JP6089162B2 - Atomic diffusion bonding method and manufacturing method of packaged electronic component sealed by the method - Google Patents

Description

  The present invention relates to an atomic diffusion bonding method, and more specifically, for use when firmly bonding two substrates as materials to be bonded, such as stacking IC substrates, sealing packages, and combining various devices. In the bonding method, two substrates are bonded via a microcrystalline thin film formed on the bonding surface of at least one substrate, thereby bonding atoms between the substrates by causing atomic diffusion at the bonding interface and grain boundaries. The present invention relates to a new joining method.

  In the present invention, “microcrystal” includes “polycrystal” and “amorphous”.

  In addition, the “thin film” in the present invention includes not only a continuous film but also a film having an intermittent portion such as an island structure formed in the process of nucleus growth.

  Further, the “crystal grain boundary” in the present invention refers to an intermittent part of the regularity of atomic arrangement, and in addition to the crystal grain boundary in a polycrystal (“crystal grain boundary” in a general sense), long-range order (number The above-mentioned amorphous structure having the short-range order (regularity of arrangement in an atomic group of several tens atoms or less) that has no short-range order (regularity of arrangement in an atomic group of about 10 atoms or more). ”Is the“ crystal grain boundary ”in the present invention, and when there is a void in the amorphous metal film and the volume ratio (filling rate) is lower than 100%, the interface between the void and the amorphous metal is also high. Since it is considered to have an atomic diffusion coefficient, it corresponds to the “crystal grain boundary” in the present invention as in the above-mentioned intermittent portion of the short-range order.

  Joining techniques for bonding two or more materials to be joined are used in various fields. For example, in the field of electronic components, such joining techniques are used for wafer bonding, package sealing, and the like.

  As an example, the above-described wafer bonding technique will be described as an example. In the conventional general wafer bonding technique, a method of applying high pressure and high heat between stacked wafers is generally used.

  However, in this method, it is not possible to bond or integrate substrates on which electronic devices or the like that are sensitive to heat or pressure are formed. Therefore, the materials to be bonded can be bonded to each other without causing such physical damage. There is a demand for a technique for joining the two.

  As described above, as a technique for joining the materials to be joined at room temperature and without applying pressure, each of the joining surfaces of the materials to be joined is irradiated with an ion beam such as a rare gas to form oxides or By removing organic matter, etc., the atoms on the surface of the bonding surface are brought into an active state (activation) that is easy to form a chemical bond, and in this state, heating is performed by overlapping the bonding surfaces of the materials to be bonded. There has been proposed a “normal temperature bonding method” that enables bonding at room temperature without using an adhesive or the like, for example, as a bonding method for silicon wafers or the like (see Patent Document 1).

  However, in the method described in Patent Document 1, the bonding surface of the material to be bonded is irradiated with a rare gas beam or the like to clean the bonding surface to make it active, and then the two bonding surfaces are bonded firmly. Although a sufficient bonding force can be obtained, the materials that can be bonded are limited between some metals and metals, and some metals and compounds, and the application is limited.

  In addition, when bonding is performed by the above method, even if the bonding surface is macroscopically bonded, there is a portion that is not microscopically bonded due to the roughness or waviness of the bonding surface, and at the wafer level. It cannot be used for bonding for stacking and integration.

  In this way, in order to prevent the occurrence of a part that is not partially bonded, it is conceivable to suppress the surface roughness by polishing the bonding surface, but the bonding surface that can be suppressed by polishing is also considered. There are limits to roughness and swell.

  For this reason, if the conventional room temperature bonding method is used to reduce the occurrence of unbonded parts, it is necessary to perform processing such as pressurization and pressure bonding when polymerizing the materials to be joined. Damage may occur.

  In the bonding by the above method, the surfaces of both substrates are activated as described above to generate a metal or chemical bond between atoms only at the contact interface. It does not involve atomic diffusion.

  For this reason, although the bonding itself can be performed relatively firmly, there is still a bonding interface at the bonding portion of both substrates, and an altered layer such as an oxide film is formed at the bonding interface at the time of bonding. When used as an electronic device or the like, such a bonding interface or an altered layer acts as a barrier or the like that prevents the passage of electrons, resulting in a decrease in performance.

In order to eliminate the drawbacks of the room temperature bonding method described in Patent Document 1, the inventor of the present invention provides each bonding surface of a wafer, a chip, a substrate, a package, and other various materials to be bonded. In addition, in a vacuum atmosphere having a high vacuum of 1 × 10 ⁻⁴ Pa or less in the ultimate pressure, for example, by using a vacuum film-forming method such as sputtering or ion plating, and preferably in the generation of plasma, A thin film having a microcrystalline structure is formed on the bonding surface, and the thin films formed on the bonding surface of the material to be bonded are polymerized at room temperature while maintaining the vacuum during or after the formation of the thin film. Thus, a “room temperature bonding method” in which the materials to be bonded are bonded by bonding generated between the bonding surfaces has already been proposed (see Patent Document 2).

  According to this room temperature bonding method, the bonding surfaces of the same type or different types of thin films can be firmly bonded by metal bonds or intermolecular bonds at the atomic level without heating, pressurization, voltage application, etc. , The internal stress of the thin film can be released and the joint distortion can be relaxed. The joint obtained here does not delaminate at the interface. Yes) a joined state can be obtained (Patent Document 2, “0021” column).

Japanese Patent No. 2791429 JP 2008-207221 A

  Among the conventional room temperature bonding methods described above, the method described in Patent Document 1 is active by irradiating a bonding surface of a material to be bonded with a rare gas beam or the like to remove oxides or organic substances existing on the bonding surface. After making it into a state, it is intended to perform the joining by superimposing both joint surfaces.

  Therefore, in the invention described in the above-mentioned Patent Document 1, a pair of wafer holding members positioned opposite to each other in the vacuum chamber are arranged, one wafer holding member is fixed to the vacuum chamber, and the other wafer holding member is fixed. It is attached to the lower end of a push rod that can move linearly while keeping the air tightness of the vacuum chamber, and by superimposing the joint surfaces in the same vacuum vessel where the rare gas beam was irradiated (Patent Document 1, “0005” column) ), The bonding surface that has been activated by irradiation with a rare gas beam or the like is bonded again with oxygen, organic matter, or the like in the air so that the bonding is not lost.

  Further, the room temperature bonding method described in Patent Document 2 not only presupposes that the bonding surfaces of the materials to be bonded are overlapped together with film formation in the same vacuum (for example, claims in Patent Document 2). 1) Even when bonding is performed in the same vacuum, “As the contamination progresses due to the reaction with the impurity gas remaining on the surface of the thin film, the adhesion strength between the thin films decreases. In the meantime, the bonding itself can no longer be performed ”(Patent Document 2“ 0055 ”column).

  As described above, in the conventional room temperature bonding method, after the bonding surface is processed (cleaning with a rare gas beam or forming a thin film having a microcrystalline structure), the subsequent bonding of the bonding surfaces is performed by processing the bonding surfaces. In the same vacuum vessel and with the vacuum vessel maintained in a high vacuum state, for example, the bonding surface after cleaning with a rare gas beam or forming a microcrystalline thin film should be at atmospheric pressure. It is the recognition of those skilled in the art of the present invention, including the inventor of the present invention, that the bonding itself becomes impossible once exposed to the atmosphere. A configuration is adopted in which the matching is performed in a high vacuum space.

  For this reason, it is considered necessary to perform the work of superimposing the joining surfaces of the materials to be joined in a limited space in a vacuum vessel maintained at a high vacuum in a limited condition. In addition to being extremely difficult to perform the joining work, in order to realize the joining method described above, the work of superimposing the joining surfaces of the materials to be joined placed in the vacuum container while keeping the inside of the vacuum container at a high vacuum is performed. This requires a robot arm, jig, and other sticking device with a special structure, and requires a large initial investment.

  In addition, for example, when packaging electronic parts by the above method, the package after sealing is also evacuated, and the compatibility with a structure in which an inert gas having a pressure close to atmospheric pressure is sealed inside is intended. Was considered impossible.

Regardless of the above-mentioned recognition by those skilled in the art, as a result of the research by the inventors of the present invention, in the room-temperature bonding method with atomic diffusion similar to that described as Patent Document 2, the bonding surface is satisfied by satisfying predetermined conditions. Even after the superposition of each other is exposed to a low-vacuum pressure higher than the vacuum (1 × 10 ⁻⁴ Pa) described in the above-mentioned Patent Document 2 or an atmosphere under atmospheric pressure, the Patent Document As in the case of bonding in vacuum as described in 2, it was found that bonding with atomic diffusion at the bonding interface is possible.

The present invention has been made on the basis of the knowledge obtained as a result of the above research by the inventor. After forming the microcrystalline thin film on the bonding surface of the material to be bonded under vacuum, the above-mentioned 1 × 10 ^{− is applied. It} can also be used for bonding between a wide range of materials, including bonding between dissimilar materials, by superimposing the bonding surfaces under a pressure higher than ⁴ Pa (low vacuum), for example, under atmospheric pressure. In addition, by providing a bonding method with atomic diffusion (atomic diffusion bonding method) that performs bonding without physically damaging the substrates to be bonded, the workability of bonding with such atomic diffusion is improved. The purpose is to eliminate the need for a vacuum device or a sticking device having a special structure for performing the superposition work.

  In addition, the present invention enables bonding under such atmospheric pressure, so that strong bonding with atomic diffusion is performed. For example, the pressure close to atmospheric pressure without vacuuming the inside of the package. An object of the present invention is to provide a package type electronic component such as a MEMS sealed with an inert gas.

