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`(19) World Intellectual Property Organization
`International Bureau
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`(43) International Publication Date
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`(10) International Publication Number
`W0 02/103078 A]
`
`
`(51)
`
`International Patent Classification7:
`H01J 37/34, HOSH 1/50
`
`C23C 14/35,
`
`[RU/SE]; Backlurav'a'gen 3|
`Vladimir
`Nynashamn (SE).
`
`(3,
`
`8—149 43
`
`(21)
`
`International Application Number:
`
`PCT/SEOZ/Ol 160
`
`(22)
`
`International Filing Date:
`
`14 June 2002 (14.06.2002)
`
`(25)
`
`Filing Language:
`
`(26)
`
`Publication Language:
`
`(30)
`
`Priority Data:
`0102134—4
`
`English
`
`English
`
`14 June 2001 (14.06.2001)
`
`SE
`
`(74)
`
`(81)
`
`Agent: BERGENSTRAHLE & LINDVALL AB; PO.
`Box 17704, $118 95 Stockholm (SE).
`
`Designated States (national): AE, AG, AL, AM, AT, AU,
`AZ, BA, BB, BG, BR, BY, BZ, CA, CH, CN, CO, CR, CU,
`CZ, DE, DK, DM, DZ, EC, EE, ES, 171, GB, GD, GE, GH.
`GM, 11R, IIU, ID, IL, IN, IS, JP. KE, KG, KP. KR, KZ. LC,
`LK, LR, LS, LT, LU, LV, MA, MD, MG, MK, MN, MW,
`MX, MZ, NO, NZ. OM, PH, PL, PT, RO, RU, SD, SE, SG,
`SI, SK, SL, TJ, TM, TN, TR, Tl‘, TZ, UA, L'G, US. UZ,
`VN, YU, ZA, ZM, ZW.
`
`(71)
`
`Applicant (for all designated Slates excep/ US): CHEM-
`FILT R & D AKTIEBOLAG [SE/SE]; Kumla Girdsvag
`28, S 145 63 Norsborg (SE).
`
`(84)
`
`(72)
`(75)
`
`Inventor; and
`Inventor/Applicant
`
`(for US only): KOUZNE’I‘SOV,
`
`
`
`Designated States (regional): ARIPO patent (GII, GM,
`KE, LS, MW. MZ. SD, SL, SZ,
`'17., UG. ZM. ZW),
`Eurasian patent (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM),
`European patent (AT, BE, CH, CY, DE, DK, ES, F1, FR,
`GB, GR, 113, IT, LU, MC, NL, PT, SE, TR), OAPI patent
`
`[Continued on next page]
`
`(54) Title: METHOD AND APPARATUS FOR PLASMA GENERATION
`
`ionizing
`
`In a simple method and device for
`(57) Abstract:
`producing plasma [lows of a metal and/or 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
`by 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 be produced without
`forming contracted arc discharges, The sclfsputtering
`phenomenon can he used.
`
`"
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`WO02/103078A1
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`
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`Sputtering
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`Sputtering
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`
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`Ionizing
`
`GILLETTE 1106
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`GILLETTE 1106
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`(BF, BJ, CF, CG, CI, CM, GA, GN, GQ, GW, ML, MR,
`NE, SN, TD, TG).
`
`Published:
`v with international search report
`
`For two~letter codes and other abbreviations, refer to the "Guid—
`ance Notes on Codes and Abbreviations " appearing at the begin—
`ning ofeach regular issue ofthe PCT Gazelle.
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`METHOD AND APPARATUS FOR PLASMA GENERATION
`
`TECHNICAL FIELD
`
`The present invention relates to methods and apparatus for generating plasma flows and in
`particular metals plasma flows obtained by discharges in crossed electric and magnetic fields.
`
`5
`
`BACKGROUND OF THE INVENTION
`
`Electrical discharges in crossed fields (EXB discharges) attract much attention due to their
`importance for science and technology. In science EXB discharges are important in the field of
`plasma physics and cosmic physics. In technology EXB discharges are used in devices for
`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
`
`emitters in ion sources.
`
`15
`
`The motion of charged particles in stationary crossed fields and quasi—stationary EXB
`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.
