U.S. patent application number 11/080272 was filed with the patent office on 2005-09-29 for stack structure and method of manufacturing the same.
This patent application is currently assigned to Casio Computer Co., Ltd.. Invention is credited to Nakamura, Osamu, Nomura, Masatoshi, Takeyama, Keishi, Terazaki, Tsutomu.
Application Number | 20050212111 11/080272 |
Document ID | / |
Family ID | 34964039 |
Filed Date | 2005-09-29 |
United States Patent
Application |
20050212111 |
Kind Code |
A1 |
Terazaki, Tsutomu ; et
al. |
September 29, 2005 |
Stack structure and method of manufacturing the same
Abstract
A stack structure is formed by stacking and bonding a plurality
of substrates. The stack structure includes. Bonding films each of
which is interposed in a bonding region between, adjacent glass
substrates, and bonded to oxygen atoms in the glass of the
substrate by anodic bonding.
Inventors: |
Terazaki, Tsutomu;
(Fussa-shi, JP) ; Nakamura, Osamu; (Kodaira-shi,
JP) ; Takeyama, Keishi; (Hamura-shi, JP) ;
Nomura, Masatoshi; (Fussa-shi, JP) |
Correspondence
Address: |
FRISHAUF, HOLTZ, GOODMAN & CHICK, PC
220 5TH AVE FL 16
NEW YORK
NY
10001-7708
US
|
Assignee: |
Casio Computer Co., Ltd.
Tokyo
JP
|
Family ID: |
34964039 |
Appl. No.: |
11/080272 |
Filed: |
March 14, 2005 |
Current U.S.
Class: |
257/686 |
Current CPC
Class: |
B81C 2201/019 20130101;
B81C 2203/031 20130101; B81C 1/00119 20130101; B81B 2201/058
20130101 |
Class at
Publication: |
257/686 |
International
Class: |
H01L 021/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 23, 2004 |
JP |
2004-084846 |
Mar 23, 2004 |
JP |
2004-084907 |
Mar 23, 2004 |
JP |
2004-084939 |
Claims
What is claimed is:
1. A stack structure formed by stacking and bonding a plurality of
substrates, comprising: a bonding film which is interposed in a
bonding region between, of the plurality of substrates, a first
substrate and a second substrate containing glass, and bonded to
oxygen atoms in the glass of the second substrate by anodic
bonding.
2. A stack structure according to claim 1, wherein the bonding film
contains a material having one of a metal and an alloy whose
melting point is at least 2,000.degree. C. when the bonding film is
not bonded to oxygen by anodic bonding.
3. A stack structure according to claim 1, wherein the bonding film
has a material containing at least one of Ta, W, Mo, TaSi.sub.2,
WSi.sub.2, and MoSi.sub.2 when the bonding film is not bonded to
oxygen by anodic bonding.
4. A stack structure according to claim 1, further comprising a
buffer film which is interposed between the oxidized bonding film
and the first substrate and has a resistivity lower than the
plurality of substrates.
5. A stack structure according to claim 1, wherein at least one of
the first substrate and second substrate has a space in which a
chemical reaction occurs.
6. A stack structure according to claim 1, wherein the glass of the
second substrate contains alkali alone.
7. A stack structure according to claim 1, wherein the glass of the
second substrate is doped with at least one of sodium oxide,
lithium oxide, potassium oxide, and lithium carbonate.
8. A stack structure according to claim 1, further comprising a
bonding film which is interposed between, of the plurality of
substrates, the second substrate and a third substrate containing
glass, and bonded to oxygen atoms in the glass of the third
substrate by anodic bonding.
9. A stack structure according to claim 1, wherein the first
substrate comprises a glass substrate.
10. A stack structure according to claim 1, further comprising a
reformer which has, in the plurality of substrates, a space in
which a reforming reaction occurs.
11. A stack structure formed by stacking and bonding a plurality of
substrates including at least a glass substrate, comprising: a
buffer film which is interposed in a bonding region of the glass
substrate of the plurality of substrates and receives an alkali
component in the glass substrate, which has moved due to a voltage
applied to the glass substrate.
12. A stack structure according to claim 11, wherein the buffer
film has a material having a resistivity lower than the glass
substrate.
13. A stack structure according to claim 11, wherein the buffer
film has an amorphous oxide.
14. A stack structure according to claim 11, wherein at least one
of a compound containing Ta, Si, and O as component elements, a
compound containing La, Sr, Mn, and O as component elements, and
lead glass is used as the buffer film.
15. A stack structure according to claim 11, wherein the buffer
film is interposed on an entire bonding surface between the glass
substrate and another substrate.
16. A stack structure according to claim 11, further comprising a
reformer which has, in the plurality of substrates, a space in
which a reforming reaction occurs.
17. A method of manufacturing stack structure including a plurality
of substrates, comprising: executing anodic bonding to bond a
bonding film which is interposed between, of the plurality of
substrates, a first substrate and a second substrate containing
glass to oxygen atoms in the glass of the second substrate.
18. A stack structure manufacturing method according to claim 17,
further comprising executing anodic bonding to bond a bonding film
which is interposed between, of the plurality of substrates, the
second substrate and a third substrate containing glass to oxygen
atoms in the glass of the second substrate.
19. A stack structure manufacturing method according to claim 18,
wherein a direction of an electric field in anodic bonding between
the first substrate and the second substrate is the same as a
direction of an electric field in anodic bonding between the second
substrate and the third substrate.
20. A stack structure manufacturing method according to claim 18,
wherein anodic bonding between the first substrate and the second
substrate and anodic bonding between the second substrate and the
third substrate are executed separately.
21. A stack structure manufacturing method according to claim 18,
wherein anodic bonding between the first substrate and the second
substrate and anodic bonding between the second substrate and the
third substrate are executed simultaneously.
22. A stack structure manufacturing method according to claim 17,
wherein anodic bonding between the first substrate and the second
substrate is executed by connecting a positive electrode of an
anodic bonding apparatus to the bonding film and a negative
electrode of the anodic bonding apparatus to the glass of the
second substrate.
23. A stack structure manufacturing method according to claim 17,
wherein the bonding film contains a material having one of a metal
and an alloy whose melting point is not less than 2,000.degree. C.
when the bonding film is not bonded to oxygen by anodic
bonding.
24. A stack structure manufacturing method according to claim 17,
wherein the bonding film has a material containing at least one of
Ta, W, Mo, TaSi.sub.2, WSi.sub.2, and MoSi.sub.2 when the bonding
film is not bonded to oxygen by anodic bonding.
25. A method of manufacturing a stack structure including a
plurality of substrates, comprising steps of: bringing one surface
of a glass substrate of the plurality of substrates into contact
with another substrate; and anodic-bonding the glass substrate to
the other substrate in a state in which a buffer film capable of
receiving an alkali component in the glass substrate is provided on
the other surface of the glass substrate.
26. A stack structure manufacturing method according to claim 25,
wherein anodic bonding is executed to make a potential on a side of
said one surface of the glass substrate higher than that on a side
of said other surface.
27. A stack structure manufacturing method according to claim 25,
wherein the buffer film has a material having a resistivity lower
than the glass substrate.
28. A stack structure manufacturing method according to claim 25,
wherein the buffer film contains an amorphous oxide.
29. A stack structure manufacturing method according to claim 25,
wherein at least one of a compound containing Ta, Si, and O as
component elements, a compound containing La, Sr, Mn, and O as
component elements, and lead glass is used as the buffer film.
