(12) United States Patent
`Chistyakov
`
`(10) Patent N0.:
`(45) Date of Patent:
`
`US 6,896,775 B2
`May 24, 2005
`
`US006896775B2
`
`(54) HIGH-POWER PULSED MAGNETICALLY
`ENHANCED PLASMA PROCESSING
`
`W0
`W0
`
`WO 98/40532
`W0 01/98553 A1
`
`9/1998
`12/2001
`
`OTHER PUBLICATIONS
`US 5,863,392, 1/1999, Drummond et al. (withdrawn)
`Encyclopedia Of Low Temperature Plasma, p. 119, Vol. 3.
`Encyclopedia Of Low Temperature Plasma, p. 123, Vol. 3.
`Ch'tak,H'h—P
`PuldM t Stt',
`U SIS Z (iVNO Iglo/OZISVZI77 Fislzdj SeagII3e0I02I:)02pu ermg
`' ,'
`pp '
`"
`,’
`’
`'
`P’
`’
`'
`Chistyakov, Roman, High—PoWer Pulsed Magnetron Sput-
`tering, U.S. Appl. No.: 10/065,277, Filed: Sep. 30, 2002.
`Booth, et al., The Transition From Symmetric To Asymmet-
`ric Discharges In Pulsed 13.56 MHZ Capacity Coupled
`Plasmas, J. Appl. Phys., Jul. 15, 1997, pp. 552-560, Vol. 82
`(2), American Institute of Physics.
`.
`(commued)
`
`Primary Examiner—R0dney G,McD0na1d
`(74) Attemey» Agem»
`0’ F‘""—K‘“t Raueehenbaehé
`Raueehenbaeh Patent Law Gre“P> LLC
`(57)
`ABSTRACT
`
`.
`.
`Magnetically enhanced plasma processing methods and
`apparatus are described. A magnetically enhanced plasma
`processing apparatus according to the present
`invention
`includes an anode and a cathode that is positioned adjacent
`to the anode. An ionization source generates a Weakly-
`ionized plasma proximate to the cathode. A magnet
`is
`Peeltlehed F0 generate *1 maghetle field Prexlmate t0, the
`Weakly-ionized plasma. The magnetic field substantially
`traps electrons in the Weakly-ionized plasma proximate to
`the cathode. A power supply produces an electric field in a
`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 sec-
`ondar electrons ionize the excited atoms thereb creatin
`5’
`1
`.
`.
`d
`1
`A 1
`’1
`b. g
`a Strong y'1°“1Z‘°* P “ma” . "0 ‘a.g.‘°' Supp Y aPP 165 a “S
`Veltage t0 a Substrate that 15 Peeltlehed Ptexlmate t0 the
`eath0de that Causes 10hS.1h the Phlrahty 0f M15 t0 Impact a
`surface of the substrate in a manner that causes etching of
`the surface of the substrate.
`
`(75)
`
`Inventor: Roman Chistyakov, Andover, MA
`(US)
`
`,
`(73) Asslgneei Zond’ Inc" Mansfidd’ MA (US)
`.
`.
`.
`..
`( * ) Notice:
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`USC. 154(b) by 386 days.
`
`,
`(21) App1'NO"10/065551
`(22)
`Filed:
`Oct. 29, 2002
`_
`_
`_
`Prior Publication Data
`Us 2004/0082187 A1 Apr. 29, 2004
`
`(65)
`
`Int. Cl.7 .......................... .. C23C 14/34, C23F 1/00
`(51)
`(52) U.s. Cl.
`.......................... .. 204/192.32, 204/298.31;
`204/298.33; 204/298.34; 204/298.37; 216/67;
`216/71; 156/345.43; 156/345.44; 156/345.46
`(58) Field of Search ..................... .. 204/192.32, 298.31,
`204/298.33, 298.34, 298.37; 216/67, 71;
`15634543, 34544, 345.46
`
`(56)
`
`References Cited
`
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`4,588,490 A
`5/1986 Cuomo et al.