`31 - 57, and by H. C. Early, W. G. Dow, "Supersonic Wind at Low Pressures Produced by Arc in
`Magnetic Field", Phys. Rev. 79, 1950, p. 186. Such discharges could be classified according to
`different parameters such as gas pressure, strength and configuration of the magnetic field used,
`electrode configuration etc. For the purposes herein these discharges are best classified according
`
`20
`
`to the intensity or generally the behaviour of the discharge or driving current.
`According to this classification using the driving current, quasi—stationary discharges in
`crossed fields could be divided in two classes: low intensity and high intensity current discharges.
`It is necessary to note that the transition current depends on many parameters, in particular on the
`dimensions of the apparatus used, and can vary for hundreds of amperes. Low intensity current
`discharges in crossed fields could be called such discharges which produce a plasma inside a
`25 magnetic configuration with a density less than 1018 In3 and high intensity current discharges
`could be called such discharges which produce a plasma having a density of more than 1018 n1'3,
`
`the plasma density defined as the number of particles per unit volume.
`Low intensity current discharges in crossed fields are widely used in vacuum technology
`such as in vacuum pumps, for coating work pieces, e.g. in magnetron sputter deposition. Typical
`discharge devices are Penning cells and cylindrical and planar DC-magnetrons. The low driving
`current results in a low-density plasma, less than 1018 m'3 as indicated above.
`
`30
`
`High intensity current discharges have been mostly used for generating dense plasma for
`the goals of thermonuclear fusion. Typical discharge devices include Homopolar I, Ixion and F I
`devices. The typical plasma density is about 1018 « 1023 In3 .
`
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`The second important characteristic of discharges in crossed fields is the voltage drop
`
`between the electrodes.
`
`For a low intensity driving current the rate of neutral gas ionization is low and balances the
`
`plasma losses to form an equilibrium plasma density at a low level. The electrical resistance of
`
`the anode—cathode gap is high resulting in a high anode—cathode potential drop. As soon as an
`
`opposite process becomes energetically possible a strongly enhanced ionization process should
`
`arise.
`
`Two methods have been described for plasma ionization in systems using with discharges
`
`in crossed electric and magnetic fields. Their practical applicability depends on system dimen—
`
`sions and the strength of the magnetic field. The method generally accepted in systems of suffi—
`
`ciently large dimensions using a strong magnetic field is the so called "Rotating Plasma
`
`Approach". This approach is based on the fact that the electric field penetrates into the plasma
`
`and that the plasma is magnetized, see B. Lehnert, "Rotating Plasmas", Nuclear Fusion 1 l, 1971,
`
`pp. 485 — 533. Another approach is based on fact that the electric field is concentrated preferably
`
`near the cathode of the discharge. This approach is used for processes in systems using a low
`
`magnetic field and non—magnetized ions. This approach could be called e. g. "Secondary Electron
`
`Approach", see B. S. Danilin and B. K. Sirchin, Magnetron Sputtering Systems, Moskva, Radio i
`
`Sviaz, 1982. As will be obvious from the following this invention deals with both kinds of
`
`systems and therefore both plasma approaches will be used.
`
`Alfvén has postulated, see H. Alfvén, "On the Origin of the Solar System", Clarendon
`
`Press, Oxford, 1954, that a strongly enhanced ionization process should arise when the mutual
`
`plasma-neutral gas velocity reaches the critical value vs, the Alfvén limit, given by
`
`vc=(2e¢i/mi)1/2
`
`where ¢i is the ionization potential, e is the charge of the electron and mg is the ion mass.
`
`For devices having a low sputtering rate and low plasma losses it results in an anode-
`
`cathode voltage drop limitation during the starting period of the discharge. For devices having a
`
`high sputtering rate it results in an anode—cathode voltage drop limitation during all of the
`
`discharge time. The voltage drop or critical voltage V0 is given by
`
`Vc= Cch
`
`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 ¢i of the sputtered atoms creates the metal vapor.
`
`It means that the discharge voltage has to depend on the sputtering cathode material.
`
`This phenomenon was demonstrated both by investigation of plasma motion through a
`
`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 ~
`
`127, and D. V. Mozgrin, I. K. Fetisov, and G. V. Khodachenko, "High—Current Low-Pressure
`
`Quasi-Stationary Discharge in a Magnetic Field: Experimental Research", Plasma Physics
`
`Reports, Vol. 21, No. 5, 1995, pp. 400 - 409. In the latter publication the high current, low
`
`voltage discharge in a magnetron magnetic configuration is called as a "high—current diffuse
`
`10
`
`regime".
