(12) United States Patent
`Us 6,806,652 B1
`(45) Date of Patent:
`Chistyakov
`*Oct. 19, 2004
`
`(10) Patent N0.:
`
`USOO6806652B1
`
`(54)
`
`(75)
`
`HIGH-DENSITY PLASMA SOURCE USING
`EXCITED ATOMS
`
`Inventor: Roman Chistyakov, Andover, MA
`(US)
`
`FOREIGN PATENT DOCUMENTS
`
`W0
`W0
`
`WO 98/40532
`WO 01/98553 A1
`
`9/1998
`12/2001
`
`OTHER PUBLICATIONS
`
`(73)
`
`Assignee: Zond, Inc., Mansfield, MA (US)
`
`( * )
`
`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 dis-
`claimer.
`
`(21)
`
`(22)
`
`Appl. No.:
`Filed:
`
`10/249,844
`
`May 12, 2003
`
`(63)
`
`(51)
`(52)
`
`(58)
`
`(56)
`
`Related US. Application Data
`
`Continuation—in—part of application No. 10/249,595, filed on
`Apr. 22, 2003.
`
`Int. Cl.7
`US. Cl.
`
`....................... H01J 7/24
`............................. 315/111.21; 315/111.41;
`156/345.44; 118/723 DC
`Field of Search ....................... 315/111.21, 111.41,
`315/111.61, 111.71, 111.81, 111.91, 204/29807,
`298.08, 298.121, 298.161, 298.2, 298.21,
`298.22; 156/34533, 345.35, 345.38, 345.39,
`345.4, 345.41, 345.42, 345.43, 345.44,
`345.46; 118/723 ME, 723 DC, 723 I, 723 IR
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`3,619,605 A
`4,060,708 A
`4,148,612 A
`
`................. 250/419
`11/1971 Cook et al.
`
`11/1977 Walters ................ 219/121
`4/1979 Taylor et al.
`................. 23/232
`
`al., The Transition From Symmetric To
`et
`Booth,
`Asymemtric Discharges In Pulsed 13.56 MHZ Capacitively
`Coupled Plasmas, J. Appl. Phys., Jul. 15, 1997, pp. 552—560,
`vol. 82, No. 2, American Institute of Physics.
`Bunshah, et al., Deposition Technologies For Films And
`Coatings, pp. 178—183, Noyes Pubications, park Ridge, New
`Jersey.
`Daugherty, et al., Attachment—Dominated Electron—Bea-
`m—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.
`
`(List continued on next page.)
`
`Primary Examiner—Don Wong
`Assistant Examiner—Ephrem Alemu
`(74) Attorney, Agent, or Firm—Kurt Ranuschenbach;
`Rauschenbach Patent Law Group, LLC
`
`(57)
`
`ABSTRACT
`
`The plasma source includes a cathode assembly. An anode
`is positioned adjacent to the cathode assembly. An excited
`atom source generates an initial plasma and excited atoms
`from a volume of feed gas. The initial plasma and excited
`atoms are located proximate to the cathode assembly. A
`power supply generates an electric field between the cathode
`assembly and the anode. The electric field super-ionizes the
`initial plasma so as to generate a high-density plasma.
`
`(List continued on next page.)
`
`35 Claims, 19 Drawing Sheets
`
`FIRST
`POWER
`
`SUPPLY
`
`GILLETTE 1013
`
`GILLETTE 1013
`
`

