JP4862762B2 - Bonded substrate and reaction apparatus using the same - Google Patents

Description

  The present invention relates to a bonded substrate and a reaction apparatus using the bonded substrate.

In recent years, small reactors called microreactors have been developed and put into practical use. Since the entire reactor is small, the microreactor has an advantage that the heat exchange rate is extremely high and temperature control can be performed efficiently. Therefore, a reaction that requires precise temperature control or a reaction that requires rapid heating or cooling can be easily performed.
Specifically, the microreactor is formed with a channel (flow channel) for flowing chemical substances, a reactor (reaction tank) for reacting chemical substances or decomposing chemical substances, and the like. In Patent Document 1, a silicon substrate having a groove having a predetermined pattern and a heat-resistant glass substrate are anodically bonded together to form a channel in a sealed region between the two substrates.

Here, the anodic bonding is a high voltage in which a glass substrate and a silicon substrate are brought into contact with each other in a high temperature environment (for example, 300 ° C. to 400 ° C.), and an anode is brought into contact with the silicon substrate and a cathode is brought into contact with the glass substrate. This is a bonding technique in which Si having a positive charge on the silicon substrate side and oxygen atom having a negative charge on the glass substrate side are covalently bonded at the interface. Because it has features such as bonding substrates in the atmosphere and bonding at a relatively low temperature compared to diffusion bonding and frit glass bonding, it is considered to be a particularly excellent technology for bonding substrates. .
When glass substrates are bonded to each other, a metal thin film is provided on one glass substrate, an anode is brought into contact with the glass substrate provided with the metal thin film, and a cathode is brought into contact with the other glass substrate to apply a high voltage. Thus, the metal having a positive charge on the metal thin film side and the oxygen atom having a negative charge on the glass substrate side can be covalently bonded at the interface to perform bonding (see, for example, Patent Document 2).
Moreover, as a metal thin film used for anodic bonding, a metal bonded to an oxygen atom of a glass substrate can be used. For example, a metal thin film containing Ta which is a refractory metal can be used (see, for example, Patent Document 3). .
JP 2001-228159 A Japanese Patent Laid-Open No. 8-293533 JP 2001-232903 A

However, when a Ta film is formed on a glass substrate, the Ta film may be peeled off after a process step such as anodic bonding, and this peeling may cause a decrease in airtight reliability in anodic bonding.
The present invention has been made in view of the above circumstances, and provides a bonded substrate capable of improving the airtight reliability in anodic bonding by forming a Ta film that is difficult to peel off, and a reaction apparatus using the bonded substrate The purpose is to do.

In order to solve the above-mentioned problem, the invention of claim 1 is a bonding substrate,
A first glass substrate having a metal thin film formed on one surface;
A second glass substrate anodically bonded by the metal thin film,
At least a part of the metal thin film is Ta, has a tetragonal crystal structure, and the space group belongs to P4 ₂ / mnm.

The invention of claim 2 is a bonding substrate,
A first glass substrate having a metal thin film formed on one surface;
A second glass substrate anodically bonded by the metal thin film,
At least a part of the metal thin film is Ta, has a tetragonal crystal structure, and has a density of 16.7 g / cm ³ .

The invention of claim 3 is the reaction apparatus,
The bonding substrate according to claim 1 or 2 is used.

  According to the present invention, it is possible to improve the airtight reliability in anodic bonding by forming a Ta film that is difficult to peel off.

The best mode for carrying out the present invention will be described below with reference to the drawings. However, although various technically preferable limitations for implementing the present invention are given to the embodiments described below, the scope of the invention is not limited to the following embodiments and illustrated examples.
FIG. 1 is a block diagram of a power generation apparatus 100 in which a reaction apparatus 10 to which the present invention is applied is used.
The power generation apparatus 100 is provided in a notebook personal computer, a mobile phone, a PDA (Personal Digital Assistant), an electronic notebook, a wristwatch, a digital still camera, a game device, a game machine, and other electronic devices. It is used as a power source for operating.

  The power generation device 100 includes a fuel container 101, a vaporizer 102, a reaction device 10, a power generation cell 103, a DC / DC converter 104, a secondary battery 105, and a control unit 106. The fuel container 101 stores fuel such as methanol, ethanol, butane, and water separately or in a mixed state, and supplies a mixed liquid of fuel and water to the reaction apparatus 10 via the vaporizer 102 by a micro pump (not shown). . In the following description, the case where methanol is used as the fuel will be described, but the same applies to fuels such as ethanol and butane.

