5,045,166
`[11] Patent Number:
`[19]
`United States Patent
`
`Bobbio
`[45] Date of Patent:
`Sep. 3, 1991
`
`[54] MAGNETRON METHOD AND APPARATUS
`E315‘ ggggiglgg Hm“ DENSITY IQNIC
`,
`-
`Inventor.
`Isqtecphen M. Bobbio, Wake Forest,
`'
`'
`_
`[73] Assigneei MCNC’ Research Triangle park,
`N_C_
`
`[75]
`
`'
`
`22
`
`[21] Appit No; 526,572
`.
`M 21, 1990
`F1 d:
`ay
`le
`Int. CL5 ...................... .. B01J 19/12; HOIH 1/46;
`C23F 4/04; C23C 14/35
`
`]
`[
`[51]
`
`U.S. C]. ........................ ..
`204/298.06; 204/298.16; 204/298.37;
`209298.38; 118/723: 156/345: 156/643
`[53] Field Of Search .................... .. 204/192.12, 192.32,
`204/298.06, 298.16, 298.37, 298.38; 156/345,
`643; 118/723
`
`[56]
`
`_
`Refe"""°°5 Clted
`-
`U.S. PATENT DOCUMENTS
`
`FOREIGN PATENT DOCUMENTS
`0027553 10/1979 European Pat. Off.
`204/192.25
`0162643
`5/1984 European Pat. Off.
`..... .. 204/298.19
`0163445
`5/1984 European Pat. Off.
`..... .. 204/298.18
`3434698
`4/1986 Fed. Rep. of
`204/298.19
`Germany .... ..
`
`8/1986 Switzerland ....... ..
`.. 204/298.19
`9/1982 United Kingdom ......... .. 204/298.19
`
`CH657381
`2093866
`
`OTHER PUBLICATIONS
`Thin Film Processes, Cylindrical Magnetron Sputtering
`’
`.
`J. A. Thornton and A. S. Penfold, Academic Press,
`Inc., 1978, PD. 76-113.
`Silicon Processing for the VLSI Era, Dry Etching for
`Fabficatign,
`and R’ N‘ Tauber,
`533.535
`“MCNC Technical Bulletin’’, Plasma Etching, s. M.
`Bobbie and Y. 5. HO’ Jui._Aug., 1986’ pp. 2 and 8.
`-
`
`Primary Examiner-—Aaron Weisstuch
`Aztorney, Agent, or Firm—Be1l, Seltzer, Park & Gibson,
`P-A-
`
`[57]
`
`ABSTRACT
`
`.
`A method and apparatus for magnetron gas discharge
`processing of Substrates using 8 remote plasma Source
`provides a uniform magnetic field (B) created across the
`suffacg of a substrate in an evacuable chamber_ An
`electric field (E) is created perpendicular to the sub-
`strate by an electrically powered. cathode located be-
`_“°a‘h ‘h"—,5“b5“‘“e- The mag“e“° and elecmc 59195
`lmofaot W}th the Plasma to Create an EX 3 olo-Ctron drift
`region adjacent to the surface of a substrate. A remote
`plasma source is provided and oriented so that
`the
`plasma stream from the remote source is coupled to the
`EXB region adjacent to the substrate surface parallel to
`the magnetic field with minimal movement of the
`plasma stream perpendicular to the magnetic field to
`.
`.
`.
`-
`thereby provide a high density plasma stream into the
`EXB drifl 19830”
`
`.............. .. 204/192.15
`204/298.06
`204/i92_i2
`. . . .. 204/192.13
`204/298.06
`
`. . . ..
`
`3,627,663 12/1971 Davidse et al.
`3,654,123
`4/1972 Hajzak .......... ..
`3,860,507
`1/1975 Vossen,Jr..
`4,155,825
`5/1979 Foumier . . . . . . . . .
`4,175,029 11/1979 Kovalsky et al
`4,198,283
`C1388 CI 8.1.
`. . . . . . . .
`2041;
`ggifiizgttfi "
`156/643
`9/1982 Shibayama et at
`4,349,409
`. 204/298.26
`9/1982 Kuriyama ..............