`
`It means that the transition from a low intensity current EXB discharge to a high intensity
`
`current discharge has to be followed by a decrease of the discharge voltage. Typical anode-
`
`cathode potential drops for low intensity current, quasi-stationary discharges are in the range of
`
`about 10 — 0.3 kV and for high intensity current discharges in the range of about 300 — 10 V.
`
`If quasi-stationary discharges are implemented in magnetron sputtering devices, in a first
`
`regime effective cathode sputtering is obtained but a low ionization rate of the sputtering gas and
`
`metal vapor. In a second regime an opposite state occurs having a low sputtering rate but a high
`
`ionization rate of the sputtering gas. Thus, it can be said that it is impossible to generate, by a
`
`separate low intensity current quasi-stationary discharge, or by a separate high intensity current
`
`discharge in crossed fields, highly ionized metal plasma fluxes.
`
`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
`
`voltage as well for high current discharges, see the article by B. Lehneit cited above. High
`
`current, high voltage non—quasi—stationary discharges occur in magnetron sputtering devices and
`
`are very important for magnetron sputtering applications because those discharges allow obtain—
`
`ing a fully ionized impermeable plasma in the magnetron magnetic configuration. But, as will be
`
`shown hereinafter, if transient discharges are implemented in magnetron sputtering devices by
`
`either high intensity current discharges or by low intensity current discharges it is impossible to
`
`generate highly ionized intensive metal plasma fluxes.
`
`Metal plasma fluxes can be produced by low current quasi-stationary EXB discharges in a
`
`magnetron configuration for sputtering atoms in a moderate pressure, of e.g. 1 - 100 mTorr, and
`
`with a low—density plasma. In this case the plasma is produced by an RF~induction coil mounted
`in the deposition chamber. The electron density produced in induction plasmas is about 1017—1 018
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`m'3.
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`This method of coating work pieces has important implications for the filling of high-
`
`aspect-ratio trenches and vias encountered in microelectronic fabrication processes as well as in
`
`sputtering magnetic materials and modifying the properties of thin films by energetic ion
`
`deposition, see J. Hopwood and F. Qian, "Mechanisms for highly ionized magnetron sputtering",
`
`J. Appl. Phys. 78 (12), 15 July 1995, pp. 758 — 765.
`
`The drawbacks of this method of metal plasma production include the complexity of the
`
`RF-ionization technique and the high pressure of the sputtering gas required for producing the
`
`low-density plasma. The high pressure of the sputtering gas is required because of the high
`
`energy consumption necessary for producing a low-density plasma.
`
`The discharges in crossed fields could be implemented by simple techniques and within an
`
`extremely wide range of operating pressures: from 10'11 up to 102 Torr. Low-pressure magnetron
`
`discharges, up to 10'5 Torr, can be achieved because of the selfsputtering phenomenon, see for
`
`example S. Kadlec and J. Musil, "Low pressure magnetron sputtering and selfsputtering dis—
`
`charges", Vacuum, Vol. 47, pp. 307 - 311, 1996. This method of coating work pieces has im—
`
`portant implications for the etching of surfaces by metal ions for increasing the adhesion of de-
`
`posited layers and for the filling of high—aspect—ratio trenches and Vias encountered in micro-
`
`electronic fabrication.
`
`The currents necessary for generating a dense plasma and sustaining it by high intensity
`
`current EXB discharges are large enough for cathode spots, and possibly also for anode spots, to
`
`be formed at the cold electrode surfaces. Devices having such electrodes should therefore have a
`
`natural tendency of forming spoke—shaped azimuthal plasma inhomogeneities, arc discharges, see
`
`B. A. Tozer, "Rotating Plasma", Proc. IEEE, Vol. 112, 1965, pp. 218 - 228. Such conditions are
`
`strongly pronounced in all types of devices during the starting period of the discharges where a
`
`large driving current is needed for neutral gas burn—out.
`
`Having cold electrodes and neutral-plasma phenomena in mind, the experiments on plasma
`
`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.
