U.S. patent application number 15/130282 was filed with the patent office on 2016-08-11 for chemical-liquid mixing method and chemical-liquid mixing apparatus.
This patent application is currently assigned to TOKYO ELECTRON LIMITED. The applicant listed for this patent is TOKYO ELECTRON LIMITED. Invention is credited to Koukichi HIROSHIRO, Fumihiro KAMIMURA, Hiroshi TANAKA.
Application Number | 20160228832 15/130282 |
Document ID | / |
Family ID | 38561789 |
Filed Date | 2016-08-11 |
United States Patent
Application |
20160228832 |
Kind Code |
A1 |
TANAKA; Hiroshi ; et
al. |
August 11, 2016 |
CHEMICAL-LIQUID MIXING METHOD AND CHEMICAL-LIQUID MIXING
APPARATUS
Abstract
The present invention provides a chemical-liquid mixing method
and a chemical-liquid mixing apparatus capable of sufficiently
generating a peroxomonosulfuric acid that is effective in removing
a resist from a substrate, when a sulfuric acid and a hydrogen
peroxide solution are mixed with each other. At first, an inner
tank 10 is filled up with a sulfuric acid and the sulfuric acid
overflowing from the inner tank 10 is allowed to flow into an outer
tank 12. Then, a hydrogen peroxide solution is supplied Into the
inner tank 10 and the hydrogen peroxide solution is allowed to flow
into the outer tank 12 whereby the two kinds of liquids of the
hydrogen peroxide solution and the sulfuric acid are stored in the
outer tank 12. Simultaneously when the hydrogen peroxide solution
flows into the outer tank 12, a return pump 16 is activated.
Inventors: |
TANAKA; Hiroshi; (Tosu-Shi,
JP) ; HIROSHIRO; Koukichi; (Tosu-Shi, JP) ;
KAMIMURA; Fumihiro; (Tosu-Shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TOKYO ELECTRON LIMITED |
Tokyo-To |
|
JP |
|
|
Assignee: |
TOKYO ELECTRON LIMITED
Tokyo-To
JP
|
Family ID: |
38561789 |
Appl. No.: |
15/130282 |
Filed: |
April 15, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14750319 |
Jun 25, 2015 |
9339775 |
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15130282 |
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|
11882402 |
Aug 1, 2007 |
9099502 |
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14750319 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01F 2215/0036 20130101;
B01F 15/0243 20130101; C11D 11/0047 20130101; B01J 2219/00103
20130101; B01F 15/00396 20130101; C01B 15/08 20130101; B01J 19/24
20130101; B01F 15/06 20130101; B01F 15/00331 20130101; B01F 3/0865
20130101; B01F 15/00253 20130101; B01F 15/0437 20130101; C11D
3/3947 20130101; B01F 3/0861 20130101; H01L 21/67057 20130101; B01F
15/0412 20130101; B01F 5/10 20130101; B01J 2219/24 20130101; B01F
2015/062 20130101; B01F 3/088 20130101 |
International
Class: |
B01F 3/08 20060101
B01F003/08; C01B 15/08 20060101 C01B015/08; B01F 15/06 20060101
B01F015/06; B01J 19/24 20060101 B01J019/24; B01F 5/10 20060101
B01F005/10; B01F 15/00 20060101 B01F015/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 3, 2006 |
JP |
2006211732 |
Claims
1-3. (canceled)
4. A chemical-liquid mixing apparatus for mixing a sulfuric acid
and a hydrogen peroxide solution, the apparatus comprising: an
inner tank; an outer tank disposed around the inner tank, into
which outer tank a liquid overflowing from the inner tank flows; a
return pipe configured to return the liquid in the outer tank to
the inner tank; and a return pump provided on the return pipe for
sending the liquid in the outer tank to the inner tank; a heater
provided on the return pipe; a sulfuric-acid supply unit configured
to supply a sulfuric acid into the inner tank; a
hydrogen-peroxide-solution supply unit configured to supply a
hydrogen peroxide solution to the inner tank or the outer tank; and
a hydrogen-peroxide-solution replenishing pipe for replenishing a
hydrogen peroxide solution that extends through the outer tank to
reach an inside of the return pipe such that a hydrogen peroxide
solution can be directly fed into the return pipe, with an outlet
of the replenishing pipe downstream in the return pipe from an
inlet of the return pipe.
5. The chemical-liquid mixing apparatus according to claim 4,
further comprising a controller configured to control the heater
such that the heater is activated after a preset period of time has
passed from an activation of the return pump, the activation of the
return pump being simultaneous with a start of an activation of the
hydrogen-peroxide-solution supply unit.
6. (canceled)
7. The chemical-liquid mixing apparatus according to claim 4,
wherein the replenishing pipe is configured to supply hydrogen
peroxide solution to the return pipe with the supplied hydrogen
peroxide solution being received at the return pipe without first
passing through the inner tank.
8. The chemical-liquid mixing apparatus according to claim 7,
wherein the replenishing pipe is configured to supply hydrogen
peroxide solution to the return pipe with the supplied hydrogen
peroxide solution being received at the return pipe without first
contacting a liquid in the outer tank.
9. The chemical-liquid mixing apparatus according to claim 4,
wherein the replenishing pipe is configured to supply hydrogen
peroxide solution to the return pipe with the supplied hydrogen
peroxide solution being received at the return pipe without first
contacting a liquid in the outer tank.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a chemical-liquid mixing
method for mixing a sulfuric acid and a hydrogen peroxide solution,
and a chemical-liquid mixing apparatus therefor. In particular, it
pertains to a chemical-liquid mixing method and chemical-liquid
mixing apparatus capable of generating an enough peroxomonosulfuric
acid that is effective in removing a resist from a substrate, when
a sulfuric acid and a hydrogen peroxide solution are mixed with
each other.
