U.S. patent application number 10/170686 was filed with the patent office on 2004-10-14 for apparatus for purifying ruthenium using ozone.
Invention is credited to Phillips, James E., Spaulding, Len D..
Application Number | 20040202593 10/170686 |
Document ID | / |
Family ID | 26849476 |
Filed Date | 2004-10-14 |
United States Patent
Application |
20040202593 |
Kind Code |
A1 |
Phillips, James E. ; et
al. |
October 14, 2004 |
Apparatus for purifying ruthenium using ozone
Abstract
The present invention relates to an apparatus for obtaining high
purity ruthenium metal without the need for high temperature
processing, expensive reagents, complex series of wet processes, or
expensive equipment. According to the present invention, a gas
stream including ozone (O.sub.3) is brought into contact with a
ruthenium source in one or more reaction vessels. The ozone reacts
with the ruthenium source to form ruthenium tetraoxide (RuO.sub.4),
a compound that is a gas at the reaction conditions. The ruthenium
tetraoxide, along with unreacted ozone and the remainder of the gas
stream is then fed into a collection vessel where a major portion
of the m gaseous ruthenium tetraoxide is thermally reduced to form
ruthenium dioxide (RuO.sub.2) deposits within the collection
vessel. The deposited ruthenium dioxide is then reduced to produce
highly pure ruthenium metal.
Inventors: |
Phillips, James E.;
(Somerville, NJ) ; Spaulding, Len D.; (Newark,
DE) |
Correspondence
Address: |
HARNESS, DICKEY & PIERCE, P.L.C.
P.O. BOX 8910
RESTON
VA
20195
US
|
Family ID: |
26849476 |
Appl. No.: |
10/170686 |
Filed: |
June 14, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10170686 |
Jun 14, 2002 |
|
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09655307 |
Sep 5, 2000 |
|
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|
6458183 |
|
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60152342 |
Sep 7, 1999 |
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Current U.S.
Class: |
422/187 ;
422/186.07; 422/198; 422/600 |
Current CPC
Class: |
C01G 55/004 20130101;
C01P 2006/80 20130101; C22B 11/02 20130101; C22B 9/14 20130101;
C22B 61/00 20130101 |
Class at
Publication: |
422/187 ;
422/189; 422/198; 422/186.07 |
International
Class: |
B01J 008/00; C01G
055/00 |
Claims
What we claim is:
1. An apparatus for the manufacture of high purity ruthenium
comprising: an oxygen source, an ozone generator, a first
container, a heated collection vessel, a nitrogen source, and a
hydrogen source; the oxygen source being connected to the ozone
generator for supplying a stream consisting essentially of oxygen
to the ozone generator; the ozone generator operating on the stream
of oxygen to produce a mixed gas stream consisting essentially of
oxygen and ozone; the first container designed to contain a
ruthenium source and promote the mixing of the ruthenium source and
the mixed gas stream, the reaction of the ozone and the ruthenium
source producing a reaction gas stream comprising oxygen, ozone,
and ruthenium tetraoxide; the heated collection vessel comprising
heated collection surfaces, the collection surfaces being
maintained at a temperature sufficient to cause the spontaneous
reduction of the ruthenium tetraoxide in the reaction gas stream to
form deposits of ruthenium dioxide on the collection surfaces; the
nitrogen source connected to the heated collection vessel for
purging the collection vessel to remove essentially all of the
remaining portion of the reaction gas stream; and the hydrogen
source connected to the heated collection vessel for selectively
introducing hydrogen gas into the collection vessel for reducing
the deposited ruthenium dioxide to form highly pure ruthenium.
2. An apparatus for the manufacture of high purity ruthenium
according to claim 1 wherein the first container comprises a series
of perforated trays for supporting the ruthenium source and
permitting the flow of the mixed gas stream.
3. An apparatus for the manufacture of high purity ruthenium
according to claim 1 wherein the first container comprises a
fluidized bed in which pieces of the ruthenium source are suspended
in and agitated by the flow of the mixed gas stream.
