JP5401661B2 - Atomic diffusion bonding method and structure bonded by the above method - Google Patents

Description

  The present invention relates to an atomic diffusion bonding method and a structure bonded by the above-described method, and more specifically, for example, two materials to be bonded such as stacking of IC substrates, sealing of packages, and composite of various devices. In a bonding method used when strongly bonding between substrates, by bonding two substrates via a microcrystalline continuous thin film formed on the bonding surface of at least one substrate, at a bonding interface and a grain boundary The present invention relates to a novel bonding method for bonding substrates by causing atomic diffusion, and a structure bonded by the method.

  In this specification, “microcrystal” includes “polycrystalline” and “amorphous”. In addition, the term “grain boundary” refers to an intermittent portion of the regularity of atomic arrangement. In addition to the boundary of crystal grains in a polycrystal (“grain boundary” in a general sense), long-range order (several tens atoms) The above-mentioned amorphous structure having a short-range order (arrangement regularity in an atomic group of several tens of atoms or less) that does not have a degree of order in the atomic group of more than about) When the interrupted portion is the “crystal grain boundary” in the present invention, and there are voids in the amorphous metal film, and the volume ratio (filling rate) is lower than 100%, the interface between the void and the amorphous metal also has high atomic diffusion. Since it is considered to have a coefficient, it corresponds to the “crystal grain boundary” in the present invention as in the intermittent portion of the short-range order described above.

  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 activated (activated) to easily form chemical bonds, and in this state, the bonding surfaces of the materials to be bonded are overlapped without heating. In addition, a room temperature bonding method that enables bonding at room temperature without using an adhesive or the like is used for bonding silicon wafers, for example (see Patent Document 1).

Prior art document information of the present invention includes the following.
Japanese Patent No. 2791429

  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 be in an active state, and then the two bonding surfaces are bonded to achieve strong bonding. Although power can be obtained, the materials that can be joined are limited between some metals and metals, and some metals and compounds, which limits the application.

  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.

Therefore, the present invention has been made in order to eliminate the above-mentioned disadvantages of the prior art. Unlike the above-described joining by activation in the prior art, a wide range of materials including joining between different materials by a novel method called atomic diffusion are provided. can be used for bonding between, and aims to provide a Ki that atomic diffusion bonding method out to perform the bonding without giving physical damage to the substrate to be bonded target.

In order to achieve the above object, the atomic diffusion bonding method of the present invention includes self-diffusion or interdiffusion at room temperature (27 ° C. (300 K)) on each smooth surface of two substrates having a smooth surface in a vacuum vessel. Is a high-density fine particle having a body diffusion coefficient of 1 × 10 ⁻⁸⁰ m ² / s or more, an average grain size in the in-plane direction of crystal grains of 50 nm or less, and a density of 80% or more. A continuous crystal thin film (excluding a superplastic alloy film) is formed ( except that formed by irradiating the substrate with an inert gas ion beam or an inert gas neutral atom beam), and the two substrates are formed. By superimposing the two substrates so that the formed microcrystalline continuous thin films are in contact with each other, recrystallization due to atomic diffusion occurs at the bonding interface and grain boundaries of the microcrystalline continuous thin film, or changes to an amorphous state. Let me Two substrates are joined (claim 1).

  In the present invention, the density (%) of the microcrystalline continuous thin film is the ratio of the volume occupied by the metal constituting the microcrystalline continuous thin film excluding the formation of voids to the space occupied by the microcrystalline continuous thin film (volume ratio). Alternatively, the filling rate is expressed as a percentage.

In another atomic diffusion bonding method of the present invention, a smooth surface of one substrate is made of a material having a body diffusion coefficient at room temperature of 1 × 10 ⁻⁸⁰ m ² / s or more in a vacuum vessel, and a thin film of crystal grains Forms a high-density microcrystalline continuous thin film (excluding superplastic alloy film) with an average grain size in the in-plane direction of 50 nm or less and a density of 80% or more (in an inert gas ion beam or inert gas) And at least the surface of the other substrate provided with a smooth surface having a microcrystalline structure is formed on the one substrate. By superimposing the one and the other two substrates so that the microcrystalline continuous thin film is in contact with each other, atomic diffusion occurs at the bonding interface and the crystal grain boundary between the microcrystalline continuous thin film and the smooth surface of the other substrate. Cause recrystallization or amorph By varying the scan, characterized in that bonding the two substrates (claim 2).

In the atomic diffusion bonding method, the substrate temperature when the substrates are overlaid can be heated in a range of room temperature to 400 ° C. to increase the diffusion coefficient. Such heating is preferably performed when the body diffusion coefficient at room temperature of the material for forming the continuous crystal thin film is 1 × 10 ⁻⁴⁰ m ² / s or less.

Further, the superposition of the substrates may be performed without heating the substrates (Claim 5). In particular, the body diffusion coefficient of the material for forming the microcrystalline continuous thin film at room temperature is 1 × 10 ⁻⁴⁰ m ^2. When exceeding / s, it is possible to perform bonding by atomic diffusion to the extent that the bonding interface disappears even when bonding is performed without heating.

Further, in the above-described atomic diffusion bonding method, the microcrystalline continuous thin film is formed and / or the substrate is superposed in a vacuum vessel having an ultimate vacuum pressure of 1 × 10 ⁻⁴ Pa to 1 × 10 ⁻⁸ Pa. (Claim 6) and the formation of the microcrystalline continuous thin film and the superposition of the substrate are preferably performed in the same vacuum (Claim 7).

  The aforementioned microcrystalline continuous 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, It can be formed of any one single metal selected from the element group of Sn, Hf, Ta, Pt, Au, or can be formed of an alloy containing one or more elements selected from the element group. Item 8).

  Further, before forming the microcrystalline continuous thin film, an altered layer formed on the smooth surface of the substrate on which the microcrystalline continuous thin film is formed, for example, a gas adsorption layer, in the same vacuum as the formation of the microcrystalline continuous thin film And the natural oxide layer are preferably removed by a dry process such as reverse sputtering (Claim 9), particularly when a microcrystalline continuous thin film of Al, Cu, Ag, Pt or the like having low adhesion strength to the substrate is formed. In order to improve the adhesion strength, it is effective to remove the deteriorated layer.

  The removal of the altered layer on the surface of the substrate can also be performed by a wet process such as cleaning with a chemical solution outside the vacuum vessel in which the microcrystalline continuous thin film is formed. Is preferably in a state in which it is difficult for the altered layer to re-form due to hydrogen termination or the like.

