(12) United States Patent
`Chistyakov
`
`(16) Patent N0.:
`(45) Date of Patent:
`
`US 6,853,142 B2
`Feb. 8, 2005
`
`US006853142B2
`
`(54) METHODS AND APPARATUS FOR
`GENERATING HIGH_I)ENSITY PLASMA
`
`(75) Inventor: Roman chistyakov, Ahdover, MA
`(Us)
`
`.
`_
`(73) Asslgnee' Z‘md’ Inc" Mans?eld’ MA (Us)
`
`.
`( * ) Notice:
`
`.
`.
`.
`.
`SubJect to any disclaimer, the term of this
`patent is extended or adjusted under 35
`use 154(b) by 0 days‘
`
`6,057,244 A
`6,238,537 B1
`6,296,742 B1
`6,361,667 B1
`6,413,382 B1
`6,413,383 B1
`6,432,260 B1
`6,436,251 B2
`
`5/2000 Hausmann et al. ....... .. 438/706
`5/2001 Kahn et al. .......... .. 204/598.04
`10/2001 KouZnetsoV ......... .. 204/192.12
`3/2002 Kobayashi et a1.
`204/298.11
`7/2002 Wang et al. ......... .. 204/192.12
`7/2002 Chiang et al. ....... .. 204/192.13
`8/2002 Mahoney et al. .... .. 156/345.35
`8/2002 Gopalraja et a1.
`204/298.12
`
`6451703 B1
`’
`’
`
`92002 L'
`t
`l. .................. .. 438 710
`/
`m e a
`/
`(List continued on next page.)
`FOREIGN PATENT DOCUMENTS
`
`(21) APPL No; 10/065,629
`
`(22) Filed:
`
`Nov. 4, 2002
`
`EP
`W0
`W0
`
`4/1995
`0 650 183 A1
`9/1998
`WO 98/40532
`WO 01/98553 A1 12/2001
`
`(65)
`
`Prior Publication Data
`
`OTHER PUBLICATIONS
`
`US 2004/0085023 A1 May 6, 2004
`
`7
`
`(51) Int. Cl. ............................................ .. C23C 16/452
`(52) US. Cl. ........................... .. 315/111.41; 156/345.33;
`118/7231
`(58) Field of Search ...................... .. 315/111.01—111.91;
`156/34521, 345.29, 345.33, 345.42, 345.44,
`345; 204/298.06, 298.04, 298.08; 118/723 FE,
`723'1> 723 MP; 423/210> 246> 248
`
`(56)
`
`References Cited
`
`US. PATENT DOCUMENTS
`4,588,490 A
`5/1986 Cuomo et a1. ............ .. 204/298
`4,953,174 A
`8/1990 Eldridge et a1.
`..... .. 372/87
`5 015 493 A
`5/1991 Gwen ____________________ __ 427/38
`5:041j760 A * 8/1991 Koloe _________________ __ 315/111_41
`5,083,061 A
`1/1992 Koshiishi et a1. ..... .. 315/111.81
`5,247,531 A
`9/1993 Muller-Horshe ........... .. 372/38
`5,286,360 A
`2/1994 SZCYTbOWSki et a1~ - 204/298~08
`5,433,258 A
`7/1995 Barnes etal. .......... .. 156/643.1
`2 1;;
`PDaSCh
`"" "
`5,728,278 A
`3/1998 Okamura et a1. .... .. 204/298.11
`5,733,418 A
`3/1998 Hershcovitch et a1‘ _ 204/192_11
`5,795,452 A
`8/1998 Kinoshita et al. .... .. 204/298.37
`5,916,455 A
`6/1999 Kumagai ................... .. 216/68
`5,993,761 A * 11/1999 CZernichoWski et a1.
`423/210
`
`rummon e a.
`
`.
`
`,
`
`,
`
`a
`
`a
`
`US 5,863,392, 1/ 1999, Drummond et al. (WithdraWn)
`Booth et al. The Transition From Symmetric To Asymmet
`ric Discharges In Pulsed 1356 MHZ Capacity Coupled
`Plasmas, J' Appl' Phys‘, Jul' 15, 1997, pp‘ 5527560, V01~
`82(2), American Institute of Physics.
`_
`_
`(Llst Con?rmed 9n mm Page)
`Primary Examiner_w?son Lee
`(74) Attorney, Agent, or Firm—Kurt Rauschenbach;
`R h b h P t
`t L G
`LLC
`ausc en ac aen aw roup’
`(57)
`ABSTRACT
`
`Nllethods anddappaift‘f fAor generatmg istrongly'lqmzed
`P asma m, 65C“ 6 ~
`n *‘Pparams or genefatmg 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. ApoWer supply produces an electric ?eld in the gap
`between the anode and the Cathode The electric ?eld
`generates excited atoms in the Weakly-ionized plasma and
`gegeratesl secondtrfelefons fro? the catttllodi' The S86
`on ary e ectr'ons' 1on1Ze t e excite atoms, t ere y creating
`the strongly'lonlzed Plasma
`
`_
`
`43 Claims, 13 Drawing Sheets
`
`202
`PULSED
`POWER _MATCHING
`SUPPLY
`UNIT
`
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`
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`
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`216
`
`TSMC-1001
`TSMC v. Zond, Inc.
`Page 1 of 28
`
`

