United States Patent
`Smolanoff et al.
`
`19
`
`54 METHOD AND APPARATUS FOR
`INCREASING THE METALION FRACTION
`IN ONIZED PHYSICAL VAPOR
`DEPOSITION
`
`75 Inventors: Jason Smolanoff, Jefferson Valley,
`N.Y.; Doug Caldwell, McKinney, Tex.;
`Jim Zilbrida, Glendale, Ariz., Bruce
`Gittleman, Gilbert, Ariz., Thomas J.
`Licata, St. Mesa, Ariz.
`73 Assignee: Tokyo Electron Limited, Tokyo, Japan
`
`21 Appl. No.: 09/190,515
`1-1.
`22 Filed:
`Nov. 12, 1998
`(51) Int. Cl." ...................................................... D06F 29/00
`52 U.S. Cl. ................................ 204/192.12; 204/298.06;
`204/298.08; 204/298.11
`58 Field of Search .......................... 204298.08, 298.11
`204/298 06 192 15
`\ \/3
`
`56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`204/298.34
`5,556,501 9/1996 Collins et all
`5,665.167 9/1997 Deguchi et al.". ... 315/111.21
`5,800,688 9/1998 Lansman et al... 204/298.06
`FOREIGN PATENT DOCUMENTS
`O 801 413 A1 10/1997 European Pat. Off. ......... HO1J 37/32
`
`USOO6117279A
`Patent Number:
`11
`(45) Date of Patent:
`
`6,117,279
`Sep. 12, 2000
`
`OTHER PUBLICATIONS
`
`European Patent Office, PCT Search Report, PCT Applica
`tion No. PCT/IB99/O1764.
`
`Primary Examiner Nam Nguyen
`Assistant Examiner Steven H. VerSteeg
`Attorney, Agent, or Firm Wood, Herron & Evans, L.L.P.
`57
`ABSTRACT
`An ionized physical vapor deposition method and apparatus
`are provided which employs a magnetron magnetic field
`produced by cathode magnet Structure behind a Sputtering
`target to produce a main Sputtering plasma, and an RF
`inductively coupled field produced by an RF coil outside of
`and Surrounding the vacuum of the chamber to produce a
`Secondary plasma in the chamber between the target and a
`Substrate to ionize Sputtered material passing from the target
`to the Substrate So that the Sputtered material can be elec
`trically or magnetically Steered to arrive at the Substrate at
`right angles. A circumferentially interrupted Shield or shield
`Structure in the chamber protects the window from material
`deposits. A low pass LC filter circuit allows the shield to
`float relative to the RF voltage but to dissipate DC potential
`on the Shield. Advantages provided are that loSS of electrons
`and ions from the Secondary plasma is prevented, preserving
`plasma density and providing high ionization fraction of the
`Sputtered material arriving at the Substrate.
`
`14 Claims, 2 Drawing Sheets
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`U.S. Patent
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`Sep. 12, 2000
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`Sheet 1 of 2
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`U.S. Patent
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`Sep. 12, 2000
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`Sheet 2 of 2
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`6,117,279
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`1
`METHOD AND APPARATUS FOR
`INCREASING THE METALION FRACTION
`IN ONIZED PHYSICAL VAPOR
`DEPOSITION
`
`This invention relates to Sputter coating, and more
`particularly, to the Ionized Physical Vapor Deposition
`(IPVD) of coating material onto substrates.
`BACKGROUND OF THE INVENTION
`Smaller and higher aspect ratio features, Such as Vias,
`trenches and contact holes, in Semiconductor manufacturing
`impose greater requirements on Semiconductor processing
`equipment. For example, coating contacts on the bottoms of
`Such features with liners and filling the features with con
`ductive films using certain preferred physical vapor depo
`sition (PVD) processes requires the achievement of a high
`degree of directionality in movement of the material being
`deposited toward the Substrate. Smaller and higher aspect
`ratio features require greater directionality. To effectively
`coat contacts, for example, on the bottoms of narrow high
`aspect ratio holes on the Surface of a Substrate, it is necessary
`for the particles of coating material to move at angles to the
`normal that are not Substantially larger than the angular
`openings of the features. Otherwise, excessive deposits on
`the upper Sides of the features or a closing of the mouth of
`a feature will result.
