Microchannel device and method for producing microchannel device

Abstract

To provide a microchannel device excellent in optical transparency. This microchannel device 1 is formed by bonding a transparent cover substrate 20 to a transparent base substrate 10 in which grooves 11 serving as microchannels 12 have been formed, via a bonding layer 40 so as to cover the grooves 11. The bonding layer 40 is a transparent oxide thin film having a film thickness of 40 nm or less, formed by a laminated structure of a first oxide thin film 41 adhered to the surface of the base substrate 10 and a second oxide thin film 42 adhered to the surface of the cover substrate 20. The interface between the first oxide thin film 41 and the second oxide thin film 42 is integrated by atomic diffusion and / or chemical bonding generated at the interface.

Description

Microchannel device and method for manufacturing the same

[0001] The present invention relates to a microchannel device comprising a substrate having a microchannel for introducing a fluid, and a method for manufacturing the same.

[0002] [Microfluidic Devices] Microfluidic devices are devices in which minute channels (microchannels) are formed on a substrate made of resin, glass, or other materials, and are also called μTAS (Micro Total Analysis Systems) or flow cells.

[0003] Microfluidic devices are able to freely mix and divide liquids or particles together with liquids within the microchannels by forming the microchannels in a pattern suited to the application or purpose. In recent years, they have been used in a wide range of applications in fields such as life science, chemistry, and analysis.

[0004] Microchannels formed on substrates are often made into intricate structures on a flat surface to perform various functions internally, and advances in microfabrication technology and microfluidics have made it possible to control the complex flow and diffusion of the channels with high precision.

[0005] As a result, it is now possible to mix, react, and separate small amounts of reagents and samples with high precision, making it extremely useful for small-scale chemical synthesis and genetic analysis.

[0006] Another major advantage is that, in tests that use rare or expensive reagents, only small amounts of reagents are required to conduct the experiment.

[0007] Such microchannel devices are typically constructed by bonding a substrate (hereinafter referred to as a "base substrate") having a groove formed on a flat surface that serves as the microchannel with another substrate (hereinafter referred to as a "cover substrate") that covers the groove, thereby forming a two-dimensional microchannel with a sealed structure within the aforementioned groove.

[0008] Such a sealed microchannel can be formed by attaching a cover substrate to only one side of the base substrate when a groove with a bottom that does not penetrate the base substrate is formed in the base substrate, but by attaching cover substrates to both sides of the base substrate when a groove that penetrates the base substrate is formed.

[0009] [Advantages of Glass Microfluidic Devices] Resins (polymers), glass, etc. are used as materials for microfluidic devices (materials for the base substrate and cover substrate).

[0010] Of these, microfluidic devices made from resin (polymer) have the advantage of being able to be mass-produced at low cost. However, glass microfluidic devices have the following advantages over resin microfluidic devices. Therefore, there is expected to be a great deal of demand for glass microfluidic devices in fields that require high-precision synthesis and analysis.

[0011] 1) Optical transparency: Glass has high light transmittance, and microfluidic devices fabricated using glass base and cover substrates can be observed by imaging, and highly accurate optical evaluations such as fluorescence and Raman spectroscopy can be performed. In particular, glass has little autofluorescence, which is a problem with resins. In addition, the glass material can be selected according to the purpose.

[0012] 2) Thermal stability Some resin microfluidic devices are subject to deterioration or damage when exposed to laser light during measurements, but glass microfluidic devices are less susceptible to deterioration or damage from laser light, making them suitable for high-precision fluorescence analysis.

[0013] 3) Chemical stability: With resin microchannel devices, depending on the type of liquid (drug) introduced into the microchannel, it is necessary to consider the risk that the drug will penetrate into the substrate and be dissolved by organic solvents. However, glass has excellent chemical resistance, and various reagents and organic solvents can be used without worrying about leaching.

[0014] 4) Processing precision Grooves are formed in a resin base substrate by cutting processes using machining, but ultrafine processing can be performed on a glass base substrate by applying semiconductor manufacturing processes, etc., which allows for precise processing of minute flow channels, including the width and shape of the channel, and also makes it easy to form wiring and electrodes inside the microchannel device.

[0015] [Importance of Bonding Technology] As explained above, microfluidic devices fabricated using glass substrates have many advantages over microfluidic devices made of resin (polymer).

[0016] However, as mentioned above, microchannel devices are fabricated by overlapping and bonding a cover substrate to a base substrate with grooves formed therein. If the base substrate and cover substrate are bonded using an organic adhesive, the organic adhesive may dissolve into the liquid passing through the reaction channel, causing contamination with impurities or peeling of the bonded portion.

[0017] Furthermore, organic adhesives do not have a sufficiently high light transmittance, which is necessary for light-based analysis, and have other problems such as poor light resistance and susceptibility to deterioration.

[0018] As a result, even if glass is selected as the material for the base substrate and cover substrate, if they are bonded using an organic adhesive, the aforementioned properties of the glass microchannel device, namely, "1) optical transparency," "2) thermal stability," and "3) chemical stability," may not be fully exhibited, and the bonding strength may not be ensured.

[0019] Thus, in order to improve the performance of microchannel devices, it is important not only to consider the materials used for the base substrate and cover substrate, but also to consider how the base substrate and cover substrate are bonded.

[0020] [Conventional bonding technology that does not use organic adhesives and its problems] As a method for manufacturing a microchannel device by bonding a base substrate and a cover substrate without using an organic adhesive, Patent Document 1 listed below describes a method in which a glass cover substrate is superimposed on the bonding surface of a glass base substrate having a metal thin film formed on the bonding surface, and the base substrate and cover substrate are anodically bonded by contacting the metal film with an anode and the cover substrate with a cathode and applying a voltage (Abstract of Patent Document 1).

[0021] However, anodic bonding is a technology that bonds glass substrates by applying a high voltage in a high-temperature environment (e.g., 300°C to 400°C) to generate an electric field within the substrates (paragraph

[0003] of Patent Document 1). This means that the substrates can be distorted by heating during bonding, and the optical performance of the microchannel device can be degraded by internal stress induced within the substrates.

[0022] Furthermore, if anodic bonding is applied to the manufacture of advanced microfluidic devices that incorporate electrodes, electronic devices, etc. into the microfluidic channels, there is a risk that the electrodes or devices will be destroyed by heat, and therefore anodic bonding cannot be applied to the manufacture of such microfluidic devices.

[0023] Surface activation using oxygen plasma, etc., is a direct bonding technique that allows bonding at lower temperatures than anodic bonding.

[0024] However, to firmly bond glass substrates using this method, the glass surface must be cleaned with chemicals or oxygen plasma, and a heating process must be carried out at temperatures exceeding 200° C. Another problem is that the glass materials that can be bonded are limited.

[0025] Therefore, there are still problems such as distortion of the substrate due to heating and deterioration of optical performance due to internal stress induced in the substrate.

[0026] As explained above, in order to solve the problems that arise when manufacturing a microchannel device by bonding using an organic adhesive or by bonding that requires heating at a temperature exceeding 200°C, Patent Document 2, which will be mentioned later, describes a method of bonding a base substrate and a cover substrate using a metal oxide layer formed by heat-treating a hydrolysis / dehydration condensation product of an organometallic compound at a relatively low temperature of 135 to 200°C as a bonding layer (Claim 2,

[0013] of Patent Document 2).

[0027] Furthermore, Patent Document 3, listed below, describes a method in which a metal coating layer of gold (Au) or the like is formed by sputtering on the surface of the base substrate and the surface of the cover substrate, respectively, and the base substrate and the cover substrate are superimposed so that the two metal coating layers come into contact with each other, thereby diffusing metal atoms in the metal coating layer of the base substrate and the metal coating layer of the cover substrate, thereby bonding them at room temperature (Claim 1 and others of Patent Document 3).

[0028] Although not related to a method for joining a base substrate and a cover substrate of a microchannel device, Patent Document 4 listed below describes a method for joining two substrates, in which an amorphous oxide thin film is formed on each smooth surface of two substrates in a vacuum chamber, and the two substrates are overlapped so that the amorphous oxide thin films formed on the two substrates come into contact with each other, thereby generating chemical bonds at the bonding interface of the amorphous oxide thin films, thereby joining the two substrates (Claim 1 and others of Patent Document 4).

[0029] Furthermore, although not related to a method for bonding a base substrate and a cover substrate of a microchannel device, Patent Document 5 listed below describes a bonding method including the steps of: forming a bonding film, which is a thin film formed by vacuum deposition and is made of a metal or semiconductor with at least an oxidized surface, on each of two smooth surfaces of two substrates; exposing the surfaces of the bonding films formed on the two substrates to a space containing moisture to hydrophilize the surfaces of the bonding films; and bonding the two substrates by overlapping them so that the surfaces of the bonding films in a hydrophilized state come into contact with each other (Claim 1 and others of Patent Document 5).

[0030] Japanese Patent Publication No. 2007-70176 Japanese Patent Publication No. 2004-74339 International Publication No. WO2021 / 090900 Japanese Patent Publication No. 2021-041458 Japanese Patent No. 7165342

[0031] Of the conventional techniques described above, the bonding method described in Patent Document 2 makes it possible to bond a base substrate and a cover substrate without using an organic adhesive and without requiring heating at high temperatures.

[0032] However, in Patent Document 2, a metal oxide layer formed by a method of hydrolysis and dehydration condensation of an organometallic compound (the so-called sol-gel method) is used as the bonding layer. However, since this method is a chemical synthesis method, the metal oxide layer serving as the bonding layer contains a large amount of organic substances as impurities inside.

[0033] As a result, when a solvent is flowed into the microchannel or when the microchannel device is heated, there is still a possibility that organic matter present as impurities in the bonding layer will dissolve into the fluid flowing through the microchannel, thereby contaminating the fluid with the organic matter.

[0034] Furthermore, metal oxides containing such organic substances as impurities have low light transmittance, and therefore, when the base substrate and cover substrate are bonded via a bonding layer made of such metal oxides, the light transmittance of the resulting microchannel device also decreases, thereby degrading the optical properties of the microchannel device.

[0035] Furthermore, Patent Document 2 states that the thickness of the bonding layer is preferably 0.1 to 3.0 μm in order to achieve a uniform thickness for bonding the base substrate and cover substrate with sufficient strength (Patent Document 2

[0014] ). If the bonding layer is thicker than 0.1 μm, the light transmittance through the bonding layer will decrease. Furthermore, because the thickness of the bonding layer is approximately the same as the optical wavelength, light interference will occur, which will affect analysis using transmitted light.

[0036] In Patent Document 3, the base substrate and the cover substrate are bonded by atomic diffusion that occurs when metal coating layers such as gold (Au) formed by sputtering are superimposed on each other, so bonding can be performed at room temperature without heating, and by making the metal coating layer thin, the bonding layer that bonds the base substrate and the cover substrate can be made transparent.

[0037] However, no matter how thin it is formed, a metal film exists between the base substrate and the cover substrate as a bonding layer, and even if the base substrate and cover substrate are made of transparent materials, the light absorption and reflection caused by the metal film existing as a bonding layer reduces the light transmittance of the microchannel device.On the other hand, if the thickness of the metal coating layer is reduced to improve the light transmittance, the required bonding strength cannot be obtained.

[0038] Furthermore, the metal coating layer present at the bonding interface reduces the insulating properties of the bonding interface, which hinders the formation of wiring and electrodes inside the microchannel device.

