{l2} INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY {PCT}
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`(I9) World Intellectual Property Organization
`International Bureau
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`|illlli|||l|ll|||||||||l||||||llill||||||l||||||||I|||||||lll|||||||ll|||||l|| ill
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`(43} International Publication Date
`27 December 2002 (27.12.2002)
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`(It!) International Publication Number
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`PCT
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`W0 02/103078 Al
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`{51} International Patent Classification":
`11111] 37334. 110511 1150
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`C23C 14.35.
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`[RUSH]; Backluraviigen 31
`Vladimir
`Nyrttishamn {SE}.
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`(f. 3-149 43
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`(21) International Application Number:
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`PCZ'l'ISL‘OZIOI IOU
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`(22} International Filing Date:
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`l4 June 2(X13t14.06.2002l
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`[74}
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`(31)
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`(25} Filing Language:
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`(26) Publication Language:
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`(30) Priority Data:
`(“02134—4
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`I'inglish
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`English
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`l4 Jun: 200! {14.06.2001}
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`SH
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`(71) Applicant Jar of! designated Stores Heep! US): C HEM-
`FILT R 8t D AKTIEBOLAG [SlifSlih Kumlu (iardsviig
`28. 5—145 63 Norsborg (Slit-
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`{34)
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`{72} Inventor; and
`(75) lnventortApplicant {for US unit-3): KOlIZNETSOV.
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`Agent: BERGENSTRAHLE & LINDVALL AB: no.
`BoxlTHM.SJI893SMcHnflmtSEt
`
`Designated States (national): AE. AG. AL, AM. AT. AU.
`AZ. BA, BB. BG. BR. BY. BZ.CA. CH. CN. CO. CR, CU.
`CZ. DIE. DK. DM. DZ. tiff. (Eli. liS. I’l. GB. GD. GIE. GH.
`GM. HR. [It]. ID. IL. IN. 13.11”. K13. KG. KP. KR. KZ. LC,
`LK. LR. LS, 1.12111, LV. MA. MD. MG. MK. MN. MW.
`MX. M2. NO. NZ. OM. Pit. PL. PT. RO. RU. SD. SE. SG.
`31. SK. 5].. TJ, TM, TN. TR. T1“. 17.. [1A. HG. US. UZ.
`VN. YU. ZA. ZM. ZW.
`
`Designated States (regionat): ARIPO patent (Gil. GM.
`K15. LS. MW. MZ. SI). 51.. 82. T1. UG. ZM. ZW'!.
`Eurasian patent (AM. AZ. BY. KG. KZ. MI). RU. '[‘1.TMi.
`European patent (AT. B13. CH. CY. DE. DK. ES. Fl. FR.
`GB. GR. IE. IT. LU. MC. NL. PT. Sli. 'I'Rt. OAPI patent
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`[Continued on new urge}
`
`(54} Title: METHOD AND APPARATUS l‘TJR PLASMA GliN'ERA’l‘lON
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`In a simple method and device for
`(57) Abstract:
`producing plasma flows of a metal auditor a gas
`electric discharges are periodically produced between
`the anode and a metal magnetron sputtering cathode
`in crossed electric and magnetic fields in a chamber
`having a low pressure of a gas. The discharges are
`produced so that each discharge comprises a first
`period with a low electrical current passing between
`the anode and cathode for producing a metal vapor
`hy magnetron sputtering. and a second period with
`a high electrical current passing between the anode
`and cathode for producing an ionization of gas and
`the produced metal vapor.
`Instead of the first period
`a constant current discharge can he used.
`Intensive
`gas or metal plasma flows can he produced without
`forming contracted arc discharges. The scll'sputtcring
`phenomenon can he used.
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`INTEL 1006
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`Ionizing
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`IlIl
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`Ionizing
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`W002/103078A1
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`INTEL 1006
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`W0 02/103078 Al
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`JI|||IIJIIIIIIllllllllllllfll|||fll|I|||||l|||||||llllllllllllll||||IIi|||||||III
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`IBF, BJ, CF, CG, CL CM, GA, GN, GQ, GW, ML, MR.