`4,351,714
`4,352,725 10/1982 Tsukada ................. .. 156/643
`4,351_472 11/1932 Morrison, in .
`_ 204/19112
`4,361,749 11/1982 Lord .................... .. 219/121.4
`4,362,611 12/1982 Logan et a1.
`. . . . . . .
`. . . .. 204/298.06
`4,359,205
`1/1933 Winterliflg 6! 31-
`---------- -- 427/39
`4,392,932
`7/1983 Harra .................... .. 204/192.32
`43991016
`8/1983 Twkada e‘ 31'
`"" " 156/643
`4,404,077
`9/1983 Foumier . . . . . . . .
`. . . .. 204/192
`£417,968 11/1983 Mcxeivey “
`_ 204/19212
`4,422,896 12/1983 Class et al.
`........................ .. 156/643
`4,426,267
`1/1984 Miinz et a1.
`.................. .. 204/192.12
`
`
`
`(List continued on next page-)
`
`52 Claims, 6 Drawing Sheets
`
`
`
`GILLETTE 1110
`
`GILLETTE 1110
`
`

`
`Page 2
`
`5,045,166
`
`................... .. 204/298.16
`4,581,118 4/1986 Class et a1.
`4,588,490
`5/1986 Cuomo et a1.
`......... .. 204/298.06
`4_609,42g
`9/1935 Fujimura , . , , , , .
`. . . .. 156/643
`4,610,770
`9/1986 Saito eta1..
`.204/192.1
`$624,757 11/1936 obinata ........................ .. 204/298.37
`4,657,619
`4/1987 O'Donnell ......................... .. 156/345
`4,668,338
`5/1987 Maydan et a1.
`156/643
`4,738,761
`4/1988 Bobbio etal..
`204/192.12
`4,778,561 10/1988 Ghanbari
`.......................... .. 156/643
`4,842,683
`6/1989 Cheng et a1.
`...................... .. 156/345
`4,885,068 12/1989 Uramoto et a1.
`............. .. 204/192.11
`
`
`
`
`
`U-3 PATENT DOCUMENTS
`4,427,524
`1/1984 Crombeeneta1- ---------- -~ 204/293-06
`4,428,816
`1/1984 Class etal. ....... ..
`.204/298.18
`4.434038
`2/1984 Morrison,Jr-
`-204/192-15
`4,464,223
`8/1984 Gorin ................................ .. 156/643
`4.465,s75
`8/1984 Love et a1.
`..
`.......... ..2o4/192.26
`4,472,259 9/1984 Class et a1.
`.... ..
`.204/298.18
`4,492,620
`1/1985 Matsuo etal. ..
`,2o4/192.12
`4,525,262
`6/1985 Class et al.
`..
`.204/192.12
`4,526,643
`7/1985 Okano eta1.
`.... .. 156/345
`4,572,759
`2/1986 Benzing ............................. .. 156/345
`
`
`
`

`
`U.S. Patent
`
`Sep. 3, 1991
`
`Sheet 1 of 6
`
`5,045,166
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`Sep. 3, 1991
`
`Sheet 2 of 6
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`

`
`U.S. Patent
`
`Sep. 3, 1991
`
`Sheet 3 of 6
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`5,045,166
`
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`Sep. 3, 1991
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`
`U.S. Patent
`
`Sep. 3, 1991
`
`Sheet 5 of 6
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`5,045,166
`
`53
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`
`Sep. 3, 1991
`
`Sheet 6 of 6
`
`5,045,166
`
` U.S.Patent
`
`

`
`1
`
`5,045,166
`
`MAGNETRON METHOD AND APPARATUS FOR
`PRODUCING HIGH DENSITY IONIC GAS
`DISCHARGE
`
`FIELD OF THE INVENTION
`
`This invention relates to magnetrons for processing
`semiconductor or other substrates and more particu-
`larly to a method and apparatus for producing a high
`density ionic gas discharge in a magnetron.