BACKGROUND ART
[0002] There has been conventionally known a method of cleaning
substrates such as semiconductor wafers (also referred to as
"wafer" below) with the use of a mixture liquid of a sulfuric acid
and a hydrogen peroxide solution as a cleaning liquid (see,
JP5-166780A, for example). To be specific, a wafer is cleaned by
fully decomposing a resist adhered to the wafer, by means of a
peroxomonosulfuric acid (H.sub.2SO.sub.5) which has been generated
by mixing a sulfuric acid and a hydrogen peroxide solution (this
theory will be described below).
[0003] With reference to FIG. 6, a chemical-liquid mixing apparatus
for producing a mixture liquid of a sulfuric acid and a hydrogen
peroxide solution is described. FIG. 6 is a schematic structural
view showing a structure of a general chemical-liquid mixing
apparatus.
[0004] As shown in FIG. 6, the general chemical-liquid mixing
apparatus includes an inner tank 10 in which a wafer is
accommodated to be cleaned, and an outer tank 12 disposed around a
circumference of the inner tank 10, into which a liquid overflowing
from the inner tank 10 flows. There is disposed a return pipe 14
for returning a liquid in the outer tank 12 into the inner tank 10.
In the return pipe 14, there are serially arranged a return pump 16
for sending a liquid in the outer tank 12 to the inner tank 10, a
dumper 18 for reducing vibrations or the like of the return pipe
14, a heater 20 for heating a liquid passing through the return
pipe 14, and a filter 22 for filtering a liquid passing through the
return pipe 14. The chemical-liquid mixing apparatus also includes
a sulfuric-acid storage tank 24 for storing a sulfuric acid
(H.sub.2SO.sub.4), and a hydrogen-peroxide-solution storage tank 30
for storing a hydrogen peroxide (H.sub.2O.sub.2) solution. The
sulfuric acid and the hydrogen peroxide solution stored in the
respective storage tanks 24 and 30 are supplied into the inner tank
10 by a sulfuric-acid supply pipe 28 and a
hydrogen-peroxide-solution supply pipe 34, respectively. Supply
operations of the respective chemical liquids can be adjusted by a
sulfuric-acid supply valve 26 and a hydrogen-peroxide-solution
supply valve 32, respectively.
[0005] Next, a method of producing a mixture liquid by such a
chemical-liquid mixing apparatus will be described below. The inner
tank 10 and the outer tank 12 are empty in their initial
states.
[0006] At first, the sulfuric-acid supply valve 26 and the
hydrogen-peroxide-solution supply valve 32 are opened, while the
return pump 16 and the heater 20 are left OFF, so as to
simultaneously supply a sulfuric acid and a hydrogen peroxide
solution from the sulfuric-acid storage tank 24 and the
hydrogen-peroxide-solution storage tank 30 into the inner tank 10.
For example, a supply ratio between the sulfuric acid and the
hydrogen peroxide solution is 5:1. Namely, a supply rate of the
sulfuric acid is, e.g., 25 liters/min, and a supply rate of the
hydrogen peroxide solution is, e.g., 5 liters/min. The reason why
the supply rate of the sulfuric acid is considerably larger than
that of the hydrogen peroxide solution is described below. The
supply of the sulfuric acid and the hydrogen peroxide solution is
continued until the inner tank 10 becomes full and the liquid
overflows to the outer tank 12.
[0007] By supplying the sulfuric acid and the hydrogen peroxide
solution into the inner tank 10, the sulfuric acid and the hydrogen
peroxide solution are mixed with each other.
[0008] Mixture of the sulfuric acid and the hydrogen peroxide
solution is classified into the following two patterns.
[0009] The first pattern is the following chemical reaction.
H.sub.2SO.sub.4+H.sub.2O.sub.2.fwdarw.H.sub.2SO.sub.4+H.sub.2O+O*
Formula (1)
[0010] The reaction represented by Formula (1) generates an active
oxygen (O*). This active oxygen is a strong oxidizer.
[0011] The second pattern is the following chemical reaction.
H.sub.2SO.sub.4+H.sub.2O.sub.2.fwdarw.H.sub.2SO.sub.5+H.sub.2O
Formula (2)
[0012] The reaction represented by Formula (2) generates a
peroxomonosulfuric acid (H.sub.2SO.sub.5). Similar to the active
oxygen, the peroxomonosulfuric acid is also a strong oxidizer.
However, the peroxomonosulfuric acid is more effective than the
active oxygen in decomposing an organic matter such as a resist
adhering to a wafer. That is to say, by mixing a sulfuric acid and
a hydrogen peroxide solution to generate a peroxomonosulfuric acid,
it is possible to fully remove a resist adhering to a wafer
therefrom.
[0013] FIG. 7 is a graph in which a horizontal axis shows a ratio
(molar ratio) of a sulfuric acid relative to a hydrogen peroxide
solution, and a vertical axis shows a generation ratio of
peroxomonosulfuric acid. As shown in FIG. 7, when the ratio (molar
ratio) of a sulfuric acid relative to a hydrogen peroxide solution
is raised, the generation ratio of peroxomonosulfuric acid is
correspondingly increased. Thus, a resist adhering to a wafer can
be more sufficiently removed. For this reason, a ratio between
supply rates of a sulfuric acid and a hydrogen peroxide solution to
be supplied into the inner tank 10 is set at, for example, 5:1.
[0014] After the supply of the sulfuric acid and the hydrogen
peroxide solution into the inner tank 10 is finished, the return
pump 16 is activated to return the liquid in the outer tank 12 into
the inner tank 10 through the return pipe 14. Again, the liquid
overflows from the inner tank 10 to the outer tank 12. In this
manner, the liquid is circulated through the combination unit of
the inner tank 10 and the outer tank 12. At the same time, the
heater 20 is activated to heat the liquid passing through the
return pipe 14. Thus, a temperature of the liquid contained in the
inner tank 10 is heated to a temperature suitable for cleaning a
wafer (e.g., 100.degree. C. to 150.degree. C.).