In order to achieve the above object, the atomic diffusion bonding method of the present invention comprises:
In a vacuum container of 1 × 10 ⁻⁴ Pa or less, a thin film having a microcrystalline structure made of a single metal or an alloy (hereinafter, abbreviated as “microcrystalline thin film”) is formed on each smooth surface of each of two substrates having a smooth surface. And superposing the two substrates so that the microcrystalline thin films formed on the two substrates are in contact with each other in a non-vacuum inert gas atmosphere exceeding 1 × 10 ⁻⁴ Pa. Thus, the two substrates are bonded by causing atomic diffusion at the bonding interface and crystal grain boundary of the microcrystalline thin film.

Another atomic diffusion bonding method of the present invention is as follows:
In a vacuum vessel of 1 × 10 ⁻⁴ Pa or less, a microcrystalline thin film made of a single metal or alloy is formed on the smooth surface of one substrate, and a non-vacuum inert gas atmosphere exceeding 1 × 10 ⁻⁴ Pa Below, the one and the other two substrates are overlapped so that the microcrystalline thin film formed on the one substrate is in contact with the smooth surface of the other substrate having at least a smooth surface having a microcrystalline structure. By combining, the two substrates are bonded by causing atomic diffusion at a bonding interface and a crystal grain boundary between the microcrystalline thin film and the smooth surface of the other substrate (claim 2). .

The inert gas in the present invention includes a narrowly defined inert gas, that is, helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and nitrogen gas (N ₂ ), Methane (CH ₄ ), carbon dioxide (CO ₂ ), carbon monoxide (CO), and the like, which include inert gases in a broad sense that hardly cause chemical reactions.

In any of the above methods, the microcrystalline thin film has a body diffusion coefficient of less than 1 × 10 ⁻⁵⁵ (m ² / s) at room temperature, or a free energy of formation of oxide at room temperature of −330 (kJ / mol of compounds). In this case, Ni, Cu, Zn, Pd, Ag, Pt, and Au are examples of single metals that deviate from this condition.

The microcrystalline thin film is a material having a body diffusion coefficient of 1 × 10 ⁻¹¹⁰ m ² / s or more at room temperature, for example, a material having a body diffusion coefficient of 6.7 × 10 ⁻¹¹⁰ m ² / s or more of tungsten (W). (Claim 4).

  Further, the superposition of the substrates may be performed in an inert gas atmosphere at a pressure equal to or higher than atmospheric pressure.

  In any of the above methods, the inert gas is any one gas selected from the group consisting of argon, helium, neon, krypton, xenon, nitrogen and methane, or 2 selected from the group gas. A mixed gas of more than one kind of gas can be used (claim 6).

  In the generation of the inert gas atmosphere described above, a gas from a gas source (for example, a gas cylinder) that supplies an inert gas having an impurity concentration of 1 ppm or less is introduced alone or mixed into the space where the substrates are overlapped. Thus, gas replacement can be performed (claim 7).

  At this time, an inert gas from the gas source may be passed through a purifier to remove impurities, and then introduced into a space where the substrates are overlapped (claim 8).

  When the inert gas atmosphere is formed of nitrogen gas or a mixed gas of nitrogen gas and another inert gas, the microcrystalline thin film has a free energy of formation of nitride of -310 ( (kJ / mol of compounds) or a single metal or an alloy may be used (claim 9).

  It is preferable that the substrates are superposed in an atmosphere from which dust is removed.

  Further, the strength of the force for superimposing the substrates can be reduced by a relatively weak force of 101 kPa or less, for example, about several kPa. However, this does not prohibit pressing with a force that does not damage the substrate or the like.

  Further, the body diffusion coefficient can be increased by heating the substrate temperature in the range of room temperature to 400 ° C. when the substrates are stacked.

The substrate may be heated when the material for forming the microcrystalline thin film has a body diffusion coefficient at room temperature of 1 × 10 ⁻⁴⁰ m ² / s or less.

  The superimposing of the substrates may be performed without heating the substrates (claim 14).

  The formation of the microcrystalline thin film and the superposition of the substrates can be performed in the same or adjacent vacuum vessels.

The microcrystalline thin film can be formed in a vacuum vessel having an ultimate vacuum pressure of 1 × 10 ⁻⁴ Pa to 1 × 10 ⁻⁸ Pa.

  The microcrystalline thin film is made of Al, Si, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ru, Rh, Pd, Ag, In, Sn, Hf, It can be formed of any one single metal selected from the element group of Ta, Pt, Au, W or an alloy containing one or more elements selected from the element group. ).

  Before forming the microcrystalline thin film, the altered layer generated on the smooth surface of the substrate on which the microcrystalline thin film is formed can be removed in the same vacuum as the formation of the microcrystalline thin film. ).

  On the smooth surface of the substrate on which the microcrystalline thin film is formed, one or more underlayers made of a thin film of a material different from the microcrystalline thin film are formed, and the microcrystalline thin film is formed on the underlayer. (Claim 19).

  The underlayer is formed of any one single metal selected from the element group of Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W, or one or more selected from the element group It can form with the alloy containing these elements (Claim 20).

  In particular, the single metal or alloy that forms the base layer has a higher melting point than the single metal or alloy that forms the microcrystalline thin film formed on the base layer, and the single metal that forms the microcrystalline thin film. Alternatively, it is preferable to use a material having a large difference in melting point with respect to the alloy (claim 21).

  A preferred film thickness of the microcrystalline thin film is 0.1 nm to 1 μm.

In addition, the method for manufacturing a packaged electronic component according to the present invention is such that a package with atomic diffusion is bonded by any of the above-described methods, whereby a pressure exceeding 1 × 10 ⁻⁴ Pa inside, preferably atmospheric pressure is achieved. An inert gas having a close pressure is sealed (claim 23).

  With the configuration of the present invention described above, the following remarkable effects can be obtained according to the atomic diffusion bonding method of the present invention.

By superimposing the flat surface of one substrate on which the thin film having the microcrystalline structure described above is formed on the other substrate having a flat surface having the same microcrystalline structure in an inert gas atmosphere, the two substrates are overlapped. Even in a space with a relatively low degree of vacuum, such as in an atmosphere with a pressure exceeding 1 × 10 ⁻⁴ Pa, or in an atmosphere with an atmospheric pressure (1 atm), or even a pressure exceeding atmospheric pressure, Atomic grain diffusion is caused in the grain boundary, thereby firmly bonding between the bonding surfaces of the same or different kinds of microcrystalline thin film or between the microcrystalline thin film and the smooth surface of the substrate by metal bonding or intermolecular bonding at the atomic level. In addition, the internal stress of the thin film can be released and the joint distortion can be reduced. Note that the bonding obtained here is a bonding state in which peeling does not occur at the interface (a portion other than the interface of the thin film or the substrate is destroyed when the film is forcibly peeled).

  As a result, it is not necessary to perform bonding between substrates in a vacuum vessel maintained at a high vacuum, and as a result, the degree of freedom in bonding conditions increases, and as a result, workability when bonding by atomic diffusion can be greatly improved. It becomes possible.

As will be described later, atomic diffusion becomes more prominent as the value of the body diffusion coefficient increases. In the method of the present invention, the microcrystalline thin film is formed by tungsten (W) having the lowest body diffusion coefficient at room temperature among single metals. Since it has been confirmed that bonding can be performed by forming a thin film, a microcrystalline thin film is made of a material having a body diffusion coefficient of tungsten (W) of 1 × 10 ⁻¹¹⁰ (m ² / s) or more, and therefore Even if it is made of a metal material, it can be joined.

  The above atomic diffusion bonding method is possible even when the substrates are superposed in an atmosphere having a pressure equal to or higher than atmospheric pressure (1 atm), and there is a wide selection of conditions necessary for bonding.

  In addition, as the inert gas, any one gas selected from the group consisting of argon, helium, neon, krypton, xenon, nitrogen and methane, or a mixture of two or more gases selected from the group gas Any gas can be used, and there is a wide range of choices according to the purpose and application.

  A gas from a gas source (for example, a G1 grade gas cylinder) that supplies a high purity inert gas having an impurity concentration of 1 ppm or less in the above-described inert gas atmosphere in the space where the substrates are superposed is used alone or mixed. The concentration of impurities such as oxygen and water, which can cause poor bonding, is less than a few ppm (several parts per 10,000), preferably less than 1 ppm (0.0001%). It can be made extremely small, and the occurrence of poor bonding can be reduced.

  In particular, when the inert gas from the gas source described above is further passed through a purifier to remove impurities, the concentration of impurities such as oxygen and water in the inert gas in the space where the substrates are superimposed is further increased. An ultra-high purity inert gas reduced to several ppb (several percent per 10 million), for example, about 2 to 3 ppb can be obtained, and bonding with atomic diffusion can be performed more reliably.

  Note that when nitrogen gas or a mixed gas of nitrogen gas and another inert gas is used as the inert gas, the microcrystalline thin film has a single crystal formation free energy of −310 (kJ / mol of compounds) or more. By forming with a metal or an alloy, it is possible to reliably prevent the occurrence of poor bonding due to nitriding of the microcrystalline thin film.

  Furthermore, by superimposing the substrates in an atmosphere from which dust has been removed, it is possible to prevent poor bonding due to the presence of impurities such as dust on the bonding surface. As an example, the cleanliness of this space should be ISO Class 5 (equivalent to Class 100 in the 1988 US Federal Standard. Number of particles of 0.5 μm or more in a cubic foot space is less than 100). More preferably, it is preferable to adjust the humidity in the atmosphere (for example, 50% or less).