`NE. SN. TD. rI‘G'l.
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`Published:
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`wah inlet-uniform! scant}: mp0”
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`I‘bi‘m'o-Iefler codes and Grim-abbreviations, refirm the} "Guid-
`mice Notes on Cafes and Abbreviations " appearing at (he begin—
`ning ofeach regular issue offhe PCT Gazelle.
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`W0 "£10307?!
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`PCT}S EIIZJ'fll 160
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`1
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`METHOD AND APPARATUS FOR PLASMA GENERATION
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`TECHNICAL FIELD
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`The present invention relates to methods and apparatus for generating plasma flows and in
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`particular metals plasma flows obtained by discharges in crossed electric and magnetic fields.
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`BACKGROUND OF THE INVENTION
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`Electrical discharges in crossed fields (EXB discharges) attract much attention due to their
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`importance for science and technology. In science EXB discharges are important in the field of
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`plasma physics and cosmic physics. In technology EXB discharges are used in devices for
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`thermonuclear fusion, in vacuum technology such as in vacuum pumps, vacuum measurements,
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`for coating work pieces using e.g. magnetron sputtering, in plasma accelerators, and as plasma
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`emitters in ion sources.
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`The motion of charged particles in stationary crossed fields and quasi-stationary EXB
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`discharges have been studied since 1921, see the article by A. W. Hull, "The effect of a uniform
`magnetic field on the motion of electrons Between coaxial cylinders", Phys. Rev. 18, 1921, pp.
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`31 - 57, and by H. C. Early, W. G. Dow, "Supersonic Wind at Low Pressures Produced by Arc in
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`Magnetic Field“, Phys. Rev. 79, 1950, p. 186. Such discharges could be classified according to
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`different parameters such as gas pressure, strength and configuration of the magnetic field used,
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`electrode configuration etc. For the purposes herein these discharges are best classified according
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`to the intensity or generally the behaviour of the discharge or driving current.
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`According to this classification using the driving current, quasi-stationary discharges in
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`crossed fields could be divided in two classes: low intensity and high intensity current discharges.
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`5
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`1O
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`It is necessary to note that the transition current depends on many parameters, in particular on the
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`dimensions of the apparatus used, and can vary for hundreds of amperes. Low intensity current
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`25
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`discharges in crossed fields could be called such discharges which produce a plasma inside a
`magnetic configuration with a density less than 1018 m‘3 and high intensity |current discharges
`could be called such discharges which produce a plasma having a density of more than 1018 m3,
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`the plasma density defined as the number ofparticles per unit volume.
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`Low intensity current discharges in crossed fields are widely used in vacuum technology
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`such as in vacuum pumps, for coating work pieces, e. g. in magnetron sputter deposition. Typical
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`'30
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`discharge devices are Penning cells and cylindrical and planar DC-magnetrons. The low driving
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`current results in a low-density plasma, less than 1013 m‘3 as indicated above.
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`High intensity current discharges have been mostly used for generating dense plasma for
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`the goals of thermonuclear fusion. Typical discharge devices include Homopolar I, Ixion and F I
`devices. The typical plasma density is about 1013 - 1023 m3.
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`The second important characteristic of discharges in crossed fields is the voltage drop
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`between the electrodes.
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`For a low intensity driving current the rate of neutral gas ionization is low and balances the
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`plasma losses to form an equilibrium plasma density at a low level. The electrical resistance of
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`the anode-cathode gap is high resulting in a high anode-cathode potential drop. As soon as an
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`opposite process becomes energetically possible a strongly enhanced ionization process should
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`arise.
