Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
  • H01J37/32—Gas-filled discharge tubes
  • H01J37/32009—Arrangements for generation of plasma specially adapted for examination or treatment of objects, e.g. plasma sources
  • H01J37/32357—Generation remote from the workpiece, e.g. down-stream
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
  • G11B5/62—Record carriers characterised by the selection of the material
  • G11B5/72—Protective coatings, e.g. anti-static or antifriction
  • G11B5/727—Inorganic carbon protective coating, e.g. graphite, diamond like carbon or doped carbon
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C17/00—Surface treatment of glass, not in the form of fibres or filaments, by coating
  • C03C17/22—Surface treatment of glass, not in the form of fibres or filaments, by coating with other inorganic material
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
  • G11B5/84—Processes or apparatus specially adapted for manufacturing record carriers
  • G11B5/8408—Processes or apparatus specially adapted for manufacturing record carriers protecting the magnetic layer
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J27/00—Ion beam tubes
  • H01J27/02—Ion sources; Ion guns
  • H01J27/16—Ion sources; Ion guns using high-frequency excitation, e.g. microwave excitation
  • H01J27/18—Ion sources; Ion guns using high-frequency excitation, e.g. microwave excitation with an applied axial magnetic field
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
  • H01J37/02—Details
  • H01J37/04—Arrangements of electrodes and associated parts for generating or controlling the discharge, e.g. electron-optical arrangement, ion-optical arrangement
  • H01J37/08—Ion sources; Ion guns
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C2217/00—Coatings on glass
  • C03C2217/20—Materials for coating a single layer on glass
  • C03C2217/28—Other inorganic materials
  • C03C2217/282—Carbides, silicides
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C2218/00—Methods for coating glass
  • C03C2218/10—Deposition methods
  • C03C2218/15—Deposition methods from the vapour phase
  • C03C2218/151—Deposition methods from the vapour phase by vacuum evaporation

Definitions

• the present invention relates generally to thin films and methods for their deposition, and more particularly, provides diamond-like films, plasma beam deposition systems, and methods useful for production of diamond-like protective overcoats on magnetic recording media and other industrial applications.
• Diamond-like carbon can generally be defined as a metastable, high density form of amorphous carbon. Diamond-like carbon is valued for its high mechanical hardness, low friction, optical transparency, and chemical inertness.
• Diamond-like carbon films often involves chemical vapor deposition techniques, the deposition processes often being plasma enhanced.
• Known diamond-like films often include carbon with hydrogen, fluorine, or some other agent.
• the durability and advantageous electrical properties of diamond-like carbon films have led to numerous proposals to apply these films to semiconductors, optics, and a wide variety of other industrial uses.
• Unfortunately, the cost and complexity of providing these advantageous diamond ⁇ like carbon films using known chemical vapor deposition processes has somewhat limited their use.
• diamond-like carbon coating films have been deposited in laboratories, many of these films have been found to have less than ideal material characteristics.
• Magnetic recording disks generally comprise a substrate having a magnetic layer and a number of underlayers and overlayers deposited thereon. The nature and composition of each layer is selected to provide the desired magnetic recording characteristics, as is generally recognized in the industry.
• the information stored in magnetic recording media generally comprises variations in the magnetic field of a thin film of ferromagnetic material, such as a magnetic oxide or magnetic alloy.
• a protective layer is formed over the top of the magnetic layer, and a layer of lubricating material is deposited over the protective layer.
• Sputtered amorphous carbon overcoats have been shown to provide a high degree of wear protection with a relatively thin protective layer.
• Magnetic recording disk structures including sputtered amorphous carbon have been very successful and allow for quite high recording densities. As with all successes, however, it is presently desired to provide magnetic recording disks having even higher recording densities. Recording densities can generally be improved by reducing the spacing between the recording transducer, called the read/write head, and the magnetic layer of the magnetic recording disk (or more specifically, between the read/write head and the middle of the magnetic layer) . In modern magnetic recording systems, the read/write head often glides over the recording surface on an air bearing, a layer of air which moves with the rotating disk.
• the disks surface is generally rougher (and the glide height therefore higher) than would otherwise be ideal for high density magnetic recording. Even if this glide height is reduced (or eliminated) , the read/write head will be separated from the recording layer by the protective amorphous carbon overcoat.
• This protective layer alone may, to provide the desired media life, limit the areal density of the media.
• overcoat layer thicknesses are dictated by durability and continuity limitations. Sputtered carbon frequently becomes discontinuous at thicknesses below about 5 ⁇ A.
• the durability requirements of rigid magnetic recording media generally dictate that the distance between the read/write head and the magnetic recording layer be maintained, even though this limits the areal density of the magnetic recording media.
• such an improved overcoat will provide durability and reliability without having to resort to the density-limiting glide heights and/or protective overcoat thickness of known rigid magnetic recording media, and without subjecting the media substrates to excessive temperatures. It would also be desirable to provide improved diamond-like carbon materials and methods for their deposition. It would be particularly desirable if such materials and methods could be utilized for practical rigid magnetic recording media with reduced spacing between the read/write head and the magnetic recording layer, ideally by providing a flatter, smoother, and thinner protective coating which maintained or even enhanced the durability of the total recording media structure. It would also be advantageous to provide alternative methods and systems for depositing such protective layers, for use in the production of magnetic recording media, as well as integrated circuits, optics, machine tools, and a wide variety of additional industrial applications.
• U.S. Patent No. 5,182,132 describes magnetic recording media having a diamond-like carbon film deposited with alternating circuit plasma enhanced chemical vapor deposition methods.
• U.S. Patent No. 5,462,784 describes a fluorinated diamond-like carbon protective coating for magnetic recording media devices.
• European Patent Application 700,033 describes a side-mounted thin film magnetic head having a protective layer of diamond-like carbon.
• European Patent Application No. 595,564 describes a magnetic recording media having a diamond-like protective film which consists of carbon and hydrogen.
