U.S. patent number RE41,249 [Application Number 11/633,136] was granted by the patent office on 2010-04-20 for quartz glass body having improved resistance against plasma corrosion, and method for production thereof.
This patent grant is currently assigned to Heraeus Quarzglas GmbH & Co. KG, Shin-Etsu Quartz Products Co., Ltd.. Invention is credited to Akira Fujinoki, Kyoichi Inaki, Tatsuhiro Sato, Tomoyuki Shirai, Nobumasa Yoshida.
United States Patent |
RE41,249 |
Sato , et al. |
April 20, 2010 |
Quartz glass body having improved resistance against plasma
corrosion, and method for production thereof
Abstract
An object of the present invention is to provide a quartz glass
body, especially a quartz glass jig for plasma reaction in
producing semiconductors having excellent resistance against plasma
corrosion, particularly, excellent corrosion resistance against
F-based gaseous plasma; and a method for producing the same. A body
made of quartz glass containing a metallic element and having an
improved resistance against plasma corrosion is provided that
contains bubbles and crystalline phase at an amount expressed by
projected area of less than 100 mm.sup.2 per 100 cm.sup.3.
Inventors: |
Sato; Tatsuhiro (Koriyama,
JP), Yoshida; Nobumasa (Koriyama, JP),
Fujinoki; Akira (Koriyama, JP), Inaki; Kyoichi
(Tokorozawa, JP), Shirai; Tomoyuki (Shiga,
JP) |
Assignee: |
Heraeus Quarzglas GmbH & Co.
KG (Hanau, DE)
Shin-Etsu Quartz Products Co., Ltd. (Tokyo,
JP)
|
Family
ID: |
27344414 |
Appl.
No.: |
11/633,136 |
Filed: |
November 30, 2006 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
09935334 |
Aug 22, 2001 |
06887576 |
May 3, 2005 |
|
|
Foreign Application Priority Data
|
|
|
|
|
Aug 23, 2000 [JP] |
|
|
2000-252993 |
Dec 22, 2000 [JP] |
|
|
2000-390823 |
Dec 26, 2000 [JP] |
|
|
2000-395988 |
|
Current U.S.
Class: |
428/426; 428/432;
428/410 |
Current CPC
Class: |
C30B
31/14 (20130101); C03B 19/1453 (20130101); C30B
35/00 (20130101); C03B 19/01 (20130101); C03B
19/066 (20130101); C30B 25/12 (20130101); C03B
20/00 (20130101); C03C 3/06 (20130101); C03B
32/00 (20130101); Y10T 428/315 (20150115); C03B
2201/50 (20130101); C03B 2201/54 (20130101); C03B
2201/40 (20130101); Y10T 428/24496 (20150115); C03B
2201/32 (20130101); C03C 2201/32 (20130101); Y10T
428/26 (20150115); C03B 2201/30 (20130101); C03B
2201/34 (20130101); C03B 2201/42 (20130101) |
Current International
Class: |
B32B
15/00 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
199 18 001 |
|
Oct 1999 |
|
DE |
|
0 466 932 |
|
Jan 1992 |
|
EP |
|
8-175840 |
|
Jul 1996 |
|
JP |
|
Other References
Patent Abstracts of Japan, vol. 1999, No. 13, Nov. 30, 1999, for JP
11-228172 A (Aug. 24, 1999). cited by examiner .
Patent Abstracts of Japan, vol. 2000, No. 9, Oct. 13, 2000, for JP
2000-169163 A (Jun. 20, 2000). cited by examiner .
Patent Abstracts of Japan, vol. 015, No. 256, Jun. 28, 1991, for JP
03-083833 A (Apr. 9, 1991). cited by examiner .
Patent Abstracts of Japan, vol. 012, No. 373, Oct. 6, 1988, for JP
63-123825 A (May 27, 1988). cited by examiner .
Patent Abstracts of Japan, vol. 012, No. 132, Apr. 22, 1988, for JP
62-252330 A (Nov. 4, 1987). cited by examiner .
Patent Abstracts of Japan, vol. 012, No. 479, Dec. 14, 1988, for JP
63-195133 A (Aug. 12, 1988). cited by examiner .
Patent Abstracts of Japan, vol. 013, No. 423, Sep. 20, 1989, for JP
01-160843 A (Jun. 23, 1989). cited by examiner .
Patent Abstracts of Japan, vol. 013, No. 236, May 30, 1989, for JP
01-045739 A (Feb. 20, 1989). cited by examiner .
Patent Abstracts of Japan, vol. 013, No. 221, May 23, 1989, for JP
01-033029 A (Feb. 2, 1989). cited by examiner .
Patent Abstracts of Japan, vol. 013, No. 199, May 11, 1989, for JP
01-018936 A (Jan. 23, 1989). cited by examiner .
Patent Abstracts of Japan, vol. 013, No. 145, Apr. 10, 1989, for JP
63-307139 A (Dec. 14, 1988). cited by examiner .
Patent Abstracts of Japan, vol. 013, No. 039, Jan. 27, 1989, for JP
63-236719 A (Oct. 3, 1988). cited by examiner .
Patent Abstracts of Japan, vol. 1996, No. 10, Oct. 31, 1996, for JP
08-165131 A (Jun. 25, 1996). cited by examiner .
Patent Abstracts of Japan, vol. 015, No. 467, Nov. 27, 1991, for JP
03-199133 A (Aug. 30, 1991). cited by examiner .
Patent Abstracts of Japan, vol. 009, No. 017, Jan. 24, 1985, for JP
59-164644 A (Sep. 17, 1984). cited by examiner.
|
Primary Examiner: Speer; Timothy M
Attorney, Agent or Firm: Wenderoth, Lind & Ponack,
L.L.P.
Claims
What is claimed is:
1. An article comprising a body made of quartz glass having
improved corrosion resistance against plasma, the quartz glass
containing bubbles and crystalline phase at a quantity accounting
for less than 100 mm.sup.2 in a projection area per 100
.[.cm.sub.3.]. .Iadd.cm.sup.3 .Iaddend.of the quartz glass body,
and said quartz glass body having a metallic element containing
surface layer having a thickness of at least 5 mm containing 0.1 to
20% by weight of a metallic element, wherein the metallic element
is selected from the group consisting of Sm, Y, Zr and Ti.
2. An article as claimed in claim 1, wherein the metallic element
has a boiling point higher than that of a Si fluoride.
3. An article as claimed in claim 1, wherein the metallic element
is able to react with fluorine to form a fluoride compound and the
fluoride compound of said metallic element .[.having.]. .Iadd.has
.Iaddend.a boiling point that is higher than that of the fluoride
compound of Si (SiF.sub.4).
4. An article as claimed in claim 1, wherein the metallic element
containing surface layer further comprises a second element
selected from the group consisting of Sm, Eu, Yb, Pm, Pr, Nd, Ce,
Tb, Gd, .[.Ba.]. .Iadd.Ba, .Iaddend.Mg, Y, .[.Tin.].
.Iadd.Tm.Iaddend., Dy, Ho, Er, Cd, Co, Cr, Cs, Zr, Al, In, Cu, Fe,
Bi, Ga and Ti.
5. An article as claimed in claim 1, wherein the metallic element
is additionally applied to a surface thereof.
6. An article as claimed in claim 1, said quartz glass body having
a surface roughness Ra of 0.01 to 10 .mu.m.
7. An article as claimed in claim 6, wherein said body has a
surface that is brought into contact with a plasma corrosive gas,
said surface being obtained by subjecting the surface to a
precision cutting treatment, or a heating and melting
treatment.
8. An article as claimed in claim 1, wherein the quartz glass has
an OH concentration of 100 to 2000 ppm.
9. An article as claimed in claim 1, wherein 2 mol/m.sup.3 or less
of a gas is discharged from the article when it heated in a
temperature range of from room temperature to 1000.degree. C.
10. An article as claimed in claim 1, wherein the quartz glass has
an internal transmittance for a visible radiation of 50%/cm or
higher.
11. An article as claimed in claim 1, wherein the body is
configured to function as a jig for supporting wafers.
12. An article as claimed in claim 7, wherein said surface is
subjected to said heating and melting treatment followed by a
chemical etching treatment.
.Iadd.13. An article comprising a body made of quartz glass having
improved corrosion resistance against plasma, the quartz glass
being doped with a metallic element, the quartz glass containing
bubbles and crystalline phase at a quantity accounting for less
than 100 mm.sup.2 in a projection area per 100 cm.sup.3 of the
quartz glass body, wherein the quartz glass body has a metallic
element-containing layer with a predetermined thickness containing
0.1 to 20% by weight of said metallic element..Iaddend.