[0015] After the return pipe 16 and the heater 20 are kept in ON
state until a temperature of the liquid in the inner tank 10
reaches a certain temperature, the return pipe 16 and the heater 20
are again switched off. Thereafter, a plurality of wafers are all
together immersed into the inner tank 10. Thus, a resist adhering
to each wafer is decomposed by the mixture liquid of the sulfuric
acid and the hydrogen peroxide solution, more specifically, a
peroxomonosulfuric acid generated by mixing the sulfuric acid and
the hydrogen peroxide solution, to thereby remove the resist from
the wafer. In this manner, a series of steps for cleaning the wafer
is completed.
DISCLOSURE OF THE INVENTION
[0016] However, there is case in which a sufficient supply amount
of a sulfuric acid into the inner tank 10 cannot be practically
ensured. That is to say, the chemical-liquid mixing apparatus as
shown in FIG. 6 is generally installed in a wafer manufacturing
factory where a sulfuric acid is directly supplied into the inner
tank 10 of the chemical-liquid mixing apparatus from a
sulfuric-acid storage tank for collectively storing a sulfuric acid
to be used in the factory or a sulfuric acid generator for
collectively generating a sulfuric acid to be used in the factory.
Since this structure elongates a supply line for a sulfuric acid,
there is a possibility that a supply of a sulfuric acid cannot be
smoothly carried out because of a high specific gravity and density
thereof. Specifically, when the chemical-liquid mixing apparatus is
installed in a wafer manufacturing factory, and a sulfuric acid is
supplied from a sulfuric-acid storage tank in the factory into the
inner tank 10 of the chemical-liquid mixing apparatus, it may occur
that a supply rate of a hydrogen peroxide solution is 5 liters/min,
while a supply rate of a sulfuric acid is only 1 to 2
liters/min.
[0017] Under this condition, since a ratio of the sulfuric acid
relative to the hydrogen peroxide solution is quite low, a
generation ratio of peroxomonosulfuric acid, which is to be
generated when a sulfuric acid and a hydrogen peroxide solution are
mixed with each other, becomes undesirably low, as shown in FIG. 7.
In this case, the chemical reaction represented by Formula (1)
takes place more actively than the chemical reaction represented by
Formula (2), and a sufficient amount of peroxomonosulfuric acid
cannot be generated. Thus, a resist cannot be fully removed from a
wafer.
[0018] Another example of a chemical-liquid mixing method is shown
in FIG. 8. FIG. 8(a) to FIG. 8(h) sequentially show steps of
another general chemical-liquid mixing method.
[0019] The chemical-liquid mixing apparatus used in the chemical
liquid mixing steps shown in FIG. 8 is identical to the
chemical-liquid mixing apparatus shown in FIG. 6, excluding that a
hydrogen peroxide solution is not supplied into an inner tank but
into an outer tank.
[0020] As shown in FIG. 8(a), the inner tank and the outer tank are
empty in their initial states. A return pump and a heater are
OFF.
[0021] At first, as shown in FIG. 8(b), a sulfuric-acid supply
valve is opened, and a sulfuric acid is supplied into the inner
tank so as to fill the inner tank. Then, as shown in FIG. 8(c), the
sulfuric-acid supply valve is closed, and a
hydrogen-peroxide-solution supply valve is opened to supply a
hydrogen peroxide solution into the outer tank. Thereafter, as
shown in FIG. 8(d), the hydrogen-peroxide-solution supply valve is
closed, and the sulfuric-acid supply valve is again opened to
further supply a sulfuric acid into the inner tank. Since the inner
tank has been already filled up with the sulfuric acid, the
sulfuric acid overflows to the outer tank so that the sulfuric acid
and the hydrogen peroxide solution are mixed with each other in the
outer tank.
[0022] Subsequently, as shown in FIG. 8(e), the sulfuric-acid
supply valve is again closed, and the return pump is switched on.
Thus, the liquid in the outer tank is returned to the inner tank,
and the liquid in the inner tank overflows to the outer tank.
Namely, the liquid is circulated through the combination unit of
the inner tank and the outer tank. After a passage of a certain
period of time, as shown in FIG. 8(f), the return pump is
temporarily made OFF, and the sulfuric-acid supply valve is opened
to supply a certain amount of a sulfuric acid into the inner tank.
Then, as shown in FIG. 8(g), the sulfuric-acid supply valve is
again closed, and simultaneously therewith the return pump is
switched on so as to circulate the liquid again. Finally, after a
previously set time period has passed, as shown in FIG. 8(h), the
heater is switched on to heat the liquid passing through the return
pipe. Thus, a temperature of the liquid in the inner tank is raised
to a temperature suitable for cleaning wafers (e.g., 100.degree. C.
to 150.degree. C.).
[0023] However, even in the chemical-liquid mixing method shown in
FIG. 8, a ratio of the sulfuric acid relative to the hydrogen
peroxide solution is low in the outer tank, a peroxomonosulfuric
acid cannot be sufficiently generated. In other words, there still
occurs the problem in that a resist cannot be fully removed from a
wafer.
[0024] The present invention has been made in view of the above.
The object of the present invention is to provide a chemical-liquid
mixing method and a chemical-liquid mixing apparatus capable of
generating an enough peroxomonosulfuric acid which is effective in
removing a resist from a substrate, when a sulfuric acid and a
hydrogen peroxide solution are mixed with each other.
[0025] The chemical-liquid mixing method according to the present
invention is a chemical-liquid mixing method for mixing a sulfuric
acid and a hydrogen peroxide solution, the method comprising the
steps of: preparing respectively an inner tank; an outer tank
disposed around the inner tank, into which outer tank a liquid
overflowing from the inner tank flows; a return pipe configured to
return the liquid in the outer tank to the inner tank; and a return
pump provided on the return pipe for sending the liquid in the
outer tank to the inner tank; supplying a sulfuric acid into the
inner tank for filling the inner tank with the sulfuric acid, and
allowing the sulfuric acid overflowing from the inner tank to flow
into the outer tank; supplying a hydrogen peroxide solution into
the inner tank or the outer tank, after the sulfuric-acid supplying
step, and allowing the hydrogen peroxide solution to flow into the
outer tank to store in the outer tank the two kinds of liquids of
the hydrogen peroxide solution and the sulfuric acid; and
activating the return pump simultaneously with the start of the
hydrogen-peroxide-solution supplying step to simultaneously send to
the inner tank the two kinds of liquids of the hydrogen peroxide
solution and the sulfuric acid in the outer tank, while mixing the
hydrogen peroxide solution and the sulfuric acid with each
other.