• U.S. Patent No. 5,156,703 describes a method for the surface treatment of semiconductors by particle bombardment, the method making use of a capacitively coupled extraction grid to produce an electrically neutral stream of plasma. V.S.
• Veerasamy et al described the properties of tetrahedral amorphous carbon deposited with a filtered cathodic vacuum arc in Solid-State Electronics, vol. 37, pp. 319-326 (1994) .
• the recent progress in filtered vacuum arc deposition was reviewed by R.L. Boxman in a paper presented at the International Conference of Metallurgical Coatings and Thin Films located at San Diego in April of 1996.
• Electron cyclotron wave resonances in low pressure plasmas with a superimposed static magnetic field were described by Professor Oechsner in Plasma Physics , vol. 15, pp. 835-844 (1974) .
• the present invention provides systems and methods for the deposition of an improved diamond-like carbon material, particularly for the production of magnetic recording media.
• the diamond-like carbon material of the present invention is highly tetrahedral, that is, it features a large number of the sp 3 carbon-carbon bonds which are found within a diamond crystal lattice.
• the material is also amorphous, providing a combination of short-range order with long-range disorder, and can be deposited as films which are ultrasmooth and continuous (pin-hole free) at thicknesses substantially lower than known amorphous carbon coating materials.
• the carbon protective coatings of the present invention will often be hydrogenated, generally providing a significantly higher percentage of carbon-carbon sp 3 bonds than known hydrogenated amorphous diamond-like carbon coatings having similar compositions, and may optionally be nitrogenated.
• capacitive coupling forms a highly uniform, selectively energized stream of ions from a dense, inductively ionized plasma.
• inductive ionization is enhanced by a relatively slow moving (or "quasi-static") magnetic field, which promotes resonant ionization and ion beam homogenization.
• the materials, systems, and methods of the present invention will find applications not only in the field of magnetic recording media and related devices, but also in integrated circuit fabrication, optics, machine tool coatings, and a wide variety of film deposition and etching applications .
• the present invention provides a method for producing magnetic recording media, the method comprising forming a magnetic layer over a substrate, and ionizing a source material so as to form a plasma containing carbon ions.
• the carbon ions are energized to form a stream from the plasma toward the substrate, so that carbon from the ions is deposited on the substrate.
• the ions impact with an energy which promotes formation of sp 3 carbon-carbon bonds.
• such a method can form a highly tetrahedral amorphous carbon protective layer, generally having more than about 15% sp 3 carbon-carbon bonds.
• the impact energy of the energetic carbon ions is within a pre-determined range to promote formation of the desired lattice structure, the bonds apparently being formed at least in part by subplantation.
• each carbon ion impacts with an energy of between about 100 and 120eV.
• the resulting highly tetrahedral amorphous carbon protective layer includes more than about 35% sp 3 carbon-carbon bonds, with particularly preferred methods producing more than about 70% sp 3 carbon-carbon bonds.
• the stream will be primarily composed of ions having a uniform weight, and the impact energy will preferably be substantially uniform. In some embodiments, this uniformity is promoted through filtering of the ion stream.
• the energizing step generally comprises striking a plasma using a solid cathodic arc of carbon source material.
• the stream will be energized by applying an alternating potential between a coupling electrode and an extraction grid so as to self-bias the plasma relative to the extraction grid through capacitive coupling, thereby extracting the ion stream through the grid. Hydrogen and/or nitrogen may also be included, both in the ion stream and the protective layer.
• the present invention provides magnetic recording media comprising a substrate, a magnetic layer disposed over the substrate, and a protective layer disposed over the magnetic layer.
• the protective layer comprises a highly tetrahedral amorphous carbon, generally having more than about 15% sp 3 carbon-carbon bonds. Preferably, these bonds are formed at least in part by directing an energetic stream of carbon ions onto the substrate.
• the protective layer includes more than about 35% sp 3 carbon-carbon bonds, with particularly preferred embodiments including more than about 70% sp 3 carbon-carbon bonds.
• Such protective layers are ultrasmooth and continuous at thicknesses of less than about 75A, and will provide durable recording media even at thicknesses of less than about 50A.
• these dense protective materials may allow highly durable recording media with areal recording densities of over 1 gigabyte per square inch with reduced read/write head glide heights of lower than about l ⁇ ", optionally within a near-contact or continuous contact recording systems.
• the present invention provides a method for enhancing an ion beam, the ion beam produced by confining a plasma within a plasma volume, inductively ionizing the plasma, and forming a stream of ions from within the plasma volume by capacitive coupling.
• the method comprises moving a magnetic field through the plasma to promote resonant inductive ionization, preferably by sequentially energizing each of a plurality of coils disposed radially about the plasma volume.
• the present invention provides an inductive ionization system for use with an ion-beam source.
• the source includes an antenna disposed about a plasma volume for inductively ionizing a plasma therein.
• a coupling electrode is exposed to the plasma volume and an extraction electrode is disposed over an opening of the plasma volume, so that the extraction electrode is capable of expelling ions of the plasma through the grid by capacitive coupling.
• the system comprises at least one coil disposed adjacent the plasma volume capable of applying a transverse magnetic field to the plasma volume so as to promote resonant inductive ionization by the antenna.
• the magnetic field can be moved through the plasma container to homogenize the expelled ion stream. This movement of the magnetic field, which is optionally provided by selectively energizing coils radially disposed about the plasma volume, may also further densify the plasma by promoting particle collisions through a churning or mixing effect.
• the present invention provides a diamond-like material comprising carbon in the range between about 72 and 92 atomic percent, and hydrogen in the range between about 8 and 18 atomic percent .
• the material is amorphous, and between about 15 and 85 percent of carbon- carbon bonds are sp 3 bonds.
• sp 3 bond formation will be promoted with subplantation using ion-beam deposition from a plasma beam source, so that the number of such bonds will be higher than known materials having similar compositions.