.Iadd.14. An article as claimed in claim 13, wherein the metallic
element has a boiling point higher than that of a Si
fluoride..Iaddend.
.Iadd.15. An article as claimed in claim 13, wherein the metallic
element is able to react with fluorine to form a fluoride compound
and the fluoride of said metallic element has a boiling point that
is higher than that of the fluoride compound of Si..Iaddend.
.Iadd.16. An article as claimed in claim 13, wherein the metallic
element is one or more elements selected from the group consisting
of rare earth elements, Ba, Mg, Cd, Co, Cr, Cs, Zr, In, Cu, Fe, Bi,
Ga and Ti..Iaddend.
.Iadd.17. An article as claimed in claim 16, wherein the quartz
glass is further doped with Al..Iaddend.
.Iadd.18. An article as claimed in claim 13, wherein said metallic
element is present in a concentration in a range from 0.1 to 20% by
weight..Iaddend.
.Iadd.19. An article as claimed in claim 13, wherein said metallic
element-containing layer is a surface layer having a thickness of
at least 5 mm..Iaddend.
.Iadd.20. An article as claimed in claim 18, wherein the metallic
element is additionally applied to the surface
thereof..Iaddend.
.Iadd.21. An article as claimed in claim 13, said quartz glass body
having a surface roughness Ra of 0.01 to 10 .mu.m..Iaddend.
.Iadd.22. An article as claimed in claim 13, wherein said body has
a surface that is brought into contact with a plasma corrosive gas,
said surface being obtained by subjecting the surface to a
precision cutting treatment, a heating and melting treatment, or a
heating and melting treatment followed by a chemical etching
treatment..Iaddend.
.Iadd.23. An article as claimed in claim 13, wherein the quartz
glass has an OH concentration of 100 to 2000 ppm..Iaddend.
.Iadd.24. An article as claimed in claim 13, wherein 2 mol/m.sup.3
or less of a gas are generated in a temperature range of from room
temperature to 1000.degree. C..Iaddend.
.Iadd.25. An article as claimed in claim 13, wherein the quartz
glass has an internal transmittance for a visible radiation of
50%/cm or higher..Iaddend.
.Iadd.26. An article as claimed in claim 13, wherein said body has
said metallic element applied to a surface thereof..Iaddend.
.Iadd.27. An article as claimed in claim 13, wherein the body is
configured to function as a jig for supporting wafers..Iaddend.
Description
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a quartz glass body, and
especially to a quartz jig for use in producing semiconductors yet
having excellent resistance against plasma corrosion, and to a
production method thereof.
RELATED ART
In the production of semiconductors, for instance, in the
production of semiconductor wafers, with the recent trend in
increasing the diameter, the process efficiency is improved by
using a plasma reaction apparatus in the etching process and the
like. For instance, in the process of etching semiconductor wafers,
etching treatment is performed by using gaseous plasma; for
example, a fluorine (F) based gaseous plasma.
However, if a conventionally used quartz glass is placed, for
instance, in a F-based gaseous plasma, SiO.sub.2 undergoes reaction
with the F-based gaseous plasma on the surface of the quartz glass
surface so as to generate SiF.sub.4. Since the boiling point of the
thus generated SiF.sub.4 is -86.degree. C., it easily volatilizes
so as to cause great corrosion on the surface of the quartz glass.
Thus, quartz glass was found to be unsuitable for use as jigs
exposed to a F-based gaseous plasma because thinning and surface
roughening proceed on the surface of the quartz glass.
As described above, severe problems were found to develop on
conventional quartz glass in manufacturing semiconductors employing
plasma reaction with regard to resistance against plasma corrosion,
particularly, in case of applying etching treatment using a F-based
gaseous plasma. In the light of such circumstances, it has been
proposed that the surface of the quartz glass member be covered
with aluminum or an aluminum compound to improve the resistance
against plasma corrosion of the quartz glass member (see
JP-A-Hei9-957751, JP-A-Hei9-95772, and JP-A-Hei10-139480 (the term
"JP-A" as referred herein signifies "an unexamined published
Japanese patent application")), or to incorporate aluminum in
quartz glass to improve resistance against plasma corrosion
(JP-A-Hei11-228172).
PROBLEMS THE INVENTION IS TO SOLVE
The present inventors have made extensive studies to further
increase the resistance against plasma corrosion of quartz glass,
and among them, an investigation of the resistance against plasma
corrosion has been made for a quartz glass prepared by heating and
fusing, in vacuum, a quartz glass powder having mixed therein 5% by
weight of alumina powder. On investigating the resistance against
plasma corrosion of the thus produced quartz glass, it has been
found that the etching rate thereof was lowered by 40 to 50% as
compared with that of a quartz glass member free from doping.
However, fine bubbles have been observed to develop inside and on
the surface portion of the quartz glass body. Particularly on the
surface portion, it has been found that a great difference occurred
between the corroded portion and the non-corroded portion so as to
increase surface roughness. Furthermore, fine crystalline portions
were found to develop so as to frequently cause the problem of
peeling off on those portions. This resulted in the generation of
fine indentations (dimples) and in the increased generation of
particles that adhere to the surface of the wafer, thereby leading
to problems such as an increase in defective wafers. In addition to
the above, since such bubbles and indentations accelerate etching,
even though the concentration of the metal dopant is increased, the
resistance against plasma corrosion has been found to result in a
relatively poor improvement.
One of the reasons for this effect may be that the boiling point of
AlF.sub.3, which is generated on the reaction with the F-based
plasma gas, is 1290.degree. C., a temperature far higher than that
of SiF.sub.4. Hence, presumably, while a large amount of the
SiF.sub.4 portion is corroded, little evaporation occurs on the
surface of the AlF.sub.3 portion, and this leads to a great
difference in the etched quantity. Furthermore, if doped aluminum
is locally concentrated, a clear difference in energy state occurs
as compared with the neighboring SiO.sub.2 portions, and this
causes a loss in balance so as to easily cause a transition of
SiO.sub.2 to a crystalline state having lower energy.
The crystalline phase can be visually observed as fine white
foreign matter. Since the crystalline portions that are formed in
the vicinity of the surface have a thermal expansion differing from
that of quartz glass, they tend to easily peel off with the change
in temperature. Furthermore, since the metallic elements that are
locally concentrated have lower boiling points than that of
SiO.sub.2, they convert into gaseous phase on heating and fusing
SiO.sub.2 as to generate bubbles. The bubbles that are present in
the vicinity of the surface easily burst with a change in
temperature. The facts described above all lead to a cause of
generating particles. Furthermore, since plasma gas concentrates on
the bubbles and the indented portions to easily increase the
etching rate, the total amount of etching of the entire glass
increases so as to shorten the usable life of the glass.
The present invention has been completed based on the above
findings, and an object of the present invention is to provide a
quartz glass as a material for jigs to use in the plasma reaction
during the manufacture of semiconductors, but having excellent
corrosion resistance against plasma, particularly, F-based gaseous
plasma. Another object of the present invention is to provide a
quartz glass jig, and a further object of the present invention is
to provide methods for producing the above.
MEANS FOR SOLVING THE PROBLEMS
In order to accomplish the aforementioned objects, the present
invention provides a quartz glass body having improved resistance
against plasma corrosion, provided that the quartz glass contains
bubbles and crystalline phase (foreign matters) at an amount
expressed by projected area of less than 100 mm.sup.2 per 100
cm.sup.3.
As an embodiment for incorporating the metallic element above, as a
matter of course, not only doping and/or surface coating is
included, but also, so long as the metallic element is incorporated
at a predetermined concentration, any mode of incorporation can be
employed.
If the content of the bubbles and the crystalline phase of quartz
glass is set to an amount expressed by projected area of less than
100 mm.sup.2 per 100 cm.sup.3, this level provides a quartz glass
member for general use, and no particles develop in the plasma
etching step. However, if the content of the bubbles and the
crystalline phase is not less than the range above, a large
quantity of particles generates in the plasma etching step.
The metal element to be incorporated in the quartz glass is not
limited to Al (aluminum) or aluminum compounds that are disclosed
in the aforementioned proposals, but other metallic elements are
usable in F-based gaseous plasma etching so long as the fluoride of
the metallic element yields a boiling point higher than that of the
fluoride of Si (SiF.sub.4).