[0039] Furthermore, depending on the material of the metal coating layer, when it comes into contact with the liquid flowing through the microchannel, it may leach out and contaminate the liquid in the microchannel. To prevent such contamination, it is necessary to use gold (Au), which is chemically stable but expensive, as the material for the metal coating layer (Patent Document 3

[0060] ), which increases the manufacturing cost of the microchannel device. In addition, precious metals such as gold have poor light transmittance, and in order to obtain high bonding strength, an underlayer made of another metal is required.

[0040] In this way, in conventional microfluidic devices in which the base substrate and cover substrate are bonded via a bonding layer, the presence of the bonding layer reduces the optical transparency, thermal stability, chemical stability, and electrical insulation of the microfluidic device.

[0041] Although the above-mentioned Patent Documents 4 and 5 disclose a bonding method using an oxide thin film, they do not disclose or suggest at all about the application of this bonding method to a microchannel device, nor do they disclose or suggest at all about the light transmittance at the bonding interface.

[0042] Therefore, the present invention has been made to overcome the drawbacks of the above-mentioned conventional technology, and aims to provide a microchannel device in which the base substrate and the cover substrate are bonded via a bonding layer, and which exhibits excellent optical transparency, preferably thermal stability, chemical stability, and electrical insulation in addition to optical transparency, and which can ensure sufficient bonding strength between the base substrate and the cover substrate, and a method for manufacturing such a microchannel device.

[0043] The means for solving the problems will be described below together with the reference numerals used in the description of the embodiment of the invention. These reference numerals are used to clarify the correspondence between the description of the claims and the description of the embodiment of the invention, and needless to say, are not used to restrict the interpretation of the technical scope of the present invention.

[0044] In order to achieve the above object, the microfluidic device 1 of the present invention is a microfluidic device 1 having a microchannel 12, which is a fine channel through which a fluid is introduced, comprising: a transparent base substrate 10 in which grooves 11 of a predetermined pattern that become the microchannel 12 are formed; and a transparent cover substrate 20 bonded to the base substrate 10 so as to cover the grooves 11, wherein a non-groove portion 13, which is a portion of the surface of the base substrate 10 where the grooves 11 are not formed, and a bonding portion 23, which is a portion of the cover substrate 20 that overlaps with the non-groove portion 13, are bonded by a bonding layer 40 made of a transparent oxide thin film with a thickness of 40 nm or less, and the bonding layer 40 is a laminated structure of a first oxide thin film 41 made of a metal or semiconductor oxide attached to the non-groove portion 13 of the base substrate 10 and a second oxide thin film 42 made of a metal or semiconductor oxide attached to the bonding portion 23 of the cover substrate 20, and the interface between the first oxide thin film 41 and the second oxide thin film 42 is bonded by atomic diffusion and / or chemical bonding that occurs at the interface (claim 1).

[0045] It is preferable that both the base substrate 10 and the cover substrate 20 be made of glass, which has superior optical transparency, thermal stability, chemical stability, and micro-machining properties compared to resin (claim 2). It is even more preferable that one or both of the base substrate 10 and the cover substrate 20 be made of quartz glass, which is compatible with semiconductors and semiconductor devices and allows the use of semiconductor micro-machining techniques (claim 3).

[0046] It is also preferable that the first oxide thin film 41 and the second oxide thin film 42 have an amorphous structure.

[0047] The first oxide thin film 41 and the second oxide thin film 42 may be formed only on the non-groove portion 13 of the base substrate 10 and the joint portion 23 of the cover substrate 20 (see Figures 2 and 5), or the first oxide thin film 41 may be formed so as to cover the inner wall surface of the groove 11 together with the non-groove portion 13 of the base substrate 10, and the second oxide thin film 42 may be formed so as to cover the groove cover portion 21, which is the portion that covers the groove 11, together with the joint portion 23 of the cover substrate 20 (claim 5; see Figures 3 and 6).

[0048] The light transmittance of the bonding layer 40 is preferably 94% or more, and more preferably 97% or more.

[0049] The bonding strength between the first oxide thin film 41 and the second oxide thin film 42 in the bonding layer 40 is 0.6 J / m in terms of the magnitude of the surface free energy γ of the bonding interface evaluated by the blade method. 2 It is preferable that the concentration is 1 J / m or more. 2 It is more preferable if it is equal to or greater than this (claims 7 and 8).

[0050] The first oxide thin film 41 can have any one oxide selected from the group consisting of SiO2, Al2O3, Y2O3, and ZrO2 as a main element, and the second oxide thin film 42 can have any one oxide selected from the group consisting of SiO2, Al2O3, Y2O3, and ZrO2 as a main element, and the first oxide thin film 41 and the second oxide thin film 42 can have the same or different elements as the main element (claim 9).

[0051] It is preferable that the purity of the oxides in the first oxide thin film 41 and the second oxide thin film 42 is 99.5% or more (claim 10).

[0052] Furthermore, a method for manufacturing a microchannel device according to the present invention is a method for manufacturing a microchannel device 1 equipped with microchannels, which are fine channels into which a fluid is introduced, comprising the steps of: preparing a base substrate 10, which is a transparent substrate, and having grooves 11 of a predetermined pattern formed on its surface to become the microchannels 12; and bonding a cover substrate 20, which is also a transparent substrate, to the base substrate 10 so as to cover the grooves 11, wherein the bonding step comprises a film formation step of forming, by vacuum film formation, a transparent first oxide thin film 41 which is an oxide of a metal or semiconductor with an amorphous structure on non-groove portions 13, which are at least portions of the surface of the base substrate 10 where the grooves 11 are not formed, and forming a transparent second oxide thin film 42 which is an oxide of a metal or semiconductor with an amorphous structure on bonding portions 23, which are portions of the cover substrate 20 that overlap at least the non-groove portions 13; The method includes a bonding step of bonding the first oxide thin film 41 and the second oxide thin film 42 on the non-groove portion 13 in a vacuum at room temperature without exposing them to the atmosphere, thereby causing atomic diffusion at the bonding interface to bond the first oxide thin film 41 and the second oxide thin film 42, and is characterized in that the base substrate 10 and the cover substrate 20 are bonded between the non-groove portion 13 and the bonding portion 23 by a transparent bonding layer 40 having a thickness of 40 nm or less and consisting of a laminated structure of the first oxide thin film 41 and the second oxide thin film 42 bonded by the bonding step (claim 11).

[0053] In the manufacturing method of the microchannel device having the above configuration, the bonding step may further include a heating step of heating the base substrate 10 and the cover substrate 20 at a temperature of 200°C or less after the bonding step (claim 12).

[0054] Another method for manufacturing a microchannel device according to the present invention is a method for manufacturing a microchannel device 1 equipped with microchannels 12, which are fine channels into which a fluid is introduced, comprising the steps of: preparing a base substrate 10, which is a transparent substrate, and having grooves 11 of a predetermined pattern formed on its surface to form the microchannels 12; and bonding a cover substrate 20, which is also a transparent substrate, to the base substrate 10 so as to cover the grooves 11, wherein the bonding step comprises: forming, by vacuum film formation, a transparent first oxide thin film 41 made of a metal or semiconductor oxide on non-groove portions 13, which are at least portions of the surface of the base substrate 10 where the grooves 11 are not formed, and forming a transparent second oxide thin film 42 made of a metal or semiconductor oxide on bonding portions 23, which are portions of the cover substrate 20 that overlap with at least the non-groove portions 13; and exposing the first oxide thin film 41 on the non-groove portions 13 and the second oxide thin film 42 on the bonding portions 23 to a space containing moisture to make them hydrophilic, and then superposing them together at room temperature. By heating the base substrate 10 and the cover substrate 20 at a temperature of 200° C. or less, a chemical bond or a chemical bond and atomic diffusion is generated at the bonding interface between the first oxide thin film 41 on the non-groove portion 13 and the second oxide thin film 42 on the bonding portion 23, and the bonding interface is evaluated by a blade method to have a surface free energy γ of 0.6 J / m 2 More than 1 J / m, preferably 1 J / m 2 The method includes a bonding step of bonding the first oxide thin film 41 and the second oxide thin film 42 with a bonding strength of at least 100%, and is characterized in that the base substrate 10 and the cover substrate 20 are bonded between the non-groove portion 13 and the bonding portion 23 by a transparent bonding layer 40 having a thickness of 40 nm or less and consisting of a laminated structure of the first oxide thin film 41 and the second oxide thin film 42 bonded by the bonding step (claim 13).

[0055] Furthermore, still another method for manufacturing a microchannel device according to the present invention is a method for manufacturing a microchannel device 1 equipped with a microchannel 12, which is a fine channel into which a fluid is introduced, comprising the steps of: preparing a base substrate 10, which is a transparent substrate, and having grooves 11 of a predetermined pattern formed on its surface to become the microchannels 12; and bonding a cover substrate 20, which is also a transparent substrate, to the base substrate 10 so as to cover the grooves 11, wherein the bonding step comprises: depositing, by vacuum deposition, a first thin film made of a metal or semiconductor on non-groove portions 13, which are at least portions of the surface of the base substrate 10 where the grooves 11 are not formed, and depositing a second thin film made of a metal or semiconductor on bonding portions 23, which are portions of the cover substrate 20 that overlap at least the non-groove portions 13; a step of exposing the first thin film and the second thin film to moisture or a space containing moisture and oxygen to oxidize them, thereby obtaining a transparent first oxide thin film 41 formed by the oxidation of the first thin film and a transparent second oxide thin film 42 formed by the oxidation of the second thin film, and making them hydrophilic, and then laminating the first oxide thin film 41 on the non-groove portion 13 and the second oxide thin film 42 on the bonding portion 23 at room temperature; and a step of heating the base substrate 10 and the cover substrate 20 at a temperature of 200° C. or less to generate chemical bonds, or chemical bonds and atomic diffusion, at the bonding interface between the first oxide thin film 41 on the non-groove portion 13 and the second oxide thin film 42 on the bonding portion 23, thereby increasing the magnitude of the surface free energy γ of the bonding interface, as evaluated by a blade method, to 0.6 J / m 2 More than 1 J / m, preferably 1 J / m 2 The method includes a bonding step of bonding the first oxide thin film 41 and the second oxide thin film 42 with a bonding strength of at least 100%, and is characterized in that the base substrate 10 and the cover substrate 20 are bonded between the non-groove portion 13 and the bonding portion 23 by a transparent bonding layer 40 having a thickness of 40 nm or less and consisting of a laminated structure of the first oxide thin film 41 and the second oxide thin film 42 bonded by the bonding step (claim 14).

[0056] In both of the above-mentioned methods for manufacturing a microchannel device, the first oxide thin film 41 may be provided so as to cover the inner wall surface of the groove 11 together with the non-groove portion 13 of the base substrate 10, and the second oxide thin film 42 may be provided so as to cover the groove cover portion 21, which is the portion that covers the groove 11, together with the bonding portion 23 of the cover substrate 20 (claim 15).

[0057] In any of the above-mentioned methods for manufacturing a microchannel device, it is preferable that the film formation step be carried out by a method that involves rapid cooling of the source atoms on the surfaces of the base substrate 10 and the cover substrate 20 (claim 16).

[0058] With the configuration of the present invention described above, it is possible to obtain a microchannel device 1 that has excellent optical transparency, thermal stability, chemical stability, and electrical insulation while ensuring the bonding strength between the base substrate 10 and the cover substrate 20, without heating at a high temperature exceeding 200°C.