  Furthermore, at least one underlayer made of a thin film of a material different from the microcrystalline continuous thin film is formed on the smooth surface of the substrate on which the microcrystalline continuous thin film is formed, and the microcrystalline continuous thin film is formed on the underlayer. (Claim 10), in the same manner as the removal of the deteriorated layer described above, particularly when a microcrystalline continuous thin film of Al, Cu, Ag, Pt or the like having low adhesion strength to the substrate is formed. The formation of the base layer is effective in improving the thickness.

  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 (Claim 11), and in particular, it is preferably formed of a material having a melting point higher than that of the microcrystalline continuous thin film to be formed and having a large difference in melting point. ).

  The film thickness of the microcrystalline continuous thin film can be 0.2 nm to 1 μm.

  Furthermore, the present invention includes a structure bonded by the above-described atomic diffusion bonding method (claim 14).

  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.

  Contact between the microcrystalline continuous thin films formed on the smooth surfaces of the two substrates or the microcrystalline continuous thin film formed on one substrate and the smooth surface of the other substrate having a smooth surface having a microcrystalline structure on at least the surface. As a result, atomic diffusion occurs at the bonding interface and at the grain boundaries, thereby heating, pressurizing, and applying voltage between the bonding surfaces of the same or different microcrystalline continuous thin film or between the microcrystalline continuous thin film and the smooth surface of the substrate. It was possible to bond firmly by metal bonds or intermolecular bonds at the atomic level without application, etc., and to release the internal stress of the thin film and relieve the bonding strain. 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).

  By increasing the diffusion coefficient by heating the substrate temperature in the range of room temperature to 400 ° C. when superimposing the substrates, the diffusion rate and diffusion length of atoms can be increased. A more uniform and strong bonding can be achieved by improving the diffusibility of atoms at the grain boundaries, and it is possible to bond even a substrate with a relatively rough surface, especially by increasing the diffusion length of atoms. .

  In addition, when the heating of the substrate is in the range of room temperature to 400 ° C. or less, the above-described effects can be obtained without causing damage due to heating even if the substrate is a relatively heat-sensitive electronic device or the like.

By performing the above heating when the microcrystalline continuous thin film is formed with a material having a body diffusion coefficient of 1 × 10 ⁻⁴⁰ m ² / s or less at room temperature, the microcrystalline continuous thin film is formed with a material having a relatively low diffusion coefficient. Even in this case, it is possible to improve the diffusion rate of the atoms and increase the diffusion length. In particular, the diffusion coefficient after heating exceeds 1 × 10 ⁻⁴⁰ m ² / s within the above temperature range. By heating, it is possible to cause atomic diffusion to the extent that the disappearance of the bonding interface can be obtained.

However, even when the substrates were stacked without heating, the substrates could be bonded satisfactorily, thereby preventing the substrate from being damaged by heat. In particular, when a microcrystalline continuous thin film is formed with a material having a body diffusion coefficient exceeding 1 × 10 ⁻⁴⁰ m ² / s at room temperature, the bonding interface disappears even when bonded at room temperature without heating. The junction by atomic diffusion was able to be obtained.

The formation of the continuous microcrystalline thin film and / or the superposition of the substrates in a vacuum vessel having a ultimate vacuum pressure of 1 × 10 ⁻⁴ Pa to 1 × 10 ⁻⁸ Pa, By superimposing the substrates in the same vacuum, the formed microcrystalline continuous thin film reacts with an impurity gas (for example, O ₂ or H ₂ O), etc. to bond the substrates in a clean state before forming a deteriorated layer. In addition to being able to bond the substrates with high adhesion strength, it was possible to prevent the formation of a deteriorated layer such as an oxide film that would serve as a barrier at the time of the passage of electrons or the like at the bonding interface.

  In addition, by forming the microcrystalline continuous thin film in the vacuum of the ultimate vacuum, it is possible to prevent the adhesion strength of the microcrystalline continuous thin film to the substrate from decreasing, and not only the peeling at the bonding interface of the microcrystalline continuous thin film. Therefore, the occurrence of delamination between the substrate and the microcrystalline continuous thin film can be suitably prevented.

  A microcrystalline continuous thin film is formed of Al, Si, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ru, Rh, Pd, Ag, In, Sn, Hf, An atom according to the method of the present invention is formed by using any one single metal selected from the element group of Ta, Pt, Au, or an alloy containing one or more elements selected from the element group. Diffusion bonding could be performed suitably.

  Before forming the microcrystalline continuous 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 continuous thin film is removed by a dry process such as reverse sputtering. Thus, the adhesion strength of the microcrystalline continuous thin film to the substrate can be improved, and the decrease in the adhesion strength between the substrates due to the separation between the substrate surface and the microcrystalline continuous thin film can be suitably prevented.

  Further, on the smooth surface of the substrate on which the microcrystalline continuous thin film is formed, a thin film made of a material different from the microcrystalline continuous thin film, for example, Ti, V, Cr, Zr, which are elements of Group 4A-6A in the periodic table The underlayer is formed from a thin film of any one single metal selected from the group of elements Nb, Mo, Hf, Ta, and W, or a thin film of an alloy containing one or more elements selected from the group of elements. As a result, the adhesion strength of the microcrystalline continuous thin film to the substrate can be increased, thereby preventing peeling between the substrate and the microcrystalline continuous 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 continuous thin film. The two-dimensionality of the continuous thin film (atomic wettability during thin film growth) is improved, and the microcrystalline continuous thin film can be prevented from growing in the form of islands. It is extremely thin, corresponding to the thickness of one atomic layer such as 0.2 nm. Formation of a microcrystalline continuous thin film is facilitated.

  In the atomic diffusion bonding method of the present invention, atomic diffusion bonding can be suitably performed when the film thickness of the formed microcrystalline continuous thin film is in the range of 0.2 nm (2 mm) to 1 μm, respectively. Bonding can also be performed by forming a microcrystalline continuous thin film with a thickness of a few millimeters that is sufficiently thinner than the mean free process. Therefore, even when used for bonding silicon wafers, etc. It was possible to provide a joining method in which movement and the like are not hindered.

Outline of Bonding Method The atomic diffusion bonding method of the present invention is a method in which continuous microcrystalline thin films formed in a vacuum by vacuum film formation such as sputtering or ion plating in a vacuum vessel, or a microcrystalline continuous thin film and microcrystals at least on the surface. It is found that when a substrate having a structure is overlapped during film formation or after film formation, atomic diffusion occurs at the bonding interface and crystal grain boundary, and strong bonding is performed between the two. It is adapted and the substrates are joined 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, a vacuum container having a high vacuum level of 1 × 10 ⁻⁴ to 1 × 10 ⁻⁸ Pa, such as sputtering or ion plating, is used. Any material can be used as long as it can form a continuous microcrystalline thin film by vacuum film formation in a high-vacuum atmosphere used. In addition to various pure metals and alloys, semiconductors such as Si substrates, glass As long as it is possible to form a microcrystalline continuous thin film by the above method, ceramics, resins, oxides, etc., the substrate (bonded material) in the present invention can be obtained.