• the highly tetrahedral amorphous carbon and hydrogenated carbon of the present invention will have fewer polymer-like hydrogen chains, and will generally exhibit enhanced thermal and mechanical stability.
• the present invention provides a method for deposition of highly tetrahedral amorphous carbon over a substrate, the method comprising ionizing a source material to form a plasma and confining the plasma within a plasma volume.
• the plasma is capacitively coupled to form a stream flowing outwardly from within the plasma volume.
• the stream includes carbon ions from the plasma and is directed onto the substrate.
• Such a method allows deposition of carbon ions of uniform size with a uniform energy, and allows tailoring of the energetic carbon ions to specifically promote sp 3 bonding through subplantation.
• the source material typically comprises a gas having a substantially coherent dissociation energy spectra, the source gas ideally comprising acetylene.
• the ions strike the substrate with an impact energy of between about 57 and 130 eV for each carbon atom, ideally being between about 80 and 120 eV each.
• the present invention provides an ion-beam source comprising a container defining a plasma confinement volume.
• the container has an opening, and an antenna is disposed about the plasma volume so that application of a first alternating potential to the antenna is capable of inductively ionizing a plasma therein.
• a coupling electrode is electrically coupled to the plasma volume and an extraction electrode is disposed over the opening of the container.
• the extraction electrode has a surface area which is substantially less than the coupling electrode surface, so that application of a second alternating potential between the coupling electrode and the extraction electrode is capable of expelling ions of the plasma through the grid.
• At least one coil is disposed adjacent the container, and is capable of applying a transverse magnetic field to the plasma volume, thereby promoting highly efficient inductive ionization resonance by the antenna.
• the magnetic field can be moved through the plasma container to homogenize the expelled ion stream. This movement of the magnetic field, which is optionally provided by selectively energizing coils radially disposed about the plasma confinement volume, may further density the plasma by promoting particle collisions with a churning or mixing effect.
• the present invention provides an ion-beam source comprising plasma containment means for confining a plasma within a plasma volume.
• Inductive ionization means inductively couples a first alternating current with the plasma so as to ionize the plasma within the plasma volume.
• a moving magnetic field generation means provides resonant densification and homogenization of the ionized plasma within the plasma volume.
• Ion extraction means forms a stream of ions out from the plasma volume.
• the present invention provides a method for producing an ion beam, the method comprising confining a plasma within a plasma volume, inductively ionizing the plasma, and forming a stream of ions from within the plasma volume by capacitively coupling the plasma with an extraction grid.
• This capacitive coupling self-biases the plasma relative to the grid, and can be used to produce a quasi-neutral plasma stream.
• a transverse magnetic field is applied to density the plasma by promoting resonant inductive ionization.
• the magnetic field is moved through the plasma volume to homogenize the plasma and plasma stream.
• Fig. 1 is a cross-sectional view of a magnetic recording disk including the tetrahedral amorphous hydrogenated carbon protective layer of the present invention.
• Figs. 1A and B illustrate the effects of nitrogen doping on the tetrahedral amorphous hydrogenated carbon of the present invention.
• Figs. 2 schematically illustrates a method for depositing the highly tetrahedral amorphous hydrogenated carbon over the disk of Fig. 1, and also shows a hybrid inductive/capacitive plasma beam source according to the principles of the present invention.
• Fig. 2A is a cross-sectional view of the hybrid source of Fig. 2, showing the inductive ionization antenna and quasi-static magnetic field generating coils which density and homogenize the plasma.
• Fig. 3A illustrates an alternative method and system for depositing highly tetrahedral amorphous hydrogenated carbon over the disk of Fig. 1 using an acetylene plasma from a plasma beam source.
• Figs. 3B and C illustrate capacitive coupling of the plasma to extract a stream of ions when using the plasma beam source of Fig. 3A.
• Fig. 3D illustrates an alternative embodiment of a plasma beam source, in which the effective area of the coupling electrode can be varied to provide further control over the ion density and ion energy.
• Figs. 3E and F illustrate operating characteristics of plasma beam sources for deposition of diamond-like carbon.
• Figs 4A and B illustrate known resonant inductive ionization of a plasma with a fixed magnetic field.
• Figs. 4C and D explain densification of the plasma provided by Electron Cyclotron Wave Resonance.
• Fig. 5 illustrates an alternative method and deposition system for producing the recording disk of Fig. 1, which system relies upon a filtered cathodic arc for deposition of the highly tetrahedral amorphous hydrogenated carbon material of the present invention.
• Figs. 6A-8 show experimental data, as described in detail in the experimental section.
• a rigid magnetic recording disk 2 comprises a non-magnetic disk substrate 10, typically composed of an aluminum alloy, glass, ceramic, a glass-ceramic composite, carbon, carbon-ceramic composite, or the like.
• An amorphous nickel-phosphorus (Ni-P) layer 12 is formed over each surface of the disk substrate 10, typically by plating.
• the Ni-P layer is hard, and imparts rigidity to the aluminum alloy substrate.
• a chromium ground layer 14 is formed over Ni-P layer 12, typically by sputtering, and a magnetic layer 16 is formed over the ground layer 14. Please note that these layers are shown schematically only, as NiP layer 12 will typically be much thicker than the other layers.
• the magnetic layer 16 comprises a thin film of a ferromagnetic material, such as a magnetic oxide or magnetic alloy. Magnetic layer 16 is typically sputtered over ground layer 14 in a conventional manner.
• the magnetic layer will often be composed of a cobalt alloy, such as a CoCrTaPtB, CoCrPtB, CoCrTa, CoPtCr, CoNiCr, CoCrTaXY (X and Y being selected from Pt, Ni, W, B, or other elements) or the like.
• the magnetic layer may be formed as a single layer, or may comprise two or more layers formed over one another.
• the 12 thickness of magnetic layer 16 is typically in the range from about 200A to 800A.