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`Two methods have been described for plasma ionization in systems using with discharges
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`in crossed electric and magnetic fields. Their practical applicability depends on system dimen-
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`sions and the strength of the magnetic field. The method generally accepted in systems of suffi-
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`ciently large dimensions using a strong magnetic field is the So called "Rotating Plasma
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`Approac ". This approach is based on the fleet that the electric field penetrates into the plasma
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`and that the plasma is magnetized, see B. Lehnert, "Rotating Plasmas", Nuclear Fusion 11, 1971,
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`pp. 485 — S33. Another approach is based on fact that the electric field is concentrated preferably
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`near the cathode of the discharge. This approach is used for processes in systems using a low
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`magnetic field and non-magnetized ions. This approach could be called e.g. "Secondary Electron
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`Approach", see B. S. Danilin and B. K- Sirchin, Magnetron Sputtering Systems, Moskva, Radio i
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`Sviaz, 1982. As will be obvious from the following this invention deals with both kinds of
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`systems and therefore both plasma approaches will be used.
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`Alfvén has postulated, see H. Alfvén, "On the Origin of the Solar System", Clarendon
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`Press, Oxford, 1954, that a strongly enhanced ionization process should arise when the mutual
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`plasma-neutral gas velocity reaches the critical value vc, the Alfvén limit, given by
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`v,=(2e¢ifmi)m
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`where ¢§ is the ionization potential, e is the charge of the electron and m is the ion mass.
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`For devices having a low sputtering rate and low plasma losses it results in an anode-
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`cathode voltage drop limitation during the starting period of the discharge. For devices having a
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`high sputtering rate it results in an anode-cathode voltage drop limitation during all of the
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`discharge time. The voltage drop or critical voltage Va is given by
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`Va: '8ch
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`Where C is a constant and B is the strength of magnetic field in the discharge device. In the case
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`of a high sputtering rate, the ionization potential 5:; of the sputtered atoms creates the metal vapor.
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`It means that the discharge voltage has to depend on the sputtering cathode material.
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`This phenomenon was demonstrated both by investigation of plasma motion through a
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`neutral gas and by experiments with planar magnetron sputtering devices, see U. V. Fahleson,
`
`"Experiments with Plasma Moving through Neutral Gas", Physics Fluids, Vol. 4, 1961, pp. 123 —
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`127, and D. V. Mozgrin, l. K. Fetisov, and G. V. Khodachenko, "High-Current Low—Pressure
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`Quasi—Stationary Discharge in 3 Magnetic Field: Experimental Research", Plasma Physics
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`Reports, Vol. 21, N0. 5, 1995, pp. 400 — 409. In the latter publication the high current, low
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`voltage discharge in a magnetron magnetic configuration is called as a "high-current diffuse
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`1O
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`regime".
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`It means that the transition from a low intensity current EXB discharge to a high intensity
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`current discharge has to be followed by a decrease of the discharge voltage. Typical anode-
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`cathode potential drops for low intensity current, quasi-stationary discharges are in the range of
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`about 10 — 0.3 kV and for high intensity current discharges in the range of about 300 — 10 V.
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`If quasi-stationary discharges are implemented in magnetron sputtering devices, in a first
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`regime effective cathode sputtering is obtained but a low ionization rate of the sputtering gas and
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`metal vapor. In a second regime an opposite state occurs having a low sputtering rate but a high
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`ionization rate of the sputtering gas. Thus, it can be said that it is impossible to generate, by a
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`separate low intensity current quasi-stationary discharge, or by a separate high intensity current
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`discharge in crossed fields, highly ionized metal plasma fluxes.
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`The devices using EXB discharges can operate for a short time in the transient, i.e. the non-
`quasi-stationary, regime. In this regime it is possible to overcome the Alfvén limit of discharge
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`voltage as Well for high current discharges, see the article by B. Lehnert cited above. High
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`current, high voltage non—quasi—stationary discharges occur in magnetron sputtering devices and
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`are very important for magnetron sputtering applications because those discharges allow obtain-
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`ing a fully ionized impermeable plasma in the magnetron magnetic configuration. But, as will be
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`shown hereinafter, if transient discharges are implemented in magnetron sputtering devices by
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`either high intensity current discharges or by low intensity cmrent discharges it is impossible to
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`generate highly ionized intensive metal plasma fluxes.
