TECHNICAL FIELD
[0001] The present invention relates to a method for forming stainless steel passivated
films, stainless steel, and gas-contacting and liquid-contacting parts, and in particular
relates to a method for forming passivated films of oxidized passivated stainless
steel, as well as stainless steel, and gas-contacting and liquid-contacting parts
which can be preferably applied to ultra-high vacuum apparatuses, ultra-high clean
apparatuses, ultra-pure water apparatuses and the like.
BACKGROUND ART
[0002] Recently, a technique for realizing ultra-high vacuum, or a technique for allowing
a small amount of predetermined gas in a vacuum chamber to produce a ultra-high clean
pressure-reduced atmosphere has become extremely important. These techniques are widely
used for research on material characteristics, formation of various thin films, production
of semiconductor devices and the like, and consequently higher degrees of vacuum have
been increasingly realized, however, further it is extremely strongly desired to realize
a pressure-reduced atmosphere in which contamination of impurities is decreased to
the limit.
[0003] For example, as exemplified by semiconductor devices, the size of a unit element
becomes small year by year in accordance with high integration of LSI, and research
and development for semiconductor devices having a size of 1 µm to sub micron, and
further 0.5 µm or below is being actively performed directing realization of practical
use.
[0004] In the production of such semiconductor devices, a step of forming a thin film, a
step of etching the formed thin film into a predetermined circuit pattern and the
like are repeatedly performed. And it is common that these processes are performed
in a ultra-high vacuum state, or in a pressure-reduced atmosphere in which predetermined
gas is introduced. If these steps are contaminated by impurities, problems are caused
such that, for example, the film quality of thin films to be formed is deteriorated,
the accuracy of fine processing is not obtained and the like. This is the reason why
the ultra-high vacuum and the ultra-high clean pressure-reduced atmosphere are required.
[0005] As one of the most important causes which have been obstructed the realization of
the ultra-high vacuum and the ultra-high clean pressure-reduced atmosphere until now,
the gas released from the surface of stainless steel widely used for chambers and
pipe arrangements may be pointed out. Especially, the moisture absorbed to the stainless
surface which disengages in the vacuum or the pressure-reduced atmosphere has served
as the most important pollution source.
[0006] Fig. 16 is a graph showing the relation between the gas pollution and the total leak
amount of a system including a gas pipe arrangement line and a reaction chamber (the
sum of the external leak and the release gas amount from the inner surface of the
pipe arrangement line and the reaction chamber) in a conventional apparatus. A plurality
of lines in the figure show the relation between the impurity concentration in the
atmosphere and the total leak amount of the system with respect to cases in which
the flow rate of gas is changed to various values.
[0007] The semiconductor process is in a tendency that the flow rate of gas is more and
more decreased in order to realize a process having higher accuracy, and for example,
it becomes common to use a flow rate of 10 cc/min or less. As understood from Fig.
16, when a flow rate of 10/min is used (symbol V), if there is a system total leak
of a degree of 10-
3 to 10-
6 Torr-1/sec as in apparatuses widely used at present, the impurity concentration in
the gas becomes 10 ppm to 1 %, which is far from a high clean process.
[0008] The present inventors have invented a ultra-high clean gas supply system, and succeeded
to suppress the leak amount from the outside of the system to be not more than 1 x
10-
11 Torr·l/sec which is the detection limit of a detector in the present circumstance.
However, there is leak from the inside of the system, that is the above-mentioned
gas release from the surface of stainless steel, so that consequently it was impossible
to lower the impurity concentration in the pressure-reduced atmosphere.
[0009] The minimum value of the surface release gas amount obtained by the surface treatment
in the present ultra-high vacuum technique is 1 x 10-
11 Torr·l/sec·cm
2 in the case of stainless steel. In this case, even when the surface area exposed
at the inside of the chamber is estimated to be, for example, 1 m
2 which is the smallest, a leak amount of 1 x 10-
7 Torr·l/sec is given as a total, and consequently in the case of a gas flow rate of
10 cc/min, gas having a purity of an impurity concentration of about 1 ppm is only
obtained. It is needless to say that when the gas flow rate is made further small,
the purity further drops.
[0010] Therefore, in order to lower the disengaged gas component from the chamber inner
surface to be in the same degree as 1 x 10-
11 Torr·l/sec which is the same as the external leak amount of the system, it is necessary
to make the degassing from the surface of stainless steel to be not more than 1 x
10-
15 Torr·l/sec-cm
2. Thus, a treatment technique for the stainless steel surface for decreasing the gas
release amount has been strongly demanded.
[0011] On the other hand, in the semiconductor production process, various gases ranging
from relatively stable general gases (0
2, N
2, Ar, H
2, He) to special gases having strong reactivity, corrosion property and toxicity are
used. Especially, among the special gases, there are gases which generate hydrochloric
acid or hydrofluoric acid exhibiting a strong corrosion property when moisture exists
in the atmosphere such as for example hydrogen chloride (HCI), chlorine (C1
2), trichloroboron (BC1
3), trifluoroboron (BF
3) and the like. Usually, stainless steel is often used for pipe arrangements and chamber
materials for handling these gases because of corrosion resistance, high strength,
easiness of secondary processing, easiness of welding, and easiness of polishing treatment
for the inner surface.
[0012] The stainless steel is excellent in corrosion resistance in a ultra-high purity atmosphere
of an extremely minute amount of moisture, however, it is easily corroded in a chlorine
type or a fluorine type gas atmosphere in which moisture exists. Thus, a treatment
for corrosion resistance becomes indispensable after the surface polishing of stainless
steel.