[0059] That is, in the microchannel device 1 of the present invention, the bonding layer 40 that bonds the base substrate 10 and the cover substrate 20 is configured as a laminated structure of a first oxide thin film 41 and a second oxide thin film 42. Such oxide thin films, particularly oxide thin films with an amorphous structure, are optically transparent and have a thin film thickness of 40 nm or less, and therefore have high light transmittance.

[0060] Furthermore, in addition to the bonding layer 40 being a thin oxide film, its film thickness is 40 nm or less, which is an order of magnitude smaller than the wavelength of light (e.g., visible light) used in optical evaluation. Therefore, the effect of the refractive index of the bonding layer 40 on the transmitted light can be ignored. Furthermore, the bonding layer 40 being a thin oxide film has little autofluorescence, which is a problem with resins. Therefore, the presence of the bonding layer 40 does not interfere with high-precision optical evaluation such as imaging observation, fluorescence measurement, or Raman spectroscopy measurement.

[0061] Furthermore, compared to organic adhesives, oxide thin films are chemically and thermally stable, and therefore by bonding via a bonding layer 40 made of an oxide thin film, it is possible to improve the chemical and thermal stability of the microchannel device 1, allowing various reagents and organic solvents to be used in reactions within the channel.Furthermore, there is little deterioration or damage caused by lasers, making it applicable to high-precision fluorescence analysis, etc.

[0062] Furthermore, contamination and deterioration due to temperature rise can be prevented, and a strong bonded state can be maintained in a chemically and thermally stable manner, thereby preventing leakage of sample solutions and reaction solutions.

[0063] In addition, the bonding layer 40, which is a thin oxide film, is insulating, and the presence of the bonding layer 40 does not hinder the provision of wiring, electrodes, electronic devices, etc. on the microchannel device.

[0064] Furthermore, the bonding of the base substrate 10 and the cover substrate 20 via the bonding layer 40 having such excellent properties can be achieved by overlapping the first oxide thin film 41 formed on the non-groove portion 13 of the base substrate 10 with the second oxide thin film 42 formed on the bonding portion 23 of the cover substrate 10 at room temperature, or by heating at a temperature of 200°C or less after overlapping. This prevents the deterioration of optical properties that accompanies high-temperature heating, and also enables electrodes and electronic devices to be mounted on the microchannel device 1.

[0065] In a configuration in which the base substrate 10 and the cover substrate 20 are made of glass, such as quartz glass used in semiconductor devices, the optical transparency, thermal stability, chemical stability, and electrical insulation of not only the bonding layer 40 but also the base substrate 10 and the cover substrate 20 are improved, and this, combined with the fact that the bonding layer 40 is made of an oxide thin film, further improves the optical transparency, thermal stability, chemical stability, and electrical insulation of the microchannel device 1.

[0066] Furthermore, by forming the above-mentioned first oxide thin film 41 not only on the non-groove portion 13 of the base substrate but also on the inner wall surface of the groove 11, and by forming the second oxide thin film 42 so as to cover not only the bonding portion 23 of the cover substrate 20 but also the groove cover portion 21 which is the portion that covers the groove 11, the inner wall of the microchannel 12 formed in the microchannel device 1 is coated with a thin film of oxide (oxide-based ceramics) such as Al2O3 or ZrO2, and it is possible to prevent the fluid (chemical) introduced into the microchannel 12 from coming into direct contact with the base material of the base substrate 10 or the cover substrate 20.

[0067] As a result, not only when glass is used as the material for the base substrate 10 or the cover substrate 20, but also when a material other than glass, such as a resin (polymer), is used, it is possible to suppress the elution of the base material of the base substrate 10 or the cover substrate 20 due to contact with fluids (chemicals), etc., and the chemical stability of the microchannel device 1 can be improved without impairing the translucency, etc., of the microchannel device 1.

[0068] (A) is a perspective view, and (B) is an exploded perspective view, of a microchannel device of the present invention. (A) is a widthwise cross-sectional view of the microchannel device of FIG. 1, and (B) is a widthwise cross-sectional view in a disassembled state. (A) is a widthwise cross-sectional view of a modified example of the microchannel device of FIG. 1, and (B) is a widthwise cross-sectional view in a disassembled state. (A) is a perspective view, and (B) is an exploded perspective view of another microchannel device of the present invention. (A) is a widthwise cross-sectional view of the microchannel device of FIG. 4, and (B) is a widthwise cross-sectional view in a disassembled state. (A) is a widthwise cross-sectional view of a modified example of the microchannel device of FIG. 4, and (B) is a widthwise cross-sectional view in a disassembled state. An explanatory diagram of the "blade method" used to measure the bonding strength (surface free energy of the bonding interface) γ. (A) is a correlation diagram between film thickness and light transmittance, and (B) is a correlation diagram between film thickness and bonding strength γ, of the sample of Example 1-1 bonded in a vacuum using a YO thin film. (A) is a correlation diagram between film thickness and optical transmittance, and (B) is a correlation diagram between film thickness and bonding strength γ, for the sample of Example 1-2 bonded in a vacuum using an Al2O3 thin film. (A) is a correlation diagram between film thickness and optical transmittance, and (B) is a correlation diagram between film thickness and bonding strength γ, for the sample of Example 1-3 bonded in a vacuum using a ZrO2 thin film. Cross-sectional electron microscope photograph (TEM) of Si wafers bonded in a vacuum using a 5 nm ZrO2 thin film (bonding layer thickness 10 nm) on one side. (A) is a correlation diagram between film thickness and optical transmittance, and (B) is a correlation diagram between film thickness and bonding strength γ, for the sample of Example 2 bonded in the atmosphere using a YO3 thin film formed by vacuum deposition. Cross-sectional electron microscope photograph (TEM) of Si wafers (heated at 150°C after bonding) bonded in the atmosphere using a YO3 thin film (bonding layer thickness 10 nm) on one side. Amorphous SiO obtained by oxidizing an amorphous Si thin film formed by vacuum deposition in the atmosphere. X (A) is a correlation diagram of film thickness vs. light transmittance, and (B) is a correlation diagram of film thickness vs. bonding strength γ for the sample of Example 3 bonded using a thin film. Amorphous SiO X(A) is a cross-sectional electron microscope (TEM) photograph of Si wafers (heated at 150°C after bonding) bonded using a thin film, and (B) is a graph showing the results of structural analysis by electron energy loss spectroscopy (EELS). (A) is a correlation diagram between film thickness and light transmittance, and (B) is a correlation diagram between film thickness and bonding strength γ for a sample of Comparative Example 1 bonded in a vacuum using a Ti thin film formed by vacuum deposition, a sample of Comparative Example 2 bonded in a vacuum using a Zr thin film formed by vacuum deposition, and a sample of Comparative Example 3 bonded in the atmosphere using an Au thin film formed by vacuum deposition.

[0069] The microchannel device and the method for manufacturing the same of the present invention will be described below with reference to the drawings.

[0070] [Overall Structure of Microchannel Device] Reference numeral 1 in FIG. 1 denotes the microchannel device of the present invention. As shown in FIG. 2(A), this microchannel device 1 is composed of a base substrate 10 on which grooves 11 of a predetermined pattern (linear patterns in the illustrated example) that become microchannels 12 are formed, and a cover substrate 20 bonded to the base substrate 10 via a bonding layer 40. By bonding the cover substrate 20 to the base substrate 10 so as to cover the grooves 11, the grooves 11 of the base substrate 10 are sealed by the cover substrate 20, thereby forming microchannels 12 that have a sealed structure within the grooves 11.

[0071] The cover substrate 20 described above has fluid inlet ports 24 and outlet ports 25, etc., penetrating the cover substrate 20 at positions communicating with the grooves 11 formed in the base substrate 10, thereby enabling fluid to be injected into the microchannel 12 and fluid to be discharged from the microchannel 12.

[0072] The groove 11 formed in the base substrate 10 may be a bottomed groove 11 that does not penetrate the base substrate 10, as shown in Figures 1 to 3. In this case, a microchannel 12 with a sealed structure is formed within the groove 11 by bonding a cover substrate 20 to only one surface (top surface) of the base substrate 10.

[0073] On the other hand, the groove 11 formed in the base substrate 10 may be formed by penetrating the base substrate 10 as shown in Figures 4 to 6. In this case, by bonding cover substrates 20, 20 to both surfaces (upper and lower surfaces) of the base substrate 10, a microchannel 12 with a sealed structure is formed within the groove 11.

[0074] [Base Substrate and Cover Substrate] The above-mentioned base substrate 10 and cover substrate 20 can be manufactured using transparent materials such as glass and resin, and it is preferable to use glass because it has superior optical transparency, thermal stability, chemical stability, and micro-machining properties compared to resin.

[0075] Such glass is not particularly limited as long as it has high optical transparency, excellent thermal stability, and excellent chemical stability. When using fluorescence measurement, Raman spectroscopy, or the like to observe a fluid, the base substrate 10 and the cover substrate 20 may be made of glass whose composition is adjusted to be suitable for the optical evaluation to be used.

[0076] Among types of glass, quartz glass is a high-purity glass formed from SiO2 (silicon dioxide), and is superior to ordinary glass in terms of light transmittance, corrosion resistance, heat resistance, etc., and is also highly compatible with microfabrication techniques used in semiconductor manufacturing processes. Therefore, when glass is used as the material for the base substrate 10 and cover substrate 20 described above, the use of quartz glass is particularly preferable.

[0077] Moreover, instead of such glass, the base substrate 10 and the cover substrate 20 may be made of a transparent crystalline substrate such as sapphire, a transparent ceramic substrate, or the like.

[0078] The base substrate 10 and the cover substrate 20 do not necessarily have to be made of the same material, and different materials may be used for the base substrate 10 and the cover substrate 20 .

[0079] [Bonding Layer] (1) Structure of the Bonding Layer The base substrate 10 and the cover substrate 20 are bonded together via a bonding layer 40, which is a transparent thin film made of an oxide of a metal or semiconductor.

[0080] The base substrate 10 and the cover substrate 20 are joined by joining the non-groove portion 13, which is the portion of the surface of the base substrate 10 where the aforementioned groove 11 is not formed, to the joining portion 23, which is the portion of the cover substrate 20 that overlaps with the non-groove portion 13, via the aforementioned joining layer 40.

[0081] As shown in Figures 2(A) and 5(A), this bonding layer 40 is configured as a laminated structure of a first oxide thin film 41 made of an oxide of a metal or semiconductor attached to the non-groove portion 13 of the base substrate 10 and a second oxide thin film 42 made of an oxide of a metal or semiconductor attached to the bonding portion 23 of the cover substrate 20, and the interface between the first oxide thin film 41 and the second oxide thin film 42 is bonded by atomic diffusion or chemical bonding that occurs at the interface, preferably in a state where the interface has disappeared.

[0082] (2) Areas of formation of the first oxide thin film and the second oxide thin film The first oxide thin film 41 and the second oxide thin film 42 described above may be formed using a resist, an anti-adhesion mask, or the like, so that the first oxide thin film 41 is formed only on the non-groove portion 13 of the base substrate 10 and the second oxide thin film 42 is formed only on the bonding portion 23 of the cover substrate 20, as shown in Figures 2 and 5, and are not formed on the inner wall of the groove 11 of the base substrate 10 or the groove cover portion 21 of the cover substrate 20.

[0083] Alternatively, as shown in Figures 3 and 6, the first oxide thin film 41 may be formed to cover not only the non-groove portion 13 of the base substrate 10 but also the inner wall of the groove 11, and the second oxide thin film 42 may be formed to cover not only the bonding portion 23 of the cover substrate 20 but also the groove cover portion 21.