As the metallic elements above, there can be used one type or two
or more types of elements selected from the group consisting of Sm,
Eu, Yb, Pm, Pr, Nd, Ce, Tb, Gd, Ba, Mg, Y, Tm, Dy, Ho, Er, Cd, Co,
Cr, Cs, Zr, Al, In, Cu, Fe, Bi, Ga, and Ti. The boiling point or
the gasification temperature of the fluorides of metallic elements
other than those enumerated above are too low to cause further
etching. Since the metallic elements above each provide a fluoride
having a boiling point higher than that of Si, etching does not
proceed as in the case of Si. The metallic elements are listed in
the descending order of boiling point or gasification temperature;
for instance, the boiling point of SmF is 2427.degree. C., and
gasification temperature of TiF is 284.degree. C.
The boiling point or the gasification temperature of the fluorides
of metallic elements other than those enumerated above are too low
to cause further etching. The concentration of the metallic
elements above is preferably in a range of from 0.1 to 20 wt. %. If
the metallic element should be incorporated at a concentration of
less than 0.1 wt. %, no improvement in the resistance against
etching would be expected; if the metallic element should be
incorporated at a concentration exceeding 20 wt. %, bubbles or
crystalline phase would be generated in large quantities to make
the glass unfeasible for use as jigs.
For instance, specially preferred usable elements are those such as
Ti, Zr, and Y, and rare earth elements having a high resistance
against etching corrosion, such as Sm. However, in case of a
metallic element not favorable in the semiconductor industry, it
should be used under the condition that the element imparts an
extremely high corrosion resistance against etching of the quartz
glass.
In case of employing mixing the metal oxide with quartz glass
powder as a means for doping, melting is performed in a heating
furnace or by Verneuil method; however, if the doped metal oxide
yields a melting point of 2,500.degree. C. or higher, it is
difficult to sufficiently melt the powder of the metallic oxide so
long as a production method of the present art is employed. In such
a case, a powder aggregate or a crystalline bulk remains to yield
visually observable minute white foreign matter. Accordingly, it is
preferred to dope metal oxides having a melting point lower than
2,500.degree. C.
Furthermore, not only can a single metallic element be employed,
but it is also effective to co-dope with a plurality of metallic
elements.
The concentration of the metallic elements above is preferably in a
range of from 0.1 to 20% by weight, and more preferably, 1.0 to 15%
by weight. As a result of the experiments performed by changing the
concentration of the metallic elements, if the concentration of the
metallic elements is less than 0.1% by weight, no improvement is
observed on the resistance against etching corrosion. On the other
hand, if the concentration should exceed 20% by weight, the amount
of doping becomes too large to find any feasible means to suppress
the generation of bubbles and crystalline phase.
The quartz glass body according to the present invention preferably
has a metallic element-containing layer with a predetermined
thickness containing 0.1 to 20% by weight of said metallic element.
Preferably, the metallic element-containing layer is a surface
layer having a thickness of at least 5 mm.
In incorporating the metallic elements in the metallic
element-containing layer, the metallic element may be doped in the
quartz glass during manufacturing, or, in a preferred embodiment of
the invention, an additional surface coating may be employed to
coat the surface of the quartz glass body.
The quartz glass body according to the present invention preferably
shows a surface roughness Ra falling in a range of from 0.01 to 10
.mu.m. Such a surface roughness can be obtained by subjecting the
quartz glass body to a precision cutting treatment, a heating and
melting treatment, or a frost treatment (=a heating and melting
treatment followed by a chemical etching treatment, as explained
below). By providing such a surface state, fine cracks on the
surface can be removed after mechanical processing to suppress the
generation of initial particles on applying plasma etching.
The precision cutting treatment comprises precision cutting the
surface of the glass body by using a machine, and is advantageous
in that less surface cracks are generated. The heating and melting
treatment comprises performing surface heating and thereby fusion
removing the surface cracks by means of gas combustion using
oxyhydrogen, acetylene, etc., or by utilizing an electric heating
source such as arc power.
The frost treatment (frosting) comprises subjecting a surface of
the glass body to a heating and melting treatment, followed by
immersing the resulting surface into a mixed solution of HF, acetic
acid, ammonium fluoride, and pure water (which may be substituted
by a solution containing 10 to 50 wt. % HF), thereby removing the
surface layer by etching while simultaneously forming a uniform
surface. The quartz glass bodies thus obtained by any of the
processes above contain residual OH at a high concentration
attributed to the production method.
The OH concentration of the quartz glass according is in a range of
from 100 wtppm to 2,000 wtppm. If the OH concentration should be
100 ppm or higher, the effect of holding the alkali metals passing
and diffusing through the quartz glass body becomes higher to
prevent external contamination from occurring on the wafer.
However, if the OH concentration should exceed 2,000 ppm, the
viscosity becomes excessively low so as to disadvantageously cause
undesirable deformation of the wafer.
The amount of gas generated in a temperature range of from room
temperature to 1000.degree. C. is 2 mol/m.sup.3 or less. Since the
quartz glass body obtained through the above process is produced in
the high temperature region of 1000.degree. C. or higher, the
previously occluded gas that is discharged up to 1000.degree. C.
amounts to a total of 2 mol/m.sup.3 or less. Since the etching
process is carried out in the temperature range of several hundreds
of degrees Celsius, the actual amount of evolved gas is less than
the total. Such a trace quantity of generated gas does not affect
the quality of the wafer when brought into contact with the wafer,
nor influences the gaseous plasma.
Preferably, the quartz glass above has an internal transmittance
for a visible radiation of 50%/cm or higher.
In a further (second) embodiment of the invention, the metallic
elements are incorporated into the quartz glass of the body by
surface coating, whereby a metallic element is applied to a surface
thereof, characterized in that the resulting quartz glass contains
bubbles and crystalline phase at a quantity accounting for less
than 100 mm.sup.2 in a projection area per 100 cm.sup.3 of the
quartz glass body.
The body thus obtained has a metallic element containing surface
layer as explained above. The above explanations are also valid for
this metallic element containing surface layer since the properties
and the preferred modifications of the surface layer obtained by
surface coating are the same as for the metallic element containing
surface layer obtained by doping.
In a preferred embodiment, the quartz glass body is a jig for
general use, especially a jig for supporting wafers. Under
conditions of general use, the depth of corrosion occurring in
contact with gaseous plasma is about 1 to 2 mm, or about 5 mm
maximum. Accordingly, to improve the etching resistance of the
quartz glass jig, the preferred condition for using the quartz
glass having excellent resistance against plasma corrosion of the
present invention is to set the thickness of the metallic
element-containing layer containing the metallic elements above at
a concentration in a range of from 0.1 to 20% by weight to at least
5 mm.
A first embodiment of producing the quartz glass having improved
resistance against plasma corrosion according to the present
invention comprises employing Verneuil process, i.e., a method for
producing an ingot by using an oxyhydrogen flame, comprising
providing a mixture of an SiO.sub.2-powder and a metal containing
substance containing an metallic element or a compound thereof,
heating an fusing the mixture by dropping the heated and fused
SiO.sub.2-powder and the metal containing substance on a target
area of said ingot while heating the target area of said quartz
glass ingot to a temperature not lower than the melting temperature
of the oxide of said metal.
Preferably said target area is heated to a temperature of
1800.degree. C. or higher, and preferably, at a temperature not
higher than 3000.degree. C.
According to a first embodiment of the present invention, by
employing Verneuil method as the production process, the metal
containing substance is provided in form of a metal containing
powder which contains the metallic element or a compound thereof.
The metal containing powder is mixed with SiO.sub.2-powder and the
powder mixture is heated and melted onto the growing target surface
of the ingot.
In case of doping the quartz glass with a metallic element or a
compound thereof in the form of powder, heating and fusing must be
carried out while applying sufficient heat energy in a manner such
that the powder of the metallic element or the powder of the
compound may be decomposed to the atomic or molecular level and be
uniformly diffused and mixed with the quartz powder.
According to a second embodiment of the present invention by
employing Verneuil method as the production process, the metal
containing substance is provided in form of a metal containing
solution prepared by dissolving a metallic element or a compound
thereof in pure water, an acidic solution, an alkaline solution, or
an organic solvent.
The metal containing substance is preferably applied into the
quartz glass in the form of a gas or a liquid. However, in case it
is mixed in the form of powder, the powder is preferably as finely
divided as possible; in particular, since a metallic element tends
to remain and concentrate in the SiO.sub.2 network in the form of
an oxide, preferably the melting point of the oxide is as low as
possible.
In general, with respect to the most commonly employed method
comprising fusing a mixture of a quartz powder and a powder of a
metallic element to be doped in a heating furnace, there is a limit
in the high temperature region.