`............ .. 204/298
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`1/1991 Wolfe et a1.
`5,083,061 A
`1/1992 Koshfishi et a1,
`5,728,261 A
`3/1998 Wolfe et al.
`---- -- 204/298-11
`5,728,278 A
`3/1998 Okamllfa et a1-
`---- -- 204/298-37
`5»795a452 A
`8/1998 Kineshite et 31-
`630573244 A
`5/2000 Hangman“ et al‘ ““““ " 438/706
`6’447’69I BI
`9/2002 Denda CI III‘ """""" " 216/61
`6,451,703 B1
`9/2002 Liu et al. ................. 438/710
`6,471,833 B2
`10/2002 Kumar et al.
`204/192.37
`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 a1,
`,,,,,, ,, 156/345,46
`FOREIGN PATENT DOCUMENTS
`
`
`
`,,,,, ,, 315/111,81
`
`EP
`
`0428 161 A2
`
`5/1991
`
`37 Claims, 18 Drawing Sheets
`
`230
`
`7\
`
`Hmrs
`rr
`
`GILLETTE 1101
`
`.9.
`
`'////////
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`
`GILLETTE 1101
`
`

`
`US 6,896,775 B2
`Page 2
`
`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., Attachment—Dominated Electron—Bea-
`m-Ionized Discharges, Applied Science Letters, May 15,
`1976, vol. 28, No. 10, American Institute of Physics.
`Goto, et al., Dual Excitation Reactive Ion Etcher for Low
`Energy Plasma Processing, J. Vac. Sci. Technol. A, Sep./Oct.
`1992, pp. 3048-3054, vol. 10, No. 5, American Vacuum
`Society.
`Kouznetsov, et al., A Novel Pulsed Magnetron Sputter
`Technique Utilizing Very High Target Power Densities,
`Surface & Coatings Technology, pp. 290-293, Elsevier
`Sciences S.A.
`
`Lindquist, et al., High Selectivity Plasma Etching Of Silicon
`Dioxide With A Dual Frequency 27/2 MHz Capacitive RF
`Discharge.
`Macak, Reactive Sputter Deposition Process of A1203 and
`Characterization Of A Novel High Plasma Density Pulsed
`Magnetron Discharge, Linkoping Studies In Science And
`Technology, 1999, pp. 1-2, Sweden.
`
`Ionized Sputter Deposition Using An
`Macak, et al.,
`Extremely High Plasma Density Pulsed Magnetron Dis-
`charge,
`J. Vac Sci. Technol. A., Jul./Aug. 2000, pp.
`1533-1537, vol. 18, No. 4, American Vacuum Society.
`
`Mozgrin, et al., High-Current Low-Pressure Quasi -Sta-
`tionary Discharge In A Magnetic Field: Experimental
`Research, Plasma Physics Reports, 1995, pp. 400-409, vol.
`21, No. 5, Mozgrin, Feitsov, Khodachenko.
`
`Rossnagel, et al., Induced Drift Currents In Circular Planar
`Magnetrons, J. Vac. Sci. Technol. A., Jan./Feb. 1987, pp.
`88-91, vol. 5, No. 1, American Vacuum Society.
`
`Sheridan, et al., Electron Velocity Distribution Functions In
`ASputtering Magnetron Discharge For The EXB Direction,
`J. Vac. Sci. Technol. A., Jul./Aug. 1998, pp. 2173-2176, vol.
`16, No. 4, American Vacuum Society.
`
`Steinbruchel, A Simple Formula For Low-Energy Sputter-
`ing Yields, Applied Physics A., 1985, pp. 37-42, vol. 36,
`Springer-Verlag.