[0084] As shown in Figures 3 and 6, when the first oxide thin film 41 and the second oxide thin film 42 are formed on the inner wall of the groove 11 provided in the base substrate 10 and on the groove lid portion 21 of the cover substrate 20, the portion of the first oxide thin film 41 formed on the inner wall of the groove 11 and the portion of the second oxide thin film 42 formed on the groove lid portion 21 do not contribute to the bonding between the base substrate 10 and the cover substrate 20 (do not constitute the bonding layer 40).

[0085] However, by forming a thin oxide film on the inner wall of the groove 11 and the groove cover portion 21, the inner wall of the microchannel 12 formed in the microchannel device 1 is entirely coated with a thin oxide film of a metal or semiconductor that has excellent chemical stability, as shown in Figures 3(A) and 6(A), and the fluid (chemical) flowing inside the microchannel 12 does not come into direct contact with the base material of the base substrate 10 or the cover substrate 20.

[0086] As a result, not only when the base substrate 10 and the cover substrate 20 are made of glass, but also when they are made of a material other than glass (for example, resin), elution of the base substrate 10 and the cover substrate 20 can be prevented, and the chemical stability of the microchannel device 1 is improved.

[0087] (3) Characteristics of the bonding layer and the first and second oxide thin films (chemical and thermal stability) The oxides of metals and semiconductors, particularly oxides with an amorphous structure, which are the constituent materials of the first and second oxide thin films 41, 42 and the bonding layer 40 formed in the overlapping portion of the first oxide thin film 41 and the second oxide thin film 42, are chemically and thermally stable and can prevent the occurrence of degradation due to elution caused by contact with the fluid flowing through the microchannel 12 or irradiation with laser light, etc. In particular, when the base substrate 10 and the cover substrate 20 are made of glass, it is possible to form a chemically and thermally stable microchannel device 1 that takes advantage of the properties of glass.

[0088] (Light Transmittance and Film Thickness) In a configuration in which the first oxide thin film 41 is not formed on the inner wall of the groove 11 of the base substrate 10 and the second oxide thin film 42 is not formed on the groove lid portion 21 of the cover substrate 20 as shown in FIGS. 2 and 5 , it is possible to observe the fluid introduced into the microchannel 12 as long as the transparency of the base substrate 10 and the cover substrate 20 is ensured. However, in a configuration in which the first oxide thin film 41 is formed also on the inner wall of the groove 11 of the base substrate 10 and the second oxide thin film 42 is formed also on the groove lid portion 21 of the cover substrate 20 as shown in FIGS. 3 and 6 , when observing the fluid in the microchannel 12, the second oxide thin film 42 formed on the groove lid portion 21 of the cover substrate 20 and the first oxide thin film 41 formed on the bottom of the groove 11 need to have high light transmittance, which enables highly accurate optical measurements using high-intensity light such as laser light.

[0089] In this case, by making the thickness of the first oxide thin film 41 formed on the bottom of the groove 11 of the base substrate 10 and the second oxide thin film 42 formed on the groove lid portion 21 of the cover substrate 20 thinner by at least one order of magnitude than the wavelength of the light used for optical evaluation, the influence of the refractive index of the first oxide thin film 41 formed on the bottom of the groove 11 and the second oxide thin film 42 formed on the groove lid portion 21 on the optical evaluation can be ignored.

[0090] Furthermore, in a microchannel device 1 having such a structure, it is important to increase the light transmittance of the bonding layer 40 (the portion where the first oxide thin film 41 and the second oxide thin film 42 overlap) formed between the non-groove portion 13 of the base substrate 10 and the bonding portion 23 of the cover substrate 20, which is particularly important when providing a microchannel 12 with a narrow channel width.

[0091] In this way, by increasing the light transmittance of the bonding layer 40 and evaluating the physical properties of the fluid by irradiating it with light wider than the width of the flow path, highly efficient and accurate optical measurements are possible, and light that passes through the bonding layer 40 can also be used for measurements.

[0092] When the first and second oxide thin films 41, 42 are formed by sputtering or the like, the sputtered raw material atoms are unlikely to penetrate into the interior of the groove 11, and the first oxide thin film 41 formed on the inner wall of the groove 11 becomes thinner than the first oxide thin film 41 formed on the non-groove portion 13.

[0093] Furthermore, while only the first oxide thin film 41 exists on the inner wall of the groove 11 and only the second oxide thin film 42 exists on the groove cover portion 21, the bonding layer 40, which is a laminated structure of the first oxide thin film 41 and the second oxide thin film 42, exists between the non-groove portion 13 and the bonding portion 23. Therefore, deterioration of optical properties such as light transmittance becomes noticeable in the portion of the bonding layer 40, which is the thickest oxide thin film.

[0094] Therefore, it is important to evaluate the optical properties such as the light transmittance of the oxide thin film formed on the microchannel device 1 at the thickest part, the bonding layer 40, and the light transmittance of the bonding layer 40 is preferably 94% or more, and more preferably 97% or more. This allows for efficient evaluation of the physical properties of the liquid flowing through the microchannel 12.

[0095] In the present invention, the light transmittance of the bonding layer 40 was measured by the following method.

[0096] The intensity of light passing through two glass substrates stacked together (without bonding layer 40) was measured as a reference value, and the same optical system was used to measure the light intensity of two glass substrates of the same material and thickness as those used to measure the reference value, joined together via a bonding layer 40, and the light intensity was measured as an evaluation value.The light intensity of the evaluation value (with bonding layer) expressed as a percentage, with the light intensity of the reference value (without bonding layer) being set to 100%, was taken as the light transmittance.

[0097] The reference value and evaluation value were both measured with the incident angle of light set to be nearly perpendicular to the glass substrate surface, and evaluation was performed using light of 590 nm, which is a typical wavelength of visible light.

[0098] Furthermore, in order to suppress the influence of the refractive index of the bonding layer 40 on the transmitted light, it is preferable to make the thickness of the bonding layer 40 thinner by at least one order of magnitude than the wavelength used for optical evaluation. From this perspective, it is preferable to make the thickness of the bonding layer 40 40 nm or less, more preferably 10 nm or less, and even more preferably 6 nm or less.

[0099] On the other hand, if the thickness of the bonding layer 40 is too thin, the bonding strength will decrease, so it is desirable that the thickness of the bonding layer 40 be 1 nm or more, which will enable excellent light transmission performance and high bonding strength to be obtained industrially and stably.

[0100] The optical transmittance and film thickness of the bonding layer 40 described above may be the same values ​​in the microchannel device 1 having the cover substrates 20, 20 bonded to both sides of the base substrate 10 as shown in Figures 5 and 6, and therefore having bonding layers 40, 40 on both sides of the base substrate 10.

[0101] (Electrical insulation) In the microchannel device 1 created by bonding the base substrate 10 and the cover substrate 20, in order to electrically measure the physical properties of the liquid in the microchannel 12, it is important that the first and second oxide thin films 41, 42 are electrically insulators.

[0102] Furthermore, the fact that the first and second oxide thin films 41 and 42 are electrically insulating is also necessary when forming electrical devices and the like within the microchannel device 1 .

[0103] Therefore, when the physical properties of the liquid in the microchannel 12 are to be electrically measured, excellent electrical insulation can be obtained by forming the first and second oxide thin films 41 and 42 to be insulating.

[0104] (Material) The first and second oxide thin films 41, 42 may be oxide thin films formed from any oxide, as long as they are oxide thin films having high optical transparency, excellent thermal stability, and excellent chemical stability, and preferably amorphous oxide thin films.

[0105] As a result, the bonding layer 40, which is a laminated structure of the first and second oxide thin films 41 and 42, also becomes an oxide thin film with high optical transparency, excellent thermal stability, and excellent chemical stability.

[0106] Furthermore, the first oxide thin film 41 formed on the base substrate 10 and the second oxide thin film 42 formed on the cover substrate 20 may be the same oxide or different oxides. However, if the same oxide is used, it is convenient in that the film formation process can be simplified, for example, by forming the first oxide thin film 41 on the base substrate 10 and the second oxide thin film 42 on the cover substrate 20 simultaneously.

[0107] Thin films of oxides such as SiO, AlO, YO, and ZrO are excellent in optical transparency, bonding strength, thermal stability, chemical stability, and electrical insulation, and can be suitably used as the material for the first and second oxide thin films 41 and 42.

[0108] (Film Formation Method) The first and second oxide thin films 41 and 42 are formed by sputtering, ion plating, or the like, for example, at a vacuum level of 1×10 -3 ~1 x 10 -8 Pa, preferably 1×10 -4 ~1 x 10 -8 This can be performed by vacuum film formation in a high-vacuum atmosphere using a vacuum container with a high vacuum of 100 Pa, and preferably by vacuum film formation accompanied by rapid cooling of the source atoms on the base substrate 10 or the cover substrate 20. This allows the formation of a highly pure oxide thin film, preferably an amorphous oxide film.

[0109] (Bonding Strength) The bonding strength between the first oxide thin film 41 and the second oxide thin film 42 in the bonding layer 40 was 0.6 J / m in terms of the magnitude of the surface free energy γ of the bonding interface (hereinafter, the "surface free energy γ of the bonding interface" may be referred to as "bonding strength γ"). 2 More than 1J / m 2 It is desirable that the value be equal to or greater than this.

[0110] Thus, 0.6 J / m 2 By bonding with a bonding strength γ of 1 J / m or more, it is possible to sufficiently prevent the fluid from penetrating into the bonding interface between the first oxide thin film and the second oxide thin film. 2 When the first oxide thin film 41 and the second oxide thin film 42 are bonded with the above bonding strength γ, peeling at the bonding interface between them can be prevented even when the microchannel device is cut or processed by dicing or the like.

[0111] (4) Bonding structure of the bonding interface in the bonding layer The bonding layer 40 formed between the non-grooved portion 13 of the base substrate 10 and the bonding portion 23 of the cover substrate 20 is composed of a laminated structure of the first oxide thin film 41 and the second oxide thin film 42 as described above, and has a structure in which the bonding interface between the first oxide thin film 41 and the second oxide thin film 42 is bonded by atomic diffusion and / or chemical bonding that occurs at the interface.

[0112] (Atomic Diffusion) The bonding layer 40 in which the bonding interface between the first oxide thin film 41 and the second oxide thin film 42 is in a bonded state accompanied by atomic diffusion can be obtained by the following method.

[0113] The first amorphous transparent oxide thin film 41 is formed on the base substrate 10, and the second amorphous transparent oxide thin film is formed on the cover substrate 20 by vacuum film formation such as sputtering.

[0114] Thereafter, the first and second oxide thin films 41, 42 are superimposed in a vacuum at room temperature so that the first oxide thin film 41 formed in the non-groove portion 13 of the base substrate 10 and the second oxide thin film 42 formed in the bonding portion 23 of the cover substrate 20 come into contact with each other without exposing the first and second oxide thin films 41, 42 to the atmosphere. As a result, atomic diffusion occurs between the first oxide thin film 41 and the second oxide thin film 42, thereby bonding the bonding interface between the first oxide thin film 41 and the second oxide thin film.

[0115] In this way, bonding involving atomic diffusion in a vacuum using the first oxide thin film 41 and the second oxide thin film 42 with an amorphous structure can be performed using the oxide thin films 41 and 42 with a high purity and chemically and thermally stable amorphous structure, so the bonding layer 40, which is a laminated structure of these, also becomes chemically and thermally stable.If glass is used as the base substrate 10 or the cover substrate 20, it becomes possible to form a microchannel device 1 that takes advantage of the chemical and thermal stability of glass.