`

`US 6,806,652 B1
`Page 2
`
`U.S. PATENT DOCUMENTS
`
`............ 250/288
`10/1985 Tsuchiya et al.
`4,546,253 A
`10/1987 Yoshikawa et al.
`...... 313/362.1
`4,703,222 A
`4,716,340 A * 12/1987 Lee et al.
`.............. 204/298.18
`.......... 315/39
`4,792,725 A
`12/1988 Levy et al.
`
`..
`4,802,183 A
`1/1989 Harris et al.
`372/57
`
`4/1990 Lovelock ................ 55/2
`4,919,690 A
`
`.......... 372/87
`4,953,174 A
`8/1990 Eldridge et al.
`.
`
`4,977,352 A * 12/1990 Williamson ......
`315/111.21
`5/1991 Gruen ......................... 427/38
`5,015,493 A
`5,083,061 A
`1/1992 Koshiishi et al.
`....... 315/111.81
`5,247,531 A
`9/1993 Muller—Horsche ............ 372/38
`5,247,535 A
`9/1993 Muller—Horsche et al.
`372/86
`5,382,457 A
`1/1995 Coombe ..................... 427/596
`5,506,405 A
`4/1996 Yoshida et al.
`............. 250/251
`5,733,418 A
`3/1998 Hershcovitch et al.
`. 204/192.11
`5,821,548 A
`10/1998 Hinchliffe .............. 250/492.21
`6,057,244 A
`5/2000 Hausmann et al.
`......... 438/706
`6,094,012 A *
`7/2000 Leung et al.
`........... 315/111.81
`6,124,675 A
`9/2000 Bertrand et al.
`........ 315/111.91
`6,137,231 A * 10/2000 Anders etal.
`.......... 315/111.21
`6,207,951 B1
`3/2001 Yamauchi et al.
`.......... 250/251
`6,296,742 B1
`10/2001 Kouznetsov ........... 204/192.12
`6,395,641 B2
`5/2002 Savas ......................... 438/714
`6,413,382 B1
`7/2002 Wang et al.
`........... 204/192.12
`6,413,383 B1
`7/2002 Chiang et al.
`......... 204/192.13
`6,462,482 B1 * 10/2002 Wickramanayaka
`et al.
`..................... 315/111.21
`10/2002 Maddocks ............. 156/345.46
`
`2002/0153103 A1
`
`OTHER PUBLICATIONS
`
`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 Sili-
`cone Dioxdie With A Dual Frequency 27/2 MHZ Capacitiv
`RF Discharge.
`Macak, Reactive Sputter Deposition Process Of A1203 And
`Characterization Of A Novel High Plasm aDensity Pulsed
`Magnetron Discharge, Linkoping Studies In Science And
`Technology, pp. 1—2.
`
`Ionized Sputter Deposition Using an
`al.,
`Macak, et
`Extremely High Plasma Density Pulsed Magnetron Dis-
`charge,
`J. Vac. Sci. Technol. A., Jul/Aug. 2000, p.
`1533—1537, vol. 18, N0. 4, American Society.
`Mozgrin, et al., High—Current Low—Pressure Quasi—Station-
`ary Discharge In A Magnetic Field: Experiemtnal Research,
`Plasma Physics Reports, 1995, pp. 400—409, vol. 21, N0. 5.
`Rossnagel, et al., Induced Drift Currents In Circular Planar
`Magnetrons, J. Vac. Sci. Technol. A., Jan/Feb. 1987, pp.
`88—91, vol. 5, N0. 1, American Vacuum Society.
`Sheridan, et al., Electron Velocity Distribution Functions In
`ASputtering Magnetron Discharge For The E X B Direction,
`J. Vac. Sci. Technol., Jul.Aug. 1998, pp. 2173—2176, vol. 16,
`N0. 4, American Vacuum Society.
`Steinbruchel, A Simple Formula FOr Low—Energy Sputter-
`ing Yields, APpl. Phys. A., 1985, p. 37—42, vol. 36, Sprigner
`Verlag.
`Encyclopedia Of Low Temperature Plasma, p. 119, vol. 3,
`2000.
`
`Encyclopedia Of Low Temperature Plasma, p. 123, vol. 3,
`2000.
`
`Lymberopoulos, et al., Fluid Simulations Of Glow DIs-
`charges: Effect Of Metastable Atoms In Argon, J. Appl.
`Phys., Apr. 1993, pp. 3668—3679, vol. 73, N0. 8, American
`Inststiute of Physics.
`Burnham, et al., Efficient Electric Discharge Lasers In XeF
`and KrF, Applied Physics Letters, Jul. 1976, pp. 30—32, vol.
`29, N0. 1, American Instistute of Physics.
`Fabrikant, et al., Electron Impact Formation Of Metastable
`Atoms, pp. 3, 31, 34—37, Amsterdam.
`Fahey, et al., High Flux Beam Source Of Thermal Rare—Gas
`Metastable Atoms, 1980, J. Phys. E. Sci. Instrum., vol. 13,
`The Institute of Physics.
`Verheijen, et al., A Discharge Excited Supersonic Source Of
`Metastable Rare Gas Atoms, J. Phys. E. Sci. Instrum, 1984,
`vol. 17.
`
`Eletskii, Excimer Lasers, Sov. Phys. Usp., Jun. 1978, pp.
`502—521, vol. 21, N0. 6.
`
`* cited by examiner
`
`