  According to the atomic diffusion bonding method of the present invention, it is not necessary to apply a large pressure when superposing the substrates, and the strength of the force for superposing the substrates is 101 kPa or less, for example, a pressure of about several kPa. Even if it is a case, it is possible to join suitably. As a result, it is possible to suitably prevent the base from being damaged by the pressure applied during bonding.

  The bonding is performed by heating the substrate at a relatively low temperature of room temperature or higher and 400 ° C. or lower, while minimizing the damage caused by the heat applied to the members to be bonded as low as possible. By increasing the body diffusion coefficient, it is possible to realize bonding that promotes atomic diffusion.

In particular, the substrate is heated when the material for forming the microcrystalline thin film has a body diffusion coefficient at room temperature of 1 × 10 ⁻⁴⁰ m ² / s or less. Even when a microcrystalline thin film is formed, it is possible to suitably perform bonding with atomic diffusion.

Here, the body diffusion coefficient D is
D = D ₀ exp (−Q / RT)
D ₀ : Frequency term (entropy term)
Q: Activation energy R: Gas constant T: It can be expressed by an absolute temperature, and when the temperature T is raised, the body diffusion coefficient D increases exponentially.

  However, in the case where the joining is performed without heating the base, there is no burden caused by heat on the base or a member attached to the base, such as an electronic component.

  When the formation of the microcrystalline thin film and the superposition of the substrate are carried out in the same container, the equipment can be simplified. About devices that do not have vacuum resistance by sealing devices placed in a container adjacent to the container in a package of electronic components formed with a crystalline thin film, eliminating the need to place the device in a vacuum In addition, it is possible to perform packaging by strong bonding accompanied by atomic diffusion.

By forming the microcrystalline thin film in a vacuum vessel having an ultimate vacuum pressure of 1 × 10 ⁻⁴ Pa to 1 × 10 ⁻⁸ Pa, the adhesion strength of the microcrystalline thin film to the substrate can be prevented from being lowered. Not only the peeling at the bonding interface of the crystalline thin film but also the occurrence of peeling between the substrate and the microcrystalline thin film can be suitably prevented.

  The microcrystalline thin film is made of Al, Si, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ru, Rh, Pd, Ag, In, Sn, Hf, Even if it is formed of any one single metal selected from the element group of Ta, Pt, Au, W, or an alloy containing one or more elements selected from the element group, It is possible to perform atomic diffusion bonding by the method of the invention.

  Before forming the microcrystalline thin film, the altered layer formed on the smooth surface of one or both of the substrates in the same vacuum as the formation of the microcrystalline thin film is removed by a dry process such as reverse sputtering, The adhesion strength of the microcrystalline thin film to the substrate can be improved, and a decrease in the adhesion strength between the substrates due to separation between the substrate surface and the microcrystalline thin film can also be suitably prevented.

  Further, a thin film of a material different from that of the microcrystalline thin film, for example, Ti, V, Cr, Zr, Nb which is an element belonging to Group 4A to 6A in the periodic table is formed on the smooth surface of the substrate on which the microcrystalline thin film is formed. Forming an underlayer from a thin film of any one single metal selected from the group of elements Mo, Hf, Ta, and W, or a thin film of an alloy containing one or more elements selected from the group of elements The adhesion strength of the microcrystalline thin film to the substrate can be increased, thereby preventing the peeling between the substrate and the microcrystalline thin film.

  In particular, as a material for forming such an underlayer, a microcrystal formed on the underlayer by using a material having a high melting point and a large difference in melting point relative to the material for forming a microcrystalline thin film. The two-dimensionality of the thin film (atomic wettability during thin film growth) is improved, and it is possible to prevent the microcrystalline thin film from growing in the shape of islands. Formation of a thin film becomes easy.

  In the atomic diffusion bonding method of the present invention, atomic diffusion bonding can be suitably performed when the film thickness of the microcrystalline thin film to be formed is in the range of 0.1 nm to 1 μm, respectively. In addition, since bonding can be performed by forming a microcrystalline thin film with a thickness of about several tens of millimeters, even when used for bonding a silicon wafer or the like, movement of electrons is hindered by the bonding surface. It is possible to provide a non-bonding method.

In addition, since bonding is performed in an inert gas atmosphere at a pressure exceeding 1 × 10 ⁻⁴ Pa by the above method, for example, when this is used for sealing a package in a package type electronic component, It is also possible to seal an inert gas having a pressure exceeding 1 × 10 ⁻⁴ Pa, for example, atmospheric pressure or a pressure close thereto, together with the device or the like.

Schematic explanatory drawing which showed an example of the joining process of the base | substrate by the atomic diffusion bonding method of this invention. Sectional transmission electron microscope (TEM) image of a Si / Si wafer bonded in 0.1 atm ultra-high purity Ar gas by forming a Ti / Ti thin film (20 nm on one side) (Example 6). Cross-sectional transmission electron microscope (TEM) image of a Si / Si wafer bonded in a high vacuum of 1 × 10 ⁻⁶ Pa or less by forming a Ti / Ti thin film (20 nm on one side) (Comparative Example 1). Cross-sectional transmission electron microscope (TEM) image of a Si / Si wafer bonded in 0.1 atm ultra-high purity Ar gas by forming a Ta / Ta thin film (20 nm on one side) (Example 9). Cross-sectional transmission electron microscope (TEM) image of a Si / Si wafer bonded in a high vacuum of 1 × 10 ⁻⁶ Pa or less by forming a Ta / Ta thin film (20 nm on one side) (Comparative Example 2). Sectional transmission electron microscope (TEM) image of a Si / Si wafer bonded in 0.1 atm G1-Ar gas by forming a Ti / Ti thin film (20 nm on one side) (Example 12). Sectional transmission electron microscope (TEM) image of a Si / Si wafer bonded in 0.1 atm G1-nitrogen gas by forming a Ti / Ti thin film (20 nm on one side) (Example 17).

Outline of Bonding Method The atomic diffusion bonding method of the present invention is a method in which thin films having a microcrystalline structure made of a single metal or an alloy formed in vacuum by vacuum film formation such as sputtering or ion plating in a vacuum vessel are overlapped. Or by superposing the thin film having the microcrystalline structure on a flat surface having a microcrystalline structure made of at least a single metal or an alloy, and thereby superposing the superposition to an atmosphere having a pressure exceeding 1 × 10 ⁻⁴ Pa. Even if the bonding is performed under an atmosphere of atmospheric pressure or higher, for example, by performing this bonding in an inert gas atmosphere, atomic diffusion occurs at the bonding interface and the crystal grain boundary. It is found that strong bonding is performed between the two, and this is adapted for bonding between the substrates, and the substrates are bonded together under the following conditions.

Substrate (material to be joined)
Material As a substrate to be bonded by the atomic diffusion bonding method of the present invention, the ultimate vacuum is 1 × 10 ⁻³ to 1 × 10 ⁻⁸ Pa, preferably 1 × 10 ⁻ , for example, sputtering or ion plating. Any material can be used as long as it can form a thin film having the above-described microcrystalline structure by vacuum film formation in a high vacuum atmosphere using a vacuum vessel having a high vacuum of ⁴ to 1 × 10 ⁻⁸ Pa. It is possible to form a thin film having a microcrystalline structure by the above method, such as various kinds of pure metals and alloys, semiconductors such as Si substrate and SiO ₂ substrate, glass, ceramics, resin, oxide, etc. It can be set as the base | substrate (to-be-joined material) in invention.

  The substrate can be bonded not only between the same materials, for example, between metals, but also between different materials, such as metal and ceramics.

The state of the joining surface, etc. The shape of the substrate is not particularly limited, and for example, from flat to various complex three-dimensional shapes, various shapes can be targeted depending on the application and purpose. The portion (joint surface) to be joined with the other substrate needs to have a smooth surface formed smoothly with a predetermined accuracy.

  In addition, it is good also as what joins a several base | substrate with respect to one base | substrate by providing two or more this smooth surfaces with which another base | substrate is joined to one base | substrate.

  The surface roughness of the bonding surface is, for example, a surface roughness exceeding the maximum height (Rmax) of 5 nm (for example, 50 nm or less) when the purpose is achieved simply by bonding, such as sealing of a package. However, bonding can be performed, but Rmax is preferably 5 nm or less.

  As for the smooth surface of the substrate, it is preferable that the modified layer such as the gas adsorption layer and the natural oxidation layer on the surface is removed before forming the microcrystalline thin film. For example, the aforementioned modified layer is obtained by a known wet process such as cleaning with a chemical solution. A substrate on which hydrogen termination or the like has been performed can be suitably used in order to remove the layer and to prevent gas adsorption again after removing the deteriorated layer.

  In addition, the removal of the altered layer is not limited to the wet process described above, but can also be performed by a dry process. The altered layer such as a gas adsorption layer or a natural oxide layer is reverse-sputtered by bombardment of rare gas ions in a vacuum vessel. Can also be removed.

  In particular, when the altered layer is removed by the dry process as described above, gas adsorption and oxidation occur on the substrate surface after the altered layer is removed and before a thin film having a microcrystalline structure described later is formed. In order to prevent this, it is preferable to remove such a deteriorated layer in the same vacuum when a thin film having a microcrystalline structure described later is formed, and to form a thin film having a microcrystalline structure following the removal of the deteriorated layer. More preferably, the altered layer is removed using an ultra-high purity inert gas to prevent the oxide layer or the like from being re-formed after the altered layer is removed.