[0116] In the bonding method involving atomic diffusion in a vacuum using the first and second oxide thin films 41, 42 with an amorphous structure, these characteristics can be obtained simply by overlapping them in a vacuum at room temperature, and since heating is not required for bonding, bonding can be performed without causing problems such as distortion of the base substrate 10 and cover substrate 20 due to heating, or deterioration of optical performance due to internal stress induced within the substrates 10, 20.

[0117] As shown in the examples described later, the bonding layer 40 has a thickness of 40 nm or less, a high transmittance of more than 94%, and a bonding strength γ of 0.6 J / m 2As described above, a strong bond can be obtained, and furthermore, a bonding layer having electrical insulating properties can be obtained.

[0118] In bonding involving atomic diffusion in a vacuum using the first and second oxide thin films 41 and 42 with an amorphous structure, any kind of base substrate 10 and cover substrate 20 can be bonded.

[0119] Furthermore, the first oxide thin film 41 and the second oxide thin film 42 can be bonded to each other regardless of the oxide formed therefrom, and as a result, the bonding layer 40 also becomes an amorphous oxide thin film that has high optical transparency, excellent thermal stability, and excellent chemical stability.

[0120] As mentioned above, the bonding between the first oxide thin film 41 and the second oxide thin film 42 is 0.6 J / m 2 Although bonding with a high bonding strength γ of 1000 kJ / cm or more is possible, by heating at a relatively low temperature of 200° C. or less after bonding, it is possible to further increase the bonding strength while maintaining optical transparency.

[0121] When the first and second oxide thin films 41, 42 are formed by sputtering, they may be formed by sputtering an oxide target, or by reactive sputtering, in which a metal target (unoxidized) is used and oxide-forming elements released by sputtering the metal target are reacted with oxygen in a vacuum chamber to produce an oxide, which is then deposited on the base substrate 10 or the cover substrate 20.

[0122] (Chemical Bonding) The bonding layer 40 having a structure in which the first oxide thin film 41 and the second oxide thin film 42 are bonded by chemical bonding generated at the bonding interface can be obtained by any of the following methods.

[0123] In the first method, the transparent first oxide thin film 41 is formed on the base substrate 10 and the transparent second oxide thin film 42 is formed on the cover substrate 20 by vacuum film formation such as sputtering.

[0124] Thereafter, the first oxide thin film 41 and the second oxide thin film 42 are exposed to a space containing moisture (e.g., the atmosphere) to make the first oxide thin film 41 and the second oxide thin film 42 hydrophilic, and when the first oxide thin film 41 formed in the non-groove portion 13 of the base substrate 10 and the second oxide thin film 42 formed in the bonding portion 23 of the cover substrate 20 are superimposed at room temperature in the space (e.g., the atmosphere) so that they come into contact with each other, the first oxide thin film 41 and the second oxide thin film 42 are bonded (hydrogen bonded) via water.

[0125] Thereafter, the base substrate 10 and the cover substrate 20 are heated at a relatively low temperature of 200° C. or less to cause dehydration condensation at the bonding interface, changing the chemical bond at the bonding interface from a hydrogen bond to a covalent bond, thereby increasing the bonding interface to 0.6 J / m 2 Over 1 J / m 2 A bonding layer 40 bonded with the above bonding strength γ can be obtained. Note that when dehydration condensation of the bonding interface is performed to change the chemical bond at the bonding interface from a hydrogen bond to a covalent bond, if atomic diffusion occurs near the bonding interface, an even stronger bond can be obtained.

[0126] As another method, the first thin film (unoxidized) on the base substrate 10 and the second thin film (unoxidized) on the cover substrate 20 are both formed by vacuum film formation such as sputtering, and then the first thin film and the second thin film are exposed to moisture or a space containing moisture and oxygen (e.g., the atmosphere) to oxidize the first thin film and the second thin film, thereby obtaining a transparent first oxide thin film 41 and a transparent second oxide thin film 42 and making them hydrophilic.

[0127] Thereafter, when the first oxide thin film 41 formed on the non-groove portion 13 of the base substrate 10 and the second oxide thin film 42 formed on the bonding portion 23 of the cover substrate 20 are superimposed at room temperature in the space (atmosphere) so that they come into contact with each other, the bonding interface between the first oxide thin film 41 and the second oxide thin film 42 is bonded (hydrogen bonded) via water.

[0128] Thereafter, the base substrate 10 and the cover substrate 20 are heated at a relatively low temperature of 200° C. or less to cause dehydration condensation at the bonding interface, changing the chemical bond at the bonding interface from a hydrogen bond to a covalent bond, thereby increasing the bonding interface to 0.6 J / m 2Over 1 J / m 2 A bonding layer 40 bonded with the above bonding strength γ can be obtained. Note that when dehydration condensation of the bonding interface is performed to change the chemical bond at the bonding interface from a hydrogen bond to a covalent bond, if atomic diffusion occurs near the bonding interface, an even stronger bond can be obtained.

[0129] In this way, even in the bonding layer 40 in which the bonding interface between the first oxide thin film 41 and the second oxide thin film 42 is bonded by chemical bonding, or by chemical bonding and atomic diffusion, bonding can be performed using a highly pure, chemically and thermally stable oxide thin film, making it possible to form a chemically and thermally stable microchannel device 1 that makes use of the characteristics of the base substrate 10 and the cover substrate 20.

[0130] In addition, in the bonding layer 40 having a structure in which the bonding interface between the first oxide thin film 41 and the second oxide thin film is bonded by chemical bonding or chemical bonding and atomic diffusion, the bonding energy is 0.6 J / m 2 More than 1 J / m, preferably 1 J / m 2 To obtain a bonding strength γ of 0.6 J / m, a further heat treatment is required after bonding at room temperature. However, by performing such heat treatment at a relatively low heating temperature of 200°C or less, a bonding strength of 0.6 J / m 2 The bonding strength γ (in the examples given below) is 1 J / m 2 As a result, problems such as distortion of the base substrate 10 and the cover substrate 20 due to heating and deterioration of optical performance due to internal stress induced in the substrates 10 and 20 do not occur.

[0131] In the examples (Examples 2 and 3) described later, when the thickness of the bonding layer 40 is in the range of 20 nm or less, a high transmittance exceeding 98% is obtained by heating at 150° C., and the bonding strength γ is 1 J / m 2 As described above, strong bonding can be achieved, and excellent electrical insulation properties are also obtained.

[0132] In this way, even if the bonding layer 40 has a structure in which the bonding interface between the first oxide thin film 41 and the second oxide thin film 42 is bonded by chemical bonding, or by chemical bonding and atomic diffusion, bonding is possible using any type of glass for the base substrate 10 or the cover substrate 20, and further, bonding is possible using oxide films made of any oxide for the first oxide thin film 41 and the second oxide thin film 42.

[0133] As a result, the bonding layer 40 also becomes an oxide thin film that has high optical transparency, excellent thermal stability, and excellent chemical stability.

[0134] The results of a performance evaluation test of the bonding layer 40 used in the manufacture of the microchannel device of the present invention will be described below.

[0135] (1) Example 1 (Bonding in a vacuum using amorphous oxide thin film) (1-1) Test overview Two glass substrates representing the base substrate 10 and cover substrate 20 of the microchannel device 1 were bonded via a bonding layer 40 consisting of a laminated structure of a first oxide thin film 41 and a second oxide thin film 42 bonded together with atomic diffusion at the interface.

[0136] A typical glass substrate, a quartz glass substrate, was used as the glass substrate. Hereinafter, the quartz glass substrate will be referred to as the quartz substrate.

[0137] First and second amorphous oxide thin films were formed on the smooth surfaces of two quartz substrates, respectively, and the two quartz substrates were then bonded together by overlapping them at room temperature in a vacuum so that the first amorphous oxide thin film and the second oxide thin film were in contact with each other.

[0138] The quartz substrate used was a synthetic quartz wafer with a diameter of 2 inches and a thickness of 500 μm and a smooth surface.

[0139] The arithmetic mean height Sa (ISO 4287) of the quartz wafer used in the experiment was 0.14 nm, and the surface roughness was measured over a 2 μm square area using an atomic force microscope (AFM).

[0140] Experiments were conducted using amorphous Y2O3 thin film (Example 1-1), Al2O3 thin film (Example 1-2), and ZrO2 thin film (Example 1-3) as the first and second amorphous oxide thin films, respectively.

[0141] The ZrO2 thin film referred to here is a Y2O3-ZrO2 thin film (stabilized zirconia) containing 8 mol % of Y2O3.

[0142] After bonding, samples were prepared in an unheated state and after heat treatment in air at temperatures of 200°C and 300°C for 5 minutes, and the light transmittance and bonding strength of each bonding layer were measured.

[0143] (1-2) Bonding method (bonding layer formation method) Two quartz substrates were bonded together in a vacuum chamber with an ultimate vacuum of 1 × 10 -6 The substrates were placed in a vacuum chamber with a pressure of 100 Pa or less, and an amorphous oxide thin film was formed on each of the smooth surfaces of the two quartz substrates by RF magnetron sputtering.

[0144] For the formation of the Y2O3 thin film, the Al2O3 thin film, and the ZrO2 thin film, targets of Y2O3, Al2O3, and Y2O3-ZrO2 containing 8 mol % of Y2O3 were used.

[0145] The purity of each target was 99.9% or higher, and amorphous oxide thin films with the same purity were formed on two quartz substrates by sputtering.

[0146] Following the formation of the amorphous oxide thin film, the amorphous oxide films formed on the respective smooth surfaces of the two quartz substrates were superimposed and bonded together without applying pressure or heat in the same vacuum as that used to form the amorphous oxide thin film.

[0147] After bonding, samples were prepared in an unheated state and after heat treatment in air at temperatures of 200° C. and 300° C. for 5 minutes.

[0148] (1-3) Performance Evaluation (1-3-1) Evaluation of Light Transmittance Measurements were made using monochromatic light with a wavelength of 590 nm (orange light) as a representative visible light.

[0149] The intensity of light passing through two quartz substrates (without a bonding layer) made of the same material and with the same thickness as those used for bonding using an amorphous oxide thin film was measured as a reference value, and the intensity of light passing through two quartz substrates bonded via a bonding layer made of an amorphous oxide thin film using the same optical system was measured as an evaluation value, and the light intensity of the evaluation value (with a bonding layer) was evaluated as a percentage, assuming the light intensity of the reference value (without a bonding layer) to be 100%.

[0150] The light was incident almost perpendicularly to the surface of each quartz substrate.

[0151] (1-3-2) Evaluation of bonding strength (surface free energy of bonding interface) γ The bonding strength (surface free energy of bonding interface) γ of two substrates bonded via an amorphous oxide thin film was measured using the "blade method."

[0152] Here, the "blade method" evaluates the bonding strength (surface free energy of the bonding interface) γ based on the peel length L from the tip of the blade when the blade is inserted into the bonding interface of two quartz substrates, as shown in Figure 7. The bonding strength γ is expressed by the following formula [MP Maszara, G. Goetz, A. Cavigila and JB McKitterick: J. Appl. Phys. 64 (1988) 4943]: γ=3 / 8×Et 3 y 2 / L 4 Here, E is the Young's modulus of the wafer, t is the thickness of the wafer, and y is 1 / 2 of the thickness of the blade.