`A Sputter coating process is typically carried out by
`placing a Substrate and a target of high purity coating
`material into a vacuum chamber filled with an inert gas Such
`as argon or a reactive gas Such as nitrogen and creating a
`plasma in the gas. The plasma is typically generated by
`maintaining the target, either constantly or intermittently, at
`a negative potential, So that the target functions as a cathode
`to Supply electrons that eXcite the gas in the chamber and
`form a plasma adjacent to the target Surface. The plasma
`generation is usually enhanced with a magnetron cathode
`assembly in which magnets behind the target trap electrons
`at high density over the Surface of the target where they
`collide with atoms of the proceSS gas, Stripping electrons
`from atoms of gas to produce positive ions. The gas ions
`accelerate toward the target, which is negatively biased, to
`collide with the target Surface and eject from the target
`Surface atoms and atomic clusters or particles of target
`material, as well as Secondary electrons, which play a role in
`Sustaining the plasma.
`In conventional Sputter coating, the large majority of the
`ejected atoms of target material are neutral in charge and
`propagate through the vacuum space in various directions
`with Some Striking the Substrate, to which they adhere to
`form a film. The directions of travel of the ejected particles
`from the target Surface follow a Somewhat broad Statistical
`distribution of angles to the target Surface. Various Schemes
`have been used to cause the propagating particles to move in
`Straighter lines toward and normal to the Substrate Surface.
`In Ionized Physical Vapor Deposition or IPVD, coating
`material is Sputtered from a target using magnetron
`Sputtering, other conventional Sputtering or evaporation
`techniques, and then the directionality of the particles is
`improved by ionizing the particles So that they can be
`electroStatically accelerated or otherwise electrically Steered
`in a direction toward and normal to the Substrate.
`In IPVD, additional or secondary plasma is created in the
`Space within the chamber between the target or Source of the
`material and the Substrate. The particles of Sputtered mate
`rial passing through this space collide with electrons or
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`metastable neutrals of the ionized process gas, which tend to
`Strip electrons from the atoms of the Sputtered particles
`leaving the particles positively charged. Those positive ions
`of Sputtered material that are positively charged are capable
`of being electrically accelerated toward the Substrate, for
`example, by application of a negative bias to the Substrate.
`The effectiveness of the IPVD process in normalizing the
`direction of coating particles at the Substrate is proportional
`to the fraction of ionization of the Sputtered material pro
`duced by the Secondary plasma.
`Obtaining a high ion fraction of Sputtered material
`requires the Secondary plasma to have a high electron
`density. LOSS of electrons from the Secondary plasma into
`the main plasma at the target, or into chamber Structure Such
`as walls or shields, can cause a Substantial reduction in the
`effectiveness of the Secondary plasma to ionize Sputtered
`material and can result in the extinguishing of the Secondary
`plasma. It is important to minimize the depletion of electrons
`from the Secondary plasma and to otherwise produce a high
`ionization fraction of sputtered material in IPVD processing.
`In addition, Structure Such as walls or shields that bound
`a Secondary plasma is in direct contact with the Secondary
`plasma in a region called the sheath. The sheath width
`depends in part on the potential difference between the
`Secondary plasma and this Structure. Where the Structure is
`electrically grounded, the typical sheath width is a few
`electron Debye lengths of about 0.14 mm, for example,
`where the electron density and temperature are about 10'
`cm and 4 volts, respectively. However, if a negative DC
`potential is allowed to exist on this structure, it has the effect
`of attracting positive ions from the plasma due to an increase
`in the width of the plasmasheath, which thereby reduces the
`effectiveness of the plasma in producing a high ion fraction
`of the Sputtered material. Where it is necessary to facilitate
`the coupling of energy into the Secondary plasma, Such as
`from a peripheral coil to form an inductively coupled
`plasma, the plasma Surrounding Shields and other Structure
`are electrically floating, which increases the tendency for
`electrons, which have a higher Velocity than the positive ions
`in the plasma, to build up a negative DC charge on the shield
`or other Structure. This causes the plasma sheath to encroach
`into the Space desired for the Secondary plasma.