[0013] As the treatment method, there is Ni-W-P coating (cleanness coating method) for coating
the stainless steel with metal having strong corrosion resistance, or a passivated
film formation method in which a thin oxide film is made on the metallic surface in
a nitric acid solution and the like.
[0014] However, they are wet methods, so that a lot of remaining residues of the moisture
and the treatment solution exist on the film surface, in the film and at the boundary
between the film and stainless, and they do not become capable of application to ultra-high
vacuum apparatuses, ultra-high clean apparatuses and the like.
[0015] Thus, a method has been proposed in which stainless steel is oxidized in a gaseous
phase so as to form a passivated film.
[0016] As a result of repeated research by the present inventors on the relation between
degassing characteristics of oxidized passivated films and formation conditions thereof,
it has been elucidated that the moisture in the oxidizable atmosphere during passivated
film formation greatly affects the surface state and the degassing characteristic
of the passivated film, and following knowledge has been obtained in relation thereto.
[0017] As shown in Fig. 1 (a), an oxidized passivated film formed in a high purity atmosphere
having a moisture content of, for example, about 100 ppb is improved in the degassing
characteristic as compared with a passivated film formed by the wet method ((b) in
Fig. 1). However, the degassing characteristic was not sufficient yet, which could
not result in the use as a material for ultra-high vacuum or ultra-high clean pressure-reduced
apparatuses.
[0018] Concentration profiles of each of component atoms in the depth direction in which
this passivated one was measured by XPS (X-ray photoelectron spectroscopy) are shown
in Fig. 17, and scanning type electron microphotographs of the film surface are shown
in Fig.18. As can be seen in the electron microphotographs in Fig. 18, a large number
of cracks and pin holes are observed on the surface of the passivated film, and a
smooth and close film is not obtained. In addition, as shown in Fig. 16, it has been
found that little chromium oxide having high corrosion resistance exists at the outermost
surface of the passivated film in which a layer containing iron oxide as a main component
is formed.
[0019] As described above, when the oxidized passivated film is formed in the oxidizable
atmosphere containing moisture, the smoothness and closeness of the passivated film
obtained are affected depending on the moisture concentration in the atmosphere even
in the case of an extremely minute amount of the moisture, and the cracks and pin
holes are generated in the passivated film. In addition, according to the analysis
by XPS, it has been found that these cracks, pin holes and the like exist in the layer
containing much iron oxide at the outermost surface, and the degassing characteristic
is deteriorated because the moisture is absorbed and occluded by these cracks, pin
holes and the like.
[0020] On the other hand, when an oxidized passivated film is formed on the stainless steel
surface in a ultra-high purity atmosphere having a moisture amount of 10 ppb or below,
the passivated film having excellent degassing characteristic is obtained as shown
in Fig. 1 (c), which can be used as a material for ultra-high vacuum or ultra-high
clean pressure-reduced apparatuses, however, this passivated film also does not achieve
at a degree in which surface irregularity can be completely neglected.
[0021] That is to say, electrolytic polishing is performed before the formation of the passivated
film in order to smooth the surface, however, the surface roughness which can be achieved
by the electrolytic polishing at present has a limit of R
max:0.05-0.1 /1.m, and usually a surface roughness of 0.5 /1.m is used. However, when
the formation of the passivated film is performed after the electrolytic polishing,
the surface roughness during the electrolytic polishing is not maintained, and the
surface becomes rough. For example, even if the surface of a base material (bulk portion)
is finished to have R
max: 0.05-0.1 µm before the formation of the passivated film, the surface roughness of
the passivated film becomes rougher than R
max: 0.1 after the passivated film is formed. Consequently, stainless steel formed with
a passivated film in which R
max is below 0.1 for the surface roughness does not exist at present. And the present
inventors have elucidated that the surface roughness of the passivated film greatly
affects the degassing characteristic, and the rougher the surface roughness is, the
more the gas release amount is.
[0022] The present invention has been made on the basis of the finding of the above-mentioned
problems with respect to the oxidized passivated film.
[0023] It is an object of the present invention to achieve realization of ultra-flatness
and closeness of the passivated film, and provide a method for forming passivated
films of stainless steel excellent in degassing characteristics and corrosion resistance,
as well as stainless steel, and gas-contacting and liquid-contacting parts.
DISCLOSURE OF THE INVENTION
[0024] The first gist of the present invention lies in a method for forming stainless steel
passivated films characterized in that the surface of stainless steel is subjected
to an electrolytic polishing treatment, thereafter an oxidation treatment is performed
in oxidizable atmospheric gas, and subsequently iron oxide on the surface is reduced
and removed using hydrogen gas.
[0025] The second gist of the present invention lies in a method for forming stainless steel
passivated films characterized in that the surface of stainless steel is subjected
to an electrolytic polishing treatment, thereafter welding is performed, an oxidation
treatment is performed in oxidizable atmospheric gas after the welding while heating
a welded portion, and then iron oxide on the surface is reduced and removed using
hydrogen gas.
[0026] The third gist of the present invention lies in stainless steel characterized in
that it has a passivated film in which R
max is 0.1 /1.m or below for the surface roughness.
[0027] The fourth gist of the present invention lies in a gas-contacting part and a liquid-contacting
part characterized in that they have on the surface a stainless steel passivated film
formed such that the surface of stainless steel is subjected to an electrolytic polishing
treatment, thereafter an oxidation treatment is performed in oxidizable atmospheric
gas, and subsequently iron oxide on the surface is reduced and removed using hydrogen
gas.