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`Metal plasma fluxes can be produced by low current quasi—stationary EXB discharges in a
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`magnetron configuration for sputtering atoms in a moderate pressure, of e.g. l - 100 mTorr, and
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`with a low-density plasma. In this case the plasma is produced by an RF-induction coil mounted
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`in the deposition chamber. The electron density produced in induction plasmas is about 1017-10m
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`111'3.
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`This method of coating work pieces has important implications for the filling of high-
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`aspect—ratio trenches and visa encountered in microelectronic fabrication processes as well as in
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`sputtering magnetic materials and modifi/ing the properties of thin films by energetic ion
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`deposition, see J. Hopwood and F. Qian, "Mechanisms for highly ionized magnetron sputtering",
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`J. Appl. Phys. ?8 (12), 15 1111311995, pp. 758 - 765.
`
`The drawbacks of this method of metal plasma production include the complexity of the
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`RF-ionization technique and the high pressure of the sputtering gas required for producing the
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`low-density plasma. The high pressure of the Sputtering gas is required because of the high
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`energy consumption necessary for producing a low-density plasma.
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`The discharges in crossed fields could be implemented by simple techniques and within an
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`extremely wide range of operating pressures: Erorn 10'” up to 102 Torr. Low-pressure magnetron
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`discharges, up to 10'5 Torr, can be achieved because of the selfsputtering phenomenon, see for
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`example S. Kadlec and I. Musil, "Low pressure magnetron sputtering and seIfSputtering dis-
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`charges", Vacumn, Vol. 47, pp. 307 - 311, 1996. This method of coating work pieces has im-
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`portant implications for the etching of surfaces by metal ions for increasing the adhesion of de-
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`posited layers and for the filling of high-aspect—ratio trenches and vias encountered in micro—
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`electronic fabrication.
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`The currents necessary for generating a dense plasma and sustaining it by high intensity
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`current EXB discharges are large enough for cathode spots, and possibly also for anode spots, to
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`he formed at the cold electrode surfaces. Devices having such electrodes should therefore have a
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`natural tendency of forming spoke-shaped azimuthal plasma inhomogeneities, arc discharges, see
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`B. A. Tozer, "Rotating Plasma", Proc. IEEE, Vol. 112, 1965, pp. 218 - 228. Such conditions are
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`strongly pronounced in all types of devices during the starting period of the discharges where a
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`large driving current is needed for neutral gas burn—out.
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`Having cold electrodes and neutral—plasma phenomena in mind, the experiments on plasma
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`spoke formation can be summarized as follows:
`
`a. In the Homopolar III experiments it Was found that during the starting period the discharge cur-
`
`rent was confined to a set of about 10 to 12 narrow radial spokes, arcs, rotating with the plasma.
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`See W. R. Baker, A. Bratenal, A. W. De Slivag W. B. Knnkel, Proc. 4m Int. Conf. Ionization Phe-
`
`nomena in Gases 2, Uppsala 1959, North-Holland Publishing Comp, Amsterdam, p. 11751, and
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`W. B. Kunkel, W. R. Baker, A. Bratenahl, K. Halbach, "Boundary Effects in Viscous Rotating
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`Plasmas", Physics Fluids, Vol. 6, 1963, pp. 699 - 7’03.
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`1). In the Leatherhead Homopolar device having a negative polarity one or two spokes Were ob—
`served to arise during the initial breakdown of the discharge. They were soon smeared out to
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`PCTISEIIZKIII 160
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`form spirals with an increasing velocity in the outward radial direction, see P. B. Barber, M. L.
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`Pilcher, D. A. Swift, B- A. Tozer, C. r. de la VIe conference internationale sur les phenoménes
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`d‘ionization dans le gas 2, Paris, 1963, p. 395.