4. An apparatus for the manufacture of high purity ruthenium
according to claim 2 wherein the ruthenium source comprises
ruthenium sponge.
5. An apparatus for the manufacture of high purity ruthenium
according to claim 4 wherein the ruthenium sponge is characterized
by a purity of at least 99.5%.
6. An apparatus for the manufacture of high purity ruthenium
according to claim 3 wherein the ruthenium source is selected from
a group consisting of ruthenium powder, ruthenium shot, ruthenium
pellets and crushed ruthenium sponge.
7. An apparatus for the manufacture of high purity ruthenium
according to claim 3 wherein the ruthenium source comprises
ruthenium provided on particles of an inert carrier.
8. An apparatus for the manufacture of high purity ruthenium
according to claim 7 wherein the inert carrier comprises a ceramic
material.
9. An apparatus for the manufacture of high purity ruthenium
according to claim 1 further comprising a second container designed
to contain a second ruthenium source and promote mixing of the
second ruthenium source and the reaction gas stream.
10. An apparatus for the manufacture of high purity ruthenium
according to claim 9 wherein the second container further comprises
an inlet for the mixed gas stream, the design of the second
container promoting mixing of the mixed gas stream, the reaction
gas stream and the ruthenium source to form a second reaction gas
stream that is fed into the heated collection vessel.
11. A method for manufacturing high purity ruthenium dioxide the
steps of: placing a ruthenium source in a first container; feeding
an ozone-containing gas stream into the first container; forming a
reaction gas stream comprising ozone, oxygen, and ruthenium
tetraoxide; feeding the reaction gas into a collection vessel;
reducing the ruthenium tetraoxide to form ruthenium dioxide
deposits within the collection vessel; purging the collection
vessel to remove essentially all remaining reaction gas; and
removing the highly pure ruthenium dioxide from the collection
vessel.
12. A method for manufacturing high purity ruthenium dioxide
according to claim 11, wherein the highly pure ruthenium dioxide is
at least 99.99% pure.
13. A method for manufacturing high purity ruthenium dioxide
according to claim 12, wherein the highly pure ruthenium dioxide is
characterized by a predominate crystalline morphology.
14. A method for manufacturing high purity ruthenium dioxide
according to claim 12, wherein the predominate crystalline
morphology is a crystalline needle.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a method and apparatus for
the production of highly pure ruthenium and ruthenium dioxide and
is a divisional of application Ser. No. 09/655,307, filed Sep. 5,
2000, now allowed.
[0003] 2. Description of the Related Art and General Background
[0004] A member of the platinum group, ruthenium occurs naturally
with other members of the platinum group in ores found in Russia's
Ural mountains, North and South America, and particularly, South
Africa. It is also found along with other platinum metals in small
but commercial quantities in both the pentlandite of the Sudbury,
Ontario, nickel-mining region, and in the pyroxinite deposits of
South Africa. Commercially, ruthenium may be isolated from the
other platinum metals through several complex chemical processes,
the final stage of which generally includes the hydrogen reduction
of ammonium ruthenium chloride or nitrosylruthenium chloride, to
produce ruthenium metal powder.
[0005] Ruthenium, a hard, white metal, is one of the most effective
hardeners for platinum and palladium and is typically alloyed with
these metals to produce electrical contacts for severe wear
resistance. There have also been reports that a ruthenium alloy,
specifically a ruthenium-molybdenum alloy, exhibits
superconductivity at 10.6.degree. K. It has also been reported that
the corrosion resistance of titanium can be improved over 100 times
by adding as little as 0.1% ruthenium. Ruthenium is also a
versatile catalyst and is frequently used in petrochemical and
other industrial processes to remove H.sub.2S.
[0006] One method for extracting ruthenium is disclosed in U.S.