`Accordingly, there is a need for an IPVD apparatus and
`method that will provide a high ionization fraction of
`Sputtered material, and particularly that will minimize the
`loSS of electrons from the plasma that is provided for
`Sputtered material ionization. Further, there is a need for an
`IPVD apparatus and method that will provide a high ion
`ization fraction of Sputtered material, particularly by avoid
`ing an extension of the plasma sheath that Surrounds the
`plasma provided for Sputtered material ionization into the
`Space of the Secondary plasma.
`SUMMARY OF THE INVENTION
`A primary objective of the present invention is to provide
`a method and apparatus by which a high ionization fraction
`of Sputtered material is achieved in ionized physical vapor
`deposition. A particular objective of the present invention is
`to provide Such a method and apparatus in which the loSS of
`charged particles from a plasma that is provided for coating
`material ionization is minimized or reduced.
`A further objective of the present invention is to provide
`an ionized physical vapor deposition apparatus and method
`in which the components are configured and operated to
`prevent adverse affects on electro-magnetic fields within the
`region occupied by the plasma provided to ionize the coating
`material.
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`A further objective of the present invention is to provide
`a method and apparatus for ionized physical vapor deposi
`tion that utilizes a magnetron magnetic field Source to
`provide a main plasma for Sputtering coating material effi
`ciently from a Sputtering target and that employs a Secondary
`plasma by which is produced a high ionization fraction of
`the material Sputtered from the target. A more particular
`objective of the present invention is to provide Such a
`method and apparatus in which the loSS of charged particles
`from the Secondary plasma is minimized or reduced.
`A still further specific objective of the present invention is
`to provide an ionized physical vapor deposition method and
`apparatus with walls, Shields or other Structure that physi
`cally bound the Secondary plasma that will reduce the
`diversion of positive ions from the Secondary plasma. A
`15
`more specific objective of the present invention is to provide
`an ionized physical vapor deposition apparatus and method
`in which a Secondary plasma bounding shield or other
`Structure resists the build-up of negative potential thereon or
`the diversion of positive ions from the plasma without
`interfering with the coupling of energy into the plasma.
`The present invention is predicated at least in part upon a
`principle that Substantial loSS of charged particles from a
`Secondary plasma and a resulting reduction in the ionization
`fraction of Sputtered material by the plasma, and even the
`extinguishing of a Secondary plasma, can be prevented by
`configuring components in ionized physical deposition pro
`ceSSes to affect the electromagnetic fields in the region
`occupied by the Secondary plasma to optimize retention of
`the charged particles in the plasma.
`The present invention is further predicated in part upon a
`principle that a Substantial loSS of positive ions from a
`Secondary plasma and a resulting reduction in the ionization
`fraction of Sputtered ions by the Secondary plasma, and even
`the extinguishing of a Secondary plasma, are prevented
`when electrically conductive shields employed in ionized
`physical deposition processes on the periphery of the Sec
`ondary plasma used for the ionization of the Sputtered
`material are prevented from developing a Substantial nega
`tive DC potential. The invention is further predicated in part
`upon the concept that the existence of conductive shields or
`chamber walls bounding the Secondary plasma, if prevented
`from developing a strongly negative DC potential or if kept
`far from the center of the chamber, will reduce the Steering
`of positive ions from the Secondary plasma into the walls or
`shields, and decrease the width of the plasma sheath. The
`invention is particularly predicated on the concept of pro
`viding these effects while maintaining an RF shield that will
`allow effective and efficient coupling of energy into the
`Secondary plasma.
`According to certain principles of the present invention,
`an ionized physical vapor deposition (IPVD) method and
`apparatus are provided utilizing a target energized with a DC
`or pulsed DC Source to energize a main plasma adjacent to
`55
`a Sputtering target and an RF reactively coupled Source to
`energize a Secondary plasma in the Space between the target
`and a Substrate oriented preferably parallel to the target at
`the opposite end of a Sputtering chamber. The Space in which
`the Secondary plasma is generated is bounded by electrically
`conductive Structure that is electrically floating and presents
`a high impedance to the RF source. This structure is further
`connected through a low pass filter which provides a low
`impedance DC path to ground or to Some other potential.