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`c. In the Kruisvuur I device a single eccentric structure rotating around the axis with a velocity
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`5 close to BIB was observed , see C. E. Rasmussen, E. P. Barbian, J. Kistemaker, "Ionization and
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`current growth in an ExB discharge", Plasma Physics, Vol. 11, 1969, pp. 183 - 195.
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`From the experiments mentioned above and others, are formation is clearly seen to be
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`connected with the starting period of the high intensity current EXB discharges in most devices.
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`SUMMARY OF THE INVENTION
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`10
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`It is an object of the present
`
`invention to provide methods and apparatus allowing
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`production of intensive, preferably gas or gas-metal or most preferably metal plasma flows-
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`The problems, which the invention thus intends to solve, comprise:
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`1. How to produce intensive, preferably gas or gas-metal or preferably metal plasma flows by
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`ionization of gas and metal vapor produced using planar magnetron sputtering cathodes by a
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`15' simple technique for producing discharges in crossed fields.
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`2. How to produce these plasma flows Without forming contracted arc discharges.
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`3. How to provide pulsed discharges in crossed fields using the selfsputtering phenomenon.
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`Thus, generally in a method for producing a plasma flow successive low and high intensity
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`current quasi-stationary and non quasi-stationary discharges in crossed electric and magnetic
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`20 fields are used, the term "crossed fields" meaning "crossed electric and magnetic fields" herein.
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`For producing the plasma a succession of discharges is thus used, i.e. pulsed discharges are used.
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`The discharges that are well separated in time are defined to be quasi-stationary in the cases
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`where at
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`least
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`the most
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`important physical parameters, such as current and voltage, are
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`substantially constant or slowly varying during most of the discharge time, and are, if this
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`25 condition is not fiilfilled, non-quasi stationary. The plasma flow producing procedure can include
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`the following steps:
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`1. A low intensity current, high voltage discharge in a magnetron magnetic configuration is used
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`for metal vapor production. The following ionization of vapor is obtained by a high intensity
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`current, low or high voltage discharge in the same magnetic configuration. The second, ionizing
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`so discharge starts hrmrediately after the first one or with some, relatively small time delay. The
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`parameters of the pulses and time delay of the second pulse are defined by the requirements hu-
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`posed by the high ionization of sputtered vapor blobs.
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`2. The metal vapor can be produced by a direct current discharge, i.e. not by pulsed discharges. In
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`this case the metal vapor produces a continuous vapor flow out of the magnetic configuration
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`Where the discharge is made. If ionizing pulses follow having a sufficient frequency and driving
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`current it is possible to produce a continuous metal plasma flow having a modulated intensity.
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`The following basic schemes can be used:
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`1. The plasma can be produced in a magnetron magnetic configuration in which combined or
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`successive low and high intensity current non-quasi-stationary discharges in crossed fields are
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`used.
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`2. The plasma can be produced in a magnetron magnetic configuration in which a low intensity
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`current quasi—stationary discharge is combined with or followed by a high intensity current non-
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`quasi-stationary discharge, the discharges made in crossed fields.
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`3. The plasma can he produced in a magnetron magnetic configuration in which combined direct
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`current discharges and high current non-quasi-stationary discharges in crossed fields are used.
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`4. The plasma can be produced in a magnetron magnetic configuration in which combined low
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`intensity current non-quasi-stationary discharges and high intensity current quasi-stationary dis-
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`charges in crossed fields are used.
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`5. The plasma can be produced in a magnetron magnetic configuration in which combined
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`successive low and high intensity current non-quasi-stationary discharges and high intensity
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`current quasi-stationary discharges in crossed fields are used.
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`6. The plasma can be produced in a magnetron magnetic configuration in which combined high
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`intensity current non-quasi-stationary discharges and high intensity current quasi—stationary dis-
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`charges in crossed fields are used.
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`The combinations of discharges in crossed electric and magnetic fields mentioned above
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`made in a magnetron magnetic configuration allow the production of plasma flows of preferably
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`gas or gas and metal or most preferably of a metal plasma flow. For quasi-stationary discharges
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`the choice of method can be based on the different efficiencies of the low and high current
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`intensity discharges for Sputtering and ionization in the different cases.