`BACKGROUND OF THE INVENTION
`
`Plasma etching, deposition, and other processing
`techniques using a magnetron to contain the plasma
`above a substrate are well known to those having skill in
`the microelectronic device fabrication art. In a typical
`magnetron, magnetic confinement of a low pressure
`radio frequency (RF) ionic discharge is used to generate
`a high density plasma in order to expose a substrate to
`an ionic flux. As is well known to those having skill in
`the art, a magnetron may be employed to increase the
`ionic flux density, at a given plasma sheath voltage
`(defined below), to produce an anisotropic (directional)
`etch of a pattern into a substrate resulting in minimal
`undercutting and minimal unwanted enlargement of the
`etch pattern. The plasma sheath voltage is the electric
`potential that develops in the area between the substrate
`and the plasma. Electrons are largely excluded from
`this area due to the force exerted on the electrons by the
`electric field.
`
`Magnetrons may also be used to deposit materials
`onto a substrate by exposing a material to be deposited
`to the high ionic flux. The substrate is placed outside of
`the region of intense flux such that the atoms and mole-
`cules ejected from the target material by the ionic flux,
`condense upon the substrate to be processed.
`In order to efficiently process a substrate at a high
`rate without causing unwanted damage to the substrate,
`it is important that a high density plasma be developed,
`at low plasma sheath voltage. A high plasma density is
`necessary so that large numbers of ionic species can
`strike the substrate to process the substrate at an accept-
`able rate of production. Low sheath voltage is required
`so that the energy of the impinging ions is sufficiently
`low to restrict the effects of the impinging ions close to
`the substrate surface where material removal (etching)
`or build up (deposition) occurs. Higher energy ions
`impinge the surface and distribute excess energy to a
`greater depth in the substrate. This excess energy is
`ineffective for the etching or deposition processes and is
`undesirable since it results in the production of un-
`wanted heat and substrate damage. Even in cases where
`the chemical activation energy for etching of the sub-
`strate being processed is typically less than one electron
`volt (eV), conventional etching devices must use ener-
`gies on the order of many hundreds of eV in order to
`have sufficient ion current across the plasma sheath for
`useful etch rates. This higher ion energy produces un-
`wanted heat and substrate damage.
`The magnetron configuration attempts to obtain high
`ionic density at a low plasma sheath voltage by using a
`magnetic field to increase the density of electrons that
`_ cause ionizing collisions in the region above the sub-
`strate to be processed. In a typical magnetron, a mag-
`netic field (B) is produced parallel to the substrate sur-
`face. This parallel magnetic field reduces the mobility of
`electrons to the surface of the substrate. An electric
`field (E)is produced perpendicular to the substrate sur-
`
`10
`
`15
`
`20
`
`25
`
`30
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`35
`
`40
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`45
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`50
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`55
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`60
`
`65
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`2
`face (and therefore perpendicular to the magnetic field)
`by energizing a cathode below the substrate, thereby
`creating a plasma sheath. The combined effect of the E
`and B fields produces an electron drift velocity de-
`scribed by the cross product of the electric field and
`magnetic field vectors (EX B). Accordingly, the region
`in which the electrons are confined, and therefore the
`ionic concentration is greatest,
`is known as the EXB
`drift region.
`A remote plasma source or generator is desirable to
`increase plasma density in the E><B region,
`thereby
`increasing the processing rate. With a remote plasma
`source, the cathode requires a lower power input to
`create a large flux of ions to impinge the substrate sur-
`face. The cathode need only be biased to create an
`electric field perpendicular to the substrate surface in
`order to create an E><B electron drift region. The
`sheath voltage, and hence the electric field in the re-
`gion, may be independently adjusted to produce the
`desired ion flux energy for a particular processing oper-
`ation.
`The art has attempted to couple remote sources to a
`substrate surface through various techniques. In U.S.
`Pat. No. 4,738,761, to Bobbio et al., and assigned to the
`assignee of the present
`invention, coupling of the
`plasma between the split cathode source and the sub-
`strate is accomplished through a continuous sheath
`voltage region. Therefore, the EXB electron drift ve-
`locity allows the electrons to move in a continuous
`closed path above the substrate surface and below the
`cathode surface, thereby creating a high density plasma
`in the region above the substrate.
`In U.S. Pat. No. 4,588.’-190 to Cuoumo et al., the re-
`mote source penetrates the wall of the chamber and is
`disposed above and to one side of the magnetron target.