• the protective layer 18 of the present invention will generally comprise a highly tetrahedral amorphous carbon, typically having more than about 15% sp carbon-carbon bonds, preferably being more than about 35% sp 3 carbon-carbon bonds, and ideally being over about 70% sp 3 carbon-carbon bonds, as measured using Raman fingerprinting and electron energy loss spectroscopy.
• protective layer 18 may also include hydrogen, generally forming in the range between about 2 and 30 atomic percent of the protective material, preferably being between 8 and 18 atomic percent.
• a conventional lubricating layer 20 is disposed over the protective layer.
• protective layer 18 will generally include significantly less hydrogen than comparable known diamond-like films. This compositional difference may be explained in part by the formation of sp 3 bonds through subplantation of the energetic carbon ions during deposition. Effectively, the energetic ions deposited using the methods described hereinbelow impact on the growing film surface, and are driven into the film so as to cause densification. This process may also explain why the protective layer of the present invention includes a higher percentage of quartenary carbon sites (sp 3 carbon sites with no hydrogen neighbors) and greater hardness than known alternative amorphous carbon materials.
• the microstructure of conventional hydrogenated amorphous carbons includes polymer-like hydrocarbon chains. Although hydrogen enhances the formation of tetrahedrally bonded carbon atoms, above a certain threshold value of hydrogen content, carbon films become polymeric and hence lose their protective properties. Through subplantation, the materials of the present invention overcome this limitation. As subplantation promotes formation of sp 3 bonds without relying on additional hydrogen content alone, polymerization can be avoided. This represents a substantial advantage over known, more highly hydrogenated diamond-like carbon materials, in which polymerization significantly limits both thermal and mechanical stability.
• the carbon-carbon sp 3 bonds of the materials of the present invention will generally be stable up to temperatures of about 700°C, so that an enhanced percentage of sp 3 bonds with a low hydrogen content represents a significant advantage.
• the films of the present invention may also be nitrogenated.
• the electrical conductivity of the present highly tetrahedral amorphous carbon can be controllably varied over a wide range by the selective incorporation of nitrogen during the C 2 H 2 plasma beam deposition process described hereinbelow.
• this variation will be provided without significantly varying the structural properties of the film.
• nitrogen incorporation may be related to the formation of sp 2 bonds.
• the highly tetrahedral amorphous carbon materials of the present invention also provide a number of advantages over known protective layers for recording media.
• the bond structure of this material provides physical properties approaching those of diamond, including a hardness of over about 50GPa, with certain species having hardness of up to about 80GPa.
• the present protective overcoats have high density, generally being over about 2.5 grams per cubic centimeter, and are also very chemically inert.
• these coatings are smooth and continuous (pinhole-free) at very low thicknesses, and provide a durable protective layer when deposited to a thickness of less than 75A, preferably being less than 50A thick.
• films of over 150A may be more susceptible to delamination, and surface roughness may increase with thickness.
• the high mechanical hardness and low friction surfaces provided by these materials lead to enhanced tribological performance, providing recording media which are highly tolerant to the mechanical abrasion and contact start- stop demands of modern recording media systems, and allowing increased areal density through reduced separation between the read/write and the magnetic layer. This separation may be reduced by either a reduction in the protective layer thickness, or by a reduction in head glide height, and preferably by a reduction in both.
• Protective layer 18 is generally in the range between about 30A and 70A, which will allow the disk to meet recording media industry durability and stiction test requirements.
• composition and characterization of the protective film of the present invention are highly dependent on the deposition method, and in particular, depend strongly on the energy and uniformity of carbon ions striking the deposition surface.
• Hybrid ion beam source 30 generally includes an inductive ionization system 32, a quasi-static magnetic field system 34, and a capacitive ion beam extraction system 36.
• induction system 32 ionizes a plasma 38.
• the energy transfer between induction system 32 and plasma 38 is greatly enhanced and homogenized by a transverse magnetic field generated by quasi-static field system 34.
• the deposition ions of plasma 38 are actually directed to recording disk 2 (or to any other substrate on which deposition is desired, or from which etching will be performed) using capacitive coupling system 36.
• hybrid source 30 provides a particularly advantageous system for deposition of the protective coating 18, a variety of alternative deposition systems may also be used. As a plasma beam source deposition system shares a number of the features of hybrid source 30, but is simpler in operation, diamond-like carbon deposition using a plasma beam source 50 will be described with reference to Figs. 3A-F, after which other aspects of hybrid source 30 will be explained in more detail .
• Plasma beam source 50 includes a plasma container 52 which defines a plasma volume 54 therein.
• Container 52 is typically an 8 cm diameter glass tube, or may alternatively comprise quartz or the like.
• a coupling electrode 56 having a relatively large surface 58 here forms one end of the container.
• the coupling electrode may be disposed within or external to the container, and may optionally extend axially along the walls of the container.
• coupling electrode 56 is generally electrically coupled to the plasma, to a matching network 60, and to a radiofrequency coupling power supply 62.
• Plasma coupling system 36 includes coupling electrode 56, the frequency generator and matching network 60, 62, and an extraction grid 64.
• the extraction grid will be grounded as shown.
• extraction grid 64 has a much smaller surface area exposed to the plasma than the coupling electrode 56.
• RF power typically at about 13.56 MHz, is supplied by the frequency generator through the matching network and a capacitor to the coupling electrode. This frequency will often be set by government regulations, and may alternatively be about 27.12 MHz, or some other multiple thereof.
• the extraction grid typically comprises a graphite rim 66 defining an aperture, and tungsten filaments which are maintained under tension. Hence, extraction grid 64 resists any distortion due to thermal expansion.
• a number of alternative materials may be used in the filaments, the filament materials preferably having a low sputtering yield.
• vacuum port 68 internal pressure within plasma volume 54 is reduced by removing gas through vacuum port 68. While the vacuum port is here shown behind the grid, it will preferably be disposed between grid 64 and disk 2.
• the plasma shifts to a positive DC potential with respect to the extraction grid, due to the relative mobility of the electrons as compared to the ions within the plasma.