  The structure of the substrate is not particularly limited, such as single crystal, polycrystal, amorphous, glass state, etc., and various structures can be targeted for bonding, but only one of the two substrates will be described later. When a thin film having a microcrystalline structure is formed and bonding is performed without forming a thin film having a microcrystalline structure on the other substrate, the bonding surface of the other substrate on which the thin film is not formed is In order to obtain atomic diffusion at the junction interface and the grain boundary, at least the surface thereof needs to have a microcrystalline structure (including amorphous) similar to a thin film having a microcrystalline structure described later.

Material of microcrystalline thin film As the material of the microcrystalline thin film to be formed, a thin film of the same material as the base may be formed, or a microcrystalline thin film of a different material from the base may be formed according to the purpose. The material of the microcrystalline thin film formed on one side of the substrate and the material of the microcrystalline thin film formed on the other side of the substrate may be different from each other. The combination which becomes non-solid solution like this may be sufficient, and the combination, such as a metal and a semimetal, can be arbitrarily arbitrarily performed according to the objective.

According to the method of the present invention, the microcrystalline thin film is formed of any material as long as the material has a body diffusion coefficient of 1 × 10 ⁻¹¹⁰ m ² / s or more at room temperature. As materials for such a microcrystalline thin film, Al, Si, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ru, Rh, Pd, Ag, In, Sn, Hf, Ta, Pt, Au, any single metal selected from the element group, or an alloy containing at least one element of these element groups Can be used.

Of these substances, Ni having a body diffusion coefficient of 1 × 10 ⁻⁵⁵ (m ² / s) or more at room temperature and a free energy of formation of oxide at room temperature of −330 (kJ / mol of compounds) or more. , Cu, Zn, Pd, Ag, Pt, Au single metals, or alloys that satisfy the above conditions, atomic diffusion is achieved even when bonding is performed in air at atmospheric pressure by satisfying the predetermined conditions. As the material of the microcrystalline thin film according to the present invention, which must be joined in an inert gas atmosphere, body diffusion at room temperature, excluding those that can be joined in the atmosphere, is possible. A single metal or an alloy having a coefficient of less than 1 × 10 ⁻⁵⁵ (m ² / s) or an oxide free energy of formation less than −330 (kJ / mol of compounds) at room temperature may be used.

Of the constituent materials of the microcrystalline thin film, when the microcrystalline thin film is formed of In, Al, Zr, Ti or the like having a body diffusion coefficient at room temperature of 1 × 10 ⁻⁴⁰ m ² / s or more, the substrate is heated. Even when bonded at room temperature, the bonding interface disappears, and recrystallization occurs between the bonded microcrystalline thin films, resulting in crystal grains having a particle size covering substantially the entire area between the two substrates. For example, it is possible to obtain an integration of two microcrystalline thin films by metal bonding.

However, if the material having a body diffusion coefficient of 1 × 10 ⁻¹¹⁰ m ² / s or more at room temperature is used, the microcrystalline thin film is formed of a material having a body diffusion coefficient of less than 1 × 10 ⁻⁴⁰ m ² / s at room temperature. Even so, it is possible to obtain a sufficient bonding strength between the substrates by metal bonding at the bonding interface, and if necessary, by heating the substrates within a temperature range of 400 ° C. or less, It is possible to promote atomic diffusion at the bonding interface.

  As will be described later, when the inert gas atmosphere in the space where the substrates are overlapped is nitrogen gas or a mixed gas of nitrogen gas and another inert gas, the formation of the microcrystalline thin film described above is performed. It is preferable to use a substance having a free energy of formation of nitride of −310 (kJ / mol of compounds) or more.

The film thickness to be formed is not particularly limited, but bonding can be performed even when each microcrystalline thin film is formed with a thickness of one constituent element. In the embodiment described later in which a thin film is formed, bonding is possible even when the film thickness is 0.1 nm (0.2 nm for two layers), and the thickness of the microcrystalline thin film interposed between the substrates to be bonded is determined. , It can be formed with a thickness below the mean free path of electrons and spin current.

  As a result, the layer of the microcrystalline thin film interposed between the substrates does not become a barrier against the movement of electrons, etc., and it is possible to create a new functional device by bonding an arbitrary silicon wafer. It is possible to use an atomic diffusion bonding method.

  Note that the microcrystalline thin film to be formed does not need to continuously cover the entire bonding surface, and may partially cover this. Therefore, the “microcrystalline thin film” here includes, for example, the state of an island structure formed in the process of nucleation. For example, when thin films having an island structure are overlapped and joined, Bonding by atomic diffusion described later occurs at the overlapping portion between the islands forming the island and the islands forming the other thin film, whereby a bond is obtained.

  On the other hand, as the film thickness increases, the surface roughness of the obtained microcrystalline thin film increases and bonding becomes difficult, and it takes a long time to form a thick microcrystalline thin film, resulting in decreased productivity. Therefore, the upper limit is about 1 μm, and about 0.1 nm to 1 μm is a preferable range of the thickness of each microcrystalline thin film in the atomic diffusion bonding method in the present invention.

Grain size and density The microcrystalline thin film to be formed has a higher atomic diffusion rate than that of the solid of the same microcrystalline metal, and in particular, it has a microcrystalline structure with a large proportion of grain boundaries where the diffusion rate is extremely high. Preferably, the average grain size in the in-plane direction of the crystal grains may be 50 nm or less, and more preferably 20 nm or less.

  Note that the microcrystalline thin film may have an island-like structure as described above. However, the microcrystalline thin film is configured by excluding a portion where a void or the like is formed with respect to 100% of the volume occupied by the microcrystalline thin film. It is preferable to form the metal so that the volume ratio is 80% or more, preferably 80 to 98%.

Forming surface of the microcrystalline thin film Further, the microcrystalline thin film may be formed on each of the two substrates to be joined. However, the microcrystalline thin film is formed only on one of the substrates, It is also possible to obtain bonding to the substrate without forming a microcrystalline thin film.

  In this case, the bonding surface of the other substrate on which the microcrystalline thin film is not formed has a microcrystalline structure of a single metal or an alloy at least near the surface of the bonding surface, as described above. Need to be. However, the bonding surface of the substrate on which the thin film is not formed and the material of the microcrystalline thin film need not be common.

  In addition, on the smooth surface of the substrate on which the microcrystalline thin film is formed, one or more underlayers made of a thin film of a material different from the microcrystalline thin film can be formed before the microcrystalline thin film is formed. When the microcrystalline thin film to be formed has a relatively low adhesion strength to the substrate, the formation of the underlayer is effective in improving the adhesion strength.

  Such an underlayer can be formed by a vacuum film formation technique similar to the film formation method to be described later of the microcrystalline thin film, and the material thereof is Ti, Zr which is an element belonging to Group 4A-6A of the periodic table. , Hf, V, Nb, Ta, Cr, Mo, W, and the thickness is 0.2 to 20 nm as an example.

  As the material of the underlayer, it is preferable to use a material having a large difference in melting point with respect to the material for forming the microcrystalline thin film formed thereon, and a high melting point for the material for forming the thin film having a microcrystalline structure Are preferably used.

  The formation of such an underlayer not only suitably prevents the microcrystalline thin film from peeling from the substrate, but also the two-dimensionality of the microcrystalline thin film formed on the underlayer (atomic wettability during the formation of the microcrystalline thin film). ) And the microcrystalline thin film can be prevented from growing in the form of islands during film formation, and it becomes easy to form a very thin microcrystalline thin film of 0.1 nm.

Film Forming Method Film Forming Technology In the atomic diffusion bonding method of the present invention, as a method for forming a microcrystalline thin film formed on a bonding surface of a substrate which is a material to be bonded, PVD such as sputtering and ion plating, CVD, Various film-forming methods for vacuum film formation in a vacuum atmosphere in a vacuum vessel having a high vacuum degree of 1 × 10 ⁻⁴ to 1 × 10 ⁻⁸ Pa, such as vapor deposition, can be cited, and the diffusion rate is For relatively slow materials and alloys and compounds thereof, a vacuum film formation method in which film formation is preferably performed under the generation of plasma capable of increasing the internal stress of the formed thin film, for example, film formation by sputtering is preferable.

Degree of vacuum The pressure in the vacuum vessel during the formation of the thin film may be a vacuum atmosphere with an ultimate degree of vacuum of 1 × 10 ⁻³ to 1 × 10 ⁻⁸ Pa, and a lower pressure (high degree of vacuum) is preferable. .

Inert gas (Ar gas) pressure When the film formation method is sputtering, the pressure of the inert gas (generally Ar gas) during film formation should be a dischargeable region, for example, 0.01 Pa or more. In addition, if it exceeds 30 Pa (300 μbar), bonding may not be possible, so the upper limit is preferably about 30 Pa (300 μbar). This is because when the Ar gas pressure is increased, the surface roughness of the formed thin film is increased, the film density is significantly decreased, and the concentration of impurities such as oxygen in the film is significantly increased.

Conditions for superposition Atmospheric pressure As described above, the substrates having the microcrystalline thin film formed on the surface, or the substrate having the microcrystalline thin film and the substrate surface having the microcrystalline structure are 1 × 10 ⁻⁴ Pa. The two substrates are bonded to each other by causing atomic diffusion at the bonding interface and the crystal grain boundary by superimposing them in an atmosphere having a pressure exceeding 1, for example, an atmospheric pressure or higher pressure atmosphere.