`The plasma stream emanating from the remote source is
`transported to the substrate surface across magnetic
`field lines.
`
`Notwithstanding the above described attempts to
`improve magnetron performance, and in particular to
`improve coupling of remote plasma sources, present
`magnetrons are still limited as to the ionic flux density
`which can be achieved for a given energy imparted
`from the ionic flux to the substrate surface. Accord-
`ingly, high energy plasma must be used to achieve use-
`ful etch or deposition rates, thereby resulting in sub-
`strate damage and other unwanted effects, or slower
`processing rates must be tolerated to avoid substrate
`damage.
`
`SUMMARY OF THE INVENTION
`
`It is therefore an object of the present invention to
`provide a magnetron method .and apparatus which pro-
`duces a high plasma density gas discharge near the
`surface of a substrate.
`It
`is another object of the invention toprovide a
`magnetron method and apparatus for producing a high
`plasma density gas discharge near the substrate surface
`with low plasma sheath voltage to thereby reduce sub-
`strate damage and other unwanted effects while still
`providing processing rates that are suitable for practical
`use.
`
`It is still another object of the invention to efficiently
`couple a plasma stream from a remote source to the
`EXB drift region in a magnetron.
`These and other objects are provided according to
`the present invention by a method and apparatus for
`
`

`
`5,045,166
`
`3
`efficiently coupling a plasma stream from a remote
`plasma generator to the substrate surface in a magne-
`tron having a magnetic field (B) parallel to the substrate
`surface and an electric field (E) perpendicular thereto,
`to produce an EXB electron drift region above the 5
`substrate surface. The remote plasma generator is lo-
`cated outside the EX B drift region and is oriented rela-
`tive to the magnetic field,
`to transport
`the plasma
`stream into the EXB drift region parallel to the mag-
`netic field with minimal movement of the plasma stream
`across magnetic field lines. A low cathode voltage may
`thereby be used to create an electric field perpendicular
`to the substrate and to extract the ions at low energy.
`Known cathodes, such as flat plate cathodes, hollow
`oval cathodes, or split cathodes may be used at low
`cathode voltages.
`It has been found, according to the invention, that
`prior art magnetrons using remote sources, such as the
`Cuoumo et al. patent described above, were unable to
`achieve desired processing rates or extract ions at low
`energy because ionic flux density could not be increased
`without a corresponding increase in substrate damage.
`To couple the plasma stream from the source to the
`E X B drift region, the prior art required that the plasma
`from the remote source move across, or perpendicular
`to, the magnetic field lines. Such movement across mag-
`netic field lines is inefficient due to its dependence on
`gas-phase scattering to couple the plasma stream to the
`E X B region.
`The present invention overcomes these problems by
`transporting plasma from the remote source to the
`EXB drift region, substantially along magnetic field
`lines. For example, a uniform magnetic field may be
`generated parallel to the surface of the substrate with
`the EXB drift region also being above the surface and
`parallel thereto. The plasma generated by the remote
`source is transported to the EXB electron drift region
`above the surface of the substrate along the uniform
`parallel magnetic field lines.
`In a preferred embodiment of the present invention,
`the magnetic field is provided by first and second per-
`manent magnets of opposite polarity located at opposite
`ends of a substrate. The plasma stream generator is
`located remote from the substrate and positioned to
`provide a plasma stream parallel to the magnetic field
`and parallel to the surface of the substrate to be pro-
`cessed. An electron cyclotron resonance (ECR) source,
`a hollow cathode source, a radio frequency powered
`inductively coupled quartz tube plasma source, or other
`plasma source may be employed and may be positioned
`to provide a plasma stream parallel to the surface of the
`substrate.
`
`10
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`4
`along with the reactive gas fed into the chamber, for a
`particular application. The use of multiple source and
`independent control of process gases and energy may
`permit the processing of substrates having substantially
`greater surface area than substrates that current magne-
`trons can efficiently and uniformly process.
`The plasma stream sources may also be located out-
`side the planar magnets in which case at least one of the
`planar magnets may include a passageway, such as a
`slot, to allow passage of the plasma stream from the
`source located outside the pair of permanent magnets to
`the substrate parallel to the magnetic field direction.