`
`

`
`U.S. Patent
`
`May 24, 2005
`
`Sheet 1 of 18
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`US 6,896,775 B2
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`PRIOR ART
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`U.S. Patent
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`May 24, 2005
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`U.S. Patent
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`May 24, 2005
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`US 6,896,775 B2
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`U.S. Patent
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`May 24, 2005
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`Sheet 13 of 18
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`US 6,896,775 B2
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`U.S. Patent
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`May 24, 2005
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`Sheet 14 of 18
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`
`U.S. Patent
`
`May 24, 2005
`
`Sheet 15 of 18
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`US 6,896,775 B2
`
`600
`
`
`CHAM
`
`PUMP DOWN CHAMBER
`
`604
`
`PRESSURE
`CORRECT?
`
`Y
`
`608
`
`PASS FEED GAS INTO CHAMBER
`PROXIMATE TO CATHODE
`
`
`
`CHAMBER
`PRESSURE
`CORRECT?
`
`GAS
`P RESSURE
`CORRECT?
`
`
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`
`APPLY APPROPRIATE MAGNETIC
`FIELD PRDXIMATE TO FEED GAS
`
`614
`
`FIELD
`PROPER?
`
`Y
`
`IONIZE FEED GAS TO GENERATE
`WEAKLY-IONIZED PLASMA
`
`GAS
`WEAKLY-
`
`
`IONIZED?
`
`
`
`
`FIG. 12A
`
`FIG. 12A
`
`FIG- 12B
`
`FIG. 12
`
`

`
`U.S. Patent
`
`May 24, 2005
`
`Sheet 16 of 18
`
`US 6,896,775 B2
`
`621
`
`
`
`PLASMA FROM WEAKLY-IONIZED PLASMA
`
`APPLY NEGATIVE BIAS T0 SUBSTRATE
`
`
`
`GENERATE STRONGLY-IONIZED
`
`
`
`
`PLASMA
`STRONGLY-
`IONIZED?
`
`MONITOR PLASMA ETCH
`
`
` PLASMA
`
`
`ETCH
`COMPLETE
`
`

`
`U.S. Patent
`
`May 24, 2005
`
`Sheet 17 of 18
`
`US 6,896,775 B2
`
`650
`
`502 604
`
`PUMP DOWN CHAMBER
`
`
`
` CHAMBER
`PRESSURE
`CORRECT?
`
`
`
`
`
`GAS
`CHAMBER
`PRESSURE
`PRESSURE
`CORRECT?
`CORRECT?
`
`
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`
`
`
`Y
`
`618
`
`IONIZE FEED GAS T0 GENERATE
`WEAKLY-IONIZED PLASMA
`
`
`GAS
`WEAKLY-
`IONIZED?
`
`
`
`
`
`Y
`
`FIG. 13A
`
`FIG. 13A
`
`FIG. 13B
`
`FIG. 13
`
`

`
`U.S. Patent
`
`May 24, 2005
`
`Sheet 18 of 18
`
`US 6,896,775 B2
`
`0
`
`APPLY NEGATIVE BIAS TO SUBSTRATE
`
`621
`
`622
`
`GENERATE STRONGLY-IONIZED
`PLASMA FROM WEAKLY-IONIZED PLASMA
`
`
`
`PLASMA
`STRONGLY-
`
`IONIZEDT
`
`
`Y
`
`MONITOR ETCH RATE
`
`652
`
`656
`
`INCREASE
`HIGH-POWER PULSE
`T0 CATHODE TO
`INCREASE ETCH RATE
`
`Y
`
`658
`
`CONTINUE
`ETCHING
`
`660
` PLASMA
`?
`
`ETCH
`COMPLETE
`
`313
`
`FIG. 133
`
`

`
`US 6,896,775 B2
`
`1
`HIGH-POWER PULSED MAGNETICALLY
`ENHANCED PLASMA PROCESSING
`
`BACKGROUND OF INVENTION
`
`Plasma processes are widely used in many industries,
`such as the semiconductor manufacturing industry. For
`example, plasma etching is widely used in the semiconduc-
`tor manufacturing 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.
`Sputter etching is the ejection of atoms from the surface
`of a substrate due to energetic ion bombardment. Pure
`chemical etching uses a plasma discharge to supply gas-
`phase etchant atoms or molecules that chemically react with
`the surface of a substrate to form gas-phase products.