`In accordance with a preferred embodiment of the
`invention, an IPVD method and apparatus employs a direct
`current (DC) rotating magnetron cathode that includes a
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`rotating magnet assembly positioned behind a target to
`produce a main Sputtering plasma close to the Surface of the
`target. The target is situated at one end of a deposition
`chamber opposite a Substrate Support parallel to the target at
`the other end of the chamber and preferably centered on the
`axis of the target and chamber. A radio frequency Source is
`inductively coupled into the volume within the chamber
`between the target and the Substrate, to produce an induc
`tively coupled plasma (ICP) preferably in the volume
`between the main plasma and a Substrate mounted on the
`substrate Support. The lateral boundaries of the ICP are
`defined by the walls of the chamber and a quartz dielectric
`window or barrier behind which is positioned a coil that
`encircles the Volume within the chamber to couple energy
`into the Volume of the chamber to Support the Secondary
`plasma. Preferably, the window is Sealed in an opening in the
`wall and constitutes part of the vacuum containment Struc
`ture of the chamber, with the coil Situated in an atmospheric
`preSSure environment outside of the vacuum environment of
`the chamber. A metal shield positioned inside of the window
`shields the window from the deposition of conductive sput
`tered material thereon which, if permitted to accumulate on
`the window, would isolate the chamber from the coil. The
`properties of the magnet producing the magnetron magnetic
`field, or MMF, are also useful where the coil is situated
`inside of the chamber and energy is at least in part capaci
`tively coupled into the Secondary plasma.
`The shield is electrically floating with respect to the RF
`plasma, presenting a high impedance to the RF plasma. A
`low pass filter, for example in the form of an LC circuit, is
`connected between the Shield and either ground or Some
`other predetermined fixed or otherwise controlled potential
`to present a low DC impedance to the shield while main
`taining high impedance to the RF energy of the plasma.
`Preferably also, the shield is situated radially outwardly
`from the rim of the target, preferably by a distance of one to
`two inches. As a result, negative potential is prevented from
`accumulating on a Surface close to the Volume of the
`chamber, between the target and the Substrate, where it is
`desirable to maintain the Secondary plasma. Preventing the
`formation of the DC potential from accumulating on the
`Surface will decrease the length of the near sheath or
`pre-sheath and raise the plasma potential of the Secondary
`plasma. Decreasing the pre-sheath and increasing the poten
`tial difference between the Secondary plasma and the Sub
`Strate will lead to an increase in the ion density bombarding
`the Substrate.
`The present invention maintains a dense Secondary
`plasma, which may have an ion density of, for example,
`1000 times that of a typical Sputtering plasma, and which
`occupies the Volume between the target and the Substrate,
`enabling the Secondary plasma to produce a high ionization
`fraction of the Sputtered material passing from the target to
`the Substrate. The application of electrical or magnetic fields
`applies forces to the charged particles to enable them to be
`electrically Steered toward the Substrate. In particular, estab
`lishing a bias potential on the Substrate increases the com
`ponent of the direction of the ionized Sputtered material at
`angles normal to the Substrate Surface, providing Superior
`coating of the bottoms of high aspect ratio features on the
`Substrate.
`With the present invention, high aspect ratio holes can be
`effectively filled and contacts at the bottoms of such features
`can be more effectively coated.
`These and other objectives and advantages of the present
`invention will be more readily apparent from the following
`detailed description of the preferred embodiments of the
`invention, in which:
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`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is an elevational diagrammatic representation of a
`IPVD apparatus according to certain embodiments of the
`present invention.
`FIG. 1A is a partial croSS Sectional view taken along the
`line 1A-1A of FIG. 1.
`FIG. 2 is a cross-sectional view of a magnetron magnet
`assembly taken along the line 2-2 of FIG. 1.
`FIG. 3 is a cross-sectional diagram taken along the line
`3-3 of FIG. 2 depicting the magnetic field shape of the
`magnetron magnet assembly of the apparatus of FIG. 2.
