrate various simulated mag-
`netic field distributions proximate to the cathode for various
`electron ExB drift currents according to the present invention.
`FIG. 6A through FIG. 6D illustrate cross-sectional views
`of various embodiments of plasma generating systems
`according to the present invention.
`FIG. 7 illustrates a graphical representation of the pulse
`power as a function of time for periodic pulses applied to the
`plasma in the plasma generating system of FIG. 6A.
`FIG. 8 is a flowchart of an illustrative method of generating
`a high-density plasma according to the present invention.
`
`DETAILED DESCRIPTION
`
`FIG. 1 illustrates a cross-sectional view of a known plasma
`generating apparatus 100 having a radio-frequency (RF)
`power supply 102. The known plasma generating apparatus
`100 includes a vacuum chamber 104 where the plasma 105 is
`generated. 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 10'1 Torr. A feed gas from
`a feed gas source 109, such as an argon gas source, is intro-
`duced into the vacuum chamber 104 through a gas inlet 110.
`The gas flow is controlled by a valve 112.
`The plasma generating apparatus 100 also includes a cath-
`ode 114. The cathode 114 is generally in the shape of a
`circular disk. The cathode 114 is electrically connected to a
`first terminal 118 of a blocking capacitor 120 with an electri-
`cal transmission line 122. A second terminal 124 ofthe block-
`
`ing capacitor 120 is coupled to a first output 126 of the RF
`power supply 102. An insulator 128 can be used to pass the
`electrical transmission line 122 through a wall of the vacuum
`chamber 104 in order to electrically isolate the cathode 114
`from the vacuum chamber 104.
`
`An anode 130 is positioned in the vacuum chamber 104
`proximate to the cathode 114. The anode 130 is typically
`coupled to ground using an electrical transmission line 132.A
`second output 134 of the RF power supply 102 is also typi-
`cally coupled to ground. In order to isolate the anode 130
`from the vacuum chamber 104, an insulator 136 can be used
`to pass the electrical transmission line 132 through a wall of
`the vacuum chamber 104. The vacuum chamber 104 can also
`
`be coupled to ground.
`In operation, the RF power supply 102 applies a RF voltage
`pulse between the cathode 114 and the anode 130 that has a
`sufficient amplitude to ionize the argon feed gas in the
`vacuum chamber 104. A typical RF driving voltage is
`between 100V and 1000V, and the distance 138 between the
`cathode 114 and the anode is between about 2 cm and 10 cm.
`
`Typical pressures are in the range of 10 mTorr to 100 mTorr.
`Typical power densities are in the range of 0.1 W/cm2 to l
`W/cmz. The driving frequency is typically 13.56 MHZ. Typi-
`cal plasma densities are in the range of 109 cm‘3 to 101 1 cm‘3 ,
`and the electron temperature is on the order of 3 eV.
`This typical ionization process is referred to as direct ion-
`ization or atomic ionization by electron impact and can be
`described as follows:
`Ar+e’—>Ar++29’
`
`where Ar represents a neutral argon atom in the feed gas
`and e" represents an ionizing electron generated in response
`
`

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`US 7,604,716 B2
`
`3
`to the voltage applied between the cathode 114 and the anode
`130. The collision between the neutral argon atom and the
`ionizing electron results in an argon ion (Ar+) and two elec-
`trons.
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`The plasma discharge is maintained, at least in part, by 5
`secondary electron emission from the cathode. However,
`typical operating pressures must be relatively high so that the
`secondary electrons are not lost to the anode 130 or the walls
`of the chamber 104. These pressures are not optimal for most
`plasma processes.
`It is desirable to operate a plasma discharge at higher
`current densities, lower voltages, and lower pressures than
`can be obtained in a conventional glow discharge. This has led
`to the use of a DC magnetic field near the cathode 114 to
`confine the secondary electrons. Confining the secondary 15
`electrons substantially confines the plasma at a location (not
`shown) in the chamber 104 thereby increasing the plasma
`density at that location for a given input power, while reduc-
`ing the overall loss area.
`The magnetic confinement primarily occurs in a confine- 20
`ment region (not shown) where there is a relatively low mag-
`netic field intensity. The shape and location of the confine-
`ment region depends on the design ofthe magnets. Generally,
`a higher concentration of positively charged ions in the
`plasma is present in the confinement region than elsewhere in 25
`the chamber 104. Consequently, the uniformity of the plasma
`can be severely diminished in magnetically enhanced sys-
`tems.
`
`The non-uniformity of the plasma in magnetron sputtering
`systems can result in undesirable non-uniform erosion of 30
`target material and thus relatively poor target utilization. The
`non-uniformity of the plasma in magnetron etching systems
`can result in non-uniform etching of a substrate.