Pat. No. 3,997,337 ("the '337 patent"). The '337 patent included a
discussion of both earlier methods for the separation and
purification of precious metals, including ruthenium, from a
concentrate of by-metals and the improved method taught by the
patent. The improvement disclosed in the '337 patent for the
separation and purification of precious metals, including
ruthenium, from a concentrate of by-metals comprised heating the
concentrate to a temperature between 1100.degree. C. and
1500.degree. C., preferably at about 1300.degree. C., in a gaseous
stream which comprises oxygen. This heating step is continued for a
period sufficient to ensure quantitative removal of one or more of
lead, arsenic, silver, bismuth and/or tellurium and the oxidation
of ruthenium, rhodium and iridium. The referenced by-metal
concentrate is obtained as a by-product of the separation of
platinum, palladium, and gold from an ore or other mixed
source.
[0007] In the previous process, the by-metal concentrate was fused
with potassium bisulphate (KHSO.sub.4) to convert the rhodium to
the water-soluble sulphate, Rh.sub.2(SO.sub.4).sub.3, which can be
removed by washing. The remaining residue was then subjected to a
sodium peroxide (Na.sub.2O.sub.2) fusion to convert the ruthenium
and osmium to water soluble sodium salts of their oxo-anions (e.g.
RuO.sub.4.sup.2- and OsO.sub.4.sup.2- respectively) and to convert
the iridium to an acid soluble hydrous oxide (probably
IrO.sub.2.nH.sub.2O). The ruthenium and osmium were then separated
from the iridium by treating the sodium peroxide melt with water to
form a precipitate, and treating the precipitate with hydrochloric
acid to dissolve the iridium. The ruthenium and osmium were then
normally purified by a collective chlorine distillation, followed
by a nitric acid distillation for osmium. The rhodium is treated
for the removal of impurities such as palladium, tellurium and
other base metals that are also rendered soluble by the KHSO.sub.4
fusion. The iridium has to be separated from large quantities of
lead and other impurities present in the concentrate which have
been rendered soluble by the sodium peroxide (Na.sub.2O.sub.2)
fusion. As can be appreciated, this method used both large
quantities of concentrates and correspondingly large quantities of
costly reagents. Further, the impurities, in particular tellurium
were sometimes difficult to remove.
[0008] The improvement outlined in the '337 patent was intended to
provide a process for the treatment of a by-metal concentrate for
1) to remove troublesome impurities such as Te, As, Bi, Ag, and Pb;
2) the removal of osmium; and 3) to reduce the bulk of the
by-metals being refined thereby providing saving in both reagents
and equipment. This was accomplished by treating a concentrate of
by-metals by heating to between about 1100.degree. C. and
1500.degree. C. in an oxygen-containing gaseous stream for a period
of time (examples include times of 20 hours) sufficient to ensure
both quantitative removal of one or more of lead, arsenic, silver,
bismuth and/or tellurium and the oxidation of ruthenium, rhodium
and iridium to their oxides. According to the patent, the
oxygen-containing gaseous stream could be air and the exhaust gas
could be scrubbed with a liquid to recover osmium. The '337 patent
also provided for the separation of ruthenium from the other
platinum group metals by fusing the ignited by-metal concentrate
with potassium hydroxide and leaching the melt with water to
dissolve ruthenium complexes formed during the fusion process. As
described in the '337 patent, a by-metal concentrate was heated to
about 1300.degree. C. for 20 hours in a stream of air, a process by
which osmium, together with lead, arsenic, silver, bismuth and
tellurium, were quantitatively removed from the concentrate while
less than 10% of the ruthenium and only traces of the other
platinum group metals were volatilized. The vapors were scrubbed
with a 10% NaOH solution to precipitate all the metals, with the
exception of ruthenium and osmium, as hydrous oxides (which settle
to the bottom of the receiving vessel). The ruthenium and osmium
oxides which are converted to soluble sodium salts according to the
following reactions:
RuO.sub.4+NaOH.fwdarw.Na.sub.2(RuO.sub.4)+{fraction
(1/2)}O.sub.2+H.sub.2O (a)
OsO.sub.4+2NaOH.fwdarw.Na.sub.2(OsO.sub.4(OH).sub.2) (b)
[0009] The ruthenium was then precipitated from the alkali solution
by the addition of ethanol to reduce the oxo-anion RuO.sub.4.sup.2-
and precipitate the insoluble hydrous oxide (reported as
Ru.sub.2O.sub.3.nH.sub.2O but the applicants believe
RuO.sub.2.nH.sub.2O may be more accurate). This precipitate is
filtered off together with the sludge in the receiver which
contains the other metals which have been volatized and is recycled
to the lead alloying stage of the metal process or to some other
convenient point if lead alloying is not utilized. The osmium
remaining in solution is then precipitated at room temperature as a
hydrous oxide (reported as Os.sub.2O.sub.3.nH.sub.2O, but the
applicants believe OsO.sub.2.nH.sub.2O may be more accurate) by
acidifying the solution with HCl to a pH of 4.0.