`
`US 6,853,142 B2
`Page 2
`
`US. PATENT DOCUMENTS
`
`6,471,833 B2 10/2002 Kumar et al. ........ .. 204/192.37
`6,488,825 B1 * 12/2002 Hilliard ........ ..
`204/298.06
`2002/0019139 A1
`2/2002 Zhang et al.
`438/714
`2002/0114897 A1
`8/2002 Sumiya et al. ..
`427/569
`2003/0006008 A1
`1/2003 Horioka et al. ...... .. 156/345.46
`
`OTHER PUBLICATIONS
`
`Bunshah, et al., Deposition Technologies For Films And
`Coatings, Materials Science Series, pp. 176—183, Noyes
`Publications, Park Ridge, NeW Jersey.
`Daugherty, et al., Attachrnent—Dorninated Electron—Bea
`rn—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 Plasrna Processing, J. Vac. Sci. Technol. A, Sep./Oct.
`1992, pp. 3048—3054, vol. 10, No. 5, American Vacuurn
`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 Plasrna 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 Plasrna Density Pulsed
`Magnetron Discharge, Linkoping Studies In Science And
`Technology, 1999, pp. 1—2, Sweden.
`
`Macak, et al., IoniZed Sputter Deposition Using An
`Extrernely High Plasrna Density Pulsed Magnetron Dis
`charge, J. Vac. Sci. Technol. A., Jul/Aug. 2000, pp.
`1533—1537, vol. 18, No. 4, American Vacuurn Society.
`MoZgrin, et al., High—Current LoW—Pressure Quasi—Station
`ary Discharge In A Magnetic Field: Experirnental 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 Vacuurn 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 Vacuurn Society.
`Steinbruchel, A Simple Forrnula For LoW—Energy Sputter
`ing Yields, Applied Physics A., 1985, pp. 37—42, vol. 36,
`Springer—Verlag.
`Chistyakov, Rornan, High—PoWer Pulsed Magnetron Sput
`tering, Application No.: 10/065,277, Filed: Sep. 30, 2002.
`Chistyakov, Rornan, High—PoWer Pulsed Magnetically
`Enhanced Plasrna Processing, Application No.: 10/065,551,
`Filed: Oct. 30, 2002.
`Encyclopedia Of Low Temperature Plasrna, p. 119, 123, vol.
`3.
`
`* cited by examiner
`
`TSMC-1001 / Page 2 of 28
`
`

`
`U.S. Patent
`
`Feb. 8,2005
`
`Sheet 1 of 13
`
`US 6,853,142 B2
`
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`
`PRIOR ART
`
`TSMC-1001 I Page 3 of 28
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`TSMC-1001 / Page 3 of 28
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`

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`U.S. Patent
`
`Feb. 8, 2005
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`Sheet 2 0f 13
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`US 6,853,142 B2
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`TSMC-1001 / Page 4 of 28
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`

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`U.S. Patent
`
`Feb. 8,2005
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`Sheet 3 0f 13
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`US 6,853,142 B2
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`
`TSMC-1001 / Page 5 of 28
`
`

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`U.S. Patent
`
`Feb. 8,2005
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`Sheet 4 0f 13
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`US 6,853,142 B2
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`TSMC-1001 / Page 6 of 28
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`U.S. Patent
`
`Feb. 8,2005
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`TSMC-1001 I Page 7 of 28
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`TSMC-1001 / Page 7 of 28
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`

`
`U.S. Patent
`
`Feb. 8,2005
`
`Sheet 6 0f 13
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`US 6,853,142 B2
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`TSMC-1001 / Page 8 of 28
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`U.S. Patent
`
`Feb. 8,2005
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`Sheet 7 0f 13
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`US 6,853,142 B2
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`TSMC-1001 / Page 9 of 28
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`U.S. Patent
`
`Feb. 8,2005
`
`Sheet 8 0f 13
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`US 6,853,142 B2
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`TSMC-1001 / Page 10 of 28
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`
`U.S. Patent
`
`Feb. 8,2005
`
`US 6,853,142 B2
`
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`
`TSMC-1001 / Page 11 of 28
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`

`
`U.S. Patent
`
`Feb. 8,2005
`
`Sheet 10 0f 13
`
`US 6,853,142 B2
`
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`TSMC-1001 / Page 12 of 28
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`