30. A stack structure manufacturing method according to claim 25,
wherein the buffer film is interposed on an entire bonding surface
between the glass substrate and the other substrate.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from prior Japanese Patent Applications No. 2004-084846,
filed Mar. 23, 2004; No. 2004-084907, filed Mar. 23, 2004; and No.
2004-084939, filed Mar. 23, 2004, the entire contents of all of
which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a stack structure formed by
stacking a plurality of including at least one substrate substrates
and a method of manufacturing the same.
[0004] 2. Description of the Related Art
[0005] In recent years, small reactors called "microreactors" have
been developed and put into practical use. Microreactors are small
reactors which cause a plurality of kinds of reactants such as raw
materials, reagents, and fuels to react with each other while
mixing them. The microreactors are used for chemical reaction
experiments in the microdomain, drug developments, artificial organ
developments, genome/DNA analysis tools, and fundamental analysis
tools for micro-fluid engineering. A chemical reaction using a
microreactor has characteristic features different from those of a
normal chemical reaction using a beaker or flask. For example,
since the entire reactor is small, the heat exchange effectiveness
is very high, and temperature control can efficiently be executed.
For this reason, even a reaction which needs fine temperature
control or a reaction which requires abrupt heating or cooling can
easily be done.
[0006] More specifically, a microreactor has one or more channels
(flow paths) which make reactants to flow and a reactor (reaction
tank) in which the reactants react with each other. In Jpn. Pat.
Appln. KOKAI Publication No. 2001-228159, a silicon substrate in
which a trench is formed in a predetermined pattern and a PYREX
(registered trademark) substrate made of glass are stacked and
anodic-bonded, thereby forming a channel in the closed region
between the two substrates. The term "anodic bonding" indicates a
bonding technique. In this technique, a positive electrode is
arranged on the silicon substrate while a negative electrode is
arranged on the glass substrate in a hot environment. A high
voltage is applied between both electrodes to generate an electric
field in the glass substrate. Oxygen atoms in the glass substrate,
which have negative charges, are moved to the silicon substrate
side so that the oxygen atoms in the glass substrate are
interatomic-bond to silicon atoms in the silicon substrate at the
interface between the glass substrate and the silicon substrate.
This technique is known as excellent especially in substrate
bonding because substrates can be bonded without using any
adhesive, or substrates can be bonded in air.
[0007] An attempt has been made to alternately stack a plurality of
glass substrates and a plurality of silicon substrates and
anodic-bond them to create a microreactor having a stack structure.
In this case, it is difficult to bond silicon substrates to both
surfaces of a glass substrate. Hence, a stack structure can hardly
be manufactured. As shown in FIG. 12A, in the first anodic bonding
step, a silicon substrate 301 and glass substrate 302 are arranged
while making one surface 302a of the glass substrate 302 contact
one surface 301a of the silicon substrate 301. A voltage is applied
between them to generate an electric field in the direction of
solid arrows and cause bonding at the interface between the
surfaces 301a and 302a. Subsequently, in the second anodic bonding
step, as shown in FIG. 12B, a new silicon substrate 303 and the
glass substrate 302 are arranged while making one surface 303a of
the silicon substrate 303 contact the other surface 302b of the
glass substrate 302. A voltage is applied between the silicon
substrates to generate an electric field in the direction of solid
arrows. The direction of this electric field is reverse to the
direction (broken arrows in FIG. 12B) of the electric field in the
first anodic bonding step. This adversely affects the bonding
between the silicon substrate 303 and the other surface of the
glass substrate 302 which is anodic-bonded to the silicon substrate
301 in the first anodic bonding step.
BRIEF SUMMARY OF THE INVENTION
[0008] The present invention advantageously makes it possible to
easily manufacture a stack structure from at least three
substrates.
[0009] A stack structure according to a first aspect of the present
invention is a stack structure formed by stacking and bonding a
plurality of substrates, comprising:
[0010] a bonding film which is interposed in a bonding region
between, of the plurality of substrates, a first substrate and a
second substrate containing glass, and bonded to oxygen atoms in
the glass of the second substrate by anodic bonding.
[0011] According to the stack structure of this aspect, the bonding
film bonded to the oxygen atoms in the glass of the second
substrate by anodic bonding can satisfactorily be bonded between
the first substrate and the second substrate. When the bonding film
is provided on a predetermined surface of the substrate, the
electric field in anodic bonding between the surface and the
substrate containing glass can be set in a predetermined
direction.
[0012] A stack structure according to a second aspect of the
present invention is a stack structure formed by stacking and
bonding a plurality of substrates including at least a glass
substrate, comprising:
[0013] a buffer film which is interposed in a bonding region of the
glass substrate of the plurality of substrates and receives an
alkali component in the glass substrate, which has moved due to a
voltage applied to the glass substrate.
[0014] A stack structure manufacturing method according to a third
aspect of the present invention is a method of manufacturing stack
structure including a plurality of substrates, comprising:
[0015] executing anodic bonding to bond a bonding film which is
interposed between, of the plurality of substrates, a first
substrate and a second substrate containing glass to oxygen atoms
in the glass of the second substrate.
[0016] According to this manufacturing method, the bonding film
bonded to the oxygen atoms in the glass of the second substrate by
anodic bonding can satisfactorily be bonded between the first
substrate and the second substrate. When the bonding film is
provided on a predetermined surface of the substrate, the electric
field in anodic bonding between the surface and the substrate
containing glass can be set in a predetermined direction.
[0017] A stack structure manufacturing method according to a fourth
aspect of the present invention is a method of manufacturing a
stack structure including a plurality of substrates, comprising
steps of:
[0018] bringing one surface of a glass substrate of the plurality
of substrates into contact with another substrate; and
[0019] anodic-bonding the glass substrate to the other substrate in
a state in which a buffer film capable of receiving an alkali
component in the glass substrate is provided on the other surface
of the glass substrate.
[0020] In the manufacturing method according to the fourth aspect,
even when the alkali components in the glass substrate move to the
other surface side of the glass substrate due to the electric field
in anodic bonding, the buffer film receives the alkali components.
Hence, deposition of the alkali components on the other surface
side of the glass substrate can be suppressed.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0021] FIGS. 1A to 1D are sectional views showing steps in
manufacturing a stack microreactor according to an embodiment of
the present invention;
[0022] FIG. 2 is a sectional view for explaining a step executed
instead of FIG. 1C;
[0023] FIG. 3 is a sectional view showing a completed stack
microreactor;
[0024] FIGS. 4A to 4C are sectional views for illustrating steps in
manufacturing a stack microreactor according to another embodiment
of the present invention;
[0025] FIG. 5 is a graph showing the relationship between the
voltage and the distance from the surface of a buffer film 3;
[0026] FIG. 6 is a graph showing the relationship between time from
the start of anodic bonding and the current which flows between the
electrodes;
[0027] FIGS. 7A and 7B are sectional and plan views, respectively,
for illustrating a step in manufacturing a microreactor having a
stack structure;
[0028] FIG. 8 is a sectional view for illustrating a step next to
FIGS. 7A and 7B;
[0029] FIG. 9 is a sectional view for illustrating a step next to
FIG. 8;
[0030] FIG. 10 is a sectional view for illustrating a step next to
FIG. 9;
[0031] FIG. 11 is a sectional view of a completed microreactor 200;
and
[0032] FIGS. 12A and 12B are sectional views for illustrating an
anodic bonding step.