FUNCTION AND EMBODIMENT EXAMPLES
[0028] The function of the present invention will be explained hereinafter together with
embodiment examples.
(Electrolytic polishing)
[0029] In the present invention, the electrolytic polishing is performed before the formation
of the passivated film. As an electrolytic polishing method, for example, a combined
electrolytic polishing method may be used. The combined electrolytic polishing method
is a method in which anodic metal subjected to polishing is electrolyzed and eluted
by electrolysis, and a passivated film generated on the surface of the metal subjected
to polishing is processed to have a specular face by means of an abrasive action using
polishing abrasive grains (for example, official gazette of Japanese Patent Publication
No. SHO-57-47759-1982).
[0030] By means of the electrolytic polishing of stainless steel, a processed denatured
layer on the surface is removed. In addition, it is possible to allow the surface
roughness to have R
max: 1 /1.m or below. It is preferable that the surface roughness after the electrolytic
polishing is as fine as possible, and hence it is possible to make it to be 0.05-0.1
tim.
[0031] The change in the surface state by the electrolytic polishing is shown in Fig. 2.
In Fig. 2, Fig. 2 (a) shows a surface state after the polishing, and Fig. 2 (b) shows
a surface state before the polishing. As clarified from Fig. 2, large irregularity
of crystal grains exists before the polishing, and no continuous film is obtained
even when an oxidized passivated film is formed in this state, resulting in a film
inferior in corrosion resistance. Further, moisture and the like is occluded and adsorbed
between crystal grains, so that no film having a good degassing characteristic is
obtained. By means of the application of the electrolytic polishing treatment, the
irregularity on the surface disappears, and a smooth face is provided. As a result,
the surface area decreases, and the adsorption and occlusion amount of moisture greatly
decreases.
[0032] Incidentally, it is preferable to perform fine washing and drying after the electrolytic
polishing in the same manner as washing of wafers.
(High temperature baking pretreatment)
[0033] In the present invention, the passivated film formation treatment may be performed
immediately after the electrolytic polishing, however, it is preferable that high
temperature baking is performed before the passivated film formation treatment. When
the high temperature baking treatment is performed before the passivated film formation
treatment, the chromium concentration at the stainless surface side increases, and
a passivated film which is close and excellent in corrosion resistance is formed.
[0034] The high temperature baking pretreatment is performed, for example, in an inert gas
atmosphere such as Ar, He, N
2 gas and the like. The time is preferably 1-10 hours. The treatment temperature is
preferably 300-600
°C, and more preferably 400-520
° C. When it is performed in a temperature range of 400-520
° C, the roughness on the surface is further suppressed, an oxidized passivated film
formed becomes a closer film as compared with cases of execution in other temperature
ranges, and the degassing characteristic is more improved.
[0035] Incidentally, the oxidized passivated film is also formed in this high temperature
baking treatment. The baking is performed in an inert gas atmosphere. The reason why
the oxidized passivated film is formed on the surface irrelevant to the fact that
the baking is performed in the inert gas atmosphere (that is to say, an atmosphere
containing no oxygen) is not necessarily clear, however, it is considered that a porous
oxide layer is formed on the stainless steel surface by the electrolytic polishing,
and oxygen in the layer serves as a supply source of oxygen for the passivated film
formation. In addition, the surface roughness of the passivated film formed by the
high temperature baking maintains a surface roughness after the electrolytic baking.
The thickness of this passivated film changes also depending on the baking temperature
and time, which becomes, for example, a thickness of about 30A in the case of 500
° C x 10 hours, so that an exact state after the high temperature baking can be also
put to practical use.
(Oxidation treatment - passivated film formation treatment)
[0036] Oxidizable gas (for example, mixed gas of Ar/0
2 = 4/1 (molar ratio)) is introduced after the high temperature baking treatment, which
is heated to, for example, 350-450
° C to form an oxidized passivated film on the stainless surface. By means of this oxidation
treatment, a layer containing much chromium oxide on the stainless surface is formed,
and a layer containing much iron oxide is formed thereon. The layer containing much
iron oxide is a porous film having cracks and pin holes as described above, The degree
of these cracks, pin holes and the like changes depending on the moisture amount in
the oxidizable atmosphere, and the more minute the moisture content is, the more preferable
it is.
(Hydrogen gas treatment)
[0037] The oxidizable gas is exhausted after the passivated film formation treatment, and
successively hydrogen gas is introduced to reduce and remove the layer of the passivated
outermost surface. By means of this hydrogen treatment, the outermost surface of the
passivated film becomes a clean and flat face. This is considered to result from the
fact that the layer containing much iron oxide in which the pin holes and crack exist
is reduced and removed by hydrogen, and the close layer containing much chromium oxide
appears.
[0038] It is generally said that hydrogen molecules are subjected to radical formation at
a temperature not less than 700
° C to cause a reduction reaction, and the reason why the reduction reaction takes place
at a low temperature of about 300 oC has not been confirmed yet, however, it is postulated
to be due to the fact that Ni contained in stainless serves as a catalyst. The hydrogen
concentration in the hydrogen treatment gas is preferably 0.1 ppm to 10 %, and more
preferably 0.5-100 ppm. In the range of 0.5-100 ppm, the close passivated film having
a more excellent degassing characteristic is formed. In addition, the temperature
for the hydrogen treatment is preferably 200-500 °C, and more preferably 300-400 °C.