  The reaction apparatus 10 has a high temperature reaction unit 11 and a low temperature reaction unit 12 and is accommodated in a heat insulating container (not shown). The high temperature reaction unit 11 includes a reformer 13, a combustor 15, and a high temperature heater 17, and the low temperature reaction unit 12 includes a carbon monoxide remover 14 and a low temperature heater 16.

  The fuel and water supplied from the fuel container 101 are vaporized by the vaporizer 102 and supplied to the reformer 13. The reformer 13 causes the fuel / water mixture supplied from the vaporizer 102 to react as shown in the chemical reaction formula (1), so that hydrogen gas and carbon dioxide gas as main products (and byproducts described later) are produced. (Including carbon monoxide). The carbon monoxide remover 14 converts carbon monoxide, which is by-produced in a trace amount by an equation such as the chemical reaction equation (2) that occurs sequentially after the chemical reaction equation (1), as in the chemical reaction equation (3). It is removed from the gas mixture by oxidation. Hereinafter, the mixed gas from which the carbon monoxide is removed is referred to as a reformed gas. The reformed gas is supplied to the fuel electrode side of the power generation cell 103.

CH ₃ OH + H ₂ O → 3H ₂ + CO ₂ (1)
H ₂ + CO ₂ → H ₂ O + CO (2)
2CO + O ₂ → 2CO ₂ (3)

  The reformed gas is supplied from the carbon monoxide remover 14 to the fuel electrode side of the power generation cell 103. Hydrogen gas in the reformed gas is separated into hydrogen ions and electrons by a catalyst provided in the fuel electrode as shown in the electrochemical reaction formula (4). Hydrogen ions pass through the electrolyte membrane and move to the oxygen electrode side, and electrons move to the oxygen electrode through an external circuit. On the oxygen electrode side, as shown in the electrochemical reaction formula (5), a chemical reaction between hydrogen ions that have passed through the electrolyte membrane, electrons supplied from the oxygen electrode through an external circuit, and oxygen gas supplied from the outside air Produce water. Electrical energy can be extracted from the difference in electrode potential between the fuel electrode and the oxygen electrode.

H ₂ → 2H ⁺ + 2e ⁻ (4)
2H ⁺ + 2e ⁻ + 1 / 2O ₂ → H ₂ O (5)

  Note that hydrogen gas remaining without performing the electrochemical reaction (hereinafter referred to as off-gas) may be supplied to the combustor 15.

The combustor 15 burns oxygen mixed with fuel or off-gas supplied from the fuel container 101 and heats the high-temperature reaction unit 11 to 250 ° C. or higher, for example, about 250 to 400 ° C. The high temperature heater 17 heats the high temperature reaction part 11 instead of the combustor 15 at the time of starting.
The low temperature heater 16 heats the low temperature reaction part 12 to less than 200 ° C., for example, about 110 to 190 ° C. at the time of activation.

  The DC / DC converter 104 converts the electric energy generated by the power generation cell 103 into an appropriate voltage, and then supplies the electric energy generated by the power generation cell 103 to the secondary battery 105. When the power generation cell 103 side is not operated, the function of supplying electric energy from the secondary battery side to the electronic device 200 can also be achieved. The control unit 106 controls pumps and valves (not shown) necessary for operating the vaporizer 102, the reactor 100, and the power generation cell 103, the heaters, the DC / DC converter 104, and the like. Control to supply electric energy.

Next, the structure of the reaction apparatus 10 will be described. 2 is a plan view of the reaction apparatus 10, and FIG. 3 is a cross-sectional view taken along the line III-III in FIG.
The reaction apparatus 10 is provided with a slit 50 between the high temperature reaction section 11 and the low temperature reaction section 12 for preventing heat conduction. In addition, a supply pipe 51 that supplies a mixture of fuel and water from the vaporizer 102 to the reformer 13 and a supply pipe that supplies the off-gas discharged from the power generation cell 103 to the combustor 15 are provided at the outer periphery of the reactor 10. 52, a discharge pipe 53 for discharging the combustion gas from the combustor 15, a supply pipe 54 for supplying oxygen to the carbon monoxide remover 14, and a discharge pipe 55 for discharging the reformed gas from the carbon monoxide remover 14. Yes.

For example, as shown in FIG. 3, the reaction apparatus 10 uses a bonded substrate formed by bonding three glass substrates 20, 30, and 40 together. On the opposing surfaces of the upper glass substrate (second glass substrate) 20 and the central glass substrate (first glass substrate) 30, grooves 21 and 31 forming the reformer 13 are arranged opposite to each other. Thus, grooves 22 and 32 for forming the carbon monoxide remover 14 are formed.
In the grooves 21 and 31, reforming catalysts 23 and 33 for promoting the reforming reactions of the chemical reaction formulas (1) and (2) are provided. Further, in the grooves 22 and 32, carbon monoxide selective oxidation catalysts 24 and 34 for promoting the carbon monoxide selective oxidation reaction of the chemical reaction formula (3) are provided.