Thus, it is extremely difficult to carry out a treatment at
temperatures of 2000.degree. C. or higher.
In case a Verneuil method is employed as the production process,
the thermal energy that is supplied to a powder can be set high and
at uniform density. Thus, a quartz glass body having less bubbles
or crystalline phase can be implemented. So long as a metal oxide
having a melting point up to about 2500.degree. C. is used, fusion
and diffusion of the metallic oxide can be realized by setting the
surface temperature of the ingot being formed in the vicinity of
the melting temperature or even higher.
As the powder, a quartz powder is used containing mixed therein the
metallic powder, an oxide, a nitrate compound, a chloride, and
other compounds. Concerning the mode of doping, it is extremely
effective to use, in the place of a powder, a solution having
uniformly dissolved therein a metallic element disintegrated to the
atomic or molecular level, which is dropped in the form of a liquid
onto the growing surface of the ingot being formed, or sprayed to
the growing surface of the ingot in the form of a volatilized gas,
or by using a carrier gas. As such a solution, there can be used a
solution obtained by dissolving the metallic powder in an acidic or
an alkaline solution, a solution obtained by dissolving a nitrate
compound in pure water, a solution obtained by dissolving a
chloride compound in ethanol, a solution of an organometallic
compound, or a solution obtained by dissolving the organometallic
compound in an organic solvent.
In accordance with a second embodiment of the present invention for
producing quartz glass having excellent resistance against plasma
corrosion, a method is provided comprising a preparation of a
porous SiO.sub.2 body and heat treating it in an atmosphere
containing the metallic element at concentration in the range from
0.1 to 10 mol per 22.4 liter and applying a heat treatment
thereto.
The second embodiment of the present invention, which comprises
diffusing and doping a doping substance in the gaseous state inside
the porous body, can be defined as a CVD process. The porous
SiO.sub.2 body is allowed to stand still and subjected to a heat
treatment in an atmosphere containing the metallic element at a gas
density of 0.1 mol/22.4 liter to 10 mol/22.4 liter. After the
treatment is continued for a long time, until the gas is
sufficiently diffused in the porous body, the temperature is
lowered so that the metallic element may reside uniformly inside
the porous body in the form of oxides without causing local
concentration. Since an increase in gas density increases the
concentration of the oxide residing in the porous body, it is more
effective to set the heating temperature as low as possible while
setting the pressure as high as possible. The heating temperature
is preferably set to a temperature not lower than the boiling
point, the gasification point, or the decomposition point of the
metallic element or of the compound thereof, and the pressure is
preferably set in a range of from 1 to 10 atomspheres.
In accordance with a third embodiment of the present invention for
producing the quartz glass having excellent resistance against
plasma corrosion, a method is provided which comprises preparing a
slurry by dissolving in pure water, an acidic solution, an alkaline
solution, or an organic solvent, a mixture of a quartz glass powder
having a particle size distribution in a range of from 0.01 to
1,000 .mu.m and containing from 1 to 50% by weight of particles
with size ranging from 0.01 to 5 .mu.m, with a metallic element or
a compound thereof soluble in pure water, an acidic solution, an
alkaline solution, or an organic solvent; drying and solidifying
said slurry; and heating and fusing the solidified slurry in
vacuum. This method is generally defined as a slip casting
method.
In the method comprising dissolving a quartz powder in pure water,
mixing it with an aqueous solution of a metallic element to prepare
a slurry, and forming therefrom a transparent solid by drying and
heating in vacuum, it is necessary, for the drying and
solidification, that the quartz powder has a particle size
distribution such that the particles 5 .mu.m or less in size
account for 1 to 50% by weight of the powder. The particles 5 .mu.m
or less in size can be obtained by finely dividing the same quartz
powder, or by using fumed silica prepared by flame hydrolysis of
silicon tetrachloride.
As an aqueous solution of the metallic element, there can be used
that obtained by dissolving a metallic powder in an acidic or an
alkaline solution, that obtained by dissolving a nitrate compound
in pure water, that obtained by dissolving a chloride compound in
an organic solvent such as ethanol, an organometallic compound or
that obtained by dissolving it in an organic solvent. Particularly
preferred is to use a solution obtained by dissolving a nitrate
compound in pure water, because the resulting quartz glass body
contains less bubbles.
The method for preparing a quartz glass jig having an improved
resistance against plasma corrosion comprises coating the surface
of a previously prepared quartz glass jig with a solution prepared
by mixing and dissolving in pure water, an acidic solution, an
alkaline solution, or an organic solvent, a metallic element or a
compound thereof soluble in pure water, an acidic solution, an
alkaline solution, or an organic solvent; followed by heating and
fusing the thus coated surface.
In case there is particular interest in increasing the
concentration of the metallic element on the surface of the quartz
glass jig, it is effective to employ a method comprising coating
the surface of the quartz glass jig with the solution containing
the metallic element and then applying heating thereto for fusion.
As the solution containing the metallic element, there can be used
that prepared by dissolving a nitrate compound of the metallic
element in pure water, obtained by dissolving a chloride compound
of the metallic element in an organic solvent such as ethanol, an
organometallic compound containing the metallic element or that
obtained by dissolving it in an organic solvent. The solution thus
obtained is then supplied dropwise, applied by using a brush, or
sprayed onto the surface of the quartz glass jig. As the solution
of the metallic element, particularly preferred is an
organometallic compound containing the metallic element or a
solution prepared by dissolving it in an organic solvent.
Then, the metallic element is fused on the surface and baked by
means of flame melting, electric heating, arc melting, etc. In such
a case, it is preferred to use a quartz glass jig previously doped
with a metallic element, because the metallic element can be
incorporated at a high concentration in the entire body.
Furthermore, such a quartz glass jig exhibits affinity with the
surface containing the metallic element at a high concentration to
prevent cracks and the like from being formed during cooling.
As a previously prepared quartz glass jig, a known quartz glass jig
can be used, but preferably used is a quartz glass jig produced in
accordance with the methods of the present invention for producing
a quartz glass having excellent resistance against plasma corrosion
described hereinbefore.
As a means for measuring the local concentration of the metallic
elements, EPMA (Electron Probe Micro Analysis) can be used to
measure the planar distribution. Since the other portions are
crystalline, X-ray diffraction or polarized optical microscope can
be used for the detection.
EXAMPLES
The present invention is described in further detail below by way
of examples, but it should be understood that these are provided
only for exemplification, and are by no means limiting.
Example 1
A 1900-g portion of quartz particles were mixed with 100 g of
Al.sub.2O.sub.3 powder, and the resulting mixture was dropped and
fused in an oxyhydrogen flame at a rate of 50 g/min on a target
ingot being rotated at a speed of 1 rpm to obtain a quartz glass
ingot 200 mm in diameter and 50 mm in length. The gas condition was
set to flow gaseous H.sub.2 at a rate of 200 liter/min and gaseous
O.sub.2 at a rate of 100 liter/min. The target ingot was then set
inside a vessel having a volume 300 mm.times.300 mm and 200 mm in
height. If the gases were flowed at a rate lower than the
conditions above, bubbles and crystalline phase were observed to
generate, and if they were flowed at a rate higher than above, the
shape of the ingot was no longer retained. The temperature of the
growing plane of the ingot was found to be 2,200.degree. C.
The ingot thus prepared was subjected to fluorescent X-ray analysis
to obtain aluminum concentration. As a result, the average
concentration in a region from the surface ranging to a depth of
0.1 mm was found to be 3.0% by weight, and the concentration at a
position 5.0 mm in depth from the surface was found to be 2.0% by
weight. Excluding the surface, the average concentration for the
overall region of the thus formed ingot was found to be
approximately 2.0% by weight. The outermost surface portion is
believed to yield a high concentration due to progressive
gasification of quartz.
Then, the content of bubbles and crystalline phase of thus formed
ingot was measured, and the presence of crystalline phase of thus
formed ingot was detected by means of X-ray diffraction. The
results are given in Table 1. No crystalline phase was present, and
the content of bubbles and crystalline phase was found to be 39
mm.sup.2.
Furthermore, as described hereinafter, the amount of particle
generation and the etching rate were measured, and the results are
given in Table 1. The amount of generated particles was found to be
low, and the etching rate was sufficiently low. Thus, it has been
confirmed that the product has excellent resistance against plasma
corrosion.