  In addition, by continuing to introduce the inert gas into the space so that the pressure in the space where the substrates are overlapped is slightly higher than the atmospheric pressure, it is possible to prevent the outside air from entering the space and to supply the air. Like the air-treatment type clean room and glove box, the internal space can be kept clean.

Components of the atmosphere The two substrates are superposed in an inert gas atmosphere. Examples of such inert gases include argon (Ar), helium (He), neon (Ne), In addition to krypton (Kr) and xenon (Xe), inert gases in a broad sense such as nitrogen, methane, carbon dioxide, and carbon monoxide, which are difficult to cause chemical reaction, can be used. Any one selected from these groups One type of gas or a mixed gas of two or more types of gases selected from the group of gases can be used.

  The concentration of components (impurities) other than the inert gas in the inert gas atmosphere is several ppm or less, preferably 1 ppm or less. The various high-purity gases provided in a state sealed in the gas cylinder The inert gas atmosphere is generated by introducing the gas into the space where the substrates are overlapped and replacing the gas in the space.

In the so-called “G1” grade pure gas available as a high purity gas cylinder with guaranteed purity, the purity of argon gas is 99.9999% or more (impurity concentration 1 ppm or less), and nitrogen (N ₂ ) gas is 99.99995%. This is the above (impurity concentration of 0.5 ppm or less). By introducing these gases into the space where the substrates are superposed and performing gas replacement, the gas can be introduced using a general stainless steel gas piping system. Even if the impurity concentration increases due to desorption of the adsorbed gas adhering to the inside of the pipe, the inert gas atmosphere of high purity with the impurity concentration in the space being several ppm or less, preferably about 1 ppm or less It can be.

  In general, the term “impurity” for “pure nitrogen” in the case of “pure nitrogen gas” refers to components other than nitrogen, for example, oxygen and water as well as inert gas other than nitrogen. Even if an inert gas such as argon gas is contained as an impurity with respect to the nitrogen gas of the present invention, it does not affect the realization of the bonding method in the present invention. Therefore, in the present invention, components other than the inert gas, mainly It is preferable to form an inert gas atmosphere in the bonding space so that oxygen and water become problems as “impurities” and these are several ppm or less, preferably 1 ppm or less.

In addition, in the gas provided as pure CO ₂ gas or pure CO gas, it is considered that the oxygen (O) of CO ₂ or CO is dissociated to form an oxide on the surface of the microcrystalline thin film. Therefore, for example, when a microcrystalline thin film is formed of a material that easily oxidizes, there is a possibility that bonding force may be reduced or bonding failure may occur, and that pure G ₂ gas or pure CO gas in which purity is guaranteed. Since the impurity concentration in the grade gas is 1 to 2 orders of magnitude higher than other pure gases, even if these gases are introduced directly into the space for polymerization, an inert gas atmosphere such as impurities Since an inert gas atmosphere having a concentration of several ppm or less cannot be obtained, when these gases are used as the inert gas, it is sometimes necessary to adjust the impurity concentration.

  Therefore, preferably, among the inert gases exemplified above, argon (Ar), helium (He), neon (Ne), krypton (Kr), xenon (Xe), excluding carbon dioxide and carbon monoxide, Use of any one kind of inert gas selected from nitrogen and methane or a mixed gas of a plurality of kinds of inert gases is preferable.

  However, this does not deny the use of carbon dioxide and carbon monoxide as inert gases in the present invention.

  If the inert gas from the gas source has a high impurity concentration, or if it is necessary to form a higher purity inert gas atmosphere, the inert gas introduced from the gas source is further purified. It is good also as what introduce | transduces into the above-mentioned space which joins a base | substrate after purifying through.

  In this case, an ultra-high purity inert gas atmosphere in which the impurity concentration in the inert gas atmosphere in the space is about several ppb (1 ppb = 0.0001 ppm) may be generated.

Elapsed time after formation of microcrystalline thin film In an example in which a Ti film is formed as a microcrystalline thin film, the substrate is exposed after exposing the Ti film in a pure Ar gas atmosphere at 1 atm (1 × 10 ⁵ Pa) for 10 minutes (600 seconds). It has been confirmed that a sufficient bonding force can be obtained even when superposed on each other, and bonding is performed even after exposure to an inert gas atmosphere at atmospheric pressure for a sufficiently long time for 10 minutes. It is possible.

Cleanliness of the atmosphere The atmosphere in which the substrates are superposed is preferably performed in a dust-free space in order to prevent poor bonding due to the presence of dust etc. on the joint surface. This can be done in a box or the like.

  The cleanliness of such an atmosphere is, for example, ISO class 5 (corresponding to class 100 in the 1988 US federal standard. 0.5 μm or more and less than 100 particles in a space of 1 cubic foot). Is preferred.

Temperature conditions at the time of bonding The substrates may be bonded at room temperature, or may be heated at a temperature of 400 ° C. or lower as necessary.

In particular, when a microcrystalline thin film is formed of a material having a body diffusion coefficient of 1 × 10 ⁻⁴⁰ (m ² / s) or less at room temperature, it is preferable to heat the substrate during bonding. The heating temperature is preferably set higher as the body diffusion coefficient at room temperature becomes smaller.

Example of Bonding Method An example of a bonding process by the atomic diffusion bonding method according to the present invention will be described with reference to FIG. In FIG. 1, a magnetron cathode for performing sputtering is disposed at the upper part in a vacuum vessel for forming a microcrystalline thin film, and a jig for placing substrates to be bonded to each other is disposed under the magnetron cathode. A microcrystalline thin film is formed on the bonding surface of the substrate that is arranged and attached to the jig.

  In the illustrated embodiment, the table provided in the above-described jig is configured to be rotatable between a thin film formation position indicated by a broken line and a bonding position indicated by a solid line in the drawing on the right side of FIG. The one end of the table on which one of the bases is placed and the one end of the table on which the other base is placed are placed in abutment with each other, and the two tables rotate around the abutting part. Thus, the other surfaces of both tables are lifted upward so that the joint surfaces of the two substrates placed on the tables are superposed.

  When bonding by forming a thin film with a microcrystalline structure with a metal within the numerical range of the body diffusion coefficient and the free energy of formation of the oxide, which require heating of the substrates during bonding, electric heating is included in the aforementioned table. A heater or the like may be embedded so that the bonding surfaces of the two substrates can be polymerized and heated to a predetermined temperature.

  Note that the jig for bonding substrates is not limited to the one shown in the figure, and various shapes and structures can be used according to the shape of the substrate to be bonded. For example, one or both of the bases may be operated by a robot arm or the like, and the bases may be overlapped by a human hand.

  For example, as shown in FIG. 1, a gas source for introducing an inert gas is connected to the vacuum container in which such a jig is accommodated so that the inner space can be replaced with the inert gas. In addition, a glove box or the like that is communicated with the inlet / outlet of the vacuum vessel and similarly configured to be communicated with an inert gas source and capable of gas replacement with the inert gas is provided.

In the apparatus configuration configured as described above, the inside of the vacuum vessel in which the above-described jig is disposed is reduced to an ultimate vacuum pressure of 1 × 10 ⁻⁴ Pa to 1 × 10 ⁻⁸ Pa, and the above-described jig is formed. A microcrystalline thin film is formed on the bonding surface of the substrate in the state where the film is positioned.

When a microcrystalline thin film having a predetermined thickness is formed on the bonding surface of the substrate, the formation of the microcrystalline thin film is finished, an inert gas is introduced into the vacuum vessel from the gas source, and the pressure in the vacuum vessel is reduced. The pressure exceeds 1 × 10 ⁻⁴ Pa, for example, atmospheric pressure, or a pressure slightly higher than atmospheric pressure.

  In addition, the inside of the glove box connected to the inlet / outlet of the vacuum vessel is also replaced with an inert gas so as to have the same pressure, the inlet / outlet of the vacuum vessel is opened, and the base body is attached together with the jig described above from the inside of the vacuum vessel. The table provided on the jig is rotated to the bonding position described above, and the base is bonded with a relatively weak force of 101 kPa or less, for example, several kPa.

  As a result, it is possible to perform bonding in which atomic diffusion is caused at the bonding interface and crystal grain boundary between the two microcrystalline thin films and the bonding strain is reduced.

  In the above description, the case where the substrates on which the microcrystalline thin film made of the same material is bonded is described. However, if the substrates on which the microcrystalline thin film made of different materials are bonded together, for example, two vacuums are used. The above-mentioned glove box is provided between the entrances and exits of the container, and the above-described magnetron cathode is disposed in each of the two vacuum containers so that a microcrystalline thin film of a different material can be formed in each vacuum container. After forming microcrystalline thin films of different materials on the bonding surfaces of the substrates, bonding may be performed by superimposing the substrates taken out of the vacuum containers in the above-described glove box.

  Further, the formation of the microcrystalline thin film on both the substrates is not necessarily performed at the same time, and may be performed with a time difference.

  In addition, if at least the surface portion of the other substrate has a microcrystalline structure of a single metal or alloy in the numerical ranges of the above-described body diffusion coefficient and oxide formation free energy, two substrates to be joined It is also possible to form the above-mentioned microcrystalline thin film only on one of the substrates, and directly bond both substrates without forming the microcrystalline thin film on the other substrate.

  In the above-described bonding example described with reference to FIG. 1, the substrate taken out from the vacuum vessel is described as being bonded in the glove box. However, it is assumed that bonding is performed as it is in the vacuum vessel in which the film is formed. In this case, it is not always necessary to provide a glove box.