DETAILED DESCRIPTION OF THE INVENTION
[0033] The best mode for carrying out the present invention will be
described below with reference to the accompanying drawings.
Various kinds of limitations which are technically preferable in
carrying out the present invention are added to the embodiments to
be described below. However, the spirit and scope of the present
invention are not limited to the following embodiments and
illustrated examples.
First Embodiment
[0034] A method of manufacturing a first stack microreactor to
which the present invention is applied will be described with
reference to FIGS. 1A to 4.
[0035] As shown in FIG. 1A, an ionic conductive glass substrate 2
is prepared, which contains an alkali metal such as sodium,
lithium, or potassium by doping an alkali compound such as an
alkali oxide (e.g., sodium oxide (Na.sub.2O), lithium oxide
(Li.sub.2O), or potassium oxide (K.sub.2O)) or alkali carbonate
(e.g., lithium carbonate (Li.sub.2CO.sub.3)). Especially, glass
containing Li is preferably used because Li ions have a small
radius and therefore readily move in the glass in an electric
field. For example, PYREX (registered trademark) glass containing
Na atoms or a glass substrate containing Li atoms (SW-YY available
from ASAHI TECHNOGLASS CORPORATION) can be used as the glass
substrate 2.
[0036] As shown in FIG. 1B, a conductive buffer film 3 which has a
moderate alkali ionic permeability and a resistivity lower than
that of the glass substrate 2 and higher than that of a metal alone
is formed on an entire surface 2a of the glass substrate 2. A
bonding film 4 including a single-layered film made of a metal or
an alloy containing the metal, or a multilayered film thereof is
formed on the buffer film 3. A zigzag trench 2c is formed in the
other surface 2b of the glass substrate 2. When the other surface
2b is bonded to another glass substrate 2 (FIG. 1D) to be described
later, through the bonding film 4, the trench 2c forms a space
(flow path) where a chemical reaction occurs in a microreactor
having a closed upper surface. The width and depth of the flow path
are, e.g., 500 .mu.m or less.
[0037] The bonding film 4 is oxidized by oxygen atoms in the other
glass substrate 2 (FIG. 1D) to be described below and causes
covalent bond to the other glass substrate 2 so that the bonding
film 4 is anodic-bonded to the other glass substrate 2. Preferably,
the bonding film 4 exhibits a conductivity before oxidation to
easily make a current flow by anodic bonding, a low oxidation
progress speed at room temperature and atmospheric pressure, and a
moderate oxidation progress speed under anodizing conditions. As a
detailed material of the bonding film 4 before oxidation, a metal
or alloy having a melting point of 2,000.degree. C. or more is
preferably used. More specifically, the bonding film 4 preferably
contains at lease one of Ta (melting point: 2,990.degree. C.), W
(melting point: 3,400.degree. C.), Mo (melting point: 2,620.degree.
C.), TaSi.sub.2 (melting point: 2,200.degree. C.), WSi.sub.2
(melting point: 2,170.degree. C.), and MoSi.sub.2 (melting point:
2,050.degree. C.). A metal having a melting point lower than
2,000.degree. C. tends to be easily oxidized in air, and anodic
bonding must be executed in a vacuum atmosphere. This makes the
management and manufacturing process complicate and increases the
cost.
[0038] The buffer film 3 relaxes deposition of alkali ions in the
glass substrate 2, which are deposited as a deposite on the surface
of the glass substrate 2 by anodic bonding. The buffer film 3 is
preferably made of a conductive substance which has a resistivity
lower than that of the glass substrate 2 and, more particularly, a
resistivity of about 0 to 10 k.OMEGA..multidot.cm and an alkali
ionic permeability to contain alkali ions in the glass substrate 2
to some extent at the time of anodic bonding. An oxide can be used
as the buffer film 3. Especially, an amorphous (noncrystalline)
oxide is more preferable than a polycrystal. The reasons for this
are as follows. The interatomic distance in an amorphous oxide is
longer than that in a polycrystalline oxide. The alkali ions more
readily pass through the amorphous oxide than the polycrystalline
oxide. Since the grain boundary of a polycrystalline film has a
high resistance, and the field distribution readily becomes
nonuniform, an in-plane variation occurs in the bonding
reaction.
[0039] More specifically, a compound containing Ta, Si, and O as
component elements (to be referred to as a "Ta--Si--O based
material" hereinafter), a compound containing La, Sr, Mn, and O as
component elements at a composition ratio of
La:Sr:Mn:O=0.7:0.3:1:(3-x) (to be referred to as
La.sub.0.7Sr.sub.0.3MnO.sub.3-x hereinafter), or lead glass can be
used as the buffer film 3. In this case, 0.ltoreq.x<1. Both the
Ta--Si--O based material and La.sub.0.7Sr.sub.0.3MnO.sub.3-x are
amorphous oxides.
[0040] To form the buffer film 3 of the Ta--Si--O based material,
the glass substrate 2 is set in a sputtering apparatus as a coating
target. Sputtering is executed by using, as a target, a plate which
is made of Ta and contains Si in an atmosphere containing Ar gas
and O.sub.2 gas. In the sputtering step, when ions collide against
the target, secondary ions are emitted from the target. The emitted
secondary ions collide against the glass substrate 2 so that the
buffer film 3 of the Ta--Si--O based material is formed on the
lower surface of the glass substrate 2. Especially when the bonding
film 4 is made of Ta, the buffer film 3 of the Ta--Si--O based
material has an excellent bonding effect between them.
[0041] To form the buffer film 3 of
La.sub.0.7Sr.sub.0.3MnO.sub.3-x, first, each of lanthanum nitrate
(La(NO.sub.3).sub.3.6H.sub.2O), strontium nitrate
(Sr(NO.sub.3).sub.3), and manganese nitrate
(Mn(NO.sub.3).sub.3.6H.sub.2O) is dissolved separately in
1-methyl-2-pyrrolidone. The lanthanum nitrate solution, strontium
nitrate solution, and manganese nitrate solution are then mixed.
The prepared solution is applied to the surface of the glass
substrate 2. The glass substrate 2 whose surface with the applied
solution faces up is set in a vacuum desiccator. When a vacuum
pressure is set in the vacuum desiccator by using a vacuum pump,
the applied solution evaporates, and the viscosity increases. Next,
the glass substrate 2 is unloaded from the vacuum desiccator and
sets in an electric furnace. When a vacuum pressure is set in the
electric furnace, and the glass substrate 2 is heated therein, the
buffer film 3 of La.sub.0.7Sr.sub.0.3MnO.sub.3-x is formed.
[0042] A plurality of samples each having the buffer film 3 and
bonding film 4 sequentially formed on the surface 2a of the glass
substrate 2 are prepared in the above-described way.