The central glass substrate 30 is provided with a high temperature heater 17 on the back side of the groove 31 and a low temperature heater 16 on the back side of the groove 32. The high temperature heater 17 is covered with an insulating protective film 18. The insulating protective film 18 is made of, for example, SiO ₂ . Such an insulating protective film 18 is formed by applying spin-on glass (SOG) to the high-temperature heater 17 and baking the entire central glass substrate 30 at 400 to 500 ° C. The SOG contains an organic compound containing Si and O, such as methyl siloxane, and a SiO ₂ layer is formed by baking the applied SOG.
The high-temperature heater 17 is disposed in the combustor 15 as will be described later, but is not affected by hydrogen contained in the off-gas because it is covered with the insulating protective film 18.

The high temperature heater 17 includes a heat generation resistance layer 17a and adhesion / diffusion prevention layers 17b and 17c, and the low temperature heater 16 includes a heat generation resistance layer 16a and an adhesion layer / diffusion prevention layer 16b.
The heating resistance layers 17a and 16a are made of a material having a low resistivity and a large temperature coefficient, for example, Au, and improve the conductivity of the high temperature heater 17 and the low temperature heater 16.
The adhesion / diffusion prevention layers 17b and 16b are made of a material having excellent adhesion that improves the adhesion between the heating resistance layers 17a and 16a and the glass substrate 30, such as W. The adhesion / diffusion prevention layers 17b and 16b may be provided on a metal thin film 36 for anodic bonding, which will be described later, formed on the glass substrate 30.
The adhesion layer / diffusion prevention layer 17c is made of a material having excellent adhesion that improves the adhesion between the heating resistance layer 17a and the insulating protective film 18, such as W. (The high-temperature heater 17 and the low-temperature heater 16 can also be used as thermometers.)

The lower glass substrate (second glass substrate) 40 is provided with a groove 41 that becomes the combustor 15 and a groove 42 that houses the low-temperature heater 16 on the surface facing the central glass substrate 30. By superposing the central glass substrate 30 and the lower glass substrate 40, the high temperature heater 17 is disposed in the groove 41, and the low temperature heater 16 is disposed in the groove 42.
A combustion catalyst 43 that burns fuel is provided in the groove 41. The inside of the groove 41 is covered with the central glass substrate 30 to form the combustor 15.
A combustor may also be provided on the low temperature reaction unit 12 side.

  The grooves 21, 22, 31, 32, 41, 42 are formed by cutting the glass substrates 20, 30, 40 by sandblasting or the like.

  Further, a metal thin film 35 for anodic bonding is formed on the central glass substrate 30 at a contact portion with the upper glass substrate 20. Similarly, a metal thin film 36 for anodic bonding is formed at a contact portion with the lower glass substrate 40.

As the metal used for the metal thin films 35 and 36, a metal that binds to oxygen can be used, and a metal thin film containing at least Ta can be used.
On the other hand, since the metal on the surface of the metal thin films 35, 36 is bonded to oxygen atoms at the interface when anodically bonded to the upper glass substrate 20 and the lower glass substrate 40, the metal thin films 35, 36 are manufactured from the central glass substrate 30. It is preferable that the oxidation resistance is high so as not to be oxidized in the process.

  Here, the manufacturing process of the central glass substrate 30 will be described with reference to FIG. First, on one surface of the glass substrate, a Ta-containing layer that becomes the metal thin film 36, a W layer that becomes the adhesion / diffusion prevention layers 17b and 16b, an Au layer that becomes the heating resistance layers 17a and 16a, an adhesion layer / diffusion prevention layer A W layer to be 17c is sequentially laminated to form a Ta / W / Au / W laminated structure (step S1). Further, a metal thin film to be the metal thin film 36 is formed on the other surface of the glass substrate (step S2). Next, the stacked structure of Ta / W / Au / W is patterned to form the metal thin films 35 and 36, the high temperature heater 17, and the low temperature heater 16 (step S3).

Next, SOG is applied to the surface of the glass substrate on which the metal thin film 36, the high-temperature heater 17, and the low-temperature heater 16 are formed, pre-fired at 400 to 500 ° C., and finally fired to form a SiO ₂ layer by sputtering (step S4). -Step S7). At this time, the heating resistance layers 17a and 16a are annealed simultaneously.
Then, by patterning the SiO ₂ layer formed by SiO ₂ layer and Suppatta firing the SOG (step S8), and an insulating protective film 18. Thereafter, the grooves 31 and 32 are formed by sandblasting (step S9), and the central glass substrate 30 is manufactured by cutting (dicing) (step S10).