[0153] (1-4) Test Results (1-4-1) Bonding Test Results Using Y2O3 Film (Example 1-1) The thickness of the Y2O3 thin film formed on the bonding surfaces of both quartz substrates was changed to 0.5 nm, 1 nm, 2 nm, 5 nm, 10 nm, and 20 nm per side, and bonded samples were created using Y2O3 thin films of each thickness, and the light transmittance % and bonding strength γ of the bonding layer (a laminated structure of two Y2O3 thin films) formed on each sample were measured.

[0154] The measurement results are shown in Table 1 below, and the change in light transmittance (%) with respect to the change in film thickness is shown in FIG. 8(A), and the change in bonding strength (γ) with respect to the change in film thickness is shown in FIG. 8(B), for each heating condition (unheated, 200°C, 300°C).

[0155] Although the light transmittance decreased with increasing film thickness, a high transmittance of over 95% was obtained even without heating, even at a film thickness of 20 nm, and there was almost no change in light transmittance before and after heating, or with the heating temperature, and the transmittance was approximately consistent.

[0156] The bonding strength γ was 2.27 J / m when the film thickness on one side was in the range of 0.5 nm to 10 nm (the film thickness of the bonding layer was in the range of 1 nm to 20 nm) even without heating. 2 The values ​​were as large as above, and in particular, for film thicknesses of 2 nm and 5 nm on one side (bonding layer thicknesses of 4 nm and 10 nm), the fracture strength of quartz was exceeded, and such a large bonding strength was obtained that the bonding strength γ could not be measured by the blade method (the quartz substrate would fracture before the bonding interface peeled off).

[0157] The bonding strength γ was lowest when the film thickness was 20 nm on one side (the film thickness of the bonding layer was 40 nm), but even at this film thickness, it was 0.63 J / m 2 This was a relatively high figure.

[0158] The bonding strength γ further increases as the heat treatment temperature increases, and after heat treatment at 300°C, even with a film thickness of 20 nm on one side (film thickness of the bonding layer: 40 nm), the bonding strength γ is 1 J / m 2 The above values ​​were shown, and even when the film thickness on one side was 1 nm and 10 nm (film thickness of the bonding layer was 2 nm and 20 nm), the bonding strength γ increased to such an extent that it could not be evaluated by the blade method.

[0159] From the above results, it can be seen that bonding using a Y2O3 thin film has an excellent light transmittance of over 94% even when not heated, and a light transmittance of 0.6 J / m2, in the entire range of film thickness per side from 0.5 to 20 nm (bonding layer thickness from 1 to 40 nm). 2 It was confirmed that the above bonding strength (γ) was industrially sufficient, and that the bonding strength γ could be further increased by heating after bonding.

[0160]

[0161] (1-4-2) Bonding test results using Al2O3 film (Example 1-2) The thickness of the Al2O3 thin film formed on the bonding surfaces of two quartz substrates was changed to 0.5 nm, 1 nm, 1.5 nm, 2 nm, and 5 nm per side, and bonded samples were prepared using Al2O3 thin films of each thickness, and the light transmittance % and bonding strength γ of the bonding layer (a laminated structure of two Al2O3 thin films) formed on each sample were measured.

[0162] The measurement results are shown in Table 2 below, and the change in light transmittance (%) versus film thickness of the bonding layer for each sample is shown in Figure 9(A), and the change in bonding strength (γ) versus film thickness is shown in Figure 9(B), for each heating condition (unheated, 200°C, 300°C).

[0163] Although the light transmittance decreased slightly with increasing film thickness, an extremely high transmittance of over 98.6% was obtained even without heating and with a film thickness of 5 nm, and the value remained almost constant even after heating.

[0164] The bonding strength γ was 0.73 J / m across the entire range of film thicknesses of 0.5 to 5 nm (bonding layer thicknesses 1 to 10) on one side, even without heating. 2 Above 0.6 J / m 2 It exceeds 1.45 J / m when the film thickness on one side is 1 nm or more (the film thickness of the bonding layer is 2 nm or more). 2 Above 1J / m 2 In particular, when the film thickness on one side was 1.5 nm, 2 nm, and 5 nm (the film thickness of the bonding layer was 3 nm, 4 nm, and 10 nm), the value exceeded 2 J / m 2 showed a large value exceeding

[0165] The bonding strength γ further increased as the heat treatment temperature increased, and after heat treatment at 200°C, it was 2.29 J / m across all film thickness ranges. 2 After heat treatment at 300°C, a bonding strength so great that it could not be evaluated by the blade method was obtained in a film thickness range of 1.5 nm or more on one side (3 nm film thickness of the bonding layer).

[0166] From the above results, it was confirmed that bonding using an Al2O3 thin film can achieve an extremely excellent light transmittance of over 98.5% and a bonding strength sufficient for industrial use over the entire range of film thickness per side from 0.5 to 5 nm (1 to 10 nm for the bonding layer thickness).

[0167] Furthermore, from these results, it is believed that even when the film thickness on one side exceeds 5 nm (the film thickness of the bonding layer is 10 nm), an excellent light transmittance of more than 94% and bonding strength sufficient for industrial use can be obtained.

[0168]

[0169] (1-4-3) Bonding test results using ZrO2 film (Example 1-3) The thickness of the ZrO2 thin film formed on the bonding surfaces of two quartz substrates was changed to 0.5 nm, 1 nm, 2 nm, 5 nm, and 10 nm per side, and bonded samples were created using ZrO2 thin films of each thickness, and the light transmittance % and bonding strength γ of the bonding layer (a laminated structure of two ZrO2 thin films) formed on each sample were measured.

[0170] The measurement results are shown in Table 3 below, and the change in light transmittance (%) versus film thickness is shown in FIG. 10(A), and the change in bonding strength (γ) versus film thickness is shown in FIG. 10(B), for each heating condition (unheated, 200°C, 300°C).

[0171] Although the optical transmittance decreased slightly with increasing film thickness, an extremely high transmittance of over 99% was obtained even without heating, even with a film thickness of 5 nm on one side (with a bonding layer thickness of 10 nm), and the value remained almost constant even after heating.

[0172] The bonding strength γ was 1.58 J / m across all film thickness ranges, even without heating. 2 The values ​​above were shown, and especially for film thicknesses of 2 nm and 5 nm on one side (film thicknesses of the bonding layer of 4 nm and 10 nm), the values ​​were 3 J / m 2 showed a large value exceeding

[0173] The bonding strength γ further increased as the heat treatment temperature increased, and after heat treatment at 200°C, a bonding strength so great that it could not be evaluated by the blade method was obtained when the film thickness on one side was in the range of 1 nm to 5 nm (bonding layer thickness: 2 nm to 10 nm), and after heat treatment at 300°C, a bonding strength so great that it could not be evaluated by the blade method was obtained when the film thickness on one side was in the range of 1 nm to 10 nm (bonding layer thickness: 2 nm to 20 nm).

[0174] From the above results, it was confirmed that bonding using a ZrO2 thin film can achieve an excellent light transmittance of over 94% and a bonding strength sufficient for industrial use over the entire range of film thickness per side from 0.5 to 10 nm (bonding layer thickness from 1 to 20 nm).

[0175]

[0176] FIG. 11 shows a transmission electron microscope (TEM) photograph of the cross section of an unheated sample after bonding a Si wafer using a ZrO2 thin film with a thickness of 5 nm on one side (thickness of the bonding layer: 10 nm).

[0177] The white layer between the Si substrate and the ZrO2 thin film is a natural oxide layer of Si present on the surface of the Si substrate. The bonding interfaces between the ZrO2 thin films are bonded without any gaps.

[0178] (2) Example 2 (Bonding in the atmosphere using vacuum-deposited oxide thin films) (2-1) Test overview After forming first and second oxide thin films on the smooth surfaces of two quartz substrates, these were taken out into the atmosphere and the two quartz substrates were bonded by overlapping them at room temperature so that the first oxide thin film and the second oxide thin film were in contact with each other.

[0179] The quartz substrate used was the same as that used in Example 1 (Examples 1-1 to 1-3).

[0180] Two quartz substrates were bonded together by forming an amorphous Y2O3 thin film as an oxide thin film on each of the substrates.

[0181] After bonding, samples were prepared in an unheated state, and samples were heat-treated in air at temperatures of 150°C and 200°C for 5 minutes, and the light transmittance and bonding strength of each bonding layer were measured.

[0182] (2-2) Bonding method The above-mentioned quartz substrates (two sheets) were bonded to a vacuum chamber with an ultimate vacuum of 1 × 10 -6 The substrates were placed in a vacuum chamber at a pressure of 100 Pa or less, and an amorphous Y2O3 thin film was formed on the smooth surface of each of the two substrates by RF magnetron sputtering.

[0183] A Y2O3 target with a purity of 99.9% or higher was used to form the Y2O3 thin film. A Y2O3 thin film with an amorphous structure and equivalent purity was formed on each of two quartz substrates by sputtering.

[0184] The quartz substrate on which the Y2O3 thin film was formed was taken out into the atmosphere with a humidity of 50% (room temperature of 20°C) to make it hydrophilic, and the two substrates were then superimposed and bonded without applying pressure or heat so that the Y2O3 thin films were in contact with each other.

[0185] After bonding, samples were prepared in an unheated state, and samples were heat-treated in air at temperatures of 150° C. and 200° C. for 5 minutes.

[0186] (2-3) Performance Evaluation The light transmittance of the bonding layer and the bonding strength (surface free energy of the bonding interface) γ were measured and evaluated by the same method as in Test Example 1 described above.

[0187] (2-4) Test results The thickness of the Y2O3 thin film formed on the bonding surfaces of both quartz substrates was varied to 2 nm, 5 nm, and 10 nm per side, and bonded samples were prepared using Y2O3 thin films of each thickness. The light transmittance % and bonding strength γ of the bonding layer (layered structure of Y2O3 thin films) formed on each sample were measured.

[0188] The measurement results are shown in Table 4 below, and the change in light transmittance (%) with respect to the change in film thickness is shown in FIG. 12(A), and the change in bonding strength (γ) with respect to the change in film thickness is shown in FIG. 12(B), for each heating condition (unheated, 150°C, 200°C).

[0189] Although the optical transmittance decreased as the film thickness increased, an extremely high transmittance of 98.8% or more was obtained even when the film was not heated and the film thickness on one side was 10 nm (the film thickness of the bonding layer was 20 nm), and the value remained almost constant even after heating.

[0190] The bonding strength γ is 0.25 J / m without heating. 2 Although the value is small, it is 1 J / m after heat treatment at 150 °C. 2 A large value exceeding this was obtained.

[0191] The bonding strength γ after heat treatment at 150°C was a maximum of 1.94 J / m when the film thickness on one side was 10 nm (the film thickness of the bonding layer was 20 nm). 2 The bonding strength γ after heat treatment at 200°C was a maximum of 2.00 J / m when the film thickness on one side was 5 nm (the film thickness of the bonding layer was 10 nm). 2 showed.

[0192] From the above results, it was confirmed that even when bonding is performed in the atmosphere using a thin Y2O3 film, by performing a low-temperature heat treatment at just 150°C, it is possible to obtain an excellent light transmittance of over 98% and a bonding strength sufficient for industrial use over the entire range of film thickness per side from 2 to 10 nm (4 to 20 nm in terms of bonding film thickness).

[0193]

[0194] FIG. 13 shows a transmission electron microscope (TEM) photograph of the cross section of a sample that was heated at 150°C after bonding a Si wafer using a 5-nm-thick Y2O3 thin film on one side (10-nm-thick bonding layer).