• the greater mobility of electrons than ions in the plasma causes the plasma to form a sheath between itself and each electrode. The sheaths act as diodes, so that the plasma acquires a positive DC bias with respect to each electrode.
• the total radiofrequency potential V 0 will be divided between the sheaths adjacent the powered electrode and the grounded electrode, according to their respective capacitances. As the extraction electrode is grounded, the voltage of the plasma itself is given by the equation
• V V 0 (C e /(C g + C e ))
• C e is the capacitance of the coupling electrode, while C g is the capacitance of the extraction grid.
• this plasma voltage biases the plasma relative to the grid, accelerating the ions through the extraction grid and toward the substrate.
• the plasma beam source allows the biasing voltage to be selectively controlled, providing a highly advantageous mechanism for controlling ion impact energy.
• the size of the bias voltage at each electrode can be controlled by varying the electrode areas.
• the biasing of the plasma relative to the coupling electrode is relatively low, so that source 50 provides a fairly efficient use of the source gas material, which is generally provided through source inlet 70 adjacent coupling electrode 56. While some material will be deposited on the container walls at higher power settings, use of the plasma beam source in an etching mode may allow self cleaning.
• FIG. 3B The relationship of electron current, ion current, and the radiofrequency potential is illustrated in Fig. 3B.
• Fig. 3C A simplified electrical diagram for analysis of the plasma, the extraction grid sheath, and the coupling grid sheath, is shown in Fig. 3C.
• Plasma 74 is here contained within a hyperbolic magnetic field produced by magnets 78.
• An axially movable coupling electrode 80 is supported by a movable ceramic pipe 82 which slides axially through a ceramic end 84 of the plasma container vessel.
• the magnetic confinement of the plasma allows the effective area of coupling electrode 80 to be varied by moving the coupling electrode axially relative to the plasma. This allows the bias voltage (and hence the ion energy) to be varied without changing the radiofrequency power or the gas pressure.
• the ion saturation current density (deposition rate) and ion energy can be varied by changing the radiofrequency power and gas feed stock flow rate.
• the ion current and ion energy distribution can be measured with a Faraday cup 86 in the substrate plane 88.
• Fig. 3E shows variations of ion current and mean ion energy with electrode position D for a range of radiofrequency powers.
• the ion energy depends on at least two factors : the acceleration potential across the grid sheath, and the energy lost by collisions within the sheath.
• the effects of these factors are illustrated in Fig. 3F.
• the inset to Fig. 3F shows that the ion energy distribution of the plasma beam is quite sharp, with a width of approximately 5% about the bias voltage. The sharpness apparently arises for at least two reasons. First, ions lose little energy in the low plasma pressure through collisions within the sheath. Second, the sheath width varies inversely with the square root of pressure, so that the sheath is quite wide at low pressures.
• the ions may be accelerated by the mean voltage rather than the instantaneous voltage.
• the ion energy distribution width is also found to vary linearly with pressure, which indicates that the ion energy distribution width is controlled mainly by ion collisions in and above the sheath.
• the decomposition or dissociation of hydrocarbons in plasma 74 depends strongly on the source gas, the operation pressure, and the gas flow rate. Usually, hydrocarbon plasmas exhibit a wide spectrum of hydrocarbon radicals in an ionized and/or neutral state.
• the plasma composition depends on the various chemical pathways in the plasma, and these depend on the plasma parameters such as electron temperature, electron density, and degree of ionization. As a result, a number of different ions may be present in the plasma, and the composition may change markedly under different conditions, making uniform deposition of homogeneous hydrogenated carbon materials fairly problematic.
• acetylene provides a highly advantageous source gas because of its relatively simple dissociation pattern.
• the plasma decomposition of a molecule can be described in terms of electron-molecule (primary) and ion-molecule (secondary) collisions, and their associated rate coefficients or their related appearance potentials.
• the dissociation of acetylene is dominated by its ionization at an appearance potential of 11.2 eV.
• Acetylene may be unique among the hydrocarbons in having such a well-defined reaction path.
• the ionic composition of a plasma beam produced using an acetylene source gas produces a mass spectra at various plasma pressures which are dominated by the C 2 H 2 + ion and other hydrocarbon ions having two carbon atoms, collectively referred to as the C 2 species.
• the next most significant ions are the C 4 ions, which have been found to decrease in intensity as the pressure is lowered, being below 5% if the pressure is maintained below 5 x 10 "5 mbar.
• carbon deposition using the plasma beam source and hybrid source of the present invention is preferably performed using a feed stock which comprises acetylene.
• N 2 , NF 3 , or some other nitrogen feedstock may also be included to provide nitrogenated films.
• the particle flux or stream provided by a plasma beam deposition system or a hybrid deposition system will generally have a higher degree of ionization than conventional deposition techniques.
• the formation of carbon-carbon sp 3 bonds through the subplantation effect may only be significant if sufficient ions are present in the particle stream.
• Preferably, at least 15% of the particles will comprise ions.
• the film-forming particle flux will comprise over 90% ions.
• the incident power provided to the coupling electrode will generally be between about 50 and 700 watts, ideally being between about 200 and 300 watts.
• two plasma beam sources may be provided, preferably having independent radiofrequency generators which are phase-matched, ideally being synchronized in a master/slave configuration.
• Radiofrequency reflected power will generally be between about 5 and 70 watts, and should be minimized by selection of proper network elements.
• the magnetic containment field coil nearest the substrate may be provided with a current of between 1 and 8 amps, ideally being about 7 amps.
• the outer field coil will have between one-half and 5 amps of current flowing therethrough, wherein the current is the reverse polarity of the inner coil current.
• Gas flow rates of from 5 seem to 30 seem are sufficient to maintain the plasma, with the gas flow rate ideally being about 18 seem. Igniting the plasma is facilitated by providing an initial burst of between 40 and 50 seem of N 2 gas. A nitrogen gas flow may be maintained for nitrogenation of the film.