`
`U.S. Patent
`
`Feb. 8,2005
`
`Sheet 11 0f 13
`
`US 6,853,142 B2
`
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`TSMC-1001 / Page 13 of 28
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`

`
`U.S. Patent
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`US 6,853,142 B2
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`TSMC-1001 / Page 14 of 28
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`

`
`U.S. Patent
`
`Feb. 8, 2005
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`Sheet 13 0f 13
`
`US 6,853,142 B2
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`600
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`START / 602
`‘
`
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`
`FIG. 8
`
`TSMC-1001 / Page 15 of 28
`
`

`
`US 6,853,142 B2
`
`1
`METHODS AND APPARATUS FOR
`GENERATING HIGH-DENSITY PLASMA
`
`BACKGROUND OF INVENTION
`Plasma is considered the fourth state of matter. Aplasma
`is a collection of charged particles moving in random
`directions. Aplasma 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 elec
`trodes. 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 ?lms 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 ?lms 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 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 ?lm 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 ?elds 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.
`
`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 ?gures. 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
`supply 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.
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`2
`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
`apparatus of FIG. 2A.
`FIG. 5A through FIG. 5D illustrate various simulated
`magnetic ?eld distributions proXimate to the cathode for
`various electron E><B 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 ?oWchart of an illustrative method of gener
`ating a high-density plasma according to the present inven
`tion.
`
`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 ?uid 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 introduced into the vacuum
`chamber 104 through a gas inlet 110. The gas How is
`controlled by a valve 112.
`The plasma generating apparatus 100 also includes a
`cathode 114. The cathode 114 is generally in the shape of a
`circular disk. The cathode 114 is electrically connected to a
`?rst terminal 118 of a blocking capacitor 120 With an
`electrical transmission line 122. A second terminal 124 of
`the blocking capacitor 120 is coupled to a ?rst 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
`typically 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 suf?cient 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 1
`W/cm2. The driving frequency is typically 13.56 MHZ.
`Typical plasma densities are in the range of 109 cm-3 to 1011
`cm_3, and the electron temperature is on the order of 3 eV.
`This typical ioniZation process is referred to as direct
`ioniZation or atomic ioniZation by electron impact and can
`be described as folloWs:
`
`TSMC-1001 / Page 16 of 28
`
`