`Dramatically increasing the RF power applied to the
`plasma alone will not result in the formation of a more uni- 35
`form and denser plasma. Furthermore, the amount of applied
`power necessary to achieve even an incremental increase in
`uniformity and density can increase the probability of gener-
`ating an electrical breakdown condition leading to an unde-
`sirable electrical discharge (an electrical arc) in the chamber 40
`104.
`
`Pulsing direct current (DC) power applied to the plasma
`can be advantageous since the average discharge power can
`remain relatively low while relatively large power pulses are
`periodically applied. Additionally, the duration of these large 45
`voltage pulses can be preset so as to reduce the probability of
`establishing an electrical breakdown condition leading to an
`undesirable electrical discharge. An undesirable electrical
`discharge will corrupt the plasma process and can cause con-
`tamination in the vacuum chamber 104. However, very large 50
`power pulses can still result in undesirable electrical dis-
`charges regardless of their duration.
`FIG. 2A through FIG. 2D illustrate cross-sectional views
`of a plasma generating apparatus 200 having a pulsed power
`supply 202 according to one embodiment of the invention.
`For example, FIG. 2A illustrates a cross-sectional view of a
`plasma generating apparatus 200 having a pulsed power sup-
`ply 202 at a time before the pulsed power supply 202 is
`activated. In one embodiment, the plasma generating appara-
`tus 200 includes a chamber (not shown), such as a vacuum 60
`chamber that supports the plasma. The chamber can be
`coupled to a vacuum system (not shown).
`The plasma generating apparatus 200 also includes a cath-
`ode 204. In one embodiment, the cathode 204 can be com-
`posed of a metal material such as stainless steel or any other 65
`material that does not chemically react with reactive gases. In
`another embodiment, the cathode 204 includes a target that
`
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`can be used for sputtering. The cathode 204 is coupled to an
`output 206 of a matching unit 208. An input 210 of the
`matching unit 208 is coupled to a first output 212 ofthe pulsed
`power supply 202. A second output 214 of the pulsed power
`supply 202 is coupled to an anode 216. An insulator 218
`isolates the anode 216 from the cathode 204.
`
`In one embodiment, the first output 212 ofthe pulsed power
`supply 202 is directly coupled to the cathode 204 (not shown).
`In one embodiment (not shown), the second output 214 ofthe
`pulsed power supply 202 is coupled to ground. In this
`embodiment, the anode 216 is also coupled to ground.
`In one embodiment (not shown), the first output 212 of the
`pulsed power supply 202 couples a negative voltage impulse
`to the cathode 204. In another embodiment (not shown), the
`second output 214 of the pulsed power supply 202 couples a
`positive voltage impulse to the anode 216.
`In one embodiment, the pulsed power supply 202 generates
`peak voltage levels of up to about 30,000V. Typical operating
`voltages are generally between about 50V and 30 kV. In one
`embodiment, the pulsed power supply 202 generates peak
`current levels of less than 1 A to about 5,000 A or more
`depending on the volume of the plasma. Typical operating
`currents varying from less than one hundred amperes to more
`than a few thousand amperes depending on the volume of the
`plasma. In one embodiment, the pulses generated by the
`pulsed power supply 202 have a repetition rate that is below 1
`kHz. In one embodiment, the pulse width of the pulses gen-
`erated by the pulsed power supply 202 is substantially
`between about one microsecond and several seconds.
`
`The anode 216 is positioned so as to form a gap 220
`between the anode 216 and the cathode 204 that is sufficient
`
`to allow current to flow through a region 222 between the
`anode 21 6 and the cathode 204. In one embodiment, the width
`of the gap 220 is between approximately 0.3 cm and 10 cm.
`The surface area of the cathode 204 determines the volume of
`
`the region 222. The gap 220 and the total volume ofthe region
`222 are parameters in the ionization process as described
`herein.
`
`In one embodiment, the plasma generating apparatus 200
`includes a chamber (not shown), such as a vacuum chamber.
`The chamber is coupled in fluid communication to a vacuum
`pump (not shown) through a vacuum valve (not shown). In
`one embodiment, the chamber (not shown) is electrically
`coupled to ground potential. One or more gas lines 224 pro-
`vide feed gas 226 from a feed gas source (not shown) to the
`chamber. In one embodiment, the gas lines 224 are isolated
`from the chamber and other components by insulators 228. In
`other embodiments, the gas lines 224 can be isolated from the
`feed gas source using in-line insulating couplers (not shown).
`The gas source can be any feed gas 226 including but not
`limited to argon. In some embodiments, the feed gas 226 can
`include a mixture of different gases, reactive gases, or pure
`reactive gas gases. In some embodiments, the feed gas 226
`includes a noble gas or a mixture of gases.