The hydrogen brittleness of stainless is suppressed in this range, and the passivated
film which contains close chromium oxide having an excellent degassing characteristic
as a main component is obtained.
[0039] The surface roughness of the passivated film manufactured as described above is extremely
smooth, and for example, when the above-mentioned passivated film formation treatment
is performed after finishing into 0.05-0.1 µm by the electrolytic polishing, and further
the hydrogen gas treatment is performed, then the passivated film having a surface
roughness of not more than 0.01 µm is obtained.
(Annealing treatment)
[0040] Annealing treatment is further performed in inert gas after the hydrogen gas treatment,
thereby the chromium oxide concentration in the outermost surface of the thermally
oxidized passivated film is much increased, and stainless steel having the passivated
film with much more excellent corrosion resistance is obtained. The annealing is preferably
performed at 200-500 °C for 1-10 hours, and by performing the annealing under a condition
within this range, the surface state of the thermally oxidized passivated film becomes
smoother, the chromium oxide concentration in the outermost surface is much increased,
and the corrosion resistance is much improved. As the inert gas to be used for the
annealing treatment, for example, Ar, He, N
2 and the like are used.
(Passivating treatment for welded portions)
[0041] It has been found that when the stainless steel, in which the passivated film formation
treatment is performed in the oxidizable atmospheric gas after performing the electrolytic
polishing treatment of the surface of the stainless steel, and successively the iron
oxide on the surface is reduced and removed by hydrogen gas to form the passivated
film, or the stainless steel, in which the above-mentioned high temperature baking
is performed in the inert gas atmosphere after performing the electrolytic polishing
of the surface of the stainless steel so as to form the passivated film, is welded,
the surface of welded portions is coated with a passivated film containing a larger
amount of Fe oxide than one before the welding (Fig. 4).
[0042] Thus, a passivated film containing much Cr oxide can be formed at the welded portions
by heating the welded portions after the welding and again performing the high temperature
baking (300-600
° C x 1-10 hours) in the inert gas atmosphere, or by performing the passivated film
formation treatment in the oxidizable atmospheric gas and successively reducing and
removing iron oxide on the surface using hydrogen gas. Incidentally, the surface roughness
of the passivated film at the welded portions formed by the method of ② becomes to
have R
max: 0.1 µm or below.
(Stainless steel)
[0043] As described in the item of the background of the invention, no stainless steel having
a passivated film with a surface roughness of R
max: 0.1 µm or below has hitherto existed. This results from the fact that in the prior
art, even when the surface roughness is made minute by the electrolytic polishing,
the surface becomes rough when the passivated film is formed thereafter by the thermal
oxidation.
[0044] However, according to the above-mentioned method of the present invention, it is
possible to easily manufacture the stainless steel having the passivated film with
the surface roughness of R
max: 0.1 /1.m or below.
[0045] That is to say, one is the method in which the surface roughness is finished to be
0.05-0.1 µm by means of the electrolytic polishing, and the above-mentioned high temperature
baking is performed. The fact that the passivated film is also formed by the high
temperature baking is as described above, and the fact that the surface roughness
during the electrolytic polishing is maintained also by the high temperature baking
is also as described above. Therefore, when the high temperature baking is performed
after the electrolytic polishing with respect to the surface roughness of 0.05-0.1
µm, the passivated film having the surface roughness of 0.05-0.1 µm is obtained. Incidentally,
this passivated film is an extremely close passivated film in which the surface is
extremely rich in chromium, Cr/Fe is of course 1 and more, and one having Cr/Fe of
about 7 is also achieved (see Fig. 5).
[0046] Consequently, this stainless steel is extremely excellent in the degassing characteristic
because R
max is 0.1 µm and more for the surface roughness, and it has the close passivated film.
[0047] Another method for obtaining the stainless steel having the passivated film with
the surface roughness of R
max: not more than 0.1 µm is the method in which the surface of stainless steel is finished
to have the surface roughness of R
max: 0.05-0.1 µm by means of the electrolytic polishing, and the above-mentioned hydrogen
gas treatment is performed (the high temperature baking may be performed before the
hydrogen gas treatment). Using this method, it is also possible to manufacture the
stainless steel having the passivated film having the surface roughness of R
max:not more than 0.01 /1.m. Incidentally, Cr/Fe at the surface of the passivated one
after the hydrogen gas treatment becomes larger than Cr/Fe in the base material (see
Fig. 6, for example, Cr/Fe is 0.35 in Fig. 6 (a)), so that the stainless steel which
is also excellent in the gas disengage characteristic and the corrosion resistance
is obtained.
(Object stainless steel)
[0048] In addition, the stainless steel of the present invention is, for example, those
of the Fe-Cr type and the Fe-Cr-Ni type. In addition, also with respect to the structure,
any stainless steel of the ferrite type, the martensite type or the austenite type
is available. Especially SUS 316 is preferable.
[0049] The passivated stainless steel manufactured according to the passivated film formation
method of the present invention as described above exhibits extremely good degassing
characteristics and corrosion resistance, which makes it possible to use as constituting
materials for ultra-high vacuum apparatuses, ultra-high clean pressure-reducing apparatuses
and the like.
(Gas-contacting parts and liquid-contacting parts)
[0050] The passivated stainless steel manufactured according to the passivated film formation
method of the present invention as described above exhibits extremely good degassing
characteristics and corrosion resistance, which is preferably used also for gas-contacting
parts.