`Ion-enhanced energy driven etching uses a plasma discharge
`to supply both etchant and energetic ions to a surface of a
`substrate. Ion inhibitor etching uses a discharge to provide
`etchant, energetic ions, and inhibitor precursor molecules
`that deposit on the substrate to form a protective layer film.
`It is desirably to increase the uniformity and etch rate of
`known sputter etching systems.
`BRIEF DESCRIPTION OF DRAWINGS
`
`This invention is described with particularity in the
`detailed description. The above and further advantages of
`this invention may be better understood by referring to the
`following description in conjunction with the accompanying
`drawings,
`in which like numerals indicate like structural
`elements and features in various figures. The drawings are
`not necessarily to scale, emphasis instead being placed upon
`illustrating the principles of the invention.
`FIG. 1 illustrates a cross-sectional view of a known
`
`magnetically enhanced etching apparatus having a having a
`radio-frequency (RF) power supply.
`FIG. 2 illustrates a cross-sectional view of an embodiment
`
`of a magnetically enhanced plasma processing apparatus
`according to the present invention.
`FIG. 3 illustrates a cross-sectional view of the anode and
`
`the cathode of the magnetically enhanced plasma processing
`apparatus of FIG. 2.
`FIG. 4 illustrates a graphical representation of the applied
`power of a pulse as a function of time for periodic pulses
`applied to the plasma in the magnetically enhanced plasma
`processing apparatus of FIG. 2.
`FIG. 5 illustrates graphical representations of the applied
`voltage, current, and power as a function of time for periodic
`pulses applied to the plasma in the magnetically enhanced
`plasma processing apparatus of FIG. 2.
`FIG. 6A through FIG. 6D illustrate various simulated
`magnetic field distributions proximate to the cathode for
`various electron E><B drift currents according to the present
`invention.
`FIG. 7 illustrates a cross-sectional view of another
`
`embodiment of a magnetically enhanced plasma processing
`apparatus according to the present invention.
`FIG. 8 illustrates a graphical representation of pulse
`power as a function of time for periodic pulses applied to the
`plasma in the magnetically enhanced plasma processing
`apparatus of FIG. 7.
`FIG. 9A through FIG. 9C are cross-sectional views of
`various embodiments of cathodes according to the present
`invention.
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`2
`FIG. 10 illustrates a cross-sectional view of another
`
`illustrative embodiment of a magnetically enhanced plasma
`processing apparatus according to the present invention.
`FIG. 11 is a cross-sectional view of another illustrative
`
`embodiment of a magnetically enhanced plasma processing
`apparatus according to the present invention.
`FIG. 12 is a flowchart of an illustrative process for
`magnetically enhanced plasma etching according to the
`present invention.
`FIG. 13 is a flowchart of an illustrative process for
`controlling etch rate according to the present invention.
`
`DETAILED DESCRIPTION
`
`FIG. 1 illustrates a cross-sectional view of a known
`
`magnetically enhanced etching apparatus 100 having a
`radio-frequency (RF) power supply 102. The known mag-
`netically enhanced etching apparatus 100 includes a vacuum
`chamber 104 for confining a plasma 105. A vacuum pump
`106 is coupled in fluid communication with the vacuum
`chamber 104 via a conduit 108. The vacuum pump 106 is
`adapted to evacuate the vacuum chamber 104 to high
`vacuum and to maintain the chamber at a pressure that is
`suitable for plasma processing. A gas source 109, such as an
`argon gas source, introduces gas into the vacuum chamber
`104 through a gas inlet 110. A valve 112 controls the gas
`flow to the chamber 104.
`
`The magnetically enhanced etching apparatus 100 also
`includes a cathode 114.
`
`The cathode 114 is an electrode that 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 electrical transmission line 122. A second terminal
`
`124 of the blocking capacitor 120 is coupled to a first output
`126 of the RF power supply 102. The cathode 114 is isolated
`from the vacuum chamber 104 by an insulator 128 that is
`used to pass the electrical transmission line 122 through a
`wall of the vacuum chamber 104.