• the plasma beam source is capable of depositing ions with an energy of between about 10 eV and 500 eV, while the optimal energy for deposition of carbon is generally between about 80 and 120 eV per carbon atom.
• the hydrogen content may be between about 8 and 18 atomic percentage, while dopant gases of between .7 atomic percent and 10 atomic percent, typical dopant gases including N 2 , or PH 3 .
• Carbon deposition rates of between 2 and 12A per second can be provided by plasma beam source deposition methods within the above operating ranges, ideally being between about 8 and 9A per second to provide the highest quality films. Deposition times of between about 6 and 30 seconds are generally used at these rates to provide a sufficient protective coating for magnetic recording media. In work in connection with the present invention, M.
• plasma beam source deposition systems and methods described with reference to Figs. 3A and 3D have several advantages, including the ability to accurately control the ion deposition energy and flux, these plasma beam sources do have some disadvantages.
• One primary disadvantage of plasma beam source deposition is that the capacitively coupled plasma density, and hence the deposition rate, is relatively low.
• the ionization coefficient tends to drop off at these higher pressures, thereby limiting the total plasma density.
• the proportion of ions in the particle stream decreases with increasing pressures. Basically, at higher operating pressures, gas scattering will reduce and disperse the ion energy. In fact, deposition of highly tetrahedral amorphous carbon at pressures of over 30mTorr when using the exemplary system is problematic, as films deposited at such pressures are formed primarily with low energy radicals.
• the particle flux increasingly includes varying particle masses (C 2 , C 4 , C 6 , C 8 ... ) .
• plasma beam deposition will preferably take place with pressures below lmTorr, ideally at a pressure of between about 0.1 and 0.5MTorr. This, in turn, generally limits the deposition rates which may be achieved by plasma beam sources and methods which rely solely on capacitative coupling to maintain the plasma.
• hybrid source 30 maintains the advantageous ion energy control of the plasma beam source, but provides higher plasma densities and enhanced deposition rates without relying on increases in pressure.
• hybrid source 30 combines an inductive ionization system 32 with a capacitive coupling system 36 (similar to that used in the plasma beam sources described above) to provide a high density and low pressure plasma.
• the inductive ionization system will again be explained in isolation, here with referenced to Figs. 4A and B.
• Inductive ionization system 32 comprises an alternating power source 90 capable of generating frequencies in roughly the radiofrequency-microwave range, preferably providing a potential with a frequency of about 27.12 MHz (or some multiple thereof) .
• a frequency matching network 92 is provided, but the power is here coupled to the plasma using antenna 94 disposed around the plasma container 52.
• this minimizes any self-biasing of the plasma relative to the antenna, and minimizes deposition of source materials onto the walls of the container itself.
• Plasma within an inductive discharge may be energized in a non-resonant or resonant inductive mode.
• a small DC magnetic field is superimposed on the plasma volume to provide enhanced ion energy transfer and plasma densification through a process which is generally described as resonant ionization.
• Antenna 94 may be described as a dielectric wall around the axis of the plasma container.
• antenna 94 may be modeled as a single loop inductive coil disposed about the plasma. Regardless, the potential of the plasma with respect to the container surface remains low, while the plasma density is quite high.
• antenna 94 surrounds a cylindrical plasma container having a length between one third and three times its diameter, preferably being of nearly equal length and diameter.
• the antenna consists of a metal cylinder with a longitudinal slit.
• the superimposed static magnetic field B is generally normal to the axis of the plasma cylinder, and is applied by at least one magnetic coil 96 adjacent the plasma container. Resonant ionization potentials and magnetic field strengths are more fully described by Professor Oechsner in Plasma Physics, vol. 15, pp. 835-844 (1974) , the full disclosure of which is incorporated herein by reference.
• Electron Cyclotron Wave Resonance ECWR
• ECR Electron Cyclotron Resonance
• n is the refractive index
• c is the speed of light
• ⁇ is the frequency of the electromagnetic wave
• k is the magnitude of the propagation vector for the electromagnetic wave.
• ⁇ is the plasma frequency.
• wave propagation is possible when the phase velocity (and therefore the refractive index) is positive.
• Schematic plots of the refractive index of a cold plasma and the phase velocity of a cold plasma (both as a function of frequency) are given in Figs. 4C and 4D. Examination of these plots reveals that both are positive below ⁇ c .
• the refractive index for a driving potential having a frequency of 13.56 MHz will reach values above 100. This means that wavelengths within the plasma may be reduced by 1/100 or more. If the wavelength can be reduced to the dimensions of the plasma container, it is possible to create standing waves in the plasma which provide a resonant effect. This ECWR will depend on the magnetic filed strength as well as the plasma container dimensions. If our plasma container has a diameter a, this resonant effect can generally be achieved if:
• ⁇ 1, 2, 3, ..., ⁇ is the wavelength, and k r being the resonant magnetic field.
• the resonance can be tuned by varying the refractive index of the plasma.
• the refractive index for the right-hand polarized wave will depend on both the magnetic field and the plasma frequency.
• the variation of n r with the plasma frequency complicates this tuning somewhat, because the plasma frequency itself depends on the plasma density, which will, in turn, change with the degree of excitation of the plasma.
• hybrid source 30 makes use of a plasma which is capacitively coupled so as to provide a stream of plasma ions through extraction grid 64.
• the plasma is maintained at a relatively low pressure, preferably below 1 mTorr.
• an inductive power transfer is locally achieved using antenna 94 of inductive coupling system 32.
• the DC plasma potentially from capacitative coupling, and hence the ion acceleration energy, is typically about 20 to 40 volts at all surfaces.
• ion energy can be selectively controlled by varying the DC bias of the extraction grid, as described above.
• inductive and capacitative coupling was described for sputter treatment of dielectric samples by Dieter Martin in a 1995 dissertation for
• Ion/radical fluxes from hybrid source 30 may be enhanced using the inductive coupling system 32.