[0051] In addition, it has been found that when this stainless steel is allowed to contact
with pure water, there is no elution of impurities from the stainless steel to pure
water, and it is also excellent in corrosion resistance against corrosive chemical
solutions. Therefore, the stainless steel according to the present invention can be
preferably used also for liquid-contacting parts such as liquid supply tubes, liquid
storing tanks and the like.
[0052] Next, concrete examples of the gas-contacting parts will be explained.
[0053] A system of a gas supply line for supplying gas from a gas bomb to a use point of
the gas such as a film formation apparatus or the like generally has constitution
as shown in Fig. 7. In Fig. 7, 100 is the gas cylinder, 101 is a gas cylinder valve,
102 is a regulator, 103 is a valve, 104 is an integrated branched valve, 105 is a
mass flow controller, 106 is the film formation apparatus, 107 is a pipe arrangement,
and 108 is a filter.
[0054] As the gas-contacting parts, for example, there are exemplified parts such as the
gas cylinder valve, a pressure gauge, the regulator, the valve, the mass flow controller,
the filter, the regulator and the like, or for example, a valve seat, a valve chamber,
a valve main body, a diaphragm, a seal ring, a stem and the like constituting these
parts.
[0055] As the cylinder valve, for example, one having a structure shown in Fig. 8 is exemplified
(official gazette of Japanese Utility Model Application Laid- open No. HEI-1-178281-1989).
In addition, those shown in Fig. 9 for the pressure gauge, in Fig. 10 for the regulator,
in Fig. 11 for the valve and in Fig. 12 for the mass flow controller are exemplified
as each of examples, respectively.
[0056] For example, in the case of the diaphragms exemplified in Fig. 8, Fig. 9 and Fig.
11, following effects are also provided. Preferably the diaphragm has its small surface
roughness from a viewpoint of the sealing property. In addition, in order to give
deflection, resiliency is required. Further, in order to ensure a good sealing property
for a long time, an excellent fatigue resistance characteristic is required. However,
in the present invention, R
max is not more than 0.1 /1.m for its surface roughness, so that the sealing property
is extremely good. In addition, it is generally considered that metal having a passivated
film is inferior in resiliency to metal having no passivated film, however, in the
present invention, resiliency which is not different from that of stainless having
no passivated film at all has been exhibited. Further, as a result of a fatigue test,
a critical fatigue strength which is more excellent than that of stainless steel formed
with a conventional passivated film has been exhibited. In addition, in the case of
the stainless formed with the conventional passivated film, generation of small cracks
was found on its surface, however, in the case of the stainless according to the present
invention, generation of such cracks was not found.
[0057] In addition, the good sealing property is also required in the case of the valves
such as the cylinder valve for gas cylinders and the like, however, the valve of the
present invention has a better sealing property than a valve having a conventional
passivated film on the gas-contacting surface, in which the leak amount is remarkably
reduced, and it has become possible to supply gas of ultra-high purity.
[0058] Further, when a pure water supply tube was manufactured using the stainless steel
according to the present invention, ultra-pure water having a resistivity of about
18 Mit · cm was supplied in the tube, and the resistivity at an outlet was measured,
then the resistivity value scarcely changed.
[0059] In addition, when the stainless steel according to the present invention was immersed
in an HCI solution, and the surface was observed by microphotograph, then no corrosion
on the surface was found.
BRIEF DESCRIPTION OF THE DRAWINGS
[0060]
Fig. 1 is a graph showing degassing characteristics of oxidized passivated stainless
tubes manufactured by various methods, wherein
(a): a thermally oxidized passivated film manufactured by a conventional method,
(b): an oxidized passivated film manufactured by a wet method,
(c): a thermally oxidized passivated film manufactured in a ultra-high purity oxidizable
atmosphere of a moisture content of not more than 10 ppb,
(d): a thermally oxidized passivated film of Embodiment 1,
(e): a thermally oxidized passivated film of Embodiment 2,
(f): a thermally oxidized passivated film of Embodiment 3,
(g): a thermally oxidized passivated film of Embodiment 4, and
(h): a thermally oxidized passivated film of Embodiment 5.
Fig. 2 is scanning type electron microphotographs showing inner surface states of
a stainless tube before and after an electrolytic polishing treatment.
Fig. 3 is scanning type electron microphotographs showing inner surface states of
a stainless tube after electrolytic polishing.
Fig. 4 is a graph showing concentration profiles in the depth direction by XPS after
welding.
Fig. 5 is a graph showing concentration profiles in the depth direction by XPS of
the electrolytic polishing surface after baking in an Ar gas atmosphere.
Fig. 6 is graphs showing concentration profiles in the depth direction by XPS of the
thermally oxidized passivated film surface after the hydrogen reduction treatment.
(a): treatment time 10 minutes, (b): treatment time 30 minutes.
Fig. 7 is a figure of concept showing a system of a gas supply line.
Fig. 8 is a cross-sectional view of a bomb valve according to one embodiment of the
present invention.
Fig. 9 is a cross-sectional view of a pressure gauge according to one embodiment of
the present invention.
Fig. 10 is a cross-sectional view of a regulator according to one embodiment of the
present invention.
Fig. 11 is a cross-sectional view of a valve according to one embodiment of the present
invention.
Fig. 12 is a cross-sectional view of a mass flow controller according to one embodiment
of the present invention.