`The slot and magnet may be configured to provide a
`uniform magnetic field at the substrate surface. Electro-
`magnets or permanent magnets may be used to shape
`the plasma stream prior to its entering the slot in the
`planar magnet.
`According to the invention, a high density plasma at
`low plasma sheath voltage may created in the EXB
`region by the efficient coupling of a remote plasma
`source along, rather than across, magnetic field lines.
`The substrate may then be processed with minimal
`substrate damage and at a useful processing rate.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`1 is a simplified schematic diagram of the
`FIG.
`plasma coupling configuration of the present invention.
`FIG. 2 is a side perspective view of a first embodi-
`ment ofa magnetron discharge processing apparatus of
`the present invention,
`including multiple quartz tube
`remote plasma sources disposed within planar magnets.
`FIG. 3A is a side perspective view of a section of the
`apparatus of FIG. 2.
`'
`FIG. 3B is a detailed View of a single remote quartz
`tube source of FIG. 3A including its mounting arrange-
`ment.
`
`FIG. 4 is a top view of the planar magnet construc-
`tion of FIG. 2.
`
`FIG. 5 is a side perspective view of an alternate em-
`bodiment of the present
`invention with the remote
`source disposed outside the planar magnets.
`FIG. 6 is a side perspective view of another embodi-
`ment ofa magnetron discharge processing apparatus of
`the present
`invention,
`including multiple
`remote
`sources located on opposite ends of an evacuable cham-
`ber.
`
`FIG. 7 is a side perspective view of another embodi-
`ment ofa magnetron discharge processing apparatus of
`the present
`invention,
`including a cathode assembly
`disposed near the bottom of an evacuable chamber.
`FIG. 8 is a simplified schematic diagram of the cou-
`pling scheme of the present invention used in an oval
`cross-section hollow cathode magnetron configuration.
`DESCRIPTION OF THE PREFERRED
`EMBODIMENT
`
`The present invention will now be described more
`fully hereinafter with reference to the accompanying
`drawings, in which a preferred embodiment of the in-
`vention is shown. This invention may, however, be
`embodied in many different forms and should not be
`construed as limited to the embodiment set forth herein;
`rather, this embodiment is provided so that this disclo-
`sure will be thorough and complete, and will fully con-
`vey the scope ofthe invention to those skilled in the art.
`Like numbers refer to like elements throughout.
`FIG. 1 is schematic illustration of the coupling con-
`figuration of the present invention. A remote plasma
`
`50
`
`The permanent magnets may be a pair of planar per-
`manent magnets, perpendicular to the substrate surface
`and parallel to one another, at opposite ends of the 55
`substrate surface, to thereby provide a magnetic field of
`uniform intensity over
`the substrate and parallel
`thereto. The plasma stream source may be located in-
`side the pair of permanent magnets and oriented to
`generate a plasma stream over the substrate and parallel
`to the magnetic field. Multiple sources may be used to
`provide a more uniform and higher density plasma
`above the substrate surface. In addition, each of the
`multiple sources may be coupled to a separate reactive
`gas source and the input energy of each source may be
`independently controlled. Therefore,
`the chemical
`makeup of the reactive ionic discharge and the dis-
`charge energy from each source may be customized,
`
`65
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`

`
`5,045,166
`
`6
`
`5
`source, or sources 30, are disposed to generate the
`plasma stream 40 parallel with the magnetic field (B)
`lines 34 above the substrate 32 to be processed. The
`cathode 35, upon which the substrate 32 is disposed, is
`powered by a remote electrical energy source, not
`shown, to create an electric field (E) 33 perpendicular
`to the substrate surface 32 and to extract ions in a direc-
`
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`tion to impinge the substrate 32 causing the etching
`process to occur. As is well known to those skilled in
`the art, the cathode may be powered by electrical en-
`ergy in a wide frequency range, for example, a range
`from direct current to thirty megahertz has been used in
`prior art magnetrons. The cathode 35 may function as a
`substrate holder, or a separate substrate holder, not
`shown, may be provided.