`FIG. 4 is a circuit diagram of one embodiment of a filter
`circuit of the apparatus of FIG. 1.
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENT
`FIG. 1 diagrammatically illustrates a Sputter coating appa
`ratus 10 embodying principles of the present invention. The
`apparatus 10 includes a vacuum tight chamber 12 bounded
`by a chamber wall 13. Within the chamber 12 is a plasma
`processing Space 11. Mounted in the chamber 12 at one end
`thereof is a wafer Support or Susceptor 14 for Supporting a
`Semiconductor wafer 15 mounted thereon for processing by
`the application of a coating or film in an ionized physical
`Vapor deposition process. The wafer 15, when mounted on
`the Support 14, is parallel to and faces a target 16 mounted
`to, and which is part of, a cathode assembly 17 mounted in
`the chamber 12 and at the opposite end of the chamber 12
`from the substrate holder 14. The target 16 may include a
`target backing plate 18 to which the target 16 is secured The
`cathode assembly 17 includes magnet Structure in the form
`of a magnet assembly 20 which is typically provided behind
`the target 16 on the opposite Side thereof from the Space 11.
`A dark space shield (not shown) may also be provided
`around the periphery of the target 16. The chamber 12, target
`16 and Substrate Support 14 are aligned on a common axis
`29.
`The magnet Structure 20 preferably includes magnets that
`produce a closed magnetic tunnel over the Surface of the
`target 16 that traps electrons given off into the chamber 12
`by the cathode assembly 17 when the cathode assembly 17
`is electrically energized to a negative potential as is familiar
`to one skilled in the art. The magnet Structure, magnet
`assembly or magnet pack 20 may include fixed magnets or
`rotating or otherwise moving magnets, which may be per
`manent or electromagnets, and other features of any one of
`a number of magnetron Sputtering assemblies known in the
`art, consistent with the description herein.
`A target power Supply or Source 21 provides electrical
`energy to the target 16. The target power Supply 21 is usually
`a Source of constant or pulsed DC power and is connected
`between the cathode assembly 17 and some element such as
`the chamber wall 13 which is at ground potential and serves
`as the system anode. The cathode assembly 17 is insulated
`from the wall of the chamber 12. The power supply 21
`preferably is connected to the cathode assembly 17 through
`an RF filter 22. An alternative Source of energy Such as an
`RF generator 24 may be optionally connected to the cathode
`assembly 17 through a matching network 25. A bias circuit
`27 is also provided and connected to the substrate holder 14
`through a matching network 28. The bias circuit 27 applies
`a bias potential to a wafer 15 mounted on the holder 14. A
`bipolar DC Supply or an RF supply can be used for this
`purpose.
`Power from the steady or pulsed DC power supply 21
`and/or RF generator 24 produces a negative potential on the
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`target 16. The negative potential accelerates ions toward the
`Surface of the target which, upon impact, cause electrons to
`be emitted from the surface of the target 16. These electrons
`become trapped over the surface of the target 16 by the
`magnetic field generated by the magnet pack 20, until,
`eventually, the electrons Strike and thereby ionize atoms of
`process gas in close proximity to the Surface of the target 16,
`forming a main plasma in a region 23 of the Volume 11
`adjacent to the Surface of the target 16. This main plasma in
`the region 23 becomes a Source of positive ions of gas that
`are accelerated toward, and collide against, the negatively
`charged Surface of the target 16, thereby ejecting particles of
`coating material from the target 16.
`The space 11 between the surface of the target 16 and the
`Substrate Support 14 can be considered as formed of two
`parts. One part 23 is primarily occupied by the main plasma,
`which is shaped by the magnet assembly 20 to produce a
`desired erosion pattern on the Sputtering Surface of the target
`16, while the Second part of the Space 11 is a remaining
`Volume 26 that lies between the main plasma region 23 and
`the substrate 15 on the Support 14. The particles of sputtered
`material from the target 16 generally leave the Surface of the
`target 16 as electrically neutral particles that propagate by
`momentum only through the Space 11. In a conventional
`Sputtering apparatus, neutral Sputtered particles passing
`through the main plasma region 23 are not ionized signifi
`cantly Since the main plasma is not relatively dense, occu
`pies a relatively Small Volume near the Surface of the target
`16 and, at the low operating pressures employed in
`Sputtering, few collisions occur between the neutral Sput
`tered particles and particles of the main plasma. AS Such, the
`Sputtered particles exit the main plasma region 23 mostly
`neutral and, in conventional Sputtering, these particles would
`remain neutral when deposited as a thin film on substrate 15.