[0026] In addition, the chemical-liquid mixing apparatus according
to the present invention is a chemical-liquid mixing apparatus for
mixing a sulfuric acid and a hydrogen peroxide solution, the
apparatus comprising: an inner tank; an outer tank disposed around
the inner tank, into which outer tank a liquid overflowing from the
inner tank flows; a return pipe configured to return the liquid in
the outer tank to the inner tank; and a return pump provided on the
return pipe for sending the liquid in the outer tank to the inner
tank; a sulfuric-acid supply unit configured to supply a sulfuric
acid into the inner tank; a hydrogen-peroxide-solution supply unit
configured to supply a hydrogen peroxide solution to the inner tank
or the outer tank; and a controller configured to control the
sulfuric-acid supply unit, the hydrogen-peroxide-solution supply
unit, and the return pump, the controller controlling at first the
sulfuric-acid supply unit to fill the inner tank with a sulfuric
acid, allowing the sulfuric acid overflowing from the inner tank to
flow into the outer tank, then the controller controlling the
hydrogen-peroxide-solution supply unit to supply a hydrogen
peroxide solution into the inner tank or the outer tank, allowing
the hydrogen peroxide solution to flow into the outer tank whereby
the two kinds of liquids of the hydrogen peroxide solution and the
sulfuric acid are stored in the outer tank, and the controller
activating the return pump simultaneously with the start of the
activation of the hydrogen-peroxide-solution supply unit.
[0027] According to the chemical-liquid mixing method and the
chemical-liquid mixing apparatus, since the hydrogen peroxide
solution is added to the sulfuric acid which has been already
stored in the outer tank, a ratio of the sulfuric acid relative to
the hydrogen peroxide solution is increased in the outer tank.
Therefore, a generation ratio of a peroxomonosulfuric acid can be
elevated. Further, since the return pump is activated
simultaneously when the hydrogen peroxide solution flows into the
outer tank, there is performed a so-called stirring of the sulfuric
acid and the hydrogen peroxide solution in the return pipe. During
the stirring operation, since an amount of the hydrogen peroxide
solution is relatively small, generation of a peroxomonosulfuric
acid is further promoted in the return pipe. Therefore, a ratio of
the amount of peroxomonosulfuric acid contained in a finally
produced mixture liquid of the sulfuric acid and the hydrogen
peroxide solution is increased. As a result, a mixture liquid that
is effective in removing a resist from a substrate can be
provided.
[0028] In the chemical-liquid mixing method according to the
present invention, it is preferable that a heater is provided on
the return pipe, and that a heater activating step for activating
the heater is performed after a preset period of time has passed
from the start of the return-pump activating step.
[0029] In the chemical-liquid mixing apparatus according to the
present invention, it is preferable that a heater is provided on
the return pipe, and that the controller controls the heater such
that the heater is activated after a preset period of time has
passed from the activation of the return pump.
[0030] In generating a peroxomonosulfuric acid by mixing a sulfuric
acid and a hydrogen peroxide solution with each other, if
temperatures of the liquids which have not been mixed yet are
excessively high, a peroxomonosulfuric acid cannot be sufficiently
generated. However, since there is an enough period of time in
which the return pump is operated while the heater is not operated,
in other words, since there is a period of time in which only a
circulation of the liquids is performed, an enough amount of
peroxomonosulfuric acid can be generated.
[0031] Preferably, the chemical-liquid mixing method according to
the present invention further comprises a
hydrogen-peroxide-solution replenishing step for replenishing a
hydrogen peroxide solution by a hydrogen-peroxide-solution
replenishing pipe that is communicated with the return pipe.
[0032] In the chemical-liquid mixing apparatus according to the
present invention, it is preferable that a
hydrogen-peroxide-solution replenishing pipe for replenishing a
hydrogen peroxide solution is arranged in communication with the
return pipe.
[0033] With this structure, when a hydrogen peroxide solution is
replenished, the hydrogen peroxide solution is directly sent to the
return pipe. Thus, a so-called stirring of the replenished hydrogen
peroxide solution and the sulfuric acid is performed in the return
pipe. During the stirring operation, since an amount of the
hydrogen peroxide solution is relatively small, an enough
peroxomonosulfuric acid can be generated in the return pipe.
Therefore, a ratio of the amount of a peroxomonosulfuric acid
generated by the replenishment of the hydrogen peroxide solution is
increased. As a result, a resist removing efficiency of the mixture
liquid can be maintained.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] FIG. 1 is a schematic structural view showing a structure of
a chemical-liquid mixing apparatus in one embodiment of the present
invention;
[0035] FIG. 2 is a top view showing an inner tank and an outer tank
in the chemical-liquid mixing apparatus shown in FIG. 1;
[0036] FIG. 3 shows views (a) to (f) illustrating sequential steps
of a chemical-liquid mixing method carried out by the
chemical-liquid mixing apparatus shown in FIG. 1;
[0037] FIG. 4 is a top view showing an inner tank and an outer tank
in another embodiment of the chemical-liquid mixing apparatus shown
in FIG. 1;
[0038] FIG. 5 is a structural view showing still another embodiment
of the chemical-liquid mixing apparatus shown in FIG. 1;
[0039] FIG. 6 is a schematic structural view showing a structure of
a conventional chemical-liquid mixing apparatus;
[0040] FIG. 7 is a graph in which a horizontal axis shows a ratio
(molar ratio) of a sulfuric acid relative to a hydrogen peroxide
solution, and a vertical axis shows a generation ratio of a
peroxomonosulfuric acid;
[0041] FIG. 8 shows views (a) to (h) illustrating sequential steps
of a conventional chemical-liquid mixing method; and
[0042] FIG. 9 shows a view (a) illustrating a condition of residue
of a resist on a cleaned wafer of Present Example, and a view (b)
illustrating a condition of residues of a resist on a cleaned wafer
of Comparative Example.