Example 2
Quartz particles were dropped and fused in an oxyhydrogen flame at
a rate of 50 g/min on a target ingot being rotated at a speed of 1
rpm, and simultaneously, a 30% aqueous solution of aluminum nitrate
was supplied dropwise to the growing surface of the ingot at a rate
of 10 cc/min to obtain a quartz glass ingot 200 mm in diameter and
50 mm in length. The gas condition was set to flow gaseous H.sub.2
at a rate of 150 liter/min and gaseous O.sub.2 at a rate of 75
liter/min. The target ingot was then set inside a vessel having a
volume 300 mm.times.300 mm.times.200 mm high.
On measuring the aluminum concentration of the thus prepared quartz
glass ingot by means of fluorescent X-ray analysis, a concentration
of 3.0 wt. % was obtained for the outermost surface portion (to a
depth of 0.1 mm from the surface) and 1.0 wt. % for the portion at
a depth of 5 mm from the surface. The outermost surface portion is
believed to yield a high concentration due to progressive
gasification of quartz. The average concentration over the entire
length of the thus formed ingot was found to be approximately 1.5
wt. %. Furthermore, measurements were performed for items similar
to those described in Example 1, and the thus obtained results are
given in Table 1. From the results shown in Table 1, it has been
confirmed that the product yields excellent resistance against
plasma corrosion.
Example 3
A quartz glass ingot was prepared in the same manner as in Example
2, except for using zirconium oxynitrate as a doping material in
the place of aluminum nitrate. The zirconium concentration was
measured for the thus prepared quartz glass ingot, and measurements
were performed for the items similar to those described in Example
1. The results are given in Table 1. It has been confirmed that the
product yields excellent resistance against plasma corrosion.
Example 4
A quartz glass ingot was prepared in the same manner as in Example
2, except for using yttrium nitrate as a doping material in the
place of aluminum nitrate. The yttrium concentration was measured
for the thus prepared quartz glass ingot, and measurements were
performed for the items similar to those described in Example 1.
The results are given in Table 1. It has been confirmed that the
product yields excellent resistance against plasma corrosion.
TABLE-US-00001 TABLE 1 Example No. 1 2 3 4 Production Verneuil
Verneuil Verneuil Verneuil method Metallic Al.sub.2O.sub.35 Pure
water + Pure water + Pure water + element wt. % aluminum zirconium
yttrium compound nitrate oxynitrate nitrate State of sample before
etching test Bubbles (mm.sup.2) 19 18 18 29 Crystalline 20 20 17 28
phase (mm.sup.2) XRD*.sup.1 None None None None Foreign matters
Concentration 2.0 1.5 1.9 1.8 of metallic element (wt. %) Particles
11 13 11 9 generated (particles) Etching rate 35 35 33 40 (nm/min)
*.sup.1Here in and the following tables 2-8 XRD means "X-ray
diffraction"
Example 5
A quartz glass ingot was prepared in the same manner as in Example
2, except for using samarium nitrate as a doping material in the
place of aluminum nitrate. The samarium concentration was measured
for the thus prepared quartz glass ingot, and measurements were
performed for the items similar to those described in Example 1.
The results are given in Table 2. It has been confirmed from the
results in Table 2 that the product yields excellent resistance
against plasma corrosion.
Example 6
A quartz glass ingot was prepared in the same manner as in Example
2, except for using a solution prepared by dissolving 30 wt. % of
aluminum chloride in ethanol for use as the doping material in the
place of the 30 wt. % aqueous solution of aluminum nitrate. The
aluminum concentration was measured for the thus prepared quartz
glass ingot, and measurements were performed for the items similar
to those described in Example 1. The results are given in Table 2.
It has been confirmed from the results in Table 2 that the product
yields excellent resistance against plasma corrosion.
Example 7
A quartz glass ingot was prepared in the same manner as in Example
2, except for using a solution prepared by dissolving 5 wt. % of
aluminum in hydrochloric acid for the doping material in the place
of the 30 wt. % aqueous solution of aluminum nitrate. The aluminum
concentration was measured for the thus prepared quartz glass
ingot, and measurements were performed for the items similar to
those described in Example 1. The results are given in Table 2. It
has been confirmed from the results in Table 2 that the product
yields excellent resistance against plasma corrosion.
Example 8
A quartz glass ingot was prepared in the same manner as in Example
2, except for using a solution prepared by dissolving 30 wt. % of
Al isopropoxide in propanol for the doping material in the place of
the 30 wt. % aqueous solution of aluminum nitrate. The aluminum
concentration was measured for the thus prepared quartz glass
ingot, and measurements were performed for the items similar to
those described in Example 1. The results are given in Table 2. It
has been confirmed from the results in Table 2 that the product
yields excellent resistance against plasma corrosion.
TABLE-US-00002 TABLE 2 Example No. 5 6 7 8 Production Verneuil
Verneuil Verneuil Verneuil method Metallic Pure water + Ethanol +
Hydrochloric Propanol + element samarium AlCl.sub.3 acid + Al iso-
compound nitrate propoxide aluminum State of sample before etching
test Bubbles (mm.sup.2) 17 20 15 20 Crystalline 29 23 29 28 phase
(mm.sup.2) XRD*.sup.1 None None None None Foreign matters
Concentration 1.3 2.0 2.4 1.3 of metallic element (wt. %) Particles
13 15 13 10 generated (particles) Etching rate 32 31 30 30
(rm/min)
Example 9
A quartz glass ingot was prepared in the same manner as in Example
2, except for using a solution prepared by dissolving 30 wt. % of
aluminum isopropoxide in ethyl silicate for the doping material in
the place of the 30 wt. % aqueous solution of aluminum nitrate. The
aluminum concentration was measured for the thus prepared quartz
glass ingot, and measurements were performed for the items similar
to those described in Example 1. The results are given in Table 3.
It has been confirmed from the results in Table 3 that the product
yields excellent resistance against plasma corrosion.
Example 10
A silica glass preform 500 mm in diameter and 1,000 mm in height
prepared by soot method was set inside a quartz glass vessel 600 mm
in diameter and 1,200 mm in height together with 500 g of aluminum
chloride granules, and after replacing the atmosphere to gaseous
N.sub.2, the gas inlet line was stopped, and heating was initiated
to elevate the temperature to 400.degree. C., thereby gasifying all
of aluminum chloride to obtain an atmosphere containing 100%
aluminum chloride. The state was maintained for 10 hours under the
atmospheric condition, at which time heating was stopped to lower
the temperature to room temperature. The soot was taken out of the
vessel, and was placed inside a vacuum furnace to elevate the
temperature to 1,800.degree. C. to obtain a transparent glass
body.
From the surface portion of the thus obtained quartz glass, 3 wt. %
of aluminum was detected, but for a portion at a depth of 5 mm from
the surface, the aluminum concentration was found to be 2.0 wt. %.
Thus formed quartz glass was found to have an average aluminum
concentration of ca. 1.1 wt. %. Aluminum was detected in high
concentration on the surface, presumably due to the residual
alumina while SiO.sub.2 underwent gasification during the
vitrification of the soot into a transparent body.
The boiling point of aluminum chloride is 180.degree. C., however,
at a treatment temperature of 150.degree. C. or lower, the
gasification vapor pressure decreases to 70 mmHg or lower. The
concentration of gaseous aluminum chloride in the atmosphere was
found to be 0.08 mol/22.4 liter, and that in the glass was found to
be about 0.01 wt. %. Thus, at a temperature exceeding 633.degree.
C., the aluminum concentration in the atmosphere became 0.5
mol/22.4 liter, and that of the glass thus obtained was found to be
halved.
Measurements were made on the same items as those in Example 1, and
the results are given in Table 3. It has been confirmed from the
results in Table 3 that the product yields excellent resistance
against plasma corrosion.
Example 11
A silica glass preform 500 mm in diameter and 1,000 mm in length
prepared by soot method was set inside an airtight high pressure
vessel together with 500 mg of aluminum chloride granules, and,
after replacing the atmosphere to gaseous N.sub.2, the gas inlet
line was stopped, and heating was initiated to elevate the
temperature to 250.degree. C., thereby gasifying all of aluminum
chloride to obtain a high pressure atmosphere of 10 kg/cm.sup.2,
i.e., an atmosphere having a concentration of 9 mol/22.4 liter. The
state was maintained for 10 hours, at which time heating was
stopped to lower the temperature to room temperature and the soot
was taken out of the vessel.
The soot taken out of the vessel was placed inside a vacuum furnace
to elevate the temperature to 1,800.degree. C. to obtain a
transparent glass body. From the surface portion of the thus
obtained quartz glass, 6 wt. % of aluminum was detected, but for a
portion at a depth of 5 mm from the surface, the aluminum
concentration was found to be 3.0 wt. %. Thus formed quartz glass
was found to have an average aluminum concentration of ca. 4.0 wt.