[0010] U.S. Pat. No. 4,105,442 ("the '442 patent") teaches an
alternative process for the separation and purification of
ruthenium involving the conversion of the ruthenium present in
solution to a nitrosylruthenium complex with the ruthenium in the
Ru+2 oxidation state. The nitrosylruthenium complex is then
converted to a nitrosylruthenium chlorocomplex, which is then
removed from solution using a suitable liquid or resin anion
exchanger.
[0011] The '442 patent notes the existence of conventional
techniques for the recovery and purification of ruthenium and
osmium based on the formation of low boiling temperature oxides in
solution, with the oxides being subsequently removed from the
solution by heating. For osmium, oxidation of the metal to the VIII
oxidation state is relatively easy, and a number of oxidizing
agents can be used. Furthermore, osmium can be efficiently removed
as the tetraoxide forms even under fairly strongly acid conditions.
In the case of ruthenium however, the oxidation is more difficult
and control of the solution pH at a relatively high value is
essential. Under these circumstances, removal of ruthenium from
solution is incomplete, typically leaving several hundred parts per
million of ruthenium in the solution. This not only represents a
loss in ruthenium recovery, but the remaining ruthenium constitutes
an impurity element during the refining and recovery of the other
platinum group metals. Further disadvantages of this process
include contamination of the ruthenium distillate with an acid and
the explosion danger associated with the highly unstable nature of
ruthenium tetraoxide.
[0012] Other methods for the separation and purification of
ruthenium using solvent extraction and ion exchange methods have
met with limited success and usually involve solvent extraction
from a nitric acid solution. In such solutions ruthenium occurs as
a series of nitrosylruthenium nitrate complexes that can be
separated from the solution by solvent extraction with, typically,
long chain tertiary amines. It is well known that ruthenium forms a
very large number of nitrosylruthenium complexes and that the
stability of such complexes is greater for ruthenium than for any
other element. Thus, for example, in hydrochloric acid solution the
nitrosylruthenium complex RuNOCl.sub.2-5 can be formed. This
complex is highly extractable, may be formed preferentially, and
allows for the separation of ruthenium from the other platinum
group metals. This process, however, has its own drawbacks,
including 1) the available methods of making the nitrosylruthenium
complex typically yield only 90-95% and 2) the other platinum group
metals present tend to form complexes that exhibit similar behavior
towards anionic solvent extractants.
[0013] The '442 patent goes on to address these issues to provide a
process for the extraction of ruthenium as a nitrosylruthenium
complex with both high yield and selectivity with respect to the
other platinum group metals.
[0014] Yet another alternative process for the purification of
ruthenium metal involved zone-refining. According to this process,
a sample of impure ruthenium metal is subjected to one or more heat
treatments to form a zone of molten ruthenium, surrounded by solid
ruthenium, and move this molten zone along the ruthenium sample and
thereby segregate impurities from the ruthenium. Although this
technique can produce very pure ruthenium, ruthenium's relatively
high melting point (approximately 2280.degree. C.) makes this
process very energy intensive and requires more specialized
equipment to implement than the applicants' invention.