BEST MODE FOR CARRYING OUT THE INVENTION
[0043] An embodiment of the present invention will be described
below with reference to the accompanying drawings. FIGS. 1 to 3 are
views showing a chemical-liquid mixing apparatus in one embodiment
according to the present invention. FIG. 1 is a schematic
structural view showing a structure of the chemical-liquid mixing
apparatus in this embodiment. FIG. 2 is a top view showing an inner
tank and an outer tank in the chemical-liquid mixing apparatus
shown in FIG. 1. FIG. 3 shows views (a) to (f) illustrating
sequential steps of a chemical-liquid mixing method carried out by
the chemical-liquid mixing apparatus shown in FIG. 1.
[0044] In FIGS. 1 to 3, the same members as those in the
conventional chemical-liquid mixing apparatus shown in FIG. 6 are
depicted by the same reference numbers as those in FIG. 6.
[0045] As shown in FIG. 1, the chemical-liquid mixing apparatus in
this embodiment includes an inner tank 10 in which a wafer W is
accommodated, and an outer tank 12 disposed around the inner tank
10, into which a liquid overflowing from the inner tank 10 flows.
There is disposed a return pipe 14 for returning the liquid in the
outer tank 12 into the inner tank 10. In the return pipe 14, there
are serially arranged a return pump 16 for sending a liquid in the
outer tank 12 to the inner tank 10, a dumper 18 for reducing
vibrations or the like of the return pipe 14, a heater 20 for
heating a liquid passing through the return pipe 14, and a filter
22 for filtering a liquid passing through the return pipe 14. The
chemical-liquid mixing apparatus also includes a sulfuric-acid
storage tank 24 for storing a sulfuric acid (H.sub.2SO.sub.4), and
a hydrogen-peroxide-solution storage tank 30 for storing a hydrogen
peroxide (H.sub.2O.sub.2) solution, The sulfuric acid and the
hydrogen peroxide solution stored in the respective storage tanks
24 and 30 are supplied into the inner tank 10 by a sulfuric-acid
supply pipe 28 and a hydrogen-peroxide-solution supply pipe 34,
respectively. Supply operations of the respective chemical liquids
are adjusted by a sulfuric-acid supply valve 26 and a
hydrogen-peroxide-solution supply valve 32, respectively. Further,
the chemical-liquid mixing apparatus includes a controller 40 that
controls the return pump 16, the heater 20, the sulfuric-acid
supply valve 26, and the hydrogen-peroxide-solution supply valve
32.
[0046] Herebelow, the respective components of the chemical-liquid
mixing apparatus are described in detail with reference to FIGS. 1
and 2.
[0047] As shown in FIG. 2, the inner tank 10 is of substantially a
rectangular solid shape. The outer tank 12 is also of substantially
a rectangular solid shape which is larger than the inner tank 10.
The outer tank 12 is disposed to surround the circumference of the
inner tank 10. As described above, a liquid overflowing from the
inner tank 10 is sent to the outer tank 12. The return pipe 14 is
diverged into two parts whose ends are connected to a bottom of the
inner tank 10. Thus, a liquid sent from the return pipe 14 can
enter the inner tank 10 through the bottom thereof. As shown in
FIG. 2, the inner tank 10 is provided with a pair of wafer holders
10a for holding a plurality of wafers W that are arranged in
order.
[0048] As shown in FIGS. 1 and 2, an intake 14a of the return pipe
14 is connected to a bottom of the outer tank 12. A sulfuric-acid
supply port 28a of the sulfuric-acid supply pipe 28 is positioned
above the inner tank 10 near a side periphery thereof. A
hydrogen-peroxide-solution supply port 34a of the
hydrogen-peroxide-solution supply pipe 34 is positioned above the
inner tank 10 near a corner thereof.
[0049] As shown in FIG. 1, the sulfuric-acid storage tank 24, the
sulfuric-acid supply valve 26, and the sulfuric-acid supply pipe 28
constitute a sulfuric-acid supply unit for supplying a sulfuric
acid into the inner tank 10. On the other hand, the
hydrogen-peroxide-solution storage tank 30, the
hydrogen-peroxide-solution supply valve 32, and the
hydrogen-peroxide-solution supply pipe 34 constitute a
hydrogen-peroxide-solution supply unit for supplying a hydrogen
peroxide solution into the inner tank 10.
[0050] As shown in FIG. 1, the controller 40 is connected to and
communicated with the return pump 16, the heater 20, the
sulfuric-acid supply valve 26, and the hydrogen-peroxide-solution
supply valve 32. The controller 40 controls each of these members
by sending control signals thereto. Specifically, the controller 40
opens at first the sulfuric-acid supply valve 26 to fill the inner
tank 10 with a sulfuric acid, so that the overflowing sulfuric acid
from the inner tank 10 flows into the outer tank 12. Then, the
controller 40 opens the hydrogen-peroxide-solution supply valve 32
to supply a hydrogen peroxide solution into the inner tank 10, so
that the hydrogen peroxide solution flows into the outer tank 12,
whereby the two kinds of liquids, i.e., the hydrogen peroxide
solution and the sulfuric acid, are stored in the outer tank 12.
Then, the controller 40 opens the hydrogen-peroxide-solution supply
valve 32, and simultaneously activates the return pump 16. In
addition, the controller 40 activates the heater 20 after an elapse
of a preset period (e.g., 15 minutes) from the activation of the
return pump 16. Details of the control operations by the controller
40 are described hereafter.
[0051] Next, operations of the chemical-liquid mixing apparatus in
this embodiment are described. Specifically, with reference to FIG.
3, there is described a method of producing a mixture liquid by
using the above chemical-liquid mixing apparatus shown in FIG. 1
and so on.