`

`US. Patent
`
`Oct. 19, 2004
`
`Sheet 1 0f 19
`
`US 6,806,652 B1
`
`100
`
`127
`
`
` DC
`POWER
`
`SUPPLY
`
`102
`
`
`I8§S
`f1Wll/l/<<
`' \v/x/
`///////////f
`
`\ \VA \\\\\\\\\\I§
`
`lvt'lnll/x‘s'nlln/A\\ \\\\ ‘.\ \
`
`
`—__._..—_..___—_____.___.__._.-—-
`
`
`
`
`
`FIG. 1
`PRIOR ART
`
`

`

`US. Patent
`
`Oct. 19, 2004
`
`Sheet 2 0f 19
`
`US 6,806,652 B1
`
`I\\\\
`
`
`
`fi§N\+\\§\\\\\\\\\\\IV\\\I”
`
`
`
`‘mgom6mm.7.on
`
`3&8
`
`meEm
`
`0mm
`
`3N
`
`,o>._n_n5wm—MM>>OQ
`\1.SN
`\\vm-
`
`lfvall
`
`III
`
`
`
`
`
`
`

`

`Ill-I'll'lll--nllll
`
`'lcll'll'
`‘l'll'ul"
`
`l"
`I,
`Ill-‘
`
`I
`
`
` II \\\\\\\\\\\\\\\\;<\\\\\\\1
`’
`
`mmmmmmmmm
`
`’I
`
`AmIw1%:N
`
`Em
`
`
`

`

`US. Patent
`
`Oct. 19, 2004
`
`Sheet 4 0f 19
`
`US 6,806,652 B1
`
`IIIIIIIIIIIII
`
`
`~Illllll‘lllllIIIIIHHHHHHIHHHHHH
`\\\\\\\\\\\\\\\\\\\\\\\\\\m0mm
`
`momowm.mmNo—N
`
`OVN
`
`momwzxww<O-IIIIIIIIIIIL-
`
`v".
`
`0200mm
`
`MESOm
`
`>4ma3m
`
`meE
`
`mm>aua
`
`>4mmDm
`
`0mm
`
`va
`
`
`
`

`

`US. Patent
`
`Oct. 19, 2004
`
`Sheet 5 0f 19
`
`US 6,806,652 B1
`
`FIG.4
`
`TIME
`
`tste
`
`0
`
`408
`
`1
`
`400
`
`402
`
`404
`
`POWER
`
`0.01kW-100kW
`
`-1kW-1OMW
`
`

`

`US. Patent
`
`Oct. 19, 2004
`
`Sheet 6 0f 19
`
`US 6,806,652 B1
`
`,-%H.HHW/Mr
`
`.vomw2
`
`
`
`u5.x.conumw>d
`
`\\.n7
`
`7
`
`6958Ball
`
`a.
`
`mm
`
`._.E
`
`0
`N
`
`me
`
`Now>3wEOn.
`
`.En.
`
`m>>
`
`
`
`
`
`

`

`US. Patent
`
`Oct. 19, 2004
`
`Sheet 7 0f 19
`
`US 6,806,652 B1
`
`UJ
`
`I\\IIII V,
`IN!
`‘°
`
`O0
`
`:DO(
`
`mVIII
`
`FIG.6
`
`I\\1EII
`i\itlll
`
`D U
`
`)<0
`
`

`

`US. Patent
`
`Oct. 19, 2004
`
`Sheet8 0f19
`
`US 6,806,652 B1
`
`\\\\L
`a$WV
`
`ozoomm
`
`\\\\\\\\\\\\\l,\\\\-,
`
`mmgoa
`
`>4mm3m
`
`

`

`US. Patent
`
`Oct. 19, 2004
`
`Sheet 9 0f 19
`
`US 6,806,652 B1
`
`mOKDOmw<ol
`
`n.
`
`ozoomw
`
`mESOm
`
`>4aa3m
`
`lull
`
`omw
`
`mOKDme<O
`
`1m>zum
`
`>4aa3m
`
`HmmEN
`
`\\\\
`
`

`

`US. Patent
`
`Oct. 19 2004
`
`Sheet 10 0f 19
`
`US 6,806,652 B1
`
`\llI'll'll'll'lllll"’lllllIIIIIIII'I‘III-II
`000000000 .IJ‘VI/
`
`
`mmmmm
`
`wwwwwwwwwwwwww
`
`.
`
`mmmmm
`
`>>>>>>
`
`