[0043] As shown in FIG. 1C, a conductive silicon substrate 5 is
anodic-bonded to the other surface 2b of the glass substrate 2. At
this time, the negative pole of an anodic bonding apparatus 10 is
connected to the bonding film 4 through a conductive stage 8. The
positive pole of the anodic bonding apparatus 10 is connected to
the silicon substrate 5. A voltage is applied such that the
potential of the silicon substrate 5 becomes higher than that of
the bonding film 4. Since the bonding film 4 is formed on the
buffer film 3, the silicon substrate 5 has a higher potential than
the buffer film 3. The stage 8 serves as a resistive heating
element by itself or separately includes a heating element to heat
the glass substrate 2 to a predetermined temperature. The silicon
substrate 5 is pressed against the glass substrate 2 by using a
weight plate 9 which applies a load uniformly in the in-plane
direction. Then, a voltage is applied by the anodic bonding
apparatus 10 and the glass substrate 2 is heated to a predetermined
temperature such as 300.degree. C. to 400.degree. C. by the
heat-producing stage 8, thereby executing anodic bonding. Alkali
ions in the glass substrate 2 are attracted to the buffer film 3
near the negative electrode. Electrons in the glass substrate 2
concentrate to the surface 2b which is in contact with the silicon
substrate 5. Firm interatomic bond (covalent bond) occurs between
the glass substrate 2 and the silicon substrate 5 so that both
substrates 2, 5 are anodic-bonded. The silicon substrate 5 to be
used can be either a silicon amorphous silicon or a substrate made
of crystalline silicon such as single-crystal silicon or
polysilicon.
[0044] Since the buffer film 3 capable of receiving alkali ions is
formed on one surface 2a of the glass substrate 2, the alkali ions
in the glass substrate 2 are moderately dispersed into the buffer
film 3 through which the alkali ions pass at the time of anodic
bonding. Since the alkali ions are not localized at (entirely
distributed over) the interface between the glass substrate 2 and
the buffer film 3 or the interface between the buffer film 3 and
the bonding film 4, any bonding failure at these interfaces is
suppressed. In addition, since a solid body such as an oxide
composed of alkali ions is rarely deposited on the surface of the
bonding film 4, any adverse influence on the bonding effect on the
surface can be prevented.
[0045] As shown in FIG. 2, a glass substrate 6 having, on one
surface 6a, a bonding film 7 formed from a metal film, alloy film,
or a multilayered film thereof may be used in place of the silicon
substrate 5, and the surface 6a may be anodic-bonded to the glass
substrate 2 at 300.degree. C. to 400.degree. C. In this case, the
bonding film 7 is selected from the above-described materials of
the bonding film 4. The bonding films 4, 7 can use either the same
material composition or different material compositions. The
negative pole of the anodic bonding apparatus 10 electrically is
connected to the bonding film 4 of the glass substrate 2 through
the stage 8 (that is, a negative electrode (not shown)is attached
to the stage 8). The positive pole of the anodic bonding apparatus
10 is electrically connected to the bonding film 7 of the glass
substrate 6. A voltage is then applied such that the potential of
the bonding film 7 becomes higher than that of the bonding film 4.
The solid arrows in FIG. 2 indicate the direction of the electric
field by anodic bonding. When the substrate 6 made of glass is
used, a film like the buffer film 3 may be interposed between the
glass substrate 6 and the bonding film 7.
[0046] After the silicon substrate 5 or the bonding film 7 of the
glass substrate 6 is anodic-bonded to the first glass substrate 2,
as shown in FIG. 1D, the other or second glass substrate 2 which
has the buffer film 3 and bonding film 4 formed on one surface 2a
is placed on the precedingly bonded glass substrate 2 such that the
other surface 2b of the second glass substrate 2 comes into contact
with the bonding film 4 of the first glass substrate 2. Then, the
both substrates 2 are anodic-bonded at 300.degree. C. to
400.degree. C. The second glass substrate 2 is arranged such that
the surface of the bonding film 4 of the first glass substrate 2 is
partially exposed. The positive electrode of the anodic bonding
apparatus 10 is connected to the exposed surface of the bonding
film 4 of the first glass substrate 2. The negative electrode of
the anodic bonding apparatus 10 is connected to the bonding film 4
of the second glass substrate 2 through the conductive stage 8. A
voltage is then applied such that the potential of the new bonding
film 4 becomes higher than that of the preceding bonding film 4.
The broken arrows in FIG. 1D indicate the direction of the electric
field by the first anodic bonding (anodic bonding in FIG. 1C). The
solid arrows indicate the direction of the electric field by the
new anodic bonding. At the newly anodic-bonded interface, atoms
contained in the bonding film 4 of the first glass substrate 2 are
firmly bonded to oxygen atoms in the second glass substrate 2.
[0047] In this case, the subsequent anodic bonding can be executed
in the same electric field direction as that of the preceding
anodic bonding shown in FIG. 1C. For this reason, the bonding
effect in the precedingly anodic-bonded portion is not degraded by
the electric field in the subsequent anodic bonding.
[0048] When the other surface 2b of the second glass substrate 2 is
to be anodic-bonded to the bonding film 4 of the first glass
substrate 2, the bonding film 4 need not always be formed on the
second substrate 2. In this case, the negative electrode of the
anodic bonding apparatus 10 is connected to the buffer film 3 of
the second glass substrate 2 through the stage 8. The positive
electrode of the anodic bonding apparatus 10 is connected to the
exposed bonding film 4 of the first glass substrate 2. After anodic
bonding, the bonding film 4 is formed on the buffer film 3 of the
new glass substrate 2.
[0049] After that, the step shown in FIG. 1D is repeated to
sequentially stack and anodic-bond the plurality of glass
substrates 2 each having the buffer film 3 and bonding film 4, as
shown in FIG. 3. Anodic bonding is executed sequentially from the
upper glass substrate 2 to the lower glass substrate 2 in FIG. 3.
In this way, a stack microreactor 1 serving as a chemical reaction
furnace is completed by stacking the glass substrates 2. Referring
to FIG. 3, of the two adjacent glass substrates 2, the upper glass
substrate 2 has the buffer film 3 and bonding film 4 sequentially
formed on the surface on the side of the lower glass substrate 2.
The lower glass substrate 2 is anodic-bonded to the bonding film 4
of the upper glass substrate 2.
[0050] As another example of anodic bonding, the buffer film 3 is
arranged on the stage 8. Neither buffer film 3 nor bonding film 4
is formed on the surface 2a of the glass substrate 2 whose other
surface 2b should be anodic-bonded to the silicon substrate 5 or
glass substrate 6. The glass substrate 2 having the silicon
substrate 5 or glass substrate 6 thereon it is located on the stage
8 such that the surface 2a comes into contact with the buffer film
3. The negative pole of the anodic bonding apparatus 10 is
electrically connected to the buffer film 3 through the stage 8.
The positive pole of the anodic bonding apparatus 10 is
electrically connected to the silicon substrate 5 or the bonding
film 7 of the glass substrate 6. Anodic bonding may be executed in
this state. At this time, the deposite by alkali ions is rarely
produced on the stage 8 by the buffer film 3. After the bonding
film 4 is formed on the surface 2a of the preceding or first glass
substrate 2, which is almost free from the deposite, the new or
second glass substrate 2 is anodic-bonded to the surface 2a of the
first glass substrate 2.
[0051] Referring to FIG. 3, each glass substrate 2 is anodic-bonded
to the lower bonding film 4 by applying a voltage to make the
potential of the upper bonding film 4 (the silicon substrate 5 for
the uppermost glass substrate 2) higher than that of the lower
bonding film 4. Hence, in anodic bonding, an electric field
directed downward is applied to all glass substrates 2, as
indicated by the solid arrows. The arrows shown in FIG. 3 indicate
the direction of the electric field which acts in anodic bonding of
each glass substrate 2.
[0052] In the example shown in FIG. 3, the glass substrates 2 are
anodic-bonded one by one. Instead, as shown in FIGS. 4A to 4C, the
plurality of anodic-bonded glass substrates 2 may be anodic-bonded.