  Examples in which substrates are bonded by the atomic diffusion bonding method of the present invention will be described below.

[Jointing in Ar gas atmosphere]
Experimental Method Immediately after the formation of the microcrystalline thin film by the sputtering method, Ar gas was introduced into the sputtered vacuum vessel, and bonding was performed with the inside of the vacuum vessel being an inert gas atmosphere at a predetermined pressure (Examples 1 to 12). ).

  As a comparative example, after the formation of the microcrystalline thin film by the sputtering method, bonding was performed immediately with the inside of the vacuum vessel maintained at a high vacuum (Comparative Examples 1 and 2).

  The material and film thickness of the microcrystalline thin film in each of the examples and comparative examples, the substrates to be joined, the Ar gas used (Ar gas purity), the pressure in the vacuum vessel, the thin film formed in the Ar gas atmosphere after the thin film was formed The exposure time (hereinafter referred to as “exposure time”) is shown in Table 1 below.

  In “Ar purity” in Table 1 below, “G1-Ar gas” refers to Ar gas extracted from a G1 grade Ar gas cylinder having an impurity concentration of 1 ppm or less, and “ultra high purity Ar gas” The G1-Ar gas is further passed through a purifier to indicate Ar gas whose impurity concentration is lowered to 2 to 3 ppb.

  “Exposure time” indicates the time until the Ar gas pressure in the container reaches the bonding pressure and before the bonding, and those without “Exposure time” are those after the formation of the microcrystalline thin film. In this test example, after the formation of the microcrystalline thin film, the time required to increase to the bonding pressure [5 minutes (300 seconds)] has elapsed. In the comparative example, it is shown that bonding was performed immediately after the formation of the microcrystalline thin film.

Experimental results Confirmation of change in bonding state with change in film thickness The film thickness of the microcrystalline thin film to be formed is 2 nm on one side (Example 1), 0.2 nm on one side (Example 2), and 0.1 nm on one side (Example 3). And a Ti film of 0.05 nm (Example 4) on one side, and a Si wafer and a SiO ₂ wafer were bonded together in an ultrahigh purity Ar gas atmosphere of 0.1 atm (1 × 10 ⁴ Pa).

As a result, it has been confirmed that bonding can be performed at any film thickness, and the thin film is exposed in an atmosphere of a pressure exceeding 1 × 10 ⁻⁴ Pa by the method of the present invention. Even in this case, it was confirmed that the bonding can be suitably performed.

  However, in the bonding with the film thickness of 0.05 nm (Example 4), although the bonding itself was possible, the bonding strength was weaker than in the other examples, and the G1-Ar gas atmosphere. Similar results were obtained with the above film thickness even when bonding was performed below.

  Therefore, in the bonding according to the method of the present invention, it is preferable to form the microcrystalline thin film to be formed (one side) with a thickness of 0.1 nm or more.

Confirmation of change in bonding due to change in pressure in container In order to confirm the influence of change in pressure in container on bonding state, as Example 5, a Si / SiO ₂ substrate on which a Ti microcrystalline thin film of 2 nm on one side was formed was used. Bonding was performed in an ultrahigh purity Ar gas atmosphere at 1 atm (1 × 10 ⁵ Pa). Other conditions are the same as those in the first embodiment.

As a result of the above, even when the bonding is performed with the pressure in the container being 1 atm (1 × 10 ⁵ Pa) (Example 5), the bonding is performed at 0.1 atm (1 × 10 ⁴ Pa) ( It was not possible to confirm a difference between Example 1) and the joining state.

In addition, the cross section of the junction part of the example (Example 6) which joined two Si wafers in which the Ti thin film of 20 nm on one side was joined in an ultra high purity Ar gas atmosphere of 0.1 atm (1 × 10 ⁴ Pa). An electron micrograph is shown in FIG.

For comparison, FIG. 3 shows a cross-sectional micrograph of the joint in an example (Comparative Example 1) in which joining was performed under the same conditions except that the joining was performed in a high vacuum of 1 × 10 ⁻⁶ or less. Show.

As is clear from FIGS. 2 and 3, even under the conditions of Example 5 bonded under a relatively high pressure of 0.1 atm (1 × 10 ⁴ Pa), a vacuum with a pressure lower by 10 digits or more than this. As in the case of bonding in the middle, it can be confirmed that the bonding interface between the Ti / Ti films has disappeared, and in the bonding method of Example 6, the difference in the bonding structure when bonded in high vacuum can be confirmed. There wasn't.

  From this, it can be seen that in the bonding mechanism in the ultra-high purity Ar gas, atomic diffusion occurs at the interface of the Ti / Ti film at room temperature, just as in the case of bonding in vacuum.

In addition, as in Example 5, it has been confirmed that good bonding can be obtained even under a pressure of 1 atm (1 × 10 ⁵ Pa), and the bonding is performed at a pressure several times higher than 1 atm. It is clear that bonding can be done even if done.

Confirmation of changes in material and bonding state of microcrystalline thin film The microcrystalline thin film to be formed is a 2 nm Ta film (Example 7) and a 2 nm W film (Example 8) on one side. The effect of the joining state due to the difference was confirmed.

  It was confirmed that both the example (Example 7) in which the bonding was performed by the formation of the Ta film and the example (Example 8) in which the bonding was performed by the formation of the W film were well bonded.

In order to make it easy to observe the state of the bonding interface of the microcrystalline thin film, Si / Si bonded in an ultrahigh purity Ar gas atmosphere of 0.1 atm (1 × 10 ⁴ Pa) with a Ta film thickness of 20 nm on one side. A transmission electron microscope (TEM) photograph in the cross section of the wafer (Example 9) is shown in FIG.

For comparison, a transmission electron microscope (TEM) in a cross section of a bonding example (Comparative Example 2) performed under the same conditions as in Example 9 except that the pressure in the container was an ultrahigh vacuum of 1 × 10 ⁻⁶ Pa or less. ) The photograph is shown in FIG.

In each of the examples in which the Ta film was bonded (Example 9 and Comparative Example 2), the Ta film bonding interface could be clearly confirmed, and the Ti film formation shown in FIGS. As in the case of bonding (Example 6 and Comparative Example 1), it was not possible to confirm the occurrence of atomic diffusion to the extent that the bonding interface of the microcrystalline thin film completely disappeared. There is no difference between the bonding interface of Example 9 performed under 1 × 10 ⁴ Pa) and the bonding interface of the Ta thin film in Comparative Example 2 bonded under high vacuum (1 × 10 ⁻⁶ Pa). Even when the microcrystalline thin film forming the film is formed of Ta or W, it was confirmed that the bonding can be performed without pressure at normal temperature.

  In addition, in the case where the substrates are bonded in a vacuum by forming a microcrystalline thin film (see Patent Document 2), atomic diffusion at the bonding interface occurs more significantly with a substance having a larger atomic diffusion coefficient (body diffusion coefficient). Accordingly, it has been confirmed that bonding with a substance having a large body diffusion coefficient is more likely to occur, and although there is a difference in the pressure of the atmosphere in which bonding is performed, in the present invention in which bonding with atomic diffusion is performed in the same manner, The larger the atomic diffusion coefficient of the material forming the material, the easier it is to bond.

Here, the body diffusion coefficient D of the solid substance can be expressed as follows using the Arrhenius equation.
D = D ₀ exp (−Q / RT)

In the above equation, D ₀ is the frequency term (entropy term), Q is the activation energy, R is the gas constant, and T is the absolute temperature.

Table 2 shows D ₀ and Q of representative substances and calculated D values at 300 K (27 ° C.). In Table 2, each material is listed in order of the size of D.

The values of Ru D ₀ and Q have not been reported in the available literature, and it is assumed that the D value of Ru is approximately proportional to the melting point as in the case of other materials. It is a rough estimate. The approximate D value is shown in parentheses in the table for reference.

As shown in Table 2, Ti has the largest D value in the above materials, and W has 6.7 × 10 ⁻¹¹⁰ m ² / s, the smallest D value among single metals. Yes.

  Therefore, since the bonding could be confirmed by the formation of the microcrystalline thin film of W by the method of the present invention (Example 8), according to the method of the present invention, any metal was used to form the microcrystalline thin film. However, it can be seen that good bonding can be achieved.

Confirmation of change in exposure time and change in bonding state In order to confirm the influence of the change in exposure time to inert gas on the bonding state, in Example 1, after raising the inside of the vacuum vessel to a predetermined pressure [from thin film formation 5 minutes (after 300 seconds)], in Example 10, after raising the inside of the vacuum vessel to a predetermined pressure and then exposing it to an inert gas atmosphere for 10 minutes (600 seconds) [thin film 15 minutes after formation (900 seconds)], bonding was performed. Other conditions are the same as those in the first embodiment.

  Even with such a change in exposure time, there was no difference in the bonding state between Example 1 and Example 10, and it was confirmed that the length of the bonding time did not affect the bonding state.

Confirmation of the effect of changes in Ar gas purity on the bonding state In order to confirm the influence of impurities in an inert gas atmosphere, Example 1 was performed in an ultrahigh purity Ar gas (impurity concentration of about 2 to 3 ppb) atmosphere. In Example 11, bonding was performed in an atmosphere of G1-Ar gas (impurity concentration: about 1 ppm). Other conditions are the same as those in the first embodiment.

Compared to the case of Example 1, even when bonding is performed in a G1-Ar gas atmosphere having a high impurity concentration, it can be confirmed that suitable bonding is performed between Si / SiO ₂ wafers. It was.

