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
  • H01J37/34—Gas-filled discharge tubes operating with cathodic sputtering
  • H01J37/3411—Constructional aspects of the reactor
  • H01J37/3414—Targets
  • H01J37/3426—Material
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
  • C23C14/22—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the process of coating
  • C23C14/34—Sputtering
  • C23C14/3407—Cathode assembly for sputtering apparatus, e.g. Target
  • C23C14/3414—Metallurgical or chemical aspects of target preparation, e.g. casting, powder metallurgy
• • 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
  • H01J37/34—Gas-filled discharge tubes operating with cathodic sputtering
  • H01J37/3488—Constructional details of particle beam apparatus not otherwise provided for, e.g. arrangement, mounting, housing, environment; special provisions for cleaning or maintenance of the apparatus
  • H01J37/3491—Manufacturing of targets

Definitions

• compositions containing photocatalyst particles have been spray coated, dip coated, spin coated, and poured onto substrates. Typically, the composition is then made to adhere to the substrate by a high temperature heating process (e.g., sintering).
• a coating composition is applied to a substrate.
• the coated substrate is heat treated to adhere the coating to the substrate and to improve crystallinity and, therefore, photocatalytic properties.
• U.S. Patent 5,874,701 issued to Watanabe et al., the teachings of which are incorporated herein by reference, discloses wet process applications of photocatalytic coatings.
• Watanabe et al. disclose applying a TiO 2 sol onto a tile substrate and thereafter firing the coated substrate at a high temperature to bond the coating to the substrate. This firing is believed to increase the crystallinity of the coating, thereby enhancing photocatalytic properties. It would be desirable to provide an application method that requires only a single processing step.
• Sputter deposition is fairly conventional in the architectural and automotive glass industries.
• the process involves use of a sputtering target formed from material that is to be deposited onto a substrate.
• the target is provided with a negative charge and a relatively positively charged anode is positioned within the sputtering chamber adjacent the target.
• the chamber is then evacuated.
• a plasma of that gas can be established. Atoms in this plasma collide with the target, knocking material from the target and sputtering it onto the substrate.
• magnetron sputtering It is also known in the art to include a magnet behind the target to help shape the plasma and focus the plasma in an area adjacent a desired surface of the target (e.g., the surface of the target that is oriented toward the substrate). This process is generally referred to as magnetron sputtering.
• the photocatalyst particles are titanium dioxide particles and the plasma spraying is carried out under conditions that result in the target base being coated with substoichiometric titanium oxide, TiO x , where x is less than 2.
• a further embodiment of the invention provides sputtering targets formed by such methods. Still another embodiment provides a deposition method that comprises sputtering targets of this nature. Yet another embodiment provides a coated substrate produced by sputtering these targets.
• Figure 1 is a schematic illustration of a rotatable target in accordance with a particularly preferred embodiment of the present invention
• This backing tube is commonly formed of an electrically conductive material.
• preferred backing materials include aluminum, stainless steel, titanium, and copper.
• Use of a rigid backing tube allows a magnet to be positioned within the interior of the target, permitting the shape of the charged plasma adjacent the surface of the target to be more carefully controlled.
• the chamber is provided with at least one pair of opposed end blocks, with one end block being used to hold each of the exposed lateral extensions 83 of the backing tube 82.
• Rotatable targets are also well known in the art.
• the target 80 illustrated in Figure 2 includes a relatively thin bonding layer 70 between the backing tube 82 and the target material 85. If so desired, the target material 85 can be formed directly upon the backing tube 82. However, a bonding layer 70 is advantageous as it helps insure that the target material 85 is securely adhered to the backing tube 82.
• the bonding layer 70 should be conductive and ideally has a coefficient of thermal expansion between that of the backing tube and the sputterable material. This reduces target degeneration that can occur during heating and cooling as a result of the different thermal expansion rates of the backing tube 82 and the target material 85. Bonding layers of this nature are well known in the art as well.
• the present targets are formed from photocatalyst particles.
• a number of metal oxides are known photocatalysts.
• suitable photocatalysts include oxides of a metal selected from the group consisting of titanium, iron, silver, copper, tungsten, aluminum, zinc, strontium, palladium, gold, platinum, nickel, and cobalt. While titanium oxide appears to be the most powerful of these materials, any desired photocatalyst can be used. A variety of alloys are also believed to exhibit photocatalytic properties.
• the targets are formed from photocatalyst particles that are substantially free of inert coating, that is, any coating that is intended to suppress the photoactivity of the particles.
• Photocatalyst particles are commonly treated with inorganic coatings that reduce the photoactivity of the particles.
• titanium dioxide pigment particles are commonly coated with alumina and/or silica to suppress the photoactivity of the pigment (i.e., to render the particles photocatalytically inert).
• these coatings are believed to enhance the durability of paints and other products formed from such pigments. Contrary to the experience of the paint industry, particles bearing inorganic coatings are not believed to be well suited for use in the production of photocatalytic sputtering targets.
• the targets are formed from particles that are substantially free of inorganic coating.
• the present targets are formed from photocatalyst particles that are free of any type of coating.