• a slow moving resonant ionization magnetic field is applied by quasi- static magnetic field generation system 34.
• the preferred quasi-static magnetic field generation system makes use of a plurality of coils 96 disposed radially about the plasma containment volume. Field rotator 100 selectively energizes coils 96 in opposed pairs, to apply a fairly uniform magnetic field throughout the plasma.
• the opposed coils are energized in the same direction, but only briefly, after which an alternate pair of transverse magnetic coils are energized to apply a magnetic field B 2 . Thereafter, the original coils may be reenergized, but with the opposite polarity so that magnetic field B 3 , and then field B 4 are produced.
• Field rotator 100 produces a magnetic field which effectively rotates through the plasma containment volume with a rotational frequency which is much less than the driving frequency of inductive coupling system 32, generally being less than 10,000 Hz, and often being less than 100 Hz.
• the rotating magnetic field provides resonant enhancement of the inductive coupling of a truly static resonant field.
• the rotation of the magnetic field densities a much broader region of the plasma, and thereby provides a much more homogeneous ion stream.
• the moving magnetic field may also further density the plasma by a churning effect, increasing the collisions between the energetic plasma particles to provide still further increases in deposition rate and energy transfer efficiency.
• a typical hybrid source will have a container volume with an internal radius of about 5 cm, and a length between the coupling electrode and the extraction grid of about 8% cm. Such a hybrid source will require an ionizing energy of between about 100 and 1000 watts, when driven at a frequency of about 13.56 MHz (or some multiple thereof) .
• the plasma container and deposition vessel surrounding the substrate are evacuated, preferably at a relatively high speed of about 2,000 liters per second.
• the ambient pressure during deposition will preferably be kept at about 5 x 10 "4 mbar.
• a short burst of N 2 gas is superimposed on a steady flow of the source gas to facilitate striking of the plasma, and a gas comprising nitrogen may be continuously supplied where nitrogenation is desired.
• a burst on the order of a few milliseconds will suffice, or, alternatively, a high voltage pulse striker circuit may be used with similar results.
• Ion current densities are substantially higher than the .1 to .7 mA/cm 2 provided by plasma beam sources, and may provide carbon deposition rates of between about 20 to 100 A per second.
• hybrid source 30 is a preferred embodiment, a wide variety of alternative systems may also be used.
• the moving magnetic field may be provided by W
• FIG. 5 A still further alternative deposition system will be described with reference to Fig. 5.
• magnetic disk 2 is simultaneously coated on both sides by a pair of filtered cathodic arc sources 100.
• Each cathodic arc source includes a high density carbon target 102 which is used as a cathode.
• a plasma is maintained by an electrical potential of the cathode relative to a graphite extractor anode 104 once the chamber has been evacuated through evacuation port 106.
• cathodic arc deposition relies on a low voltage discharge at pressures of less than 10 ⁇ 5 mbar.
• Vaporized electrode material in the form of highly ionized intraelectrode plasma provides current transport between the cathode and anode.
• the solid cathode is consumed through microscopic localized regions of very high current density and temperature, the cathode typically being an electrically conductive deposition material such as a metal, carbon, or highly doped semiconductor.
• the kinetic energy of ions can be electrostatically varied by biasing the substrate relative to the cathode.
• Energetic bombardment of the film using cathodic arc source 100 can produce dense and continuous films through subplantation, as described above. High deposition rates of between 30 and 100 A per second, together with high throwing power (the ability to coat uniformly in three dimensions) are also provided by the intense ion flux.
• piezo system 108 passes through the wall of the deposition chamber using a linear and rotary feedthrough 110 so as to initially energize a graphite striker 112.
• Water cooling 114 helps confine the discharged energy to the deposition system.
• source 100 blocks the direct path between the cathode and the magnetic recording media or other substrate to be coded using a curvilinear duct 116.
• Magnetic field coils 118 direct the desired particles through curvilinear duct 116, effectively filtering out the majority of the macroparticles.
• baffles 120, and an irregular duct surface formed by bellows 122 helps to prevent the macroparticles from bouncing along the curvilinear duct, thereby providing a more effective filter.
• the duct will typically be about 7.3 inches in diameter, while the curve may have a centerline radius of about ten inches.
• the filtered ion stream may be optionally accelerated towards the substrate using an acceleration grid 124.
• the substrate itself may be biased.
• the filtered ion stream may also be scanned over the substrate surface using a raster magnetic field supplied by raster coils 126.
• the ion stream may be monitored through viewport 128. Steering magnetic fields may also be provided at the cathode by steering coils 129.
• the present invention provides cathodes which are adapted to distribute an arc over a diffuse cathodic surface area, rather than forming a number of discrete arc spots or jets.
• the power per unit area is generally raised to a sufficient level for the active region to reach a critical temperature.
• Cathodic arc deposition of graphite is particularly problematic, as graphite in general is difficult to evaporate or sublime by electrical heating, largely because of its anomalous negative temperature coefficient of electrical resistivity (up to about 1,200°K) .
• Graphite is generally porous in nature, leading to large quantities of macroparticles being ejected during arcing. While the curvilinear duct filter described above has proven effective at limiting the amount of macroparticles reaching the substrate, this structure also produces a magnetic pinching of the plasma stream, which reduces the area of deposition and tends to produce inhomogeneity in the thickness of the deposited films. Additionally, over a long period of time, the contamination of the filter duct walls can be disadvantageous, as charged carbon dust from the wall may become entrapped in the plasma stream and contaminate the film.
• the temperature of the cathode at or near the surface is increased to a temperature above the minimum point in the resistivity versus temperature curve for various types of graphite. Ideally, the temperature will be raised substantially beyond this minimum resistivity temperature to enhance ohmic heating and thus evaporate the graphite more effectively.
• the goal here is to enhance the effect of local heat accumulation at the surface of the cathode, and to promote this heat trapping process on a time scale which is significantly longer than that of known arc deposition systems.
