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Publication numberUS20020081465 A1
Publication typeApplication
Application numberUS 09/966,636
Publication dateJun 27, 2002
Filing dateSep 28, 2001
Priority dateJan 5, 1996
Also published asCA2241878A1, CA2241878C, CN1208495C, CN1212026A, CN1727514A, DE69715592D1, DE69715592T2, DE69723053D1, DE69723053T2, EP0871792A1, EP0871792B1, EP0871794A1, EP0871794B1, US6461686, US6468402, US6511587, US20010010288, US20010019738, US20020036135, US20020071971, US20020125129, US20020127349, US20040069623, US20060249373, WO1997025450A1, WO1997025451A1
Publication number09966636, 966636, US 2002/0081465 A1, US 2002/081465 A1, US 20020081465 A1, US 20020081465A1, US 2002081465 A1, US 2002081465A1, US-A1-20020081465, US-A1-2002081465, US2002/0081465A1, US2002/081465A1, US20020081465 A1, US20020081465A1, US2002081465 A1, US2002081465A1
InventorsJohan Vanderstraeten
Original AssigneeVanderstraeten Johan Emile Marie
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Sputtering targets and method for the preparation thereof
US 20020081465 A1
Abstract
Sputtering targets comprising sub-stoichiometric titanium dioxide, TiOx, where x is below 2, are provided. The targets are preferably formed by plasma spraying so as to have an electrical resistivity of less than 0.5 ohm.cm.
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Claims(15)
1. A sputtering target which comprises sub-stoichiometric titanium dioxide, TiOx, where x is below 2.
2. A sputtering target as claimed in claim 1 wherein the TiOx is coated onto an electrically conductive base.
3. A process for the preparation of a sputtering target as claimed in claim 1 or claim 2, which process comprises plasma spraying titanium dioxide, TiO2, onto a target base.
4. A process as claimed in claim 3 wherein the target base is cooled during the plasma spraying.
5. A process as claimed in claim 3 or claim 4 wherein the plasma spraying is carried out using argon as the plasma gas and hydrogen as the secondary plasma gas.
6. A process as claimed in any one of claims 3 to 5 wherein the target bas e is titanium.
7. A process as claimed in any one of claims 3 to 6 wherein the titanium dioxide which is plasma sprayed has particle size in the range of from 1 to 60 micrometers.
8. A process for coating a substrate surface with titanium dioxide, which process comprises the use as a sputtering target of a target as claimed in claim 1 or claim 2.
9. A process as claimed in claim 8 wherein the sputtering from the target is carried out using as the plasma gas argon, a mixture of argon and oxygen, a mixture or argon and nitrogen, or a mixture of nitrogen and oxygen.
10. A process as claimed in claim 9 wherein the plasma gas comprises 70 to 90% by volume argon and 30 to 10% by volume oxygen.
11. A process as claimed in any one of claims 8 to 10 wherein the substrate which is coated is optical glass, the screen of a cathode ray tube, a flexible film or an oxygen barrier film.
12. A substrate which has been coated by a process as claimed in any one of claims 8 to 11.
13. A process for the preparation of sub-stoichiometric titanium dioxide, TiOx, where x is below 2 which process comprises subjecting titanium dioxide to a plasma flame.
14. A process as claimed in claim 13 wherein titanium dioxide is sprayed through a plasma flame.
15. A process as claimed in claim 13 wherein the titanium dioxide is sprayed using a combustion flame.
Description
  • [0001]
    The present invention relates to improved sputtering targets and, in particular to sputtering targets of titanium dioxide, and to a method for the preparation thereof.
  • [0002]
    Sputtered coatings of various oxides (e.g. silica) and nitrides (e.g. silicon nitride) are used to form optical coatings showing interesting properties on a number of substrates. Known applications include low emissivity films on window glasses, cold mirrors on reflectors, enhanced mirrors for photocopiers and antireflective coatings on picture glass or TV screens. These coatings are usually made of stacks of several different layers with different refractive indices, preferably of low and high refractive index, to produce optical filters. For antireflective coatings it is preferred to combine two materials showing the highest and the lowest possible refractive indices. Such materials are titania and silica. Another advantage of these materials is their durability.