`For Some Sputtering processes, Such as those used for
`coating contacts at the bottoms of high aspect ratio holes and
`other features on the substrate 15 and for metallizing such
`holes by filling them with Sputtered conductive material, it
`is highly preferred in VLSI semiconductor device manufac
`turing that the particles impinge onto the Substrate 15 in a
`narrow angular distribution around the normal to the Sub
`Strate So that they can proceed directly into the features and
`onto the feature bottoms without Striking or being Shadowed
`by the feature SideS. This perpendicular impingement of
`particles on the Substrate 15 is, in the apparatus 10, facili
`tated by ionizing the Sputtered particles as they pass through
`the Volume 26, So that the particles develop a positive
`electrical charge. Once positively charged, the Sputtered
`particles can be electrostatically accelerated or otherwise
`electrically or magnetically directed into paths that are
`parallel to the axis 29 of the chamber 12 and perpendicular
`to the Surface of the Substrate 15. Such attraction of the
`positive ions of Sputtered material toward the substrate 15
`can be achieved, for example, by applying a negative bias to
`the substrate 15 through the operation of the bias power
`Supply 27. Such bias attracts the positive Sputtered ions,
`increasing the directionality of the ionized Sputtered par
`ticles toward the substrate 15 by producing an electrical
`potential gradient in the plasma Sheath in front of Substrate
`holder 14, which provides the force to accelerate the posi
`tively ionized Sputtered particles toward and onto the Sub
`Strate Surface. For Silicon Semiconductor wafers, this bias
`power Supply 27 is preferably an RF generator that operates
`in the range of from about 0.05 to 80 MHz. Such a process
`of utilizing forces available by ionizing the Sputtered par
`ticles is characteristic of the processes referred to as ionized
`physical vapor deposition (IPVD) or ion assisted sputter
`coating.
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`The in-flight ionization of Sputtered particles as they pass
`through the Space 11 is carried out creating a Secondary
`plasma in the Volume 26. There are Several ways known in
`the prior art for generating Such a plasma. In the apparatus
`10, this plasma is preferably generated by inductively cou
`pling RF energy into the volume 26 from an RF coil 30 that
`surrounds the volume 26 and preferably lies outside of the
`vacuum chamber 12. The coil 30 Surrounds the chamber 12
`and is centered on an axis that corresponds to the axis 29 of
`the chamber 12. The coil 30 is preferably in the form of a
`helical coil, though coil configurations other than helical
`may be used. The RF energy may be fed into the coil 30 by
`leads connected across the ends of the coil, as shown in FIG.
`1, by adding a center RF tap to the center of the coil and
`grounding the other two leads or vice versa. The coil 30
`inductively couples energy into process gas in the Volume
`26, forming a dense plasma that generally fills the Space 26.
`An RF generator 32, preferably operative at a frequency of
`approximately 2 MHz, is connected to the coil 30 through a
`matching network 33 to provide the energy to the coil 30 to
`form the plasma in the volume 26.
`A Source of processing gas 40 is connected to the chamber
`11, through a flow control device 41. For Sputter processing,
`the gas from the Supply 40 is typically an inert gas Such as
`argon. For reactive processes, additional gases, Such as
`nitrogen, hydrogen, ammonia, oxygen or other gas, can be
`introduced through auxiliary flow controllers. A high
`vacuum pump 39 is also connected to the chamber 12 to
`pump the chamber to a vacuum in 10 to 10 Torr range,
`and maintain a vacuum in the mili-Torr range during depo
`sition. For most processes, pressures in the 1 to 50 milli-Torr
`range are typically preferred. The pump 39 may by baffled,
`for example, to maintain process pressure of 0.5 to 40 mTorr
`using gas flows of, for example, 1-500 Standard cubic
`centimeters per Second (Scem).