[0052] As shown in FIG. 3(a), the inner tank 10 and the outer tank
12 are empty in their initial states. At this time, the return pump
16 and the heater are in OFF state, p At first, as shown in FIG.
3(b), while the return pump 16 and the heater 20 are kept OFF, the
sulfuric-acid supply valve 26 is opened by a control command from
the controller 40 so as to supply a sulfuric acid into the inner
tank 10. The supply of the sulfuric acid is continued until the
inner tank 10 is filled up with the sulfuric acid and the sulfuric
acid overflows into the outer tank 12.
[0053] Then, as shown in FIG. 3(c), in accordance with a control
command from the controller 40, the sulfuric-acid supply valve 26
is closed, and the hydrogen-peroxide-solution supply valve 32 is
opened so as to supply a hydrogen peroxide solution into the inner
tank 10. Since the hydrogen-peroxide-solution supply port 34a of
the hydrogen-peroxide-solution supply pipe 34 is positioned near
the corner of the inner tank 10, a hydrogen peroxide solution
falling into the inner tank 10 by gravity from the
hydrogen-peroxide-solution supply port 34a immediately overflows
into the outer tank 12. In this manner, the hydrogen peroxide
solution flows into the outer tank 12, and thus the two kinds of
liquids of the hydrogen peroxide solution and the sulfuric acid are
stored in the outer tank 12.
[0054] As shown in FIG. 3(d), the hydrogen-peroxide-solution supply
valve 32 is closed by a control command from the controller 40.
Simultaneously, the controller 40 activates the return pump 16.
Thus, while the hydrogen peroxide solution is being continuously
supplied into the outer tank 12, the two kinds of liquids of the
hydrogen peroxide solution and the sulfuric acid are withdrawn from
the outer tank 12 by the return pump 16 through the return pipe 14.
In this manner, the liquid is circulated through the combination
unit of the inner tank 10 and the outer tank 12. At this time,
there is performed a so-called stirring of the two kinds of liquids
of the hydrogen peroxide solution and the sulfuric acid, in the
return pipe 14 by the return pump 16, whereby the two kinds of
liquids are mixed with each other.
[0055] Subsequently, as shown in FIG. 3(e), when the mixture liquid
reaches a certain level in the outer tank 12, the
hydrogen-peroxide-solution supply valve 32 is closed by a control
command from the controller 40 to stop the supply of the hydrogen
peroxide solution. However, the operation of the return pump 16 is
continued so that the liquid is continuously circulated through the
combination unit of the inner tank 10 and the outer tank 12. Due to
the circulation of the liquid, the mixture operation of the
hydrogen peroxide solution and the sulfuric acid is consecutively
carried out.
[0056] Finally, as shown in FIG. 3(f), after an elapse of a preset
period (e.g.,15 minutes) from the activation of the return pump 16,
the controller 40 activates the heater 20. Thus, the liquid passing
through the return pipe 14 is heated, and a temperature of the
liquid in the inner tank 10 is raised at a temperature suitable for
cleaning wafers W, specifically, 100.degree. C. to 150.degree. C.,
for example.
[0057] At last, when the temperature of the liquid in the inner
tank 10 reaches a certain temperature, the controller 40 stops the
return pump 16 and the heater 20. Following thereto, a plurality of
wafers W are all together immersed into the inner tank 10, to
decompose a resist adhering to each wafer by the mixture liquid of
the sulfuric acid and the hydrogen peroxide solution, more
specifically a peroxomonosulfuric acid generated by mixing the
sulfuric acid and the hydrogen peroxide solution, to thereby remove
the resist from the wafer. In this manner, a series of steps for
cleaning the wafers is completed.
[0058] According to the chemical-liquid mixing method and the
chemical-liquid mixing apparatus in this embodiment, the inner tank
10 is firstly filled up with a sulfuric acid, and the sulfuric acid
overflowing from the inner tank 10 flows into the outer tank 12.
Then, by supplying a hydrogen peroxide solution into the inner tank
10, the hydrogen peroxide solution flows into the outer tank 12,
whereby the two kinds of liquids of the hydrogen peroxide solution
and the sulfuric acid are stored in the outer tank 12. The return
pump 16 is activated simultaneously when the hydrogen peroxide
solution flows into the outer tank 12. Since the hydrogen peroxide
solution is added to the sulfuric acid which has been already
stored in the outer tank 12, a ratio of the sulfuric acid relative
to the hydrogen peroxide solution is increased in the outer tank
12. Therefore, a generation ratio of a peroxomonosulfuric acid can
be elevated. Further, since the return pump 16 is activated
simultaneously when the hydrogen peroxide solution flows into the
outer tank 12, there is performed a so-called stirring of the
sulfuric acid and the hydrogen peroxide solution in the return pipe
14. During the stirring operation, since an amount of the hydrogen
peroxide solution is relatively small, generation of a
peroxomonosulfuric acid is further promoted in the return pipe 14.
Therefore, a ratio of the amount of peroxomonosulfuric acid
contained in a finally produced mixture liquid of the sulfuric acid
and the hydrogen peroxide solution is increased. As a result, a
mixture liquid that is effective in removing a resist from a
substrate can be provided.
[0059] In addition, the return pipe 14 is provided with the heater
20 which is activated after a preset period has elapsed from the
activation of the return pump 16. In generating a
peroxomonosulfuric acid by mixing a sulfuric acid and a hydrogen
peroxide solution with each other, if temperatures of the liquids
which have not been mixed yet are excessively high, a
peroxomonosulfuric acid cannot be sufficiently generated. However,
since there is an enough period of time in which the return pump 16
is operated while the heater 20 is not operated, in other words,
since there is a period of time in which only a circulation of the
liquids is performed, an enough amount of peroxomonosulfuric acid
can be generated.