Fig. 13 is scanning type electron microphotographs showing inner surface states of
stainless tubes after baking in an Ar gas atmosphere.
Fig. 14a is scanning type electron microphotographs showing surface states of a thermally
oxidized passivated film after the hydrogen reduction treatment for 10 minutes.
Fig. 14b is scanning type electron microphotographs showing surface states of a thermally
oxidized passivated film after the hydrogen reduction treatment for 30 minutes.
Fig. 15 is a graph showing concentration profiles in the depth direction by XPS of
the thermally oxidized passivated film surface after the Ar annealing treatment.
(a): annealing temperature: 375 ° C,
(b): annealing temperature: 400 ° C,
(c): annealing temperature: 425 ° C,
(d): annealing temperature: 450 ° C,
(e): annealing temperature: 475 ° C,
(f): annealing temperature: 500 ° C.
Fig. 16 is a graph showing the relation between the system leak amount and the impurity
concentration in the atmospheric gas for various gas flow rates in a conventional
apparatus.
Fig. 17 is a graph showing concentration profiles in the depth direction by XPS of
the thermally oxidized passivated film surface manufactured by a conventional thermal
oxidation method.
Fig. 18 is scanning type electron microphotographs showing the surface state of a
thermally oxidized passivated film manufactured by a conventional method.
(Description of the References)
[0061]
100: cylinder, 101: gas cylinder valve, 102: pressure gauge / regulator
103: valve, 104: branched valve, 105: mass flow controller,
106: film formation apparatus, 107: pipe arrangement,
108: filter.
BEST MODE FOR CARRYING OUT THE INVENTION
[0062] Embodiments of the present invention will be explained hereinafter.
(Embodiment 1)
[0063] A SUS 316L stainless tube having a length of 2 m and a diameter of 3/8" was subjected
to electrolytic polishing, and the surface was made into a specular face in which
the maximum value of difference in irregularity (R
max) was 0.05 µm in within a circumference having a radius of 5 µm. As shown in Fig.
3, this surface state is a smooth face in which the crystal grain boundary is observed.
[0064] Next, this stainless tube was washed by the same method as a washing process of wafers,
namely in the order of ammonia/hydrogen perox- ide/water (NH
4OH:H
2O
2:H
2O=1:4:20, 90 °C), hot water washing (90
° C) and ultra-pure water, which was dried with isopropyl alcohol.
[0065] This stainless tube was installed in an oxidation furnace, Ar gas was allowed to
flow at 1 I/min, purging was performed at an ordinary temperature for 1 hour, thereafter
the temperature was raised to 450-550 °C, and a baking treatment was performed for
10 hours. Inner surface states of the stainless after the thermal treatment at various
temperatures are shown in Fig. 13. As clarified from Fig. 13, even after the thermal
treatment for a long time at a high temperature, the specular face after the electrolytic
polishing was maintained for the stainless surface. That is to say, R
max: 0.05 µm was maintained. In addition, a result of measurement by XPS of the inner
surface of the stainless tube after the baking at 500 °C is shown in Fig. 5. Owing
to the above-mentioned baking treatment, chromium atoms increased at the surface side,
while iron atoms inversely decreased, and the chromium/iron composition ratio was
inverted with respect to the inside of the bulk.
[0066] In Fig. 5, the place at which the line of Fe intersects with the line of O is a boundary
between the bulk (base material) and the passivated film, and the film thickness of
the passivated film shown in Fig. 5 is about 30 Â. In this passivated film, chromium
oxide is more than iron oxide in one of about 22 A from the surface (left end of the
graph in Fig. 5).
[0067] Subsequently the inside of the oxidation furnace was lowered to 400
° C, thereafter the Ar gas was replaced by a mixed gas of Ar and 0
2 containing 100 ppb of moisture (Ar/0
2 =4:1), and the inner surface of the stainless tube was subjected to an oxidation
treatment. A surface state after the oxidation is approximately the same surface state
as one shown in the electron microphotographs in Fig. 18, in which a large number
of cracks and pin holes were observed on the film surface.
[0068] Next, the oxidizable gas was purged by Ar gas, Ar gas containing 1 ppm of H
2 was introduced into the stainless tube, and a hydrogen reduction treatment of the
oxidized film was performed at 400
° C for 10 minutes or 30 minutes. Surface states after the treatment are shown in Fig.
14 (a) (in the case of 10 minutes) and Fig. 14 (b) (in the case of 30 minutes), respectively.
Fig. 14 (a) indicates the case in which the hydrogen gas treatment time was 10 minutes,
and Fig. 14 (b) indicates the case in which the hydrogen gas treatment time was 30
minutes. As shown by Fig. 14, the cracks and pin holes having existed after the oxidation
treatment were not observed on the surface of the passivated film subjected to the
hydrogen reduction treatment (hydrogen gas treatment), and the smooth surface state
was provided. On the other hand, as shown in Fig. 6, a high concentration of chromium
oxide existed in the passivated film, and the chromium atomic ratio with respect to
iron became by far larger than that in the base material. Incidentally, the thickness
of the passivated films shown in Fig. 6 (a) and Fig. 6 (b) was about 60 Å.
[0069] As a result of measurement of the surface roughness of this passivated film, there
was given R
max: 0.01 /1.m.
[0070] According to the above-mentioned facts, it is considered that the layer of iron oxide
in which a large number of pin holes and cracks existed was removed, the close layer
containing a large amount of chromium oxide appeared, and the surface became clean
and flat.