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`The discharges in crossed fields have, as has been mentioned above, a natural tendency of
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`forming spokevshaped azimuthal plasma inhomogeneities - are discharges. The probability of the
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`transition of an EXB discharge in magnetron type devices to a contracted arc discharge increases
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`with an increasing driving current. In low current discharges arcing occurs very rarely and it is
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`possible to prevent the transition to are discharges by specially adapted arc suppression schemes
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`in the discharge power supply. In high current. discharges there is a very high probability of arc
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`discharges being formed and solutions to the problem of suppressing arc formation using similar
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`schemes are not efficient. As will be described herein, are suppression can be achieved using a
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`now discovered phenomenon of dependence of arc formation on the plasma confinement
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`properties of the magnetron magnetic configuration and on the time between discharges. The
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`balanced magnetron magnetic configuration has relatively low plasma confinement properties.
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`Therefore, for achieving efficient arc suppression, it is necessary to use a magnetic field having a
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`high strength. In this case the plasma losses caused by diffusion will decrease as B‘2 in the case of
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`classic diffusion or as a 13'1 in the case ofBohm diffusion, Where B is the strength of the magnetic
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`field. It was found that for a balanced magnetron magnetic configuration, in order to achieve
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`efficient arc suppression, it is necessary to have a magnetic field strength of the radial B
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`component of about 0.07 - 0.3 T, the radial direction here taken as directions parallel to the
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`substantially flat surface of the cathode or target. Unbalanced and cusp-shaped magnetic confi-
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`gurations have improved plasma confinement properties; therefore, for efi'ective arc suppression
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`it is sufficient to have a magnetic field strength of about 0.04 — 0.3 T.
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`The plasma'confinement properties of the magnetic configuration strongly affect the lower
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`limit of the operating pressure used in the space at the cathode. It was found that for improving
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`the plasma confinement properties the operating pressure of the EXB discharge should be
`
`decreased. For a certain operating frequency a gas atmosphere is required only for starting the
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`discharge. After the starting period it is possible to initiate the discharge by the residual plasma
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`density left from the previous pulse. In this case metal vapor is produced by using the
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`selfsputtering phenomenon and the plasma in the magnetic trap contains primarily ions of the
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`target metal. The plasma flow from the magnetic trap contains preferably ions of the target metal
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`as well.
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`Generally, it can be said that the primary concept of the method described herein is to
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`combine the magnetic configuration having improved plasma confinement properties with low
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`and high intensity current quasi-stationary discharges and non-quasi-stationary discharges or DC
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`and high intensity current discharges for generating stable and intensive plasma flows. Low and
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`high intensity current quasi—stationary discharges and nonouasi—stafionary discharges are
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`produced one after another with a repeating frequency exceeding a minimal critical value
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`depending on the plasma confinement properties of the magnetic trap. In the case of DC
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`sputtering discharges, a high rate of ionization of gas and metal vapor is produced by a periodic
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`repetition of the ionizing discharges.
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`The methods and devices described herein can be used both in the "Rotating Plasma
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`Approach“ and the “Secondary Electron Approach" mentioned above.
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`Additional objects and advantages of the invention will be set fm‘th in the description which
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`follows, and in part will be obvious from the description, or may be learned by practice of the
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`invention. The objects and advantages of the invention may be realized and obtained by means of
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`the methods, processes,
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`instrumentalities and combinations particularly pointed out
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`in the
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`appended claims.