  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 can be obtained even if the surface roughness is more than 50 nm at the maximum height (Rmax), for example, when the purpose is achieved simply by bonding such as sealing of a package. However, Rmax is preferably 50 nm or less.

  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 the formation of the microcrystalline continuous thin film. For example, the above-mentioned 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, and can 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 are prevented from occurring on the substrate surface after the altered layer is removed and before the microcrystalline continuous thin film described later is formed. Therefore, it is preferable to remove such a deteriorated layer in the same vacuum when a microcrystalline continuous thin film to be described later is formed, and to form a continuous microcrystalline thin film following the removal of the deteriorated layer, more preferably The removal of the altered layer is performed using an ultra-pure inert gas to prevent the oxide layer and the like from being re-formed after the alteration 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. In the case of forming a continuous microcrystalline thin film and bonding the two substrates without forming a continuous microcrystalline thin film, the bonding surface of the other substrate without forming the continuous microcrystalline thin film is In order to obtain atomic diffusion at the junction interface and grain boundaries, at least the surface must have a microcrystalline structure (including amorphous) as in the microcrystalline continuous thin film described later.

Microcrystalline continuous thin film Material The material of the microcrystalline continuous thin film to be formed may be a thin film of the same type as the substrate, or a microcrystalline continuous thin film of a different material from the substrate may be formed according to the purpose. In addition, the material of the microcrystalline continuous thin film formed on one side of the substrate and the material of the microcrystalline continuous thin film formed on the other side of the substrate may be different from each other. Alternatively, it may be a non-solid combination such as Co and Cu, and the combination of metal and metalloid can be arbitrarily and appropriately performed according to the purpose.

As a material for a continuous microcrystalline thin film, a body diffusion coefficient at room temperature is required to be 1 × 10 ⁻⁸⁰ m ² / s or more. As a material for such a continuous 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 or alloy containing at least one element of these element groups can be used.

Among these, in particular, when a microcrystalline continuous thin film is formed of In, Al, Ag, Au, Cu, Zn, Zr, Ti or the like having a body diffusion coefficient of 1 × 10 ⁻⁴⁰ m ² / s or more at room temperature, Even when the substrates are bonded at room temperature without heating, the bonding interface disappears, and recrystallization occurs between the bonded microcrystalline continuous thin films, resulting in a particle size over almost the entire area between the two substrates. Integration of two continuous microcrystalline thin films by metal bonding can be obtained, for example, the provided crystal grains are generated.

However, the body diffusion coefficient at room temperature is 1 × 10 ^-80 m ² / s or more even when a microcrystalline continuous thin film is formed with a material having a body diffusion coefficient of less than 1 × 10 ^-40 m ² / s at room temperature. By performing bonding through a microcrystalline continuous thin film formed of the above material, it is possible to obtain sufficient bonding strength between the substrates by metal bonding at the bonding interface.

Although the film thickness to be formed is not particularly limited, bonding can be performed even if each microcrystalline continuous thin film is formed with a thickness equivalent to one layer of the constituent elements. When a continuous crystal thin film is formed, bonding is possible even when the film thickness is 0.2 nm (0.4 nm for two layers) corresponding to the thickness of one atomic layer, and is interposed between the substrates to be bonded. It is possible to form the microcrystalline continuous thin film with a thickness equal to or less than the mean free process of electrons and spin current.

  As a result, the microcrystalline continuous thin film layer interposed between the substrates does not become a barrier against the movement of electrons, etc., and the present invention can be applied to the creation of new functional devices by bonding arbitrary silicon wafers. It is possible to use this atomic diffusion bonding method.

  However, the microcrystalline continuous thin film to be formed needs to be a “continuous” thin film having a microcrystalline structure. For example, an island-like structure before growing into a film in the film forming process is the microcrystalline structure of the present invention. It is excluded from the continuous film.

  On the other hand, as the film thickness increases, the surface roughness of the obtained microcrystalline continuous thin film increases, making bonding difficult, and it takes a long time to form a thick microcrystalline continuous thin film. Therefore, the upper limit is about 1 μm, and about 0.2 nm to 1 μm is a preferable film thickness range of each microcrystalline continuous thin film in the atomic diffusion bonding method of the present invention.

Grain size and density The microcrystalline continuous thin film to be formed must have a microcrystalline structure in which the diffusion rate of atoms is larger than that in the solid of the same microcrystalline metal, and in particular, the proportion of grain boundaries where the diffusion rate is extremely large. The average grain size in the in-plane direction of the crystal grains may be 50 nm or less, and preferably 20 nm or less.

  In addition, the volume ratio of the metal constituting the microcrystalline continuous thin film, excluding the formation part of the voids, to the volume of 100% of the space occupied by the microcrystalline continuous thin film is 80% or more, preferably It forms so that it may become 80 to 98%.

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

  In this case, the bonding surface of the other substrate on which the microcrystalline continuous thin film is not formed needs to have a microcrystalline structure at least near the surface of the bonding surface as described above.

  In addition, on the smooth surface of the substrate on which the microcrystalline continuous thin film is formed, one or more underlayers made of a material different from the microcrystalline continuous thin film can be formed before the microcrystalline continuous thin film is formed. In particular, when the microcrystalline continuous thin film to be formed is Al, Cu, Ag, Pt or the like having 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 forming technique similar to the film forming method described later of the microcrystalline continuous thin film, and the material thereof is Ti, which is an element belonging to Group 4A-6A of the periodic table, It can be formed of Zr, Hf, V, Nb, Ta, Cr, Mo, and W. The thickness is 0.2 to 20 nm as an example, and 5 nm in the examples described later.

  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 continuous microcrystalline thin film formed thereon, and a high melting point for the material for forming the continuous microcrystalline thin film. Are preferably used. As an example of a combination of materials having such a large melting point difference and a high melting point relative to the microcrystalline continuous thin film, for example, when forming a Cu microcrystalline continuous thin film on a Ta underlayer, the formed microcrystalline continuous film In addition to suitably preventing the thin film from peeling off from the substrate, the two-dimensionality of the microcrystalline continuous thin film formed on the underlayer (atomic wettability during the formation of the continuous microcrystalline thin film) is improved, resulting in finer film formation. Cu, which is a continuous crystal thin film, can be prevented from growing in an island shape, and an extremely thin microcrystalline continuous thin film corresponding to a thickness of one atomic layer such as 0.2 nm can be easily formed.