• Certain coatings may be used for purposes other than suppressing the photoactivity of the coated particles.
• the flow characteristics of such particles through a fixed volume e.g., through the powder supply of a plasma gun
• the targets are formed from photocatalyst particles that are substantially free of any type of coating (i.e., the exterior surface of each particle is unprotected).
• the dopant When doped photocatalyst particles are plasma sprayed onto a target base, the dopant may inhibit the growth of large mono-crystals in the resulting target material. Likewise, when targets produced by such plasma spraying methods are sputtered, the dopant may again inhibit large crystal growth in the deposited film. That is, the dopant may act as a crystal growth inhibitor. It is to be understood that use herein of the term "crystal growth inhibitor" refers to any material that inhibits the growth of large crystals. Since it is important to grow large crystals to form efficient photocatalytic films, dopants of this nature are undesirable. Thus, in many cases, it will be preferable to form the present targets from particles of a photocatalyst that has an unmodified crystal lattice.
• the present targets may be desirable to form the present targets from photocatalyst particles that have an intentionally modified crystal lattice.
• the introduction of certain dopant atoms into the crystal lattice of a photocatalyst may actually enhance the photoactivity of the material.
• another embodiment of the invention involves the plasma spraying of photocatalyst particles that are doped with at least one other material that is intended to enhance the photoactivity of the particles.
• the dopant is preferably a material that does not act as a crystal growth inhibitor.
• Titanium dioxide is a particularly preferred starting material for the present targets. Titanium dioxide is trimorphous. That is, it exists in three different crystal structures: rutile, anatase, and brookite. The rutile and anatase phases have a tetragonal crystal system and are more easily produced than the brookite phase. Moreover, both of these titanium dioxide phases are known photocatalysts. Thus, the present targets are desirably formed from photocatalyst particles of rutile and/or anatase phase titanium dioxide. Titanium dioxide particles are commercially available from a variety of pigment suppliers. For example, titanium dioxide is sold in both rutile and anatase phases by Kronos, Inc.
• the targets are formed from uncoated particles of anatase phase titanium dioxide.
• Uncoated anatase titanium dioxide pigment is sold commercially under the trade name "Kemira AFDC 328", by Kemira Pigments, Inc. It has been suggested that anatase titanium dioxide exhibits higher levels of photoactivity than rutile titanium dioxide. While this suggestion has apparently not been clearly confirmed, anatase titanium dioxide does have a higher band gap energy (3.2 eV) than the rutile titanium dioxide (3.0 eV). Band gap energy indicates the minimum amount of energy needed for a semiconductor to promote an electron from the valence band to the conduction band.
• the targets are formed from a mixture of anatase and rutile titanium dioxide particles.
• both phases of titanium dioxide pigment can be mixed, milled, and/or ground together into a particulate composition.
• titanium dioxide is sold in both rutile and anatase phases by Kronos, Inc.
• the present targets are formed by plasma spraying molten (i.e., heat softened) material onto a target backing.
• a plasma gun 50 (or "jet") communicates with a gas supply (not shown) from which plasma gas flows through a channel 51 leading past a cathode 52 and an anode 54.
• the plasma gas which may comprise one or more different types of gas (e.g., argon, hydrogen, nitrogen, helium), flows past the cathode 52 and the anode 54.
• One or more electric arcs 53 are generated between the cathode 52 and the anode 54. These arcs 53 cause the gas to heat up and reach very high temperatures, which in turn results in gas dissociation and plasma formation.
• the rapid expansion of plasma gas causes a very hot stream of plasma to rapidly accelerate from the fixed interior volume of the plasma gun.
• Photocatalyst particles 56 are fed into this high temperature plasma stream, typically from a powder supply 55 mounted near the outlet of the plasma gun. This causes a molten stream of particles 59 to be accelerated toward the target backing 82.
• the molten material that accumulates on the target backing 82 forms a coating of target material 85.
• the target backing 82 is rotated and translated laterally in a back and forth manner to assure the target base 82 is uniformly coated with target material 85.
• the present photocatalytic targets can be produced in such a way that they have very low electrical resistivity.
• favored production methods yield photocatalytic targets that have such low resistivity/high conductivity, that they can be used for DC magnetron sputtering and other high power sputtering processes (i.e., sputtering processes that involve power levels in excess of 35 kW).
• sputtering processes that involve power levels in excess of 35 kW.
• the process comprises plasma spraying titanium dioxide onto a target backing.
• the plasma spraying can be performed in the manner discussed above with reference to Figure 3.
• the titanium dioxide particles preferably have an average particle size in the range of about 1-60 micrometers, most preferably in the range of about 1-20 micrometers. If the particle size greatly exceeds 60 micrometers, then the particles are less likely to become completely molten. On the other hand, if the particle size is far less than 1 micrometer, then the powder is more likely to be dispersed in the spraying chamber instead of being ⁇ uniformly deposited on the target base.
• the plasma spraying is carried out under conditions that result in the target base being coated with substoichiometric titanium oxide, TiO x , where x is less than two.
• the titanium dioxide particles are fed into a plasma flame, which preferably has a temperature of at least about 2000° C.