`
`An anode 130 is positioned in the vacuum chamber 104
`opposite the cathode 114. The anode 130 is electrically
`coupled to ground by an electrical transmission line 132. A
`second output 134 of the RF power supply 102 is also
`electrically coupled to ground. An insulator 136 is used to
`pass the electrical transmission line 132 through a wall of the
`vacuum chamber 104 in order to isolate the anode 130 from
`the vacuum chamber 104. The vacuum chamber 104 can
`
`also be electrically coupled to ground.
`A pair of magnets 140 is positioned outside the chamber
`104 to generate a magnetic field 142 in a direction that is
`substantially parallel to the top surface of the cathode 114.
`A substrate 144 is disposed on the cathode 114.
`In operation, the substrate 144 to be etched is positioned
`on the cathode 114. The chamber 104 is sufficiently evacu-
`ated to high vacuum by the vacuum pump 106. The etching
`gas from the gas source 109 is introduced into the chamber
`104 through the gas inlet 110. The RF power supply 102
`applies high-frequency radiation at 13.56 MHZ through a
`blocking capacitor 120 to the cathode 114.
`The high-frequency radiation applied to the cathode 114
`creates a high-frequency electric field 146 in a direction that
`is perpendicular to the top surface of the cathode 114. The
`magnetic field 142 and the high-frequency electric field 146
`intersect each other in a region 148 above the substrate 144.
`Electrons are trapped in the region 148 and collide with
`neutral atoms from the etching gas. These collisions gener-
`ate a high-density plasma 105. The negatively biased cath-
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`ode 114 attracts positively charged ions in the plasma 105
`with sufficient acceleration so that the ions etch a surface of
`the substrate 144.
`
`The RF power applied between the cathode 114 and the
`anode 130 has sufficient amplitude to ionize the etching gas
`and create the plasma 105 in the vacuum chamber 104. The
`plasma consists of positive ions and negative electrons. A
`typical RF driving voltage is between 500 V and 5000 V, and
`the distance 138 between the, cathode 114 and the anode 130
`is about 70 mm. Typical pressures are in the range 10 m Torr
`and 100 m Torr. Typical power densities are in the range of
`0.1 W/cm2 to 1 W/cm2. Typical plasma densities are 109
`cm‘3—10n cm‘3, and the electron temperature is on the
`order of 3 eV.
`
`The ionization process that generates the plasma 105 for
`sputter etching is sometimes referred to as direct ionization
`or atomic ionization by electron impact and can be described
`as follows:
`
`Ar+e’—>Ar*+2e’
`
`where Ar represents a neutral argon atom in the etching 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 by secondary electron
`emission from the cathode 114. 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 including plasma etching.
`The electrons, which cause the ionization, are generally
`confined by the magnetic fields produced by the magnets
`140. The magnetic confinement is strongest in a confinement
`region 148 where the magnetic field lines are parallel to the
`surface of the electrode. Generally, a higher concentration of
`positively charged ions in the plasma is present
`in the
`confinement region 148 than elsewhere in the chamber 104.
`Consequently, the substrate 144 is etched more rapidly in
`areas directly adjacent to the higher concentration of posi-
`tively charged ions. The rapid etching in these areas results
`in undesirable non-uniform etching of the substrate 144.
`Dramatically increasing the RF power applied to the
`plasma alone will not result in the formation of a more
`uniform and denser plasma that improves the etching uni-
`formity. Improved etching will not occur because the mag-
`netic field will be non-uniform across the electrode and the
`
`magnetic field distribution around the electrode will be
`insufficient
`to confine the electrons. Furthermore,
`the
`amount of applied power that is necessary to achieve a
`significant increase in uniformity can increase the probabil-
`ity of generating an electrical breakdown condition leading
`to an undesirable electrical discharge (an electrical arc) in
`the chamber 104.