`

`US. Patent
`
`Oct. 19 2004
`
`Sheet 11 0f 19
`
`mmmmmmmm
`
`
`1‘\\.\lllll|'l-llI'lllllll'l'lll||llllllllllllllllllllllllllllllllllll
`1-13:»:111....--at}:uk:a-nnu.in-u!iuuuuulI:Kuuuuuuuuuuuuuuuuuuuu :lll:\\\\
`
`\\\\\\\\\\\\\\\\\\\
`
`'IIIIII
`
`§\\\\\\
`
`
`or.9“.
`
`

`

`US. Patent
`
`Oct. 19 2004
`
`Sheet 12 0f 19
`
`US 6,806,652 B1
`
`:.OE
`
`

`

`US. Patent
`
`Oct. 19, 2004
`
`Sheet 13 0f 19
`
`US 6,806,652 B1
`
`
`
`

`

`US. Patent
`
`Oct. 19, 2004
`
`Sheet 14 0f 19
`
`US 6,806,652 B1
`
`omN
`
`we.
`
`mm“
`
`DZOUwWQ
`
`can
`
`a:
`
`.................................22808-o:
`
`
`
`m----:----:---.229-fie-
`
`NoN
`
`own
`
`m
`
`__MmBari
`
`
` wmm...............6“..............3802-o:
`
`3N“s5omm_—nmnm.........>28.<3-m_nEmmwmmM"_nn____"9:5.Wn.n.
`
`

`

`US. Patent
`
`5
`
`US 6,806,652 B1
`
`m2:NH6“wJmy-:20
`
`VI'
`
`9 U
`
`.
`
`
`9,u_1__a_u_m0................-22“?.t32
`4wmmmun"Emmi2_u__n.
`1.t_e_euhn.smwmm4.W-.............EASE-o:-
`__nn......___ mmmmwmmw_W_u_u__n_m_m_"mu»m_nm__uumwmm.uun_u._u__uwnm___nmn__ONE-FMwmmm_mw6
`
`IE...22?.we.-
`
`x:at
`
`at
`
`/QZOmeQ
`
`own3:
`
`................................E802-o:-
`
`

`

`US. Patent
`
`Oct. 19, 2004
`
`Sheet 16 0f 19
`
`US 6,806,652 B1
`
`NEE.
`
`9..QE2m“
`
`
`
`/8“
`
`we.
`
`Nwm_
`
`omx
`
`nwW
`
`m
`
`
`
`.............-5802-S
`
`W0E1...&
`
`m229-fie.“NE
`
`

`

`US. Patent
`
`Oct. 19, 2004
`
`Sheet 17 0f 19
`
`US 6,806,652 B1
`
`800
`
`Feed Gas 234 Flows Through Region 214
`Towards Inner Cathode Section 202a
`
`First Power Supply 206 Generates Electric Field
`Across Feed Gas 234 to ignite Initial Plasma
`
`Volume Exchange of Feed Gas 234 Causes initial Plasma
`to Diffuse Proximate to inner Cathode Section 2023
`
`that is More Strongly Ionized than Initial Plasma
`
`Second Power Supply 222 Generates Electric Field
`Across Initial Plasma to Generate High-Density Plasma
`
`FIG. 16A
`
`802
`
`804
`
`806
`
`808
`
`

`

`US. Patent
`
`Oct. 19, 2004
`
`Sheet 18 0f 19
`
`US 6,806,652 B1
`
`800‘
`
`Feed Gas 234 Flows Through Region 214
`Toward Inner Cathode Section 2023
`
`First Power Supply 206 Generates Electric Field
`Across Feed Gas 234 to Ignite Initial Plasma
`
`
`
`802
`
`304
`
`806
`
`810
`
`4 812
`
`814
`
`Volume Exchange of Feed Gas 234 Causes Initial Plasma to
`Diffuse Toward Inner Cathode Section 202a
`
`First Power Supply 206 Generates Strong Electric Field Across Initial
`Plasma in Region 214 to Generate High-Density Plasma that is More
`Strongly Ionized than Initial Plasma
`
`Volume Exchange of Feed Gas 234 Causes High-Density
`Plasma to Diffuse Toward Inner Cathode Section 202a where
`it Commingles with Initial Plasma
`
`Second Power Supply 222 Generates Electric Field Across
`High~DensIty Plasma to Generate Higher-Density Plasma
`that is More Strongly Ionized than High-Density Plasma
`
`FIG. 168
`
`