  In the above manufacturing process, after the insulating protective film 18 is formed by baking at 400 to 500 ° C., the metal thin films 35 and 36 may be peeled off in the sandblasting process or the dicing process. Here, since the metal thin films 35 and 36 serve as both the adhesion layer and the anodic bonding layer, the film thickness is preferably about 150 nm to 200 nm. However, when the film thickness is increased, peeling tends to occur more easily. Therefore, it is important that the metal thin films 35 and 36 have the following structure so that peeling does not easily occur.

That is, the metal thin films 35 and 36 contain at least Ta, and the Ta film needs to have a tetragonal (generally described as β-Ta) structure.
Usually, there are two known Ta films: a case where the bulk Ta has a cubic body-centered cubic structure (generally described as α-Ta) and a case where the above-mentioned tetragonal system is taken. (See Non-Patent Document 1 below) In particular, when a Ta film is formed on a substrate, the tetragonal system is often taken. Non-Patent Document 1 reports that the formed Ta film may have a cubic body-centered cubic structure, but the experience of the present inventors, unless impurities are intentionally mixed, It has been recognized that a film having a cubic body-centered cubic structure cannot be obtained in the formed Ta film.
In addition, since the tetragonal β-Ta film is usually more difficult to peel than the cubic α-Ta film (see Non-Patent Document 2 below), the present invention has a tetragonal β-Ta film. It is important to use a β-Ta film.
Further, as will be apparent from the examples described later, a tetragonal β-Ta film having a space group of P4 ₂ / mnm and a density of 16.7 g / cm ³ (βa described later) -Ta film).
By using the metal thin films 35 and 36 including such a βa-Ta film, peeling hardly occurs.

Non-Patent Document 1 DA McLean: J. Electrochem. Soc. Japan 34 (1996) 1-11]
Non-Patent Document 2 Nikkan Kogyo Shimbun “Basics of Thin Film Creation” Tatsuo Maya p229

  The metal thin films 35 and 36 having such a structure can be formed by performing sputtering using a target material mainly composed of Ta. The film forming conditions are as shown in the column of (2) βa-Ta film in Table 1 as will be described later.

Next, a procedure for bonding the upper glass substrate 20, the central glass substrate 30, and the lower glass substrate 40 by anodic bonding will be described.
First, the upper glass substrate 20 and the central glass substrate 30 are heated by exposing them to a high temperature atmosphere. Then, with the metal thin film 35 and the upper glass substrate 20 in contact with each other, the anode is brought into contact with the metal thin film 35 side, and the cathode is placed on the upper surface of the upper glass substrate 20 (the surface opposite to the bonding surface with the central glass substrate 30). And a high voltage is applied between the metal thin film 35 and the upper glass substrate 20. Then, the positively charged metal element on the metal thin film 35 side and the SiO ₂ negatively charged oxygen atom on the upper glass substrate 20 side are covalently bonded. As described above, the upper glass substrate 20 and the central glass substrate 30 are joined.

Similarly, the bonded upper glass substrate 20 and central glass substrate 30 and the lower glass substrate 40 are heated by exposing them to a high temperature atmosphere. Then, with the metal thin film 36 and the lower glass substrate 40 in contact with each other, the anode is brought into contact with the metal thin film 36 side, and the cathode is formed on the lower surface of the lower glass substrate 40 (the surface opposite to the bonding surface with the central glass substrate 30). And the central glass substrate 30 and the lower glass substrate 40 are joined by applying a high voltage between the metal thin film 36 and the lower glass substrate 40.
Note that the central glass substrate 30 and the lower glass substrate 40 may be bonded first, and then the central glass substrate 30 and the upper glass substrate 20 may be bonded.

The reaction apparatus 10 in the present embodiment includes three glass substrates 20, 30, and 40. The metal thin films 35 and 36 formed on one surface and the other surface of the central glass substrate 30 contain Ta, and are tetragonal. In the anodic bonding with the upper glass substrate 20 and the lower glass substrate 40, the metal group has a crystal structure of the system, the space group belongs to P4 ₂ / mnm, and the density is 16.7 g / cm ^3. The thin films 35 and 36 can be made difficult to peel off. As a result, airtight reliability in anodic bonding can be improved.