`
`See W. R. Baker, A. Bratenal, A. W. De Sliva, W. B. Kunkel, Proc. 4th Int. Conf. Ionization Phe—
`
`nomena in Gases 2, Uppsala 1959, North—Holland Publishing Comp, Amsterdam, p. 1171, and
`
`W. B. Kunkel, W. R. Baker, A. Bratenahl, K. Halbach, "Boundary Effects in Viscous Rotating
`
`Plasmas", Physics Fluids, Vol. 6, 1963, pp. 699 - 708.
`
`b. 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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`5
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`form spirals with an increasing velocity in the outward radial direction, see P. B. Barber, M. L.
`Pilcher, D. A. Swift, B. A. Tozer, C. r. de la VIe conference internationale sur les phenomenes
`
`d‘ionization dans le gas 2, Paris, 1963, p. 395.
`
`c. In the Kruisvuur I device a single eccentric structure rotating around the axis with a velocity
`
`close to E/B was observed , see C. E. Rasmussen, E. P. Barbian, J. Kistemaker, "Ionization and
`
`current growth in an EXB discharge", Plasma Physics, Vol. 11, 1969, pp. 183 - 195.
`
`From the experiments mentioned abOVC and others, are formation is clearly seen to be
`
`connected with the starting period of the high intensity current EXB discharges in most devices.
`
`SUMMARY OF THE INVENTION
`
`10
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`15
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`20
`
`It
`
`is an object of the present
`
`invention to provide methods and apparatus allowing
`
`production of intensive, preferably gas or gas—metal or most preferably metal plasma flows.
`
`The problems, which the invention thus intends to solve, comprise:
`1. How to produce intensive, preferably gas or gas—metal or preferably metal plasma flows by
`ionization of gas and metal vapor produced using planar magnetron sputtering cathodes by a
`
`simple technique for producing discharges in crossed fields.
`2. How to produce these plasma flows without forming contracted arc discharges.
`3. How to provide pulsed discharges in crossed fields using the selfsputtering phenomenon.
`Thus, generally in a method for producing a plasma flow successive low and high intensity
`current quasi—stationary and non quasi—stationary discharges in crossed electric and magnetic
`fields are used, the term "crossed fields" meaning "crossed electric and magnetic fields" herein.
`For producing the plasma a succession of discharges is thus used, i.e. pulsed discharges are used.
`The discharges that are well separated in time are defined to be quasi—stationary in the cases
`where at
`least
`the most
`important physical parameters, such as current and voltage, are
`
`substantially constant or slowly varying during most of the discharge time, and are, if this
`condition is not fulfilled, non—quasi stationary. The plasma flow producing procedure can include
`
`25
`
`the following steps:
`1. A low intensity current, high voltage discharge in a magnetron magnetic configuration is used
`for metal vapor production. The following ionization of vapor is obtained by a high intensity
`current, low or high voltage discharge in the same magnetic configuration. The second, ionizing
`discharge starts immediately after the first one or with some, relatively small time delay. The
`parameters of the pulses and time delay of the second pulse are defined by the requirements im-
`
`30
`
`posed by the high ionization of sputtered vapor blobs.
`2. The metal vapor can be produced by a direct current discharge, i.e. not by pulsed discharges. In
`
`this case the metal vapor produces a continuous vapor flow out of the magnetic configuration
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`6
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`where the discharge is made. If ionizing pulses follow having a sufficient frequency and driving
`
`current it is possible to produce a continuous metal plasma flow having a modulated intensity.
`
`The following basic schemes can be used:
`
`1. The plasma can be produced in a magnetron magnetic configuration in which combined or
`
`successive low and high intensity current non-quasi—stationary discharges in crossed fields are
`
`used.
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`2. The plasma can be produced in a magnetron magnetic configuration in which a low intensity
`
`current quasi-stationary discharge is combined with or followed by a high intensity current non—
`
`quasi—stationary discharge, the discharges made in crossed fields.
`
`3. The plasma can be produced in a magnetron magnetic configuration in which combined direct
`
`current discharges and high current non-quasi-stationary discharges in crossed fields are used.
`
`4. The plasma can be produced in a magnetron magnetic configuration in which combined low
`
`intensity current non—quasi—stationary discharges and high intensity current quasi—stationary dis—
`
`charges in crossed fields are used.