Referring to FIG. 4A, the first glass substrate 2 having the buffer
film 3 and bonding film 4 sequentially formed on one surface 2a is
placed on the conductive stage 8 such that the bonding film 4 comes
into contact with the stage 8. A second glass substrate 2' having
the buffer film 3 and bonding film 4 sequentially formed on one
surface 2a is placed on the other surface of the first glass
substrate 2 such that the bonding film 4 of the second glass
substrate 2' comes into contact with the first glass substrate 2. A
load is applied to the other surface 2b of the second glass
substrate 2' by the weight 9. In this state, the positive pole of
the anodic bonding apparatus 10 is electrically connected to the
exposed surface of the bonding film 4 provided on the side of the
surface 2a of the second glass substrate 2'. The negative pole of
the anodic bonding apparatus 10 is electrically connected to the
bonding film 4 provided on the first glass substrate 2 through the
conductive stage 8. The first anodic bonding is executed such that
an electric field is generated in the direction of solid arrow.
[0053] Subsequently, as shown in FIG. 4B, a third glass substrate
2" having the buffer film 3 and bonding film 4 provided on one
surface 2a is placed between the stage 8 and the first glass
substrate 2. At this time, the positive pole of the anodic bonding
apparatus 10 is electrically connected to the exposed bonding film
4 of the first glass substrate 2. The negative pole is electrically
connected to the bonding film 4 of the third glass substrate 2"
through the stage 8. In this state, the second anodic bonding is
executed. The direction of the electric field is the same as that
(broken arrow) in the first anodic bonding. A first substrate group
11 of the glass substrates 2, 2', and 2" bonded in this way is
formed.
[0054] After that, a second substrate group 11' formed by the first
anodic bonding and second anodic bonding, like the first substrate
group 11, is placed between the first substrate group 11 and the
stage 8. The positive pole of the anodic bonding apparatus 10 is
connected to the bonding film 4 provided on the second glass
substrate 2" of the first substrate group 11. The negative pole of
the anodic bonding apparatus 10 is connected to the bonding film 4
provided on the second glass substrate 2" of the second substrate
group 11' through the conductive stage 8. In this state, the third
anodic bonding is executed. The direction (solid arrows) of the
electric field at this time is the same as those (broken arrows) in
the first anodic bonding and second anodic bonding.
[0055] As described above, in this embodiment, the bonding film 4
which can be oxidized by oxygen atoms in the glass substrate 2 by
anodic bonding is formed on the side of the surface 2a to be
anodic-bonded. Hence, as shown in FIG. 1D, anodic bonding can be
executed by using the bonding film 4 as the positive electrode and
a portion of the new glass substrate 2 near the surface 2a as the
negative electrode. At this time, since a voltage is applied
between both surfaces of the new glass substrate 2, an electric
field is generated in the new glass substrate 2. However, the
electric field is rarely generated in the precedingly bonded glass
substrate 2. Especially, in bonding the new glass substrate 2, no
electric field is generated in the preceding glass substrate 2 in
the direction reverse to the electric field in the preceding anodic
bonding. When the bonding film 4 is formed on the surface opposite
to the bonding surface of the glass precedingly bonded substrate 2,
the new glass substrate 2 can be bonded to the precedingly bonded
glass substrate 2. In addition, since the electric fields in the
respective anodic bonding operations do not act in reverse
directions in the glass substrates 2, no discoloring occurs in the
glass substrates 2 due to reverse fields. For this reason, the
stack structure can easily be manufactured.
[0056] In addition, as shown in FIGS. 4A to 4C, of the
anodic-bonded glass substrates 2, the side to be newly
anodic-bonded, i.e., the surface 2a has the bonding film 4 which
can be oxidized by oxygen atoms in the glass substrate 2 by anodic
bonding. When anodic bonding is executed a plurality of number of
times, electric fields are directed in the same direction in the
respective anodic bonding operations. Hence, neither bonding
failure nor degradation in bonding effect occurs due to reverse
fields.
[0057] Of the anodic-bonded glass substrates 2, the side to be
newly anodic-bonded, i.e., the surface 2a has the buffer film 3.
Alkali ions in the glass substrate 2 are dispersed in the buffer
film 3 in the preceding anodic bonding. Hence, any deposition on
the interface between the buffer film 3 and the surface 2a to be
newly anodic-bonded or the surface of the buffer film 3 can be
suppressed. This can be explained as follows. As shown in FIG. 5,
immediately after anodic bonding, alkali compositions and oxygen in
the glass substrate 2 are ionized and serve as carriers so that a
small current flows in the glass substrate 2. Hence, an electric
field E.sub.a in the glass substrate 2 is higher than an electric
field E.sub.b in the buffer film 3. At this time, each of the
electric fields E.sub.a and E.sub.b is represented by a function of
a distance d from the surface of the buffer film 3 and time t from
the start of anodic bonding. Note that the bonding film 4 is made
of a metal or alloy and therefore has a resistivity and sheet
resistance much lower than those of the high-resistance glass
substrate 2 or the buffer film 3 formed from a metal oxide film.
Hence, the voltage division ratio is negligible. In anodic bonding,
alkali ions are attracted and moved to the negative electrode side.
Let q be the charges of alkali ions. A force F received by the
alkali ions in the glass substrate 2 is given by
F=q.multidot.E.sub.a
[0058] On the other hand, a force f received by the alkali ions in
the buffer film 3 is given by
f=q.multidot.E.sub.b
[0059] Hence, for the forces received by the alkali ions, the
electric fields E.sub.a and E.sub.b are compared. When the time t
is zero or sufficiently small, the electric fields E.sub.a and
E.sub.b as shown in FIG. 5 are obtained. The electric fields
E.sub.a and E.sub.b have almost predetermined values regardless of
the positions in the glass substrate 2 and buffer film 3. Since the
electric conductivity of the buffer film 3 is higher than that of
the glass substrate 2, the electric field E.sub.b is smaller than
the electric field E.sub.a. In addition, the electric field E.sub.b
is not zero, and the alkali ions receive a weak force in the
direction of the surface of the buffer film 3. Hence, the alkali
ions in the glass substrate 2 move to the buffer film 3 to some
extent.
[0060] When the time t has sufficiently elapsed (anodic bonding
enable time), the electric fields E.sub.a and E.sub.b have no
predetermined values in the glass substrate 2 and buffer film 3.
The graph shown in FIG. 5 changes from the straight line to a curve
projecting upward. This occurs due to the screening effect of
positive ions, qualitatively like electrons in the semiconductor
layer near the oxide film of a metal oxide semiconductor (MOS)
device or near the electrode in an electrolytic solution. If the
buffer film 3 is not present, the alkali ions move until the
charges near the negative electrode are canceled. Hence, the alkali
ions are deposited on the surface of the glass substrate 2 in a
form of, e.g., an alkali oxide. When the buffer film 3 is not
present, an electric field E.sub.A in the glass substrate 2 is also
represented by a function whose locus on the graph projects upward
because of the screening effect. Qualitatively, electric field
E.sub.b<electric field E.sub.a<electric field E.sub.A. When
the buffer film 3 is not present, the alkali ion concentration
concentrates to the surface near the surface of the glass substrate
2 or the interface. However, when the buffer film 3 which can
contain alkali ions to some extent and has a resistivity lower than
the glass substrate 2 is present, the concentration of the alkali
ions in the glass substrate 2 can be prevented from concentrating
to the surface 2a by dispersing the field intensity by anodic
bonding.