• the action of the plasma flame on the titanium dioxide causes the titanium dioxide to lose some oxygen atoms from its lattice.
• the plasma spraying is advantageously performed in a processing atmosphere that is substantially free of oxygen (i.e., free of oxygen and oxygen-containing compounds), other than that contained in the titanium dioxide being sprayed into the chamber.
• stoichiometric titanium dioxide i.e., TiO 2
• substoichiometric form i.e., TiO x , where x is less than 2.
• Argon can be used quite advantageously as a primary plasma gas in the present plasma spraying methods. It is to be understood that use herein of the term "primary plasma gas" is meant to refer to the gas that is present in the greatest concentration in a processing environment. Argon is a desirable plasma gas since it readily forms a plasma. In fact, even if a secondary plasma gas is used with argon during the actual plasma spraying, it may be preferable to start up the plasma using pure argon, since argon so easily forms a plasma. Argon is also inert to virtually all spray materials. Moreover, it tends to be less degenerative to plasma spraying hardware (e.g., the nozzle) than other gases.
• plasma spraying hardware e.g., the nozzle
• secondary plasma gas is meant to refer to a gas that is present in a processing environment in a lesser concentration than the primary plasma gas. For example, it is desirable to achieve particle temperatures on the order of at least 2000°C, and more preferably above 2500°C. In order to produce such high temperatures, it is preferable to use hydrogen and/or helium as a secondary plasma gas.
• Particularly favored plasma spraying methods yield titania targets having electrical resistivities as low as 0.02 ohm. cm. Thus, they can be sputtered at high power levels using conventional D.C. power supplies. In fact, they can be sputtered at power levels of up to 100 kW.
• plasma spraying is carried out in a processing atmosphere that results in the target base being coated with substoichiometric titanium oxide, TiO x , where x is below two and is generally in the range of about 1.55 to about 1.95.
• the plasma sprayed titania is desirably highly oxygen deficient.
• the substoichiometric titanium oxide When the substoichiometric titanium oxide is coated onto the target base, it can be solidified under conditions that prevent it from regaining oxygen and reconverting to TiO 2 . This is done by minimizing the amount of oxygen and oxygen-containing compounds that are present in the plasma-spraying environment, while cooling the target base to quench the titanium oxide in substoichiometric form.
• the target base can be provided with a water-cooling system (e.g., a series of water lines through which controlled-temperature water can be circulated).
• the disclosed plasma spraying methods yield photocatalytic targets that are highly uniform in electrical conductivity/resistivity. This is best understood with reference to Figure 2.
• the conductivity of the target material adjacent the outer surface of the target i.e., the outermost target material 85A
• ends up being substantially the same as that adjacent the backing tube (i.e., the innermost target material 85B). This allows substantially all of the target material 85 to be stably sputtered at very high rates (i.e., at high power levels).
• targets formed by hot-pressing methods would not typically exhibit such uniform resistivity.
• a target formed by hot-pressing in a reducing atmosphere e.g., a processing atmosphere comprising hydrogen
• the reducing gas would likely have less impact on the innermost target material 85B, than it would on the outermost target material 85A.
• the innermost target material 85B would contain more oxygen than the outermost target material 85A.
• the present plasma-sprayed targets are ideally suited for high power sputtering applications.
• the present targets do not require expensive arc-diverter systems, D.C. switching power supplies, or Twin-Mag Systems where two targets are sequentially used as anode and cathode with a mid- frequency power supply. These targets also have no special gas control system requirements. Accordingly, it is anticipated that the present targets will be suitable for use in most existing sputtering facilities without the need for modification.
• titanium oxide sputtering targets do not suffer significantly from arcing problems because titanium oxide (i.e., titania) has a higher melting point than titanium metal.
• Metallic titanium suffers from the so-called "vapor arcing" problem as a result of its low melting point.
• the relatively high melting point of titania assures that if arcing does occur during sputtering, there will be little attendant damage to the target.
• the photocatalytic targets of the invention have very useful applications. For example, they can be used to deposit surprisingly efficient photocatalytic films. That is, they can be used to deposit films having high photoactivity levels, even at very small thicknesses. These targets are even more desirable when formed in accordance with the present disclosure so as to have low electrical resistivity. This allows efficient photocatalytic films to be deposited at very high sputtering rates.
• a further aspect of the invention provides a method of depositing photocatalytic coatings using the present targets. The method comprises providing a sputtering target produced by plasma spraying photocatalyst particles that are free of inert particle treatment onto a target base. The resulting target is sputtered to deposit a photocatalytic coating onto a substrate (e.g., a sheet of glass). The invention also provides coated substrates that are produced by this method.

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• 2002
  • 2002-01-14 WO PCT/EP2002/000378 patent/WO2002057508A2/en active Application Filing
  • 2002-01-14 EP EP02719697A patent/EP1352105A2/de not_active Withdrawn
  • 2002-01-14 JP JP2002558558A patent/JP2004520484A/ja active Pending
  • 2002-01-14 AU AU2002250831A patent/AU2002250831A1/en not_active Abandoned

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