`

`US. Patent
`
`Oct. 19, 2004
`
`Sheet 19 0f 19
`
`US 6,806,652 B1
`
`800"
`
`Feed Gas 234 Flows Into Region 214
`
`- 816
`
`
`
`
`
`
`First Power Supply 206 Generates Electric Field
`Across Feed Gas 234 to Ignite Initial Plasma
`
`313
`
`
`First Power Supply 206 Generates Strong Electric Field Across Initial
`Plasma In Region 214 to Generate High-Density Plasma that is More
`Strongly Ionized than Initial Plasma
`
`
`
`820
`
`Volume Exchange of Feed Gas 234 Causes High-Density
`Plasma to Diffuse Toward inner Cathode Section 202a
`
`
`
`
`
`Second Power Supply 222 Generates Electric Field Across
`High-Density Plasma to Generate Higher-Density Plasma
`
`that is More Strongly Ionized than High-Density Plasma
`
`822
`
`824
`
`FIG. 16C
`
`

`

`US 6,806,652 B1
`
`1
`HIGH-DENSITY PLASMA SOURCE USING
`EXCITED ATOMS
`
`CROSS REFERENCE TO RELATED
`APPLICATIONS
`
`This application is a continuation-in-part of US. patent
`application Ser. No. 10/249,595, filed on Apr. 22, 2003, the
`entire disclosure of which is incorporated herein by refer-
`ence.
`
`BACKGROUND OF INVENTION
`
`Plasma is considered the fourth state of matter. Aplasma
`is a collection of charged particles that move 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 conducting electrodes that
`are positioned parallel to each other. Once certain param-
`eters 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 elec-
`trodes in an inert gas atmosphere (e.g., argon) at a pressure
`that is in the range of about 10 to 10 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 to etch 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 and other work pieces. Sput-
`tering 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 are then
`drawn out of the plasma and accelerated across a cathode
`dark space. The target surface has a lower potential than the
`region in which the plasma is formed. Therefore, the target
`surface attracts positive ions.
`Positive ions move towards the target with a high velocity
`and then impact the target and cause atoms to physically
`dislodge or sputter from the target surface. The sputtered
`atoms then propagate to a substrate or other work piece
`where they deposit a film of sputtered target material. The
`plasma is replenished by electron-ion pairs formed by the
`collision of neutral molecules with secondary electrons
`generated at the target surface.
`Reactive sputtering systems inject a reactive gas or mix-
`ture of reactive gases into the sputtering system. The reac-
`tive gases react with the target material either at the target
`surface or in the gas phase, resulting in the deposition of new
`compounds. The pressure of the reactive gas can be varied
`to control the stoichiometry of the film. Reactive sputtering
`is useful for forming some types of molecular thin films.
`Magnetron sputtering systems use magnetic fields that are
`shaped to trap and concentrate secondary electrons proxi-
`mate to the target surface. The magnetic fields increase the
`density of electrons and,
`therefore,
`increase the plasma
`density in a region that is proximate to the target surface.
`The increased plasma density increases the sputter deposi-
`tion rate.
`
`BRIEF DESCRIPTION OF DRAWINGS
`
`This invention is described with particularity in the
`detailed description. The above and further advantages of
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`2
`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
`
`plasma generating apparatus having a direct current (DC)
`power supply.
`FIG. 2A illustrates a cross-sectional view of a plasma
`generating apparatus having a segmented cathode according
`to the invention.
`
`FIG. 2B illustrates a cross-sectional view of the seg-
`mented cathode of FIG. 2A.
`
`FIG. 3 illustrates a cross-sectional view of a plasma
`generating apparatus including a magnet assembly accord-
`ing to the invention.
`FIG. 4 illustrates a graphical representation of applied
`power as a function of time for periodic pulses applied to an
`initial plasma in the plasma generating system of FIG. 2A.
`FIG. 5 illustrates a cross-sectional view of a plasma
`generating apparatus including the magnet assembly of FIG.
`3 and an additional magnet assembly according to the
`invention.
`
`FIG. 6 illustrates a cross-sectional view of a plasma
`generating apparatus including the magnet assembly of FIG.
`3 and an additional magnet assembly according to the
`invention.
`FIG. 7 illustrates a cross-sectional view of another
`
`embodiment of a plasma generating apparatus including a
`magnet assembly according to the invention.
`FIG. 8 illustrates a cross-sectional view of a plasma
`generating apparatus including a magnet configuration that
`includes a first magnet and a second magnet according to the
`invention.
`
`FIG. 9 illustrates a cross-sectional view of a plasma
`generating apparatus according to the present
`invention
`including a segmented cathode assembly, an ionizing
`electrode, and a first, a second and a third power supply.
`FIG. 10 illustrates a cross-sectional view of a plasma
`generating apparatus according to the present
`invention
`including a segmented cathode assembly, a common anode,
`an ionizing electrode and a first, a second and a third power
`supply.
`FIG. 11 illustrates a cross-sectional view of a plasma
`generating apparatus according to the present
`invention
`including a segmented cathode assembly and a first, a
`second and a third power supply.
`FIG. 12 illustrates a cross-sectional view of a plasma
`generating apparatus according to the present
`invention
`including a segmented cathode assembly, an excited atom
`source, and a first, and a second power supply.
`FIG. 13 illustrates a graphical representation of the power
`as a function of time for each of a first, a second and a third
`power supply for one mode of operating the plasma gener-
`ating system of FIG. 9.
`FIG. 14 illustrates a graphical representation of power
`generated as a function of time for each of a first; a second
`and a third power supply for one mode of operating the
`plasma generating system of FIG. 9.
`FIG. 15 illustrates a graphical representation of the power
`as a function of time for each of a first, a second and a third
`power supply for one mode of operating the plasma gener-
`ating system of FIG. 9.
`
`

