U.S. patent application number 09/780537 was filed with the patent office on 2001-08-02 for sputtering targets and method for the preparation thereof.
This patent application is currently assigned to bvba VANDERSTRAETEN E. Invention is credited to Vanderstraeten, Johan Emile Marie.
Application Number | 20010010288 09/780537 |
Document ID | / |
Family ID | 10786662 |
Filed Date | 2001-08-02 |
United States Patent
Application |
20010010288 |
Kind Code |
A1 |
Vanderstraeten, Johan Emile
Marie |
August 2, 2001 |
Sputtering targets and method for the preparation thereof
Abstract
A process for the preparation of a sputtering target which
comprises sub-stoichiometric titanium dioxide, TiO.sub.x, where x
is below 2 having an electrical resistivity of less than 0.5
ohm.cm, optionally together with niobium oxide, which process
comprises plasma spraying titanium dioxide, TiO.sub.2, optionally
together with niobium oxide, onto a target base in an atmosphere
which is oxygen deficient and which does not contain
oxygen-containing compounds, the target base being coated with
TiO.sub.x, which is solidified by cooling under conditions which
prevent the sub-stoichiometric titanium dioxide from combining with
oxygen.
Inventors: |
Vanderstraeten, Johan Emile
Marie; (Drongen, BE) |
Correspondence
Address: |
BACON & THOMAS
4th Floor
625 Slaters Lane
Alexandria
VA
22314
US
|
Assignee: |
bvba VANDERSTRAETEN E
|
Family ID: |
10786662 |
Appl. No.: |
09/780537 |
Filed: |
February 12, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09780537 |
Feb 12, 2001 |
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09101405 |
Jul 14, 1999 |
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09101405 |
Jul 14, 1999 |
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PCT/EP97/00020 |
Mar 1, 1997 |
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Current U.S.
Class: |
204/298.13 ;
204/298.12 |
Current CPC
Class: |
C03C 2217/212 20130101;
C03C 17/2456 20130101; C23C 4/11 20160101; C23C 4/134 20160101;
C23C 14/3414 20130101; C03C 2218/154 20130101 |
Class at
Publication: |
204/298.13 ;
204/298.12 |
International
Class: |
C23C 014/00; C23C
014/34 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 5, 1996 |
GB |
9600210.0 |
Claims
1. A process for the preparation of a sputtering target which
comprises sub-stoichiometric titanium dioxide, TiO.sub.x, where x
is below 2 having an electrical resistivity of less than 0.5
ohm.cm, optionally together with niobium oxide, which process
comprises plasma spraying titanium dioxide, TiO.sub.2, optionally
together with niobium oxide, onto a target base in an atmosphere
which is oxygen deficient and which does not contain
oxygen-containing compounds, the target base being coated with
TiO.sub.x which is solidified by cooling under conditions which
prevent the sub-stoichiometric titanium dioxide from combining with
oxygen.
2. A process as claimed in claim 1 wherein the target base is water
cooled during the plasma spraying.
3. A process as claimed in claim 1 or claim 2 wherein the plasma
spraying is carried out using argon as the plasma gas and hydrogen
as the secondary plasma gas.
4. A process as claimed in any one of the preceding claims wherein
the target base is titanium, stainless steel, aluminium or
copper.
5. A process as claimed in claim 4 wherein the target base is a
rotatable target or a flat magnetron target.
6. A process as claimed in any one of the preceding claims wherein
the titanium dioxide which is plasma sprayed has particle size in
the range of from 1 to 60 micrometers.
7. A process as claimed in any one of the preceding claims wherein
the titanium dioxide is plasma sprayed together with
Nb.sub.2O.sub.3.
8. A process as claimed in any one of the preceding claims wherein
the sub-stoichiometric titanium dioxide, TiO.sub.x, has a value of
x in the range of from 1.55 to 1.95.
9. A process as claimed in any one of the preceding claims wherein
the sputtering target has an electrical resistivity of about 0.02
ohm.cm.
10. A sputtering target comprising sub-stoichiometric titanium
dioxide, TiO.sub.x, where X is below 2 having an electrical
resistivity of less than 0.5 ohm.cm, optionally together with
niobium oxide, which is obtainable by a process which comprises
plasma spraying titanium dioxide, TiO.sub.2, optionally together
with niobium oxide, onto a target base in an atmosphere which is
oxygen deficient and which does not contain oxygen-containing
compounds, the target being coated with TiO.sub.x which is
solidified by cooling under conditions which prevent the
sub-stoichiometric titanium dioxide from combining with oxygen.
11. A sputtering target as claimed in claim 10 which has an
electrical resistivity of about 0.02 ohm.cm.