[0060] The chemical-liquid mixing method and the chemical-liquid
mixing apparatus are not limited to the above embodiment, and
various changes and modifications are possible. For example, in
place of using the sulfuric-acid supply valve 26 and the
hydrogen-peroxide-solution supply valve 32 shown in FIG. 1 as the
sulfuric-acid supply unit and the hydrogen-peroxide-solution supply
unit, supply pumps may be respectively provided on the
sulfuric-acid supply pipe 28 and the hydrogen-peroxide-solution
supply pipe 34 so as to supply a sulfuric acid and a hydrogen
peroxide solution by these supply pumps from the sulfuric-acid
storage tank 24 and the hydrogen-peroxide-solution storage tank 30,
respectively. In this case, the controller 40 controls these supply
pumps, in place of controlling the sulfuric-acid supply valve 26
and the hydrogen-peroxide-solution supply valve 32.
[0061] Further, in place of positioning the
hydrogen-peroxide-solution supply port 34a of the
hydrogen-peroxide-solution supply pipe 34 above the inner tank 10,
the hydrogen-peroxide-solution supply port 34a may be positioned
above the outer tank 12, which is shown in FIG. 4. In this case, a
hydrogen peroxide solution can be directly supplied from the
hydrogen-peroxide-solution storage tank 30 into the outer tank
12.
[0062] An amount of a peroxomonosulfuric acid contained in the
mixture liquid is decreased by repeating the wafer cleaning
process. In order to cope with this, the present method may further
include a hydrogen-peroxide-solution replenishing step for
replenishing a hydrogen peroxide solution. A hydrogen peroxide
solution is replenished through a hydrogen-peroxide-solution
replenishing pipe 36 shown in FIG. 5. One end of the
hydrogen-peroxide-solution replenishing pipe 36 is communicated
with the hydrogen-peroxide-solution storage tank 30, and the other
end thereof passes through the outer tank 12 to extend into an
inside of the return pipe 14. The hydrogen-peroxide-solution
replenishing pipe 36 is provided with a hydrogen-peroxide-solution
replenishing valve 38 for switching on and off the replenishment of
a hydrogen peroxide solution.
[0063] Since the other end of the hydrogen-peroxide-solution
replenishing pipe 36 reaches the inside of the return pipe 14, when
a hydrogen peroxide solution is replenished, the hydrogen peroxide
solution transferred from the hydrogen-peroxide-solution storage
tank 30 is directly sent to the return pipe 14. Thus, a so-called
stirring of the replenished hydrogen peroxide solution and the
sulfuric acid is performed in the return pipe 14. During the
stirring operation, since an amount of the hydrogen peroxide
solution is relatively small, an enough peroxomonosulfuric acid can
be generated in the return pipe 14. Therefore, a ratio of the
amount of a peroxomonosulfuric acid generated by the replenishment
of the hydrogen peroxide solution is increased. As a result, a
resist removing efficiency of the mixture liquid can be
maintained.
EXAMPLE
[0064] Next, a Present Example of the chemical-liquid mixing method
and the chemical-liquid mixing apparatus as shown in FIGS. 1 to 3
is described below. A Comparative Example of a chemical-liquid
mixing method as shown in FIG. 8 is described for comparison.
Present Example
[0065] A chemical-liquid mixing apparatus as shown in FIG. 1 was
prepared. The chemical-liquid mixing apparatus includes an inner
tank 10 in which a wafer W is accommodated, and an outer tank 12
disposed around a circumference of the inner tank 10, into which a
liquid overflowing from the inner tank 10 flows. There is disposed
a return pipe 14 for returning the liquid in the outer tank 12 into
the inner tank 10. In the return pipe 14, there are serially
arranged a return pump 16 for returning a liquid in the outer tank
12 to the inner tank 10, a dumper 18 for reducing vibrations or the
like of the return pipe 14, a heater 20 for heating a liquid
passing through the return pipe 14, and a filter 22 for filtering a
liquid passing through the return pipe 14.
[0066] The chemical-liquid mixing apparatus In the Present Example
also includes a sulfuric-acid storage tank 24 for storing a
sulfuric acid (H.sub.2SO.sub.4), and a hydrogen-peroxide-solution
storage tank 30 for storing a hydrogen peroxide (H.sub.2O.sub.2)
solution. The sulfuric acid and the hydrogen peroxide solution
stored in the respective storage tanks 24 and 30 are supplied into
the inner tank 10 by a sulfuric-acid supply pipe 28 and a
hydrogen-peroxide-solution supply pipe 34, respectively. A
concentration of the sulfuric acid was 98 wt %, and a concentration
of the hydrogen peroxide solution was 30 wt %. Supply operations of
the respective chemical liquids are adjusted by a sulfuric-acid
supply valve 26 and a hydrogen-peroxide-solution supply valve 32,
respectively. A supply rate of the sulfuric acid supplied by the
sulfuric-acid supply unit was 4 liters/min, and a supply rate of
the hydrogen peroxide solution by the hydrogen-peroxide-solution
supply unit was 1 liter/min.
[0067] The chemical-liquid mixing apparatus in the Present Example
further includes a controller 40 for controlling the return pump
16, the heater 20, the sulfuric-acid supply valve 26, and the
hydrogen-peroxide-solution supply valve 32. FIG. 3 shows control
operations of the controller 40, and details thereof are described
below.
[0068] As shown in FIG. 3(a), the inner tank and the outer tank
were empty in their initial states. At first, as shown in FIG.
3(b), while the return pump and the heater were kept OFF, the
sulfuric-acid supply valve was opened to supply a sulfuric acid
into the inner tank. The supply of the sulfuric acid was continued
until the inner tank was filled up with sulfuric acid and the
sulfuric acid overflowed into the outer tank.
[0069] Then, as shown in FIG. 3(c), the sulfuric-acid supply valve
was closed, and the hydrogen-peroxide-solution supply valve was
opened to supply a hydrogen peroxide solution into the inner tank.
At this time, the hydrogen peroxide solution falling from a
hydrogen-peroxide-solution supply port by gravity immediately
overflowed into the outer tank. In this manner, the hydrogen
peroxide solution flowed into the outer tank, and thus the two
kinds of liquids of the hydrogen peroxide solution and the sulfuric
acid were stored in the outer tank.