`

`US 6,806,652 B1
`
`3
`FIG. 16A through FIG. 16C are fiowcharts of illustrative
`processes of generating high-density plasmas according to
`the present invention.
`DETAILED DESCRIPTION
`
`FIG. 1 illustrates a cross-sectional view of a known
`
`plasma generating apparatus 100 having a DC power supply
`102. The known plasma generating apparatus 100 includes
`a vacuum chamber 104 where a plasma 105 is generated.
`The vacuum chamber 104 can be coupled to ground. The
`vacuum chamber 104 is positioned in fluid communication
`with a vacuum pump 106 via a conduit 108 and a valve 109.
`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 Torr. A feed
`gas 110 from a feed gas source 111, such as an argon gas
`source, is introduced into the vacuum chamber 104 through
`a gas inlet 112. The gas flow is controlled by a valve 113.
`The plasma generating apparatus 100 also includes a
`cathode assembly 114. The cathode assembly 114 is gener-
`ally in the shape of a circular disk. The cathode assembly.
`114 can include a target 116. The cathode assembly 114 is
`electrically connected to a first terminal 118 of the DC power
`supply 102 with an electrical transmission line 120. An
`insulator 122 isolates the electrical transmission line 120
`from a wall of the vacuum chamber 104. An anode 124 is
`
`electrically connected to a second terminal 126 of the DC
`power supply 102 with an electrical transmission line 127.
`An insulator 128 isolates the electrical transmission line 127
`from the wall of the vacuum chamber 104. The anode 124
`
`is positioned in the vacuum chamber 104 proximate to the
`cathode assembly 114. An insulator 129 isolates the anode
`124 from the cathode assembly 114. The anode 124 and the
`second output 126 of the DC power supply 102 are coupled
`to ground in some systems.
`The plasma generating apparatus 100 illustrates a mag-
`netron sputtering system that includes a magnet 130 that
`generates a magnetic field 132 proximate to the target 116.
`The magnetic field 132 is strongest at
`the poles of the
`magnet 130 and weakest in the region 134. The magnetic
`field 132 is shaped to trap and concentrate secondary elec-
`trons proximate to the target surface. The magnetic field
`increases the density of electrons and, therefore, increases
`the plasma density in a region that is proximate to the target
`surface.
`
`The plasma generating apparatus 100 also includes a
`substrate support 136 that holds a substrate 138 or other
`work piece. The substrate support 136 can be electrically
`connected to a first terminal 140 of a RF power supply 142
`with an electrical transmission line 144. An insulator 146
`
`isolates the RF power supply 142 from a wall of the vacuum
`chamber 104. Asecond terminal 148 of the RF power supply
`142 is coupled to ground.
`In operation, the feed gas 110 from the feed gas source 111
`is injected into the chamber 104. The DC power supply 102
`applies a DC voltage between the cathode assembly 114 and
`the anode 124 that causes an electric field 150 to develop
`between the cathode assembly 114 and the anode 124. The
`amplitude of the DC voltage is chosen so that it is sufficient
`to cause the resulting electric field to ionize the feed gas 110
`in the vacuum chamber 104 and to ignite the plasma 105.
`The ionization process in known plasma sputtering appa-
`ratus is generally referred to as direct ionization or atomic
`ionization by electron impact and can be described by the
`
`following equation:
`
`Ar+e7a
`r++2e’
`
`
`
`
`
`4
`
`where Ar represents a neutral argon atom in the feed gas
`110 and e" represents an ionizing electron generated in
`response to the voltage applied between the cathode
`assembly 114 and the anode 124. The collision between
`the neutral argon atom and the ionizing electron results
`in an argon ion (Ar+) and two electrons.
`The plasma 105 is maintained, at least in part, by sec-
`ondary electron emission from the cathode assembly 114.
`The magnetic field 132 that is generated proximate to the
`cathode assembly 114 confines the secondary electrons in
`the region 134 and,
`therefore, confines the plasma 105
`approximately in the region 134. The confinement of the
`plasma in the region 134 increases the plasma density in the
`region 134 for a given input power.
`The plasma generating apparatus 100 can be configured
`for magnetron sputtering. Since the cathode assembly 114 is
`negatively biased, ions in the plasma 105 bombard the target
`116. The impact caused by these ions bombarding the target
`116 dislodges or sputters material from the target 116. A
`portion of the sputtered material forms a thin film of
`sputtered target material on the substrate 138.
`Known magnetron sputtering systems have relatively
`poor target utilization. The term “poor target utilization” is
`defined herein to mean undesirable non-uniform erosion of
`
`target material. Poor target utilization is caused by a rela-
`tively high concentration of positively charged ions in the
`region 134 that results in a non-uniform plasma. Similarly,
`magnetron etching systems (not shown) typically have rela-
`tively non-uniform etching characteristics.
`Increasing the power applied to the plasma can increase
`the uniformity and density of the plasma. However, increas-
`ing the amount of power necessary to achieve even an
`incremental increase in uniformity and plasma density can
`significantly increase the probability of establishing an elec-
`trical breakdown condition leading to an undesirable elec-
`trical discharge (an electrical arc) in the chamber 104.
`Applying pulsed direct current (DC) to the plasma can be
`advantageous since the average discharge power can remain
`relatively low while relatively large power pulses are peri-
`odically 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.
`In one embodiment, an apparatus according to the present
`invention generates a plasma having a higher density of ions
`for a giving input power than a plasma generated by known
`plasma systems, such as the plasma generating apparatus
`100 of FIG. 1.
`
`A high-density plasma generation method and apparatus
`according to the present invention uses an electrode struc-
`ture including three or more electrodes to generate a high-
`density plasma including excited atoms, ions, neutral atoms
`and electrons. The electrodes can be a combination of
`
`cathodes, anodes, and/or ionizing electrodes. The electrodes
`can be configured in many different ways, such as a ring
`electrode structure, a linear electrode structure, or hollow
`cathode electrode structure. The plasma generation method
`and apparatus of the present invention provides independent
`control of two or more co-existing plasmas in the system.
`A high-density plasma source according to the present
`invention can include one or more feed gas injection systems
`that inject feed gas proximate to one or more of the elec-
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`