%. The gaseous aluminum chloride concentration of the atmosphere,
the aluminum concentration of the glass, and the aluminum
concentration of the resulting glass were about the same as those
obtained in Example 10.
Furthermore, measurements were performed for the same items as
those in Example 1, and the results are given in Table 3. It has
been confirmed from the results in Table 3 that the product yields
excellent resistance against plasma corrosion.
Example 12
A quartz glass ingot was prepared in the same manner as in Example
10, except for using zirconium chloride granules as the doping
material in the place of aluminum chloride granules, and for
gasifying all of zirconium chloride by elevating the temperature to
500.degree. C. The zirconium concentration of the thus obtained
quartz glass ingot was measured, and measurements were performed
for the same items as those in Example 1. The results are given in
Table 3. It has been confirmed from the results in Table 3 that the
product yields excellent resistance against plasma corrosion.
TABLE-US-00003 TABLE 3 Example No. 9 10 11 12 Production method
Verneuil CVD CVD CVD Metallic element compound Ethyl silicate +
AlCl.sub.3 AlCl.sub.3 ZrCl.sub.4 Al isopropoxide State of sample
before etching test Bubbles mm.sup.2 18 20 18 31 Crystalline phase
mm.sup.2 12 40 23 24 XRD*.sup.1 None None None None Foreign matters
Concentration of metallic element 1.2 1.1 4.0 1.8 (wt. %) Particles
generated (particles) 10 16 8 15 Etching rate (nm/min) 40 44 22
34
Example 13
Slurry was prepared by mixing 750 g of quartz powder consisting of
particles 500 to 100 .mu.m in particle diameter, 200 g of pyrolytic
silica particles 0.01 to 4 .mu.m in particle diameter, 700 g of
aluminum nitrate, and 1,500 g of pure water. The slurry was dried
for 8 days in air at 40.degree. C. to obtain a solid, and the
resulting solid was subjected to a heat treatment at 1,800.degree.
C. for 1 hour in vacuum to prepare transparent glass 100 mm in
diameter and 50 mm in height. The aluminum concentration for the
whole bulk was found to be 2.0 wt. %.
Measurements were made on the same items as those in Example 1, and
the results are given in Table 4. It has been confirmed from the
results in Table 4 that the product yields excellent resistance
against plasma corrosion.
Example 14
Quartz glass ingot was prepared in the same manner as in Example
13, except for using zirconium oxynitrate as the doping material in
the place of aluminum nitrate. Measurements were performed on the
resulting quartz glass ingot for the zirconium concentration and
the same items as those measured in Example 1. The results are
given in Table 4. It has been confirmed from the results in Table 4
that the product yields excellent resistance against plasma
corrosion.
Example 15
Quartz glass ingot was prepared in the same manner as in Example
13, except for using yttrium nitrate as the doping material in the
place of aluminum nitrate. Measurements were performed on the
resulting quartz glass ingot for the yttrium concentration and the
same items as those measured in Example 1. The results are given in
Table 4. It has been confirmed from the results in Table 4 that the
product yields excellent resistance against plasma corrosion.
Example 16
Quartz glass ingot was prepared in the same manner as in Example
13, except for using samarium nitrate as the doping material in the
place of aluminum nitrate. Measurements were performed on the
resulting quartz glass ingot for the samarium concentration and the
same items as those measured in Example 1. The results are given in
Table 4. It has been confirmed from the results in Table 4 that the
product yields excellent resistance against plasma corrosion.
TABLE-US-00004 TABLE 4 Example No. 13 14 15 16 Production Slip Slip
Slip Slip method Metallic Pure water + Pure water + Pure water +
Pure water + element aluminum zirconium yttrium samarium compound
nitrate oxynitrate nitrate nitrate State of sample before etching
test Bubbles (mm.sup.2) 18 25 24 19 Foreign matters 25 20 20 22
(mm.sup.2) XRD*.sup.1 None None None None Foreign matters
Concentration 2.1 2.2 1.9 2.1 of metallic element (wt. %) Particles
20 12 11 10 generated (particles) Etching rate 29 43 25 28
(nm/min)
Example 17
Quartz glass ingot was prepared in the same manner as in Example
13, except for using 700 g of aluminum chloride and 1,500 g of
ethanol as the doping material in the place of 700 g of aluminum
nitrate and 1,500 g of pure water. Measurements were performed on
the resulting quartz glass ingot for the aluminum concentration and
the same items as those measured in Example 1. The results are
given in Table 5. It has been confirmed from the results in Table 5
that the product yields excellent resistance against plasma
corrosion.
Example 18
Quartz glass ingot was prepared in the same manner as in Example
13, except for using a solution obtained by dissolving aluminum in
hydrochloric acid at a concentration of 5 wt. % as the doping
material in the place of 700 g of aluminum nitrate and 1,500 g of
pure water. Measurements were performed on the resulting quartz
glass ingot for the aluminum concentration and the same items as
those measured in Example 1. The results are given in Table 5. It
has been confirmed from the results in Table 5 that the product
yields excellent resistance against plasma corrosion.
Example 19
Quartz glass ingot was prepared in the same manner as in Example
13, except for using a solution obtained by dissolving Al
isopropoxide in propanol at a concentration of 30 wt. % as the
doping material in the place of 700 g of aluminum nitrate and 1,500
g of pure water. Measurements were performed on the resulting
quartz glass ingot for the aluminum concentration and the same
items as those measured in Example 1. The results are given in
Table 5. It has been confirmed from the results in Table 5 that the
product yields excellent resistance against plasma corrosion.
Example 20
Quartz glass was prepared in the same manner as in Example 13,
except for using a solution obtained by dissolving Al isopropoxide
in ethyl silicate at a concentration of 30% by weight as the doping
material in the place of 700 g of aluminum nitrate and 1,500 g of
pure water. Measurements were performed on the resulting quartz
glass ingot for the aluminum concentration and the same items as
those measured in Example 1. The results are given in Table 5. It
has been confirmed from the results in Table 5 that the product
yields excellent resistance against plasma corrosion.
TABLE-US-00005 TABLE 5 Example No. 17 18 19 20 Production Slip Slip
Slip Slip method Metallic Ethanol + Hydrochloric Propanol + Ethyl
element AlCl.sub.3 acid + Al iso- silicate + compound aluminum
propoxide Al iso- propoxide State of sample before etching test
Bubbles (mm.sup.2) 20 19 19 20 Foreign matters 23 17 20 13
(mm.sup.2) XRD*.sup.1 None None None None Foreign matters
Concentration 2.1 2.3 1.9 1.8 of metallic element (wt. %) Particles
19 17 10 10 generated (particles) Etching rate 39 43 35 45
(nm/min)
Example 21
A solution prepared by dissolving aluminum isopropoxide in propanol
was dropped on the surface of a quartz glass jig 200 mm in diameter
and 20 mm in thickness, and an alumina film was formed thereon by
hydrolyzing the solution together with water in air. The plane of
the quartz glass plate having the film formed thereon was fire
polished and baked by using an oxyhydrogen flame to thereby obtain
a smooth transparent fused plane. The average aluminum
concentration to a depth of 0.1 mm from the surface portion was
found to be 15 wt. %, but the average aluminum concentration to a
depth of 1 mm was found to be 0.5 wt. %. The average aluminum
concentration of the thus formed quartz glass jig was about 2.1 wt.
%.
Measurements were performed for the same items as those of Example
1, and the results are given in Table 6. It has been confirmed from
the results in Table 6 that the product yields excellent resistance
against plasma corrosion.
Example 22
Quartz glass ingot was prepared in the same manner as in Example
21, except for using a solution prepared by dissolving aluminum
isopropoxide in ethyl silicate in the place of the solution
prepared by dissolving aluminum isopropoxide in propanol.
Measurements were performed on the resulting quartz glass ingot for
the aluminum concentration and the same items as those measured in
Example 1. The results are given in Table 6. It has been confirmed
from the results in Table 6 that the product yields excellent
resistance against plasma corrosion.
Example 23
Quartz glass ingot was prepared in the same manner as in Example
21, except for using a solution prepared by dissolving zirconium
isopropoxide in propanol in the place of the solution prepared by
dissolving aluminum isopropoxide in propanol. Measurements were
performed on the resulting quartz glass ingot for the zirconium
concentration and the same items as those measured in Example 1.
The results are given in Table 6. It has been confirmed from the
results in Table 6 that the product yields excellent resistance
against plasma corrosion.