12. A process for the preparation of sub-stoichiometric titanium
dioxide, TiO.sub.x, where x is below 2 having an electrical
resistivity of less than 0.1 ohm.cm which process comprises
subjecting titanium dioxide to a plasma treatment in an atmosphere
which is oxygen deficient and which does not contain any
oxygen-containing compounds.
13. A process as claimed in claim 12 wherein the titanium dioxide
is sprayed through a plasma flame having a temperature of above
2000.degree. C.
14. A process as claimed in claim 13 wherein the plasma flame uses
a mixture of hydrogen and argon as the plasma gas.
Description
[0001] The present invention relates to a process for the
preparation of improved high rate sputtering targets and, in
particular, to a process for the preparation of sputtering targets
comprising sub-stoichiometric titanium dioxide with high electrical
conductivity to be used in D.C. sputtering at high power
levels.
[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 a combination 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. For low emissivity films on window
glasses it is preferred to combine a silver layer with a high
refractive index material to dereflect the silver which improves
light transmission.
[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 deposition is very slow and much slower than coating
with zinc oxide and/or tin oxide.
[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] JP-A-07-233469 describes the preparation of a sputtering
target by hot-pressing titanium dioxide powder in a nonoxidizing
atmosphere and sintering the compact. The sintered compact
comprises TiO.sub.x where 1<.times.<2 with a resistivity of
10 ohm.cm which is too high for D.C. sputtering at high power
levels. The stability of the sputtering process and the arc rate
are both very dependent upon the conductivity of the target,
particularly at high power levels.
[0006] JP-A-62-161945 describes a method of manufacturing a ceramic
sputtering target in which a ceramic material consisting mainly of
ZrO.sub.2, TiO.sub.2, SiO.sub.2, Ta.sub.2O.sub.3, Al.sub.2O.sub.3,
Fe.sub.2O.sub.3 or a compound of these materials is sprayed using a
water plasma spray to produce a formed body which may be used as a
sputtering target. The sputtering target is used for high frequency
sputtering of non-conductive target materials.
[0007] Accordingly, there is a need for an improved process for the
production of sputtering targets comprising sub-stoichiometric
TiO.sub.2 which does not involve the hot-pressing and sintering
route of JP-A-07-233469 and which can be used to produce such
targets which have a high enough electrical conductivity to be used
as large size targets with complex shapes at high power levels.
[0008] We have now surprisingly discovered that titanium dioxide
can be D.C. sputtered at high power levels from a target comprising
sub-stoichiometric titanium dioxide to provide a coating on a
substrate of sub-stoichiometric or stoichiometric titanium
dioxide.
[0009] Accordingly, the present invention provides a process for
the preparation of a sputtering target which comprises
sub-stoichiometric titanium dioxide, TiO.sub.x, where x is below 2
having an electrical resistivity of less than 0.5 ohm.cm,
optionally together with niobium oxide, which process comprises
plasma spraying titanium dioxide, TiO.sub.2, optionally together
with niobium oxide, onto a target base in an atmosphere which is
oxygen deficient and which does not contain oxygen-containing
compounds, the target base being coated with TiO.sub.x which is
solidified by cooling under conditions which prevent the
sub-stoichiometric titanium dioxide from combining with oxygen.
[0010] Sub-stoichiometric titanium dioxide, TiO.sub.x, where x is
below 2 and generally is in the range of from 1.55 to 1.95 is known
in the art. When produced according to the process of the present
invention the electrical conductivity will vary, depending upon the
stoichiometry, the most preferred form having an electrical
resistivity of 0.02 ohm.cm.
[0011] In carrying out the process of the present invention
titanium dioxide, TiO.sub.2 is plasma sprayed 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, aluminium or copper. The target may be of any type
known in the art, for example a rotatable target or a flat
magnetron target.
[0012] During the plasma spraying process, the action of the plasma
flame on the titanium dioxide causes the titanium dioxide to lose
some oxygen atoms from its lattice, preferably from the surface of
the particles. The titanium dioxide is converted into the
sub-stoichiometric form, i.e. non-stoichiometric oxygen deficient
titania. The primary plasma gas used for the plasma spraying is
preferably argon, with hydrogen as the secondary plasma gas in
order to obtain the highest temperatures of the particles. The
titanium dioxide which is subjected to plasma spraying preferably
has a particle size in the range of from 1 to 60 micrometers,
preferably in the range of from 1 to 20 micrometers. The
sub-stoichiometric titanium dioxide which is coated on the target
base is solidified under conditions which prevent it from regaining
oxygen and reconverting to TiO.sub.2. Preferably the target base is
water cooled during the plasma spraying in order to quench the
titanium dioxide in the sub-stoichiometric form and to improve the
conductivity thereof. It is also important to use a certain amount
of hydrogen or nitrogen in the plasma gas in order to produce a
high temperature plasma and to assist in the reduction. Hydrogen is
preferred because of its reducing powers. Preferably particle
temperatures of above 2000.degree. C. are used, more preferably
above 2500.degree. C.