  • [0003]
    Titanium dioxide coatings have a high refractive index and can thus be used to provide coatings of a high refractive index or to provide the high refractive index coatings in optical stacks. The existing process for producing titanium dioxide coatings comprises using titanium metal as the sputtering target and using oxygen as a component of the plasma gas. The titanium is thus converted to titanium dioxide during the sputtering process. Although satisfactory coatings of titanium dioxide can be produced, the rate of production is very slow and much slower than coating with silica.
  • [0004]
    As a substitute for titanium dioxide it has been suggested to use alternative materials such as niobium oxide. Whilst it is possible to coat a substrate with niobium oxide using a niobium metal target at slightly higher speeds than the equivalent process using titanium, niobium is very expensive.
  • [0005]
    Thus, there is a need for an improved process for coating titanium dioxide onto substrate materials. We have now surprisingly discovered that titanium dioxide can be sputtered from a target comprising sub-stoichiometric titanium dioxide to provide coatings on a substrate either of sub-stoichiometric titanium dioxide, or titanium dioxide, depending upon the sputtering conditions.
  • [0006]
    Accordingly, the present invention provides a sputtering target which comprises sub-stoichiometric titanium dioxide, TiOx, where x is below 2. Sub-stoichiometric titanium dioxide, TiOx, where x is below 2 and generally is in the range of from 1.55 to 1.95 is known in the art. It may be produced by the reduction of stoichiometric TiO2. It is a form of titanium dioxide which is conductive.
  • [0007]
    The sputtering target of the present invention may comprise sub-stoichiometric titanium dioxide, TiOx coated onto a target base. such as a backing tube or plate, for example a target base of an electrically conductive material, for example stainless steel or titanium metal. The target may be of any type known in the art, for example a rotatable target or a flat magnetron target.
  • [0008]
    The sputtering target of the present invention may be prepared by plasma spraying titanium dioxide onto a target base. During the plasma spraying process, the titanium dioxide loses some oxygen atoms from its lattice and is converted into the sub-stoichiometric form. The primary plasma gas used for the plasma spraying is preferably argon, with hydrogen as the secondary plasma gas. The titanium dioxide which is subjected to plasma spraying preferably has a particle size in the range of from 1 to 60 micrometers. It is also important to cool the sputtering target during the plasma spraying in order to quench the titanium dioxide in sub-stoichiometric form and to improve the conductivity thereof. It also important to use a certain amount of hydrogen in the plasma gas in order to produce a high temperature plasma and to assist in the reduction.
  • [0009]
    The present invention also provides in another aspect a process for coating a substrate surface with titanium dioxide, which process comprises using as a sputtering target a target comprising sub-stoichiometric titanium dioxide, TiOx. The sputtering from the target is preferably carried out using as the plasma gas argon, a mixture of argon and oxygen, a mixture of nitrogen and argon, or a mixture of nitrogen and oxygen. If the plasma gas does not contain oxygen, e.g. if pure argon is used, then the coating will comprise sub-stoichiometric titanium dioxide. The coating is not completely transparent and possesses some conductivity. If, however, the plasma gas contains oxygen then the sub-stoichiometric form of titanium dioxide is converted into the transparent form which is stoichiometric or substantially stoichiometric. The degree of transparency will depend upon the amount of oxygen contained in the plasma gas. A preferred gas mixture to form transparent titanium dioxide as the coating comprises 70-90% by volume argon and 30-10% by volume of oxygen.
  • [0010]
    The substrate which is coated according to this process may comprise, for example, optical glass, the screen of a cathode ray tube, such as a TV screen, cold mirrors, low-emissivity glasses, architectural glasses, antireflective panels, flexible films or oxygen barrier films. In this case the coating process will be carried out under conditions such that the sub-stoichiometric titanium dioxide is converted into the stoichiometric form.
  • [0011]
    In a further aspect the present invention also provides a process for the preparation of sub-stoichiometric titanium dioxide, TiOx, where x is below 2 which process comprises subjecting titanium dioxide to a plasma flame. In carrying out this process the titanium dioxide is preferably sprayed through a plasma flame, for example a plasma flame using a mixture of argon and hydrogen as the plasma gas.