Example 24
Quartz glass ingot was prepared in the same manner as in Example
21, except for using a solution prepared by dissolving titanium
isopropoxide in propanol in the place of the solution prepared by
dissolving aluminum isopropoxide in propanol. Measurements were
performed on the resulting quartz glass ingot for the titanium
concentration and the same items as those measured in Example 1.
The results are given in Table 6. It has been confirmed from the
results in Table 6 that the product yields excellent resistance
against plasma corrosion.
TABLE-US-00006 TABLE 6 Example No. 21 22 23 24 Production Coating
Coating Coating Coating method Metallic Propanol + Ethyl Propanol +
Propanol + element Al iso- silicate + Zr iso- Ti iso- compound
propoxide Al iso- propoxide propoxide propoxide State of sample
before etching test Bubbles (mm.sup.2) 24 15 18 19 Crystalline 24
28 22 18 phase (mm.sup.2) XRD*.sup.1 None None None None Foreign
matters Concentration 2.1 2.4 1.4 1.5 of metallic element (wt. %)
Particles 13 8 13 15 generated (particles) Etching rate 43 32 50 32
(nm/min)
Example 25
Quartz glass ingot was prepared in the same manner as in Example
21, except for using a solution prepared by dissolving aluminum
nitrate in pure water in the place of the solution prepared by
dissolving aluminum isopropoxide in propanol. Measurements were
performed on the resulting quartz glass ingot for the aluminum
concentration and the same items as those measured in Example 1.
The results are given in Table 7. It has been confirmed from the
results in Table 7 that the product yields excellent resistance
against plasma corrosion.
Example 26
Quartz glass ingot was prepared in the same manner as in Example
25, except for using a solution prepared by dissolving aluminum
chloride in ethanol at a concentration of 30 wt. % in the place of
the solution prepared by dissolving aluminum isopropoxide in
propanol. Measurements were performed on the resulting quartz glass
ingot for the aluminum concentration and the same items as those
measured in Example 1. The results are given in Table 7. It has
been confirmed from the results in Table 7 that the product yields
excellent resistance against plasma corrosion.
Example 27
Quartz glass ingot was prepared in the same manner as in Example
25, except for using a solution prepared by dissolving aluminum in
hydrochloric acid at a concentration of 5 wt. % in the place of the
solution prepared by dissolving aluminum isopropoxide in propanol.
Measurements were performed on the resulting quartz glass ingot for
the aluminum concentration and the same items as those measured in
Example 1. The results are given in Table 7. It has been confirmed
from the results in Table 7 that the product yields excellent
resistance against plasma corrosion.
Example 28
A disk jig 200 mm in diameter and 25 mm in thickness was prepared
by working the quartz glass body produced in Example 1. A layer
containing aluminum distributed at a high concentration was formed
on the surface of the jig by the method described in Example 21.
The average aluminum concentration of the surface to a depth of 0.1
mm was found to be 15 wt. %, but the average aluminum concentration
to a depth of 1 mm was found to be 4.0 wt. %. The average aluminum
concentration of the resulting quartz glass jig was found to be was
found to be approximately 4.0 wt. %. Measurements were performed on
the resulting quartz glass ingot for the same items as those
measured in Example 1. The results are given in Table 7. It has
been confirmed from the results in Table 7 that the product yields
excellent resistance against plasma corrosion.
TABLE-US-00007 TABLE 7 Example No. 25 26 27 28 Production Coating
Coating Coating Verneuil + method Coating Metallic Pure water +
Ethanol + Hydrochloric Al.sub.2O.sub.3 element aluminum AlCl.sub.3
acid + 5% compound nitrate Al propanol + Al iso- propoxide State of
sample before etching test Bubbles (mm.sup.2) 19 19 24 16 Foreign
matters 24 18 17 29 (mm.sup.2) XRD*.sup.1 None None None None
Foreign matters Concentration 2.0 2.1 2.2 4.0 of metallic element
(wt. %) Particles 13 16 17 7 generated (particles) Etching rate 43
34 39 17 (nm/min)
Comparative Example 1
A 1,000-g portion of quartz powder consisting of particles 500
.mu.m to 100 .mu.m in particle diameter was filled in a carbon
casting mold, and was subjected to a heat treatment at
1,800.degree. C. for a duration of 1 hour in vacuum to obtain a
transparent glass 100 mm in diameter and 50 mm in height.
Measurements were performed on the resulting quartz glass ingot for
the same items as those measured in Example 1. The results are
given in Table 8. It has been found from the results in Table 8
that the etching rate is extremely high, and that the resistance
against plasma corrosion of the product is poor.
Comparative Example 2
A 900-g portion of quartz powder consisting of particles 500 .mu.m
to 100 .mu.m in particle diameter mixed with 100 g of alumina was
filled in a carbon casting mold, and was subjected to a heat
treatment at 1,800.degree. C. for a duration of 1 hour in vacuum to
obtain a transparent glass 100 mm in diameter and 50 mm in height.
The aluminum concentration of the product was found to be 2.0 wt %.
Bubbles and crystalline phase were found to be present in the glass
body.
Measurements were performed on the resulting quartz glass ingot for
the same items as those measured in Example 1. The results are
given in Table 8. Table 8 clearly reads that the product not only
contains bubbles and crystalline phase at high quantity, but also
generates particles at a large quantity, and that the product is
found unfeasible for use as a jig for silicon wafers. Furthermore,
the etching rate is found to be extremely high, and the resistance
against plasma corrosion of the product is found to be poor.
Comparative Example 3
A 690-g portion of quartz particles was mixed with 310 g of
Al.sub.2O.sub.3 powder, and the resulting mixture was dropped and
fused in an oxyhydrogen flame at a rate of 50 g/min on a target
ingot being rotated at a speed of 1 rpm to obtain a quartz glass
ingot 200 mm in diameter and 500 liter in volume. The gas condition
was set to flow gaseous H.sub.2 at a rate of 200 liter/min and
gaseous O.sub.2 at a rate of 100 liter/min. The target ingot was
then set inside a volume 300 mm.times.300 mm.times.200 mm high. The
gas flow rate for each of the gases was doubled because bubbles and
crystalline phase generated at a large amount, but no improvement
was observed, and further increase in gas flow rate led to the
destruction of the ingot shape.
On measuring the aluminum concentration of the thus formed ingot by
means of fluorescent X ray analysis, the aluminum concentration at
the outermost surface portion was found to be 15.0 wt. %, and that
for a portion at a depth of 5 mm was found to be 13.0 wt. % . Since
gasification of quartz proceeds at the outermost surface, it is
presumed that the concentration tends to become higher at the
surface.
Measurements were performed for the same items as those measured in
Example 1, and the results are given in Table 8. Table 8 clearly
reads that, although the etching rate is low, the product not only
contains bubbles and crystalline phase at high quantities, but also
generates particles at a large quantity, and that the product is
unfeasible for use as a jig for silicon wafers.
TABLE-US-00008 TABLE 8 Example No. 1 2 3 Production method Vacuum
Vacuum Verneuil furnace furnace Metallic element compound None
Al.sub.2O.sub.3 Al.sub.2O.sub.3 5 wt. % 31 wt. % State of sample
before etching test Bubbles (mm.sup.2) 20 280 449 Crystalline phase
(mm.sup.2) 14 538 894 XRD*.sup.1 None Present Present Foreign
matters Concentration of metallic element (wt. %) 0.0 2.0 13.0
Particles generated (particles) 20 300 800 Etching rate (nm/min)
120 64 43
The content of bubbles and crystalline phase in Examples and
Comparative Examples above was measured in the following manner.
Samples 50 mm.times.50 mm.times.1 mm (thickness) in size were each
cut out from the quartz glass bodies, and the both surface planes
were mirror polished. Then, white light was allowed to pass from
the lower plane of the sample, and the projected images of the
bubbles and crystalline phase were subjected to image analyzer to
count up the quantity of bubbles and crystalline phase having a
diameter of 0.02 mm or larger. From the thus obtained results, the
area (projected area) of the bubbles and crystalline phase present
in the whole area of the sample were calculated to obtain the cross
section area (projected area) per 100 cm.sup.3.
The etching rate was measured in the following manner. From the
prepared transparent quartz glass, a sample was cut out and worked
to a piece 30 mm in diameter and 3 mm in thickness, and the surface
thereof was fire polished. The sample piece was then subjected to
an etching test using a plasma gas containing CF.sub.4 and O.sub.2
(20%) flowing at a rate of 50 sccm under a pressure of 30 mTorr, a
power of 1 kW, and for duration of 10 hours. From the weights
obtained before and after the test, the change in thickness was
calculated, and the calculated result was further divided by the
process time to calculate the etching rate.