[0061] The concentration of the alkali ions in the glass substrate
2 can be prevented from concentrating to the interface between the
buffer film 3 and the glass substrate 2. In addition, a compound
formed by alkali ions can be prevented from being deposited on the
surface of the bonding film 4. Even when the new glass substrate 2
is anodic-bonded to the bonding film 4 of the precedingly
anodic-bonded glass substrate 2, the new glass substrate 2 does not
peel from the bonding film 4 of the precedingly anodic-bonded glass
substrate 2. For this reason, a stack structure having a high
bonding strength can be provided.
[0062] The concentration of the alkali ions in the glass substrate
2 can be prevented from concentrating to the interface between the
buffer film 3 and the glass substrate 2. In addition, alkali can be
prevented from being deposited on the surface of the bonding film
4. For these reasons, another material can be bonded to the bonding
film 4.
[0063] When a glass substrate containing lithium (e.g., SW-YY) is
used as the glass substrate 2, the application voltage in anodic
bonding can be made low. FIG. 6 is a graph showing the relationship
between time from the start of anodic bonding and the current which
flows between the electrodes in anodic bonding using a glass
substrate containing lithium (SW-YY) and anodic bonding using a
glass substrate without lithium (PYREX (registered trademark) of
product number #7740 available from CORNING). The buffer film 3 was
made of a Ta--Si--O based material having a thickness of 300 nm.
The voltage applied between the electrodes was 300V for the glass
substrate containing lithium. The voltage applied between the
electrodes was 800V for the glass substrate without lithium. As is
apparent from FIG. 6, even when the glass substrate containing
lithium is anodic-bonded at 300V, the current and time change
exhibit almost the same behavior as in anodic-bonding the glass
substrate without lithium at 800V. For this reason, when the glass
substrate containing lithium (e.g., SW-YY available from ASAHI
TECHNOGLASS CORPORATION) is used as the glass substrate 2, the
application voltage in anodic bonding can be made low. Lithium ions
have a radius of about 0.59 .ANG., which is much smaller than
sodium ions, and therefore easily move in the glass substrate 2 in
anodic bonding.
[0064] As shown in FIG. 3, the plurality of glass substrates 2 each
of which has the bonding film 4 and is not anodic-bonded yet are
stacked. The bonding film 4 of the uppermost glass substrate 2 is
connected to the positive electrode or pole of the anodic bonding
apparatus 10. The negative electrode or pole of the anodic bonding
apparatus 10 is connected to the lowermost glass substrate 2 or the
bonding film 4 of the lowermost glass substrate 2. In this state,
the plurality of glass substrates 2 and the plurality of bonding
films 4 in contact with them may be anodic-bonded at once. The
lowermost glass substrate 2 need not always have the buffer film 3
and bonding film 4 if the glass substrate 2 is not bonded to
another glass substrate or conductive film after anodic
bonding.
[0065] When a plurality of anodic bonding processes are executed in
the same electric field direction by the above manufacturing
method, bonding is possible even when the bonding film 4 is
directly provided on the surface 2a of the glass substrate 2
without the buffer film 3.
[0066] In the above manufacturing method, the new glass substrates
2 are sequentially stacked on the side of the stage 8 and
anodic-bonded. However, the present invention is not limited to
this. The silicon substrate 5 and glass substrate 2 shown in FIGS.
1A to 1D, the glass substrates 2 and 6 shown in FIG. 2, or the
glass substrates 2, 2', and 2" shown in FIG. 4, whose relative
positions in the vertical direction and upper and lower surfaces
are inverted, may be anodic-bonded. More specifically, the stage 8
on which the silicon substrate 5, glass substrate 6, or glass
substrate 2' is placed is arranged on the lower side. The glass
substrate 2 is placed while making the other surface 2b with the
trench 2c contact the upper surface of the silicon substrate 5, the
bonding film 7 provided on the upper surface of the glass substrate
6, or the bonding film 4 provided on the upper surface side of the
glass substrate 2'. The weight plate 9 is placed on the bonding
film 4 provided on the side of the surface 2a of the glass
substrate 2. The silicon substrate 5, the bonding film 7 provided
on the glass substrate 6, or the bonding film 4 provided on the
side of the surface 2a of the glass substrate 2' is connected to
the positive electrode of the anodic bonding apparatus 10. The
bonding film 4 provided on the side of the surface 2a of the glass
substrate 2 is connected to the negative electrode. In this state,
anodic bonding is done. Subsequently, the new glass substrate 2
having the buffer film 3 and bonding film 4 is sequentially stacked
while making the surface 2a directed upward. The weight plate 9 is
placed on the new glass substrate 2. The bonding film 4 of the
uppermost glass substrates 2 is connected to the negative
electrode. In this state, anodic bonding is executed. When the
plate weight 9 made of a conductive material is used, the negative
electrode of the anodic bonding apparatus 10 can be electrically
connected to the uppermost bonding film 4 through the weight plate
9.
[0067] The stack structure (stack microreactor 1) is used for a
reformer which obtains hydrogen to be supplied to a fuel cell by
reforming hydrocarbon fuel such as methanol. Especially, the stack
structure can be used for a vaporizer which vaporizes hydrocarbon
fuel, a hydrogen reformer which reforms vaporized hydrocarbon fuel
into hydrogen, or a carbon monoxide remover which removes, by
chemical reaction, carbon monoxide as a by-product generated by the
hydrogen reformer.
[0068] In the above embodiment, the buffer film 3 is provided on
the side of the surface opposing the bonding surface of the glass
substrate 2. However, the present invention is not limited to this.
Anodic bonding may be executed by providing the buffer film 3 on
the stage 8 which comes into contact with the entire opposing
surface. In consideration of misalignment which occurs when the
glass substrate 2 is placed on the stage 8, the buffer film 3
preferably has an area larger than the glass substrate 2 so that
the entire surface of the glass substrate 2 can be covered.
[0069] In the above embodiment, the bonding film 4 is provided on
the glass substrate 2. However, the buffer film 3 may be provided
directly on the glass substrate 2 without providing the bonding
film 4. Alternatively, the glass substrate 2 without the bonding
film 4 may be placed on the buffer film 3 on the stage 8 and
anodic-bonded.
Second Embodiment
[0070] A method of manufacturing a second stack microreactor to
which the present invention is applied will be described with
reference to sectional views shown in FIGS. 7A to 11.
[0071] FIG. 7B is a plan view of the first glass substrate 101.
FIG. 7A is a sectional view taken along a line VIIA-VIIA in FIG.
7B.
[0072] As shown in FIGS. 7A and 7B, a first glass substrate 101 is
prepared. A zigzag trench 101a is formed in one surface of the
first glass substrate 101. A bonding film 102 is formed on a
portion of said one surface of the first glass substrate 101 except
the trench 101a. The component composition of the first glass
substrate 101 is the same as that of the glass substrate 2 of the
first embodiment. All glass substrates used in the second
embodiment have the same component composition as that of the glass
substrate 2 of the first embodiment.
[0073] To form the trench 101a, one surface of the first glass
substrate 101 may be subjected to known sandblasting.
Alternatively, known photolithography and etching may be
executed.