`
`Pulsing the direct current (DC) power applied to the
`plasma can be advantageous since the average discharge
`power can remain low while relatively large power pulses
`are periodically applied. In addition,
`the duration of the
`voltage pulses can be chosen so as to reduce the probability
`of establishing an electrical breakdown condition. However,
`very large power pulses can still result
`in an electrical
`breakdown condition regardless of their duration. An unde-
`sirable electrical discharge will corrupt the etching process,
`cause contamination in the vacuum chamber 104, and can
`damage the substrate and/or any process layers already
`
`4
`fabricated. In addition, using a magnetron-type plasma gen-
`erator results in a magnetic field that significantly improves
`confinement. The electrons generated in a magnetron-type
`plasma generator will have a closed-loop path that generates
`an E><B drift current that significantly improves confine-
`ment.
`FIG. 2 illustrates a cross-sectional view of an embodiment
`of a magnetically enhanced plasma processing apparatus
`200 according to the present invention. In one embodiment,
`the magnetically enhanced plasma processing apparatus 200
`can be configured for magnetically enhanced reactive ion
`etching. In another embodiment, the magnetically enhanced
`plasma processing apparatus 200 can be configured for
`sputter etching.
`The magnetically enhanced plasma processing apparatus
`200 includes a chamber 202, such as a vacuum chamber. The
`chamber 202 is coupled in fluid communication to a vacuum
`pump 204 through a vacuum valve 206. In one embodiment,
`the chamber 202 is electrically coupled to ground potential.
`The chamber 202 is coupled to a feed gas source 208 by
`one or more gas lines 207. In one embodiment, the gas lines
`207 are isolated from the chamber and other components by
`insulators 209. In addition, the gas lines 207 can be isolated
`from the feed gas source 208 using in-line insulating cou-
`plers (not shown). A gas flow control system 210 controls
`the gas flow to the chamber 202. The gas source 208 can
`contain any type of feed gas, such as argon.
`In some
`embodiments, the feed gas is a mixture of different gases.
`The different gases can include reactive and non-reactive
`gases. In one embodiment, the feed gas is a noble gas or a
`mixture of noble gases.
`A substrate 211 to be processed is supported in the
`chamber 202 by a substrate support 212. The substrate 211
`can be any type of work piece such as a semiconductor
`wafer. In one embodiment,
`the substrate support 212 is
`electrically coupled to an output 213 of a bias voltage source
`214. An insulator 215 isolates the bias voltage source 214
`from the chamber 202. In one embodiment, the bias voltage
`source 214 is an alternating current (AC) power source, such
`as a radio frequency (RF) power source. In other embodi-
`ments (not shown), the substrate support 212 is coupled to
`ground potential or is electrically floating.
`The magnetically enhanced plasma processing apparatus
`200 also includes a cathode 216. In one embodiment, the
`cathode 216 is formed of a metal. In one embodiment, the
`cathode 216 is formed of a chemically inert material, such
`as stainless steel. The distance from the cathode 216 to the
`
`substrate 211 can vary from a few centimeters to about one
`hundred centimeters.
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`The cathode 216 is coupled to an output 222 of a matching
`unit 224. An insulator 226 isolates the cathode 216 from a
`
`grounded wall of the chamber 202. An input 230 of the
`matching unit 224 is coupled to a first output 232 of a pulsed
`power supply 234. A second output 236 of the pulsed power
`supply 234 is coupled to an anode 238. An insulator 240
`isolates the anode 238 from a grounded wall of the chamber
`202. Another insulator 242 isolates the anode 238 from the
`cathode 216.
`
`In one embodiment (not shown), the first output 232 of the
`pulsed power supply 234 is directly coupled to the cathode
`216. In one embodiment (not shown), the second output 236
`of the pulsed power supply 234 and the anode 238 are both
`coupled to ground. In one embodiment (not shown), the first
`output 232 of the pulsed power supply 234 couples a
`negative voltage impulse to the cathode 216. In another
`embodiment (not shown),
`the second output 236 of the
`pulsed power supply 234 couples a positive voltage impulse
`to the anode 238.