`The magnetic field lines 34 and the electric field 33
`created by the cathode 35 interact to create an EXB
`electron drift region 31 in the direction of the cross
`product of the electric and magnetic fields. The plasma
`40 emitted by the source, or sources 30. is contained in
`the EXB region 31 while the electrons are confined in
`circulating patterns 42 above the substrate 32 and which
`may,
`in certain magnetron configurations, continue
`below the cathode 35. It will be understood to one
`skilled in the art to substitute a non-closed loop system
`for the closed loop electron circulating pattern 42 in
`order to reduce the mechanical complexity of the oath-
`ode connections and suspension system. It will also be
`understood by those having skill
`in the art that the
`EX B region 31 does not end abruptly as shown in FIG.
`1, but rather the plasma density gradually decreases
`near the boundaries shown.
`the remote source, or
`According to the invention,
`sources 30, are disposed to transport the plasma stream
`40 into the EXB region 31 above the substrate 32 so
`that
`the plasma stream need not traverse across the
`magnetic field lines 34. The height of the EXB drift
`region 31 above the area of the substrate 32 is deter-
`mined primarily by the strengths of the electric (E) 33
`and magnetic fields (B) 34. The electric field (E)
`strength is a function of the voltage developed in the
`area between the substrate and the plasma wherein the
`electrons are largely excluded, also known as the
`plasma sheath voltage. For a typical sheath voltage
`used in reactive ion etching, between l0 and 200 volts,
`this EXB region 31 begins essentially at the surface of
`the substrate 32. For a typical magnetic field (B) 34 of
`two hundred gauss, this region extends upwards for a
`distance of about 4 millimeters above the substrate 32.
`The remote source 30 is preferably disposed such that
`the maximum quantity of the disgorged plasma inter- ’
`sects the EX B drift region 31. It is understood that one
`skilled in the art could vary the emitting aperture of the
`remote source, or sources 30, or employ a plasma
`stream shaping means, such as permanent magnets or
`electromagnets,
`to further concentrate the plasma
`stream to provide greater coupling of the plasma stream
`into the EXB drift region 31.
`The use of a remote source 30 in the present invention
`allows a lower power to be applied to the cathode 35
`compared to heretofore available magnetrons. This
`lowering of the cathode power consequently reduces
`unwanted heat and damage to the substrate 32. Trans-
`porting the plasma stream 40 into a parallel magnetic
`field 34 above the substrate 32 results in greater cou-
`pling efficiency of the source to the EXB region 31.
`The greater coupling efficiency yields a higher plasma
`density above the substrate surface 32, allowing for
`
`50
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`55
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`60
`
`65
`
`greater throughput for the processing operation. Be-
`cause the plasma stream 40 is transported into a parallel
`magnetic field (B) 34 according to the invention, the
`source need not be placed so close to the edge of the
`substrate so as to become a physical or electrical barrier
`to the EXB drift region 31, nor need the source be
`placed such that its plasma stream must cross perpen-
`dicular to magnetic field lines 34 as in previous magne-
`tron designs.
`FIG. 2 is a side perspective view of a first embodi-
`ment of a magnetron discharge processing apparatus 56
`according to the present invention. One or more remote
`plasma sources 50 are disposed between the planar mag-
`nets 55A, 55B to disgorge plasma 53 into the EX B drift
`region 67 along magnetic field lines 60 parallel to the
`substrate surface 65. A conventional gas tight evacuable
`chamber 52 is shown disposed within a mounting sup-
`port and flux return 57 for the permanent planar mag-
`nets 55A, 55B. The flux return confines and intensifies
`the magnetic field between planar magnets 55A and
`55B. The chamber 52 may also contain one or more
`viewing or diagnostic ports 54 and an access hatch 58.
`A cathode 70, with external radio frequency connec-
`tions not shown, is disposed within the chamber 52 and
`may be secured by mounting on insulating frames 66A,
`66B attached to the chamber 52 side walls. It would be
`known to one skilled in the art to substitute conductive
`non-magnetic "wings" energized at the cathode poten-
`tial and extending above the surface of the substrate 65
`in place of the insulating frames 66A, 66B for further
`electrostatic confinement of the plasma stream in the
`EX B region 67 above the surface of the substrate 65. It
`would also be known to one skilled in the art to create
`
`an opening in the wing 66A nearest the source to allow
`the plasma to flow into the EX B region 67. The action
`of the “wings" and their use in plasma confinement is
`more fully described in J. Thornton and A. Penfold,
`Chapter 2 “Cylindrical Magnetron Sputtering" of F.