`
`5. The plasma can be produced in a magnetron magnetic configuration in which combined
`
`successive low and high intensity current non-quasi—stationary discharges and high intensity
`
`current quasi—stationary discharges in crossed fields are used.
`
`6. The plasma can be produced in a magnetron magnetic configuration in which combined high
`
`intensity current non-quasi—stationary discharges and high intensity current quasi—stationary dis—
`
`charges in crossed fields are used.
`
`The combinations of discharges in crossed electric and magnetic fields mentioned above
`
`made in a magnetron magnetic configuration allow the production of plasma flows of preferably
`
`gas or gas and metal or most preferably of a metal plasma flow. For quasi—stationary discharges
`
`the choice of method can be based on the different efficiencies of the low and high current
`
`intensity discharges for sputtering and ionization in the different cases.
`
`The discharges in crossed fields have, as has been mentioned above, a natural tendency of
`
`forming spoke—shaped azimuthal plasma inhomogeneities — arc discharges. The probability of the
`
`transition of an EXB discharge in magnetron type devices to a contracted arc discharge increases
`
`with an increasing driving current. In low current discharges arcing occurs very rarely and it is
`
`possible to prevent the transition to arc discharges by specially adapted arc suppression schemes
`
`in the discharge power supply. In high current discharges there is a very high probability of arc
`
`discharges being formed and solutions to the problem of suppressing arc formation using similar
`
`schemes are not efficient. As will be described herein, are suppression can be achieved using a
`
`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
`
`balanced magnetron magnetic configuration has relatively low plasma confinement properties.
`
`Therefore, for achieving efficient arc suppression, it is necessary to use a magnetic field having a
`high strength. In this case the plasma losses caused by diffusion will decrease as B‘2 in the case of
`classic diffusion or as a B"1 in the case of Bohm diffusion, where B is the strength of the magnetic
`field. It was found that for a balanced magnetron magnetic configuration, in order to achieve
`
`efficient arc suppression,
`
`it is necessary to have a magnetic field strength of the radial B
`
`component of about 0.07 ~ 0.3 T, the radial direction here taken as directions parallel to the
`
`substantially flat surface of the cathode or target. Unbalanced and cusp-shaped magnetic confi—
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`10
`
`gurations have improved plasma confinement properties; therefore, for effective are suppression
`
`it is sufficient to have a magnetic field strength of about 0.04 — 0.3 T.
`
`The plasma‘confinement properties of the magnetic configuration strongly affect the lower
`
`limit of the operating pressure used in the space at the cathode. It was found that for improving
`
`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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`15
`
`discharge. After the starting period it is possible to initiate the discharge by the residual plasma
`
`density left from the previous pulse.
`
`In this case metal vapor is produced by using the
`
`selfsputtering phenomenon and the plasma in the magnetic trap contains primarily ions of the
`target metal. The plasma flow from the magnetic trap contains preferably ions of the target metal
`
`20
`
`as well.
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`25
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`30
`
`Generally, it can be said that the primary concept of the method described herein is to
`
`combine the magnetic configuration having improved plasma confinement properties with low
`
`and high intensity current quasi~stationary discharges and non—quasi—stationary discharges or DC
`
`and high intensity current discharges for generating stable and intensive plasma flows. Low and
`
`high intensity current quasi—stationary discharges and non—quasi—stationary discharges are
`produced one after another With a repeating frequency exceeding a minimal critical value
`
`depending on the plasma confinement properties of the magnetic trap. In the case of DC
`sputtering discharges, a high rate of ionization of gas and metal vapor is produced by a periodic
`
`repetition of the ionizing discharges.
`
`The methods and devices described herein can be used both in the "Rotating Plasma
`
`Approach" and the "Secondary Electron Approach" mentioned above.