[0074] To pattern the bonding film 102, lift-off can be used. More
specifically, while keeping the trench 101a covered with a resist,
the bonding film is entirely formed on said one surface of the
first glass substrate 101 by vapor deposition. The part of the
bonding film overlapping the trench 101a is removed together with
the resist, thereby leaving the bonding film 102 on the portion
except the trench 101a. The component of the bonding film 102 is
the same as that of the bonding film 4 (FIGS. 1A to 1D) of the
first embodiment. All bonding films used in the second embodiment
have the same component as that of the bonding film 4 of the first
embodiment.
[0075] As shown in FIG. 8, a second glass substrate 103 having a
zigzag trench 103a formed in one surface is prepared. A buffer film
104 is formed on the other surface of the second glass substrate
103. A bonding film 105 is formed on the buffer film 104. The
component and forming method of the buffer film 104 are the same as
those of the buffer film 3 of the first embodiment. All buffer
films used in the second embodiment have the same component
composition as that of the buffer film 3 of the first embodiment.
The trench 103a is plane-symmetrical to the trench 101a of the
first glass substrate 101.
[0076] As shown in FIG. 9, while making the trench 101a oppose the
trench 103a, said one surface of the second glass substrate 103 is
pressed against the bonding film 102. A voltage is applied between
the bonding films 102 and 105 by the electric source 10 such that
the potential of the bonding film 105 becomes higher than that of
the bonding film 102. In addition, the structure is heated to
300.degree. C. to 400.degree. C. With this process, anodic bonding
is done. Since the buffer film 104 is formed on the second glass
substrate 103, the alkali ion concentration can be suppressed from
concentrating to the other surface of the second glass substrate
103.
[0077] As shown in FIG. 10, a third glass substrate 106 for heat
buffering, which has a buffer film 107 and bonding film 108
sequentially formed on one surface, is prepared. The other surface
of the third glass substrate 106 is pressed against the bonding
film 105. A voltage is applied between the bonding films 105 and
108 by the voltage source 10 such that the potential of the bonding
film 108 becomes higher than that of the bonding film 105. In
addition, the structure is heated to 300.degree. C. to 400.degree.
C. With this process, anodic bonding is done. A thin film heater
151 (FIG. 11) made of an electrothermal material is patterned on
part of the bonding film 108. The resultant structure is used as a
combustion fuel vaporizer 171 which vaporizes, by heat from the
thin film heater 151, combustion fuel flowing through the flow path
formed by the trenches 101a and 103a of the glass substrates 101
and 103. The vaporized combustion fuel is supplied to a flow path
formed by a trench 115a formed in a glass substrate 115 (to be
described later), a flow path formed by a trench 124a formed in a
glass substrate 124, and a flow path formed by trenches 133a and
136a formed in glass substrates 133 and 136.
[0078] Glass substrates 109, 112, 115, 118, 121, 124, 127, 130,
133, and 136 are bonded in this order by sequentially repeating the
following steps (a) and (b) below like when the first glass
substrate 101 is bonded to the second glass substrate 103 or when
the third glass substrate 106 is bonded to the second glass
substrate 103.
[0079] (a) A buffer film and bonding film are sequentially formed
on one surface of a new glass substrate.
[0080] (b) The other surface of the new glass substrate is pressed
against the bonding film formed on the precedingly anodic-bonded
glass substrate. A voltage is applied between the preceding bonding
film and the new bonding film such that the potential of the
bonding film of the preceding glass substrate becomes higher than
that of the bonding film of the new glass substrate. In addition,
the structure is heated to 300.degree. C. to 400.degree. C. That
is, anodic bonding is done.
[0081] When the glass substrates 109, 112, 115, 118, 121, 124, 127,
130, 133, and 136 are sequentially bonded in the above-described
way, a stack microreactor 200 shown in FIG. 11 serving as a
chemical reaction furnace is completed. Referring to FIG. 11, each
of the glass substrates 103, 106, 109, 112, 115, 118, 121, 124,
127, 130, 133, and 136 is anodic-bonded to the upper bonding film
by applying a voltage such that the lower bonding film has a
potential higher than that of the upper bonding film. Hence, in
each of the glass substrates 103, 106, 109, 112, 115, 118, 121,
124, 127, 130, 133, and 136, an electric field directed upward is
applied in anodic bonding. In the example shown in FIG. 11, the
positions of the end faces of the glass substrates match. To easily
connect the structure to the anodic bonding apparatus, the
positions of the end faces of the glass substrates are preferably
shifted, as shown in FIG. 4C.
[0082] The stack microreactor 200 will be described.
[0083] The fourth glass substrate 109 is anodic-bonded to the
bonding film 108 while forming a space around the thin film heater
151. A zigzag trench 109a is formed in the surface of the fourth
glass substrate 109 opposite to the bonding surface to the bonding
film 108. A buffer film 110 and bonding film 111 are sequentially
formed on a portion of the surface except the trench 109a.
[0084] The fifth glass substrate 112 is anodic-bonded to the
bonding film 111. A trench 112a plane-symmetrical to the trench
109a is formed in the bonding surface of the fifth glass substrate
112 to the bonding film 111. A buffer film 113 and bonding film 114
are sequentially formed on the surface opposite to the bonding
surface.
[0085] The sixth glass substrate 115 is anodic-bonded to the
bonding film 114. A zigzag trench 115a is formed in the bonding
surface of the sixth glass substrate 115 to the bonding film 114. A
combustion catalyst 152 is formed on the wall surface of the trench
115a. A buffer film 116 and bonding film 117 are sequentially
formed on the surface of the sixth glass substrate 115 opposite to
the bonding surface to the bonding film 114. A thin film heater 153
is formed on part of the bonding film 117. A reformed fuel
vaporizer 172 includes a microreactor including the glass
substrates 109 and 112, buffer film 110, and bonding film 111, a
reformed fuel vaporization combustor which includes the sixth glass
substrate 115 and combustion catalyst 152 to heat the microreactor,
and the thin film heater 153. The reformed fuel vaporizer 172
supplies vaporized reformed fuel to a hydrogen reformer 174 (to be
described later).
[0086] The seventh glass substrate 118 is anodic-bonded to the
bonding film 117 while forming a space around the thin film heater
153. A zigzag trench 118a is formed in the surface of the seventh
glass substrate 118 opposite to the bonding surface to the bonding
film 117. A carbon monoxide oxidation catalyst 154 is formed on the
wall surface of the trench 118a. A buffer film 119 and bonding film
120 are sequentially formed on a portion of the opposite surface
except the trench 118a.
[0087] The eighth glass substrate 121 is anodic-bonded to the
bonding film 120. A zigzag trench 121a plane-symmetrical to the
trench 118a is formed in the bonding surface of the eighth glass
substrate 121 to the bonding film 120. A carbon monoxide oxidation
catalyst 155 is formed on the wall surface of the trench 121a. A
buffer film 122 and bonding film 123 are sequentially formed on the
surface of the eighth glass substrate 121 opposite to the bonding
surface to the bonding film 120.
[0088] The ninth glass substrate 124 is anodic-bonded to the
bonding film 123. A zigzag trench 124a is formed in the bonding
surface of the ninth glass substrate 124 to the bonding film 123. A
combustion catalyst 142 is formed on the wall surface of the trench
124a. A buffer film 125 is formed on the surface of the ninth glass
substrate 124 opposite to the bonding surface to the bonding film
123. A bonding film 126 is formed around the buffer film 125. A
thin film heater 156 is formed at the central portion of the buffer
film 125.