Further, in order to make it easy to observe the state of the bonding interface of the microcrystalline thin film, as Example 12, the Si film thickness is 20 nm on one side and Si atmosphere under a G1-Ar gas atmosphere of 0.1 atm (1 × 10 ⁴ Pa). / Si wafer was bonded. The cross-sectional transmission electron microscope (TEM) photograph in this junction part is shown in FIG.

  In the case of Example 6 (see FIG. 2) bonded in an ultra-high purity Ar gas atmosphere, the bonding interface between the Ti films completely disappeared, whereas bonding was performed in the G1-Ar gas atmosphere. In the example of Example 12 (see FIG. 6), the presence of the bonding interface was confirmed.

  Further, in the bonding example of Example 12, there are intermittently low contrast layers (portions appearing whitish in the photograph) having a thickness of about 1 to 2 nm at the bonding interface. This is because, in the bonding performed in the G1-Ar atmosphere, impurities (mainly oxygen and water vapor) present in the Ar gas are adsorbed on the surface of the Ti thin film, and atomic diffusion at the Ti / Ti interface is partially suppressed. It shows that.

  Therefore, in order to completely prevent the disappearance of the bonding interface and the adhesion of impurities to the thin film surface, it is preferable that the impurities (mainly oxygen and water) in the inert gas atmosphere for bonding be about several ppb. It was confirmed.

  However, in the bonding example of Example 12 where bonding was performed in a G1-Ar gas atmosphere, there was no void at the Ti / Ti interface, and bonding was performed over the entire surface of the film. If the adsorption of slight impurities does not impede the performance required for products, the impurity concentration in the inert gas atmosphere for bonding is about 1 ppm required for the G1 grade, and more It is also possible to perform bonding in an inert gas atmosphere with a high impurity concentration.

  Note that the strength of the bond (chemical bond) between an impurity in an inert gas such as oxygen or water vapor and the metal varies greatly depending on the type of metal.

  In this bonding test, the most dominant bond that determines the quality of bonding is chemical bonding (oxidation) with oxygen. The ease of oxidation of the main material is expressed as the free formation energy (ΔG) of the oxide as follows. Table 3 shows. In Table 3 below, Au and Pt that do not form oxides at room temperature are not shown.

As shown in Table 3, Ti easily generates an oxide. In particular, Ti ₃ O _{5 has} a ΔG of −2309 kJ / mol, which makes it easier to form an oxide than other metals. From this, it is considered that in the bonding example of Example 12, the low contrast layer intermittently present at the bonding interface between the Ti film and the Ti film is caused by the formation of oxide.

  On the other hand, from this result, when forming a microcrystalline thin film using a metal other than Ti, it is difficult to form an oxide as compared with the case of forming a microcrystalline thin film with Ti. Even when bonding is performed in a G1-Ar gas atmosphere using a metal film, it is clear that the microcrystalline thin films can be bonded over the entire film interface without generating voids at the bonding interface of the microcrystalline thin film boundary. is there.

  If the impurity concentration in the Ar gas that fills the space for bonding is higher than that of the G1-Ar gas used in Example 12, even if other conditions are used in the same manner as in Example 12, The formation of oxides and the like due to the adsorption of impurities on the surface of the microcrystalline thin film is further promoted, and this oxide further suppresses the atomic diffusion at the bonding interface of the microcrystalline thin film. become unable.

  However, since the amount of impurity gas adsorbed on the substrate surface is considered to be more easily adsorbed as the absolute value of −ΔG is larger, and is approximately proportional to the pressure and time of the impurity gas. Even when Ar gas having a higher impurity concentration than Ar gas is used, a microcrystalline thin film is formed with a material having a small absolute value of -ΔG, and the time from formation of the microcrystalline thin film to bonding is shortened. In addition, by setting the pressure of the atmosphere in which the bonding is performed to be low within the predetermined pressure range of the present application, and by combining these conditions, a good bonding state can be performed.

[Joint under nitrogen gas atmosphere]
Experimental Method Immediately after forming the microcrystalline thin film by the sputtering method, N ₂ nitrogen gas was introduced into the sputtered vacuum vessel, and bonding was performed with the inside of the vacuum vessel being an inert gas atmosphere at a predetermined pressure (Example 13). To 17).

  The material and film thickness of the microcrystalline thin film in each of the examples and comparative examples, the substrates to be joined, the Ar gas used (Ar gas purity), the pressure in the vacuum vessel, the thin film formed in the Ar gas atmosphere after the thin film was formed The exposure time (hereinafter referred to as “exposure time”) is shown in Table 4 below.

  The nitrogen gas used in the experiment was nitrogen gas extracted from a G1 grade nitrogen gas cylinder having an impurity concentration of about 0.5 ppm or less (hereinafter referred to as “G1-nitrogen gas”).

  The impurity concentration in the vacuum vessel was not measured, but is considered to be maintained at 1 ppm or less.

  “Exposure time” indicates the time left for the joining after the nitrogen gas pressure in the container reaches the pressure for joining, and those without “Exposure time” are those after the formation of the microcrystalline thin film. In the following examples, after the formation of the microcrystalline thin film, the time required to increase the bonding pressure [about 3 minutes (180 seconds)] It shows that it joined after progress.

  Table 4 below shows the test conditions of the bonding example under nitrogen gas.

Experimental Results As a result of the above test, when bonding was performed in a nitrogen gas atmosphere of 0.1 atm (1 × 10 ⁴ Pa) (Example 13), and in a nitrogen gas atmosphere of 1 atm (1 × 10 ⁵ Pa) In any of the cases (Example 14) in which bonding was performed, bonding was possible over the entire bonding surface of the microcrystalline thin film, and the bonding method of the present invention used nitrogen gas as the inert gas. It was also confirmed that this can be suitably performed.

  In addition, in the joining example of Example 15 in which the thickness of the microcrystalline thin film to be formed was reduced to 0.1 nm on one side, it was confirmed that bonding could be performed without any problem even in the formation of the microcrystalline thin film having this thickness.

Further, after the nitrogen gas pressure in the container was raised to 0.1 atm (1 × 10 ⁴ Pa), the microcrystalline thin film was further exposed for 10 minutes (600 seconds) in this nitrogen gas atmosphere and then bonded. Also in Example 16, it was confirmed that bonding could be performed.

In order to facilitate the observation of the bonding interface state of the microcrystalline thin film, the Ti film thickness to be formed is 20 nm on one side, and in a nitrogen gas atmosphere at 0.1 atm (1 × 10 ⁴ Pa) as in Example 13. FIG. 7 shows a transmission electron microscope (TEM) photograph of a cross-section at the joint portion of the joint example (Example 17) in which the joints are made in the above.

  In Example 17 (see FIG. 7), a low-contrast layer having a thickness of about 1 to 2 nm is present at the bonding interface, as in the case of bonding in a G1-Ar gas atmosphere (Example 12: see FIG. 6). However, it can be confirmed that the entire film is bonded without forming a void at the Ti / Ti film interface.

Influence of nitriding Note that the low-contrast layer was formed so as to partially cover the surface of the microcrystalline thin film at the junction interface of Example 12 shown in FIG. 6, whereas Example 17 shown in FIG. A low-contrast layer was uniformly formed over the entire surface of the microcrystalline thin film at the bonding interface.

  Due to the difference from the bonding state in the G1-Ar gas atmosphere, in Example 17 in which the wafer on which the Ti / Ti thin film was formed was bonded in the G1-nitrogen gas, the adsorption on the surface of the thin film was only influenced by the oxidation. It is considered that the surface of the thin film was affected by nitriding because the microcrystalline thin film was formed of Ti which is easily nitrided.

  Here, ΔG, which is the free energy of formation of Ti nitride (TiN), has a large absolute value of −308.1 (kJ / mol of compounds), and Ti is a substance that easily forms nitrides.

  Therefore, in the examples of Examples 13 to 17 in which such a Ti thin film that is easily nitrided is formed, it has been confirmed that bonding can be performed. Therefore, a material that is harder to nitride than Ti, that is, a nitride is used. When the microcrystalline thin film is formed of a material having a large free generation energy ΔG (small absolute value), it is apparent that bonding can be performed in a nitrogen atmosphere.

Further, as a typical metal material having a smaller ΔG than TiN (larger absolute value) and thus easily nitriding, Mg (Mg ₃ N ₂ : ΔG = −399.4 kJ / mol of compounds), Sr (Sr ₃ N ₂ : ΔG = −323.6 kJ / mol of compounds), Zr (ZrN: ΔG = −336.2 kJ / mol of compounds), etc., and these are relatively similar to TiN. Since it has a close ΔG, it can be considered that bonding can be performed by forming a microcrystalline thin film using almost all metals even when bonding is performed in a nitrogen gas atmosphere.

[Other inert gases]
As described above, bonding in an Ar gas atmosphere and a nitrogen gas atmosphere can be performed even under a pressure higher than 1 × 10 ⁻⁴ Pa. It can be considered that bonding can be performed in an active gas atmosphere as well.

  In particular, since He, Ne, Kr, and Xe contained in an inert gas in a narrow sense are completely inert gases like Ar, the structure at the bonding interface between microcrystalline thin films is bonded in an Ar gas atmosphere. It is considered that the structure is exactly the same as that performed.

In addition, in CH ₄ gas contained in an inert gas in a broad sense, there is a possibility that the dissociated C and the metal constituting the microcrystalline thin film may chemically bond (carbonize). Since it is difficult to form carbides, there are fewer elements that hinder bonding when CH ₄ gas is used than when bonding is performed in a nitriding gas atmosphere.