Film Formation Method Film Formation Technology In the atomic diffusion bonding method of the present invention, as a method for forming a microcrystalline continuous thin film formed on a bonding surface of a substrate that is a material to be bonded, in addition to PVD such as sputtering and ion plating, CVD, Various deposition methods such as vacuum deposition in a vacuum atmosphere in a vacuum vessel having a high degree of vacuum of 1 × 10 ⁻⁴ to 1 × 10 ⁻⁸ Pa, such as various depositions, can be cited, and the diffusion rate For materials that are relatively slow and their alloys, compounds, etc., 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.
Here, “plasma” means “a state of a substance that is electrically neutral as a whole, with positive and negative charged particles (positive ions and electrons) moving freely”. A flow in which ions created from molecules by electron impact are controlled by an electric or magnetic field to adjust their direction, and is made up of a device composed of an ion source (gun), an acceleration unit, an electromagnetic lens, a deflection unit, etc. " It is distinguished from “ion beam” which can be defined as

Degree of vacuum The pressure in the vacuum vessel when forming a thin film may be a vacuum atmosphere having a degree of vacuum of 1 × 10 ⁻⁴ to 1 × 10 ⁻⁸ Pa, and a lower pressure (higher degree of vacuum) is preferable. .

  If the thin film to be formed is made of a material that is difficult to oxidize, such as gold, bonding may be possible even when the film is formed at a pressure higher than the above pressure (low vacuum level). If there is, for example, when bonding is performed by forming a thin film of an easily oxidizable material such as aluminum at the upper limit (low vacuum level) of the above pressure, it is possible to bond appropriately by bonding immediately after film formation. In addition, it is possible to suitably prevent the generation of oxide at the bonding interface.

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.

Cleanliness of thin film surface The surface of the thin film to be polymerized is preferably clean. As the surface of the thin film is contaminated by reaction with impurity gas remaining in the vacuum vessel, the adhesion strength between the thin films It will decrease and eventually the bonding itself will not be possible.

  In addition, even when bonding is possible, impurities generated by oxidation of the thin film are generated on the bonding surface of the thin film. For example, when the method of the present invention is used for manufacturing semiconductor devices, Occasionally, it may not be desirable. From this point of view, in addition to the use of a vacuum vessel with a high degree of vacuum and the purification of process gas, the process from film formation to bonding is performed in the same vacuum, or relatively It is important to maintain the cleanliness of the surface of the microcrystalline continuous thin film by performing polymerization in a short time.

  However, when the bonding method of the present invention is used even when oxide or the like is generated on the bonding surface, such as when used for sealing a package, for example, after the thin film is formed, Bonding itself is possible if it is performed within a predetermined holding time.

The holding time enabling such bonding varies depending on the material of the formed thin film, the degree of vacuum in the vacuum vessel, the degree of purification of the process gas, etc. For example, the material of the thin film remains in the vacuum vessel. In the case of a material that does not easily react with impurity gases such as H ₂ O and O ₂ , for example, a precious metal that is relatively difficult to oxidize, although the adhesion strength is reduced, it is polymerized after a relatively long holding time. Even if it exists, it is possible to perform joining. On the other hand, when a thin film of a metal that easily reacts with an impurity gas, such as Ti or Al, which is relatively easily oxidized, is formed in a relatively short time after film formation, depending on the cleanliness in the vacuum vessel. become unable.

  For example, in the case of a thin film of Pt, bonding is possible even when polymerized after a retention time of 60 minutes has elapsed after the formation of the thin film. However, bonding is performed within an appropriate holding time depending on the material of the thin film to be formed.

Bonding Method Example An example of an apparatus for realizing the room temperature bonding method according to the present invention is shown in FIG. In FIG. 1, a magnetron cathode for performing sputtering is disposed at the upper part in a vacuum vessel for forming a thin film, and a jig for placing substrates to be bonded to each other is disposed at the lower part of the magnetron cathode. A microcrystalline continuous thin film is formed on the bonding surface of the substrate attached to the jig.

  In the illustrated embodiment, the table provided on the above-described jig is configured to be rotatable between a thin film formation position indicated by a broken line in FIG. 1 and a bonding position indicated by a solid line. One end of the placed table and one end of the table on which the other of the bases are placed are in abutment with each other, and the two tables are rotated around the abutted portion to By lifting the other end upward, the joining surface of the two substrates placed on the table is superposed.

  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. The bonding may be performed by operating one or both of the substrates with a robot arm or the like disposed in the vacuum vessel.

  In the vacuum vessel in which the jig configured as described above is arranged, the microcrystalline continuous thin film is formed on the bonding surface of the substrate under the above-described conditions in a state where the jig is at the film forming position indicated by the broken line in FIG. Form.

  When a microcrystalline continuous thin film having a predetermined thickness is formed on the bonding surface of the substrate, subsequently, the table provided on the jig is rotated to the bonding position indicated by the solid line, and the substrate is moved. Bond with a relatively weak force of about several tens of grams.

  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 bases on which the continuous microcrystalline thin film of the same material is bonded is described. However, when the bases on which the continuous microcrystalline thin film of different materials are bonded together, they can be opened and closed. The above-described magnetron cathode is disposed in each of the two vacuum vessels communicated by the communication path configured as described above, so that a microcrystalline continuous thin film of a different material can be formed in each vacuum vessel. After forming microcrystalline continuous thin films of different materials on the bonding surfaces, the communication path is opened, and one substrate is transported and bonded into a vacuum vessel in which the other substrate is disposed by a robot arm or the like. It may be equal.

  It is also possible to form the aforementioned microcrystalline continuous thin film only on one of the two substrates to be joined and to join both substrates directly to the other substrate without forming a microcrystalline continuous thin film. Is possible.

The mechanism of bonding It is not always clear by what principle the bonding by atomic diffusion described above is achieved, but in the bonding by the method of the present invention using a microcrystalline continuous thin film, as described below, It is considered that strong bonding by atomic diffusion has been realized by increasing the diffusion rate and diffusion length.

Increased diffusion rate and diffusion length The general formula for the diffusion coefficient of atoms is:
D = D ₀ exp (−Q / RT)
D: Diffusion coefficient D ₀ : Frequency term (entropy term)
Q: activation energy R: gas constant T: can be expressed in absolute temperature.

  Atomic diffusion at the bonding interface and grain boundaries is faster than atomic diffusion (body diffusion) in a solid, and the Q value in the above equation is reduced to 1/2 to 2/3.

  Therefore, the diffusion coefficient at the bonding interface and the crystal grain boundary is 10 to 20 orders of magnitude lower than the diffusion coefficient in the solid, and diffusion is likely to occur.

  Moreover, in the bonding method of the present invention, a microcrystalline continuous thin film is used for bonding, so that many crystal grain boundaries exist in the thin film.