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`BRIEF DESCRIPTION OF THE DRAWINGS
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`While the novel features of the invention are set forth with particularly in the appended
`
`claims, a complete understanding of the invention, both as to organization and content, and of the
`
`above and other features thereof may be gained from and the invention will be better appreciated
`
`from a consideration of the following detailed description of non-limiting embodiments presented
`
`hereinhelow with reference to the accompanying drawings, in which:
`
`- Figs. 1a - If are schematic views of different magnetron magnetic configurations used in
`
`1U
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`15
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`magnetron sputtering, in which
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`- Fig. la is a view of a first type of an unbalanced magnetron magnetic configuration,
`
`— Fig. 1b is a view of a balanced magnetron magnetic configuration,
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`- Fig. 1c is a view of a second type of an unbalanced magnetron magnetic configuration,
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`— Figs. 16. and le are views illustrating the magnetic configuration created by permanent magnets
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`placed behind the target and an electromagnetic coil placed in front of the target,
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`— Fig. If is a view of a cusp—shaped magnetic configuration,
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`- Fig. 1g is a view from above of a magnetic configuration typical of magnetrons having a
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`rotating magnet,
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`- Fig. lh is a schematic cross-sectional View showing the magnetic force lines in the magnetic
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`20
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`configuration of Fig. 1g,
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`- Figs. 2a and 2b are schematic diagrams illustrating limits between low and high current
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`discharges of the quasi—stationary and non-quasi—stationary type respectively,
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`- Figs. 3a and 3b are schematic diagrams of current and. voltage pulses respectively as functions
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`of time for Sputtering and ionizing discharges in crossed fields,
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`25
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`— Fig. 4 is a schematic diagram of periodic current pulses of the kind illustrated in Fig. 3a as a
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`function of time,
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`- Fig. 5 is a schematic diagram similar to that of Fig. 4 showing an alternative shape of the
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`current pulses,
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`- Fig. 6 is a schematic diagram similar to that of Fig. 4 showing current pulses superimposed on a
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`30
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`constant current level,
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`_
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`— Fig. 7a is a schematic diagram of the conductivity and plasma density as a function of time in a
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`plasma confinement region,
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`- Fig. 7b is a schematic diagram substantially identical to that of Fig. 4 showing the driving
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`current pulses for producing the conductivity and plasma density of Fig. ”la,
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`- Fig. 8a is an electrical circuit diagram of a device for producing a metal vapor and the ionization
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`thereof, the device having two pulsed power supplies connected in parallel,
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`- Fig. 8b is a diagram similar to that of Fig. 8a of a device including a single pulsed power supply
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`having a variable impedance,
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`- Fig. 8c is a diagram similar to that of Fig. 8a of a device having a single pulsed power supply
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`combined with a DC power supply,
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`- Fig. 9 is a detailed electrical circuit diagram corresponding to the diagram of Fig. 8a,
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`- Fig. 10 is a detailed electrical circuit diagram corresponding to the diagram of Fig. 8b,
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`- Fig. 11 is a detailed electrical circuit diagram corresponding to the diagram of Fig. Sc,
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`- Fig. 12a is a schematic cross-sectional view of a plasma source utilizing discharges in crossed
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`electric and magnetic fields for gas or gas and metal or metal plasma production, corresponding
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`to the second type of unbalanced magnetron magnetic configuration shown in Fig. 1e, and
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`- Fig. 12b is a schematic view similar to that of Fig. 12a illustrating a plasma source utilizing
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`discharges in crossed electric and magnetic fields for gas or gas and metal or metal plasma
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`production, corresponding to the types of magnetron magnetic configurations shown in Figs. Id
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`and 1f.
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`DETAILED DESCRIPTION
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`The magnet configurations of magnetron sputtering cathodes preferably used in the
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`conventional art for a magnetic field strength of up to 0.1 T are illustrated in Figs. 1b — 1f. Thus,
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`in Fig. 1b a balanced magnetron magnetic configuration is shown whereas in Figs. 1a and 1c
`unbalanced magnetron magnetic configurations are shown. The altering of the magnetic field
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`configuration is here made by altering the configuration of the permanent magnets in the
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`magnetron source.