Therefore, since bonding can be performed in a nitrogen gas atmosphere, bonding should be performed in a CH ₄ gas atmosphere.

The inert gas in a broad sense further includes CO ₂ gas and CO gas, and it is considered that bonding is possible even when these gases are used. In such a case, it is easy to form an oxide with the metal, and when the microcrystalline thin film is formed with a metal that easily oxidizes, the bonding strength may be reduced.

Further, it is difficult to remove impurities such as oxygen and water from CO ₂ gas and CO gas, and the impurity concentration in industrially used G1 grade gas is lower than that of Ar gas and N ₂ gas of the same grade. _Since it is 1 digit larger with 2 gases and 2 digits larger with CO gas, it is difficult to obtain an inert gas atmosphere (with an impurity concentration of several ppm or less as an example) when using CO ₂ gas or CO gas. Therefore, it is preferable to use an inert gas excluding CO ₂ gas and CO gas.

  The bonding method of the present invention described above is capable of bonding at an atomic level without heating or heating at a relatively low temperature, without applying pressure, with low interface stress after bonding, and with a microcrystalline thin film. Since the work surface has been improved because the bonding surfaces can be superposed in an atmosphere exposed to an inert gas at atmospheric pressure, for example, an atmospheric pressure higher than that of the vacuum where It can be easily used in applications such as creation of high-function devices, downsizing of information appliances, and high integration. Examples of these applications are as follows.

Creation of new and high-performance devices Application to creation of new functional devices stacked and integrated at the wafer level Integration of integrated circuits and short-wavelength optical devices (for example, Si devices / GaN, photonic crystals, LEDs), new Bonding when creating a functional photo-electronic conversion device.

  Manufacture of spin-electronic hybrid devices. By bonding by the method of the present invention, it is possible to bond between wafers in an average free process of electrons or spin current.

Bonding between dissimilar material wafers For the purpose of forming ultra-hybrid substrates and components, manufacturing of potential barrier hybrid wafers in which semiconductor wafers are laminated with microcrystalline thin films sandwiched, and special laminated glass with microcrystalline thin films in between In the production of optical wafers (optical filtering), the method of the present invention can be used.

Increasing the brightness of a light emitting diode By the method of the present invention, a mirror layer is bonded to the light emitting diode to increase the brightness.

Lamination of quartz resonators By the method of the present invention, for example, a gold thin film is formed on a quartz crystal and the quartz crystals are bonded to each other, thereby bonding the quartz crystals that are relatively difficult to bond.

Miniaturization and high integration of information appliances Three-dimensional stacking for SiP technology, high-functionality of package substrate (three-dimensional mounting); 3D bonding of Si device and Si device stack and substrate by this bonding method To achieve higher integration.

MEMS manufacturing technology Sealing of micro elements that also serve as three-dimensional wiring, especially sealing with inert gas. This bonding method is used for stacking with Si devices. In the case of use in this application, there may be an interface on the joint surface as long as the inert gas is sealed inside.

Realization of efficient heat conduction (cooling) for higher performance and ultra-low power consumption Heat sinks and heat spreaders made of materials with a large heat dissipation coefficient such as copper, diamond, DLC, etc., semiconductor devices, etc. by the method of the present invention Bonding directly to, improve heat dissipation performance, heat diffusion performance, etc.

Others In each of the applications described above, examples of using the joining method of the present invention in the field of electric and electronic parts have been described. However, the method of the present invention is not limited to the field of use exemplified above. It can be used in various fields and applications that require joining.

Claims (23)

In a vacuum vessel of 1 × 10 ⁻⁴ Pa or less, a thin film having a microcrystalline structure made of a single metal or an alloy is formed on each smooth surface of each of two substrates having a smooth surface, and 1 × 10 ⁻⁴ Pa is applied. By joining the two substrates so that the thin films of the microcrystalline structure formed on the two substrates are in contact with each other in a non-vacuum inert gas atmosphere, the bonding interface of the thin films of the microcrystalline structure And an atomic diffusion bonding method comprising bonding the two substrates by causing atomic diffusion in a crystal grain boundary. In a vacuum vessel of 1 × 10 ⁻⁴ Pa or less, a thin film of a microcrystalline structure made of a single metal or an alloy is formed on the smooth surface of one substrate, and non-vacuum inertness exceeding 1 × 10 ⁻⁴ Pa In the gas atmosphere, at least the surface of the other substrate having a smooth surface having a microcrystalline structure is in contact with the smooth surface of the other substrate so that the thin film having the microcrystalline structure formed on the one substrate is in contact with the other one. The two substrates are bonded to each other by causing atomic diffusion at a bonding interface and a crystal grain boundary between the thin film having the microcrystalline structure and the smooth surface of the other substrate by superimposing two substrates. Atom diffusion bonding method. The thin film having the microcrystalline structure is formed by a metal or alloy having a body diffusion coefficient of less than 1 × 10 ⁻⁵⁵ (m ² / s) at room temperature, or an oxide free energy of formation at room temperature of −330 (kJ / mol of compounds). The atomic diffusion bonding method according to claim 1, wherein the atomic diffusion bonding method is formed of a single metal or an alloy of less than 1). 4. The atomic diffusion bonding method according to claim 1, wherein the microcrystalline thin film is made of tungsten (W) having a body diffusion coefficient of 6.7 × 10 ⁻¹¹⁰ m ² / s at room temperature. .   The atomic diffusion bonding method according to any one of claims 1 to 4, wherein the superposition of the substrates is performed in an inert gas atmosphere having a pressure equal to or higher than atmospheric pressure.   The inert gas is selected from the group consisting of argon, helium, neon, krypton, xenon, nitrogen, methane, carbon dioxide, and carbon monoxide, or a gas from the group The atomic diffusion bonding method according to claim 1, wherein the atomic diffusion bonding method is a mixed gas of two or more kinds of gases.   The inert gas atmosphere was generated by introducing a gas from a gas source supplying an inert gas having an impurity concentration of 1 ppm or less into the space where the substrates were overlapped alone or by mixing them. The atomic diffusion bonding method according to claim 1, wherein:   7. The atomic diffusion bonding method according to claim 6, wherein an inert gas from the gas source is passed through a purifier to remove impurities, and then introduced into a space where the substrates are superimposed.   The inert gas atmosphere is formed by nitrogen gas or a mixed gas of nitrogen gas and another inert gas, and the microcrystalline thin film has a free energy of formation of nitride of −310 (kJ / mol of room temperature). 9) The atomic diffusion bonding method according to any one of claims 1 to 8, wherein the compound is formed of a single metal or an alloy as described above.   The atomic diffusion bonding method according to claim 1, wherein the superposition of the substrates is performed in an atmosphere from which dust is removed.   The atomic diffusion bonding method according to any one of claims 1 to 10, wherein the strength of overlapping the substrates is 101 kPa or less.   The atomic diffusion bonding method according to any one of claims 1 to 11, wherein the body diffusion coefficient is increased by heating the substrate temperature when the substrates are overlapped in a range of room temperature to 400 ° C. 13. The atomic diffusion bonding method according to claim 12, wherein the substrate is heated when a body diffusion coefficient of the forming material of the microcrystalline thin film at room temperature is 1 × 10 ⁻⁴⁰ m ² / s or less.   The atomic diffusion bonding method according to claim 1, wherein the substrates are superposed without heating the substrates.   The atomic diffusion bonding method according to claim 1, wherein the formation of the microcrystalline thin film and the superposition of the substrate are performed in the same or adjacent containers. The atomic diffusion bonding method according to claim 1, wherein the microcrystalline thin film is formed in a vacuum vessel having an ultimate vacuum pressure of 1 × 10 ⁻⁴ Pa to 1 × 10 ⁻⁸ Pa. .   The microcrystalline thin film is made of Al, Si, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ru, Rh, Pd, Ag, In, Sn, Hf, It is formed with any one single metal selected from the element group of Ta, Pt, Au, and W, or formed of an alloy containing one or more elements selected from the element group. 3. The atomic diffusion bonding method according to 1 or 2.   The modified layer generated on the smooth surface of the substrate on which the microcrystalline thin film is formed is removed in the same vacuum as the formation of the microcrystalline thin film before forming the microcrystalline thin film. The atomic diffusion bonding method according to any one of 1 to 17.   Forming one or more underlayers made of a thin film of a material different from the microcrystalline thin film on the smooth surface of the base on which the microcrystalline thin film is formed, and forming the microcrystalline thin film on the underlayer The atomic diffusion bonding method according to claim 1, wherein the atomic diffusion bonding method is characterized in that:   The underlayer is formed of any one single metal selected from the element group of Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W, or one or more selected from the element group The atomic diffusion bonding method according to claim 19, wherein the atomic diffusion bonding method is formed of an alloy containing any of the elements.   The single metal or alloy forming the underlayer has a higher melting point than the single metal or alloy forming the microcrystalline thin film formed on the underlayer, and the single metal or alloy forming the microcrystalline thin film 21. The atomic diffusion bonding method according to claim 19 or 20, wherein a material having a large difference in melting point with respect to the above is used.   21. The atomic diffusion bonding method according to claim 1, wherein the thickness of the microcrystalline thin film is 0.1 nm to 1 [mu] m. 23. Production of a package-type electronic component in which an inert gas having a pressure exceeding 1 × 10 ⁻⁴ Pa is sealed by bonding a package with atomic diffusion by the method according to claim 1. Way .