BRIEF SUMMARY OF THE INVENTION
[0015] The present invention comprises a new and improved method
capable of purifying ruthenium sources to obtain high purity
ruthenium without the need for high temperature processing,
expensive reagents, complex series of wet processes, or expensive
equipment required to practice prior art processes. According to
the present invention, a gas stream including ozone (O.sub.3) is
brought into contact with a ruthenium source in one or more
reaction vessels. The ozone reacts with the ruthenium present in
the ruthenium source to form ruthenium tetraoxide (RuO.sub.4), a
compound that is a gas at the reaction conditions. The ruthenium
tetraoxide, along with unreacted ozone and the remainder of the gas
stream is then fed into a heated collection vessel where a major
portion of the gaseous ruthenium tetraoxide is reduced to form
ruthenium dioxide (RuO.sub.2) deposits within the collection
vessel. The deposited ruthenium dioxide is then reduced, preferably
with hydrogen, to produce the purified ruthenium.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 illustrates a basic embodiment of an apparatus that
may be used to practice the disclosed method of ruthenium
purification.
[0017] FIG. 2 illustrates an alternative embodiment of an apparatus
that may be used to practice the disclosed method of ruthenium
purification that includes a hydrogen source.
[0018] FIG. 3 illustrates an alternative embodiment of an apparatus
that may be used to practice the disclosed method of ruthenium
purification that includes only a single reaction vessel.
[0019] FIG. 4a illustrates a possible configuration for a reaction
vessel in which a series of perforated plates are provided for the
support of the ruthenium source in the ozone-containing gas
stream.
[0020] FIG. 4b illustrates a possible configuration for a reaction
vessel in which the ruthenium source is supported within a
fluidized bed by the flow of the ozone-containing gas stream.
[0021] FIG. 5 illustrates a basic series of process steps that
could be used to etch a ruthenium layer during semiconductor
processing.
[0022] FIG. 6 illustrates a possible configuration for a collection
vessel that provides a series of collection surfaces upon which the
RuO.sub.2 would be deposited and subsequently reduced to form
Ru.
DETAILED DESCRIPTION OF THE INVENTION
[0023] The present invention comprises a new and improved method
capable of purifying ruthenium sources to obtain high purity
ruthenium without the need for high temperature processing,
expensive reagents, complex series of wet processes, or expensive
equipment required to practice prior art processes. According to
the present invention, a gas stream including ozone (O.sub.3) is
brought into contact with a ruthenium source in one or more
reaction vessels. The ozone reacts with the ruthenium present in
the ruthenium source, likely according to the reaction (1), to form
ruthenium tetraoxide (RuO.sub.4) a compound that is a gas at the
reaction conditions.
Ru+mO.sub.3.fwdarw.RuO.sub.4+nO.sub.2 (1)
[0024] In its crystal form, ruthenium (VIII) oxide (RuO.sub.4), is
a golden yellow, highly volatile, solid at room temperature. It has
a melting point of 25.4 degrees C. and a boiling point of 40
degrees C. It is sparingly soluble in water (2% w/v at 20 degrees
C.) and, although freely soluble in carbon tetrachloride, can react
violently with other organic solvents such as ether, alcohol,
benzene and pyridine. Ruthenium tetraoxide is a strong oxidizing
agent that also reacts with many other organic compounds like
olefins, sulfides, primary and secondary alcohols, and aldehydes,
and will also degrade benzene rings.