The quantity of generated particles was obtained by mounting a Si
wafer having the same area as that of the sample on the
plasma-irradiated surface of the sample after etching, and the
irregularities on the contact plane of the wafer ware detected by
laser scattering. Thus, particles 0.3 .mu.m or larger in size were
counted up by using a particle counter.
In the Examples 1 to 28 and Comparative Examples 1 to 3, it was
found that the usable portion of the Si wafer was 90% or higher in
case the quantity of generated particles was 50 counts or less, but
the yield was greatly reduced to 50% or lower in case the quantity
of generated particles exceeded 200 counts. In case the etching
rate was 100 nm/min or higher, the etching thickness resulted in
0.6 mm or more for a use of about 100 hours, thereby making it
unfeasible as a member; but with an etching rate of 50 nm/min or
lower, the usable duration was doubled to confirm the effect. In
particular, an etching rate of 20 nm/min or lower resulted to
provide a considerably high economical effect.
Example 29
A 28,500-g portion of quartz particles consisting of particles from
100 to 500 .mu.m in particle diameter was mixed with 1,500 g of
Al.sub.2O.sub.3 powder, and the resulting mixture was dropped and
fused in an oxyhydrogen flame at a rate of 50 g/min on a target
ingot being rotated at a speed of 1 rpm to obtain a quartz glass
ingot of 200 mm in diameter and 400 mm in length. The gas condition
was set as such to flow gaseous H.sub.2 at a rate of 300 liter/min
and gaseous O.sub.2 at a rate of 100 liter/min.
The ingot thus prepared was then set inside a heating furnace, and
was kept at 1,800.degree. C. for a duration of 2 hours under
gaseous N.sub.2 atmosphere at a pressure of 1 kg/cm.sup.2 to obtain
a shaped body of 400 mm in diameter and 100 mm in length. A quartz
glass disk of 350 mm in diameter and 20 mm in thickness was cut out
from the thus obtained quartz glass shaped body, and the upper and
the bottom planes were subjected to a cutting. The surface Ra value
was found to be 2.0 .mu.m, and the quartz glass disk was found to
contain OH at a concentration of 300 wt. ppm.
Further, qualitative and quantitative analysis of the generated gas
was performed in the temperature range of from room temperature to
1,000.degree. C. on the sample cut out from the same quartz glass
shaped body obtained above. As a result, it was found that gaseous
CO, H.sub.2O, O.sub.2, and H.sub.2 were generated in total amount
of 0.4 mol/m.sup.3. The bubbles and foreign matters inside the
quartz glass disk amounted to 10 mm.sup.2 per 100 cm.sup.3, and the
internal transmittance of the visible radiation was found to be
85%/cm.
The Al concentration as obtained by means of fluorescent X-ray
analysis was 3.0 wt. %. A sample of 30 mm in diameter and 3 mm in
thickness was cut out, and the surface thereof was subjected to
cutting to result in a surface roughness Ra of 2.0 .mu.m. Then, an
etching test was performed on the resulting sample in gaseous
plasma of CF.sub.4 and O.sub.2 (accounting for 20%) flowing at a
rate of 50 sccm, under a pressure of 30 mTorr and a power of 1 kW
for time duration of 10 hours. The etching rate was calculated from
the change of mass before and after the test to obtain a result of
30 nm/min.
The quantity of generated particles was obtained by mounting a Si
wafer having the same area as that of the sample on the
plasma-irradiated surface of the sample after etching, and the
irregularities on the contact plane of the wafer were detected by
laser scattering. Thus, particles 0.3 .mu.m or larger in size were
counted up by using a particle counter to obtain 10 counts as a
result.
Example 30
Slurry was prepared by mixing 22,500 g of quartz particles from 100
to 500 .mu.m in particle diameter with 6,000 g of pyrolytic silica
particles from 0.01 .mu.m to 4 .mu.m in particle diameter, 2,100 g
of aluminum nitrate, and 4,500 g of pure water. The slurry was
dried for 8 days in air at 40.degree. C., and, after holding the
dried slurry in air at 500.degree. C. for 4 hours, heating
treatment was applied thereto in vacuum at 1,800.degree. C. for 1
hour to obtain a transparent quartz glass body of 380 mm in
diameter and 25 mm in length. A quartz glass disk of 350 mm in
diameter and 20 mm in thickness was cut out from the thus obtained
quartz glass body, and the upper and bottom planes were subjected
to cutting. The surface Ra value was found to be 3.0 .mu.m, and the
quartz glass disk was found to contain OH at a concentration of 300
ppm. The Al concentration of the sample cut out in the same manner
as above was measured by means of fluorescent X-ray analysis to be
3.0 wt % as a result. The other results were found to be the same
as those obtained in Example 29.
Example 31
An aqueous aluminum nitrate solution was applied to the surface of
the quartz glass jig of 350 mm in diameter and 20 mm in thickness,
and the resulting coated plane was melted by means of oxyhydrogen
flame to form a smooth transparent fused surface. The surface Ra
value of the thus obtained quartz glass jig was found to be 0.2
.mu.m, and the OH concentration was found to be 300 ppm. The Al
concentration of the fused plane of the quartz glass jig was
measured by means of fluorescent X-ray analysis to find 5.0 wt. %
as a result. The other results were found to be the same as those
obtained in Example 29.
Comparative Example 4
A 30,000-g portion of quartz particles consisting of particles from
100 to 500 .mu.m in particle diameter was mixed, charged in a
carbon casting mold, and subjected to a heat treatment at
1,800.degree. C. for a time duration of 1 hour in vacuum to obtain
a transparent quartz glass body of 400 mm in diameter and 100 mm in
length. The Al concentration of the sample cut out from the
resulting glass body was measured by means of fluorescent X-ray
analysis to find 0.0 wt. % as a result. Furthermore, a sample was
prepared and plasma etching test was performed in a manner similar
to that described in Example 29. The etching rate was found to be
120 nm/min. The other evaluation results were the same as those
described in Example 29.
Comparative Example 5
A 27,000-g portion of quartz particles consisting of particles from
100 to 500 .mu.m in particle diameter was mixed with 300 g of A1203
powder, and the resulting mixture was charged in a carbon casting
mold for a heat treatment at 1,800.degree. C. for a time duration
of 1 hour in vacuum to obtain a transparent quartz glass body of
400 mm in diameter and 100 mm in length. Numerous bubbles and
foreign matters were observed to be present inside the transparent
quartz glass body to yield a projected area per 100 cm.sup.3 of 300
mm.sup.2. The internal transmittance for a visible radiation was
found to be 15%/cm. The Al concentration of the sample cut out from
the resulting glass body was measured by means of fluorescent X-ray
analysis to be 5.0 wt % as a result. Furthermore, a sample was
prepared in the same manner as in Example 29, and evaluations
similar to those in Example 29 were performed thereon to obtain an
etching rate of 64 nm/min and a particle generation amounting to
300 counts.
Comparative Example 6
A 17,000-g portion of quartz particles consisting of particles from
100 to 500 .mu.m in particle diameter was mixed with 1,300 g of
Al.sub.2O.sub.3 powder, and a transparent quartz glass body was
prepared in the same manner as in Example 29. Numerous bubbles and
foreign matters were observed to be present inside the transparent
quartz glass body to yield a projected area per 100 cm.sup.3 of 300
mm.sup.2. The internal transmittance for a visible radiation was
found to be 15%/cm. The Al concentration of the sample cut out from
the resulting glass body was measured by means of fluorescent X-ray
analysis to be 21 wt % as a result. Furthermore, a sample was
prepared in the same manner as in Example 29, and evaluations
similar to those in Example 29 were performed thereon to obtain an
etching rate of 40 nm/min and a particle generation amounting to
800 counts.
In the Examples 29 to 31 and the Comparative Examples 4 to 6 above,
the usable portion of a Si wafer with particle generation of 50
counts or less accounted for 90% or more, but the yield was lowered
to 50% or less in case the particle generation exceeded 200 counts.
Further, in case the etching rate was 120 nm/min or higher, the
etching proceeded to a depth of 1.0 mm after using for about 100
hours, and the quartz glass body was found unfeasible for a member.
However, the effect of the invention was confirmed as the etching
rate decreased to 50 nm/min or lower because the usable life was
doubled. In particular, a great economical effect was obtained as
the etching rate decreased to 20 nm/min or lower.
* * * * *