[0195] The white layer between the Si substrate and the Y2O3 thin film is a natural oxide layer of Si present on the surface of the Si substrate.

[0196] Even when bonding is performed in the atmosphere, the bonding interfaces between the Y2O3 thin films are bonded without any gaps.

[0197] (3) Example 3 (Vacuum-formed unoxidized thin films were oxidized in the atmosphere and then bonded) (3-1) Overview of the test In Example 2 described above, oxide thin films were formed on the surfaces of two quartz substrates in the vacuum deposition stage, and then the substrates were taken out into the atmosphere and bonded.

[0198] In contrast to this, in this example (Experimental Example 3), a thin metal film (unoxidized) was formed on two quartz substrates by vacuum film formation, and the substrates on which this thin metal film had been formed were then taken out into the atmosphere and subsequently oxidized, resulting in a thin oxide film, which was used as a bonding film to bond the two quartz substrates at room temperature.

[0199] The quartz substrate used was the same as that used in Example 1 (Examples 1-1 to 1-3).

[0200] (3-2) Bonding method The above-mentioned quartz substrates (two sheets) were bonded to a vacuum chamber with an ultimate vacuum of 1 × 10 -5 The substrates were placed in a vacuum chamber at a pressure of 100 Pa or less, and a metal film was formed on the smooth surface of each of the two substrates by DC magnetron sputtering.

[0201] The amorphous Si thin film, Zr thin film, and Ti thin film were formed using targets of Si, Zr, and Ti, respectively.

[0202] The purity of each target was 99.9% or higher, and thin Si films, thin Zr films, and thin Ti films with purities equivalent to those of the targets were formed on the quartz substrate.

[0203] The quartz wafer on which the metal thin film was formed by the vacuum film deposition was taken out into the atmosphere with a humidity of 50% (room temperature of 20°C), where it was oxidized by oxygen in the atmosphere to form an oxide thin film and made hydrophilic. After that, two quartz substrates were superimposed and bonded at room temperature without pressure so that the oxide thin films were in contact with each other.

[0204] After bonding, samples were prepared in an unheated state, and samples were heat-treated in air at temperatures of 150° C. and 200° C. for 5 minutes.

[0205] (3-3) Performance Evaluation The light transmittance of the bonding layer and the bonding strength (surface free energy of the bonding interface) γ were measured and evaluated using the same method as in the above-mentioned test example.

[0206] (3-4) Test results (3-4-1) SiO obtained by atmospheric oxidation X Bonding test results using film (Example 3-1) The thickness of the amorphous Si thin film formed on the bonding surfaces of both quartz substrates was changed to 0.5 nm, 0.7 nm, and 1 nm per side, and the amorphous Si thin film of each thickness was taken out into the air and subsequently oxidized and hydrophilized to form an amorphous SiO film with a hydrophilized surface. X A thin film was obtained, and amorphous SiO X Two quartz substrates were bonded together so that the thin films were in contact with each other, and samples were prepared. X The light transmittance % and bonding strength γ of the laminated structure of the film were measured (X is a number that varies depending on the degree of oxidation).

[0207] The above-mentioned film thicknesses are all those before exposure to the atmosphere and oxidation.

[0208] The measurement results are shown in Table 5 below, and the change in light transmittance (%) with respect to the change in film thickness is shown in FIG. 14(A), and the change in bonding strength (γ) with respect to the change in film thickness is shown in FIG. 14(B), for each heating condition (unheated, 150°C, 200°C).

[0209] In addition, Table 5 lists the film thickness of one side and the film thickness of the bonding layer as film thicknesses, but the film thickness of one side and the film thickness of the bonding layer listed here are the film thickness of the unoxidized amorphous Si film (one side) formed on the surface of the quartz substrate by vacuum film deposition and a value simply doubled (bonding layer). The actual film thickness of one side and the film thickness of the bonding layer increase due to the incorporation of oxygen by oxidation.

[0210] Although the light transmittance decreased with increasing film thickness, a high transmittance of 98.7% was obtained even without heating and with a film thickness of 1 nm, and by heating to 150°C, the light transmittance increased to a high value of 99.5%.

[0211] In Examples 1 and 2, almost no improvement in light transmittance was observed due to heating, but in this example, the amorphous Si film was oxidized by exposure to the atmosphere to form amorphous SiO XThe amorphous SiO film obtained was incompletely oxidized by simply exposing it to the atmosphere. X It is presumed that the oxidation of the film progresses further due to heating, resulting in improved light transmittance.

[0212] The bonding strength γ is 0.11 J / m without heating. 2 Although the value is small, it is 1 J / m only by performing heat treatment at a relatively low temperature of 150°C. 2 rose to a large value exceeding

[0213] The bonding strength γ after heat treatment at 150°C was 1.5 J / m regardless of the film thickness. 2 The values ​​were around the same, and even when the heat treatment temperature was increased from 150°C to 200°C, no significant change in the bonding strength γ was observed.

[0214] From the above results, it was confirmed that when bonding is performed using an atmospheric bonding method in which a quartz substrate on which an amorphous Si thin film has been formed by vacuum deposition is taken out into the atmosphere and the amorphous Si thin film is oxidized and made hydrophilic before bonding, by performing heat treatment at a relatively low temperature of just 150°C, it is possible to obtain excellent light transmittance of over 99.5% and bonding strength that is sufficient for industrial use over the entire range of film thicknesses per side from 0.5 to 1 nm (1 to 2 nm for the bonding layer thickness).

[0215]

[0216] Figure 15(A) shows a thin film (a-SiO in the figure) that was oxidized by taking an amorphous Si thin film with a thickness of 0.5 nm (one side) out into the air. X 1 shows a transmission electron microscope (TEM) photograph of a cross section of a sample that was heated at 150° C. after bonding a Si wafer using a SiO2 bonding agent.

[0217] Si substrate and amorphous SiO X The slightly white layer between the thin films is a native oxide layer of silicon present on the surface of the silicon substrate. X The bonding interface between the thin films is bonded without any gaps. XThe thickness of the oxide film is about 2.8 nm, which is 2.8 times the total thickness of the two amorphous Si films before oxidation, 1.0 nm.

[0218] Such an increase in film thickness occurs because the amorphous Si film is oxidized by oxygen in the atmosphere to form amorphous SiO X This is caused by the formation of a membrane.

[0219] To confirm that the amorphous Si film was oxidized by oxygen in the atmosphere to form a thin oxide film, the same sample was subjected to structural analysis using electron energy loss spectroscopy (EELS), and the results are shown in Figure 15(B).

[0220] (a), (b), and (c) in the figure are the spectra of the EELS signal versus the energy loss. (a) is the spectrum of the bonded amorphous SiO X The spectra near the center of the film thickness (near the bonded interface), (b) and (c) are the spectra of the bonded amorphous SiO X The spectra of the areas close to the Si wafer above and below the thin film are shown.

[0221] The signals in (a) to (c) overlap each other, indicating that the internal structure of the membrane is homogeneous.

[0222] Furthermore, the signal pole positions of these spectra are in good agreement with the SiO2 spectrum shown for reference, and this indicates that the amorphous Si thin film is oxidized by oxygen in the atmosphere (including oxidation due to heating) to form amorphous SiO2, which has a structure similar to SiO2. X This confirms that the film is a thin film.

[0223] (3-4-2) TiO oxidized in air X (Example 3-2) and ZrO XBonding test results using (Example 3-3) In a test example in which bonding was performed using a Ti film formed by vacuum deposition, the thickness of the Ti thin film formed on the bonding surfaces of both quartz substrates was changed to 0.5 nm and 1 nm per side, and the Ti thin films of each thickness were taken out into the atmosphere to be oxidized afterwards and the surface was made hydrophilic. X A bonded sample was prepared by overlapping two quartz substrates so that the thin films (X is a number that varies depending on the degree of oxidation) were in contact with each other.

[0224] The thickness of the Ti thin film shown above is the thickness before it is taken out into the air and oxidized.

[0225] In a test example in which bonding was performed using a Zr film formed by vacuum deposition, the thickness of the Ti thin film formed on the bonding surfaces of both quartz substrates was set to 1 nm per side, and the quartz substrate on which the Zr thin film thus formed was then taken out into the atmosphere to be subsequently oxidized and the surface was made hydrophilic. X The quartz substrate on which the thin film (X is a number that varies depending on the degree of oxidation) was formed was X The thin films were stacked so that they were in contact with each other to create a bonded sample.

[0226] Table 6 shows the relationship between the light transmittance and bonding strength (surface free energy of the bonding interface) γ of these samples and the film thickness per side of the Ti or Zr thin film used for bonding, for each heating condition (unheated, 150°C, 200°C).

[0227] It should be noted that while Table 6 shows the film thickness of the bonding layer, the film thickness shown here indicates the total value of the two Ti thin films and the Zr thin film before oxidation in the atmosphere, and the actual film thickness of the bonding layer is thicker than the film thickness shown here due to the intake of oxygen during oxidation.

[0228] When a 0.5 nm thick Ti film was used on one side, the optical transmittance was as high as 98.0% even without heating, and it increased further with heating. The bonding strength γ was 0.18 J / m without heating. 2However, it increases when heated after bonding, reaching 1.3 J / m after heat treatment at 200°C. 2 That's all.

[0229] When a 1 nm thick Ti film is used on one side, the optical transmittance is a low value of 91.9% before heating, but increases with heating, reaching 95% after heat treatment at 200°C. The bonding strength γ is 0.16 J / m before heating. 2 However, it increases with heating, reaching 1.31 J / m after heat treatment at 150°C. 2 , 1.80 J / m after heat treatment at 200 °C 2 have risen to .

[0230] When a 1 nm thick Zr film is used, the optical transmittance is as high as 99.0% even without heating, and increases further with heating. The bonding strength γ is 0.10 J / m 2 However, it increases with heating, reaching 1.23 J / m after heat treatment at 150°C. 2 , and after heat treatment at 200°C, it was 1.51 J / m 2 have been achieved respectively.

[0231] From the above results, it was confirmed that even when bonding is performed via a bonding layer obtained by bonding thin Ti and Zr films that have been vacuum-deposited on the surface of a quartz substrate, exposing them to the atmosphere to oxidize, and then bonding them, by performing a low-temperature heat treatment at just 150°C or 200°C, it is possible to obtain a light transmittance of 95% or more and a bonding strength that is sufficient for industrial use, with a film thickness per side in the range of 0.5 to 1 nm (1 to 2 nm for the bonding film thickness).

[0232]

[0233] (4) Comparative Example [Bonding Using Metal Thin Film (Unoxidized)] (4-1) Test Overview A metal thin film was vacuum-formed on each of two quartz substrates of the same material and dimensions as those used in Examples 1 to 3, and the two quartz substrates were then stacked at room temperature so that the unoxidized metal thin films were in contact with each other to produce a bonded sample. The light transmittance and bonding strength of the bonding layer (a laminated structure of two metal thin films) of the sample were measured.

[0234] Samples were prepared by depositing a Ti thin film (Comparative Example 1), a Zr thin film (Comparative Example 2), or an Au thin film (Comparative Example 3) on both of two quartz substrates to a film thickness of 0.5 nm or 1 nm per side for comparison with Example 3 (Examples 3-1 to 3-3).

[0235] (4-2) Bonding Method In the bonding using the Ti thin film (Comparative Example 1) and the Zr thin film (Comparative Example 2), all the processes from the deposition of the metal thin film on the quartz substrate to the superposition of the two quartz substrates were carried out in the same vacuum.