• Work in connection with the present invention has shown that continuous DC arcs may be produced with durations of over 1 minute and preferably of over 3 minutes .
• Energy conservation at the cathode implies that the energy input and energy output are equal. Energy is generally supplied to the cathode surface through ohmic heating, ion bombardment, and Nottingham heating. Energy will be lost during the process through electron emission cooling, evaporation cooling, and heat transfer by conduction, radiation, and convection.
• the carbon cathode itself may optionally be prepared by compressing high purity graphite powder at a hydrostatic pressure of between about 130 and 150MPa.
• the density of such a cathode will typically be between about 1.5 and 1.7g/cm 3 .
• the cathode can be thermally insulated with thermal insulation 132.
• the single cathodic spot will evolve into a diffuse active area, preferably being at least 2cm 2 .
• the surface temperature within that area reaches a value nearing the sublimation temperature of graphite, often being over 2,000°C.
• the steady state distributed arc mode may be characterized by a mean arc voltage value that fluctuates over about 25 volts, ideally being between about 30 and 33 volts.
• the imposition of a steering magnetic field may decrease the transition time from the spot mode to the distributed arc mode.
• a reduction in macroparticle content may be visible observed as a reduction of the number of incandescent particles within the plasma as compared to the standard spot arc.
• a diffuse plasma cloud is formed over the cathode surface, and the wide amplitude fluctuations characteristic of the spot arc are reduced. Additionally, the audible rattling noise often provided by filter cathodic arcs is replaced by a notably quieter erosion process. Erosions of 2mg/s have been measured over a series of runs accumulating a total of 5 minutes of arcing. Rise in the cathodic temperature may conveniently be produced by the reverse ion bombardment and Joule heating of cathode 102. Thermal insulation 132 may also prevent dissipation of the heat energy to cooling water system 114. Thermal insulation may be disposed over a selected portion of cathode 102 so as to selectively control the size and position of active region 130.
• Disk 2 may optionally be at an angle relative to cathodic arc source 100 to decrease the macroparticle content of the deposited film. Biasing of disk 2 will help to maintain uniform deposition over the disk's surface from the ion stream. The larger macroparticles will be more likely to glance off and less likely to adhere to a surface which is oblique (or parallel to) the particle stream from curvilinear duct 116. In fact, supporting the disk at an angle relative to the particle stream may be advantageous for many deposition methods, particularly where the disk (or other substrate) is biased. Maintaining a continuous arc when removing and replacing disk 2 may also minimize transient macroparticles which are expelled from cathode 102 during and after striking of the plasma.
• the distributed cathodic arc of the present invention produces a significantly lower total current density and a higher spatial uniformity in ion current density.
• Such a distributed arc may make use of a higher arc voltage than in the more conventional cold cathodic arc sources, as well as a reduced amplitude in arc current oscillations, which will help to decrease the macroparticle content of the associated plasma. Reduction of macroparticles will reduce cleaning and maintenance of a filter duct, and may even allow unfiltered deposition.
• Unfiltered carbon distributed arc films may be produced having densities of over 3g/cm 3 with a mean ion energy of 18eV, at over 50A/s, by a particle flux with an ionization of over about 60%.
• the acetylene gas flow rate was pre-set (by an electronic controller) to promote diamond-like bonding in the ta-C:H carbon films, rather than optimizing the deposition rate. Gas flow rates are in standard cubic centimeters per second (seem) .
• the matching-network circuit passive elements were pre-tuned so as to minimize the ratio of P ref /Pi n (power reflected over power input) at the above-mentioned acetylene flow rate.
• the rate phase state was triggered using a short burst of N 2 gas (lasting less than 0.1 s) superimposed on the steady flow of C 2 H 2 .
• the pressure of the chamber during deposition was in the region of 5 * 10 ⁇ 4 mbar.
• Textured and untextured smooth disks were coated, and the carbon coatings were characterized using ellipsometry, electron energy loss spectroscopy (EELS) and Raman finger-printing.
• the textured disks were lubed using conventional lube processes, and underwent abrasive tape tests as well as accelerated start- stop tests.
• Table II summarizes the variation of physical properties of the films as a function of thickness.
• the average ion energy per carbon ion was uniformly maintained at about 100 eV.
• the spatial homogeneity of the films is gauged in both the radial as well as angular positions.
• G-peak and D-peak are V-peak positions in Raman spectroscopy, while the associated ⁇ values describe peak widths.
• Selket voltage is the output voltage of a light sensor for abrasive wear test equipment manufactured by Selket Co. The higher the output voltage, the more serious the wear.
• the Plasmon-peak E p is representative of the density of the films.
• E of diamond taking the E of diamond to be 34 eV, it is estimated that the most-diamond-like ta-C:H films have above 80 % C-C sp 3 bonding (this is independent of whether there is long range order or not) .
• Disks were coated with ta-C:H films under a wide variety of rf-power and gas-feedstock flow rates. These films were then tested for friction build-up and wear durability using a conventional accelerated contact start/stop (CSS) test. Prior to testing, the disks were lubed and lube thickness was found to vary between 16-23 A, corresponding to a carbon film thickness range of 30 A to 150 A. Each test consisted of 500 cycles, and the disks were tested on both sides at 300 rpm. The averaged coefficients of friction ( ⁇ s ) are plotted against thickness of the films in Table III. The variation of ⁇ s is found to be between 0.5 to 1.5, corresponding to a thickness range from 40 A to 150 A. Of the 16 disks that underwent the accelerated CSS test, all but one passed.
• SCS contact start/stop
• Disks were also coated with highly tetrahedral amorphous carbon using a filtered cathodic arc. Initially, two disks were coated with a static ion stream, producing coatings which varied considerably from the center to the edge. Estimating coating thicknesses using interference colors, and assuming an index of refraction of 2.5, coating thicknesses varied at least between 1,250 A and 500 A.

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