[0025] The ruthenium tetraoxide, along with unreacted ozone and
other gases is then fed from one or more reaction vessels into a
heated collection vessel, the conditions in the collection vessel
being sufficient to convert a major portion of the gaseous
ruthenium tetraoxide into ruthenium dioxide (RuO.sub.2) according
to the reaction (2) below:
RuO.sub.4.fwdarw.O.sub.2+RuO.sub.2 (2)
[0026] The ruthenium dioxide deposits on the walls of the
collection vessel and/or collection surfaces or substrates disposed
within the collection vessel. The collected ruthenium dioxide is
then reduced to produce the purified ruthenium. When using hydrogen
gas as the reducing agent, the reduction proceeds according to the
reaction (3) below:
RuO.sub.2+2H.sub.2.fwdarw.Ru+2H.sub.2O (3)
[0027] The morphology of both the ruthenium dioxide and the
resulting ruthenium was related to the temperature of the
collection vessel. The collection vessel employed by the applicants
was surrounded by a single zone furnace that resulted in a
non-uniform temperature profile along the length of the collection
vessel. The furnace temperature set point was achieved near the
midpoint of the collection vessel, with the temperature decreasing
towards both ends of the collection vessel. The predominant
morphology of the purified ruthenium deposited in the collection
vessel was crystalline needles, but a finer grained mirror-like
region was also observed toward the inlet side of the collection
vessel. If desired, a collection vessel with a more uniform profile
could be utilized to produce deposits comprising essentially a
single morphology, either crystalline needles or a mirror-like
layer. This crystallographic selectivity could also be employed to
coat selected substrates, e.g. wafers or metallic substrates, with
either the crystalline needles or a mirror-like layer of ruthenium
dioxide or, after reduction, ruthenium.
[0028] Similarly, a collection vessel could be provided with a
series of heated collection surfaces (201) that could be more
easily removed from the collection vessel for recovery of the
ruthenium as depicted in FIG. 6. Depending on the construction, the
walls of the collection vessel itself (202) could be kept at or
near room temperature to reduce the potential for RuO.sub.2
deposition. Alternatively, a cooling fluid could be introduced into
optional shell (203) to cool the walls of the collection vessel
below room temperature or simply to control the heating resulting
from the proximity of the collection surfaces (201). For coating a
substrate, a configuration similar to that shown in FIG. 6 could be
utilized with the collection surfaces (201) serving as platens or
chucks that will both hold and heat the substrates to be coated.
For the production of ruthenium, however, the crystalline needle
morphology is preferred as the crystals may be gently removed from
the walls of the collection vessel to collect the desired ruthenium
product.
EXAMPLE 1
[0029] Using the apparatus generally depicted in FIG. 1, 487.1 g of
ruthenium metal sponge was charged in the first reaction vessel (2)
and 499.6 g of ruthenium metal sponge was charged in the second
reaction vessel (3). The ozone generator (1) supplied a mixture of
ozone (11.5%) and oxygen to the first reaction vessel at a rate of
3 liters/min. The observed reaction efficiency was just under 4%,
assuming that reaction (4) is the primary reaction, resulting in
the reaction of 2.5 g of
Ru+2O.sub.3.fwdarw.RuO.sub.4+O.sub.2 (4)
[0030] ruthenium in the first reaction vessel and 11.0 g of
ruthenium in the second reaction vessel. The ozone reacted with the
ruthenium metal sponge at room temperature and pressure to form
ruthenium tetraoxide which was visible in the reaction vessels (1,
2) as a pale green gas. The ruthenium tetraoxide, together with the
unreacted ozone and oxygen, was then fed into the collection vessel
(4) which comprised a 32".times.23/8" i.d. (approximately 813
mm.times.60 mm) glass tube with a wall temperature of approximately
450.degree. C. After a reaction time of 160 minutes, the collection
vessel exhibited an accumulation of ruthenium dioxide, the
predominant morphology being crystalline needles. The system was
then purged with nitrogen gas to remove the residual oxygen and
ozone. Hydrogen gas was then fed into the collection vessel, again
with a wall temperature of approximately 450.degree. C. at the
midpoint, to reduce the deposited ruthenium dioxide to obtain
ruthenium metal. Clearly, if there was a need to obtain ruthenium
dioxide, the deposits within the collection vessel could simply be
removed prior to the reduction treatment. The collection vessel was
then disassembled and the ruthenium metal collected. An analysis of
the composition of the starting ruthenium metal sponge and the
recovered ruthenium metal is shown in Table 1 below.