[0236] The Ti thin film (Comparative Example 1) and the Zr thin film (Comparative Example 2) were formed by placing two quartz substrates in a vacuum chamber with an ultimate vacuum of 1×10 -6 The two quartz substrates were placed in a vacuum chamber of 0.1 Pa or less, and a thin Ti film or a thin Zr film was formed on the smooth surface of each of the two quartz substrates by DC magnetron sputtering. Subsequently, in the same vacuum, the two quartz substrates were overlapped so that the metal films were in contact with each other, thereby bonding the quartz substrates without heating.

[0237] In the bonding using the Au thin film (Comparative Example 3), the Au thin film was vacuum-formed on the quartz substrate, and then the quartz substrate was taken out into the atmosphere and the Au thin films were placed one on top of the other so that they were in contact with each other.

[0238] The Au thin film (Comparative Example 3) was formed by placing two quartz substrates in a vacuum chamber with an ultimate vacuum of 1×10 -5 The substrates were placed in a vacuum chamber at a pressure of 100 Pa or less, and an Au thin film was formed on the smooth surface of each of the two substrates by DC magnetron sputtering.

[0239] Thereafter, the two quartz substrates on which the Au thin film had been formed were taken out into the atmosphere, and the two quartz substrates were overlapped so that the Au thin films formed on the respective smooth surfaces of the quartz substrates were in contact with each other, thereby bonding the quartz substrates without heating.

[0240] (4-3) Evaluation Method The light transmittance and bonding strength (surface free energy of the bonding interface) γ of the bonding layer of each sample prepared as described above were measured in the same manner as described in Test Example 1 above.

[0241] (4-4) Test Results The measurement results of Comparative Examples 1 to 3 are shown in Table 7 below, and the changes in light transmittance (%) of each sample of Comparative Examples 1 to 3 are shown in Figure 16(A) and the changes in bonding strength (γ) are shown in Figure 16(B).

[0242] The light transmittance of all the samples in Comparative Examples 1 to 3 was low, at 91.5% to 92.6%, even when the film thickness on one side was 0.5 nm (the film thickness of the bonding layer was 1 nm), and dropped to around 80% when the film thickness on one side was 1 nm (the film thickness of the bonding layer was 2 nm).

[0243] In particular, the sample bonded using a thin Au film (Comparative Example 3) had a bluish color, suggesting that the poor two-dimensionality of the thin Au film, resulting in nanoparticle formation, caused plasmon resonance to scatter short-wavelength visible light.

[0244] Although each sample was heated up to 200° C., the light transmittance value was hardly improved.

[0245] The bonding strength γ was 1 J / m for the samples bonded using Ti thin film and Zr thin film, which were formed in a vacuum from the beginning to the end. 2 The above values ​​were large.

[0246] On the other hand, the bonding strength γ of the sample (Comparative Example 3) bonded using an Au thin film in which the film was formed and then superimposed in the atmosphere was 0.15 J / m 2 This value was small, and it hardly changed even when heated up to 200°C.

[0247] Although the data is omitted, when the film thickness was reduced to less than 0.5 nm on one side in order to increase the light transmittance of the samples bonded using Ti thin film and Zr thin film, the bonding strength γ was 1 J / m 2 It dropped sharply to the following values:

[0248] From the above results, it was confirmed that it is difficult to achieve both an excellent light transmittance of over 94% and a bonding strength sufficient for industrial use when using the atomic diffusion bonding method using a metal film.

[0249]

[0250] REFERENCE SIGNS LIST 1 Microchannel device 10 Base substrate 11 Groove 12 Microchannel 13 Non-groove portion 20 Cover substrate 21 Groove lid portion 23 Bonding portion 24 Inlet 25 Outlet 40 Bonding layer 41 First oxide thin film 42 Second oxide thin film

Claims

1. A microchannel device equipped with microchannels, which are fine channels through which a fluid is introduced, comprising: a transparent base substrate on which grooves of a predetermined pattern that form the microchannels are formed; and a transparent cover substrate bonded to the base substrate so as to cover the grooves; wherein non-groove portions, which are portions of the surface of the base substrate where the grooves are not formed, and bonding portions, which are portions of the cover substrate that overlap with the non-groove portions, are bonded by a bonding layer made of a transparent oxide thin film with a thickness of 40 nm or less; and wherein the bonding layer is a laminated structure made of a first oxide thin film made of a metal or semiconductor oxide attached to the non-groove portions of the base substrate, and a second oxide thin film made of a metal or semiconductor oxide attached to the bonding portion of the cover substrate; and wherein the interface between the first oxide thin film and the second oxide thin film is bonded by atomic diffusion and / or chemical bonding that occurs at the interface.

2. The microfluidic device according to claim 1, wherein the base substrate and the cover substrate are both made of glass.

3. The microfluidic device according to claim 2, wherein one or both of said base substrate and said cover substrate are made of quartz glass.

4. The microchannel device according to claim 1, wherein the first oxide thin film and the second oxide thin film both have an amorphous structure.

5. A microchannel device according to any one of claims 1 to 4, characterized in that the first oxide thin film is formed to cover the inner wall surface of the groove together with the non-groove portion of the base substrate, and the second oxide thin film is formed to cover the groove lid portion, which is the portion that covers the groove together with the bonding portion of the cover substrate.

6. The microfluidic device according to any one of claims 1 to 4, wherein the bonding layer has a light transmittance of 94% or more.

7. The bonding strength between the first oxide thin film and the second oxide thin film in the bonding layer is 0.6 J / m in terms of the magnitude of the surface free energy of the bonding interface evaluated by the blade method. 2 The microchannel device according to any one of claims 1 to 4.

8. The bonding strength between the first oxide thin film and the second oxide thin film in the bonding layer is 0.6 J / m in terms of the magnitude of the surface free energy of the bonding interface evaluated by the blade method. 2 The microchannel device according to claim 6, wherein the microchannel device is a microchannel device having the above structure.

9. A microchannel device according to any one of claims 1 to 4, characterized in that the first oxide thin film has one oxide selected from the group consisting of SiO2, Al2O3, Y2O3, and ZrO2 as its main element, and the second oxide thin film has one oxide selected from the group consisting of SiO2, Al2O3, Y2O3, and ZrO2 as its main element, and the first oxide thin film and the second oxide thin film have the same or different elements as their main elements.

10. A microchannel device according to any one of claims 1 to 4, characterized in that the purity of the oxide in the first oxide thin film and the second oxide thin film is 99.5% or higher.

11. A method for manufacturing a microchannel device equipped with microchannels, which are fine channels through which a fluid is introduced, comprising: a step of preparing a transparent base substrate having grooves of a predetermined pattern formed on its surface to form the microchannels; and a bonding step of bonding a transparent cover substrate to the base substrate so as to cover the grooves, the bonding step comprising: a film formation step of forming, by vacuum film formation, a transparent first oxide thin film which is an oxide of an amorphous structure of a metal or semiconductor on non-groove portions, which are at least portions of the surface of the base substrate where the grooves are not formed, and a transparent second oxide thin film which is an oxide of an amorphous structure of a metal or semiconductor on bonding portions, which are at least portions of the cover substrate that overlap with the non-groove portions; and a bonding step of bonding the first oxide thin film and the second oxide thin film by causing atomic diffusion at the bonding interface by overlapping the first oxide thin film on the non-groove portions and the second oxide thin film on the bonding portions in a vacuum at room temperature without exposure to the atmosphere, a transparent bonding layer having a thickness of 40 nm or less, which is made of a laminated structure of the first oxide thin film and the second oxide thin film bonded by the bonding step, and which bonds the base substrate and the cover substrate between the non-groove portion and the bonding portion.

12. The method for manufacturing a microchannel device according to claim 11, wherein the bonding step further comprises a heating step of heating the base substrate and the cover substrate at a temperature of 200° C. or less after the bonding step.

13. A method for manufacturing a microchannel device having microchannels, which are fine channels through which a fluid is introduced, comprising: a step of preparing a transparent base substrate having grooves of a predetermined pattern formed on its surface to form the microchannels; and a bonding step of bonding a transparent cover substrate to the base substrate so as to cover the grooves, the bonding step comprising: a film-forming step of forming, by vacuum film-forming, a transparent first oxide thin film made of a metal or semiconductor oxide on non-groove portions, which are at least portions of the surface of the base substrate where the grooves are not formed, and a transparent second oxide thin film made of a metal or semiconductor oxide on bonding portions, which are at least portions of the cover substrate that overlap with the non-groove portions; and a step of exposing the first oxide thin film on the non-groove portions and the second oxide thin film on the bonding portions to a space containing moisture to make them hydrophilic, and then superposing them at room temperature. By heating the base substrate and the cover substrate at a temperature of 200°C or less, a chemical bond or a chemical bond and atomic diffusion is generated at the bonding interface between the first oxide thin film on the non-groove portion and the second oxide thin film on the bonding portion, and the bonding interface is evaluated by a blade method to have a surface free energy of 0.6 J / m 2 a bonding step of bonding the first oxide thin film and the second oxide thin film with a bonding strength of at least 1000 kJ / cm, and bonding the base substrate and the cover substrate between the non-groove portion and the bonding portion by a transparent bonding layer having a thickness of 40 nm or less and consisting of a laminated structure of the first oxide thin film and the second oxide thin film bonded by the bonding step.

14. A method for manufacturing a microchannel device having microchannels, which are fine channels through which a fluid is introduced, comprising: a step of preparing a transparent base substrate having grooves of a predetermined pattern formed on its surface to form the microchannels; and a bonding step of bonding a transparent cover substrate to the base substrate so as to cover the grooves, the bonding step comprising: a film-forming step of forming, by vacuum film-forming, a first thin film made of a metal or semiconductor on non-groove portions, which are at least portions of the surface of the base substrate where the grooves are not formed, and forming a second thin film made of a metal or semiconductor on joint portions, which are at least portions of the cover substrate that overlap with the non-groove portions; and a step of exposing the first thin film and the second thin film to moisture or a space containing moisture and oxygen to oxidize them, thereby obtaining a transparent first oxide thin film formed by oxidation of the first thin film and a transparent second oxide thin film formed by oxidation of the second thin film, and making them hydrophilic, and then superposing, at room temperature, the first oxide thin film on the non-groove portions and the second oxide thin film on the joint portions. By heating the base substrate and the cover substrate at a temperature of 200°C or less, a chemical bond or a chemical bond and atomic diffusion is generated at the bonding interface between the first oxide thin film on the non-groove portion and the second oxide thin film on the bonding portion, and the bonding interface is evaluated by a blade method to have a surface free energy of 0.6 J / m 2 a bonding step of bonding the first oxide thin film and the second oxide thin film with a bonding strength of at least 1000 kJ / cm, and bonding the base substrate and the cover substrate between the non-groove portion and the bonding portion by a transparent bonding layer having a thickness of 40 nm or less and consisting of a laminated structure of the first oxide thin film and the second oxide thin film bonded by the bonding step.

15. A method for manufacturing a microchannel device according to any one of claims 11 to 14, characterized in that the first oxide thin film is provided to cover the inner wall surface of the groove together with the non-groove portion of the base substrate, and the second oxide thin film is provided to cover the groove lid portion, which is the portion that covers the groove, together with the bonding portion of the cover substrate.

16. A method for manufacturing a microchannel device according to any one of claims 11 to 14, characterized in that the film formation step is carried out by a method that involves rapid cooling of raw material atoms on the surfaces of the base substrate and the cover substrate.

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