Here, assuming that the crystal particle is approximately spherical and its radius is r, its volume V and surface area S are:
V ∝ r ³
S ∝ r ²
Thus, the ratio S / V between the volume of the crystal grains and the surface area is proportional to 1 / r.

Thus, for example, if a single crystal 2 inch wafer is changed to a microcrystalline structure with a crystal grain radius r of 10 nm, the S / V increases by 2 × 10 ⁷ times (seven digits).

  Therefore, when a microcrystalline continuous thin film is used for bonding, a very large atomic diffusion coefficient can be obtained, and the range in which atomic diffusion occurs (surface area ratio to crystal volume) increases dramatically. Therefore, it is considered that atomic diffusion at the bonding interface and the grain boundary can be easily generated.

  FIG. 2 is a cross-sectional TEM image of a Si substrate formed by bonding a Pt thin film as a microcrystalline continuous thin film. In FIG. 2, a zigzag crystal grain boundary is created by shifting the joint interface toward the grain boundary from the position where it was the joint interface of the microcrystalline continuous thin film. However, it is clear that atomic diffusion occurs at the grain boundaries.

  Next, examples of the joining method of the present invention will be described below.

Example of joining Joining method About 1 inch (2.7 cm) in diameter, using ultra high vacuum (UHV) 5-pole cathode-magnetron sputtering equipment (final vacuum 2 × 10 ⁻⁶ Pa) for physical experiments, or A microcrystalline continuous thin film was formed on each of two Si substrates having a diameter of 2 inches (about 5.08 cm) and subjected to a bonding test. For sputtering, an ultra-high purity argon gas having an impurity concentration of 2 to 3 ppb (2 to 3 × 10 ⁻⁹ ) or less at the gas introduction part (use point) into the vacuum chamber was used.

  The surface roughness of the Si substrate was 0.16 nm for Ra and 1.6 nm for Rmax, and a natural oxide film of Si was formed on the surface of the Si substrate, but this was used without removing it.

  In the example in which a thin film of Ag, Al, Cu, Pt is formed as a microcrystalline continuous thin film on the substrate, about 5 nm is formed by sputtering on one side of each of the two Si substrates before forming the microcrystalline continuous thin film. A Ta thin film was formed as an underlayer.

  In the example in which a Cr, Ti, Ta thin film was formed as the microcrystalline continuous thin film, the microcrystalline continuous thin film was formed directly on the Si substrate without forming the base layer as described above.

  The two Si substrates on which the microcrystalline continuous thin films are formed in this way can be applied with a weak force of about several tens of grams without heating both substrates so that the microcrystalline continuous thin films formed on both substrates overlap. They were superposed and joined.

Test Results Example of Ag Fine Crystal Continuous Thin Film Formed FIG. 3 shows a cross section of a Si substrate bonded by superimposing Ag thin films.

  As is clear from FIG. 3A, the bonding interface between the Ag thin films disappears, and a metal structure reflecting the crystal orientation is formed between the Ta thin films. Further, as apparent from the dark field image of FIG. 3B, the crystal grains after bonding form a single particle reaching between the two Ta thin films. It was confirmed that metal bonds accompanied by rearrangement of atoms occurred between the two Ag thin films over the entire region in the film thickness direction due to the diffusion of Ag atoms.

Example of forming Al microcrystalline continuous thin film FIG. 4 shows a cross section of a Si substrate bonded by overlapping Al thin films.

  As is clear from FIG. 4A, it was confirmed that the bonding interface between the Al thin films almost disappeared.

  Further, from the dark field image of FIG. 4B, since there are many single crystal particles reaching between the two Ta thin films in the Al film after bonding, the bonding by the above method results in Al It was confirmed that Al atoms in the thin film were diffused and metal bonds accompanied by rearrangement of atoms were generated between the two Al thin films.

  In addition, although the Al microcrystal continuous thin film having a thickness of 5 nm was formed and bonded by the same method, it was confirmed that the two Si substrates can be bonded firmly in this case as well. Further, by forming Al microcrystalline continuous thin films each having a thickness of 20 nm by a similar method, the surface roughness of the quartz substrate having a surface roughness of Rmax = 7.6 nm can be overcome and the two can be bonded. confirmed.

Example of Forming Cu Microcrystalline Continuous Thin Film FIG. 5 shows a cross section of a Si substrate bonded by superposition of Cu thin films.

  As is clear from FIG. 5A, it was confirmed that the bonding interface between the Cu thin films lost clarity and a part of the bonding interface disappeared.

  In addition, since the bonding surface is greatly shifted for each crystal grain, it is also confirmed from the dark field image shown in FIG. 5B that there is a crystal grain reaching from one Ta thin film to the other Ta thin film. , It was confirmed that the diffusion of Cu atoms reached nearly 20 nm, which is the thickness of the Cu thin film.

  In the observation with high resolution shown in FIG. 5C, it can be confirmed that the lattice image of the Cu layer is continuously connected from one Ta thin film to the other Ta thin film. It is clear that lattice continuity at the interface, that is, metal-to-metal bonding, occurs even in the portion where the bonding interface appears to remain without disappearing.

  Further, the formation of the Ta underlayer described above is omitted, and a Cu thin film is directly formed on a similar Si substrate for bonding, and the film thickness of the Cu thin film corresponds to the thickness of one Cu atom. When bonding was performed by superimposing layers formed at .2 nm, it was confirmed that bonding was possible even with this film thickness.

  Therefore, in the atomic diffusion contact bonding method of the present invention, the thickness of the microcrystalline continuous thin film formed on each of the substrates is set to the thickness of one atom of the material forming the same (two atoms after superposition). It was confirmed that the bonding was made only by forming as (min).

Example of Forming Pt Microcrystalline Continuous Thin Film FIG. 6 shows a cross section of a Si substrate bonded by superposition of Pt thin films.

  As can be seen from FIG. 6, when bonding is performed with a Pt thin film, the bonding interface between the Pt thin film and the Pt thin film has not completely disappeared, but it has been confirmed that strong bonding is being performed between the two. .

  In FIGS. 2 and 6, the degree of the zigzag at the interface is different because the vacuum apparatus and bonding conditions are different.

Example of Forming Cr Microcrystalline Continuous Thin Film FIG. 7 shows a cross section of a Si substrate bonded by superposition of Cr thin films.

  As shown in FIG. 7, a whitish band-like line appears in the vicinity of the bonding interface between the two thin films, and it was confirmed that the bonding interface was formed by changing the bonding interface of the Cr thin film to amorphous in this portion.