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`"Thus, in the schematic diagram of'Fig. 1a a first type of an unbalanced magnetron magnetic
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`configuration is illustrated. The magnetron sputtering cathode l is a substantially flat body of the
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`material to be sputtered and can have the shape of circular disc or a rectangular plate. At the rear
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`or bottom surface of the cathode a lit-“Ht magnet assembly is illustrated comprising an outer
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`magnet 2 and a central magnet 3, the central magnet located at the center of the rear side of the
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`cathode and the outer magnet located at the edge of the rear side ofthe cathode. The lines having
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`arrows show the direction of magnetic force lines. The strength of the central permanent magnet
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`3 is selected to be larger than the strength of the outer magnet 2 so that among the magnetic field
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`lines 4, generally going from the. north poles to the south poles of the magnets, some field lines
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`extend only between the poles of the central permanent magnet.
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`In the View of a balanced magnetron magnetic configuration in Fig. lb it is seen to have
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`substantially the same set-up as the magnetron configuration as in Fig. is. However, the strength
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`of the central magnet is selected to be equal to the strength of the outer magnet so that sub—
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`stantially all magnetic. field lines extend between a pole of the central magnet 3 and a pole of the
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`outer magnet 2. The shaded area in the figure is the area of plasma confinement and also the area
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`in which the power dissipation of the discharge occurs.
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`In the schematic of Fig. lo a view of a second type of an unbalanced magnetron magnetic
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`configuration is illustrated, in which the strength of the permanent magnets is selected in still an-
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`other way. Hero, some field lines extend between the poles of the outer magnet, the field lines
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`starting or ending at the central magnet all having their other ends at the outer magnet.
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`The unbalanced configurations as shown in Figs. 1a and 1b are classified as Type I or Type
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`II reapectively, see B. Window and N. Savvides, "Charged particle fluxes fiom planar magnetron
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`sputtering sources", J. Vac. Sci. Technol, A 4(2), 1986, pp. 196 - 202.
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`An alternative way to accomplish difl‘erent magnetic configurations is to use an external,
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`preferably toroidal, magnetic coil, see I. Ivanov, P. Kazansky, L. Hultman, I. Petrov, and J-E.
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`Sundgren, "Influence of an external axial magnetic. field on the plasma characteristics and
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`deposition conditions dining direct current planar magnetron sputtering", J. Vac. Sci. chhnol., A
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`12(2), 1994, pp. 314 - 320. Thus, in the views of Figs. ld, 1e and if magnetic configurations
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`created by permanent magnets 2, 3 placed behind the target 1 and an electromagnetic coil 5
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`10
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`placed in front of the target are shown. In Figs. 1d and 1c the coil has a diameter larger than the
`diameter of the target. The arrows show the direction of the magnetic field. In Fig. 1f a cusp-
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`20
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`shaped magnetic configuration is shown in which the coil 5 has a diameter smaller than the
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`diameter of the target and of the outer magnet. The electromagnetic coil 5 has a height hmn, i.e.
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`the extension thereof in a direction perpendicular to the plane of the cathode 1, and an inner
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`diameter Dean. h and D are generally the height and diameter of the region of plasma confine-
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`ment, the power dissipation of the discharge occurring in this region. The shape of the plasma
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`confinement region can roughly be considered as a cylinder, having a diameter D and a height h,
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`for a planar circular cathode 1 or as rectangular parallelepiped for a planar rectangular cathode. In
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`the latter case D is the smallest dimension of cathode and the smallest dimension of the base sur-
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`face of the parallelepiped and h is the height of the parallelepiped.
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`30
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`Depending on the direction of the electric current in the coil 5, its field can be used for as-
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`sisting either the outer pole 2 or the center pole 3 of the permanent magnets as illustrated by Figs.
`1d and 1e. This technique provides a plasma density inside the plasma confinement region of
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`about 10“5 111's and provides for means of varying the ion flux at the cathode or substrate by more
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`than one order of magnitude. But still,
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`the ionization rate is less than 10%. Therefore, the
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`variation only of magnetic field strength and its geometry cannot give a sputtering magnetron
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`cathode acting as a metal plasma source having a high equivalent current.
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`The mega-shaped magnetic configuration of Fig. lf has been used for production of a dense
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`plasma by high current quasi-sta