`

`US 6,806,652 B1
`
`5
`trodes in the plasma source. The feed gas can be any mixture
`of gases as described herein. The one or more feed gas
`injection systems can also inject plasma proximate to one or
`more of the electrodes in the plasma source. The injected
`plasma can be a high-density plasma or a low-density
`plasma. In one embodiment, an initial plasma is generated
`and then it is super-ionized to form a high-density plasma.
`The term “super-ionized” is defined herein to mean that at
`least 75% of the neutral atoms in the plasma are converted
`to ions.
`
`The high-density plasma source of the present invention
`can operate in a constant power, constant voltage, or con-
`stant current mode. These modes of operation are discussed
`herein. In addition, the high-density plasma source can use
`different
`types of power supplies to generate the high-
`density plasma. For example, direct-current
`(DC),
`alternating-current (AC), radio-frequency (RF), or pulsed
`DC power supplies can be used to generate the high-density
`plasma. The power supplies can generate power levels in the
`range of about 1W to 10MW.
`The plasma generated by the high-density plasma source
`of the present invention can be used to sputter materials from
`solid or liquid targets. Numerous types of materials can be
`sputtered. For example, magnetic, non-magnetic, dielectric,
`metals, and semiconductor materials can be sputtered.
`In one embodiment, the high-density plasma source of the
`present invention generates relatively high deposition rates
`near the outer edge of a sputtering target. The target can be
`designed and operated such that the increase in the deposi-
`tion rate near the outer edge of the sputtering target com-
`pensates for the decrease of the sputtering rate typically
`associated with the edge of a sputtering target. This embodi-
`ment allows the use of relatively small targets, which can
`reduce the overall footprint of a process tool, the cost of the
`target and the cost to operate the process tool.
`The high-density plasma source of the present invention
`provides high target utilization and high sputtering unifor-
`mity. Additionally, the plasma generated by the high-density
`plasma source of the present invention can be used for
`producing ions or atoms from molecules for numerous
`applications, such as sputter etch, reactive etch, chemical
`vapor deposition, and for generating ion beams.
`FIG. 2A illustrates a cross-sectional view of a plasma
`generating apparatus 200 having a segmented cathode 202
`according to the invention. In one embodiment, the seg-
`mented cathode 202 includes an inner cathode section 202a
`and an outer cathode section 202b. In some embodiments
`
`(not shown), the segmented cathode 202 includes more than
`two sections. The segmented cathode 202 can be composed
`of a metal material, such as stainless steel or any other
`material that does not chemically react with reactive gases.
`The segmented cathode 202 can include a target (not shown)
`that is used for sputtering. The inner cathode section 202a
`and the outer cathode section 202b can be composed of
`different materials.
`
`The outer cathode section 202b is coupled to a first output
`204 of a first power supply 206. The first power supply 206
`can operate in a constant power mode. The term “constant
`power mode” is defined herein to mean that the power
`generated by the power supply has a substantially constant
`power level regardless of changes in the output current and
`the output voltage level. In another embodiment, the first
`power supply 206 operates in a constant voltage mode. The
`term “constant voltage mode” is defined herein to mean that