1TABLE 1 Starting After Purification Trace Metal (ppm) (ppm) Ni 2
0.3 Cu 2 0.1 Fe 88 2.0 Al <10 0.3 Ca 15 0.2 Si 76 10 Mg 8 0.1 Cr
4.1 0.6
[0031] Among the advantages provided by the present invention is
the high purity achieved by an essentially "dry" process that does
not require temperatures above 500.degree. C. and eliminates the
need for expensive reagents or resins and does not require highly
specialized equipment. Another advantage is that the concentration
of ruthenium tetraoxide is relatively low and its residence time in
the apparatus is relatively short (as it flows from the reactor
into the collection vessel) so the risk of explosion is minimized.
The applicants also believe that the relatively limited residence
time also reduces the formation of undesireable byproducts within
the apparatus and/or on the ruthenium source.
[0032] The reaction rates obtained with experimental apparatus
utilized by the applicants (FIG. 1) were limited by the physical
limitations of the equipment. The applicants fully anticipate that
both major and minor changes in the apparatus and process
conditions would improve, perhaps substantially, the system
performance without compromising the advantages of the present
invention. In particular, changes that resulted in an increase the
degree of contact between the ozone and the ruthenium source during
the residence time would be beneficial. Based on limited
experimental observation, the applicants believe that the
ruthenium-ozone reaction rate does not exhibit a linear
relationship with increasing ozone concentration. Indeed, it
appears that the reaction efficiency improves dramatically above a
threshold ozone concentration of between 10% and 11% for reactants
near room temperature.
[0033] One configuration that would achieve this improvement would
involve flowing the ozone/oxygen mixture through a large chamber
(150) containing a series of trays (151) loaded with a thin layer
of the ruthenium source as depicted in FIG. 4a. Another
configuration that would achieve this improvement would be a
fluidized-bed chamber (170) in which the particles of the ruthenium
source (171) are suspended and agitated by the oxygen/ozone flow as
depicted in FIG. 4b. Yet another configuration would employ
mechanical means to induce turbulent gas flow and/or agitate the
ruthenium source to promote more uniform mixing between the gas and
solid phases. The applicants also anticipate that adjustments to
the oxygen/ozone mixture composition, the gas flow rate, and the
reaction temperature may provide further improvements to the
efficiency of the basic process for ruthenium purification.
[0034] In addition to the purification of ruthenium and ruthenium
compounds, the basic chemistry embodied in the present invention
has practical application as an etch process for semiconductor,
circuit board, or other instances in which a thin ruthenium film is
to be etched. Compared to other metal etching processes, the low
temperature and relatively high pressures (near ambient pressure
and temperature) at which ozone could be used to etch ruthenium
layers eliminate the need for expensive process gases, vacuum
chambers and their associated load locks and vacuum pumps, and
reduce the overall power consumption associated with the etch
process. Any ozone necessary for the process could be produced on
site, thereby, avoiding the risks associated with the
transportation, storage, and use of high pressure gas cylinders.
Similarly, any unreacted ozone could be removed from the exhaust
stream by known catalytic or temperature treatments, thereby
reducing any environmental impact of the present process when
compared with some of the prior art etch chemistries. The
advantages provided by the on-site production of the ozone are, of
course, equally applicable to the disclosed process for the
purification of ruthenium. As envisioned by the applicants, a
typical etch process would start with a semiconductor wafer having
as its surface layer ruthenium metal. The wafer would be patterned
with some barrier material, such as photoresist, and then contacted
with an ozone-containing gas stream to oxidize the exposed
ruthenium metal to produce the volatile ruthenium tetraoxide
RuO.sub.4 that is then removed from the etch chamber. The basic
process flow for such a process is provided in FIG. 5.
* * * * *