[0013] In a particular embodiment of the present invention, the
titanium dioxide may be plasma sprayed together with niobium
oxide.
[0014] In a further aspect the present invention also provides a
process for the preparation of sub-stoichiometric titanium dioxide,
TiO.sub.x, where x is below 2 having an electrical resistivity of
less than 0.1 ohm.cm, which process comprises subjecting titanium
dioxide to a plasma treatment in an atmosphere which is oxygen
deficient and which does not contain oxygen-containing compounds.
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. Preferably the
plasma flame will operate at a high temperature to raise the
temperature of the particles to above 2000.degree. C.
[0015] The sputtering targets which are produced according to the
process of the invention have a high electrical conductivity and
thus are able to run at high power levels using conventional D.C.
power supplies, without the need for expensive arc diverter
systems, or D.C. switching power supplies, or the Twin-Mag System
where two targets are sequentially used as anode and cathode with a
mid-frequency power supply, or any special requirements of a gas
control system. Using the targets produced according to the present
invention, D.C. sputtering can be carried out at power levels of up
to 100 Kw. The main consequence is that large target bases, e.g.
rotatable 3.5 meters long and 150 mm in diameter can be coated up
to a typical coating thickness of 6 mm.
[0016] The targets produced by the process of the present invention
do not suffer from significant arcing problems because titanium
dioxide has a higher melting point than titanium metal for which so
called "vapour arcing" is a problem due to the lower melting point
of the metal. Even if some arcing does occur for titanium dioxide
there is little accompanying damage to the target.
[0017] The present invention will be further described with
reference to the following Examples.
EXAMPLE 1
[0018] A rotatable target, water cooled on the inside to 35.degree.
C., comprising a tube of stainless steel of diameter 133 mm and
length 800 mm was coated to a thickness of from 4 to 10 mm with
sub-stoichiometric titanium dioxide, TiO.sub.x, where x is below 2
as hereinbefore described by plasma spraying titanium dioxide
(rutile) having a particle size of from 10 to 40 .mu.m 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).
EXAMPLE 2
[0019] A commercial white pigment consisting of titanium dioxide in
the anatase crystal form was used. This powder is stoichiometric
and electrically insulating. The powder was mechanically
agglomerated and compacted into flakes, ground, sieved (70-100
.mu.m) and sintered at 1300.degree. C. in air. The sintered body
was then ground and sieved to a particle size of 10-40 .mu.m. The
particles were yellow stoichiometric, non-conductive, titanium
dioxide with a rutile crystalline structure.
[0020] A rotatable target comprising a backing tube of aluminium
(2.50 m long and 133 mm diameter) was prepared by plasma spraying
of the above rutile powder using argon as the primary gas and
hydrogen as the secondary gas. 75 liters (40% argon, 60% hydrogen)
were used. The power level was 50 kW (110V, 455A). The plasma
spraying was carried out under a nitrogen atmosphere.
[0021] The target was rotated at 100 rpm and the torch translation
was 2.5 m/min until a coating 4 mm thick was obtained. The inside
of the aluminium tube was water cooled to a temperature of
35.degree. C. The coated target had a resistivity of 0.07 ohm.cm.
The target was subsequently tested at power levels of up to 100 kW
and worked well in the sputtering equipment without significant
arcing. The deposition of titanium dioxide was six times higher
than the rate from a titanium metal target in reactive
sputtering.
EXAMPLE 3
[0022] Example 2 was repeated with a low pressure vacuum plasma
operating at 200 mBar using titanium dioxide in the anatase form
having a particle size in the range of from 1 to 10 .mu.m. Using
the low pressure plasma, powders with a smaller particle size can
be used.
[0023] On spraying onto a target base under the conditions of
Example 2 the anatase was converted into a sub-stoichiometric
rutile form of titanium dioxide. The coated target had a
resistivity of 0.02 ohm.cm.
EXAMPLE 4
[0024] A mixture of niobium oxide (25 parts by weight) and titanium
dioxide (75 parts by weight) having a particle size of from 0.1 to
2 .mu.m was agglomerated and compacted, dried and sintered at
1300.degree. C. in air. The sintered body was then ground to a
particle size of 10 to 40 .mu.m.
[0025] The powder mixture was then plasma sprayed under the
conditions given in Example 2 onto an aluminium backing tube to a
coating thickness of 4 mm. The coated target had an electrical
resistivity of 0.5 ohm.cm and thus could be used as a D.C.
sputtering target.
* * * * *