  Therefore, in the joining with the continuous microcrystalline thin film of Cr, alteration due to atomic diffusion occurs in the amorphous part. Compared with the joining using the continuous microcrystalline thin film formed of other metals, the atomic diffusion It was confirmed that the length was short.

  However, it was confirmed that the Si substrate can be strongly bonded also in this example in which the Si substrate is bonded by forming a Cr microcrystalline continuous thin film.

Example of Forming Ti Microcrystalline Continuous Thin Film FIG. 8 shows a cross section of a Si substrate bonded by overlapping Ti thin films.

  As shown in FIG. 8, it was confirmed that the junction interface between the two thin films had almost disappeared, and it was confirmed that recrystallization occurred due to atomic diffusion.

  In addition, even when bonding is performed by forming a thin film of Ti microcrystals each having a thickness of 0.2 nm by the same method, it is possible to bond Si substrates having a surface roughness Rmax of 40 nm. It was.

Example of forming a Ta microcrystalline continuous thin film FIG. 9 shows a cross section of a Si substrate bonded by superposition of Ta thin films.

  In FIG. 9, the white line appearing at the bonding interface between the two thin films is amorphous formed at the bonding interface, and in the bonding with the Ta microcrystalline continuous thin film, atomic diffusion occurs near the bonding interface changed to amorphous. It was confirmed that the atomic diffusion length was relatively short.

  However, in this example also, it was confirmed that two Si substrates could be joined firmly.

Others As a result of forming a thin film of Au, Co, Ni, and Ru and conducting a similar bonding test, it was confirmed that the Si substrate can be firmly bonded by forming any of the microcrystalline continuous thin films.

  Further, when the state after the bonding was confirmed, the bonding interface disappeared almost completely in the bonding between the Au thin films, but in Ni, Co and Ru, the bonding interface remained without disappearing.

Measurement of atomic diffusion length In order to confirm how long atomic diffusion occurs during bonding, the film thickness of the continuous microcrystalline thin film to be formed is increased, and the crystal grains created by recrystallization during bonding are The size was measured.

  The measurement was performed by forming an Al microcrystalline continuous thin film, and two Si substrates were bonded by the same method as the bonding test described above except that the thickness of the formed Al thin film was 50 nm. .

  FIG. 10 shows a cross section of the Si substrate after bonding in this way.

  As shown in FIG. 10 (A) to FIG. 10 (C), it can be confirmed that many crystal grains form one crystal grain in the range of 100 nm which is the total thickness of the Al thin film after bonding. Therefore, it was confirmed that the rearrangement of atoms due to atomic diffusion reached at least 50 nm at room temperature in the example in which the Al microcrystalline continuous thin film was formed and bonded.

Confirming the correspondence between the diffusion coefficient of atoms and the bonding interface state From the results of the bonding test described above, it is possible to suitably bond two substrates even when a microcrystalline continuous thin film of any material is formed. However, it was confirmed that there was a clear difference in the state of the microcrystalline continuous thin film after bonding due to the difference in the material forming the microcrystalline continuous thin film.

Therefore, as shown in FIG. 11, among the elements subjected to the experiment, those having a face-centered cubic lattice (fcc) structure are shown in a table in which the vertical axis represents the body diffusion coefficient at room temperature and the horizontal axis represents the melting point. When plotting each, the disappearance of the bonding interface is observed at the boundary where the diffusion coefficient of Cu is 1 × 10 ⁻⁴⁰ m ² / s, where a part of the bonding interface has disappeared. It was confirmed that crystal grains were formed over the entire region in the thickness direction between the two substrates.

The D ₀ (frequency term, entropy term) and Q (activation energy) used in the calculation are both “Metal Data Book (Revised 3rd Edition)” [edited by the Japan Institute of Metals, Maruzen Co., Ltd. ), (1993) P21-P25], and the temperature is 27 ° C. (300 K).

  In particular, in the case of Al, crystal grains extending over 100 nm are formed in the film thickness direction even in the junction where the thickness of each microcrystalline continuous thin film is 50 nm. Therefore, the rearrangement of atoms accompanying atomic diffusion occurs at room temperature. Has been confirmed to cover at least 50 nm.

On the other hand, in the joining using the microcrystalline continuous thin film formed by the element whose diffusion coefficient is smaller than 1 × 10 ⁻⁴⁰ m ² / s which is the body diffusion coefficient of Cu, the bonding interface remains, and both substrates The generation of crystal grains across the entire area has not been confirmed.

Similarly, when the structure other than the fcc structure is plotted in the table as shown in FIG. 12, the body diffusion coefficient is 1 × 10 ⁻⁴⁰ m ² / For Cr and Ta in which the remaining of the bonding interface is confirmed and amorphous formation is confirmed in a limited range near the bonding interface, the body diffusion coefficient is 1 × 10 ⁻⁴⁰ m It can be seen that it is lower than ² / s.

  From the above results, it can be seen that when the diffusion coefficient of atoms decreases, the diffusion length of atoms decreases, diffusion is limited to the vicinity of the bonding interface, and the bonding interface does not disappear.

  In FIG. 12, “hcp / bcc” means a group in which the hcp structure is stable near room temperature and the bcc structure is stable at high temperatures.

  As described above, when the diffusion length of atoms is shortened, even if the microcrystalline continuous thin film formed is thick, atomic diffusion occurs only in a part of the thin film. If the length of the diffusion exceeds the atomic diffusion length, bonding between the substrates becomes impossible.

  On the other hand, if the diffusion length of atoms can be increased, the surface roughness of the substrates can be overcome, and even substrates with relatively rough surfaces can be joined.

Here, the general formula D = D ₀ exp (−Q / RT) relating to the diffusion coefficient of atoms described above
Thus, it can be seen that the temperature T is increased and the diffusion coefficient D increases exponentially.

  Therefore, in the atomic diffusion bonding method of the present invention, particularly when bonding is performed by forming a microcrystalline continuous thin film with an element having a small body diffusion coefficient, the diffusion coefficient is increased by increasing the substrate temperature during superposition. Noted that is advantageous.

FIG. 13 shows changes in the diffusion coefficient of each element as the temperature rises. As shown in the figure, even when Ta has a relatively low diffusion coefficient, the diffusion coefficient is increased to 1 × 10 ⁻⁴⁰ m ² / s or more, which is the diffusion coefficient of Cu, by heating at 400 ° C. or lower. Thus, it can be seen that atomic diffusion can be performed to the extent that the disappearance of the bonding interface can be obtained.

Thus, the heating of the substrate is advantageous for increasing the diffusion coefficient, and thus for overcoming the surface roughness by increasing the diffusion length of the atoms, and for the diffusion coefficient to more than 1 × 10 ⁻⁴⁰ m ² / s. It has been confirmed that the increase in the temperature can be performed in a temperature range of 400 ° C. or lower that does not damage even a substrate used for an electronic device or the like.