[0070] As shown in FIG. 3(d), the hydrogen-peroxide-solution supply
valve was opened, and the return pump was activated at the same
time. Thus, while the hydrogen peroxide solution was being
continuously supplied into the outer tank, the two kinds of liquids
of the hydrogen peroxide solution and the sulfuric acid were
withdrawn from the outer tank by the return pump through the return
pipe. In this manner, the liquids are circulated through the
combination of the inner tank and the outer tank, whereby the
hydrogen peroxide solution and the sulfuric acid were mixed with
each other.
[0071] Subsequently, as shown in FIG. 3(e), when an amount of the
liquid stored in the outer tank reached about 90 percent of a total
storage amount of the outer tank, the hydrogen-peroxide-solution
supply valve was closed to stop the supply of the hydrogen peroxide
solution. However, the return pump continued its operation so that
the liquids were continuously circulated through the combination
unit of the inner tank and the outer tank. Due to the circulation
of the liquids, the hydrogen peroxide solution and the sulfuric
acid were consecutively mixed with each other.
[0072] Finally, as shown in FIG. 3(f), after a passage of 10
minutes from the activation of the return pump, the heater was
activated. Thus, the liquid passing through the return pipe was
heated, and a temperature of the liquid in the inner tank was
raised at 100.degree. C. in the last place.
[0073] At last, the return pump and the heater were stopped.
Following thereto, a wafer was immersed into the inner tank so as
to remove a resist adhering to the wafer therefrom by the mixture
liquid of the sulfuric acid and the hydrogen peroxide solution.
FIG. 9(a) shows a condition of residues of a resist on the wafer
which had been immersed in the mixture liquid in the inner tank and
was taken up therefrom.
Comparative Example
[0074] Also in the Comparative Example, a chemical-liquid mixing
apparatus as shown in FIG. 1 was prepared. Volumes of an inner tank
10 and an outer tank 10 of the chemical-liquid mixing apparatus
were identical to those in the chemical-liquid mixing apparatus of
the Present Example. Similarly, structures of a return pipe and a
return pump 16, and structures of sulfuric-acid supply unit and
hydrogen-peroxide-solution supply unit were identical to those in
the chemical-liquid mixing apparatus of the Present Example.
However, control operations conducted by a controller 40 was
different from the method of the Present Example as shown in FIG.
3. The control operations in the Comparative Example are shown in
FIG. 8, which are described in detail below.
[0075] As shown in FIG. 8(a), the inner tank and the outer tank
were empty in their initial states, Under this condition, as shown
in FIG. 8(b), a sulfuric-acid supply valve was opened to supply a
sulfuric acid into the inner tank until the inner tank was filled
up with the sulfuric acid. Then, as shown in FIG. 8(c), the
sulfuric-acid supply valve was closed, and a
hydrogen-peroxide-solution supply valve was opened to supply a
hydrogen peroxide solution into the outer tank. After that, as
shown in FIG. 8(d), the hydrogen-peroxide-solution supply valve was
closed, and the sulfuric-acid supply valve was again opened to
supply a sulfuric acid into the inner tank. Since the inner tank
had been already filled up with the sulfuric acid, the sulfuric
acid overflowed into the outer tank where the sulfuric acid and the
hydrogen peroxide solution were mixed with each other.
[0076] Subsequently, as shown in FIG. 8(e), the sulfuric-acid
supply valve was again closed, and the return pump was switched on.
Thus, the liquid in the outer tank was returned to the inner tank
and the liquid in the inner tank overflowed into the outer tank,
whereby the liquid was circulated in the combination unit of the
inner tank and the outer tank. After about 10 minutes had passed,
as shown in FIG. 8(f), the return pump was temporarily made OFF,
and the sulfuric-acid supply valve was opened to supply a sulfuric
acid into the inner tank. Thereafter, as shown in FIG. 8(g), the
sulfuric-acid supply valve was again closed, and the return pump
was switched on so as to again circulate the liquid. Finally, after
a passage of about 10 minutes, as shown in FIG. 8(h), the heater
was switched on to heat the liquid passing through the return pipe.
Thus, a temperature of the liquid in the inner tank was raised at
100.degree. C.
[0077] At last, the return pump and the heater were stopped.
Following thereto, a wafer was immersed into the inner tank so as
to remove a resist adhering to the wafer therefrom by the mixture
liquid of the sulfuric acid and the hydrogen peroxide solution.
FIG. 9(b) shows a condition of residues of a resist on the wafer
which had been immersed in the mixture liquid in the inner tank and
was taken up therefrom.
[0078] As described above, a peroxomonosulfuric acid is generated
by mixing a sulfuric acid and a hydrogen peroxide solution.
However, a method of directly measuring an amount of the
peroxomonosulfuric acid has not been established yet. Thus, the
following method is generally carried out. Namely, a wafer to which
a resist adheres is immersed in a mixture liquid of a sulfuric acid
and a hydrogen peroxide solution in which a peroxomonosulfuric acid
is contained, and a relative amount of the peroxomonosulfuric acid
is estimated based on a degree of removal of the resist.
[0079] As described above, FIG. 9(a) and FIG. 9(b) show the
conditions of the residual resist on the cleaned wafers of the
Present Example and the Comparative Example. In the drawings, the
black particles depict residues of the resist. When FIG. 9(a) and
FIG. 9(b) are compared to each other, it can be understood that an
amount of the resist (an amount of the residual resist) remaining
on the wafer of the Present Example is significantly smaller than
that of the wafer of the Comparative Example. That is to say, as
compared with the chemical-liquid mixing method of the Comparative
Example, it can be seen that the chemical-liquid mixing method of
the Present Example can remove a larger amount of the resist when
the wafer is immersed in the mixture liquid. Therefore, it was
found that a peroxomonosulfuric acid that is effective in removing
a resist from a substrate can be sufficiently generated with the
use of the chemical-liquid mixing method and the chemical-liquid
mixing apparatus of the Present Example.
* * * * *