`In the wall of the chamber 12, between the coil 30 and the
`space 11 there is provided a dielectric window 60. The
`window 60 is formed of a vacuum compatible dielectric
`material Such as quartz or other material that does not
`impede the magnetic field Surrounding the coil 30 from
`reaching into the volume 26. The window 60 is mounted to
`form a vacuum tight seal with the wall of the chamber 12,
`allowing the coil 30 to lie in an annular cavity 62 at
`atmospheric pressure on the outside of the window 60. The
`window 60 is preferably a single cylindrical piece of the
`electrically insulating and magnetically-transparent
`material, but it may be formed of joined Segments of
`material arranged to form a generally cylindrical protective
`Structure in the form of electrically insulating windows in an
`enclosing Structure. A conductive metal outer closure 61
`forms the outer wall of the sealed annular cavity 62 which
`electrically isolates the coil 30 from the outside environment
`and prevents electromagnetic energy from radiating from the
`coil 30 and from within the chamber 12 to the outside of the
`chamber 12. The space within the closure 61 may be in
`communication with the outside atmosphere or may be filled
`with inert gas, at atmospheric or low preSSure, provided that
`formation of a plasma is not Supported by the gas in the
`cavity 62 when the coil 30 is energized. The space may also
`include facilities for cooling the shield 70.
`While the window 60 itself is not electrically conductive,
`it is Susceptible to the accumulation of a coating of conduc
`tive material Sputtered from the target 16. Electrical con
`ductivity in or on the window 60 Supports the induction of
`azimuthal currents around the chamber which reduce, cancel
`or otherwise undermine the effectiveness of the RF coupling
`of energy from the coil 30 to the secondary plasma in the
`
`15
`
`25
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`6,117,279
`
`8
`volume 26. Such conductivity on the window 60, particu
`larly in the azimuthal (circumferential) direction, that is, a
`direction that extends around the axis 29 of the chamber 12
`produces an inductively coupled Short circuit for electron
`currents, which can negate all or much of the energy being
`inductively coupled into the volume 26.
`To prevent Such buildup of conductive Sputtered material
`on the window 60, a shield 70 is provided in the vacuum of
`the chamber 12 between the space 11 and the window 60, in
`close proximity to the inside surface of the window 60. The
`shield 70 is preferably generally cylindrical in shape. The
`shield 70 shadows the window 60 from material sputtered
`from the target 16, and preferably blocks all direct line-of
`Sight paths between any point on the Surface of the target 16
`and the window 60. The shield 70, like the window 60, must
`not, itself, provide an electrically conductive circumferential
`short circuit when it is placed in the chamber 12. To this end,
`the shield 70 is provided with a longitudinal slit 73 that is
`parallel to the axis 29 of the chamber 12. The slit 73
`interrupts circumferential current paths around the axis 29.
`Shields with a single slit or with a plurality of slits, fashioned
`to interrupt currents Such as circumferential currents and
`eddy currents in the Shield, can alternatively be used, or the
`Shield may be formed as a Segmented Shield or a shield array.
`The single slit 73 in a shield of an otherwise generally
`cylindrical shape is a suitable embodiment of the shield 70
`which Substantially interrupts circumferential paths in the
`shield 70 around the chamber 12 to prevent the induction of
`circumferential or azimuthal currents in the shield 70. The
`edges of the shield 70 adjacent the slit 73 preferably overlap
`So that, while interrupting circumferential current paths
`around the chamber 12, the slit 73 does not permit the
`passage of Sputtered particles propagating in Straight paths
`from the space 11 onto the window 60. The width of the slit
`73 is maintained by a pair of dielectric beads or spacers 74
`between the opposite edges of the shield 70 adjacent the slit
`73, as illustrated in FIG. 1A. In the case of a plurality of slits,
`the slits preferably extend above and below the coil turns
`and have approximately the same pitch as the orthogonal
`coil pitch.
`The shield 70 also preferab