Here, with respect to the β-Ta film which is the metal thin films 35 and 36 described above, two kinds of β-Ta films (βb-Ta film and βa-Ta film) are formed and peeled off under the following two conditions. As described above, it was confirmed that it is preferable to use βa-Ta films as the metal thin films 35 and 36 in the present invention.
(1) βb-Ta film A Ta film was formed on a glass substrate under the film forming conditions shown in Table 1 below. And the measurement and analysis of the X-ray diffraction were performed about the produced Ta film | membrane. As a result, as shown in FIG. 5, the Ta film described in Non-Patent Document 3 below could be indexed. Therefore, it was confirmed that the produced Ta film (hereinafter referred to as βb-Ta film) has the same crystal structure as the β-Ta film of Non-Patent Document 3.
(2) βa-Ta film A Ta film was formed on a glass substrate under the film forming conditions shown in Table 1 below. And the measurement and analysis of the X-ray diffraction were performed about the produced Ta film | membrane (henceforth a beta-Ta film | membrane). As a result, as shown in FIG. 6, the Ta film described in Non-Patent Document 4 below could be indexed. Further, according to the following non-patent document 5, the space group of the βa-Ta film is P4 ₂ / mnm.

The X-ray diffraction of the two types of βb-Ta film and βa-Ta film prepared as described above was measured after the manufacturing process shown in FIG. 4 described above. There was no significant difference between the diffraction patterns after the process.
Table 2 shows the frequency of peeling for two types of films, a βb-Ta film (in 24 chips) and a βa-Ta film (in 48 chips). The peeling of the Ta film was confirmed by visually observing the chip after dicing. That is, the case where even a slight peeling was observed in one chip was regarded as a chip with peeling, and the determination was made based on the ratio in the evaluation target chip. As is clear from this result, it can be seen that the βa-Ta film is more difficult to peel than the βb-Ta film.

Non-Patent Document 3 MHRead and Carl Altman: Applied Physics letters 7 (1965) 51-52
Non-Patent Document 4 PTMoseley and CJSeabrook: Acta Cryst. B29 (1973) 1170-1171
Non-Patent Document 5 JCPDS card pdf number 00-025-1280

Further, the density described in Non-Patent Documents 1 and 4 for the bulk Ta, α-Ta film, βb-Ta film, and βa-Ta film is shown in Table 3 together with the lattice constant and the crystal system or crystal structure. . These films are, in descending order of density, bulk Ta> βa-Ta film> βb-Ta film> α-Ta film. From the results of Non-Patent Document 2 and Tables 2 and 3, the ease of film peeling is α-Ta film> βb-Ta film> βa-Ta film. Therefore, it is recognized that the higher the density, the less the relationship between the density and the Ta film peeling.

Table 4 shows the density of βb-Ta film and βa-Ta film obtained from Rutherford backscattering (RBS) and film thickness.

Since the density determination method in Table 4 is different from that in Table 3, the density of βb-Ta film and βa-Ta film in Table 3 is higher than the density of βb-Ta film and βa-Ta film in Table 4. . However, the magnitude relationship of density is βa-Ta film> βb-Ta film, which is the same as that of Table 3.
From the above, it is desirable that the Ta film has a high density in order to be a film that does not easily peel off. Of the Ta films described above, a βa-Ta film (density 16.7 g / cm ³ , space group P4 ₂ / mnm) Is most preferred.

It is a block diagram of the electric power generating apparatus 100 with which the reaction apparatus 10 with which this invention is applied is used. 1 is a plan view of a reaction device 10. FIG. It is arrow sectional drawing at the time of cut | disconnecting along the cutting line III-III of FIG. 5 is a diagram showing a manufacturing process of the central glass substrate 30. FIG. 2 is an X-ray diffraction spectrum of a βb-Ta film. 2 is an X-ray diffraction spectrum of a βa-Ta film.

Explanation of symbols

10 Reactor (bonded substrate)
20 Upper glass substrate (second glass substrate)
30 Central glass substrate (first glass substrate)
40 Lower glass substrate (second glass substrate)
35, 36 Metal thin film

Claims (3)

A first glass substrate having a metal thin film formed on one surface;
A second glass substrate anodically bonded by the metal thin film,
A bonded substrate, wherein at least a part of the metal thin film is Ta, has a tetragonal crystal structure, and the space group belongs to P4 ₂ / mnm. A first glass substrate having a metal thin film formed on one surface;
A second glass substrate anodically bonded by the metal thin film,
At least a part of the metal thin film is Ta, has a tetragonal crystal structure, and has a density of 16.7 g / cm ³ . A reaction apparatus using the bonding substrate according to claim 1.

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