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`US 6,896,775 B2
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`In one embodiment, the pulsed power supply 234 gener-
`ates peak voltage levels that are on the order of 5-10 kV. In
`one embodiment, operating voltages are between about 50 V
`and 1000 V. In one embodiment, the pulsed power supply
`234 sustains a discharge current level that is between about
`1A and about 5,000A depending on the volume of the
`plasma. Typical operating currents varying from less than
`about one hundred amperes to more than about a few
`thousand amperes depending on the volume of the plasma.
`In one embodiment,
`the pulses generated by the pulsed
`power supply 234 have a repetition rate that is below 1 kHz.
`In one embodiment, the pulse width of the pulses generated
`by the pulsed power supply 234 is substantially between
`about one microsecond and several seconds.
`
`The anode 238 is positioned so as to form a gap 244
`between the anode 238 and the cathode 216 that is sufficient
`
`to allow current to flow through a region 245 between the
`anode 238 and the cathode 216. In one embodiment, the
`width of the gap 244 is between approximately 0.3 cm and
`10 cm. The surface area of the cathode 216 and the dimen-
`
`sions of the gap determine the volume of the region 245. The
`dimensions of the gap 244 and the total volume of the region
`245 are parameters in the ionization process as described
`herein.
`
`An anode shield 248 is positioned adjacent to the anode
`238 and functions as an electric shield to electrically isolate
`the anode 238 from the plasma. In one embodiment, the
`anode shield 248 is coupled to ground potential. An insulator
`250 is positioned to isolate the anode shield 248 from the
`anode 238.
`
`The magnetically enhanced plasma processing apparatus
`200 also includes a magnet assembly 252.
`In one
`embodiment, the magnet assembly 252 is adapted to create
`a magnetic field 254 proximate to the cathode 216. The
`magnet assembly 252 can include permanent magnets 256,
`or alternatively, electromagnets (not shown). The configu-
`ration of the magnet assembly 252 can be varied depending
`on the desired shape and strength of the magnetic field 254.
`The magnet assembly 252 can have either a balanced or
`unbalanced configuration.
`In one embodiment, the magnet assembly 252 includes
`switching electro-magnets, which generate a pulsed mag-
`netic field proximate to the cathode 216.
`In some
`embodiments, additional magnet assemblies (not shown) are
`placed at various locations around and throughout the cham-
`ber 202 depending on the plasma process.
`In one embodiment, the magnetically enhanced plasma
`processing apparatus 200 is operated by generating the
`magnetic field 254 proximate to the cathode 216. In the,
`embodiment shown in FIG. 2, the permanent magnets 256
`continuously generate the magnetic field 254.
`In other
`embodiments, electro-magnets (not shown) generate the
`magnetic field 254 by energizing a current source that is
`coupled to the electro-magnets. In one embodiment,
`the
`strength of the magnetic field 254 is between about 50 and
`2000 gauss. After the magnetic field 254 is generated, the
`feed gas from the gas source 208 is supplied to the chamber
`202 by the gas flow control system 210.
`In one embodiment,
`the feed gas is supplied to the
`chamber 202 directly between the cathode 216 and the
`anode 238. Directly injecting the feed gas between the
`cathode 216 and the anode 238 can increase the flow rate of
`
`the gas between the cathode 216 and the anode 238. Increas-
`ing the flow rate of the gas allows longer duration impulses
`and thus, can result in the formation higher density plasmas.
`The flow of the feed gas is discussed further in connection
`with FIG. 3.
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`In one embodiment, the pulsed power supply 234 is a
`component of an ionization source that generates a weakly-
`ionized plasma. The pulsed power supply 234 applies a
`voltage pulse between the cathode 216 and the anode 238.
`In one embodiment, the pulsed power supply 234 applies a
`negative voltage pulse to the cathode 216. The amplitude
`and shape of the voltage pulse are chosen such that a
`weakly-ionized plasma is generated in the region 246
`between the anode 238 and the cathode 216.