`
`US 6,853,142 B2
`
`3
`
`Where Ar represents a neutral argon atom in the feed gas and
`e- represents an ionizing electron generated in response 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
`electrons.
`The plasma discharge is maintained, at least in part, by
`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 ?eld near the cathode 114
`to con?ne the secondary electrons. Con?ning the secondary
`electrons substantially con?nes 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
`reducing the overall loss area.
`The magnetic con?nement primarily occurs in a con?ne
`ment region (not shoWn) Where there is a relatively loW
`magnetic ?eld intensity. The shape and location of the
`con?nement region depends on the design of the magnets.
`Generally, a higher concentration of positively charged ions
`in the plasma is present in the con?nement region than
`elseWhere in the chamber 104. Consequently, the uniformity
`of the plasma can be severely diminished in magnetically
`enhanced systems.
`The non-uniformity of the plasma in magnetron sputtering
`systems can result in undesirable non-uniform erosion of
`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
`uniform and denser plasma. Furthermore, the amount of
`applied poWer necessary to achieve even an incremental
`increase in uniformity and density can increase the prob
`ability of generating an electrical breakdoWn condition
`leading to an undesirable electrical discharge (an electrical
`arc) in the chamber 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
`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
`contamination in the vacuum chamber 104. HoWever, very
`large poWer pulses can still result in undesirable electrical
`discharges 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
`supply 202 at a time before the pulsed poWer supply 202 is
`activated. In one embodiment, the plasma generating appa
`ratus 200 includes a chamber (not shoWn), such as a vacuum
`chamber that supports the plasma. The chamber can be
`coupled to a vacuum system (not shoWn).
`The plasma generating apparatus 200 also includes a
`cathode 204. In one embodiment, the cathode 204 can be
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`composed of a metal material such as stainless steel or any
`other material that does not chemically react With reactive
`gases. In another embodiment, the cathode 204 includes a
`target that 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 ?rst output 212
`of the 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 ?rst output 212 of the pulsed
`poWer supply 202 is directly coupled to the cathode 204 (not
`shoWn). In one embodiment (not shoWn), the second output
`214 of the 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 ?rst 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 gener
`ates 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 generated 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 suf?cient
`to alloW current to How through a region 222 betWeen the
`anode 216 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
`of the 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 ?uid 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
`provide 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 insu
`lators 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
`supplied to the chamber by a gas ?oW control system (not
`shoWn). Preferably, the feed gas 226 is supplied betWeen the
`cathode 204 and the anode 216. Directly injecting the feed
`gas 226 betWeen the cathode 204 and the anode 216 can
`increase the How 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
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`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.
`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 ?eld 230 develops betWeen the
`cathode 204 and the anode 216. The amplitude and shape of
`the electric ?eld 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 ?eld proximate to the cathode
`204. The peak plasma density of the Weakly-ionized plasma
`232 depends on the properties of the speci?c plasma gen
`erating system and is a function of the location of the
`measurement in the Weakly-ionized plasma 232.
`In one embodiment, to generate the Weakly-ionized
`plasma 232, the pulsed poWer supply 202 generates a loW
`poWer pulse having an initial voltage of betWeen about 100V
`and 5 kV With a discharge current of between about 0.1 A
`and 100 A. In some embodiments, the Width of the pulse can
`be in on the order of 0.1 microseconds up to one hundred
`seconds. Speci?c 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
`supply (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 generates an initial voltage of several kilovolts
`that creates a plasma discharge voltage on the order of
`betWeen about 100V and 1 kV With a discharge current in the
`range of about 0.1 A and 100 AbetWeen 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 ?eld (not shoWn) in
`the region 222 can have a dramatic effect on the value of the
`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 of the plasma generating system and
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`the strength of a magnetic ?eld in a region 234. In one
`embodiment, before generating the Weakly-ionized plasma
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`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 Weakly-ionized or pre-ioniZed plasma 232. For example,
`the Weakly-ionized or pre-ioniZed plasma 232 can be gen
`erated 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
`techniques, ion beam techniques, or ioniZing ?lament tech
`niques. These techniques include components used in ion
`iZation 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 the Weakly-ionized or pre-ioniZed plasma 232
`substantially eliminates the probability of establishing a
`breakdoWn condition in the chamber When high-poWer
`pulses are applied betWeen the cathode 204 and the anode
`216. The probability of establishing a breakdoWn condition
`is substantially eliminated because the Weakly-ionized
`plasma 232 has a loW-level of ioniZation that provides
`electrical conductivity through the plasma. This conductiv
`ity substantially prevents the setup of a breakdoWn
`condition, even When high poWer is applied to the plasma.
`In one embodiment, as the feed gas 226 is pushed through
`the region 222, the Weakly-ionized plasma 232 diffuses
`someWhat homogeneously through the region 234. This
`homogeneous diffusion tends to facilitate the creation of a
`highly uniform strongly-ioniZed plasma in the region 234.
`In one Embodiment (not shoW), the Weakly-ionized
`plasma can be trapped proximate to the cathode 204 by a
`magnetic ?eld. Speci?cally, electrons in the Weakly-ionized
`plasma 232 can be trapped by a magnetic ?eld generated
`proximate to the cathode 204. In one embodiment, the
`strength of the magnetic ?eld is betWeen about ?fty and tWo
`thousand gauss.
`In one embodiment, a magnet assembly (not shoWn)
`generates the magnet ?eld located proximate to the cathode
`204. The magnet assembly can include permanent magnets
`(not shoWn), or alternatively, electro-magnets (not shoWn).
`The con?guration of the magnet assembly can be varied
`depending on the desired shape and strength of the magnetic
`?eld. In alternate embodiments, the magnet assembly can
`have either a balanced or unbalanced con?guration. In one
`embodiment, the magnet assembly includes sWitching
`electro-magnets, Which generate a pulsed magnetic ?eld
`proximate to the cathode 204. In some embodiments, addi
`tional magnet assemblies (not shoWn) can be placed at
`various locations around and throughout the chamber (not
`shoWn).
`Referring to FIG. 2C, once the Weakly-ionized plasma
`232 is formed, the pulsed poWer supply 202 generates
`high-poWer pulses betWeen the cathode 204 and the anode
`216 (FIG. 2C). The desired poWer level of the high-poWer
`pulses depends on several factors including the density of
`the Weakly-ionized plasma 232, and the volume of the
`plasma, for example. In one embodiment, the poWer level of
`the high-poWer pulse is in the range of about 1 kW to about
`10 MW or higher.
`Each of the high-poWer pulses is maintained for a prede
`termined time that, in some embodiments, is approximately
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`one microsecond to ten seconds. The repetition frequency or
`repetition rate of the high-poWer pulses, in some
`embodiments, is in the range of betWeen about 0.1 HZ to 1
`kHZ. The average poWer generated by the pulsed poWer
`supply 202 can be less than one megaWatt depending on the
`volume of the plasma. In one embodiment, the thermal
`energy in the cathode 204 and/or the anode 216 is conducted
`aWay or dissipated by liquid or gas cooling such as helium
`cooling (not shoWn).
`The high-poWer pulses generate a strong electric ?eld 236