Therefore, when the substrate during superposition is heated in the range of 400 ° C. or less, especially when the body diffusion coefficient of the elements constituting the microcrystalline continuous thin film is less than 1 × 10 ⁻⁴⁰ m ² / s, The advantage of heating in the range of 400 ° C. or less so that the diffusion coefficient exceeds 1 × 10 ⁻⁴⁰ m ² / s is obvious.

Verification of bonding strength Test method Adhesion strength was calculated using a special substrate (Si substrate) provided with a rim-like material.

FIG. 14 shows a schematic view of a base body provided with a rim structure. As this rim structure, a SiO ₂ rim of 425 nm (thickness) × 200 μm (width) was placed on the surface of one of the substrates, and after joining, the length L of the non-adhered gap was measured.

  The continuous microcrystalline thin film formed at the time of bonding is a Pt film having a thickness of 10 nm for both substrates. Further, a Ti film having a thickness of 5 nm was inserted as a base layer between the Pt film and the Si substrate so that the Pt film was not peeled off from the substrate.

  In order to measure the length of the non-adhered gap, an infrared beam was used, and the length of L was measured nondestructively from the image obtained by this infrared beam.

Test Result The length L of the non-adhered gap measured by the above method was 0.45 mm.

The surface energy of the joint obtained from the length L and the elastic strain of the substrate is about 5 J / m ^2, which is the same order as the predicted surface energy of solid Pt at room temperature. . Therefore, it was clear that the Pt thin films formed on the two substrates were bonded together by forming an intermetallic bond, and it was confirmed that a very strong bond was formed.

Confirmation of changes in elapsed time and bondability after film formation After forming a Pt thin film with a thickness of 20 nm on the bonding surfaces of the two substrates, they were left in the clean vacuum used for the experiment for 3 minutes before bonding (this When the introduction of Ar gas is stopped). The ultimate vacuum of the vacuum vessel is 1 × 10 ⁻⁶ Pa or less (higher vacuum than 1 × 10 ⁻⁶ Pa), and the impurity concentration in Ar gas is 2 ppb or less.

  FIG. 15A shows a cross-sectional micrograph (TEM) of the substrate bonded during the formation of the Pt film in the above environment. FIG. 15A shows a cross-sectional photo of the bonded substrate after being left in the space for 3 minutes after the film formation. (TEM) is shown in FIG.

  As is clear from FIGS. 15 (A) and 15 (B), there is no clear difference between the bonding interface between the case where the bonding is performed during the film formation and the case where the bonding is performed after the elapse of 3 minutes. Neither the occurrence of an oxidized layer or the like at the bonded interface could be confirmed.

  From this, it was confirmed that film formation and bonding in a clean vacuum, and film formation and bonding in the same vacuum are effective for good bonding, and in a clean vacuum. It was also confirmed that there was no change in the state of the bonding interface even when a time of about 3 minutes passed from the film formation to the bonding.

  FIGS. 16A and 16B show an example in which two substrates are joined by forming a Ta film having a thickness of 20 nm instead of forming the Pt film, and FIG. The cross-sectional micrograph (TEM) of what was joined in the film | membrane, FIG.16 (B) is a cross-sectional micrograph of what was joined after progress for 3 minutes after film-forming.

  As is apparent from FIGS. 16A and 16B, in the case of bonding using a Ta film having a small diffusion coefficient, as in the case of bonding using a Pt film, the difference in the bonding interface due to the elapsed time after film formation is observed. Therefore, it was confirmed that film formation and bonding in a clean vacuum, and film formation and bonding in the same vacuum are effective for good bonding, and in a clean vacuum. It was also confirmed that there was no change in the state of the bonding interface depending on the elapsed time of about 3 minutes from film formation to bonding.

Improvement of adhesion strength between continuous microcrystalline thin film and substrate The continuous microcrystalline thin film of Al, Cu, Ag, Pt has low adhesion strength to the substrate. The problem of peeling at the interface occurs.

  Therefore, in order to improve the low adhesion strength to such a substrate, it is effective to form a base layer made of a thin film of a material different from the microcrystalline continuous thin film, and the quality of the gas adsorption layer or natural oxide layer on the substrate surface is altered. It was confirmed that the removal of the layer was effective.

Formation of Underlayer A Ta underlayer of 5 nm thickness is formed on each of two Si substrates, and after forming a 20 nm thick Al microcrystalline continuous thin film on the Ta underlayer, bonding is performed. A peel test of both substrates was performed.

  As a result of the test, no peeling occurred at any of the bonding interface between the microcrystalline continuous thin films, the interface between the underlying layer and the microcrystalline continuous thin film, and the interface between the substrate and the underlying layer, and the substrate was destroyed before peeling occurred. .

  Also, when a similar experiment was conducted using a 20 nm-thick Al microcrystalline continuous thin film, the substrate was destroyed before delamination occurred.

  From the above results, adhesion strength higher than the fracture strength of the substrate was obtained, and it was confirmed that the formation of the Ta underlayer was effective in increasing the adhesion strength between the substrate and the microcrystalline continuous thin film. .

  In addition to the above-mentioned Ta, the same result was obtained by forming an underlayer of Ti and Cr.

  From the above points, it was confirmed that the formation of an underlayer of Ti, Ta, and Cr is effective in increasing the adhesion strength of the microcrystalline continuous thin film to the substrate.

  In the periodic table, Zr and Hf, which belong to the same 4A genus as Ti, V and Nb, which belong to the same 5A genus as Ta, and Mo and W, which belong to the same 6A genus as Cr, are similarly formed by these elements. By forming the film, it is expected that the adhesion strength of the microcrystalline continuous thin film to the substrate can be improved.

Removal of gas adsorption layer and natural oxide After removal of the natural oxide layer by cleaning with chemicals, Al microcrystals with a thickness of 20 nm on each of two Si substrates that have been subjected to hydrogen termination treatment to suppress oxidation A sample (sample 1) joined by forming a continuous thin film, and two Si substrates each having a natural oxide layer removed by performing reverse sputtering on the joint surface in the same vacuum as the formation of the microcrystalline continuous thin film On the other hand, a sample (sample 2) in which a 20 nm thick Al microcrystal continuous thin film was formed and bonded was prepared, and both samples were subjected to a substrate peeling test.

  As a result of the peeling test, peeling in the interface between the substrate and the microcrystalline continuous thin film was not confirmed in both the samples 1 and 2, and the substrate was broken before peeling occurred.