  • [0012]
    The main advantage of the present invention is that from the sub-stoichiometric titanium dioxide targets used in the present invention the rate of sputtering is increased by a factor of about ten as compared to sputtering from a titanium metal target, thus making the process industrially attractive.
  • [0013]
    The present invention will be further described with reference to the following Examples.
  • EXAMPLE 1 Comparative
  • [0014]
    A rotatable target comprising a tube of titanium metal of diameter 133 mm and length 800 mm was used to sputter titanium metal onto a glass plate placed at a distance of 18 cm from the target. The sputtering was carried out at a power level of 35 kW (80A, 446V) under a pressure of 510−3 mBar of argon as the plasma gas.
  • [0015]
    After 3 minutes a layer of titanium metal 18000 Angstroms in thickness as measured by a profilometer had been deposited upon the glass plate.
  • EXAMPLE 2 Comparative
  • [0016]
    The procedure of Example 1 was repeated but substituting a mixture of 80% O2 and 20% Ar as the primary plasma gas to replace the argon primary plasma gas of Example 1. The sputtering was carried out at a power level of 45 kW (97A, 460V) under a pressure of 4.510−3 mBar. Using a titanium metal target as described in Example 1 a titanium dioxide layer of thickness 1500 Angstroms was deposited on a glass plate place above the target in 3 minutes.
  • EXAMPLE 3
  • [0017]
    A rotatable target comprising a tube of stainless steel of diameter 133 mm and length 800 mm was coated with sub-stoichiometric titanium dioxide, TiOx, where x is below 2 as hereinbefore described by plasma spraying titanium dioxide onto the target using argon as the primary plasma gas and hydrogen as the secondary plasma gas. 72 liters (60% argon, 40% hydrogen) were used. The power level was 45 kW (455A, 96V).
  • [0018]
    This target was then used as a sputtering target in the manner as described in Example 1. Using argon as the primary plasma gas the sputtering was carried out at a power level of 45 kW (97A, 460V) under a pressure of 5.410−3 mBar Ar. A dark blue semitransparent layer of sub-stoichiometric titanium dioxide, TiOx, of thickness 14000 Angstroms was deposited on a glass plate placed above the target in 3 minutes. The sputtering proceeded smoothly without significant arcing.
  • EXAMPLE 4
  • [0019]
    A rotatable target prepared as described in Example 3 was used as a sputtering target in the manner as described in Example 3 using a mixture of 75% Ar and 25% O2 as the plasma gas. The sputtering was carried out at a power of 45 kW (95A, 473V) under a pressure of 510−3 mBar. A clear transparent coating of stoichiometric titanium dioxide of thickness 12500 Angstroms was deposited on a glass plate placed above the target in 3 minutes. The sputtering proceeded smoothly without significant arcing.
  • EXAMPLE 5 Comparative
  • [0020]
    A rotatable target was prepared as described in Example 3 by using pure argon (40 liters) at a power level of 34 kW (820A, 42V). The electrical conductivity of the target was ten times inferior to that of Example 3. Sputtering from the target was difficult due to arcing. The process was not stable enough to produce samples.
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US7754336Jun 29, 2007Jul 13, 2010Cardinal Cg CompanyCarbon nanotube glazing technology
US20080280078 *Jun 29, 2007Nov 13, 2008Krisko Annette JCarbon nanotube glazing technology
US20100247820 *Jun 3, 2010Sep 30, 2010Cardinal Cg CompanyCarbon nanotube glazing technology
EP2279986A2Jun 29, 2007Feb 2, 2011Cardinal CG CompanyCarbon nanotube coating technology
Classifications
U.S. Classification428/704, 427/453, 204/298.13
International ClassificationC23C4/10, G02B1/10, C23C14/08, C03C17/245, C23C14/34
Cooperative ClassificationC23C4/134, C03C2217/212, C03C2218/154, C23C4/11, C03C17/2456, C23C14/3414
European ClassificationC23C4/10B, C23C4/12L, C03C17/245C, C23C14/34B2