`Vossen and W. Kern, “Thin Film Processes," Aca-
`demic Press (1978) the disclosure of which is hereby
`incorporated herein by reference.
`A semiconductor wafer 65 or other substrate to be
`
`processed is supported by or rests upon the top of the
`cathode assembly 70. The cathode 70 may have a top
`surface which includes one or more recesses, to hold
`one or more substrates 65 thereon. A flat top cathode
`surface may also function as a substrate holder. A dis-
`crete substrate holder, separate from the cathode, may
`also be provided. For additional substrate and cathode
`cooling, the cathode 70 may contain circuitous cooling
`channels 64 for the circulation of a cooling fluid.
`Referring to FIGS. 3A and 3B, an assembly of remote
`plasma sources, in this embodiment three quartz tube
`plasma sources 50, are mounted on the large side flange
`51 of a wall of the chamber 52. The quartz tube source
`is an inexpensive source that also yields a high plasma
`density. The quartz tube source is more fully described
`in R. W. Boswell, A. J. Perry, and M. Emami, “Multi-
`pole Confined Diffusion Plasma Produced by 13.56
`MHZ Electrodeless Source," Journal of Vacuum Science
`Technology, Vol. 7, No. 6. pp. 3345-3350, November/-
`December l989 the disclosure of which is hereby incor-
`porated herein by reference. Each quartz tube source 50
`- is physically mounted to the side flange 51 by the use of
`a compression flange 68 in conjunction with a sealing
`“O” ring 69 to ensure integrity of the evacuable cham-
`ber. The compression flange 68 is secured to the side
`flange 51 by screws 63 or other suitable securing means.
`
`

`
`7
`Radio frequency energy from a source, not shown, is
`fed to the individual plasma sources 50 through induc-
`tive couplings 58 surrounding the quartz tubes 61 of the
`sources. The reactive gas is fed through tubing 59 to the
`quartz tube 61 of the source 50. The RF energy in com-
`bination with the reactive gas produces a stream of
`plasma 53 which disgorges through the opening 62 in
`the side flange 51. It will be understood by those having
`skill in the art that each plasma source may be individu-
`ally controlled as to the RF energy and the reactive gas
`parameters, including the chemical makeup and flow
`rate of the gases. Alternatively, groups of sources may
`be controlled together or all of the sources may be
`controlled as a unit. Substrate processing flexibility is
`thereby provided.
`Referring to FIGS. 2 and 3B, the sources 50 are posi-
`tioned to disgorge their plasma stream 53 through the
`chamber wall opening 62 and into the EXB electron
`drift region 67 above the wafer surface 65. For a typical
`plasma sheath voltage and magnetic field strength used
`in reactive ion etching, for example 100 volts and 200
`gauss respectively, this EXB region 67 begins at about
`the top surface of the substrate 65 and extends vertically
`for a distance of about 4 millimeters above the top sur-
`face of the substrate 65. Coupling of the source 50 to the
`EXB region is enhanced if the source 50 is vertically
`aligned to provide maximum overlap of the disgorging
`plasma stream 53 with the EXB region 67 height. It is
`readily apparent for one skilled in the art to use a single
`or multiple remote sources. In addition, it would also be
`apparent to one skilled in the art to substitute an elec-
`tron cyclotron resonance source, such as disclosed in
`U.S. Pat. No. 4,778,561 to Ghanbari, or a hollow cath-
`ode source as described in U.S. Pat. No. 4,588,490 to
`Cuomo et al., (the disclosures of which are hereby in-
`corporated herein by reference) or other plasma source
`in place of the quartz tube sources shown in the FIGS.
`2, 3A and 3B.
`Referring to FIGS. 2 and 4, planar magnets 55A, 55B
`are disposed within a mounting support and magnetic
`flux return 57 on either side of the evacuable chamber
`52 to provide a North pole at one side of the chamber
`and a South pole at the opposing side of the chamber.