  Therefore, regardless of the wet method by cleaning with chemicals or the dry method such as reverse sputtering, it is possible to remove the altered layer such as the gas adsorption layer and the natural oxide layer on the substrate surface before forming the microcrystalline continuous thin film. It was confirmed that it is effective in improving the adhesion strength of the microcrystalline continuous thin film.

  The bonding method of the present invention described above has various new features because it can be bonded at the atomic level without heating or at a relatively low temperature, without pressure, and with low interface stress after bonding. It can be used for applications such as creation of functional / 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 with semiconductor wafers laminated with nanocrystal films, and special glass with laminated nanocrystal films 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 This bonding method is used for vacuum sealing of fine elements that also serve as three-dimensional wiring and for stacking with Si devices. For use in this application, there may be an interface on the joint surface, as long as the internal vacuum and joined state can be maintained.

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.

BRIEF DESCRIPTION OF THE DRAWINGS Schematic explanatory drawing of the apparatus for enforcing the atomic diffusion bonding method of this invention. Cross-sectional photomicrograph of Si substrates joined by forming a Pt microcrystalline continuous thin film. It is a cross-sectional microscope picture of the Si substrate joined by the Ag thin film (20 nm × 20 nm), (A) is a bright field image, and (B) is a dark field image. It is a cross-sectional microscope picture of the Si substrate joined by the Al thin film (20 nm × 20 nm), (A) is a bright field image, and (B) is a dark field image. It is a cross-sectional microscope picture of the Si substrate joined by Cu thin film (20 nm x 20 nm), (A) is a bright field image, (B) is a dark field image, (C) is a high resolution image. A cross-sectional photomicrograph of a Si substrate joined by a Pt thin film (20 nm × 20 nm). Sectional micrograph of Si substrate joined by Cr thin film (20 nm × 20 nm). A cross-sectional photomicrograph of a Si substrate joined by a Ti thin film (20 nm × 20 nm). Sectional micrograph of Si substrate joined by Ta thin film (20 nm × 20 nm). It is a cross-sectional photomicrograph of a Si substrate joined by an Al thin film (50 nm × 50 nm), (A) is a bright field image, (B) is a bright field image from another direction, and (C) is a dark field image of (B). image. Body diffusion coefficient-melting point correlation diagram (fcc system only). Body diffusion coefficient-melting point correlation diagram (all types). The graph which shows the change of the body diffusion coefficient with respect to temperature. Explanatory drawing of the verification method of joining strength. It is a cross-sectional micrograph of a Si substrate bonded by a Pt thin film (20 nm × 20 nm). (A) is bonded during the deposition of the Pt thin film, and (B) is bonded after 3 minutes from the deposition. It is a cross-sectional photomicrograph of a Si substrate bonded by a Ta thin film (20 nm × 20 nm). (A) is bonded during the deposition of the Ta thin film, and (B) is bonded after 3 minutes from the film formation.

Claims (14)

In the vacuum vessel, the smooth surface of each of the two substrates having a smooth surface is made of a material having a body diffusion coefficient of 1 × 10 ⁻⁸⁰ m ² / s or more at room temperature, and the average grain size in the in-plane direction of the crystal grains Forms a high-density microcrystalline continuous thin film (excluding superplastic alloy film) having a diameter of 50 nm or less and a density of 80% or more (excluding an inert gas ion beam or an inert gas neutral atom beam) And by joining the two substrates so that the microcrystalline continuous thin films formed on the two substrates are in contact with each other. An atomic diffusion bonding method comprising bonding the two substrates by causing recrystallization accompanying atomic diffusion at an interface and a crystal grain boundary or changing to an amorphous state. In a vacuum vessel, the smooth surface of one substrate is made of a material having a body diffusion coefficient of 1 × 10 ⁻⁸⁰ m ² / s or more at room temperature , the average grain size in the in-plane direction of crystal grains is 50 nm or less, and , Forming a high-density microcrystalline continuous thin film (excluding superplastic alloy film) having a density of 80% or more ( formed by irradiating the substrate with an inert gas ion beam or an inert gas neutral atom beam) And 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 microcrystalline continuous thin film formed on the one substrate contacts the smooth surface of the other substrate. By superimposing two substrates, recrystallization due to atomic diffusion is caused at the bonding interface and crystal grain boundary between the microcrystalline continuous thin film and the smooth surface of the other substrate, or the amorphous substrate is changed to amorphous. Two substrates Atomic diffusion bonding method, characterized in that the coupling.   3. The atomic diffusion bonding method according to claim 1, wherein the diffusion coefficient is increased by heating the substrate temperature when the substrates are overlapped in a range of room temperature to 400 ° C. 4. The atomic diffusion bonding method according to claim 3, wherein the heating of the substrate is performed when a body diffusion coefficient at room temperature of the material for forming the microcrystalline continuous thin film is 1 × 10 ⁻⁴⁰ m ² / s or less.   3. The atomic diffusion bonding method according to claim 1, wherein the superposition of the bases is performed without heating the bases. 6. The microcrystalline continuous thin film is formed and / or the substrate is superposed in a vacuum vessel having an ultimate vacuum pressure of 1 × 10 ⁻⁴ Pa to 1 × 10 ⁻⁸ Pa. The atomic diffusion bonding method according to claim 1.   The atomic diffusion bonding method according to claim 1, wherein the formation of the microcrystalline continuous thin film and the superposition of the substrate are performed in the same vacuum.   The microcrystalline continuous 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. 2. It is formed of any one single metal selected from the group of elements Ta, Pt, Au, or an alloy containing one or more elements selected from the group of elements. The atomic diffusion bonding method according to any one of? 7.   Before forming the microcrystalline continuous thin film, the altered layer generated on the smooth surface of the substrate on which the microcrystalline continuous thin film is formed is removed in the same vacuum as the formation of the microcrystalline continuous thin film. The atomic diffusion bonding method according to any one of claims 1 to 8.   On the smooth surface of the substrate on which the microcrystalline continuous thin film is formed, one or more base layers made of a thin film of a material different from the microcrystalline continuous thin film are formed, and the microcrystalline continuous thin film is formed on the base layer The atomic diffusion bonding method according to claim 1, wherein the atomic diffusion bonding method is performed.   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 10, wherein the atomic diffusion bonding method is formed of an alloy containing any of the above elements.   The single metal or alloy that forms the underlayer is a single metal that has a higher melting point than the single metal or alloy that forms the microcrystalline continuous thin film formed on the underlayer and that forms the microcrystalline continuous thin film. Alternatively, an atomic diffusion bonding method according to claim 11, wherein a difference in melting point with respect to the alloy is large.   The atomic diffusion bonding method according to claim 1, wherein a thickness of the microcrystalline continuous thin film is 0.2 nm to 1 μm.   A structure joined by the method according to claim 1.