[0071] In addition, it was found that the hydrogen reduction treatment time scarcely affected
the surface state of the passivated film and the concentration profile in the depth
direction, and the reduction reaction was completed for about 10 minutes.
[0072] Next, with respect to the stainless tube having been subjected to the above-mentioned
passivating treatment, an evaluation test for the degassing characteristic was performed.
After the stainless tube was left for 1 week in a clean room at a relative humidity
of 50 % and a temperature of 20
° C, Ar gas was allowed to flow in a flow rate of 1.2 I/min, and the moisture amount
contained in the Ar gas was measured at the outlet of the tube using APIMS (atmospheric
pressure ionization mass spectrometer). A result is shown in (d) in Fig. 1. The moisture
amount in the Ar gas decreased to 10 ppb 20 minutes after the gas application, which
became not more than 3 ppb as the background level after 30 minutes.
[0073] As compared with a oxidized passivated film manufactured by the conventional method
shown in Fig. 1 (a), the degassing characteristic was greatly improved, and it has
been shown that the oxidized passivated film stainless steel manufactured according
to the present embodiment can be applied to ultra-high vacuum apparatuses and ultra-high
clean pressure-reduced apparatuses.
(Embodiment 2)
[0074] The baking treatment in the Ar atmosphere was omitted in embodiment 1, and other
things were the same as those in embodiment 1, whereby an oxidized passivated stainless
tube was manufactured in the same manner as embodiment 1, and its degassing characteristic
was evaluated. A result is shown in (e) in Fig. 1.
[0075] As clarified from Fig. 1, the moisture amount became 3 ppb about 40 minutes after
the gas application, in which the degassing characteristic was inferior to that of
the oxidized passivated film of embodiment 1, however, it was greatly improved as
compared with the conventional oxidized passivated film.
(Embodiment 3)
[0076] An oxidized passivated film was formed on the inner surface of a stainless tube,
in which the temperature of the hydrogen reduction treatment was 600 °C, and other
treatment conditions were the same as those in embodiment 1, and the same evaluation
was performed.
[0077] A result is shown in (f) in Fig. 1. Roughness was observed a little on the surface
of the passivated film manufactured herein, and the degassing characteristic was also
inferior to those of embodiments 1 and 2, however, the moisture content decreased
to 3 ppb about 70 minutes after the gas application, which was clearly improved as
compared with the conventional example.
(Embodiment 4)
[0078] An oxidized passivated film was formed on the inner surface of a stainless tube,
in which the hydrogen reduction treatment gas was Ar gas containing 20 % hydrogen,
and other conditions were the same as those in embodiment 1, and the same evaluation
was performed.
[0079] A result is shown in (g) in Fig. 1. Roughness was observed a little on the surface
of the passivated film, and the degassing characteristic was also inferior to those
of embodiments 1 and 2, however, the moisture content decreased to 3 ppb about 70
minutes after the gas application, which was clearly improved as compared with the
conventional example.
(Embodiment 5)
[0080] An oxidized passivated stainless tube was manufactured, in which the oxidizable atmosphere
was a ultra-high purity atmosphere of a moisture concentration of 5 ppb, and other
treatment conditions were the same as those in embodiment 1, and its degassing characteristics
was evaluated. The results is as in (h) in Fig. 1. The moisture amount in the Ar gas
became not more than 3 ppb as the background level 10 minutes after the gas application,
and it was found that even in the case of the film at the highest level at the present
circumstance, the degassing characteristic was improved by the treatment according
to the present embodiment.
(Embodiment 6)
[0081] The hydrogen reduction treatment was performed in the same manner as embodiment 1,
and then the annealing treatment was further performed at various temperatures for
10 hours in Ar gas. Concentration profiles in the depth direction by XPS at the surface
of the thermally oxidized passivated films are shown in Fig. 15 (a) to Fig. 15 (f).
[0082] As clarified from Fig. 8, owing to the Ar annealing, the concentration of chromium
having high corrosion resistance increased at the outermost surface layer. Moreover,
it was found that the chromium concentration increased more and more in accordance
with the increase in the treatment temperature, and the concentrations of chromium
and iron became inverted at not less than 475
°C. Incidentally, the thickness of the passivated films shown in Fig. 8 (a) to Fig.
8 (f) was about 70 Å.
[0083] In addition, with respect to the oxidized passivated film of the present embodiment,
the corrosion resistance was improved owing to the increase in the chromium concentration
at the outermost surface, and extremely good corrosion resistance was exhibited against
a strongly corrosive solution of 36 % HCI.
INDUSTRIAL APPLICABILITY
[0084] According to the present invention, it becomes possible to form the passivated film
which is extremely excellent in the degassing characteristic and the corrosion resistance,
and it becomes possible to supply the oxidized passivated stainless steel which is
applicable to ultra-high vacuum, ultra-high clean pressure-reduced apparatuses and
the like.
1. A method for forming stainless steel passivated films wherein the surface of stainless
steel is subjected to an electrolytic polishing treatment, thereafter an oxidation
treatment is performed in oxidizable atmospheric gas, and subsequently iron oxide
on the surface is reduced and removed using hydrogen gas.
2. The method for forming stainless steel oxidized passivated films according to claim
1 wherein a heat treatment is performed in an inert gas atmosphere at 300-600 ° C after said electrolytic polishing treatment and before said oxidized film formation.
3. The method for forming stainless steel oxidized passivated films according to claim
1 or 2 wherein the hydrogen concentration in the gas atmosphere is 0.1 ppm to 10 %
in said hydrogen gas treatment.