`The construction of the planar magnets 55A, 55B in-
`cludes a brick construction arrangement of individual
`alnico magnet blocks 54. Permanent magnets are illus-
`trated in the preferred embodiment because they are
`capable of generating a sufficiently uniform and high
`strength magnetic field (for example, 200 gauss) over
`the substrate surface 65. It would be readily apparent
`for one skilled in the art to substitute electromagnets,
`also referred to as Helmhotz coils, for the permanent
`planar magnets. Known commercially available elec-
`tromagnets typically contain an air core in order to
`produce a uniform field and, therefore, produce a lower
`field strength (for example, 60 gauss) above the sub-
`strate 65.
`
`An alternative embodiment of the present invention is
`shown in FIG. 5. This embodiment includes a remote
`ECR source 75 external to the planar magnet 55 cou-
`pled to the evacuable chamber 52 by a tube 81 or other
`evacuable passageway.
`It would be known to one
`skilled in the art to substitute alternative sources for the
`ECR source. Such a source may be a hollow cathode
`plasma generator, a quartz tube source, or another type
`of plasma source. It would also be known to one skilled
`in the art to use single or multiple sources to attain the
`desired plasma density over the substrate surface 65
`
`5
`
`l0
`
`l5
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`5,045,166
`
`8
`using single or multiple passageways. An opening or
`slot 82 is positioned in the planar magnet 55 to allow the
`plasma stream 53 to travel from the remote source 75 to
`the substrate surface 65 along a path parallel
`to the
`magnetic field lines 60. Stream shaping means 80 may be
`disposed between the remote source 75 and the planar
`magnet 55 to shape the plasma stream 53 for maximum
`coupling to the substrate surface 65. Such shaping
`means 80 may be either in the form of permanent mag-
`nets or electromagnets as would be readily apparent to
`on skilled in the art.
`
`Another alternative embodiment of the present in-
`vention is shown in FIG. 6. This embodiment includes
`remote quartz tube plasma sources 50A. 50B coupled to
`both opposing walls of the evacuable chamber 52. The
`plasma discharge 53A is coupled to the substrate surface
`65 from the source located nearer the planar magnet
`55A and in the same direction as the magnetic field lines
`60. Similarly, the plasma discharge 53B from the source
`50B nearer the planar magnet 55B is coupled along the
`magnetic field lines 60, but in the opposite direction
`from the magnetic field lines 60.
`FIG. 7 illustrates another alternative embodiment of
`the present invention wherein the cathode 70 is sup-
`ported on an insulator 72 resting upon the bottom ofthe
`evacuable chamber 52. This embodiment is a mechani-
`cally simpler system to implement, not requiring sus-
`pension of the cathode 70 and substrate 65, than a sys-
`tem allowing the electron current loops to continue
`below the cathode surface as illustrated by the electron
`paths 42 in FIG. 1. Cooling fluid connections, electrical
`power connection to the cathode, and automated sub-
`strate manipulation mechanisms are simplified by posi-
`tioning the substrate 65 near the bottom of the evacu-
`able chamber 52.
`
`FIG. 8 illustrates an embodiment of the present in-
`vention adapted to the hollow oval magnetron structure
`of the type described in Lin I and Ming-Shing Wu,
`“Hollow Oval Magnetron for Large-Area Low-Energy
`Ions,” Journal ofApplied Physics, vol. 60, No. 6, Sept. 15,
`1986, the disclosure of which is hereby incorporated
`herein by reference. The device consists of a main hol-
`low cathode 36 with an oval cross-section inner surface
`and two grounded electrodes 39A, 39B disposed at
`either end, and insulated from, the main hollow cathode
`36. A passageway 38 is made in the grounded electrode
`39A nearer the remote plasma source 30 to allow the
`plasma stream 40 to travel along the parallel magnetic
`field lines 34 to the Ex B region within the body of the
`main cathode 36. Due to the configuration of the de-
`vice, the Ex B region 31 forms in a loop conformal to
`the inner surface of the hollow cathode 36. The sub-
`strate 65 to be proce