`the voltage generated by the power supply has a substan-
`tially constant voltage level regardless of changes in the
`output current and the output power level. The first power
`
`6
`
`supply 206 can include an integrated matching unit (not
`shown). Alternatively, a matching unit (not shown) can be
`electrically connected to the first output 204 of the first
`power supply 206.
`A second output 208 of the first power supply 206 is
`coupled to a first anode 210. An insulator 211 isolates the
`first anode 210 from the outer cathode section 202b. In one
`
`embodiment, the second output 208 of the first power supply
`206 and the first anode 210 are coupled to ground potential
`(not shown).
`In one embodiment (not shown), the first output 204 of the
`first power supply 206 couples a negative voltage impulse to
`the outer cathode section 202b. In another embodiment (not
`shown), the second output 208 of the first power supply 206
`couples a positive voltage impulse to the first anode 210.
`Numerous types of power supplies can be used for the first
`power supply 206. For example, the first power supply 206
`can be a pulsed power supply, radio-frequency (RF) power
`supply, an alternating-current (AC) power supply, or a
`direct-current (DC) power supply.
`The first power supply 206 can be a pulsed power supply
`that generates peak voltage levels of up to about 5 kV.
`Typical operating voltages are in the range of about 50V to
`5 kV. The first power supply 206 can generate peak current
`levels in the range of about 1 mA to 100 kA depending on
`the desired volume and characteristics of the plasma. Typical
`operating currents vary from less than one hundred amperes
`to more than a few thousand amperes depending on the
`desired volume and characteristics of the plasma. The first
`power supply 206 can generate pulses having a repetition
`rate that is below 1 kHz. The first power supply 206 can
`generate pulses having a pulse width that is in the range of
`about one microsecond to several seconds.
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`The first anode 210 is positioned so as to form a gap 212
`between the first anode 210 and the outer cathode section
`
`202b that is sufficient to allow current to flow through a
`region 214 between the first anode 210 and the outer cathode
`section 202b. In one embodiment, the width of the gap 212
`is in the range of about 0.3 cm to 10 cm. The surface area
`of the outer cathode section 202b determines the volume of
`
`the region 214. The gap 212 and the total volume of the
`region 214 are parameters in the ionization process as
`described herein.
`
`For example, the gap 212 can be configured to generate
`exited atoms from ground state atoms. The excited atoms
`can increase the density of a plasma. Since excited atoms
`generally require less energy to ionize than ground state gas
`atoms, a volume of excited atoms can generate a higher
`density plasma than a similar volume of ground state feed
`gas atoms for the same input energy. Additionally, the gap
`212 can be configured to conduct exited atoms towards the
`inner cathode section 202a. The excited atoms can either be
`
`generated externally or inside the gap 212 depending on the
`configuration of the system. In one embodiment, the gap 212
`exhibits a pressure differential that forces the exited atoms
`towards the inner cathode section 202a. This can increase
`
`the density of the plasma proximate to the inner cathode
`section 202a as previously discussed.
`In this
`The gap 212 can be a plasma generator.
`configuration, feed gas is supplied to the gap 212 and a
`plasma is ignited in the gap 212. An ignition condition in the