[0089] A carbon monoxide remover 173 has a microreactor including
the glass substrates 118 and 121, buffer film 119, and bonding film
120, a carbon monoxide removing combustor which includes the glass
substrate 124 and combustion catalyst 142 to heat the microreactor,
and the thin film heater 156. The carbon monoxide remover 173
oxidizes carbon monoxide generated by the hydrogen reformer 174 (to
be described later) into carbon dioxide.
[0090] The 10th glass substrate 127 is anodic-bonded to the bonding
film 126 while forming a space around the thin film heater 156. A
zigzag trench 127a is formed in the surface of the 10th glass
substrate 127 opposite to the bonding surface to the bonding film
126. A fuel reforming catalyst 157 is formed on the wall surface of
the trench 127a. A buffer film 128 and bonding film 129 are
sequentially formed on a portion of the opposite surface except the
trench 127a.
[0091] The 11th glass substrate 130 is anodic-bonded to the bonding
film 129. A zigzag trench 130a plane-symmetrical to the trench 127a
is formed in the bonding surface of the 11th glass substrate 130 to
the bonding film 129. A fuel reforming catalyst 158 is formed on
the wall surface of the trench 130a. A buffer film 131 and bonding
film 132 are sequentially formed on the surface of the 11th glass
substrate 130 opposite to the bonding surface to the bonding film
129.
[0092] The 12th glass substrate 133 is anodic-bonded to the bonding
film 132. A zigzag trench 133a is formed in the surface opposite to
the bonding surface. A combustion catalyst 159 is formed on the
wall surface of the trench 133a. A buffer film 134 and bonding film
135 are sequentially formed on a portion of the opposite surface
except the trench 133a.
[0093] The 13th glass substrate 136 is anodic-bonded to the bonding
film 135. A zigzag trench 136a plane-symmetrical to the trench 133a
is formed in the bonding surface of the 13th glass substrate 136 to
the bonding film 135. A combustion catalyst 160 is formed on the
wall surface of the trench 136a. A buffer film and bonding film 138
are sequentially formed on the surface of the 13th glass substrate
136 to the bonding surface to the bonding film 135. A thin film
heater 161 is formed on part of the bonding film 138.
[0094] The hydrogen reformer 174 has a microreactor including the
glass substrates 127 and 130, buffer film 128, and bonding film
129, a hydrogen reforming combustor which includes the glass
substrates 133 and 136, buffer film 134, bonding film 135, and
combustion catalysts 159 and 160 to heat the microreactor, and the
thin film heater 161. The hydrogen reformer 174 reforms the
reformed fuel vaporized by the reformed fuel vaporizer 172 into
hydrogen. The hydrogen reformer 174 supplies, to the carbon
monoxide remover 173, a mixed fluid containing hydrogen and carbon
monoxide generated as a by-product.
[0095] In the combustion fuel vaporizer 171 of the microreactor
200, combustion fuel such as methanol is heated and vaporized by
heat from the thin film heater 151 or a combustor (to be described
later) when the combustion fuel flows through the trenches 101a and
103a. The combustion fuel vaporized by the vaporizer is mixed with
air and supplied to the combustors of the hydrogen reformer 174,
carbon monoxide remover 173, and reformed fuel vaporizer 172. That
is, the combustion fuel flows to the flow path formed by the
trenches 133a and 136a, the flow path formed by the trench 124a,
and the flow path formed by the trench 115a.
[0096] The vaporized combustion fuel is oxidized by the catalysis
of the combustion catalyst 152 and burns while flowing through the
flow path of the trench 115a. Similarly, the vaporized combustion
fuel is oxidized by the catalysis of the combustion catalyst 142
and burns while flowing through the flow path of the trench 124a.
The vaporized fuel is oxidized by the catalysis of the combustion
catalysts 159 and 160 and burns while flowing through the flow path
of the trenches 133a and 136a. Heat of combustion is generated to
heat the reformed fuel vaporizer 172, carbon monoxide remover 173,
and hydrogen reformer 174 to promote reactions in the reformed fuel
vaporizer 172, carbon monoxide remover 173, and hydrogen reformer
174. Main heat sources in the reformed fuel vaporizer 172, carbon
monoxide remover 173, and hydrogen reformer 174 are preferably
these combustors. The thin film heaters 153, 156, and 161 are
preferably used as auxiliary heat sources to adjust the
temperatures required in the reformed fuel vaporizer 172, carbon
monoxide remover 173, and hydrogen reformer 174.
[0097] A vaporizer is constituted by the fourth glass substrate 109
and fifth glass substrate 112. More specifically, a mixture of
water and combustion fuel such as methanol is heated mainly by the
heat of combustion by the sixth glass substrate 115 and the thin
film heater 153 and evaporates while flowing through the flow path
formed by the trenches 109a and 112a. The mixture of the vaporized
combustion fuel and water flows to the flow path formed by the
trenches 127a and 130a.
[0098] The mixture of the combustion fuel and water is heated
mainly by the heat of combustion by the combustor formed by the
glass substrates 133 and 136 and the heat from the thin film heater
161 and reformed into hydrogen by the catalysis of the fuel
reforming catalysts 157 and 158 while flowing through the trenches
127a and 130a. That is, a vapor reformer is constituted by the
glass substrates 127 and 130 and the fuel reforming catalysts 157
and 158. In this vapor reformer, carbon dioxide and carbon monoxide
are also generated as by-products. The products such as hydrogen
are mixed with air and supplied to the flow path formed by the
trenches 118a and 121a.
[0099] While the products such as hydrogen flow through the flow
path formed by the trenches 118a and 121a, carbon monoxide in the
products is oxidized by the catalysis of the carbon monoxide
oxidation catalysts 154 and 155. With this process, carbon monoxide
is removed.
[0100] The products such as hydrogen are supplied from the carbon
monoxide remover to the fuel electrode of a fuel cell. Oxygen in
air is supplied to the air electrode. An electric energy is
generated by the electrochemical reaction in the fuel cell.
[0101] Even in the microreactor 200, concentration of alkali ion
concentration in each glass substrate or deposition of alkali can
be prevented. For this reason, the bonding strength of the anodic
bonding surfaces is high. Hence, the microreactor 200 having a high
bonding strength can be provided.
[0102] As described above, in the embodiments, the electric field
which acts in a glass substrate in anodic-bonding a silicon
substrate to one surface of the glass substrate in the post-process
has the same direction as the electric field which acts in the
glass substrate in anodic-bonding another silicon substrate to the
other surface of the glass substrate in the preprocess. Hence, the
bonding between the silicon substrate and the other surface of the
glass substrate, which are precedingly anodic-bonded, can be
prevented from being adversely affected. In addition, when positive
charges such as sodium ions serving as carriers are generated in
the glass substrate in anodic bonding of the preprocess, the ions
can be prevented from being deposited as a compound near one
surface of the glass substrate due to the electric field generated
in the preprocess. Hence, bonding between the silicon substrate and
the surface of the glass substrate in the post-process is not
inhibited.
[0103] Since no electric fields in the reverse directions act in
the glass substrates 103, 106, 109, 112, 115, 118, 121, 124, 127,
130, 133, and 136, no discoloring occurs in the glass substrates
103, 106, 109, 112, 115, 118, 121, 124, 127, 130, 133, and 136. For
this reason, the microreactor 200 having a stack structure can
easily be manufactured.
[0104] When glass substrates containing lithium are used as the
glass substrates 103, 106, 109, 112, 115, 118, 121, 124, 127, 130,
133, and 136, the voltage in anodic bonding can be made low.
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