`In operation, the feed gas 226 from the gas source is sup-
`plied to the chamber by a gas flow control system (not
`shown). Preferably, the feed gas 226 is supplied between the
`cathode 204 and the anode 21 6. Directly injecting the feed gas
`226 between the cathode 204 and the anode 216 can increase
`
`the flow rate of the feed gas 226. This causes a rapid volume
`exchange in the region 222 between the cathode 204 and the
`anode 216, which permits a high-power pulse having a longer
`duration to be applied across the gap 220. The longer duration
`high-power pulse results in the formation of a higher density
`plasma. This volume exchange is described herein in more
`detail.
`
`

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`US 7,604,716 B2
`
`5
`In one embodiment, the pulsed power supply 202 is a
`component in an ionization source that generates a weakly-
`ionized plasma 232. Referring to FIG. 2B, after the feed gas
`is supplied between the cathode 204 and the anode 216, the
`pulsed power supply 202 applies a voltage pulse between the
`cathode 204 and the anode 216. In one embodiment, the
`pulsed power supply 202 applies a negative voltage pulse to
`the cathode 204. The size and shape of the voltage pulse are
`chosen such that an electric field 230 develops between the
`cathode 204 and the anode 216. The amplitude and shape of
`the electric field 230 are chosen such that a weakly-ionized
`plasma 232 is generated in the region 222 between the anode
`216 and the cathode 204.
`
`The weakly-ionized plasma 232 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 10'3 to 10 Torr or higher. The pressure can
`vary depending on various system parameters, such as the
`presence of a magnetic field proximate to the cathode 204.
`The peak plasma density of the weakly-ionized plasma 232
`depends on the properties of the specific plasma generating
`system and is a function ofthe location ofthe measurement in
`the weakly-ionized plasma 232.
`In one embodiment, to generate the weakly-ionized plasma
`232, the pulsedpower supply 202 generates a low power pulse
`having an initial voltage of between about 100V and 5 kV
`with a discharge current ofbetween about 0.1 A and 100A. In
`some embodiments, the width of the pulse can be in on the
`order of 0.1 microseconds up to one hundred seconds. Spe-
`cific parameters of the pulse are discussed herein in more
`detail.
`
`In one embodiment, prior to the generation of the weakly-
`ionized plasma 232, the pulsed power supply 202 generates a
`potential difference between the cathode 204 and the anode
`216 before the feed gas 226 is supplied between the cathode
`204 and the anode 216. In another embodiment, the pulsed
`power supply 202 generates a current through the gap 220
`after the feed gas 226 is supplied between the cathode 204 and
`the anode 216.
`
`In another embodiment, a direct current (DC) power sup-
`ply (not shown) is used in an ionization source to generate and
`maintain the weakly-ionized or pre-ionized plasma 232. In
`this embodiment, the DC power supply is adapted to generate
`a voltage that is large enough to ignite the weakly-ionized
`plasma 232. In one embodiment, the DC power supply gen-
`erates an initial voltage of several kilovolts that creates a
`plasma discharge voltage on the order ofbetween about 100V
`and 1 kV with a discharge current in the range of about 0.1 A
`and 100 A between the cathode 204 and the anode 216 in
`
`order to generate and maintain the weakly-ionized plasma
`232. The value of the discharge current depends on the power
`level of the power supply and is a function of the volume of
`the weakly-ionized plasma 232. Furthermore, the presence of
`a magnetic field (not shown) in the region 222 can have a
`dramatic effect on the value ofthe applied voltage and current
`required to generate the weakly-ionized plasma 232.
`In some embodiments (not shown), the DC power supply
`generates a current that is between about 1 mA and 100 A
`depending on the size ofthe plasma generating system and the
`strength of a magnetic field in a region 234. In one embodi-
`ment, before generating the weakly-ionized plasma 232, the
`DC power supply is adapted to generate and maintain an
`initial peak voltage between the cathode 204 and the anode
`216 before the introduction of the feed gas 226.
`In another embodiment, an alternating current (AC) power
`supply (not shown) is used to generate and maintain the
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`weakly-ionized or pre-ionized plasma 232. For example, the
`weakly-ionized or pre-ionized plasma 232 can be generated
`and maintained using electron cyclotron resonance (ECR),
`capacitively coupled plasma discharge (CCP), or inductively
`coupled plasma (ICP) discharge.
`AC power supplies can require less power to generate and
`maintain a weakly-ionized plasma than a DC power supply. In
`addition, the pre-ionized or weakly-ionized plasma 232 can
`be generated by numerous other techniques, such as UV
`radiation techniques, X-ray techniques, electron beam tech-
`niques, ion beam techniques, or ionizing filament techniques.
`These techniques include components used in ionization
`sources according to the invention. In some embodiments, the
`weakly-ionized plasma is formed outside of the region 222
`and then diffuses into the region 222.
`Forming t