`
`The weakly-ionized plasma 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. In one embodiment, the pressure in
`the chamber varies from about 10‘3 to 10 Torr. The peak
`plasma density of the pre-ionized plasma depends on the
`properties of the specific plasma processing system.
`In one embodiment, the pulsed power supply 234 gener-
`ates a low power pulse having an initial voltage of between
`about 100 V and 5 kV with a discharge current of between
`about 0.1A and 100A in order to generate the weakly-ionized
`plasma. In some embodiments the width of the pulse can be
`in on the order of about 0.1 microseconds to about one
`
`hundred seconds. Specific parameters of the pulse are dis-
`cussed herein in more detail.
`
`In one embodiment, the pulsed power supply 234 applies
`a voltage between the cathode 216 and the anode 238 before
`the feed gas is supplied between the cathode 216 and the
`anode 238. In another embodiment, the pulsed power supply
`234 applies a voltage between the cathode 216 and the anode
`238 after the feed gas is supplied between the cathode 216
`and the anode 238.
`
`In one embodiment, a direct current (DC) power supply
`(not shown) is used to generate and maintain the weakly-
`ionized or pre-ionized plasma. In this embodiment, the DC
`power supply is adapted to generate a voltage that is large
`enough to ignite the pre-ionized plasma. In one embodiment,
`the DC power supply generates an initial voltage of several
`kilovolts between the cathode 216 and the anode 238 in
`
`order to generate and maintain the pre-ionized plasma. The
`initial voltage between the cathode 216 and the anode 238
`creates a plasma discharge voltage that is on the order of
`100-1000 V with a discharge current that is on the order of
`0.1 A—100 A.
`
`The direct current required to generate and maintain the
`pre-ionized plasma is a function of the volume of the
`plasma. In addition,
`the current required to generate and
`maintain the pre-ionized plasma is a function of the strength
`of the magnetic field in the region 245. For example, in one
`embodiment, the DC power supply generates a current that
`is between about 1 mA and 100 A depending on the volume
`of the plasma and the strength of the magnetic field in the
`region 245. The DC power supply can be adapted to generate
`and maintain an initial peak voltage between the cathode
`216 and the anode 238 before the introduction of the feed
`gas.
`(AC)
`In another embodiment, an alternating current
`power supply (not shown) is used to generate and maintain
`the weakly-ionized or pre-ionized plasma. For example, the
`weakly-ionized or pre-ionized plasma can be generated and
`maintained using electron cyclotron resonance (ECR),
`capacitively coupled plasma discharge (CCP), or inductively
`coupled plasma (ICP) discharge. An AC power supply 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 can be generated by
`numerous other
`techniques, such as UV radiation
`techniques, X-ray techniques, electron beam techniques, ion
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`US 6,896,775 B2
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`7
`beam techniques, or ionizing filament techniques. In some
`embodiments, the weakly-ionized plasma is formed outside
`of the region 245 and then diffuses into the region, 245.
`Forming a weakly-ionized or pre-ionized plasma substan-
`tially eliminates the probability of establishing a breakdown
`condition in the chamber 202 when high-power pulses are
`applied between the cathode 216 and the anode 238. Uni-
`formly distributing the weakly-ionized or pre-ionized
`plasma over the cathode area results in a more uniform
`strongly ionized plasma when a high power pulse is applied.
`The probability of establishing a breakdown condition is
`substantially eliminated because the weakly-ionized plasma
`has a low-level of ionization that provides electrical con-
`ductivity through the plasma. This conductivity greatly
`reduces or prevents the possibility of a breakdown condition
`when high power is applied to the plasma.
`Once the weakly-ionized plasma is formed, high-power
`pulses are then generated between the cathode 216 and the
`anode 238. In one embodiment, the pulsed power supply 234
`generates the high-power pulses. The desired power level of
`the high-power pulse depends on several factors including
`the nature of the etch process, desired etch rate, density of
`the pre-ionized plasma, and the volume of the plasma. In one
`embodiment, the power level of the high-power pulse is in
`the range of about 1 kW to about 10 MW.
`Each of the high-power