`Additional objects and advantages of the invention will be set forth in the description which
`
`follows, and in part will be obvious from the description, or may be learned by practice of the
`
`invention. The objects and advantages of the invention may be realized and obtained by means of
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`8
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`the methods, processes,
`
`instrumentalities and combinations particularly pointed out
`
`in the
`
`appended claims.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`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
`
`hereinbelow with reference to the accompanying drawings, in which:
`
`~ Figs. la - lf are schematic views of different magnetron magnetic configurations used in
`
`10
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`25
`
`magnetron sputtering, in which
`
`— Fig. la is a View of a first type of an unbalanced magnetron magnetic configuration,
`
`- Fig. lb is a View of a balanced magnetron magnetic configuration,
`
`— Fig. lc is a view of a second type of an unbalanced magnetron magnetic configuration,
`- Figs. 1d and 1e are views illustrating the magnetic configuration created by permanent magnets
`
`placed behind the target and an electromagnetic coil placed in front ofthe target,
`
`— Fig. If is a View of a cusp—shaped magnetic configuration,
`— Fig. 1g is a View from above of a magnetic configuration typical of magnetrons having a
`
`rotating magnet,
`- Fig. lb is a schematic cross—sectional View showing the magnetic force lines in the magnetic
`
`configuration of Fig. 1 g,
`- Figs. 2a and 2b are schematic diagrams illustrating limits between low and high current
`discharges of the quasi—stationary and non-quasi—stationary type respectively,
`
`- Figs. 3a and 3b are schematic diagrams of current and voltage pulses respectively as functions
`
`of time for sputtering and ionizing discharges in crossed fields,
`
`~ Fig; 4 is a schematic diagram of periodic current pulses of the kind illustrated in Fig. 3a as a
`
`function of time,
`
`~ Fig. 5 is a schematic diagram similar to that of Fig. 4 showing an alternative shape of the
`
`current pulses,
`— Fig. 6 is a schematic diagram similar to that of Fig. 4 showing current pulses superimposed on a
`
`30
`
`constant current level,
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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,
`— 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. 7a,
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`- Fig. 8a is an electrical circuit diagram of a device for producing a metal vapor and the ionization
`thereof, the device having two pulsed power supplies connected in parallel,
`- 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,
`— 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. 80,
`- Fig. 12a is a schematic cross-sectional view of a plasma source utilizing discharges in crossed
`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. 1c, and
`— Fig. 12b is a schematic view similar to that of Fig. 12a illustrating a plasma source utilizing
`discharges in crossed electric and magnetic fields for gas or gas and metal or metal plasma
`production, corresponding to the types of magnetron magnetic configurations shown in Figs. ld
`and lf.
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`DETAILED DESCRIPTION
`
`The magnet configurations of magnetron sputtering cathodes preferably used in the
`conventional art for a magnetic field strength of up to 0.1 T are illustrated in Figs. lb — 1f. Thus,
`in Fig. lb a balanced magnetron magnetic configuration is shown whereas in Figs. la and lo
`unbalanced magnetron magnetic configurations are showu. The altering of the magnetic field
`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
`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 permanent 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
`cathode and the outer magnet located at the edge of the rear side of the 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. la. However, the strength
`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. 1c 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. Here, 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. la and lb are classified as Type I or Type
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`II respectively, see B. Window and N. Savvides, "Charged particle fluxes from planar magnetron
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`sputtering sources", J. Vac. Sci. Technol, A 4(2), 1986, pp. 196 — 202.
`An alternative way to accomplish different magnetic configurations is to use an external,
`preferably toroidal, magnetic coil, see I. lvanov, P. Kazansky, L. Hultrnan, I. Petrov, and J—E.
`Sundgren, "Influence of an external axial magnetic field on the plasma characteristics and
`deposition conditions during direct current planar magnetron sputtering", J. Vac. Sci. Technol, A,
`12(2), 1994, pp. 314 - 320. Thus, in the Views of Figs. 1d, 1e and 1f magnetic configurations
`created by permanent magnets 2, 3 placed behind the target 1 and an electromagnetic coil 5
`placed in front of the target are shown. In Figs. 1d and 1e the coil has a diameter larger than the
`diameter of the target. The arrows Show the direction of the magnetic field. In Fig. lf a cusp-
`shaped magnetic configuration is shown in which the coil 5 has a diameter smaller than the
`diameter of the target and of the outer magnet. The electromagnetic coil 5 has a height bcoil: 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 Deon. 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
`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
`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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`Depending on the direction of the electric current in the coil 5, its field can be used for as—
`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 1016 m'3 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,
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`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 cusp—shaped magnetic configuration of Fig. 1f has been used for production of a dense
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`plasma by high current quasi—stationary discharges generated by periodic pulses having a low
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