4. The method for forming stainless steel oxidized passivated film according to any
one of claims 1 through 3 wherein the treatment temperature is 200-500 ° C in said hydrogen gas treatment.
5. The method for forming stainless steel oxidized passivated films according to any
one of claims 1 through 4 wherein an annealing treatment is performed in inert gas
after said hydrogen gas treatment.
6. The method for forming stainless steel oxidized passivated films according to claim
5 wherein the condition for said inert gas annealing treatment is at 200-500 ° C for 1-10 hours.
7. The method for forming stainless steel oxidized passivated films according to claim
6 wherein the condition for said inert gas annealing treatment is at not less than
475 ° C.
8. A method for forming stainless steel passivated films wherein stainless steel,
in which the surface is subjected to an electrolytic polishing treatment, thereafter
an oxidation treatment is performed in oxidizable atmospheric gas, and subsequently
iron oxide on the surface is reduced and removed using hydrogen gas, is mutually welded,
next an oxidation treatment is performed in oxidizable atmospheric gas while heating
a welded portion, and subsequently iron oxide on the surface is reduced and removed
using hydrogen gas.
9. Stainless steel wherein it has a passivated film in which Rmax is not more than 0.1 /1.m for the surface roughness.
10. The stainless steel according to claim 9 wherein it has the passivated film in
which Rmax is not more than 0.01 µm for the surface roughness.
11. The stainless steel according to claim 9 or claim 10 wherein Cr/Fe (atomic ratio,
followings are the same) of the surface of the passivated film is larger than Cr/Fe
of the base material portion.
12. The stainless steel according to claim 9 wherein Cr/Fe of the surface of the passivated
film is not less than 1.
13. A gas-contacting part and a liquid-contacting part having on the surface a stainless
steel passivated film formed such that the surface of stainless steel is subjected
to an electrolytic polishing treatment, thereafter an oxidation treatment is performed
in oxidizable atmospheric gas, and subsequently iron oxide on the surface is reduced
and removed using hydrogen gas.
14. The gas-contacting part and the liquid-contacting part having at least on the
gas-contacting surface and the liquid-contacting surface the stainless steel passivated
film according to claim 13 wherein a heat treatment is performed in an inert gas atmosphere
at 300-600 °C after said electrolytic polishing treatment and before said oxidized film formation.
15. The gas-contacting part and the liquid-contacting part having on the surface the
stainless steel passivated film according to claim 13 or 14 wherein the hydrogen concentration
in the gas atmosphere is 0.1 ppm to 10 % in said hydrogen gas treatment.
16. The gas-contacting part and the liquid-contacting part having on the surface the
stainless steel passivated film according to any one of claims 13 to 15 wherein the
treatment temperature is 200-500 ° C in said hydrogen gas treatment.
17. The gas-contacting part and the liquid-contacting part having on the surface the
stainless steel passivated film according to any one of claims 13 through 16 wherein
an annealing treatment is performed in inert gas after said hydrogen gas treatment.
18. The gas-contacting part and the liquid-contacting part having on the surface the
stainless steel passivated film according to claim 17 wherein the condition for said
inert gas annealing treatment is at 200-500 ° C for 1-10 hours.
19. The gas-contacting part and the liquid-contacting part having on the surface the
stainless steel passivated film according to claim 18 wherein the condition for said
inert gas annealing treatment is at not less than 475 ° C.
20. A gas-contacting part and a liquid-contacting part having on the surface a stainless
steel passivated film wherein they have the passivated film in which Rmax is not more than 0.1 µm for the surface roughness.
21. The gas-contacting part and the liquid-contacting part having on the surface the
stainless steel passivated film according to claim 20 wherein they have the passivated
film in which Rmax is not more than 0.01 µm for the surface roughness.
22. The gas-contacting part and the liquid-contacting part having on the surface the
stainless steel passivated film according to claim 9 or claim 21 wherein Cr/Fe (atomic
ratio, followings are the same) of the surface of the passivated film is larger than
Cr/Fe of the base material portion.
23. The gas-contacting part and the liquid-contacting part having on the surface the
stainless steel passivated film according to claim 20 wherein Cr/Fe of the surface
of the passivated film is not less than 1.
24. The gas-contacting part and the liquid-contacting part having on the surface the
stainless steel passivated film according to any one of claims 20 through 23 wherein
said gas-contacting part and said liquid-contacting part are a diaphragm in a regulator
or a valve.
25. The gas-contacting part and the liquid-contacting part according to any one of
claims 20 through 23 wherein said gas-contacting part is a cylinder valve of a gas
cylinder, and the cylinder valve is such a cylinder valve of the gas cylinder in which
a gas inlet is allowed to communicate with a gas outlet through a gas inlet passage,
a valve chamber for gas supply and a gas outlet passage in a valve main body of the
cylinder valve,
a valve body for gas supply is provided in the valve chamber for gas supply, and the
valve body for gas supply is constituted to be capable of opening and closing operation
with respect to a valve seat of the valve chamber for gas supply by a valve for gas
supply operating unit, which is such a cylinder valve of the gas cylinder in which
a valve chamber for protection is allowed to intervene in the gas outlet passage in
the valve main body of the cylinder valve, a valve body for protection is provided
at the valve chamber for protection, and the valve body for protection is constituted
to be capable of opening and closing operation with respect to a valve seat of the
valve chamber for protection by a valve for protection operating unit.